AUTHORITYDESCRIPTION

DATE

N/A

Incorporation of IRN-IS-200K-001 through IRN-IS-200K-004

14-MAY-2020

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited

APPROVALS
Authored By: RE Anthony Flores

Checked By: RE Claudina Tiznado

AUTHORIZED SIGNATURES

REPRESENTINGDATEGPS EnterpriseSpace & Missile Systems Center (SMC) - LAAFBINTERFACE SPECIFICATION DOCUMENT
Interface Control Contractor:

UNLESS OTHERWISE SPECIFIED: NUMBERS ARE
REPRESENTED IN DECIMAL FORM.

SAIC (GPS SE&I)
200 N. Pacific Coast Highway, Suite 1800
El Segundo, CA 90245
TITLE:THIS DOCUMENT SPECIFIES TECHNICALREQUIREMENTS AND NOTHING HEREIN
CONTAINED SHALL BE DEEMED TO ALTER THE
TERMS OF ANY CONTRACT OR PURCHASEORDER BETWEEN ALL PARTIES AFFECTED

NAVSTAR GPS Space Segment/Navigation User Segment
Interfaces

SIZE ASCALE: N/A

CODE IDENT

66RP1
REV: LNO.

IS-GPS-200

IS-GPS-200L
14 May 2020

REVISION RECORD
LTR

DESCRIPTIONDATEAPPROVED

NC

Initial Release

25 Jan 1983

A

Incorporates IRN-IS-200NC-001, IRN- IS-200NC-002, and IRNIS-200NC-003

25 Sep 1984

B

Incorporates IRN-IS-200A-001A

30 Nov 1987

C

Incorporates IRN-IS-200B-001 thru IRN- IS-200B-007

10 Oct 1993

C

Re-formatted in Microsoft Word 6.0 in GEMS compatible format

10 Oct 1993

12 Jan 1996

C

Changed distribution status to Public Release

25 Sep 1997

20 Oct 1997

D

Incorporates IRN-200C-001 thru IRN-200C-005R1,
change ICD-GPS-200 to IS-GPS-200, introduce andspecify the requirements of Improved Clock andEphemeris (ICE) message for L2C signal, and otheradditional updates

7 Dec 2004

23 Nov 2004

Adds additional PRN sequences to Section 6

7 Mar 2006

09 Mar 2006

E

GPS IIIA Incorporations

8 Jun 201008 Jun 2010

N/A

SE&I Tech Pubs

29 Jul 2010

IRN200D-001

F

G

H

IRN-IS-200E-001; RFC-16B Pseudorandom Noise (PRN)
Expansion)
IRN-IS-200E-002; RFC-77B Public Document
Management (GPS III terminology and Space Service Volume(SSV) group delay))
IRN-IS-200E-003; RFC-86 User Range Accuracy (URA) Definition
IRN-IS-200E-004; RFC-89 Almanac Intervals
IRN-IS-200E-005; RFC-91A – Civil Navigation (CNAV) Durations
IRN-IS-200E-006; RFC 93 Technical Note 36
IRN-IS-200E-007; RFC-97 Pseudorange Parameters
IRN-IS-200F-002; RFC-139B Public Signals-inSpace Updates
IRN-IS-200G-001; RFC-183A L1C Data Predict Week Number(WNop)
IRN-IS-200G-002; RFC-188B Public Signals in Space
Requirements Disconnects
IRN-IS-200G-003; RFC-193 CNAV Reference Times
IRN-IS-200G-004; RFC-198 PRNs 211-1023 Mission Assignments
IRN-IS-200G-005; RFC-199 Clarification of CNAV Broadcast
Intervalsi

21 Sep 2011

5 Mar 2012

5 Sep 201231 Jan 201324 Sep 2013

21 Mar 2014

IS-GPS-200L
14 May 2020

REVISION RECORD
LTR

J

K

L

DESCRIPTION
IRN-IS-200H-001; RFC-269 Incorrect P-Code Phase Assignments
IRN- IS-200H-002; RFC-266- Coordinated Universal Time Offset
Error (UTCOE) Disconnects
IRN-IS-200H-003; RFC-288 Data Message Validation Parameters
and Clarifications
IRN-IS-200H-004; RFC-318 2016 Public Document Clean-Up
IRN-IS-200H-005; RFC-312 Definition Clarification for Time ofPredict
IRN-IS-200H-006; RFC-349 2017 Public Document Clean-Up
IRN-IS-200J-001; RFC-374 2018 Public Document Proposed
Changes
IRN-IS-200K-001; RFC-400 Leap Second and Earth Orientation
Parameters
IRN-IS-200K-002; RFC-402 Elimination of the Object Type
“Duplicate Requirement”
IRN-IS-200K-003; RFC-395 2018 Public Document Proposed
Changes
IRN-IS-200K-004; RFC-403 Health Bit Clarification

ii

DATE

APPROVED

25 Apr 201822 May 201804 Mar 201906 May 201914 May 2020

03 Aug 2020

IS-GPS-200L
14 May 2020

TABLE OF CONTENTS
1 INTRODUCTION .......................................................................................................................................... 1
1.1 Scope..................................................................................................................................................... 1
1.2 IS Approval and Changes. ..................................................................................................................... 1
2 APPLICABLE DOCUMENTS ....................................................................................................................... 2
2.1 Government Documents. ....................................................................................................................... 2
2.2 Non-Government Documents. ............................................................................................................... 2
3 REQUIREMENTS ........................................................................................................................................ 3
3.1 Interface Definition. ................................................................................................................................ 3
3.2 Interface Identification. ........................................................................................................................... 3
3.2.1 Ranging Codes. .............................................................................................................................. 3
3.2.1.1 P-Code. .................................................................................................................................... 3
3.2.1.1.1 Expanded P-Code (GPS III) ............................................................................................... 4
3.2.1.2 Y-Code. .................................................................................................................................... 4
3.2.1.3 C/A-Code. ................................................................................................................................. 4
3.2.1.3.1 Expanded C/A Code (GPS III)........................................................................................... 4
3.2.1.4 L2 CM-Code (IIR-M, IIF, and subsequent blocks)..................................................................... 5
3.2.1.4.1 Expanded L2 CM Code (GPS III and subsequent blocks) ................................................. 5
3.2.1.5 L2 CL-Code (IIR-M, IIF, and subsequent blocks)...................................................................... 5
3.2.1.5.1 Expanded L2 CL-Code (GPS III, GPS IIIF, and subsequent blocks) .................................. 5
3.2.1.6 Non-Standard Codes. ............................................................................................................. 12
3.2.2 NAV Data. ..................................................................................................................................... 12
3.2.3 L1/L2 Signal Structure. .................................................................................................................. 12
3.3 Interface Criteria. ................................................................................................................................. 13
3.3.1 Composite Signal. ......................................................................................................................... 13
3.3.1.1 Frequency Plan....................................................................................................................... 13
3.3.1.2 Correlation Loss...................................................................................................................... 14
3.3.1.3 Carrier Phase Noise. .............................................................................................................. 14
3.3.1.4 Spurious Transmissions. ........................................................................................................ 14
3.3.1.5 Signal Component Phasing. ................................................................................................... 14iii

IS-GPS-200L
14 May 2020

3.3.1.5.1 Phase Quadrature. ........................................................................................................... 14
3.3.1.5.2 Phase Crosstalk. .............................................................................................................. 15
3.3.1.5.3 Phase Continuity. ............................................................................................................. 15
3.3.1.6 User-Received Signal Levels. ................................................................................................. 16
3.3.1.6.1 Space Service Volume (SSV) User-Received Signal Levels. .......................................... 18
3.3.1.7 Equipment Group Delay. ........................................................................................................ 18
3.3.1.7.1 Group Delay Uncertainty. ................................................................................................. 19
3.3.1.7.2 Group Delay Differential. .................................................................................................. 19
3.3.1.7.3 Space Service Volume Group Delay Differential. ............................................................. 19
3.3.1.8 Signal Coherence. .................................................................................................................. 19
3.3.1.9 Signal Polarization. ................................................................................................................. 19
3.3.2 PRN Code Characteristics. ........................................................................................................... 20
3.3.2.1 Code Structure........................................................................................................................ 20
3.3.2.2 P-Code Generation. ................................................................................................................ 22
3.3.2.3 C/A-Code Generation. ............................................................................................................ 29
3.3.2.4 L2 CM-/L2 CL-Code Generation. ............................................................................................ 32
3.3.3 Navigation Data. ............................................................................................................................ 35
3.3.3.1 Navigation Data Modulation (L2 CM). ..................................................................................... 35
3.3.3.1.1 Forward Error Correction.................................................................................................. 35
3.3.4 GPS Time and SV Z-Count. .......................................................................................................... 36
6 NOTES ....................................................................................................................................................... 39
6.1 Acronyms ............................................................................................................................................. 39
6.2 Definitions ............................................................................................................................................ 42
6.2.1 User Range Accuracy. .................................................................................................................. 42
6.2.1.1 User Differential Range Accuracy. .......................................................................................... 42
6.2.2 SV Block Definitions. ..................................................................................................................... 43
6.2.2.1 Developmental SVs. ............................................................................................................... 43
6.2.2.2 Operational SVs...................................................................................................................... 43
6.2.2.2.1 Block II SVs. ..................................................................................................................... 43
6.2.2.2.2 Block IIA SVs. .................................................................................................................. 43iv

IS-GPS-200L
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6.2.2.2.3 Block IIR SVs. .................................................................................................................. 43
6.2.2.2.4 Block IIR-M SVs. .............................................................................................................. 43
6.2.2.2.5 Block IIF SVs.................................................................................................................... 44
6.2.2.2.6 GPS III SVs ...................................................................................................................... 44
6.2.3 Operational Interval Definitions. .................................................................................................... 44
6.2.3.1 Normal Operations.................................................................................................................. 44
6.2.3.2 Short-term Extended Operations. ........................................................................................... 44
6.2.3.3 Long-term Extended Operations. ............................................................................................ 44
6.2.4 GPS Week Number. ...................................................................................................................... 44
6.2.5 L5 Civil Signal. .............................................................................................................................. 45
6.2.6 Reserved Data .............................................................................................................................. 45
6.2.7 Valid Range ................................................................................................................................... 45
6.2.8 Invalid ............................................................................................................................................ 45
6.2.9 Clock, Ephemeris, Integrity (CEI) Data Set. .................................................................................. 45
6.2.9.1 Core CEI Data Set. ................................................................................................................. 45
6.2.10 CEI Data Sequence Propagation. ............................................................................................... 47
6.3 Supporting Material .............................................................................................................................. 47
6.3.1 Received Signals........................................................................................................................... 47
6.3.2 Extended Navigation Mode (Block II/IIA). ...................................................................................... 49
6.3.3 Block IIA Mode (Block IIR/IIR-M) and Extended Navigation Mode (Block II-F). ............................ 49
6.3.3.1 Block IIA Mode (Block IIR/IIR-M). ........................................................................................... 49
6.3.3.2 Extended Navigation Mode (Block II-F). ................................................................................. 50
6.3.4 Extended Navigation Mode (GPS III). ........................................................................................... 50
6.3.5 Autonomous Navigation Mode. ..................................................................................................... 50
6.3.6 Additional PRN Code Sequences ................................................................................................. 51
6.3.6.1 Additional C/A-code PRN sequences. .................................................................................... 51
6.3.6.2 Additional P-Code PRN sequences. ....................................................................................... 51
6.3.6.2.1 Additional P-code Generation. ......................................................................................... 52
6.3.6.3 Additional L2 CM-/L2 CL-Code PRN sequences. ................................................................... 57
6.3.7 Pre-Operational Use...................................................................................................................... 59v

IS-GPS-200L
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6.3.8 P-Code Verification Material .......................................................................................................... 59
6.4 Operational Protocols .......................................................................................................................... 61
6.4.1 Lower PRN Numbers Versus Upper PRN Numbers...................................................................... 61
6.4.2 PRN Number Consistency ............................................................................................................ 62
6.4.3 PRNs 33 and 37 ............................................................................................................................ 62
6.4.4 PRNs 33 through 63 ...................................................................................................................... 62
6.4.5 Health Code Setting of ‘11110’ ...................................................................................................... 62
6.4.6 User Protocol for Signal Availability and Health Information ......................................................... 62
6.4.6.1 User Protocol .......................................................................................................................... 62
6.4.6.2 Alarm Indications .................................................................................................................... 63
6.4.6.2.1 Common Alarm Indications .............................................................................................. 63
6.4.6.2.2 Specific Alarm Indications ................................................................................................ 63
6.4.6.3 "Marginal Indications" ............................................................................................................. 65
10 APPENDIX I. LETTERS OF EXCEPTION............................................................................................... 67
10.1 Scope................................................................................................................................................. 67
10.2 Applicable Documents. ...................................................................................................................... 67
10.3 Letters of Exception. .......................................................................................................................... 67
20 APPENDIX II. GPS NAVIGATION DATA STRUCTURE FOR LNAV DATA, D(t), FOR PRN 1-32.......... 75
20.1 Scope................................................................................................................................................. 75
20.2 Applicable Documents. ...................................................................................................................... 75
20.2.1 Government Documents. ............................................................................................................ 75
20.2.2 Non-Government Documents. ..................................................................................................... 75
20.3 Requirements .................................................................................................................................... 76
20.3.1 Data Characteristics. ................................................................................................................... 76
20.3.2 Message Structure. ..................................................................................................................... 76
20.3.3 Message Content. ....................................................................................................................... 88
20.3.3.1 Telemetry Word. ................................................................................................................... 88
20.3.3.2 Handover Word (HOW). ....................................................................................................... 88
20.3.3.3 Subframe 1. .......................................................................................................................... 90
20.3.3.3.1 Subframe 1 Content. ...................................................................................................... 90vi

IS-GPS-200L
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20.3.3.3.2 Subframe 1 Parameter Characteristics. ......................................................................... 93
20.3.3.3.3 User Algorithms for Subframe 1 Data. ........................................................................... 94
20.3.3.4 Subframes 2 and 3. .............................................................................................................. 98
20.3.3.4.1 Content of Subframes 2 and 3. ...................................................................................... 99
20.3.3.4.2 Subframe 2 and 3 Parameter Characteristics. ............................................................. 100
20.3.3.4.3 User Algorithm for Ephemeris Determination. .............................................................. 100
20.3.3.4.4 NMCT Validity Time. .................................................................................................... 107
20.3.3.5 Subframes 4 and 5. ............................................................................................................ 108
20.3.3.5.1 Content of Subframes 4 and 5. .................................................................................... 108
20.3.3.5.2 Algorithms Related to Subframe 4 and 5 Data. ............................................................ 122
20.3.4 Timing Relationships. ................................................................................................................ 130
20.3.4.1 Paging and Cutovers. ......................................................................................................... 130
20.3.4.2 SV Time vs. GPS Time. ...................................................................................................... 130
20.3.4.3 Speed of Light..................................................................................................................... 130
20.3.4.4 Data Sets. ........................................................................................................................... 130
20.3.4.5 Reference Times. ............................................................................................................... 134
20.3.5 Data Frame Parity. .................................................................................................................... 135
20.3.5.1 SV/CS Parity Algorithm. ...................................................................................................... 136
20.3.5.2 User Parity Algorithm. ......................................................................................................... 136
30 APPENDIX III. GPS NAVIGATION DATA STRUCTURE FOR CNAV DATA, DC(t)............................... 138
30.1 Scope............................................................................................................................................... 138
30.2 Applicable Documents. .................................................................................................................... 138
30.2.1 Government Documents. .......................................................................................................... 138
30.2.2 Non-Government Documents. ................................................................................................... 138
30.3 Requirements. ................................................................................................................................. 138
30.3.1 Data Characteristics. ................................................................................................................. 138
30.3.2 Message Structure. ................................................................................................................... 139
30.3.3 Message Content. ..................................................................................................................... 139
30.3.3.1 Message Type 10 and 11 Ephemeris and Health Parameters. .......................................... 154
30.3.3.1.1 Message Type 10 and 11 Ephemeris and Health Parameter Content. ........................ 154
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30.3.3.1.2 Message Type 10 and 11 Ephemeris Parameter Characteristics. ............................... 158
30.3.3.1.3 User Algorithm for Determination of SV Position. ......................................................... 158
30.3.3.2 Message Types 30 Through 37 SV Clock Correction Parameters...................................... 164
30.3.3.2.1 Message Type 30 Through 37 SV Clock Correction Parameter Content. .................... 164
30.3.3.2.2 Clock Parameter Characteristics. ................................................................................. 165
30.3.3.2.3 User Algorithms for SV Clock Correction Data. ............................................................ 165
30.3.3.2.4 Non-Elevation-Dependent (NED) Accuracy Estimates. ................................................ 166
30.3.3.3 Message Type 30 Ionospheric and Group Delay Correction Parameters. .......................... 170
30.3.3.3.1 Message Type 30 Ionospheric and Group Delay Correction Parameter Content. ........ 170
30.3.3.4 Message Types 31, 12, and 37 Almanac Parameters. ....................................................... 173
30.3.3.4.1 Almanac Reference Week............................................................................................ 173
30.3.3.4.2 Almanac Reference Time ............................................................................................. 173
30.3.3.4.3 SV PRN Number. ......................................................................................................... 173
30.3.3.4.4 Signal Health (L1/L2/L5)............................................................................................... 173
30.3.3.4.5 Midi Almanac Parameter Content. ............................................................................... 174
30.3.3.4.6 Reduced Almanac Parameter Content. ........................................................................ 174
30.3.3.5 Message Type 32 Earth Orientation Parameters (EOP). .................................................... 177
30.3.3.5.1 EOP Content. ............................................................................................................... 177
30.3.3.6 Message Type 33 Coordinated Universal Time (UTC) Parameters. ................................... 180
30.3.3.6.1 UTC Parameter Content............................................................................................... 180
30.3.3.6.2 UTC and GPS Time. .................................................................................................... 180
30.3.3.7 Message Types 34, 13, and 14 Differential Correction Parameters.................................... 181
30.3.3.7.1 Differential Correction Parameters Content.................................................................. 182
30.3.3.7.2 DC Data Packet. .......................................................................................................... 182
30.3.3.7.3 Application of Clock-Related DC Data.......................................................................... 185
30.3.3.7.4 Application of Orbit-Related DC Data. .......................................................................... 185
30.3.3.7.5 SV Differential Range Accuracy Estimates. ................................................................. 187
30.3.3.8 Message Type 35 GPS/GNSS Time Offset. ....................................................................... 188
30.3.3.8.1 GPS/GNSS Time Offset Parameter Content. ............................................................... 188
30.3.3.8.2 GPS and GNSS Time. ................................................................................................. 189
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30.3.3.9 Message Types 36 and 15 Text Messages. ....................................................................... 189
30.3.4 Timing Relationships. ................................................................................................................ 190
30.3.4.1 Paging and Cutovers. ......................................................................................................... 190
30.3.4.2 SV Time vs. GPS Time. ...................................................................................................... 190
30.3.4.3 Speed of Light..................................................................................................................... 191
30.3.4.4 Data Sets ............................................................................................................................ 191
30.3.4.5 Reference Times ................................................................................................................ 191
30.3.5 Data Frame Parity. .................................................................................................................... 193
30.3.5.1 Parity Algorithm. ................................................................................................................. 193
40 APPENDIX IV GPS NAVIGATION DATA STRUCTURE FOR LNAV DATA, D(t), FOR PRN 33-63 ...... 195
40.1 Scope............................................................................................................................................... 195
40.2 Applicable Documents ..................................................................................................................... 195
40.3 Requirements .................................................................................................................................. 195
40.3.1 Data Characteristics .................................................................................................................. 195
40.3.2 Message Structure .................................................................................................................... 195
40.3.3 Message Content ...................................................................................................................... 206
40.3.3.1 Telemetry Word .................................................................................................................. 206
40.3.3.2 Handover Word (HOW) ...................................................................................................... 206
40.3.3.3 Subframe 1 ......................................................................................................................... 206
40.3.3.4 Subframes 2 and 3 ............................................................................................................. 207
40.3.3.5 Subframes 4 and 5 ............................................................................................................. 207
40.3.3.5.1 Content of Subframes 4 and 5 ..................................................................................... 207
40.3.3.5.2 Algorithms Related to Subframe 4 and 5 Data ............................................................. 213
40.3.4 Timing Relationships ................................................................................................................. 213
40.3.5 Data Frame Parity ..................................................................................................................... 213

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IS-GPS-200L
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LIST OF TABLES
Table 3-Ia.

Code Phase Assignments (sheet 1 of 2) .................................................................................... 6

Table 3-Ia.

Code Phase Assignments (sheet 2 of 2) .................................................................................... 7

Table 3-Ib. Expanded Code Phase Assignments (GPS III, GPS IIIF, and subsequent blocks only) .............. 8
Table 3-IIa. Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 1 of 2) ................... 9
Table 3-IIa. Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 2 of 2) ................. 10
Table 3-IIb. Expanded Code Phase Assignments (GPS III, GPS IIIF, and subsequent blocks only) ............ 11
Table 3-III.

Signal Configuration................................................................................................................. 13

Table 3-IV.

Composite L1 Transmitted Signal Phase ** (Block II/IIA and IIR SVs Only) ........................... 17

Table 3-Va. Received Minimum RF Signal Strength for Block IIA, IIR, IIR-M, IIF, GPS III, and GPS IIIF
Satellites (20.46 MHz Bandwidth) ................................................................................................................. 17
Table 3-Vb. Received Minimum RF Signal Strength for GPS III and GPS IIIF (30.69 MHz Bandwidth)........ 18
Table 3-Vc. Space Service Volume (SSV) Received Minimum RF Signal Strength for GPS III, GPS IIIF, andSubsequent Satellites over the Bandwidth Specified in 3.3.1.1 – GEO Based Antennas.............................. 18
Table 3-VI.

P-Code Reset Timing (Last 400 sec of 7-day period) ** ........................................................ 28

Table 3-VII.

Final Code Vector States ..................................................................................................... 28

Table 6-I-1. CEI Data Set Parameters ........................................................................................................... 45
Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 1 of 5) ........................................................ 53

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 2 of 5) ........................................................ 54

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 3 of 5) ........................................................ 55

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 4 of 5) ........................................................ 56

Table 6-I.

Additional C/A-/P-Code Phase Assignments (sheet 5 of 5) .................................................... 57

Table 6-II.

Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 1 of 2) ......................................... 58

Table 6-II.

Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 2 of 2) ......................................... 58

Table 6-III. First 256 P-code Chips of the Week for Selected Code Phase Assignments.............................. 60
Table 6-IV. Last 1024 P-code Chips of the Week for Selected Code Phase Assignments ........................... 60
Table 20-I.

Subframe 1 Parameters ........................................................................................................... 94

Table 20-II. Ephemeris Data Definitions ................................................................................................... 100
Table 20-III.

Ephemeris Parameters ....................................................................................................... 101

Table 20-IV. Broadcast Navigation User Equations (sheet 1 of 4) .............................................................. 102
Table 20-IV. Broadcast Navigation User Equations (sheet 2 of 4) ............................................................. 103
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Table 20- IV. Broadcast Navigation User Equations (sheet 3 of 4) ............................................................ 104
Table 20-IV. Broadcast Navigation User Equations (sheet 4 of 4) .............................................................. 105
Table 20-V.

Data IDs and SV IDs in Subframes 4 and 5 ....................................................................... 110

Table 20-VI.

Almanac Parameters .......................................................................................................... 112

Table 20-VII.

LNAV Data Health Indications ............................................................................................ 114

Table 20-VIII. Codes for Health of SV Signal Components....................................................................... 115
Table 20-IX.

UTC Parameters ................................................................................................................ 118

Table 20-X.

Ionospheric Parameters ..................................................................................................... 119

Table 20-XI.

IODC Values and Data Set Lengths (Block II/IIA) ............................................................. 132

Table 20-XII. IODC Values and Data Set Lengths (Block IIR/IIR-M/IIF & GPS III/ IIIF) .............................. 133
Table 20-XIII. Reference Times ................................................................................................................ 135
Table 20-XIV.

Parity Encoding Equations .............................................................................................. 136

Table 30-I.

Message Types 10 and 11 Parameters (1 of 2) .................................................................... 159

Table 30-I.

Message Types 10 and 11 Parameters (2 of 2) .................................................................... 159

Table 30-II. Broadcast Navigation User Equations (sheet 1 of 4) ............................................................... 160
Table 30-II. Broadcast Navigation User Equations (sheet 2 of 4) ................................................................ 161
Table 30- II. Broadcast Navigation User Equations (sheet 3 of 4) ............................................................... 163
Table 30-II. Broadcast Navigation User Equations (sheet 4 of 4) ............................................................... 164
Table 30-III.

Clock Correction and Accuracy Parameters ....................................................................... 166

Table 30-IV.

Group Delay Differential Parameters **** ........................................................................... 171

Table 30-V.

Midi Almanac Parameters .................................................................................................. 175

Table 30-VI.

Reduced Almanac Parameters ***** ................................................................................... 176

Table 30-VII.

Earth Orientation Parameters ............................................................................................. 179

Table 30-VIII. Application of EOPs ........................................................................................................... 180
Table 30-IX.

UTC Parameters ................................................................................................................ 181

Table 30-X.

Differential Correction Parameters ..................................................................................... 184

Table 30-XI.

GPS/GNSS Time Offset Parameters .................................................................................. 189

Table 30-XII.

Message Broadcast Intervals ............................................................................................. 190

Table 30-XIII. Reference Times................................................................................................................... 193
Table 40-V.

Data IDs and SV IDs in Subframes 4 and 5 ....................................................................... 209
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LIST OF FIGURES
Figure 3-1.

Generation of P-, C/A-Codes and Modulating Signals ............................................................. 21

Figure 3-2.

X1A Shift Register Generator Configuration ............................................................................ 23

Figure 3-3.

X1B Shift Register Generator Configuration ............................................................................ 23

Figure 3-4.

X2A Shift Register Generator Configuration ............................................................................ 24

Figure 3-5.

X2B Shift Register Generator Configuration ............................................................................ 24

Figure 3-6.

P-Code Generation .................................................................................................................. 26

Figure 3-7.

P-Code Signal Component Timing........................................................................................... 27

Figure 3-8.

G1 Shift Register Generator Configuration .............................................................................. 29

Figure 3-9.

G2 Shift Register Generator Configuration .............................................................................. 30

Figure 3-10: Example C/A-Code Generation ................................................................................................. 31
Figure 3-11.

C/A-Code Timing Relationships ........................................................................................... 32

Figure 3-12.

L2 CM-/L2 CL-Code Timing Relationships ........................................................................... 33

Figure 3-13.

L2 CM/L2 CL Shift Register Generator Configuration .......................................................... 34

Figure 3-14.

Convolutional Encoder ......................................................................................................... 35

Figure 3-15.

Convolutional transmit/Decoding Timing Relationships ........................................................ 36

Figure 3-16.

Time Line Relationship of HOW Message ............................................................................ 38

Figure 6-1.

User Received Minimum Signal Level Variations (Example, Block II/IIA/IIR) ........................... 48

Figure 10.3-1. Letters of Exception .............................................................................................................. 68
Figure 10.3-2. Letters of Exception (continued) ........................................................................................... 69
Figure 10.3-3. Letters of Exception (continued) ........................................................................................... 70
Figure 10.3-4. Letters of Exception (continued) ........................................................................................... 71
Figure 10.3-5. Letters of Exception (continued) ........................................................................................... 72
Figure 10.3-6. Letters of Exception (continued) ........................................................................................... 72
Figure 10.3-7. Letters of Exception (continued) ............................................................................................ 73
Figure 10.3-8. Letters of Exception (continued) ........................................................................................... 74
Figure 20-1.

Data Format (sheet 1 of 11) ................................................................................................. 77

Figure 20-1.

Data Format (sheet 2 of 11) ................................................................................................. 78

Figure 20-1.

Data Format (sheet 3 of 11) ................................................................................................. 79

Figure 20-1.

Data Format (sheet 4 of 11) ................................................................................................. 80
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IS-GPS-200L
14 May 2020

Figure 20-1.

Data Format (sheet 5 of 11) ................................................................................................. 81

Figure 20-1.

Data Format (sheet 6 of 11) ................................................................................................. 82

Figure 20-1.

Data Format (sheet 7 of 11) ................................................................................................. 83

Figure 20-1.

Data Format (sheet 8 of 11) ................................................................................................. 84

Figure 20-1.

Data Format (sheet 9 of 11) ................................................................................................. 85

Figure 20-1.

Data Format (sheet 10 of 11) ............................................................................................... 86

Figure 20-1.

Data Format (sheet 11 of 11) ............................................................................................... 87

Figure 20-2.

TLM and HOW Formats ....................................................................................................... 89

Figure 20-3.

Sample Application of Correction Parameters ...................................................................... 98

Figure 20-4.

Ionospheric Model (Sheet 1 of 3) ....................................................................................... 127

Figure 20-4. Ionospheric Model (Sheet 2 of 3) ........................................................................................... 128
Figure 20-4. Ionospheric Model (Sheet 3 of 3) ........................................................................................... 129
Figure 20-5.

Example Flow Chart for User Implementation of Parity Algorithm ...................................... 137

Figure 30-1.

Message Type 10 - Ephemeris 1........................................................................................ 140

Figure 30-2.

Message Type 11 - Ephemeris 2........................................................................................ 141

Figure 30-3. Message Type 30 - Clock, IONO & Group Delay ................................................................... 142
Figure 30-4. Message Type 31 - Clock & Reduced Almanac ...................................................................... 143
Figure 30-5.

Message Type 32 - Clock & EOP ....................................................................................... 144

Figure 30-6.

Message Type 33 - Clock & UTC ....................................................................................... 145

Figure 30-7.

Message Type 34 - Clock & Differential Correction ............................................................ 146

Figure 30-8.

Message Type 35 - Clock & GGTO .................................................................................... 147

Figure 30-9.

Message Type 36 - Clock & Text ....................................................................................... 148

Figure 30-10.

Message Type 37 - Clock & Midi Almanac ......................................................................... 149

Figure 30-11.

Message Type 12 - Reduced Almanac .............................................................................. 150

Figure 30-12.

Message Type 13 - Clock Differential Correction ............................................................... 151

Figure 30-13.

Message Type 14 - Ephemeris Differential Correction ....................................................... 152

Figure 30-14.

Message Type 15 – Text .................................................................................................... 153

Figure 30-15.

Reduced Almanac Packet Content..................................................................................... 176

Figure 30-16.

Differential Correction Data Packet .................................................................................... 183

Figure 40-1. Data Format (sheet 1 of 11) .................................................................................................... 196
xiii

IS-GPS-200L
14 May 2020

Figure 40-1. Data Format (sheet 2 of 11) .................................................................................................... 197
Figure 40-1. Data Format (sheet 3 of 11) .................................................................................................... 198
Figure 40-1. Data Format (sheet 4 of 11) .................................................................................................... 199
Figure 40-1. Data Format (sheet 5 of 11) .................................................................................................... 200
Figure 40-1. Data Format (sheet 6 of 11) .................................................................................................... 201
Figure 40-1. Data Format (sheet 7 of 11) .................................................................................................... 202
Figure 40-1. Data Format (sheet 8 of 11) .................................................................................................... 203
Figure 40-1. Data Format (sheet 9 of 11) .................................................................................................... 204
Figure 40-1. Data Format (sheet 10 of 11) .................................................................................................. 205
Figure 40-1. Data Format (sheet 11 of 11) .................................................................................................. 206

xiv

IS-GPS-200L
14 May 2020

IS-GPS-200

1 INTRODUCTION
1.1 Scope.
This Interface Specification (IS) defines the requirements related to the interface between theSpace Segment (SS) of the Global Positioning System (GPS) and the navigation User Segment(US) of the GPS for radio frequency (RF) link 1 (L1) and link 2 (L2).

1.2 IS Approval and Changes.
The Interface Control Contractor (ICC) designated by the government is responsible for the basic
preparation, approval coordination, distribution, retention, and Interface Control Working Group(ICWG) coordination of the IS in accordance with GP-03-001. The Navstar GPS Directorate(SMC/GP) is the necessary authority to make this IS effective. SMC/GP administers approvals
under the auspices of the Configuration Control Board (CCB), which is governed by theappropriate GPS Directorate Operating Instruction (OI). Military organizations and contractors are
represented at the CCB by their respective segment member. All civil organizations and public
interest are represented by the Department of Transportation representative of the SMC/GP.
A proposal to change the approved version of this IS can be submitted by any ICWG participatingorganization to the GPS Directorate and/or the ICC. The ICC is responsible for the preparation of
the change paper and change coordination, in accordance with GP-03-001. The ICC prepares thechange paper as a Proposed Interface Revision Notice (PIRN) and is responsible for coordinationof PIRNs with the ICWG. The ICWG coordinated PIRN must be submitted to the GPS Directorate
CCB for review and approval.
The ICWG review period for all Proposed Interface Revisions Notices (PIRNs) is 45 days after
receipt by individual addressees. A written request to extend the review period may be submitted
to the ICC for consideration.

1

IS-GPS-200L
14 May 2020

2 APPLICABLE DOCUMENTS
2.1 Government Documents.
The following documents of the issue specified contribute to the definition of the interfaces
between the GPS Space Segment and the GPS navigation User Segment, and form a part of thisIS to the extent specified herein.
Specifications
FederalNone

Military

None

Other Government Activity

NoneStandards
FederalNone

Military

None

Other Publications
GP-03-001

GPS Adjudication Working Group (AWG) and Rough Order

Current Versionof Magnitude (ROM)/ Impact Assessment (IA) Charter
International Earth Rotation and Reference Systems Service(IERS) Technical Note 36

2.2 Non-Government Documents.
The following documents of the issue specified contribute to the definition of the interfaces
between the GPS Space Segment and the GPS Navigation User Segment and form a part of thisIS to the extent specified herein.
Specifications
None
Other Publications
None

2

IS-GPS-200L
14 May 2020

3 REQUIREMENTS
3.1 Interface Definition.
The interface between the GPS Space Segment (SS) and the GPS navigation User Segment (US)includes two RF links, L1 and L2. Utilizing these links, the space vehicles (SVs) of the SS shallprovide continuous earth coverage signals that provide to the US the ranging codes and thesystem data needed to accomplish the GPS navigation (NAV) mission. These signals shall beavailable to a suitably equipped user with RF visibility to an SV.

3.2 Interface Identification.
The carriers of L1 and L2 are typically modulated by one or more bit trains, each of which normallyis a composite generated by the modulo-2 addition of a pseudo-random noise (PRN) ranging codeand the downlink system data (referred to as NAV data).

3.2.1 Ranging Codes.
Three PRN ranging codes are transmitted: the precision (P) code which is the principal navigation
ranging code; the Y-code, used in place of the P-code whenever the anti-spoofing (A-S) mode ofoperation is activated; and the coarse/acquisition (C/A) code which is used for acquisition of the P(or Y) code (denoted as P(Y)) and as a civil ranging signal. Code-division-multiple-accesstechniques allow differentiating between the SVs even though they may transmit at the same
frequencies. The SVs will transmit intentionally "incorrect" versions of the C/A and the P(Y) codes
where needed to protect the users from receiving and utilizing anomalous navigation signals.
These two "incorrect" codes are termed non-standard C/A (NSC) and non-standard Y (NSY)
codes.
For Block IIR-M, IIF, and subsequent blocks of SVs, two additional PRN ranging codes aretransmitted. They are the L2 civil-moderate (L2 CM) code and the L2 civil-long (L2 CL) code. The
SVs will transmit intentionally "incorrect" versions of the L2 CM and L2 CL codes where needed toprotect the users from receiving and utilizing anomalous navigation signals. These "incorrect"
codes are termed non-standard L2 CM (NSCM) and non-standard L2 CL (NSCL) codes. The SVs
shall also be capable of initiating and terminating the broadcast of NSCM and/or NSCL code(s)independently of each other, in response to CS command.
Users shall only use non-dummy satellites as defined via current broadcast almanac. See Section
20.3.3.5.1.2 and/or Section 40.3.3.5.1.2 for the definition of information about dummy satellites in
the almanac.

3.2.1.1 P-Code.
The PRN P-code for SV ID number i, for i = 1 to 37, is a ranging code, Pi(t), of 7 days in length at achipping rate of 10.23 Mbps. The 7 day sequence is the modulo-2 sum of two sub-sequences3

IS-GPS-200L
14 May 2020referred to as X1 and X2i; their lengths are 15,345,000 chips and 15,345,037 chips, respectively.
The X2i sequence is an X2 sequence selectively delayed by 1 to 37 chips thereby allowing thebasic code generation technique to produce a set of 37 mutually exclusive P-code sequences of 7days in length. Assignment of these code phase segments by SV ID number is given in Table 3Ia. (NOTE: previous versions of this document reserved PRNs 33 through 37 for other uses. Due
to increased system capability, PRNs 33 through 37 are being redesignated to allow for use bySVs.)
An initial almanac collected from P(Y)-code in the upper PRNs must be obtained from PRNs 35,
36, or 38 through 63.

3.2.1.1.1 Expanded P-Code (GPS III)An expanded set of 26 P-code PRN sequences are generated by circularly shifting 26 of theoriginal 37 sequences (over one week) by an amount corresponding to 1 day. These expanded
sequences are therefore time shifted (i.e. offset) versions of 26 of the original sequences.
Assignment of these expanded code phase segments by SV ID number is given in Table 3-Ib.
Additional PRN P-code sequences with assigned PRN numbers are provided in Section 6.3.6.2.1,
Table 6-I.

3.2.1.2 Y-Code.
The PRN Y-code is used in place of the P-code when the A-S mode of operation is activated.

3.2.1.3 C/A-Code.
The PRN C/A-code for SV ID number i is a Gold code, Gi(t), of 1 millisecond in length at a chipping
rate of 1023 kbps. The Gi(t) sequence is a linear pattern generated by the modulo-2 addition of
two sub-sequences, G1 and G2i, each of which is a 1023 chip long linear pattern. The epochs of
the Gold code are synchronized with the X1 epochs of the P-code. As shown in Table 3-Ia, theG2i sequence is a G2 sequence selectively delayed by pre-assigned number of chips, thereby
generating a set of different C/A-codes. Assignment of these by GPS PRN signal number are
given in Table 3-Ia and Table 3-Ib.
An initial almanac collected from C/A-code in the upper PRNs must be obtained from PRNs 35, 36,
or 38 through 63.

CS will prevent the simultaneous transmission of PRNs 34 and 37 of C/A-code.

3.2.1.3.1 Expanded C/A Code (GPS III)An expanded set of 26 C/A-code PRN sequences are identified in Table 3-Ib using “G2 Delay” and“Initial G2 Setting” which is not the same as the method used in Table 3-Ia. The two-tap coder
implementation method referenced and used in Table 3-Ia is not used in Table 3-Ib due to its
limitation in generating C/A-code sequences. The “G2 Delay” specified in Table 3-Ib may be
4

IS-GPS-200L
14 May 2020

accomplished by using the “Initial G2 Setting” as the initialization vector for the G2 shift register of
Figure 3-9. Assignment of these expanded code phase segments by SV ID number is given in
Table 3-Ib. Additional PRN C/A-code sequences with assigned PRN numbers are provided in
Section 6.3.6.2.1, Table 6-I.

3.2.1.4 L2 CM-Code (IIR-M, IIF, and subsequent blocks).
The PRN L2 CM-code for SV ID number i is a ranging code, CM,i(t), which is 20 milliseconds inlength at a chipping rate of 511.5 kbps. The epochs of the L2 CM-code are synchronized with theX1 epochs of the P-code. The CM,i(t) sequence is a linear pattern which is short cycled every
count of 10230 chips by resetting with a specified initial state. Assignment of initial states by GPS
PRN signal number is given in Table 3-IIa.

3.2.1.4.1 Expanded L2 CM Code (GPS III and subsequent blocks)
An expanded set of 26 L2 CM-code PRN sequences are identified with assignment of initial states
by SV ID number in Table 3-IIb. Additional PRN L2 CM-code sequence pairs are provided in
Section 6.3.6.3, Table 6-II.

3.2.1.5 L2 CL-Code (IIR-M, IIF, and subsequent blocks).
The PRN L2 CL-code for SV ID number i is a ranging code, CL,i(t), which is 1.5 seconds in length
at a chipping rate of 511.5 kbps. The epochs of the L2 CL-code are synchronized with the X1
epochs of the P-code. The CL,i(t) sequence is a linear pattern which is generated using the samecode generator polynomial as the one used for C M,i(t). However, the CLi(t) sequence is shortcycled by resetting with a specified initial state every code count of 767250 chips. Assignment ofinitial states by GPS PRN signal number is given in Table 3-IIa.

3.2.1.5.1 Expanded L2 CL-Code (GPS III, GPS IIIF, and subsequent blocks)
An expanded set of 26 L2 CL-code PRN sequences are identified with assignment of initial states
by SV ID number in Table 3-IIb. Additional PRN L2 CL-code sequence pairs are provided in
Section 6.3.6.3, Table 6-II.

5IS-GPS-200L
14 May 2020

Table 3-Ia.

SV
ID
No.

GPS PRN
Signal
No.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

Code Phase Assignments (sheet 1 of 2)

C/A(G2i)**(X2i)

Code Delay
Chips
C/A
P

 6
 7
 8
 9
 9
 10
 8
 9
 10
 3
 4
 6
 7
 8
 9
 10
 4
 5
 6

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

5
6
7
8
17
18
139
140
141
251
252
254
255
256
257
258
469
470
471

Code Phase Selection

2
3
4
5
1
2
1
2
3
2
3
5
6
7
8
9
1
2
3

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

First
10 Chips
Octal*C/A

First
12 Chips
Octal
P

1440
1620
1710
1744
1133
1455
1131
1454
1626
1504
1642
1750
1764
1772
1775
1776
1156
1467
1633

4444
4000
4222
4333
4377
4355
4344
4340
4342
4343








4343

*

In the octal notation for the first 10 chips of the C/A code as shown in this column, the first
digit (1) represents a "1" for the first chip and the last three digits are the conventional
octal representation of the remaining 9 chips. (For example, the first 10 chips of the C/Acode for PRN Signal Assembly No. 1 are: 1100100000).
**
The two-tap coder utilized here is only an example implementation that generates a limited
set of valid C/A codes.
 = "exclusive or"
NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of a specific
C/A and a specific P-code phase, as shown above.

6

IS-GPS-200L
14 May 2020

Table 3-Ia.

SV
ID
No.

GPS PRN
Signal
No.

20
21
22
23
24
25
26
27
28
29
30
31
32
65
66
67
68
69

20
21
22
23
24
25
26
27
28
29
30
31
32
33***
34**
35
36
37**

Code Phase Assignments (sheet 2 of 2)

C/A(G2i)****(X2i)

Code Delay
Chips
C/A
P

 7
 8
 9
 3
 6
 7
 8
 9
 10
 6
 7
 8
 9
 10
 10
 7
 8
 10

20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

472
473
474
509
512
513
514
515
516
859
860
861
862
863
950
947
948
950

Code Phase Selection

4
5
6
1
4
5
6
7
8
1
2
3
4
5
4
1
2
4

20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

First
10 Chips
Octal*C/A

First
12 Chips
Octal
P

1715
1746
1763
1063
1706
1743
1761
1770
1774
1127
1453
1625
1712
1745
1713
1134
1456
1713

4343
















4343

*

In the octal notation for the first 10 chips of the C/A-code as shown in this column, the first
digit (1) represents a "1" for the first chip and the last three digits are the conventional
octal representation of the remaining 9 chips. (For example, the first 10 chips of the C/Acode for PRN Signal Assembly No. 1 are: 1100100000).
** C/A-codes 34 and 37 are identical.
*** PRN sequence 33 is reserved for other uses (e.g. ground transmitters).
**** The two-tap coder utilized here is only an example implementation that generates a limited
set of valid C/A-codes.
 = "exclusive or"
NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of a specific
C/A and a specific P-code phase, as shown above.

7

IS-GPS-200L
14 May 2020

Table 3-Ib. Expanded Code Phase Assignments (GPS III, GPS IIIF, andsubsequent blocks only)

SV
ID
No.
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95

GPS
PRN
Signal
No.
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63

Code Phase Selection
G2
Initial G2
X2
Delay
Setting
Delay(Chips)(Octal)*(Chips)
67
0017
1
103
0541
2
91
1714
3
19
1151
4
679
1651
5
225
0103
6
625
0543
7
946
1506
8
638
1065
9
161
1564
10
1001
1365
11
554
1541
12
280
1327
13
710
1716
14
709
1635
15
775
1002
16
864
1015
17
558
1666
18
220
0177
19
397
1353
20
55
0426
21
898
0227
22
759
0506
23
367
0336
24
299
1333
25
1018
1745
26

P-codeRelative
Advance(Hours) **P1(t+24)
P2(t+24)
P3(t+24)
P4(t+24)
P5(t+24)
P6(t+24)
P7(t+24)
P8(t+24)
P9(t+24)
P10(t+24)
P11(t+24)
P12(t+24)
P13(t+24)
P14(t+24)
P15(t+24)
P16(t+24)
P17(t+24)
P18(t+24)
P19(t+24)
P20(t+24)
P21(t+24)
P22(t+24)
P23(t+24)
P24(t+24)
P25(t+24)
P26(t+24)

First
10 Chips
Octal*
C/A
1760
1236
0063
0626
0126
1674
1234
0271
0712
0213
0412
0236
0450
0061
0142
0775
0762
0111
1600
0424
1351
1550
1271
1441
0444
0032

First
12 Chips
Octal
P
3373
3757
7545
5440
4402
4023
0233
2337
3375
3754
3544
7440
1402
6423
1033
2637
7135
5674
0514
6064
1210
6726
1171
6656
1105
6660

*In the octal notation for the first 10 chips of the C/A-code or the initial settings as shown in thistable, the first digit (1/0) represents a "1" or “0”, respectively, for the first chip and the last
three digits are the conventional octal representation of the remaining 9 chips.
(For example, the first 10 chips of the C/A-code for PRN Signal Assembly No. 38 are: 1111110000).
**Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Section 3.3.2.1.
NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of a specific
C/A and a specific P-code phase, as shown above.
NOTE #2: PRNs 38-63 are required per this Table if a manufacturer chooses to include these PRNs
in their receiver design.

8

IS-GPS-200L
14 May 2020

Table 3-IIa. Code Phase Assignments (IIR-M, IIF, and subsequent blocks
only) (sheet 1 of 2)
SV
ID
No.

GPS
PRN
Signal
No.

Initial Shift Register State (Octal)
L2 CM
L2 CL

End Shift Register State (Octal)
L2 CM *
L2 CL **

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

742417664
756014035
002747144
066265724
601403471
703232733
124510070
617316361
047541621
733031046
713512145
024437606
021264003
230655351
001314400
222021506
540264026
205521705
064022144

552566002
034445034
723443711
511222013
463055213
667044524
652322653
505703344
520302775
244205506
236174002
654305531
435070571
630431251
234043417
535540745
043056734
731304103
412120105

624145772
506610362
220360016
710406104
001143345
053023326
652521276
206124777
015563374
561522076
023163525
117776450
606516355
003037343
046515565
671511621
605402220
002576207
525163451

267724236
167516066
771756405
047202624
052770433
761743665
133015726
610611511
352150323
051266046
305611373
504676773
272572634
731320771
631326563
231516360
030367366
713543613
232674654* Short cycled period = 10230** Short cycled period = 767250

NOTE: There are many other available initial register states which can be used for other signaltransmitters including any additional SVs in the future.

9

IS-GPS-200L
14 May 2020

Table 3-IIa. Code Phase Assignments (IIR-M, IIF, and subsequent blocks
only) (sheet 2 of 2)
SV
ID
No.
20
21
22
23
24
25
26
27
28
29
30
31
32
65
66
67
68
69

GPS
PRN
Signal
No.
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

Initial Shift Register State (Octal)
L2 CM
L2 CL

End Shift Register State (Octal)
L2 CM *
L2 CL **

120161274
044023533
724744327
045743577
741201660
700274134
010247261
713433445
737324162
311627434
710452007
722462133
050172213
500653703
755077436
136717361
756675453
435506112

365636111
143324657
110766462
602405203
177735650
630177560
653467107
406576630
221777100
773266673
100010710
431037132
624127475
154624012
275636742
644341556
514260662
133501670

266527765
006760703
501474556
743747443
615534726
763621420
720727474
700521043
222567263
132765304
746332245
102300466
255231716
437661701
717047302
222614207
561123307
240713073

641733155
730125345
000316074
171313614
001523662
023457250
330733254
625055726
476524061
602066031
012412526
705144501
615373171
041637664
100107264
634251723
257012032
703702423* Short cycled period = 10230** Short cycled period = 767250
NOTE: There are many other available initial register states which can be used for other signaltransmitters including any additional SVs in the future.

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Table 3-IIb. Expanded Code Phase Assignments (GPS III, GPS IIIF, andsubsequent blocks only)
SV
ID
No.

GPS
PRN
Signal
No.

70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95

38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63

Initial Shift Register State (Octal)
L2 CM
L2 CL

771353753
226107701
022025110
402466344
752566114
702011164
041216771
047457275
266333164
713167356
060546335
355173035
617201036
157465571
767360553
023127030
431343777
747317317
045706125
002744276
060036467
217744147
603340174
326616775
063240065
111460621***

End Shift Register State (Octal)
L2 CM *
L2 CL **

101232630
453413162
132525726
637760505
315216367
612775765
377046065
136315217
655351360
264252240
435776513
113027466
744242321
774524245
024346717
161633757
562646415
603442167
731455342
213146546
723352536
721323277
000013134
207073253
011566642
130632332
475432222
606370621
463506741
330610170
617127534
744312067
026050332
154235152
733774235
525024652
751477772
535207413
417631550
655375733
052247456
316666241
560404163
525453337
417751005
114323414
004302173
755234667
715005045
526032633
001154457
602375063
Short cycled period = 10230
Short cycled period = 767250.

463624741
673421367
703006075
746566507
444022714
136645570
645752300
656113341
015705106
002757466
100273370
304463615
054341657
333276704
750231416
541445326
316216573
007360406
112114774
042303316
353150521
044511154
244410144
562324657
027501534
521240373

NOTE #1: There are many other available initial register states which can be used for other signaltransmitters including any additional SVs in the future.
NOTE #2: PRNs 38-63 are required per this Table if a manufacturer chooses to include these PRNs intheir receiver design.

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3.2.1.6 Non-Standard Codes.
The NSC, NSCM, NSCL, and NSY codes, used to protect the user from tracking anomalousnavigation signals, are not for utilization by the user and, therefore, are not defined in thisdocument.

3.2.2 NAV Data.
The legacy navigation (LNAV) data, D(t), includes SV ephemerides, system time, SV clock
behavior data, status messages and C/A to P (or Y) code handover information, etc. The 50 bps
data is modulo-2 added to the P(Y)- and C/A- codes; the resultant bit-trains are used to modulate
the L1 and L2 carriers. For a given SV, the data train D(t), if present, is common to the P(Y)- andC/A- codes on both the L1 and L2 channels. The content and characteristics of the LNAV data,
D(t), are given in Appendix II of this document for LNAV data transmitted by SVs assigned to thelower set of PRN numbers (PRN 1-32) and Appendix IV of this document for LNAV datatransmitted by SVs assigned to the upper set of PRN numbers (PRN 33-63).
For Block IIR-M, Block IIF, and subsequent blocks of SVs, civil navigation (CNAV) data, D C(t),also includes SV ephemerides, system time, SV clock behavior, status messages, etc. The D C(t)is a 25 bps data stream which is encoded by a rate ½ convolutional encoder. When selected byground command, the resulting 50 sps symbol stream is modulo-2 added to the L2 CM-code; theresultant bit-train is combined with L2 CL-code using chip by chip time-division multiplexing
method (i.e. alternating between L2 CM  data and L2 CL chips); the multiplexed bit-train is used
to modulate the L2 carrier. The content and characteristics of the CNAV data, D C(t), are given in
Appendix III of this document.

3.2.3 L1/L2 Signal Structure.
The L1 consists of two carrier components which are in phase quadrature with each other. Each
carrier component is bi-phase shift key (BPSK) modulated by a separate bit train. One bit train is
the modulo-2 sum of the P(Y)-code and LNAV data, D(t), while the other is the modulo-2 sum of
the C/A-code and the LNAV data, D(t). For Block II/IIA and IIR, the L2 is BPSK modulated by only
one of those two bit trains; the bit train to be used for L2 modulation is selected by groundcommand. A third modulation mode is also selectable on the L2 channel by ground command: it
utilizes the P(Y)-code without the LNAV data as the modulating signal. For a particular SV, alltransmitted signal elements (carriers, codes and data) are coherently derived from the same onboard frequency source.
For Block IIR-M, Block IIF, and subsequent blocks of SVs, the L2 consists of two carriercomponents. One carrier component is BPSK modulated by the bit train which is the modulo-2
sum of the P(Y)-code with or without LNAV data D(t), while the other is BPSK modulated by any
one of three other bit trains which are selectable by ground command. The three possible bit
trains are: (1) the modulo-2 sum of the C/A-code and D(t); (2) the C/A-code with no data and;(3) a chip-by-chip time multiplex combination of bit trains consisting of the L2 CM-code with DC(t)and the L2 CL-code with no data. The L2 CM-code with the 50 sps symbol stream of DC(t) is

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time-multiplexed with L2 CL-code at a 1023 kHz rate as described in paragraph 3.2.2. The first L2
CM-code chip starts synchronously with the end/start of week epoch.
The different configurations and combinations of codes/signals specified in this section are shownin Table 3-III.
Table 3-III.

Signal Configuration

L1

L2**

SV Blocks
In-Phase*

Block II/IIA/IIR

Block IIR-M/IIF/
and GPS III/ IIIF

Notes:

P(Y)  D(t)P(Y)  D(t)Quadrature-Phase*

In-Phase*

Quadrature-Phase*

C/A  D(t)P(Y)  D(t)
or
P(Y)
or
C/A  D(t)Not Applicable

C/A  D(t)P(Y)  D(t)orP(Y)

L2 CM  DC(t) with L2 CLorC/A  D(t)orC/A1) The configuration identified in this table reflects only the content of Section 3.2.3 and does notshow all available codes/signals on L1/L2.
 = “exclusive-or” (modulo-2 addition)
D(t) = LNAV data at 50 bps
DC(t) = CNAV data at 25 bps with FEC encoding resulting in 50 sps***

Terminology of “in-phase” and “quadrature-phase” is used only to identify the relative phasequadrature relationship of the carrier components (i.e. 90 degrees offset of each other).
The two carrier components on L2 may not have the phase quadrature relationship. They may bebroadcast on same phase (ref. Section 3.3.1.5).

3.3 Interface Criteria.
The criteria specified in the following define the requisite characteristics of the SS/US interface forthe L1 and L2.

3.3.1 Composite Signal.
The following criteria define the characteristics of the composite signals.

3.3.1.1 Frequency Plan.
For Block IIA, IIR, IIR-M, and IIF satellites, the requirements specified in this IS shall pertain to thesignal contained within two 20.46 MHz bands; one centered about the L1 nominal frequency and
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the other centered about the L2 nominal frequency (see Table 3-Vb). For GPS III, GPS IIIF, andsubsequent satellites, the requirements specified in this IS shall pertain to the signal contained
within two 30.69 MHz bands; one centered about the L1 nominal frequency and the othercentered about the L2 nominal frequency (see Table 3-Vc). The carrier frequencies for the L1 andL2 signals shall be coherently derived from a common frequency source within the SV. The
nominal frequency of this source -- as it appears to an observer on the ground -- is 10.23 MHz.
The SV carrier frequency and clock rates -- as they would appear to an observer located in the SV-- are offset to compensate for relativistic effects. The clock rates are offset by  f/f = -4.4647E10, equivalent to a change in the P-code chipping rate of 10.23 MHz offset by a  f = -4.5674E-3
Hz. This is equal to 10.2299999954326 MHz. The nominal carrier frequencies (f 0) shall be
1575.42 MHz, and 1227.6 MHz for L1 and L2, respectively.

3.3.1.2 Correlation Loss.
The correlation loss is defined as the difference between the signal power received in the
bandwidth defined in 3.3.1.1 (excluding signal combining loss) and the signal power recovered in
an ideal correlation receiver of the same bandwidth using an exact replica of the waveform within
an ideal sharp-cutoff filter bandwidth, whose bandwidth corresponds to that specified in 3.3.1.1
and whose phase is linear over that bandwidth.
The total allowable correlation loss due to SV modulation and filtering imperfections, which is afunction of signal, shall be:

Code

Correlation Loss

Correlation Loss

(IIF and prior SVs)

(GPS III/ IIIF SVs)

C/A & L2C

0.6 dB

0.3 dB

L1P(Y) & L2P(Y)

0.6 dB

0.6 dB

3.3.1.3 Carrier Phase Noise.
The phase noise spectral density of the unmodulated carrier shall be such that a phase locked
loop of 10 Hz one-sided noise bandwidth shall be able to track the carrier to an accuracy of 0.1
radians rms.

3.3.1.4 Spurious Transmissions.
In-band spurious transmissions, from the SV, shall be at or below -40 dBc over the respective
bands specified in 3.3.1.1. In-band spurious transmissions are defined as transmissions within
the bands specified in 3.3.1.1 which are not expressly components of the L1 and L2 signals.

3.3.1.5 Signal Component Phasing.
3.3.1.5.1 Phase Quadrature.
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The two L1 carrier components modulated by the two separate bit trains (C/A-code plus data andP(Y)-code plus data) shall be in phase quadrature (within ±100 milliradians) with the C/A signal
carrier lagging the P signal by 90 degrees. Referring to the phase of the P carrier when Pi(t)equals zero as the "zero phase angle", the P(Y)- and C/A-code generator output shall control therespective signal phases in the following manner: when P i(t) equals one, a 180-degree phasereversal of the P-carrier occurs; when Gi(t) equals one, the C/A carrier advances 90 degrees;
when the Gi(t) equals zero, the C/A carrier shall be retarded 90 degrees (such that when G i(t)changes state, a 180-degree phase reversal of the C/A carrier occurs). The resultant nominal
composite transmitted signal phases as a function of the binary state of only the two modulating
signals are as shown in Table 3-IV.
For Block IIR-M, IIF, and subsequent blocks of SVs, the two L2 carrier components shall be either
in phase quadrature or in the same phase (within ±100 milliradians) - see paragraph 3.3.1.5.3 foradditional information. The civil signal carrier component is modulated by any one of three (IIF) or
four (IIR-M) different bit trains as described in paragraph 3.2.3. The resultant composite
transmitted signal phases will vary as a function of the binary state of the modulating signals aswell as the signal power ratio and phase quadrature relationship. Beyond these considerations,additional carrier components in Block IIR-M, IIF, and subsequent blocks of SVs will result incomposite transmitted signal phase relationships other than the nominal special case of Table 3IV. The current phase relationship of the two L2 carrier components (L2C and L2P(Y)) shall be
indicated by means of bit 273 of the CNAV Type 10 Message (See section 30.3.3), where zero
indicates phase quadrature, with the L2C lagging the L2P(Y) by 90 degrees, and one indicatesthat L2C and L2P(Y) are in-phase. If the CNAV message is not available, then the L2C and
L2P(Y) shall be fixed in phase quadrature.

3.3.1.5.2 Phase Crosstalk.
For Block IIF, the crosstalk between the C/A, when selected, and P(Y) signals shall not exceed 20 dB in the L1 and L2. The crosstalk is the relative power level of the undesired signal to thedesired reference signal.

3.3.1.5.3 Phase Continuity.
While the satellite is broadcasting standard C/A, P(Y), and L2C codes with data that indicates that
C/A, P(Y), and L2C signal health (respectively) is OK, there will not be any commanded operation
causing an intentional phase discontinuity. This does not apply to phase discontinuities causedby signal modulation. Prior to health data being available on L2C, satellites will be set unhealthy
using the non-standard code.

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3.3.1.6 User-Received Signal Levels.
The SV shall provide L1 and L2 navigation signal strength at end-of-life (EOL), worst-case, inorder to meet the minimum levels specified in Table 3-V. Any combining operation done by the SV
and associated loss is compensated by an increase in SV transmitted power and thus transparent
to the User Segment. The minimum received power is measured at the output of a 3 dBi linearlypolarized user receiving antenna (located near ground) at worst normal orientation, when the SV
is above a 5-degree elevation angle. The received signal levels are observed within the in-band
allocation defined in para. 3.3.1.1.
The Block IIF SV shall provide L1 and L2 signals with the following characteristic: the L1 off-axis
relative power (referenced to peak transmitted power) shall not decrease by more than 2 dB fromthe Edge-of-Earth (EOE) to nadir, nor more than 10 dB from EOE to 20 degrees off nadir, and no
more than 18 dB from EOE to 23 degrees off nadir; the L2 off-axis power gain shall not decreaseby more than 2 dB from EOE to nadir, and no more than 10 dB from EOE to 23 degrees off nadir;the power drop off between EOE and 23 degrees shall be in a monotonically decreasing fashion.
The GPS III and GPS IIIF SV shall provide L1 and L2 signals with the following characteristic: theL1 off-axis relative power (referenced to peak transmitted power) shall not decrease by more than
2 dB from the Edge-of-Earth (EOE) to nadir; the L2 off-axis power gain shall not decrease by
more than 2 dB from EOE to nadir; the power drop off between EOE and ±26 degrees shall be ina monotonically decreasing fashion. Additional related data is provided as supporting material inparagraph 6.3.1.

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Table 3-IV.

Composite L1 Transmitted Signal Phase ** (Block II/IIA and IIR SVs Only)

Nominal Composite L1
Signal Phase*
0°-70.5°+109.5°180°**

Code State
P

C/A

0
1
0
1

0
0
1
1

*
Relative to 0, 0 code state with positive angles leading and negative angles lagging.
Based on the composite of two L1 carrier components with 3 dB difference in the power levels of the two.

Table 3-Va. Received Minimum RF Signal Strength for Block IIA, IIR, IIR-M, IIF, GPS III, and
GPS IIIF Satellites (20.46 MHz Bandwidth)

SignalSV Blocks

ChannelP(Y)C/A or L2C

L1-161.5 dBW-158.5 dBW

L2-164.5 dBW-164.5 dBW

L1-161.5 dBW-158.5 dBW

L2-161.5 dBW-160.0 dBW

L1-161.5 dBW-158.5 dBW

L2-161.5 dBW-158.5 dBW

IIA/IIR

IIR-M/IIF

GPS III/ IIIF

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Table 3-Vb. Received Minimum RF Signal Strength for GPS III and GPS IIIF (30.69 MHz
Bandwidth)

SignalSV Blocks

ChannelP(Y)C/A or L2C

L1-161.5 dBW-158.5 dBW

L2-161.5 dBW-158.5 dBW

GPS III/ IIIF

3.3.1.6.1 Space Service Volume (SSV) User-Received Signal Levels.
The SV shall provide L1 and L2 navigation signal strength at end-of-life (EOL), worst-case, in order
to meet the minimum levels specified in Table 3-Vc. The minimum received power is measured at
the output of a 0 dBi right-hand circularly polarized (i.e. 0 dB axial ratio) user receiving antenna at
normal orientation, at the off-nadir angles defined in Table 3-Vc. The received signal levels areobserved within the in-band allocation defined in paragraph 3.3.1.1.

Table 3-Vc. Space Service Volume (SSV) Received Minimum RF Signal Strength for GPS III,GPS IIIF, and Subsequent Satellites over the Bandwidth Specified in 3.3.1.1 – GEO Based
Antennas

SignalSV Blocks

Channel

Off Axis Angle
Relative To Nadir

III andSubsequentL1

23.5 deg-187.0 dBW*

-184.0 dBW*

L2

26.0 deg-186.0 dBW-183.0 dBWP(Y)C/A or L2C* Over 99.5% of the solid angle inside a cone with its apex at the SV and measured from 0 degrees at the centerof the Earth

3.3.1.7 Equipment Group Delay.
Equipment group delay is defined as the delay between the signal radiated output of a specific SV(measured at the antenna phase center) and the output of that SV's on-board frequency source;
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the delay consists of a bias term and an uncertainty. The bias term is of no concern to the US
since it is included in the clock correction parameters relayed in the LNAV/CNAV data, and istherefore accounted for by the user computations of system time (reference paragraphs
20.3.3.3.3.1, 30.3.3.2.3). The uncertainty (variation) of this delay as well as the group delaydifferential between the signals of L1 and L2 are defined in the following.

3.3.1.7.1 Group Delay Uncertainty.
The effective uncertainty of the group delay shall not exceed 3.0 nanoseconds (95% probability).

3.3.1.7.2 Group Delay Differential.
The group delay differential between the radiated L1 and L2 signals (i.e. L1 P(Y) and L2 P(Y), L1
P(Y) and L2C) is specified as consisting of random plus bias components. The mean differential isdefined as the bias component and will be either positive or negative. For a given navigation
payload redundancy configuration, the absolute value of the mean differential delay shall not
exceed 15.0 nanoseconds. The random plus non-random variations about the mean shall not
exceed 3.0 nanoseconds (95% probability), when including consideration of the temperature andantenna effects during a vehicle orbital revolution. Corrections for the bias components of thegroup delay differential are provided to the US in the LNAV/CNAV message using parameters
designated as TGD (reference paragraph 20.3.3.3.3.2) and Inter-Signal Correction (ISC) (reference
paragraph 30.3.3.3.1.1).

3.3.1.7.3 Space Service Volume Group Delay Differential.
The group delay differential between the radiated L1 and L2 signals with respect to the Earth
Coverage signal for users of the Space Service Volume are provided in
http://www.igs.org/products/ssv.

3.3.1.8 Signal Coherence.
All transmitted signals for a particular SV shall be coherently derived from the same on-board
frequency standard. On the L1 carrier, the chip transitions of the modulating signals, C/A and
L1P(Y), and on the L2 carrier the chip transitions of L2P(Y) and L2C, shall be such that the
average time difference between the chips on the same carrier do not exceed 10 nanoseconds.
The variable time difference shall not exceed 1 nanosecond (95% probability), when including
consideration of the temperature and antenna effect changes during a vehicle orbital revolution.
Corrections for the bias components of the time difference are provided to the US in the CNAV
message using parameters designated as ISCs (reference paragraph 30.3.3.3.1.1).

3.3.1.9 Signal Polarization.
The transmitted signal shall be right-hand circularly polarized (RHCP). For the angular range of±13.8 degrees from nadir, L1 ellipticity shall be no worse than 1.2 dB for Block IIA and shall be noworse than 1.8 dB for Block IIR/IIR-M/IIF/III/IIIF SVs. L2 ellipticity shall be no worse than 3.2 dB

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for Block II/IIA SVs and shall be no worse than 2.2 dB for Block IIR/IIR-M/IIF and GPS III/IIIF SVs
over the angular range of ±13.8 degrees from nadir.

3.3.2 PRN Code Characteristics.
The characteristics of the P-, L2 CM-, L2 CL-, and the C/A-codes are defined below in terms of
their structure and the basic method used for generating them. Figure 3-1 depicts a simplified
block diagram of the scheme for generating the 10.23 Mbps P i(t) and the 1.023 Mbps Gi(t) patterns(referred to as P- and C/A-codes respectively), and for modulo-2 summing these patterns with the
LNAV bit train, D(t), which is clocked at 50 bps. The resultant composite bit trains are then used tomodulate the signal carriers.

3.3.2.1 Code Structure.
For PRN codes 1 through 37, the Pi(t) pattern (P-code) is generated by the modulo-2 summation of
two PRN codes, X1(t) and X2(t - iT), where T is the period of one P-code chip and equals(1.023E7)-1 seconds, while i is an integer from 1 through 37. This allows the generation of 37
unique P(t) code phases (identified in Table 3-Ia) using the same basic code generator.

Expanded P-code PRN sequences, Pi(t) where 38 ≤ i ≤ 63, are described as follows:

Pi(t) = Pi-37(t + T) (where T will equal 24 hours)

therefore, the equation isPi(t) = Pi-37x(t + i * 24 hours),

where i is an integer from 64 to 210, x is an integer portion of (i-1)/37.

As an example, the P-code sequence for PRN 38 is the same sequence as PRN 1 shifted 24
hours into a week (i.e. 1st chip of PRN 38 at beginning of week is the same chip for PRN 1 at 24hours after beginning of week). The list of expanded P-code PRN assignments is identified inTable 3-Ib.

The linear Gi(t) pattern (C/A-code) is the modulo-2 sum of two 1023-bit linear patterns, G1 and G2i.
The latter sequence is selectively delayed by an integer number of chips to produce many different
G(t) patterns (defined in Tables 3-Ia and 3-Ib).

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The CM,i(t) pattern (L2 CM-code) is a linear pattern which is reset with a specified initial state every
code count of 10230 chips. Different initial states are used to generate different C M,i(t) patterns(defined in Tables 3-IIa and 3-IIb).

The CL,i(t) pattern (L2 CL-code) is also a linear pattern but with a longer reset period of 767250
chips. Different initial states are used to generate different C L,i(t) patterns (defined in Tables 3-IIaand 3-IIb).

For a given SV ID, two different initial states are used to generate different C L,i(t) and CM,i(t)patterns.

Section 6.3.6 provides a selected subset of additional P-, L2 CM-, L2 CL-, and the C/A-code
sequences with assigned PRN numbers.

EPOCH
DETECT

X1 EPOCH

EPOCH
RESET

20

50 Hz

Z-COUNT
1 KHz

ZCOUNTER

X1
GENERATOR

1.023
MHz

10

GOLD CODE
GENERATOR

EPOCH
DETECT

X1(t)Gi (t)RESET
COMMAND
GENERATOR

Gi(t)RECLOCKING
DEVICE

D(t)FORMATTEDDATA

X2i(t)Pi(t)REMOTE
COMMAND

EPOCH
RESET

CODE
SELECT
DEVICE

X2
GENERATOR

10.23 MHzFREQUENCY
SOURCED(t)DATA
ENCODER

Pi(t)

D(t)

Pi(t)

Figure 3-1. Generation of P-, C/A-Codes and Modulating Signals

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3.3.2.2 P-Code Generation.
Each Pi(t) pattern is the modulo-2 sum of two extended patterns clocked at 10.23 Mbps (X1 and
X2i). X1 itself is generated by the modulo-2 sum of the output of two 12-stage registers (X1A and
X1B) short cycled to 4092 and 4093 chips respectively. When the X1A short cycles are counted to3750, the X1 epoch is generated. The X1 epoch occurs every 1.5 seconds after 15,345,000 chipsof the X1 pattern have been generated. The polynomials for X1A and X1B, as referenced to theshift register input, are:
X1A: 1 + X6 + X8 + X11 + X12, and
X1B: 1 + X1 + X2 + X5 + X8 + X9 + X10 + X11 + X12.

Samples of the relationship between shift register taps and the exponents of the corresponding
polynomial, referenced to the shift register input, are as shown in Figures 3-2, 3-3, 3-4 and 3-5.
The state of each generator can be expressed as a code vector word which specifies the binary
sequence constant of each register as follows: (a) the vector consists of the binary state of eachstage of the register (Note that in the code vector convention, the output is on the left while in
Figures 3-2 through 3-5 the output tap is on the right.), (b) the stage 12 value appears at the left
followed by the values of the remaining states in order of descending stage numbers, and (c) theshift direction is from lower to higher stage number with stage 12 providing the current output. This
code vector convention represents the present output and 11 future outputs in sequence. Using
this convention, at each X1 epoch, the X1A shift register is initialized to code vector 001001001000
and the X1B shift register is initialized to code vector 010101010100. The first chip of the X1A
sequence and the first chip of the X1B sequence occur simultaneously in the first chip interval of
any X1 period.
The natural 4095 chip cycles of these generating sequences are shortened to cause precession of
the X1B sequence with respect to the X1A sequence during subsequent cycles of the X1A
sequence in the X1 period. Re-initialization of the X1A shift register produces a 4092 chipsequence by omitting the last 3 chips (001) of the natural 4095 chip X1A sequence. Reinitialization of the X1B shift register produces a 4093 chip sequence by omitting the last 2 chips(01) of the natural 4095 chip X1B sequence. This results in the phase of the X1B sequence
lagging by one chip for each X1A cycle in the X1 period.
The X1 period is defined as the 3750 X1A cycles (15,345,000 chips) which is not an integer
number of X1B cycles. To accommodate this situation, the X1B shift register is held in the final
state (chip 4093) of its 3749th cycle. It remains in this state until the X1A shift register completes
its 3750th cycle (343 additional chips). The completion of the 3750th X1A cycle establishes thenext X1 epoch which re-initializes both the X1A and X1B shift registers starting a new X1 cycle.

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POLYNOMIAL X1A:
1+X

6 + X 8 + X 11 + X 12

STAGE
NUMBERS

1

2

3

4

5

6

7

8

9

10

11

12

0

0

0

1

0

0

1

0

0

1

0

0

0

1

2

3

4

5

6

7

8

9

INITIAL
CONDITIONS10OUTPUT

11

12

TAP
NUMBERSSHIFT DIRECTION

Figure 3-2. X1A Shift Register Generator Configuration

POLYNOMIAL X1B:
1
2
5
8
9
10
11
12
1+X +X +X +X +X +X +X +X

STAGE
NUMBERS

0

1

2

3

4

5

6

7

8

9

10

11

12

0

0

1

0

1

0

1

0

1

0

1

0

1

2

3

4

5

6

7

INITIAL
CONDITIONS

8

9

10

TAP
NUMBERSSHIFT DIRECTION

Figure 3-3. X1B Shift Register Generator Configuration

23

11

OUTPUT

12

IS-GPS-200L
14 May 2020

POLYNOMIAL X2A:
1
3
4
5
7
8
9
10
11
12
1+X +X +X +X +X +X +X +X +X +X

STAGE
NUMBERS

1

2

3

4

5

6

7

8

9

10

11

12

1

0

1

0

0

1

0

0

1

0

0

1

0

1

2

3

4

5

6

7

8

9

INITIAL
CONDITIONS

1011OUTPUT

12

TAP
NUMBERSSHIFT DIRECTION

Figure 3-4. X2A Shift Register Generator Configuration
POLYNOMIAL X2B:
1 + X2 + X3 + X4 + X8 + X9 + X12

STAGE
NUMBERS

0

1

2

3

4

5

6

7

8

9

10

11

12

0

0

1

0

1

0

1

0

1

0

1

0

1

2

3

4

5

6

7

INITIAL
CONDITIONS

8

9

10

11

OUTPUT

12

TAP
NUMBERSSHIFT DIRECTION

Figure 3-5. X2B Shift Register Generator Configuration
The X2i sequences are generated by first producing an X2 sequence and then delaying it by aselected integer number of chips, i, ranging from 1 to 37. Each of the X2 i sequences is thenmodulo-2 added to the X1 sequence thereby producing up to 37 unique P(t) sequences.
24

IS-GPS-200L
14 May 2020

The X2A and X2B shift registers, used to generate X2, operate in a similar manner to the X1A andX1B shift registers. They are short-cycled, X2A to 4092 and X2B to 4093, so that they have thesame relative precession rate as the X1 shift registers. X2A epochs are counted to include 3750
cycles and X2B is held in the last state at 3749 cycle until X2A completes its 3750th cycle. The
polynomials for X2A and X2B, as referenced to the shift register input, are:
X2A: 1 + X1 + X3 + X4 + X5 + X7 + X8 + X9 + X10 + X11 + X12, andX2B: 1 + X2 + X3 + X4 + X8 + X9 + X12.

(The initialization vector for X2A is 100100100101 and for X2B is 010101010100).
The X2A and X2B epochs are made to precess with respect to the X1A and X1B epochs bycausing the X2 period to be 37 chips longer than the X1 period. When the X2A is in the last stateof its 3750th cycle and X2B is in the last state of its 3749th cycle, their transitions to theirrespective initial states are delayed by 37 chip time durations.
At the beginning of the GPS week, X1A, X1B, X2A and X2B shift registers are initialized to
produce the first chip of the week. The precession of the shift registers with respect to X1A
continues until the last X1A period of the GPS week interval. During this particular X1A period,
X1B, X2A and X2B are held when reaching the last state of their respective cycles until that X1A
cycle is completed (see Table 3-VI). At this point, all four shift registers are initialized and provide
the first chip of the new week.
Figure 3-6 shows a functional P-code mechanization for the 37 unique Pi(t) code phases, 1 ≤ i ≤37. Signal component timing for these original P(t) code phases is shown in Figure 3-7, while theend-of-week reset timing and the final code vector states are given in Tables 3-VI and 3-VII,
respectively.

25

IS-GPS-200L
14 May 2020

10.23 MHz

X1
EPOCH

SET X1A EPOCH

C

X1A

I

R

REGISTER
6
12

1

A

4092
DECODE

6, 8, 11, 12

3750

RESUME

HALT

Z-COUNTER
403,200

X1B CLOCKCONTROLCI
1

SET X1B
EPOCH

R

X1B
REGISTER

3749

B

12

7 DAY
RESET

4093
DECODE1, 2, 5, 8,
9, 10, 11, 12

REGISTERINPUTS

END/WEEKX2A CLOCKCONTROL

HALT

C - CLOCKI - INPUT
R - RESET TO
INITIAL
CONDITIONSON NEXT
CLOCK

3750
C
I

1

SET X2AR

X2A
REGISTER

EPOCH
C

12
4092
DECODE1, 3, 4, 5, 7,
8, 9, 10, 11, 12

START/WEEKRESUME

X2
EPOCH

37

ENABLEA
X1
END/WEEK

HALT
Pi

B

X2B CLOCKCONTROLCI

X2B
REGISTER
1 2
12

R

X2 i
SET X2B
EPOCH

3749

1
i

C

4093
DECODE2, 3, 4,8, 9, 12Figure 3-6. P-Code Generation

26

X2

SHIFT
REGISTERIS-GPS-200L
14 May 2020

0

1

2

3

0

1

2

3

0

X1 EPOCHS
37 Chips

74 Chips

X2 EPOCHS *P EpochTIME
0

1.5 sec

3.0 sec

4.5 sec

7 days14 days* Does not include any offset due to PRN delay.

Figure 3-7. P-Code Signal Component Timing

27

IS-GPS-200L
14 May 2020

Table 3-VI.

P-Code Reset Timing (Last 400 sec of 7-day period) **Code Chip
X1A-Code

X1B-Code

X2A-Code

X2B-Code

1

345

1070

967

























3023

3367

























3127

3471

4092







4093


















4092

4093

3749

4093

3989

4092

























4093

4092

4093

4092*

* Last Chip of Week.
** Does not include any X2 offset due to PRN delay.

Table 3-VII. Final Code Vector States

Code
X1A
X1B
X2A
X2B

Chip Number

Vector State

4091
4092
4092
4093
4091
4092
4092
4093

100010010010
000100100100
100101010101
001010101010
111001001001
110010010010
000101010101
001010101010

Vector State for 1st Chip
following Epoch
001001001000
010101010100
100100100101
010101010100

NOTE: First Chip in each sequence is output bit whose leading edge occurs simultaneously with the epoch.

28

IS-GPS-200L
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3.3.2.3 C/A-Code Generation.
Each Gi(t) sequence is a 1023-bit Gold-code which is itself the modulo-2 sum of two 1023-bit linear
patterns, G1 and G2i. The G2i sequence is formed by effectively delaying the G2 sequence by an
integer number of chips. The G1 and G2 sequences are generated by 10-stage shift registers
having the following polynomials as referred to in the shift register input (see Figures 3-8 and 3-9).
G1 = X10 + X3 + 1, andG2 = X10 + X9 + X8 + X6 + X3 + X2 + 1.
The initialization vector for the G1 and G2 sequences is 1111111111. The G1 and G2 shift
registers are initialized at the P-coder X1 epoch. The G1 and G2 registers are clocked at 1.023
MHz derived from the 10.23 MHz P-coder clock. The initialization by the X1 epoch phases the1.023 MHz clock to insure that the first chip of the C/A-code begins at the same time as the firstchip of the P-code.
The effective delay of the G2 sequence to form the G2i sequence may be accomplished by
combining the output of two stages of the G2 shift register by modulo-2 addition (see Figure 3-10).
However, this two-tap coder implementation generates only a limited set of valid C/A-codes. Table
3-I contains a tabulation of the G2 shift register taps selected and their corresponding P-code X2i
and PRN signal numbers together with the first several chips of each resultant PRN code. Timing
relationships related to the C/A-code are shown in Figure 3-11.
POLYNOMIAL G1:
1+X

3 + X 10STAGE
NUMBERS

INPUT

0

1

2

3

4

5

6

7

8

9

10

1

1

1

1

1

1

1

1

1

1

1

2

3

4

5

INITIAL
CONDITIONS

6

7

8

9

TAP
NUMBERSSHIFT DIRECTION

Figure 3-8. G1 Shift Register Generator Configuration

29

OUTPUT

10

IS-GPS-200L
14 May 2020

POLYNOMIAL G2:
1+X

2 + X 3 +X 6 + X 8 + X 9 + X 10

STAGE
NUMBERS

INPUT

0

1

2

3

4

5

6

7

8

9

10

1

1

1

1

1

1

1

1

1

1

1

2

3

4

5

INITIAL
CONDITIONS

6

7

8

9

TAP
NUMBERSSHIFT DIRECTION

Figure 3-9. G2 Shift Register Generator Configuration

30

OUTPUT

10

IS-GPS-200L
14 May 2020

3

10

X1 EPOCH
I
S
C

10.23 MHzG1

G1
REGISTER

SYNCH
10
2

I
C
S

SYNCH

20

G EPOCH
1 kbps

3

6

8

9

10

G2

1023
DECODEGi
G2i
PHASE SELECT
LOGIC
50 bps TO DATA ENCODER
REGISTER INPUTS
C
I
S

-

CLOCK
INPUT
SET ALL ONES

Valid for C/A PRNs 1-37. For PRNs 38-63, the G1 Register should be XOR-ed directly to the G2 Register in order to make Gi.
These PRNs do not use the Phase Select Logic box for G2i generation.

Figure 3-10: Example C/A-Code Generation

31

IS-GPS-200L
14 May 2020

X1 Epoch @ 2/3 bps

1023

1023

1023

1023

1023

1023 BIT Gold Code @ 1023 kbps

0

1

etc.

1 msec

2

18

19

0

Gold Code Epochs @ 1000/sec

Data @ 50 cps

20 msec

Figure 3-11. C/A-Code Timing Relationships

3.3.2.4 L2 CM-/L2 CL-Code Generation.
Each CM,i(t) pattern (L2 CM-code) and CL,i(t) pattern (L2 CL-code) are generated using the samecode generator polynomial each clocked at 511.5 kbps. Each pattern is initiated and reset with a32

IS-GPS-200L
14 May 2020

specified initial state (defined in Table 3-II). CM,i(t) pattern is reset after 10230 chips resulting in acode period of 20 milliseconds, and CL,i(t) pattern is reset after 767250 chips resulting in a code
period of 1.5 seconds. The L2 CM and L2 CL shift registers are initialized at the P-coder X1
epoch. The first L2 CM-code chip starts synchronously with the end/start of week epoch. Timing
relationships related to the L2 CM-/L2 CL-codes are shown in Figure 3-12.
The maximal polynomial used for L2 CM- and L2 CL-codes is 1112225171 (octal) of degree 27.
The L2 CM and L2 CL code generator is conceptually described in Figure 3-13 using modular-type
shift register generator.
01
End/start ofweek

1.5 second

X1 Epoch @ 2/3
bps
767250767250 BIT L2 CL-Code @ 511.5

1
10230

kbps
2
10230

etc.

Chips

3
4
10230 10230

10230 BIT L2 CM-Code @ 511.5

737410230 10230

75
10230
20
msec

kbps

Data @ 50
cps

L2 CM @ 511.5kbps

L2 CL @ 511.5
kbps

L2C @ 1023kbps
Figure 3-12. L2 CM-/L2 CL-Code Timing Relationships

33

etc.

3

34
2

3

3

2

4

5

6

9

11

2

3

SHIFT DIRECTION

1

1 + X + X +X + X + X + X

3

POLYNOMIAL:

INITIAL CONDITIONS ARE A FUNCTION OF PRN AND CODE PERIOD (MODERATE/LONG)

3

DELAY
NUMBERS

+X

13

1

16

+X

19

1

21

+X +X

24

3

27

+X +X

OUTPUT

IS-GPS-200L
14 May 2020

Figure 3-13. L2 CM/L2 CL Shift Register Generator Configuration

IS-GPS-200L
14 May 2020

3.3.3 Navigation Data.
The content and format of the LNAV data, D(t) are given in Appendices II/IV of this document. The
content and format of the CNAV data, Dc(t) are given in Appendix III of this document.

3.3.3.1 Navigation Data Modulation (L2 CM).
For Block IIR-M, Block IIF, and subsequent blocks of SVs, the CNAV bit train, D C(t), is rate ½
encoded and, thus, clocked at 50 sps. The resultant symbol sequence is then modulo-2 added to
the L2 CM-code.

3.3.3.1.1 Forward Error Correction.
The CNAV bit train, DC(t), will always be Forward Error Correction (FEC) encoded by a rate ½
convolutional code. For Block IIR-M, the LNAV bit train, D(t), can be selected to be convolutionallyencoded. The resulting symbol rate is 50 sps. The convolutional coding will be constraint length
7, with a convolutional encoder logic arrangement as illustrated in Figure 3-14. The G1 symbol isselected on the output as the first half of a 40-millisecond data bit period.
Twelve-second navigation messages broadcast by the SV are synchronized with every eighth of
the SV's P(Y)-code X1 epochs. However, the navigation message is FEC encoded in a continuous
process independent of message boundaries (i.e. at the beginning of each new message, theencoder registers illustrated in Figure 3-14 contains the last six bits of the previous message).
Because the FEC encoding convolves successive messages, it is necessary to define whichtransmitted symbol is synchronized to SV time, as follows. The beginning of the first symbol that
contains any information about the first bit of a message will be synchronized to every eighth X1
epoch (referenced to end/start of week). The users’ convolutional decoders will introduce a fixed
delay that depends on their respective algorithms (usually 5 constraint lengths, or 35 bits), forwhich they must compensate to determine system time from the received signal. Thisconvolutional decoding delay and the various relationships with the start of the data blocktransmission and SV time are illustrated in Figure 3-15.
G2 (133 OCTAL)OUTPUT SYMBOLS(50 SPS)DATA INPUT(25 BPS)(ALTERNATING G1/G2)

G1 (171 OCTAL)SYMBOL
CLOCK

Figure 3-14. Convolutional Encoder35

IS-GPS-200L
14 May 2020

ENCODED DATA BLOCK
TRANSMITTED ON L2

DATA BLOCKDECODED BY
USER

ENCODEDDATA BLOCKRECEIVEDBY USERUSER’S DECODING DELAY
DOWNLINK DELAY

LATER

EARLY

SV 12 SECOND EPOCHS

Figure 3-15. Convolutional transmit/Decoding Timing Relationships

3.3.4 GPS Time and SV Z-Count.
GPS time is established by the Control Segment and is referenced to Coordinated Universal Time
(UTC) as maintained by the U.S. Naval Observatory (UTC (USNO)) zero time-point defined as
midnight on the night of January 5, 1980/morning of January 6, 1980. The largest unit used instating GPS time is one week defined as 604,800 seconds. GPS time may differ from UTC
because GPS time shall be a continuous time scale, while UTC is corrected periodically with an
integer number of leap seconds. There also is an inherent but bounded drift rate between the UTC
and GPS time scales. The OCS shall control the GPS time scale to be within one microsecond of
UTC (modulo one second).
The LNAV/CNAV data contains the requisite data for relating GPS time to UTC. The accuracy ofthis data during the transmission interval shall be such that it relates GPS time (maintained by the
MCS of the CS) to UTC (USNO) within 20 nanoseconds (one sigma). This data is generated by
the CS; therefore, the accuracy of this relationship may degrade if for some reason the CS isunable to upload data to a SV. At this point, it is assumed that alternate sources of UTC are nolonger available, and the relative accuracy of the GPS/UTC relationship will be sufficient for users.
Range error components (e.g. SV clock and position) contribute to the GPS time transfer error,
and under normal operating circumstances (dual-frequency time transfers from SV(s) whosenavigation message indicates a URA of eight meters or less), this corresponds to a 28 nanosecond(one sigma) apparent uncertainty at the SV. Propagation delay errors and receiver equipment
biases unique to the user add to this time transfer uncertainty.
In each SV the X1 epochs of the P-code offer a convenient unit for precisely counting andcommunicating time. Time stated in this manner is referred to as Z-count, which is given as abinary number consisting of two parts as follows:36

IS-GPS-200L
14 May 2020a.
The binary number represented by the 19 least significant bits of the Z-count isreferred to as the time of week (TOW) count and is defined as being equal to the number of X1
epochs that have occurred since the transition from the previous week. The count is short-cycled
such that the range of the TOW-count is from 0 to 403,199 X1 epochs (equaling one week) and isreset to zero at the end of each week. The TOW-count's zero state is defined as that X1 epoch
which is coincident with the start of the present week. This epoch occurs at (approximately)
midnight Saturday night-Sunday morning, where midnight is defined as 0000 hours on the UTC
scale which is nominally referenced to the Greenwich Meridian. Over the years the occurrence ofthe "zero state epoch" may differ by a few seconds from 0000 hours on the UTC scale since UTC
is periodically corrected with leap seconds while the TOW-count is continuous without suchcorrection. To aid rapid ground lock-on to the P-code signal, a truncated version of the TOWcount, consisting of its 17 most significant bits, is contained in the hand-over word (HOW) of the L1
and L2 LNAV data (D(t)) stream; the relationship between the actual TOW-count and its truncated
HOW version is illustrated by Figure 3-16.
b.
The most significant bits of the Z-count are a binary representation of the sequential
number assigned to the current GPS week (see paragraph 6.2.4).

37

IS-GPS-200L
14 May 2020

P(Y)-CODE EPOCH(END/START OF WEEK)X1 EPOCHS

1.5 sec

0403,192

403,196

1

2

3

4

5

6

7

8

403,199
DECIMAL EQUIVALENTS
OF ACTUAL TOW COUNTSSUBFRAME EPOCHS

6 sec

100,7990

12

DECIMAL EQUIVALENTS OF HOW-MESSAGE TOW COUNTSNOTES:
1.

TO AID IN RAPID GROUND LOCK-ON THE HAND-OVER WORD (HOW ) OF EACH
SUBFRAME CONTAINS A TRUNCATED TIME-OF-WEEK (TOW) COUNT

2.

THE HOW IS THE SECOND WORD IN EACH SUBFRAME (REFERENCE
PARAGRAPH 20.3.3.2).

3.

THE HOW-MESSAGE TOW COUNT CONSISTS OF THE 17 MSBs OF THE
ACTUAL TOW COUNT AT THE START OF THE NEXT SUBFRAME.

4.

TO CONVERT FROM THE HOW-MESSAGE TOW COUNT TO THE ACTUAL TOW
COUNT AT THE START OF THE NEXT SUBFRAME, MULTIPLY BY FOUR.

5.

THE FIRST SUBFRAME STARTS SYNCHRONOUSLY WITH THE END/START OFWEEK EPOCH.

Figure 3-16. Time Line Relationship of HOW Message

38

3

IS-GPS-200L
14 May 2020

6 NOTES
6.1 Acronyms
AI-

Availability Indicator

AODO

-

Age of Data Offset

A-S-

Anti-Spoofing

BPSK

-

Bi-Phase Shift Key

CDC-

Clock Differential Correction

CEI-

Clock, Ephemeris, Integrity

CNAV

-

Civil Navigationcps-

cycles per second

CRC-

Cyclic Redundancy CheckCS-

Control Segment

DC-

Differential Correction

dBc-

Power ratio of a signal to a (unmodulated) carrier signal, expressedin decibels

dBi-

Decibel with respect to isotropic antennadBW-

Decibel with respect to 1 W

DN-

Day Number

EAROM

-

Electrically Alterable Read-Only Memory

ECEF

-

Earth-Centered, Earth-Fixed

ECI-Earth-Centered, Inertial

EDC-

Ephemeris Differential Correction

EOE-

Edge-of-EarthEOL-

End of Life

ERD-

Estimated Range Deviation

FEC-

Forward Error Correction

GGTO

-

GPS/GNSS Time Offset

GNSS

-

Global Navigation Satellite System

GPS-

Global Positioning System

39

IS-GPS-200L
14 May 2020

GPSW

-

Global Positioning System Wing

HOW-

Hand-Over Word

ICC-

Interface Control Contractor

ID-

Identification

IERS

-

International Earth Rotation and Reference Systems Service

IODC

-

Issue of Data, Clock

IODE

-

Issue of Data, Ephemeris

IRM-

IERS Reference Meridian

IRP-

IERS Reference Pole

IS-

Interface Specification

ISC-

Inter-Signal Correction

LNAV

-

Legacy Navigation

LSB-

Least Significant Bit

LSF-

Leap Seconds Future

L2C-

L2 Civil Signal

L2 CL

-

L2 Civil-Long Code

L2 CM

-

L2 Civil-Moderate Code

MCS-

Master Control Station

MSB-

Most Significant Bit

NAV-Navigation

NDUS

-

NUDET Detection User Segment

NMCT

-

Navigation Message Correction Table

NSC-

Non-Standard C/A-Code

NSCL

-

Non-Standard L2 CL-Code

NSCM

-

Non-Standard L2 CM-Code

NSY-

Non-Standard Y-Code

OBCP

-

On-Board Computer Program

OCS-

Operational Control System

PPS-

Precise Positioning Service

40

IS-GPS-200L
14 May 2020

PRN-

Pseudo-Random Noise

RF-

Radio Frequency

RMS-

Root Mean Square

SA-

Selective Availability

SEP-

Spherical Error Probable

SPS-

Standard Positioning Service

sps-

symbols per second

SS-

Space Segment

SSV-Space Service Volume

SV-

Space Vehicle

SVN-

Space Vehicle Number

TBD-

To Be DeterminedTBS-

To Be Supplied

TLM-

Telemetry

TOW-

Time Of Week

UE-

User Equipment

URA-

User Range Accuracy

URE-

User Range Error

US-

User Segment

USNO

-

U.S. Naval Observatory

UTC-

Coordinated Universal TimeWGS 84-

World Geodetic System 1984

WN-

Data Sequence Propagation Week Number

WNe-

Extended Week Number

41

IS-GPS-200L
14 May 2020

6.2 Definitions
6.2.1 User Range Accuracy.
User Range Accuracy (URA) is a statistical indicator of the GPS ranging accuracy obtainable witha specific signal and SV. URA provides a conservative RMS estimate of the user range error(URE) in the associated navigation data for the transmitting SV. It includes all errors for which theSpace and Control Segments are responsible. Whether the integrity status flag is 'off' or 'on', 4.42
times URA bounds the instantaneous URE with 1-(1e-5) per hour probability (‘legacy’ level ofintegrity assurance). When the integrity status flag is 'on', 5.73 times URA bounds theinstantaneous URE with 1-(1e-8) per hour probability (‘enhanced’ level of integrity assurance).
Integrity properties of the URA are specified with respect to the scaled (multiplied by either 4.42 or
5.73 as appropriate) upper bound values of the URA index or to the scaled composite of the upperbound values of all component URA indexes.
Note #1: URA applies over the transmission interval that is applicable to the LNAV/CNAV datafrom which the URA is read, for the worst-case location within the satellite footprint.
Note #2: The URA for a particular signal may be represented by a single index in the LNAV data
and by a composite of more than one index representing components of the total URA in the
CNAV data. Specific URA indexes and formulae for calculating the total URA for each signal aredefined in Appendix II for the LNAV message and Appendix III for the CNAV message.
Note #3: The URA is not required to bound the instantaneous URE when: (a) an alert is issued tothe users before the instantaneous URE exceeds either of the scaled URA bounds; or (b) if theintegrity status flag is 'off' an alert is issued to the users no more than 8.0 seconds after the
instantaneous URE exceeds the 4.42 times URA bound; or (c) if the integrity status flag is 'on' analert is issued to the users no more than 8.0 seconds after the instantaneous URE exceeds the
4.42 times URA bound; or (d) if the integrity status flag is 'on' an alert is issued to users no morethan 5.2 seconds after the instantaneous URE exceeds the 5.73 times URA bound. In this context,
an "alert" is defined as any indication or characteristic of the conveying signal, as specified
elsewhere in this document, which signifies to users that the conveying signal may be invalid or
should not be used, such as the health bits not indicating operational-healthy, broadcasting nonstandard code, parity error, etc.

6.2.1.1 User Differential Range Accuracy.
User Differential Range Accuracy (UDRA) is a statistical indicator of the GPS ranging accuracy
obtainable with a specific signal and SV after the application of the associated differential
corrections (DC parameters). UDRA provides a conservative RMS estimate of the differential user
range errors in the navigation data for that satellite. It includes all errors for which the Space andControl Segments are responsible.

42

IS-GPS-200L
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6.2.2 SV Block Definitions.
The following block definitions are given to facilitate discussion regarding the capability of thevarious blocks of GPS satellites to support the SV-to-US interface.

6.2.2.1 Developmental SVs.
The original concept validation satellites developed by Rockwell International and designated assatellite vehicle numbers (SVNs) 1-11 are termed "Block I" SVs. These SVs were designed toprovide 3-4 days of positioning service without contact from the CS. These SVs transmitted a
configuration code of 000 (reference paragraph 20.3.3.5.1.4). There are no longer any active
Block I SVs in the GPS constellation. The last Block I SV was decommissioned in 1995.

6.2.2.2 Operational SVs.
The operational satellites are designated Block II, Block IIA, Block IIR, Block IIR-M, Block IIF, GPS
III, and GPS IIIF SVs. Characteristics of these SVs are provided below. Modes of operation forthese SVs and accuracy of positioning services provided are described in paragraphs 6.3.2
through 6.3.4. These SVs transmit configuration codes as specified in paragraph 20.3.3.5.1.4.
The navigation signal provides no direct indication of the type of the transmitting SV.

6.2.2.2.1 Block II SVs.
The first block of full scale operational SVs developed by Rockwell International are designated as
SVNs 13-21 and are termed "Block II" SVs. These SVs were designed to provide 14 days of
positioning service without contact from the CS.

6.2.2.2.2 Block IIA SVs.
The second block of full scale operational SVs developed by Rockwell International are designatedas SVNs 22-40 and are termed "Block IIA" SVs. These SVs are capable of providing 60 days of
positioning service without contact from the CS.

6.2.2.2.3 Block IIR SVs.
The block of operational replenishment SVs developed by Lockheed Martin are designated as
SVNs 41-61 and are termed "Block IIR" SVs. These SVs have the capability of storing at least 60
days of navigation data with current memory margins, while operating in a IIA mode, to provide
positioning service without contact from the CS for that period. (Contractual requirements forthese SVs specify transmission of correct data for only 14 days to support short-term extended
operations while in IIA mode.)

6.2.2.2.4 Block IIR-M SVs.
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The subset of operational replenishment SVs developed by Lockheed Martin which are“Modernized” configuration of “Block IIR” SVs are termed “Block IIR-M”.

6.2.2.2.5 Block IIF SVs.
The block of operational replenishment SVs developed by Boeing are designated as SVNs 62-73
and are termed “Block IIF” SVs. This is the first block of operational SVs that transmit the L5 Civil
signal. These SVs will provide at least 60 days of positioning service without contact from the CS.

6.2.2.2.6 GPS III SVs
The block of operational replenishment SVs are designated as SVNs 74-105. This is the first blockof operational SVs that transmit the L1C signal. These SVs will provide at least 60 days of
positioning service without contact from the CS.

6.2.3 Operational Interval Definitions.
The following three operational intervals have been defined. These labels will be used to refer todifferences in the interface definition as time progresses from SV acceptance of the last navigation
data upload.

6.2.3.1 Normal Operations.
The SV is undergoing normal operations whenever the fit interval flag (reference paragraph20.3.3.4.3.1) is zero.

6.2.3.2 Short-term Extended Operations.
The SV is undergoing short-term extended operations whenever the fit interval flag is one and the
IODE (reference paragraph 20.3.4.4) is less than 240.

6.2.3.3 Long-term Extended Operations.
The SV is undergoing long-term extended operations whenever the fit interval flag is one and the
IODE is in the range 240-255.

6.2.4 GPS Week Number.
The GPS week numbering system is established with week number zero (0) being defined as thatweek which started with the X1 epoch occurring at midnight UTC (USNO) on the night of January
5, 1980/ morning of January 6, 1980. The GPS week number continuously increments by one (1)at each end/start of week epoch without ever resetting to zero. Users must recognize that theweek number information contained in the LNAV/CNAV message may not necessarily reflect thecurrent full GPS week number (see paragraphs 20.3.3.3.1.1, 20.3.3.5.1.5, 20.3.3.5.2.4, and30.3.3.1.1.1).

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6.2.5 L5 Civil Signal.
L5 is the GPS downlink signal at a nominal carrier frequency of 1176.45 MHz. The L5 signal is
only available on Block IIF and subsequent blocks of SVs and the signal is specified/described ininterface specification IS-GPS-705.

6.2.6 Reserved Data
Reserved bits (or a single reserved value within a defined bit) are intended for future or other use
and their values may change throughout the life of the system. In order to preserve future use of areserved value within a defined bit, the User Segment should handle those values as described foreach applicable field.

6.2.7 Valid Range
Valid Range identifies the range of values used by GPS. The Valid Range is only for PRNs 1-63.

6.2.8 Invalid
Invalid refers to a value that is within a data field’s bit allocation and scale factor, but is outside thevalid range and which GPS has no intention of functionally defining. Invalid range data is to be
used at the user's own risk.

6.2.9 Clock, Ephemeris, Integrity (CEI) Data Set.
The Clock, Ephemeris, Integrity (CEI) data set is the collection of SV-specific clock correction
polynomial parameters, ephemeris parameters, and related parameters (health flags, URA
parameters, time tags, etc.) needed to use the SV’s broadcast signal(s) in the positioning
service. The parameters in the CEI data set are explicitly listed in Table 6-I-1. The entire CEI data
set is needed for maximum accuracy. However, the core CEI data set (parameters without NOTE1in Table 6-I-1) is sufficient for an initial position solution. The t op term provides the epoch time ofweek of the state data utilized for the core CEI data set.

6.2.9.1 Core CEI Data Set.
A Core CEI Data Set are the CEI parameters necessary for a satellite to be used for a position
solution (non-almanac); broadcast to users with the shortest broadcast interval -- see Table 30-XII.
The top term provides the epoch time of week of the state data utilized for CEI data, except forparameters marked with a NOTE1 in Table 6-I-1.

Table 6-I-1. CEI Data Set Parameters

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IS-GPS-200L
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SymbolParameter Name

Subframe

Message

SV Health

SV Health (6 bits)

1

N/A

IODC

Issue of Data, Clock

1

N/A

URA

URA Index

1

N/A

WN

Data Sequence Propagation Week Number

1

10

TGD

Group Delay Differential

1

30

af0

SV Clock Bias Correction Coefficient

1

30-37

af1

SV Clock Drift Correction Coefficient

1

30-37

af2

Drift Rate Correction Coefficient

1

30-37

toc

Time of Clock

1

30-37

√𝐴

Square Root of the Semi-Major Axis

2

N/A

Mean Motion Difference from Computed Value

2

N/A

Fit Interval Flag

2

N/A

Eccentricity

2

10

M0

Mean Anomaly at Reference Time

2

10

toe

2

10, 11

2

11

2

11

2

11

IODE

Time of Ephemeris
Amplitude of the Sine Correction Term to the Orbit
RadiusAmplitude of Cosine Harmonic Correction Term to the
Argument of Latitude
Amplitude of Sine Harmonic Correction Term to the
Argument of Latitude
Issue of Data, Ephemeris

2, 3

N/A

ISF

Integrity Status Flag NOTE1

All

10

𝜔
Ω̇

Argument of Perigee

3

10

Rate of Right Ascension
Longitude of Ascending Node of Orbit Plane at Weekly
Epoch
Inclination Angle at Reference Time

3

11

3

11

3

11

Rate of Inclination Angle

3

11

3

11

3

11

3

11

N/A

10

N/A

10

N/A

10

∆𝑛
Fit Interval
Flag
e

Crs
Cuc
Cus

Ω0
i0
IDOT,
i0-n-DOT

Δ𝐴

Amplitude of the Cosine Harmonic Correction Term to
the Angle of Inclination
Amplitude of the Sine Harmonic Correction Term to
the Angle of Inclination
Amplitude of the Cosine Harmonic Correction Term to
the Orbit Radius
Semi-major Axis Difference at Reference Time

Δ𝑛0

Change Rate in Semi-major Axis
Mean Motion Difference from Computed Value at
Reference Time

Cic
Cis
Crc

𝐴̇

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(L1/L2/L5)

Rate of Mean Motion Difference from Computed
Value
Signal Health (3 bits)

N/A
N/A

10
10

URAED

Elevation Dependent User Range Accuracy

N/A

10

ISCL1C/AInter-signal Correction

N/A

30

ISCL2CInter-signal Correction

N/A

30

ISCL5I5

Inter-signal Correction

N/A

30

ISCL5Q5

Inter-signal Correction

N/A

30

top

CEI Data Sequence Propagation Time of Week

N/A

10, 30-37

URANED0

NED Accuracy Index

N/A

30-37

URANED1

NED Accuracy Change Index

N/A

30-37

URANED2

NED Accuracy Change Rate Index

N/A

30-37

Δ𝑛0̇

Alert
Alert Flag NOTE1
AllAll
NOTE1: Parameters so indicated are for CEI Refinement – not limited to curve fit. Parameters notindicated are needed for/limited to curve fit.
Updates to parameters in table shall prompt changes in toe/toc for CNAV and toe/toc/IODC/IODE for
LNAV. Any parameter marked with NOTE1 may be changed with or without a change in
toe/toc/IODC/IODE.

6.2.10 CEI Data Sequence Propagation.
A related time-ordered sequence of CEI data sets in which each successive CEI data set is a time
propagation of the preceding CEI data set. Special provisions apply to alert users to
discontinuities separating one CEI data sequence propagation from another CEI data sequence
propagation (e.g., after an upload occurs). An upload may include multiple segments of temporally
continuous CEI data sequence propagations.

6.3 Supporting Material
6.3.1 Received Signals.
The guaranteed minimum user-received signal levels are defined in paragraph 3.3.1.6. As
additional supporting material, Figure 6-1 illustrates an example variation in the minimum received
power of the near-ground user-received L1 and L2 signals from Block II/IIA/IIR SVs as a function of
SV elevation angle.
Higher received signals levels can be caused by such factors as SV attitude errors, mechanicalantenna alignment errors, transmitter power output variations due to temperature variations,voltage variations and power amplifier variations, and due to a variability in link atmospheric pathloss. For Block II/IIA and IIR SVs, the maximum received signal levels as a result of these factors
is not expected to exceed -155.5 dBW and -153.0 dBW, respectively, for the P(Y) and C/Acomponents of the L1 channel, nor -158.0 dBW for either signal on the L2 channel. For Block IIRM and IIF SVs, the maximum received signal levels as a result of these factors is not expected to
exceed -155.5 dBW and -153.0 dBW, respectively, for the P(Y) and C/A components of the L1channel and L2 channel. In addition, due to programmable power output capabilities of Block IIR47

IS-GPS-200L
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M and IIF SVs, under certain operational scenarios, individual signal components of Block IIRM/IIF SVs may exceed the previously stated maximum but are not expected to exceed -150 dBW.
-155.5

C/A - L 1

RECEIVED POWER AT 3dBi
LINEARLY POLARIZEDANTENNA (dBW)-158.5

P - L1-161.5

P - L 2 or
-164.5
C/A - L 2

0o 5o

20 o

40 o

60 o

80 o

90 o

100o

USER ELEVATION ANGLE (DEG)

Figure 6-1. User Received Minimum Signal Level Variations (Example, Block II/IIA/IIR)

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6.3.2 Extended Navigation Mode (Block II/IIA).
The Block II and IIA SVs are capable of being uploaded by the CS with a minimum of 60 days ofnavigation data to support a 60 day positioning service. Due to memory retention limitations, theBlock II SVs may not transmit correct data for the entire 60 days but are guaranteed to transmit
correct data for at least 14 days to support short-term extended operations. Under normal
conditions the CS will provide daily uploads to each SV, which will allow the SV to maintain normal
operations as defined in paragraph 6.2.3.1 and described within this IS. During normal operations,
the SVs will have a user range error that is at or below a level required to support a positioning
accuracy of 16 meters spherical error probable (SEP). In addition, the almanac data, UTC
parameters and ionospheric data will be maintained current to meet the accuracy specified in thisIS.
If the CS is unable to upload the SVs (the CS is unavailable or the SV is unable to accept andprocess the upload), each SV will individually transition to short-term extended operations andeventually to long-term extended operations (based on time from each SV's last upload) as definedin paragraphs 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As time fromupload continues through these three operational intervals, the user range error of the SV will
increase, causing a positioning service accuracy degradation. The rate of accuracy degradation isslow over the short-term extended operations interval, such that at the end of this interval(approximately 14 days after upload) the US will be able to achieve a positioning accuracy of 425
meters SEP. The rate of accuracy degradation increases in the long-term extended interval, suchthat by the 180th day after the last upload, the positioning errors will have grown to 10 kilometers
SEP. During these intervals the URA will continue to provide the proper estimate of the user range
errors.
During short-term and long-term extended operations (approximately day 2 through day 62 after an
upload), the almanac data, UTC parameters and ionospheric data will not be maintained current
and will degrade in accuracy from the time of last upload.

6.3.3 Block IIA Mode (Block IIR/IIR-M) and Extended Navigation Mode (Block IIF).
6.3.3.1 Block IIA Mode (Block IIR/IIR-M).
The Block IIR/IIR-M SVs, when operating in the Block IIA mode, will perform similarly to the BlockIIA SVs and have the capability of storing at least 60 days of navigation data, with current memory
margins, to provide positioning service without contact from the CS for that period (through shortterm and long-term extended operations). (Contractual requirements for these SVs specify
transmission of correct data for only 14 days to support short-term extended operations while in IIA
mode.) Under normal conditions, the CS will provide daily uploads to each SV, which will allow the
SV to maintain normal operations as defined in paragraph 6.2.3.1 and described within this IS.
If the CS is unable to upload the SVs (the CS is unavailable or the SV is unable to accept andprocess the upload), each SV will individually transition to short-term extended operations andeventually to long-term extended operations (based on time from each SV’s last upload) as definedin paragraph 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As time from upload
49

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continues through these three operational intervals, the user range error (URE) of the SV will
increase, causing a positioning service accuracy degradation.

6.3.3.2 Extended Navigation Mode (Block II-F).
The Block II-F SVs shall be capable of being uploaded by the CS with a minimum of 60 days ofdata to support a 60 day positioning service. Under normal conditions, the CS will provide daily
uploads to each SV, which will allow the SV to maintain normal operations as defined in paragraph6.2.3.1 and described within this IS.
If the CS is unable to upload the SVs (the CS is unavailable or the SV is unable to accept andprocess the upload), each SV shall individually transition to short-term extended operations andeventually to long-term extended operations (based on time from each SV’s last upload) as definedin paragraph 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As time from upload
continues through these three operational intervals, the user range error (URE) of the SV will
increase, causing a positioning service accuracy degradation.

6.3.4 Extended Navigation Mode (GPS III).
The GPS III and GPS IIIF SVs shall be capable of being uploaded by the CS with a minimum of 60days of data to support a 60 day positioning service. Under normal conditions, the CS will provide
daily uploads to each SV, which will allow the SV to maintain normal operations as defined inparagraph 6.2.3.1 and described within this IS.
If the CS is unable to upload the SVs (the CS is unavailable or the SV is unable to accept andprocess the upload), each SV shall individually transition to short-term extended operations andeventually to long-term extended operations (based on time from each SV’s last upload) as definedin paragraph 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As time from upload
continues through these three operational intervals, the user range error (URE) of the SV will
increase, causing a positioning service accuracy degradation.

6.3.5 Autonomous Navigation Mode.
<RESERVED><RESERVED><RESERVED>

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6.3.6 Additional PRN Code Sequences
The additional PRN sequences provided in this section are for information only. The additional
PRN sequences identified in this section are not applicable to GPS SVs. In addition, the current
valid ranges for GPS PRN signal number for C/A- and P-code are 1-37 and 38-63 as specified inTable 3-Ia and Table 3-Ib. The PRN sequences provided in this section are for other L1/L2 signal
applications, such as Satellite Based Augmentation System (SBAS) satellite signals. PRN
sequences numbered 211-1023 are reserved for internal system use and are therefore notprovided in this section.

6.3.6.1 Additional C/A-code PRN sequences.
The PRN C/A-code is described in Section 3.2.1.3 and 62 unique C/A-code sequences are
assigned by SV ID number in Tables 3-Ia and 3-Ib. An additional set of 147 C/A-code PRN
sequences are selected and assigned with PRN numbers in this section as shown in Table 6-I.
Among the 147 additional sequences;
PRN numbers 120 through 158 are reserved for SBAS; PRN numbers 64 through 119 and PRN
numbers 159 through 210 are reserved for other Global Navigation Satellite System (GNSS)
applications.
Any assignment of a C/A-code PRN number and its code sequence for any additional SV and/or
other L1/L2 signal applications, such as SBAS satellite signals, will be selected from thesequences of Table 6-I and will be approved, controlled, and managed by the GPS Directorate.
It should be noted that, in Table 6-I, the C/A-code sequences are identified by “G2 Delay” and“Initial G2 Setting” which are not the same as the method used in Table 3-Ia. The two-tap coder
implementation method referenced and used in Table 3-Ia is not used in Table 6-I due to its
limitation in generating C/A-code sequences. The “G2 Delay” specified in Table 6-I may be
accomplished by using the “Initial G2 Setting” as the initialization vector for the G2 shift register of
Figure 3-9. For higher order PRNs (>37) the two-tap output mask is not used and the output of theG2 register becomes tap -10 (10th tap) which is labeled as the "output" in Figure 3-9.

6.3.6.2 Additional P-Code PRN sequences.
The PRN P-code set of 63 mutually exclusive sequences are described in Section 3.2.1.1, andassignment of these code segments by SV ID number is given in Tables 3-Ia and 3-Ib. An
additional set of 147 P-code PRN sequences are described in this section. Among the 147
additional sequences PRN numbers 120 through 210 are reserved for other future GNSS
applications. The P-code PRN numbers and their code sequences defined in Table 6-I are not for
general use and will be approved, controlled, and managed by the GPS Directorate.

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6.3.6.2.1 Additional P-code Generation.
The generation of 37 mutually exclusive P-code PRN sequences are described in Section 3.3.2.2.
An additional set of 147 P-code PRN sequences are generated by circularly shifting each of theoriginal 37 sequences (over one week) by an amount corresponding to 1, 2, 3, 4, or 5 days. The
additional sequences are therefore time shifted (i.e. offset) versions of the original 37 sequences.
These offset P-code PRN sequences, Pi(t), are described as follows:
Pi(t) = Pi-37x(t + xT),
where i is an integer from 64 to 210, x is an integer portion of (i-1)/37, and T is defined to equal 24hours.
As an example, P-code sequence for PRN 91 would be the same sequence as PRN 17 shifted 48
hours into a week (i.e. 1st chip of PRN 91 at beginning of week is the same chip for PRN 17 at 48
hours after beginning of week). The complete list of the additional P-code PRN assignments isshown in Table 6-I. Any assignment of a P-code PRN number and its code sequence for any
additional SV and/or other L1/L2 signal applications will be selected from the sequences of Table
6-I.
As an example, P-code sequence for PRN 38 would be the same sequence as PRN 1 shifted 24
hours into a week (i.e. 1st chip of PRN 38 at beginning of week is the same chip for PRN 1 at 24hours after beginning of week). The complete list of the additional P-code PRN assignments isshown in Table 6-I. Any assignment of a P-code PRN number and its code sequence for any
additional SV and/or other L1/L2 signal applications will be selected from the sequences of Table
6-I.

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Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 1 of 5)

C/A
PRN
Signal
No.
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
*

G2 Delay(Chips)
729
695
780
801
788
732
34
320
327
389
407
525
405
221
761
260
326
955
653
699
422
188
438
959
539
879
677
586
153
792
814
446

P

Initial G2
Setting(Octal)*First 10 Chips(Octal)*X2 Delay(Chips)P-code Relative
Advance(Hours) **First 12 Chips(Octal)

0254
1602
1160
1114
1342
0025
1523
1046
0404
1445
1054
0072
0262
0077
0521
1400
1010
1441
0365
0270
0263
0613
0277
1562
1674
1113
1245
0606
0136
0256
1550
1234

1523
0175
0617
0663
0435
1752
0254
0731
1373
0332
0723
1705
1515
1700
1256
0377
0767
0336
1412
1507
1514
1164
1500
0215
0103
0664
0532
1171
1641
1521
0227
0543

27
28
29
30
31
32
33
34
35
36
37
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

P27(t+24)
P28(t+24)
P29(t+24)
P30(t+24)
P31(t+24)
P32(t+24)
P33(t+24)
P34(t+24)
P35(t+24)
P36(t+24)
P37(t+24)
P1(t+48)
P2(t+48)
P3(t+48)
P4(t+48)
P5(t+48)
P6(t+48)
P7(t+48)
P8(t+48)
P9(t+48)
P10(t+48)
P11(t+48)
P12(t+48)
P13(t+48)
P14(t+48)
P15(t+48)
P16(t+48)
P17(t+48)
P18(t+48)
P19(t+48)
P20(t+48)
P21(t+48)

5112
0667
6111
5266
4711
0166
6251
5306
0761
6152
1247
1736
2575
3054
3604
7520
5472
0417
2025
7230
5736
0575
2054
3204
7720
5572
4457
0005
2220
3332
3777
3555

In the octal notation for the first 10 chips of the C/A-code or the initial G2 settings as shown in this table, thefirst digit (1/0) represents a “1” or “0”, respectively, for the first chip and the last three digits are theconventional octal representation of the remaining 9 chips. (For example, the first 10 chips of the C/A-codefor PRN Signal Assembly No. 64 are: 1101010011).

** Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Section 6.3.6.2.1.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific C/A and a specificP-code phase, as shown above.

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Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 2 of 5)

C/A

*

P

PRN
SignalNo.

G2 Delay(Chips)

Initial G2
Setting(Octal)*First 10 Chips(Octal)*X2 Delay(Chips)P-code Relative
Advance(Hours) **First 12 Chips(Octal)

96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125

264
1015
278
536
819
156
957
159
712
885
461
248
713
126
807
279
122
197
693
632
771
467
647
203
145
175
52
21
237
235

0260
1455
1535
0746
1033
1213
0710
0721
1763
1751
0435
0735
0771
0140
0111
0656
1016
0462
1011
0552
0045
1104
0557
0364
1106
1241
0267
0232
1617
1076

1517
0322
0242
1031
0744
0564
1067
1056
0014
0026
1342
1042
1006
1637
1666
1121
0761
1315
0766
1225
1732
0673
1220
1413
0671
0536
1510
1545
0160
0701

22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
1
2
3
4
5
6
7
8
9
10
11
12
13
14

P22(t+48)
P23(t+48)
P24(t+48)
P25(t+48)
P26(t+48)
P27(t+48)
P28(t+48)
P29(t+48)
P30(t+48)
P31(t+48)
P32(t+48)
P33(t+48)
P34(t+48)
P35(t+48)
P36(t+48)
P37(t+48)
P1(t+72)P2(t+72)
P3(t+72)P4(t+72)
P5(t+72)
P6(t+72)
P7(t+72)
P8(t+72)
P9(t+72)
P10(t+72)
P11(t+72)
P12(t+72)
P13(t+72)
P14(t+72)

3444
7400
1422
2433
7037
1635
6534
5074
0614
6124
1270
6716
5165
0650
6106
5261
6752
5147
0641
6102
1263
2713
3167
3651
7506
5461
0412
6027
1231
2736

In the octal notation for the first 10 chips of the C/A-code or the initial G2 settings as shown in this table, thefirst digit (1/0) represents a "1" or “0”, respectively, for the first chip and the last three digits are theconventional octal representation of the remaining 9 chips. (For example, the first 10 chips of the C/A-codefor PRN Signal Assembly No. 64 are: 1101010011).
** Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Section 6.3.6.2.1.

NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific C/A and a specificP-code phase, as shown above.

54

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14 May 2020

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 3 of 5)

C/A

*

P

PRN
SignalNo.

G2 Delay(Chips)

Initial G2
Setting(Octal)*First 10 Chips(Octal)*X2 Delay(Chips)P-code Relative
Advance(Hours) **First 12 Chips(Octal)

126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155

886
657
634
762
355
1012
176
603
130
359
595
68
386
797
456
499
883
307
127
211
121
118
163
628
853
484
289
811
202
1021

1764
0717
1532
1250
0341
0551
0520
1731
0706
1216
0740
1007
0450
0305
1653
1411
1644
1312
1060
1560
0035
0355
0335
1254
1041
0142
1641
1504
0751
1774

0013
1060
0245
0527
1436
1226
1257
0046
1071
0561
1037
0770
1327
1472
0124
0366
0133
0465
0717
0217
1742
1422
1442
0523
0736
1635
0136
0273
1026
0003

15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
1
2
3
4
5
6
7

P15(t+72)
P16(t+72)
P17(t+72)
P18(t+72)
P19(t+72)
P20(t+72)
P21(t+72)
P22(t+72)
P23(t+72)
P24(t+72)
P25(t+72)
P26(t+72)
P27(t+72)
P28(t+72)
P29(t+72)
P30(t+72)
P31(t+72)
P32(t+72)
P33(t+72)
P34(t+72)
P35(t+72)
P36(t+72)
P37(t+72)
P1(t+96)
P2(t+96)
P3(t+96)
P4(t+96)
P5(t+96)
P6(t+96)
P7(t+96)

7175
1654
6504
1060
2612
7127
5671
4516
4065
4210
4326
0371
6356
5345
0740
6142
1243
6703
5163
4653
4107
4261
0312
2525
7070
1616
2525
3070
3616
7525

In the octal notation for the first 10 chips of the C/A-code or the initial G2 settings as shown in this table, thefirst digit (1/0) represents a "1" or “0”, respectively, for the first chip and the last three digits are theconventional octal representation of the remaining 9 chips. (For example, the first 10 chips of the C/A-codefor PRN Signal Assembly No. 64 are: 1101010011).
** Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Section 6.3.6.2.1.

NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific C/A and a specificP-code phase, as shown above.

55

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14 May 2020

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 4 of 5)

C/A

*

PRN
SignalNo.

G2 Delay(Chips)

156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185

463
568
904
670
230
911
684
309
644
932
12
314
891
212
185
675
503
150
395
345
846
798
992
357
995
877
112
144
476
193

P

Initial G2
Setting(Octal)*First 10 Chips(Octal)*X2 Delay(Chips)P-code Relative
Advance(Hours) **First 12 Chips(Octal)

0107
1153
1542
1223
1702
0436
1735
1662
1570
1573
0201
0635
1737
1670
0134
1224
1460
1362
1654
0510
0242
1142
1017
1070
0501
0455
1566
0215
1003
1454

1670
0624
0235
0554
0075
1341
0042
0115
0207
0204
1576
1142
0040
0107
1643
0553
0317
0415
0123
1267
1535
0635
0760
0707
1276
1322
0211
1562
0774
0323

8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

P8(t+96)
P9(t+96)
P10(t+96)
P11(t+96)
P12(t+96)
P13(t+96)
P14(t+96)
P15(t+96)
P16(t+96)
P17(t+96)
P18(t+96)
P19(t+96)
P20(t+96)
P21(t+96)
P22(t+96)
P23(t+96)
P24(t+96)
P25(t+96)
P26(t+96)
P27(t+96)
P28(t+96)
P29(t+96)
P30(t+96)
P31(t+96)
P32(t+96)
P33(t+96)
P34(t+96)
P35(t+96)
P36(t+96)
P37(t+96)

5470
4416
4025
4230
0336
6375
1354
6744
5140
4642
0103
6263
1313
6767
1151
2646
7101
5662
0513
2067
3211
3726
3571
3456
3405
7420
5432
0437
6035
1234

In the octal notation for the first 10 chips of the C/A-code or the initial G2 settings as shown in this table, thefirst digit (1/0) represents a "1" or “0”, respectively, for the first chip and the last three digits are theconventional octal representation of the remaining 9 chips. (For example, the first 10 chips of the C/A-codefor PRN Signal Assembly No. 64 are: 1101010011).
** Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Section 6.3.6.2.1.

NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific C/A and a specificP-code phase, as shown above.

56

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14 May 2020

Table 6-I.

Additional C/A-/P-Code Phase Assignments (sheet 5 of 5)
C/A

PRN
Signal No.
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
*

G2 Delay(Chips)
109
445
291
87
399
292
901
339
208
711
189
263
537
663
942
173
900
30
500
935
556
373
85
652
310

P

Initial G2
Setting(Octal)*First 10 Chips(Octal)*X2 Delay(Chips)P-code Relative
Advance(Hours) **First 12 Chips(Octal)

1665
0471
1750
0307
0272
0764
1422
1050
1607
1747
1305
0540
1363
0727
0147
1206
1045
0476
0604
1757
1330
0663
1436
0753
0731

0112
1306
0027
1470
1505
1013
0355
0727
0170
0030
0472
1237
0414
1050
1630
0571
0732
1301
1173
0020
0447
1114
0341
1024
1046

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

P1(t+120)
P2(t+120)
P3(t+120)
P4(t+120)
P5(t+120)
P6(t+120)
P7(t+120)
P8(t+120)
P9(t+120)
P10(t+120)
P11(t+120)
P12(t+120)
P13(t+120)
P14(t+120)
P15(t+120)
P16(t+120)
P17(t+120)
P18(t+120)
P19(t+120)
P20(t+120)
P21(t+120)
P22(t+120)
P23(t+120)
P24(t+120)
P25(t+120)

1067
6611
5126
4671
0116
6265
1310
6766
1151
2646
3101
7662
5513
4467
4011
4226
4331
0376
6355
5344
0740
6142
1243
6703
1163

In the octal notation for the first 10 chips of the C/A-code or the initial G2 settings as shown in this table, thefirst digit (1/0) represents a "1" or “0”, respectively, for the first chip and the last three digits are theconventional octal representation of the remaining 9 chips. (For example, the first 10 chips of the C/A-code for
PRN Signal Assembly No. 64 are: 1101010011).
** Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Section 6.3.6.2.1.

NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific C/A and a specific Pcode phase, as shown above.

6.3.6.3 Additional L2 CM-/L2 CL-Code PRN sequences.
The PRN L2 CM-code and L2 CL-code are described in Sections 3.2.1.4 and 3.2.1.5, respectively,
and 63 L2 CM-/L2 CL-code sequence pairs are assigned by SV ID number in Tables 3-IIa and 3IIb. An additional set of 52 L2 CM-/L2 CL-code PRN sequence pairs are selected and assignedwith PRN numbers in this section as shown in Table 6-II. Among the 52 additional sequences,
PRN numbers 159 through 210 are reserved for other GNSS applications. PRN allocations do notexist for numbers 64 through 158 for L2 CM-/L2 CL-code. Any assignment of a L2 CM-/L2 CLcode PRN number and its code sequence pair for any additional SV and/or other L2 signal
57

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14 May 2020

applications will be selected from the sequences of Table 6-II and will be approved, controlled, andmanaged by the GPS Directorate.
Table 6-II.

PRN
Signal
No.
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190

Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 1 of 2)
Initial Shift Register State (Octal)
L2 CM
L2 CL

604055104
157065232
013305707
603552017230461355
603653437
652346475
743107103
401521277
167335110
014013575
362051132
617753265
216363634
755561123
365304033
625025543
054420334
415473671
662364360
373446602
417564100
000526452
226631300
113752074
706134401
041352546
664630154
276524255
714720530
714051771
044526647

605253024
063314262
066073422
737276117
737243704
067557532
227354537
704765502
044746712
720535263
733541364
270060042
737176640
133776704
005645427
704321074
137740372
056375464
704374004
216320123
011322115
761050112
725304036
721320336
443462103
510466244
745522652
373417061
225526762
047614504
034730440
453073141***

Table 6-II.

End Shift Register State (Octal)
L2 CM *
L2 CL **

425373114
427153064
310366577
623710414
252761705
050174703
050301454
416652040
050301251
744136527
633772375
007131446
142007172
655543571
031272346
203260313
226613112
736560607
011741374
765056120
262725266
013051476
144541215
534125243
250001521
276000566
447447071
000202044
751430577
136741270
257252440
757666513

044547544
707116115
412264037
223755032
403114174
671505575
606261015
223023120
370035547
516101304
044115766
704125517
406332330
506446631
743702511
022623276
704221045
372577721
105175230
760701311
737141001
227627616
245154134
040015760
002154472
301767766
226475246
733673015
602507667
753362551
746265601
036253206

Short cycled period = 10230
Short cycled period = 767250

Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 2 of 2)
58

IS-GPS-200L
14 May 2020

PRN Signal
No.
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210

Initial Shift Register State (Octal)
L2 CM
L2 CL

End Shift Register State (Octal)
L2 CM *
L2 CL **

207164322
262120161
204244652
202133131
714351204
657127260
130567507
670517677
607275514
045413633
212645405
613700455
706202440
705056276
020373522
746013617
132720621
434015513
566721727
140633660

606512137
734247645
415505547
705146647
006215430
371216176
645502771
455175106
127161032
470332401
252026355
113771472
754447142
627405712
325721745
056714616
706035241
173076740
145721746
465052527

533654510
377016461
235525312
507056307
221720061
520470122
603764120
145604016
051237167
033326347
534627074
645230164
000171400
022715417
135471311
137422057
714426456
640724672
501254540
513322453***

202512772
701234023
722043377
240751052
375674043
166677056
123055362
707017665
437503241
275605155
376333266
467523556
144132537
451024205
722446427
412376261
441570172
063217710
110320656
113765506

Short cycled period = 10230
Short cycled period = 767250

6.3.7 Pre-Operational Use.
Before any new signal or group of signals (e.g., L2C, L5, M, L1C, etcetera) is declared operational,
the availability of and/or the configuration of the broadcast signal or group of signals may notcomply with all requirements of the relevant IS or ICD. For example, the pre-operational broadcastof L2C signals from the IIR-M satellites did not include any LNAV or CNAV data as required by ISGPS-200. Pre-operational use of any new signal or group of signals is at the users own risk.

6.3.8 P-Code Verification Material
Table 6-III and Table 6-IV provide samples of the P-code that may be used as part of theverification of specific implementations of the P-code. Table 6-III provides the first 256 chips of theP-code for selected PRNs. Table 6-IV provides the last 1024 P-code chips of the week for
selected PRNs.

59

IS-GPS-200L
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Table 6-III. First 256 P-code Chips of the Week for Selected Code Phase Assignments
PRN
Signal
No.

P-codeRelative
Advance(Hours)*P-code, Left-to-right from beginning of GPS Week (hexadecimal)

001
002
037
038
074

P1(t)
P2(t)
P37(t)
P1(t+24)
P37(t+24)

924110552BD74E7FC62D21CD7F83B3F9A4CC77E4C4A5DF081E90B013D5D49F81
800D9D1EB5EF85CA7B25290C95BF1C92131D6DB1793B8630F4D8D69D8D1C481B
8E3619D83E3F4C3E3E9FD99E5ECB86BC956F1726C018501EC071B2054E630122
6FBA7C64D4EE0839FF5EB0B376D8B5A1BCBDDDCF191940183BFE36A24FE6DE4B
2A7CBF6621E0FAFD216C4DFA3D5CBFAB75FAA743419F4ABC7DAA7BF44C35E949

075
111
112

P1(t+48)
P37(t+48)
P1(t+72)

3DECDF76407FFF921FA4515FAF512A586C2530BA5633B04C2F8CA38CFFBE7562
AB1BE13E44C590CC08255280835311B5B8623EBCDC96C46B2958D4F10D72C01B
DEAB62046E05324EAD7498317CA46457BE5F06BC689EA4207AD66250BA3A9F35

148
149

P37(t+72)
P1(t+96)185

P37(t+96)

0CA62C7F9AF1EB1B2AC2FE5D487E1D23555D6A5C21B1670B4AB205B7C8276C06
555CE90F7396574DF1632E26F61B55C70612A415035DE606C04BE275F5AD9320
29C54899D24E93AB9B1BC80D7DBF66422DF699452A35BD21DC0E3195A38EB404

186

P1(t+120)237775707E0FDBE2308A496DA3886DC4E15B41B0CD214F6E29812ABCCFB618E8

210

P25(t+120)

2735B1757E9494E7183A6A6C9B335824A2B9EBE2E4947C07C21EBD9CDB7A5E18* Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Sections 3.3.2.1, 6.3.6.2.1.

Table 6-IV. Last 1024 P-code Chips of the Week for Selected Code Phase Assignments
PRN
SignalNo.
001

P-codeRelative
Advance(Hours)*
P1(t)

002

P2(t)

037

P37(t)038

P1(t+24)074

P37(t+24)

P-code, Left-to-right to last chip of GPS Week (hexadecimal)
66297E28E08F71E0F95A694BC576072D32930112D3749C4738D09
6135E156848B7BC7B4D4FDFB8A7CBEC83ECEF009DDB09DC1E55A9
69FC2BCD922D0C404A979D34BE6976E7889E6244C51F83854C7BD
5CFF3F915FA8C4BD6B42685D59BE159FF5DCB7CA9AF42AB85A425
8AB66D8F25593C8536E73686DAF8173783FBAA32E3E1
D3165186CF86CFA0F95A694BC576072D32930112D3749C4738D09
6135E156848B7BC7B4D4FDFB8A7CBEC83ECEF009DDB09DC1E55A9
69FC2BCD922D0C404A979D34BE6976E7889E6244C51F83854C7BD
5CFF3F915FA8C4BD6B42685D59BE159FF5DCB7CA9AF42AB85A425
8AB66D8F25593C8536E73686DAF8173783FBAA32E3E1
96778423671CF933BA057BF3C576072D32930112D3749C4738D09
6135E156848B7BC7B4D4FDFB8A7CBEC83ECEF009DDB09DC1E55A9
69FC2BCD922D0C404A979D34BE6976E7889E6244C51F83854C7BD
5CFF3F915FA8C4BD6B42685D59BE159FF5DCB7CA9AF42AB85A425
8AB66D8F25593C8536E73686DAF8173783FBAA32E3E1
F7A4CB846B98ACD06BDD33AFE1DC3C0B35EA2A250E0DC70D959CE
3DBA19FB64E2441EB9B2EC5D473EF667E8258AA18DADE37D1A092
076F84E33B7DA1748635BEAA94B1DF852CCA25154CB00C34F5D32
661F4B5DDCB25FC1C70BD246E4FD531D565624F8FDB3B13C9F943
7BA9776B57BCC096E22EC56D2FD11D4C4D61EE988800
C2B55E4A0E04226972B40620CC5E728370D9A2A0B3030EF445070
3A7F4C1AF143844D6AD26E061AAADFD2521AD48320DE2A6B605B4

60

IS-GPS-200L
14 May 2020

1740D49E24C436B2A00297E7F2A354DE6A33E8D2EF5AC7F054E12
D34E8639AC06C3F1A373C1EA937A8E3E4E0883A2B0CC838B7C362
1132A8594A48CD2B71C96947E7B488093CA93A955F08
075
P1(t+48) F4FE4A61E668669524717749357D2AC58411FC6A54F18FFC9EC51
DB121ED2F6E4ECB856F4FA534D84E6E5BF20296241C7157CBD443
7C4D829D5510517CF42AD5D431B302EB207D4616C3C0F831652B3
A8935F7DFA517ECADDEACC78AC02DE1EF8419D3483DF897C15C8B
56805CC6750CC1BEA98A0DBEC9E66EB98A69F8ED6D86
111
P37(t+48) D9352A5F9E318A772A6B0A8498A4B6CD1D93B3CC581CB390B0A8C
728E47430F29043FF3F2048C745EBEB2B2B1758B05AE70575C9DE
E14173D3337616D546E448E77582A2698063C5040F91B1C06C162
274B16C1B0EE02B3A11DF3FA22D49FDDAA877B728A2DF817BBD0E
29722205C89A5F91A3E26955630EC48402CA4DAA0378
112
P1(t+72) 2DFE2345638E31C27B7CC27EEF9FF9DC383E98505F5EC50C1F741
805A821A451998BDCAFB8094C2589F283AF1C9056CA796083A50C
F95CB6A5340DDFE9E82C71C2C5A390DC0C8FF6795B3DB8B733E2B
991F8B484A3528B8F89BD695404DA2817602828C468E014C72441
33F61EC113D121F848671DB0332B578D2EF38331B99B
148
P37(t+72) D623879A83A18CE562356FF1ED546D9E603D9EFDC3DE45D310123
387EC6F20A9D8DF378CDD3CC2D9E491ECA4CB217DDF36E512E4BE
6235F4C7CB270596C0F5900E2442C828EF22CC277D5E9AC69599F
67CD400833F6CFF0FA1BB69D00838E7374438CBB72C9C9EC3785F
A14245896ECD3BB1D58FB7510D101584ED669E394931
149
P1(t+96) FA28476F17FCF42B2DD127DCFE42250039E03183B21EBFB83544E
922469EC9824641BE138193A95EE51A1E57C598C3813FD19805E2
676E5D997DC13C358246B521F8FA9D17865FA6B02AD9D1D5D5E46
B725D51A52DC20CD3ADA5013E419249B48DC6FCF8933919F24DA4
FB3F56BB4154E0BFD5C2300DB9B0040D0F41D507F7FF
185
P37(t+96) 5FFAD9744EDCEAA7C57243AF783EB3C44120433003C3AF4E2EC63
42CAECC2FBBA634C151E0C064F2270842F37DEFF400BB759BB00A
09244EC922C42B2504695E33E2E46466DCF75CFBC5F39FCA0287B
0EAFA60EE1156A15DB95261A5CA7961B1E06C4DAD12427380B7E2319113173241AF3670A7EB4574CA475F35CF2B014B2A
186
P1(t+120) B279A52DA308C52BDFF13565B40C1FEDF33A0E623C55734B7C8F1
79B9B50E5421F1C8024B8BDEB14079643AB41153FA0E5660ADF78
F527584899F4CCB03B47E4AB9214BEECEBCF5CF051A5FA049D105
D03D945B9085A58C583A392E7CA1FA6B5FF5FF0BB436CAE9C1FD4
4B0124E42332A03A54AE23A23A82223DB0B43C9BE049
210
P25(t+120) 59E2F1EEAF906B168FC5226D6E2A295C488BC1D37A7BECA8193F9
A570194E08DF23171E5EF24D150A9BF302095C0DA751C7E65B913
7D76FA51495E894B93576D456E10E9CBF556692794213711F6025
41E9871D9D030E724623596E21EF66BAEA334360B3BCEB9698A20
930D9C4E921057835D7B89E493ED33D7F9CEA001AC77* Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Sections 3.3.2.1, 6.3.6.2.1.

6.4 Operational Protocols
6.4.1 Lower PRN Numbers Versus Upper PRN Numbers
Many existing user receivers are only compatible with prior versions of this IS where the PRN
numbers and corresponding PRN code sequences were limited to the lower range of 1 - 32. To
61

IS-GPS-200L
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maintain backwards compatibility with these receivers (and promote backwards utility), the CS will
endeavor to operate as robust a constellation as practical using just the lower range of PRN
numbers. The upper range of PRN numbers (33 - 63) is intended as an enhancement formodernized receivers which are compatible with both the lower PRN numbers and the upper PRN
numbers. When feasible, the CS will endeavor to operate at least one satellite using an upper
PRN number to serve as a source of almanac data for satellites using the upper range of PRN
numbers.

6.4.2 PRN Number Consistency
For a given satellite, the same PRN number will be assigned to all operational signals (signals
modulated by standard PRN code with data that indicates the signal health is OK).

6.4.3 PRNs 33 and 37
PRN 33 should not be used by satellites because of its prior use in specialized groundapplications. PRN 37 should not be used by satellites until after PRN 37 is no longer needed for
SATZAP purposes.

6.4.4 PRNs 33 through 63
The CS must ensure that satellites broadcasting PRNs 33 through 63 are synchronized to GPS
time to avoid conflict with specialized ground applications.

6.4.5 Health Code Setting of ‘11110’
For backward compatibility reasons, the SV signal component health code setting of ‘11110’ isanticipated for potential use only with satellites broadcasting PRNs 33 through 63.

6.4.6 User Protocol for Signal Availability and Health Information
The GPS enterprise provides users with information in multiple ways which indicates the health ofeach satellite's broadcast signal components. Occasionally, the indications provided one way will
conflict with the indications provided another way. The recommended user protocol for interpretingthese indications is given below. The Control Segment will manage the GPS constellation
assuming this protocol; users should plan accordingly. Users who vary from this protocol assume
the responsibility to assess and mitigate any risk that might arise from that variance. The
information is presented in the order of a typical acquisition sequence, but once satellites are
successfully being tracked, the user should react to changing indications in any order in which they
may be received.

6.4.6.1 User Protocol
1. Constellation Almanac. LNAV almanac users should not attempt to acquire signals thatappear to be from dummy satellites as defined via a currently broadcast LNAV almanac (seeparagraphs 3.2.1). CNAV almanac users should not attempt to acquire signals that appear to be62

IS-GPS-200L
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from satellites for which a CNAV almanac is not currently being broadcast in Message Types 12,
31, and/or 37 (see paragraph 30.3.3.4).
2. SV Configuration Code. Users should not attempt to acquire signals not identified asexisting by the broadcast SV configuration code (see paragraph 20.3.3.5.1.4) for a satellite.
3. Signal Alarm Indication. Signals from a satellite that are subject to a signal alarmindication (see paragraph 6.4.6.2) should be ignored.
4. CEI Data Set. Signals from a satellite that are indicated as bad by the CEI data set inuse from that satellite should be ignored. See paragraph 6.2.9 for a description of the CEI data set.
See paragraph 20.3.3.3.1.4 or 30.3.3.1.1.2 for a description of the CEI data set health settings.
5. Marginal Indication. Signals from a satellite that are indicated as marginal (seeparagraph 6.4.6.3) by that satellite may be ignored.
6. Other. Signals from a satellite whose suitability for use are suspect for other valid
reasons (e.g., Receiver Autonomous Integrity Monitoring [RAIM]) may be ignored.
Note: Priority of SPS SIS Health Information. Satellite health indications in LNAV subframes 4 and
5 (see paragraphs 30.3.3.5.1.3 and 40.3.3.5.1.3) and CNAV health indications in Message Types
12, 31, and/or 37 (see paragraph 30.3.3.4) may not be the most recent indications of the health ofa satellite. They indicate the health of the satellites in the constellation when the almanac wasgenerated for upload to the satellite from which the almanac was obtained. The current availability
and health of a satellite signal should be determined based on the criteria described in items 1-6
above.

6.4.6.2 Alarm Indications
An otherwise healthy signal-in-space (SIS) signal or marginal SIS signal becomes unhealthy when
it is the subject of a SIS alarm indication. The presence of any of the following alarm indications
listed below means the information provided by the signal may not be correct.

6.4.6.2.1 Common Alarm Indications
The following alarm indications are common to all code signals.
The code signal becomes untrackable (e.g., ≥ 20 dB decrease in transmitted signal power,≥ 20 dB increase in correlation loss):(a)

The code signal ceases transmission.

(b)

The elimination of the standard code (e.g., gibberish code).

(c)

The substitution of non-standard code for the standard code (see paragraph 3.2.1.6)

6.4.6.2.2 Specific Alarm Indications
The following alarm indications are specific to the code signals listed below.
C/A-Code or P(Y)-Code Signal
63

IS-GPS-200L
14 May 2020(a)
The failure of parity on 5 successive words of LNAV data (3 seconds) (see paragraphs
20.3.5 and 40.3.5).
(b)
The broadcast IODE does not match the 8 LSBs of the broadcast IODC (excluding normal
data set cutovers, see paragraph 20.3.3.4.1).
(c)

The transmitted bits in words 3-10 in subframe 1, 2, or 3 are all set to 0's or all set to 1's.

(d)Default LNAV data is being transmitted in subframes 1, 2, or 3 (see paragraph 20.3.2).

(e)
The 8-bit preamble does not equal 10001011 2, decimal 139, or hexadecimal 8B (seeparagraph 20.3.3).

CM-Code Signal(a)
The failure of the cyclic redundancy check (CRC) on 5 successive CNAV messages (60seconds) (see paragraph 30.3.5).
(b)
The broadcast time of ephemeris (toe) is not current (i.e. not within the current curve-fit) or
does not match the broadcast time of clock (t oc) (excluding normal data set cutovers, seeparagraphs 30.3.3.1.1 and 30.3.4.4).
(c)
The broadcast top is not consistent across the Message Types 10, 11 and Type 30’s
messages which comprise the current (i.e. not within the current curve-fit) CEI data set (excluding
normal data set cutovers, see paragraph 30.3.4.4).
(d)
The transmitted bits (bits 39-276) in Message Types 10, 11 and Type 30’s are all set to 0's
or all set to 1's.
(e)
The 8-bit preamble does not equal 10001011 2, decimal 139, or hexadecimal 8B (seeparagraph 30.3.3).
Notes:
1. A SIS alarm indication exists when the satellite is not trackable because it is not transmitting
the standard PRN code modulation on the L-band carrier signal. These SIS alarm indications
are specifically called out above because of their relatively high probability of occurrence.
2. The SIS alarm indications related to the LNAV and CNAV message data are considered“weak” indications since receivers do not necessarily continuously read each satellite’s LNAVor CNAV message data either by design or by circumstance (e.g., radio-frequency
interference [RFI] can prevent reading LNAV or CNAV message data). These weak SIS alarmindications are assumed to have a five-minute lag time before receivers take notice of them foralerting purposes.
3. The SIS alarm indications related to the LNAV or CNAV message data are indicative of aproblem onboard the satellite. GPS receivers may perceive similar indications caused by local
effects that are unrelated to the broadcast SIS.

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4. In addition to SIS alarm indications, other conditions may also cause GPS signals to become
temporarily untrackable, such as ionospheric signal fades, local signal masking, or local
interference.

6.4.6.3 "Marginal Indications"
The C/A-code signal is marginal when the C/A-code signal would otherwise have been defined ashealthy except that one or more of the following three warning conditions is or are present:
1. The C/A-code signal indicates that any one of the satellite’s SIS components may not be
fully capable. More specifically, the Most Significant Bit (MSB) of the six-bit health status
word given in subframe 1 of the LNAV message is set to 0 2 (“all LNAV data are OK”) andthe 5 Least Significant Bits (LSBs) of the six-bit health status word in subframe 1 of the
LNAV message are set to anything other than 000002 (all signals are OK), 000102 (allsignals dead), or 111002 (“SV is temporarily out”). See paragraphs 20.3.3.3.1.4 and20.3.3.5.1.3.
2. The URA alert flag is raised (i.e., bit 18 of the LNAV HOW is set to 1) and the URA does not
apply. This means the URA may be worse than the URA index value transmitted in
subframe 1. See paragraph 20.3.3.2.
3. The transmitted URA index in subframe 1 is equal to 15 ("N"=15). See paragraph20.3.3.3.1.3.
The health of the CM-code and CL-code signals is marginal when the signals would otherwise
have been defined as healthy except that one or more of the following three warning conditions
is or are present:
1. Default CNAV data (i.e., Message Type 0) is being transmitted in lieu of Message Type 10,
11 and/or Message Type 30’s on the CM-code signal (e.g., a current and consistent CEI
data set is not available within the maximum broadcast interval defined in paragraph30.3.4.1). See paragraph 30.3.3.
2. The URA alert flag is raised (i.e., bit 38 of each CNAV message is set to 1) and therefore
the CM-code signal URA components do not apply to the CM-code and CL-code signals.
This means the CM-code and CL-code signal URA may be worse than indicated by the
URA index components transmitted in Message Type 10 and Message Type 30’s. Seeparagraph 30.3.3.
3. Either or both the URAED index in Message Type 10 and the URANED0 index in Message
Type 30’s transmitted in the CM-code signal are equal to 15 or -16 ("N"=15 or "N"=-16).
See paragraphs 30.3.3.1.1.4 and 30.3.3.2.4.
The P(Y)-code SIS health is marginal when the P(Y)-code SIS would otherwise have been
defined as healthy except that one or more of the following three warning conditions is or arepresent:
1. The Most Significant Bit (MSB) of the six-bit health status word given in subframe 1 of the
LNAV message is set to 02 and the 5 Least Significant Bits (LSBs) of the six-bit healthstatus word in subframe 1 of the LNAV message are set to anything other than 000002 (all65

IS-GPS-200L
14 May 2020

signals are OK), 000102 (all signals dead), or 111002 (SV is temporarily out). Seeparagraphs 20.3.3.3.1.4 and 20.3.3.5.1.3.
2. The URA alert flag transmitted as bit 18 of the HOW is set to 1 and the URA does not apply
as defined in ICD-GPS-224 and ICD-GPS-225.
3. The transmitted URA index "N"=15.

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10 APPENDIX I. LETTERS OF EXCEPTION
10.1 Scope.
Approval of this document, as well as approval of any subsequent changes to the document, canbe contingent upon a "letter of exception". This appendix depicts such "letters of exception" whenauthorized by the GPS Directorate.

10.2 Applicable Documents.
The documents listed in Section 2.0 shall be applicable to this appendix.

10.3 Letters of Exception.
Any letter of exception which is in force for the revision of the IS is depicted in Figure 10.3-1 - 10.38.

67

IS-GPS-200L
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Figure 10.3-1. Letters of Exception

68

IS-GPS-200L
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Figure 10.3-2. Letters of Exception (continued)

69

IS-GPS-200L
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Figure 10.3-3. Letters of Exception (continued)

70

IS-GPS-200L
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Figure 10.3-4. Letters of Exception (continued)

71

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Figure 10.3-5. Letters of Exception (continued)

Figure 10.3-6. Letters of Exception (continued)

72

IS-GPS-200L
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Figure 10.3-7. Letters of Exception (continued)73

IS-GPS-200L
14 May 2020

Figure 10.3-8. Letters of Exception (continued)

74

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20 APPENDIX II. GPS NAVIGATION DATA STRUCTURE FOR LNAVDATA, D(t), FOR PRN 1-32
20.1 Scope.
This appendix describes the specific legacy navigation (LNAV) data structure denoted by data ID
number 2 for the lower set of PRN numbers (PRN 1-32). This data ID number, when transmitted
as part of the LNAV data, shall be represented by the two-bit binary notation as 01. Data ID
number 1 is no longer in use. The LNAV data structure for the lower set of PRN numbers isdenoted as LNAV-L. The LNAV data structure for the upper set of PRN numbers (LNAV-U) is
described in Appendix IV.

20.2 Applicable Documents.
20.2.1 Government Documents.
In addition to the documents listed in paragraph 2.1, the following documents of the issue specified
contribute to the definition of the LNAV data related interfaces and form a part of this Appendix tothe extent specified herein.
Specifications
FederalNone

Military

None

Other Government Activity

NoneStandards
FederalNone

Military

None

Other Publications
GP-03-001 (GPS Interface Control Working Group Charter)

20.2.2 Non-Government Documents.
In addition to the documents listed in paragraph 2.2, the following documents of the issue specified
contribute to the definition of the LNAV data related interfaces and form a part of this Appendix tothe extent specified herein.
Specifications
None
Other Publications
None

75

IS-GPS-200L
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20.3 Requirements
20.3.1 Data Characteristics.
The data stream shall be transmitted by the SV on the L1 and L2 channels at a rate of 50 bps. In
addition, upon ground command, the data stream shall be transmitted by the Block IIR-M SV on
the L2 CM channel at a rate of 25 bps using FEC encoding resulting in 50 sps.

20.3.2 Message Structure.
As shown in Figure 20-1, the message structure shall utilize a basic format of a 1500 bit long frame
made up of five subframes, each subframe being 300 bits long. Subframes 4 and 5 shall be
subcommutated 25 times each, so that a complete data message shall require the transmission of
25 full frames. The 25 versions of subframes 4 and 5 shall be referred to herein as pages 1
through 25 of each subframe. Each subframe shall consist of ten words, each 30 bits long; theMSB of all words shall be transmitted first.
Each subframe and/or page of a subframe shall contain a telemetry (TLM) word and a handoverword (HOW), both generated by the SV, and shall start with the TLM/HOW pair. The TLM word
shall be transmitted first, immediately followed by the HOW. The HOW shall be followed by eightdata words. Each word in each frame shall contain parity (reference Section 20.3.5).
Block II and IIA SVs are designed with sufficient memory capacity for storing at least 60 days of
uploaded LNAV data. However, the memory retention of these SVs will determine the duration ofdata transmission. The memory retentivity is guaranteed for at least 60 days for SVs subsequent
to Block IIA. GPS III and GPS IIIF SVs have the capability to support operation for at least 60 days
without contact from the CS. Alternating ones and zeros will be transmitted in words 3 through 10in place of the normal LNAV data whenever the SV cannot locate the requisite valid control or data
element in its on-board computer memory. The following specifics apply to this default action: (a)the parity of the affected words will be invalid, (b) the two trailing bits of word 10 will be zeros (toallow the parity of subsequent subframes to be valid -- reference paragraph 20.3.5), (c) if the
problem is the lack of a data element, only the directly related subframe(s) will be treated in thismanner, (d) if a control element cannot be located, this default action will be applied to all
subframes and all subframes will indicate ID = 1 (Block II/IIA only) (i.e., an ID-code of 001) in the
HOW (reference paragraph 20.3.3.2) (Block IIR/IIR-M, IIF, and GPS III/IIIF SVs indicate the proper
subframe ID for all subframes). Certain failures of control elements which may occur in the SV
memory or during an upload will cause the SV to transmit in non-standard codes (NSC and NSY)
which would preclude normal use by the US. Normal LNAV data transmission will be resumed by
the SV whenever a valid set of elements becomes available.
Block II/IIA SVs are uploaded with a minimum of 60 days of LNAV data. However, the EAROM
retentivity for Block II SVs is designed and guaranteed for only 14 days. Therefore, Block II SV
memory is most likely to fail sometime during long-term extended operations after repeated write
operations. In the case of memory failure, the SV will transmit alternating ones and zeros in word
3-10 as specified in the above paragraph. The EAROM retentivity for Block IIA SVs is designed
and guaranteed for at least 60 days.
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Although the data content of the SVs will be temporarily reduced during the upload process, thetransmission of valid LNAV data will be continuous. The data capacity of specific operational SVs
may be reduced to accommodate partial memory failures.

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 571
SUBFRAME
NO.

PAGE
NO.

1

N/A

1

31

TLM
22 BITS

61

HOW
C P

73 77 83

91

121

WN
t

22 BITS

P

P

10
BITS

23 BITS***C/A OR P ON L2 - 2 BITS
URA INDEX - 4 BITS
SV HEALTH - 6 BITS

P

150 BITSIODC - 10 BITS TOTAL

1

N/A

181

24 BITS***

P

16
BITS***

WORD 8197
T GD

MSB FIRST

3 SECONDS

WORD 7151

P

L2 P DATA FLAG - 1 BIT
2 MSBs

DIRECTION OF DATA FLOW FROM SV

WORD 624 BITS***

WORD 9211 219

P

8 BITS241
t oc

16 BITS

P

a f2
8
BITS

8 LSBs271
af1
16 BITS

a f0

P

22 BITSIODC - 10 BITS TOTAL*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 1 of 11)

77

WORD 10tP

IS-GPS-200L
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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

2

N/A

WORD 2

1

WORD 3

31
TLM

61
HOW

C P

t

22 BITSMSB FIRST

3 SECONDSP

22 BITS

WORD 4

69

IODE
8
BITS

91

WORD 5

107

121

n

C rs
P
16 BITS

8BITS

16 BITSP

24 BITS

MSBs

P

LSBs

M0 - 32 BITS TOTAL

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6
151

C UC
2

N/A

16 BITS

8
BITS

MSBs
e - 32 BITS TOTAL

WORD 7

167

WORD 8

181

P

211

24 BITSMSB FIRST

3 SECONDS

C US

P

16 BITS

LSBs

WORD 9

227

8
BITS

WORD 10

241

P

271

24 BITS

toe

P

16 BITS

MSBs

LSBs

A - 32 BITS TOTALFIT INTERVAL FLAG - 1 BIT
AODO - 5 BITS

P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 2 of 11)

78

287

t

P

IS-GPS-200L
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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

3

N/A

WORD 2

1

WORD 3

31
TLM

61
HOW

WORD 4

77

WORD 5

91

121

Cic

C P

t

22 BITSMSB FIRST

3 SECONDS

C is

P

22 BITS

8BITS

16 BITSP

24 BITSP
16 BITSMSBs

150 BITSMSB FIRST

3 SECONDS

WORD 7

WORD 8181

WORD 9211

WORD 10

241

271


3

N/A

24 BITSP

C rc
16 BITS

8BITS

P24 BITSP

24 BITS

MSBs

LSBs

P

i0 - 32 BITS TOTAL

DIRECTION OF DATA FLOW FROM SV

151

8
BITS

LSBs

 - 32 BITS TOTAL
0

WORD 6137

LSBs

 - 32 BITS TOTAL

i 0 - 32 BITS TOTAL

P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 3 of 11)

79

P

IODE
8
BITS

279

IDOT
14
BITS

t

P

IS-GPS-200L
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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

5

1
THRU
24

MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63

69

HOW

e

C P

t

22 BITS

91

PP

22 BITS

16 BITS

t oa
8
BITS

99

121
i





P

16 BITS

16 BITS

8BITS

PDATA ID - 2 BITS

SV ID - 6 BITS

SV HEALTHDIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7

151

5

1
THRU
24

WORD 8181

A
24 BITS

WORD 9

211


P

0

MSB FIRST

3 SECONDS

241


P

24 BITS

WORD 10P
24 BITS

271

M0

P

290

t P

24 BITS

8 MSBs
af0 - 11 BITS TOTAL
af1 - 11 BITS TOTAL
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVEDNOTE: PAGES 2, 3, 4, 5, 7, 8, 9 & 10 OF SUBFRAME 4 HAVE THE SAME FORMAT AS PAGES 1 THROUGH 24 OF SUBFRAME 5

Figure 20-1. Data Format (sheet 4 of 11)

80

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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31

63

TLM
5

MSB FIRST

3 SECONDS

22 BITS

91

121

SV HEALTHSV HEALTH
toa WNa
6 BITS/SV
6 BITS/SVPPP88SV SV SV SV
SV SV SV SV
BITS BITS
1
2
3
4
5
6
7
8

HOW
C P

25

69

t P
22 BITSDATA ID- 2 BITS

SV (PAGE) ID- 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6151

525

WORD 7181

MSB FIRST

3 SECONDS
WORD 8211

WORD 9241

SV HEALTHSV HEALTHSV HEALTHSV HEALTH
6 BITS/SV
6 BITS/SV
6 BITS/SV
6 BITS/SVPPPPSV SV SV SV
SV SV SV SV
SV SV SV SV
SV SV SV SV
9 10 11 12
13 14 15 16
17 18 19 20
21 22 23 24
6 BITS ***** RESERVED FOR SYSTEM USE*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 5 of 11)

81

WORD 10271 277

16 BITS ** t P

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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

1, 6, 11,16 & 21MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69

91

121

HOW
C P

t

22 BITS

P

16
BITS***

22 BITSP

24 BITS***P

24 BITS***PDATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

4

1, 6, 11,16 & 21

WORD 8181

24 BITS***P

WORD 9211

24 BITS***MSB FIRST

3 SECONDSP

241

24 BITS***

P

8***
BITS

249

16
BITS***** RESERVED FOR SYSTEM USE*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 6 of 11)

82

WORD 10271

P

22 BITS**tP

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

12, 19, 20,
22, 23 & 24

MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69

91

121

HOW
C P

t

22 BITS

P

16
BITS***

22 BITSP

24 BITS***P

24 BITS***PDATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

412, 19, 20,
22, 23 & 24

WORD 8181

24 BITS***P

WORD 9211

24 BITS***MSB FIRST

3 SECONDSP

24 BITS***

P

241

249

8***
BITS

16 BITS**** RESERVED FOR SYSTEM USE*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 7 of 11)

83

WORD 10271

P

22 BITS**tP

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

18

MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69



0
1
8
8
BITS BITS

HOW
C P

t

22 BITS

77

P

22 BITS

P

91

99

107


2
8
BITS


3
8
BITS


0
8
BITS

121

P

129

137



1
2
8
8
BITS BITS


3
8
BITS

P

DATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7

151

18

WORD 8

181

A
1
4

211

219

24 BITS

8
BITS

t
WN
ot
t
8
8
BITS BITS

MSBs

LSBs

P

24 BITSMSB FIRST

3 SECONDSP

WORD 9

227

241

P

249

257

t
LS
8
8
BITS BITS

DN
8
BITS

WORD 10
271

t
P

279

LSF
8
BITS

14
BITS **WN
LSF

A 0 - 32 BITS TOTAL** RESERVED FOR SYSTEM USE
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 8 of 11)

84

t

P

IS-GPS-200L
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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

4

MSB FIRST

3 SECONDS

63 69
HOW

C P

25

t

22 BITS

91

A-SPOOF &SV CONFIGP

SV SV SV SV
1 2 3 422 BITS

121
A- SPOOF &SV CONFIG

A- SPOOF &P SV SV SV SV SV SV P SV SV
P
SV CONFIG
SV SV SV SV
5

6

7

8

9

10

11 12 13 14 15 16

DATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6MSB FIRST

3 SECONDS

WORD 7

WORD 8WORD 9WORD 10

227

151

181

A- SPOOF &SV CONFIG
425

SV SV SV SV SV SV
17 18 19 20 21 22

P

A- SPOOF &SV CONFIG
SV SV SV SV SV SV
23 24 25 26 27 28

211

229

241

SV
25

SV HEALTH
6 BITS/SVSV SV SV SV
26 27 28 29

A-SPOOF &SV CONFIG

P SV SV SV SV
29 30 31 32

P

2 BITS **** RESERVED FOR SYSTEM USE
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVEDSV HEALTH - 6 BITS

Figure 20-1. Data Format (sheet 9 of 11)

85

271
SV HEALTH
6 BITS/SVSV SV SV
P
30 31
32

4 BITS **t

P

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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUB
FRAME
NO.

PAGE
NO.

WORD 231
TLM

4

WORD 3

61
1

71

HOW
t

22 BITS

WORD 4

WORD 5

69
63

C P

13

MSB FIRST

3 SECONDSP

22 BITS

91

E
R
D
1

E
R
D
2

E
R
D
3

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

121

E
R
D
3

E
R
D
4

E
R
D
5

E
R
D
6

E
R
D
7

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

E
R
D
7

E
R
D
8

E
R
D
9

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

E
R
D
1
0

E
R
D
1
1

6
B
I
T
S

2
M
S
B
S

P

DATA ID - 2 BITS
SV (PAGE) ID - 6 BITS

AVAILABILITY INDICATOR - 2 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

413

WORD 8

181

E
R
D
1
1

E
R
D
1
2

E
R
D
1
3

E
R
D
1
4

E
R
D
1
5

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

MSB FIRST

3 SECONDS
WORD 9

211

E
R
D
1
5

E
R
D
1
6

E
R
D
1
7

E
R
D
1
8

E
R
D
1
9

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

241

E
R
D
1
9

E
R
D
2
0

E
R
D
2
1

E
R
D
2
2

E
R
D
2
3

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

271

E
R
D
2
3

E
R
D
2
4

E
R
D
2
5

E
R
D
2
6

E
R
D
2
7

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 10 of 11)

86

WORD 10

P

E
R
D
2
7

E
R
D
2
8

E
R
D
2
9

E
R
D
3
0

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

t

P

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

14, 15& 17**MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69

91

121

HOW
C P

t

22 BITS

P

16
BITS**

22 BITSP

24 BITS**P

24 BITS**PDATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

14, 15& 17**

4

WORD 8181

24 BITS**P

WORD 9211

24 BITS**MSB FIRST

3 SECONDSP

WORD 10241

24 BITS**P

271

24 BITS****P

22 BITS**THE INDICATED PORTIONS OF WORDS 3 THROUGH 10 OF PAGES 14 AND 15 ARE RESERVED FOR SYSTEM USE, WHILE
THOSE OF PAGE 17 ARE RESERVED FOR SPECIAL MESSAGES PER PARAGRAPH 20.3.3.5.1.8
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 20-1. Data Format (sheet 11 of 11)

87

t

P

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20.3.3 Message Content.
The format and contents of the TLM word and the HOW, as well as those of words three throughten of each subframe/page, are described in the following subparagraphs. The timing of thesubframes and pages is covered in Section 20.3.4.

20.3.3.1 Telemetry Word.
Each TLM word is 30 bits long, occurs every six seconds in the data frame, and is the first word ineach subframe/page. The format shall be as shown in Figure 20-2. Bit 1 is transmitted first. Each
TLM word shall begin with a preamble, followed by the TLM message, the integrity status flag, one
reserved bit, and six parity bits. The TLM message contains information needed by the precise
positioning service (PPS) user (authorized user) and by the CS, as described in the related SS/CS
interface documentation.
Bit 23 of each TLM word is the Integrity Status Flag (ISF). A "0" in bit position 23 indicates that theconveying signal is provided with the legacy level of integrity assurance. That is, the probability
that the instantaneous URE of the conveying signal exceeds 4.42 times the upper bound value ofthe current broadcast URA index, for more than 5.2 seconds, without an accompanying alert, isless than 1E-5 per hour. A "1" in bit-position 23 indicates that the conveying signal is provided withan enhanced level of integrity assurance. That is, the probability that the instantaneous URE of
the conveying signal exceeds 5.73 times the upper bound value of the current broadcast URA
index, for more than 5.2 seconds, without an accompanying alert, is less than 1E-8 per hour. The
probabilities associated with the nominal and lower bound values of the current broadcast URA
index are not defined.
In this context, an "alert" is defined as any indication or characteristic of the conveying signal, as
specified elsewhere in this document, which signifies to users that the conveying signal may beinvalid or should not be used, such as the health bits not indicating operational-healthy,
broadcasting non-standard code, parity error, etc.

20.3.3.2 Handover Word (HOW).
The HOW shall be 30 bits long and shall be the second word in each subframe/page, immediately
following the TLM word. A HOW occurs every 6 seconds in the data frame. The format andcontent of the HOW shall be as shown in Figure 20-2. The MSB is transmitted first. The HOW
begins with the 17 MSBs of the time-of-week (TOW) count. (The full TOW count consists of the 19
LSBs of the 29-bit Z-count). These 17 bits correspond to the TOW-count at the X1 epoch which
occurs at the start (leading edge) of the next following subframe (reference paragraph 3.3.4). The
HOW-message TOW count reaches a maximum value of 100,799 prior to rolling over.
Bit 18 is an "alert" flag. When this flag is raised (bit 18 = "1"), it shall indicate to the standard
positioning service (SPS) user (unauthorized user) that the signal URA may be worse than
indicated in subframe 1 and that he shall use that SV at his own risk.

88IS-GPS-200L
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Bit 19 is an anti-spoof (A-S) flag. A "1" in bit-position 19 indicates that the A-S mode is ON in that
SV.
Bits 20, 21, and 22 of the HOW provide the ID of the subframe in which that particular HOW is thesecond word; the ID code shall be as follows:
Subframe

ID CodeInvalid

000

1

001

2

010

3

011

4

100

5

101

Invalid110

Invalid111

TLM Word
1 = Reserved Bits
2 = Integrity Status Flag
MSB
Preamble

TLM Message

1 0 0 0 1 0 1 1
1 2 3 4 5 6 7 8

ParityLSB

9 10 11 12 1321

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

HOW
Solved for bits to preserve
parity check with zeros inbits 29 and 30

Anti-Spoof Flag
“Alert” Flag
MSB

ParityLSB
SubframeID

TOW-Count Message(Truncated)
1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19

0

20 21 22 23 24 25 26 27 28 29 30

Figure 20-2. TLM and HOW Formats

890IS-GPS-200L
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20.3.3.3 Subframe 1.
The content of words three through ten of subframe 1 are defined below, followed by related
algorithms and material pertinent to use of the data.

20.3.3.3.1 Subframe 1 Content.
The third through tenth words of subframe 1 shall each contain six parity bits as their LSBs; inaddition, two non-information bearing bits shall be provided as bits 23 and 24 of word ten for parity
computation purposes. The remaining 190 bits of words three through ten shall contain the clockparameters and other data described in the following.
The clock parameters describe the SV time scale during the period of validity. The parameters areapplicable during the time in which they are transmitted. The timing information for subframes,
pages, and CEI data sets is covered in Section 20.3.4.

20.3.3.3.1.1 Transmission Week Number.
The ten MSBs of word three shall contain the ten LSBs of the Week Number as defined in 3.3.4.
These ten bits shall be a modulo 1024 binary representation of the current GPS week number at
the start of the CEI data set transmission interval (see paragraph 3.3.4(b)). The GPS weeknumber increments at each end/start of week epoch. For Block II SVs in long-term extended
operations, beginning approximately 28 days after upload, the transmission week number may notcorrespond to the actual GPS week number due to curve fit intervals that cross week boundaries.

20.3.3.3.1.2 Code(s) on L2 Channel.
Bits 11 and 12 of word three shall indicate which code(s) is (are) commanded ON for the in-phasecomponent of the L2 channel, as follows:
00 = Invalid,
01 = P-code ON,
10 = C/A-code ON,
11= Invalid
These bits provide no indication of which code(s), if any, may be commanded ON for thequadrature component of the L2 channel.

90

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20.3.3.3.1.3 SV Accuracy.
Bits 13 through 16 of word three shall give the URA index of the SV (reference paragraph 6.2.1) for
the standard positioning service user. While the URA may vary over the ephemeris curve fit
interval, the URA index (N) in the LNAV message shall correspond to the maximum URA expected
over the entire ephemeris curve fit interval. The URA index (N) is an integer in the range of 0
through 15 and has the following relationship to the URA of the SV:
URA INDEXURA (meters)

0

0.00

< URA 

2.40

1

2.40

< URA 

3.40

2

3.40

< URA 

4.85

3

4.85

< URA 

6.85

4

6.85

< URA 

9.65

5

9.65

< URA 

13.65

6

13.65

< URA 

24.00

7

24.00

< URA 

48.00

8

48.00

< URA 

96.00

9

96.00

< URA 192.0010

192.00< URA 384.0011

384.00< URA 768.0012768.00< URA 1536.00

13

1536.00< URA 3072.00

143072.00< URA 6144.00

156144.00< URA (or no accuracy prediction is available - standard positioning
service users are advised to use the SV at their own risk.)91

IS-GPS-200L
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For each URA index (N), users may compute a nominal URA value (X) as given by:• If the value of N is 6 or less, X = 2(1 + N/2),• If the value of N is 6 or more, but less than 15, X = 2 (N - 2),• N = 15 shall indicate the absence of an accuracy prediction and shall advise the standard
positioning service user to use that SV at his own risk.
For N = 1, 3, and 5, X should be rounded to 2.8, 5.7, and 11.3 meters, respectively.
The nominal URA value (X) is suitable for use as a conservative prediction of the RMS signal-inspace (SIS) range errors for accuracy-related purposes in the pseudorange domain (e.g.,measurement de-weighting, receiver autonomous integrity monitoring (RAIM), figure of merit(FOM) computations). Integrity properties of the URA are specified with respect to the scaled(multiplied by either 4.42 or 5.73 as appropriate) upper bound values of the URA index (see20.3.3.1).
URA accounts for SIS contributions to user range error which include, but are not limited to, thefollowing: LNAV LSB representation/truncation error; the net effect of LNAV clock correction
polynomial error and code phase error in the transmitted signal for single-frequency L1C/A,
L1P(Y), L2P(Y), or dual-frequency P(Y) users who correct the code phase as described in Section
20.3.3.3.3; LNAV ephemeris error; anisotropic antenna errors; and signal deformation error. URA
does not account for user range error contributions due to the inaccuracy of the broadcast
ionospheric data parameters used in the single-frequency ionospheric model or for otheratmospheric effects.

20.3.3.3.1.4 SV Health.
The six-bit health indication given by bits 17 through 22 of word three refers to the transmitting SV.
The MSB shall indicate a summary of the health of the LNAV data, where
0 = all LNAV data are OK,
1 = some or all LNAV data are bad.
The five LSBs shall indicate the health of the signal components in accordance with the codes
given in paragraph 20.3.3.5.1.3. The health indication shall be given relative to the "as designed"
capabilities of each SV (as designated by the configuration code - see paragraph 20.3.3.5.1.4).
Accordingly, any SV which does not have a certain capability will be indicated as "healthy" if thelack of this capability is inherent in its design or if it has been configured into a mode which isnormal from a user standpoint and does not require that capability.
Additional SV health data are given in subframes 4 and 5. The data given in subframe 1 may differ
from that shown in subframes 4 and/or 5 of other SVs since the latter may be updated at a different
time.

92

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20.3.3.3.1.5 Issue of Data, Clock (IODC).
Bits 23 and 24 of word three in subframe 1 shall be the two MSBs of the ten-bit IODC term; bits
one through eight of word eight in subframe 1 shall contain the eight LSBs of the IODC. The IODC
indicates the issue number of the data set and thereby provides the user with a convenient meansof detecting any change in the subframe 1 core CEI data. Constraints on the IODC as well as therelationship between the IODC and the IODE (issue of data, ephemeris) terms are defined inparagraph 20.3.4.4.
Short-term and Long-term Extended Operations.
Whenever the fit interval flag indicates a fit interval greater than 4 hours, the IODC can be used todetermine the actual fit interval of the CEI data set (reference section 20.3.4.4).

20.3.3.3.1.6 Data Flag for L2 P-Code.
When bit 1 of word four is a "1", it shall indicate that the LNAV data stream was commanded OFFon the P-code of the in-phase component of the L2 channel.
This bit provides no indication of whether LNAV data is or is not present on any code modulated on
the quadrature component of the L2 channel.

20.3.3.3.1.7 Estimated Group Delay Differential.
Bits 17 through 24 of word seven contain the L1-L2 correction term, TGD, for the benefit of "L1 only"or "L2 only" users; the related user algorithm is given in paragraph 20.3.3.3.3.

20.3.3.3.1.8 SV Clock Correction.
Bits nine through 24 of word eight, bits one through 24 of word nine, and bits one through 22 ofword ten contain the parameters needed by the users for apparent SV clock correction (toc, af2, af1,
af0). The related algorithm is given in paragraph 20.3.3.3.3.

20.3.3.3.2 Subframe 1 Parameter Characteristics.
For those parameters whose characteristics are not fully defined in Section 20.3.3.3.1, the numberof bits, the scale factor of the LSB (which shall be the last bit received), the range, and the units
shall be as specified in Table 20-I.

93

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20.3.3.3.3 User Algorithms for Subframe 1 Data.
The algorithms defined below (a) allow all users to correct the code phase time received from theSV with respect to both SV code phase offset and relativistic effects, (b) permit the "singlefrequency" (L1 or L2) user to compensate for the effects of SV group delay differential (the user
who utilizes both frequencies does not require this correction, since the clock parameters accountfor the induced effects), and (c) allow the "dual-frequency" (L1 and L2) user to correct for the grouppropagation delay due to ionospheric effects (the single-frequency user may correct forionospheric effects as described in paragraph 20.3.3.5.2.5).
Table 20-I.

Subframe 1 Parameters

Parameter

No. of
Bits**

Scale
Factor(LSB)

Code on L2

2

1(see text)

Week No.

10

1

week

L2 P data flag

1

1

discrete

SV accuracy

4

SV health6

1

discretes

TGD

8*

2-31

seconds

IODC

10

toc

16

24

af2

8*

2-55

sec/sec2

af1

16*

2-43

sec/sec

af0

22*

2-31

seconds

Valid
Range***

Units(see text)(see text)
0 to 604,784

seconds*

Parameters so indicated shall be two's complement, with the sign bit (+ or -) occupying the MSB;**

See Figure 20-1 for complete bit allocation in subframe;***

Unless otherwise indicated in this column, valid range is the maximum range attainable with indicatedbit allocation and scale factor.

20.3.3.3.3.1 User Algorithm for SV Clock Correction.
94

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The polynomial defined in the following allows the user to determine the effective SV PRN code
phase offset referenced to the phase center of the antennas (tsv) with respect to GPS system time(t) at the time of data transmission. The coefficients transmitted in subframe 1 describe the offset
apparent to the dual-frequency user for the interval of time in which the parameters aretransmitted. This estimated correction accounts for the deterministic SV clock error characteristics
of bias, drift and aging, as well as for the SV implementation characteristics of group delay bias
and mean differential group delay. Since these coefficients do not include corrections for
relativistic effects, the user's equipment must determine the requisite relativistic correction.
Accordingly, the offset given below includes a term to perform this function.
The user shall correct the time received from the SV with the equation (in seconds)t=

tsv - tsv

(1)

where
t

=

GPS system time (seconds),

tsv=

effective SV PRN code phase time at message transmission
time (seconds),

tsv

=

SV PRN code phase time offset (seconds).

The SV PRN code phase offset is given bytsv= af0 + af1(t - toc) + af2(t - toc)2 + tr

(2)

where
af0, af1 and af2 are the polynomial coefficients given in subframe 1, t oc is the clock data
reference time in seconds (reference paragraph 20.3.4.5), and tr is the relativistic
correction term (seconds) which is given bytr = F e A sin Ek.
The orbit parameters (e, A , Ek) used here are described in discussions of data contained in
subframes 2 and 3, while F is a constant whose value is

2 
c2
F =

sec

= - 4.442807633 (10)-10

meter ,

where95

IS-GPS-200L
14 May 2020

meters 3

 = 3.986005 x 1014 secondc = 2.99792458 x 10

82

meterssecond=value of Earth's universal gravitational parameters=

speed of light.

Note that equations (1) and (2), as written, are coupled. While the coefficients a f0, af1 and af2 are
generated by using GPS time as indicated in equation (2), sensitivity of t sv to t is negligible. Thisnegligible sensitivity will allow the user to approximate t by t SV in equation (2). The value of t mustaccount for beginning or end of week crossovers. That is, if the quantity t - toc is greater than
302,400 seconds, subtract 604,800 seconds from t. If the quantity t - toc is less than -302,400
seconds, add 604,800 seconds to t.
The Control Segment will utilize the following alternative but equivalent expression for the
relativistic effect when estimating the LNAV/CNAV parameters:

2 R V
c2

tr =
where


R is the instantaneous position vector of the SV,

V is the instantaneous velocity vector of the SV, andc is the speed of light. (Reference paragraph 20.3.4.3).


It is immaterial whether the vectors R and V are expressed in earth-fixed, rotating coordinates orin earth-centered, inertial coordinates.

20.3.3.3.3.2 L1 or L2 Correction.
The L1 and L2 correction term, T GD, is initially calculated by the CS to account for the effect of SV
group delay differential between L1 P(Y) and L2 P(Y) based on measurements made by the SVcontractor during SV manufacture. The value of T GD for each SV may be subsequently updated toreflect the actual on-orbit group delay differential. This correction term is only for the benefit of"single-frequency" (L1 C/A, L1 P(Y) or L2 P(Y)) users; it is necessitated by the fact that the SV
clock offset estimates reflected in the af0 clock correction coefficient (see paragraph 20.3.3.3.3.1)
are based on the effective PRN code phase as apparent with dual-frequency (L1 P(Y) and L2
P(Y)) ionospheric corrections. Thus, the user who utilizes the L1 C/A signal only shall modify thecode phase offset in accordance with paragraph 20.3.3.3.3.1 with the equation(tSV)L1C/A = tSV - TGD

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where TGD is provided to the user as subframe 1 data. For the user who utilizes L1 P(Y) only, thecode phase modification is given by(tSV)L1 P(Y) = tSV - TGD
For the user who utilizes L2 P(Y) only, the code phase modification is given by(tSV)L2 P(Y) = tSV - TGD
where, denoting the nominal center frequencies of L1 and L2 as f L1 and fL2 respectively, = (fL1/fL2)2 = (1575.42/1227.6)2 = (77/60)2.
The value of TGD is not equal to the mean SV group delay differential, but is a measured value that
represents the mean group delay differential multiplied by 1/(1- ). That is,
1

TGD =

1-

(tL1P(Y) - tL2P(Y))

where tLiP(Y) is the GPS time the i th frequency P(Y) signal (a specific epoch of the signal) is
transmitted from the SV antenna phase center.

20.3.3.3.3.3 Ionospheric Correction.
The dual-frequency (L1 P(Y) and L2 P(Y)) user shall correct for the group delay due to ionosphericeffects by applying the relationship:
PR 

PR L2P(Y) -  PR L1P(Y)
1- 

where
PR

=

pseudorange corrected for ionospheric effects,

PRi=

pseudorange measured on the channel indicated by the subscript,

and  is as defined in paragraph 20.3.3.3.3.2. The clock correction coefficients are based on "dualfrequency" measurements and therefore account for the effects of mean differential delay in SV
instrumentation.

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20.3.3.3.3.4 Example Application of Correction Parameters.
A typical system application of the correction parameters for a user receiver is shown in Figure 203. The ionospheric model referred to in Figure 20-3 is discussed in paragraph 20.3.3.5.2.5 in
ERDconjunction with the related data contained in page 18 of subframe 4. The c term referred to in
Figure 20-3 is discussed in paragraph 20.3.3.5.2.6 in conjunction with the related data contained inpage 13 of subframe 4.

Figure 20-3. Sample Application of Correction Parameters20.3.3.4 Subframes 2 and 3.
The contents of words three through ten of subframes 2 and 3 are defined below, followed bymaterial pertinent to the use of the data.
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20.3.3.4.1 Content of Subframes 2 and 3.
The third through tenth words of subframes 2 and 3 shall each contain six parity bits as their LSBs;
in addition, two non-information bearing bits shall be provided as bits 23 and 24 of word ten ofeach subframe for parity computation purposes. Bits 288 through 292 of subframe 2 shall containthe Age of Data Offset (AODO) term for the navigation message correction table (NMCT)
contained in subframe 4 (reference paragraph 20.3.3.5.1.9). The remaining 375 bits of those two
subframes shall contain the ephemeris representation parameters of the transmitting SV.
The ephemeris parameters describe the orbit during the curve fit intervals described in section
20.3.4. Table 20-II gives the definition of the orbital parameters using terminology typical of
Keplerian orbital parameters; it shall be noted, however, that the transmitted parameter values are
such that they provide the best trajectory fit in Earth-Centered, Earth-Fixed (ECEF) coordinates foreach specific fit interval. The user shall not interpret intermediate coordinate values as pertaining
to any conventional coordinate system.
The issue of ephemeris data (IODE) term shall provide the user with a convenient means for
detecting any change in the ephemeris representation parameters. The IODE is provided in bothsubframes 2 and 3 for the purpose of comparison with the 8 LSBs of the IODC term in subframe 1.
Whenever these three terms do not match, a CEI data set cutover has occurred and new data
must be collected. The timing of the IODE and constraints on the IODC and IODE are defined inparagraph 20.3.4.4.
Any change in the subframe 2 and 3 core CEI data will be accomplished with a simultaneouschange in both IODE words. The CS (Block II/Block IIA/IIR/IIR-M/IIF) and SS (GPS III/IIIF) shallassure that the toe value, for at least the first CEI data set transmitted by an SV from a new CEI
data sequence propagation, is different from that transmitted for the prior CEI data sequence
propagation (reference paragraph 20.3.4.5).
A "fit interval" flag is provided in subframe 2 to indicate whether the ephemerides are based on afour-hour fit interval or a fit interval greater than four hours (reference paragraph 20.3.3.4.3.1).
The AODO word is provided in subframe 2 to enable the user to determine the validity time for the
NMCT data provided in subframe 4 of the transmitting SV. The related algorithm is given inparagraph 20.3.3.4.4.

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Table 20-II. Ephemeris Data Definitions
M0

Mean Anomaly at Reference TimenMean Motion Difference From Computed Valuee

Eccentricity

A

Square Root of the Semi-Major Axis

Ω0Longitude of Ascending Node of Orbit Plane at Weekly Epochi0

Inclination Angle at Reference Time

Argument of PerigeeRate of Right Ascension

IDOT

Rate of Inclination Angle

Cuc

Amplitude of the Cosine Harmonic Correction Term to the Argument of Latitude

Cus

Amplitude of the Sine Harmonic Correction Term to the Argument of Latitude

Crc

Amplitude of the Cosine Harmonic Correction Term to the Orbit Radius

Crs

Amplitude of the Sine Harmonic Correction Term to the Orbit Radius

Cic

Amplitude of the Cosine Harmonic Correction Term to the Angle of Inclination

Cis

Amplitude of the Sine Harmonic Correction Term to the Angle of Inclination

toe

Reference Time Ephemeris (reference paragraph 20.3.4.5)

IODE

Issue of Data (Ephemeris)

20.3.3.4.2 Subframe 2 and 3 Parameter Characteristics.
For each ephemeris parameter contained in subframes 2 and 3, the number of bits, the scale
factor of the LSB (which shall be the last bit received), the range, and the units shall be as
specified in Table 20-III.
The AODO word (which is not an ephemeris parameter) is a five-bit unsigned term with an LSB
scale factor of 900, a range from 0 to 31, and units of seconds.

20.3.3.4.3 User Algorithm for Ephemeris Determination.
The user shall compute the ECEF coordinates of position for the phase center of the SVs’
antennas utilizing a variation of the equations shown in Table 20-IV. Subframes 2 and 3
parameters are Keplerian in appearance; the values of these parameters, however, are producedby the CS (Block II/Block IIA/IIR/IIR-M/IIF) and SS (GPS III/IIIF) via a least squares curve fit of the
propagated ephemeris of the phase center of the SVs’ antennas (time-position quadruples; t, x, y,z expressed in ECEF coordinates). Particulars concerning the periods of the curve fit, the resultant
accuracy, and the applicable coordinate system are given in the following subparagraphs.
The user can compute velocity and acceleration for the SV, if required, utilizing a variation of theequations shown in Table 20- IV Part 3 and 4.

20.3.3.4.3.1 Curve Fit Intervals.
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Bit 17 in word 10 of subframe 2 is a "fit interval" flag which indicates the curve-fit interval used by
the CS (Block II/Block IIA/IIR/IIR-M/IIF) and SS (GPS III and GPS IIIF) in determining theephemeris parameters, as follows:
0 = 4 hours,
1 = greater than 4 hours.
The relationship of the curve-fit interval to transmission time and the timing of the curve-fit intervals
is covered in section 20.3.4.
Table 20-III. Ephemeris Parameters

Parameter

No. of Bits**

IODE

8

Crs

16*

2-5

meters

n

16*

2

-43

semi-circles/sec

M0

32*

2-31

semi-circles

Cuc

16*

2

-29

radians

e

32

2-33

Cus

16*

2

-29

A

32

2-19

2530 to 8192

meters

toe

16

2

4

0 to 604,784

seconds

Cic

16*

2-29

radians

Ω0

32*

2

-31

semi-circles

Cis

16*

2-29

radians

i0

32*

2

-31

semi-circles

Crc

16*

2-5

meters

32*

2

-31

semi-circles

24*

2-43

14*

-43





IDOT
*
**
***

Scale Factor (LSB)

Valid Range***Units(see text)

0.0 to 0.03

dimensionlessradians-6.33E-07 to 0

2semi-circles/sec
semi-circles/sec

Parameters so indicated shall be two's complement, with the sign bit (+ or -) occupying the MSB;
See Figure 20-1 for complete bit allocation in subframe;
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicatedbit allocation and scale factor.

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Table 20-IV. Broadcast Navigation User Equations (sheet 1 of 4)

 = 3.986005 x 1014 meters3/sec2

WGS 84 value of the earth's gravitational constant for
GPS user e = 7.2921151467 x 10-5 rad/sec
A=

 A

2

Semi-major axis



n0 =

WGS 84 value of the earth's rotation rate

Computed mean motion (rad/sec)

A3

tk = t - toe*Time from ephemeris reference epochn = n0 + n

Corrected mean motion

Mk = M0 + ntk

Mean anomaly
Kepler’s equation (𝑀𝑘 = 𝐸𝑘 − 𝑒 sin 𝐸𝑘 ) may be solved forEccentric anomaly (𝐸𝑘 ) by iteration:– Initial Value (radians)

E0 = Mk

𝐸𝑗 = 𝐸𝑗−1 +𝑀𝑘 −𝐸𝑗−1 +𝑒 sin 𝐸𝑗−1
1−𝑒 cos 𝐸𝑗−1

– Final Value (radians)

Ek = E j
k = 2 tan-1*– Refined Value, minimum of three iterations, (j=1,2,3)

(

1+𝑒
1−𝑒

tan

𝐸𝑘

)
2

True Anomaly (unambiguous quadrant)t is GPS system time at time of transmission, i.e., GPS time corrected for transit time (range/speed of light).
Furthermore, t k shall be the actual total time difference between the time t and the epoch time toe, and mustaccount for beginning or end of week crossovers. That is, if tk is greater than 302,400 seconds, subtract 604,800
seconds from t k. If t k is less than -302,400 seconds, add 604,800 seconds to tk.

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Table 20-IV. Broadcast Navigation User Equations (sheet 2 of 4)

 k = k + Argument of Latitude

uk = cussin2 k + cuccos2 krk = crssin2k + crccos2 kik = cissin2k + ciccos2 k}

Argument of Latitude Correction
Radius Correction
Inclination Correction

Second Harmonic
Perturbations

uk =  k + uk

Corrected Argument of Latitude

rk = A(1 - e cosEk) + rk

Corrected Radius

ik = i0 + ik + (IDOT) tk

Corrected Inclinationxk = rkcosukyk = rksinuk}Positions in orbital
plane.
k = 0 + (  -  e ) tk -  e toe
xk = xkcosk - ykcosiksinkyk = xksink + ykcosikcoskzk = yksinik

Corrected longitude of ascending node.

}

Earth-fixed
coordinates.

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Table 20- IV. Broadcast Navigation User Equations (sheet 3 of 4)

Element/Equation

Description

SV Velocity
Ėk = n/ (1 – e cos Ek)

Eccentric Anomaly Ratev̇k = Ėk √1 − 𝑒 2 /(1 − 𝑒 cos 𝐸𝑘 )True Anomaly Rate

(dik / dt) = (IDOT) + 2 v̇k (cis cos 2ɸk – cic sin 2ɸk)

Corrected Inclination Angle Rateu̇k = v̇k + 2v̇k (cus cos 2ɸk – cuc sin 2ɸk)

Corrected Argument of Latitude Rateṙk = eAĖk sin Ek + 2v̇k (crs cos 2ɸk – crc sin 2ɸk)

Corrected Radius RateΩ̇k = Ω̇ - Ω̇eLongitude of Ascending Node Rate

ẋ′𝑘 = ṙk cos uk – rk u̇k sin uk

In- plane x velocity

𝑦̇ 𝑘′ = ṙk sin uk + rk u̇k cos uk

In- plane y velocity𝑥̇ k = -𝑥𝑘′ Ω̇k sin Ωk + 𝑥̇ 𝑘′ cos Ωk – 𝑦̇ 𝑘′ sin Ωk cos ik– 𝑦𝑘′ (Ω̇k cos Ωk cos ik – (dik / dt) sin Ωk sin ik)

Earth- Fixed x velocity (m/s)

𝑦̇ k = 𝑥𝑘′ Ω̇k cos Ωk + 𝑥̇ 𝑘′ sin Ωk + 𝑦̇ 𝑘′ cos Ωk cos ik– 𝑦𝑘′ (Ω̇k sin Ωk cos ik + (dik / dt) cos Ωk sin ik)

Earth- Fixed y velocity (m/s)

𝑧̇ k = 𝑦̇ 𝑘′ sin ik +𝑦𝑘′ (dik / dt) cos ik

Earth- Fixed z velocity (m/s)

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Table 20-IV. Broadcast Navigation User Equations (sheet 4 of 4)
Element/Equation

Description

SV Acceleration
RE = 6378137.0 meters

WGS 84 Earth Equatorial Radius

J2 = 0.0010826262

Oblate Earth Gravity CoefficientF = - (3/2) J2 (µ/ 𝑟𝑘2 ) (RE / rk)2

Oblate Earth acceleration Factor

𝑥̈ 𝑘 = - µ (𝑥𝑘 / 𝑟𝑘3 ) + F [(1 – 5 (𝑧𝑘 / 𝑟𝑘 )2 )(𝑥𝑘 / 𝑟𝑘 ) ]+2𝑦̇ 𝑘 Ω̇𝑒 + 𝑥𝑘 Ω̇2𝑒Earth- Fixed x acceleration (m/s2)

𝑦̈ 𝑘 = - µ (𝑦𝑘 / 𝑟𝑘3 ) + F [(1 – 5 (𝑧𝑘 / 𝑟𝑘 )2 )(𝑦𝑘 / 𝑟𝑘 ) ]-2𝑥̇ 𝑘 Ω̇𝑒 + 𝑦𝑘 Ω̇2𝑒Earth- Fixed y Acceleration (m/s2)𝑧̈𝑘 = - µ (𝑧𝑘 / 𝑟𝑘3 ) + F [(3 – 5 (𝑧𝑘 / 𝑟𝑘 )2 )(𝑧𝑘 / 𝑟𝑘 ) ]Earth- Fixed z Acceleration (m/s2)

20.3.3.4.3.2 Parameter Sensitivity.
The sensitivity of the SV's antenna phase center position to small perturbations in most ephemeris
parameters is extreme. The sensitivity of position to the parameters A , Crc and Crs is about one
meter/meter. The sensitivity of position to the angular parameters is on the order of 108
meters/semicircle, and to the angular rate parameters is on the order of 10 12
meters/semicircle/second. Because of this extreme sensitivity to angular perturbations, the valueof  used in the curve fit is given here.  is a mathematical constant, the ratio of a circle's
circumference to its diameter. Here  is taken as = 3.1415926535898.

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20.3.3.4.3.3 Coordinate Systems.
20.3.3.4.3.3.1 ECEF Coordinate System.
The equations given in Table 20-IV provide the SV's antenna phase center position in the WGS 84
ECEF coordinate system defined as follows:
Origin*=Earth's center of mass

Z-Axis**=The direction of the IERS (International Earth Rotation and Reference
Systems Service) Reference Pole (IRP)
X-Axis =Intersection of the IERS Reference Meridian (IRM) and the plane passing
through the origin and normal to the Z-axis
Y-Axis =systemCompletes a right-handed, Earth-Centered, Earth-Fixed orthogonal coordinate* Geometric center of the WGS 84 Ellipsoid** Rotational axis of the WGS 84 Ellipsoid20.3.3.4.3.3.2 Earth-Centered, Inertial (ECI) Coordinate System.
In an ECI coordinate system, GPS signals propagate in straight lines at the constant speed c*(reference paragraph 20.3.4.3). A stable ECI coordinate system of convenience may be defined
as being coincident with the ECEF coordinate system at a given time t 0. The x, y, z coordinates inthe ECEF coordinate system at some other time t can be transformed to the x, y, z coordinates inthe selected ECI coordinate system of convenience by the simple** rotation:x = x cos() - y sin()y = x sin() + y cos()z = zwhere =  e (t - t0)* The propagation speed c is constant only in a vacuum. The gravitational potential also
has a small effect on the propagation speed, but may be neglected by most users.
** Neglecting effects due to polar motion, nutation, and precession which may be neglectedby most users for small values of (t - t0).

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20.3.3.4.3.4 Geometric Range.
The user shall account for the geometric range (D) from satellite to receiver in an ECI coordinate
system. D may be expressed as,

D =  r (tR) - R (tT)
where
tT and tR are the GPS system times of transmission and reception, respectively,
and where,R (tT) = position vector of the GPS satellite in the selected ECI coordinate system at time t T,r (tR) = position vector of the receiver in the selected ECI coordinate system at time t R.

20.3.3.4.4 NMCT Validity Time.
Users desiring to take advantage of the NMCT data provided in page 13 of subframe 4 shall firstexamine the AODO term currently provided in subframe 2 of the LNAV data from the transmitting
SV. If the AODO term is 27900 seconds (i.e., binary 11111), then the NMCT currently available
from the transmitting SV is invalid and shall not be used. If the AODO term is less than 27900
seconds, then the user shall compute the validity time for that NMCT (t nmct) using the ephemeris t oe
parameter and the AODO term from the current subframe 2 as follows:
OFFSET = toe [modulo 7200]
if OFFSET = 0,then tnmct = toe - AODO

if OFFSET > 0,then tnmct = toe - OFFSET + 7200 - AODO

Note that the foregoing computation of t nmct must account for any beginning or end of week
crossovers; for example,
if t* - tnmct > 302,400 then tnmct = tnmct + 604,800
if t* - tnmct < -302,400 then tnmct = tnmct - 604,800* t is GPS system time at time of transmission.
Users are advised that different SVs will transmit NMCTs with different t nmct and that the best
performance will generally be obtained by applying data from the NMCT with the latest (largest)
tnmct. As a result, users should compute and examine the t nmct values for all visible and available
SVs in order to find and use the NMCT with the latest t nmct. If the same latest (largest) tnmct isprovided by two or more visible and available SVs, then the NMCT from any SV with the latest t nmct
may be selected and used; however, the estimated range deviation (ERD) value provided by theselected NMCT for the other SVs with the same t nmct shall be set to zero if those SVs are used in
the positioning solution. It should be noted that the intended positioning solution accuracy
improvement will not be obtained if the data from two different NMCTs are applied simultaneously

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or if the data from a given NMCT is applied to just a subset of the SVs used in the positioning
solution (i.e., mixed mode operation results in potentially degraded solution accuracy).
It should be noted that the NMCT information shall be supported by the Block IIR SV.

20.3.3.5 Subframes 4 and 5.
Both subframe 4 and 5 are subcommutated 25 times each; the 25 versions of these subframes arereferred to as pages 1 through 25 of each subframe. With the possible exception of "reserved forsystem use" pages and explicit repeats, each page contains different specific data in words three
through ten. As shown in Figure 20-1, the pages of subframe 4 utilize seven different formats,while those of subframe 5 use two. The content of words three through ten of each page is
described below, followed by algorithms and material pertinent to the use of the data.

20.3.3.5.1 Content of Subframes 4 and 5.
Words three through ten of each page contain six parity bits as their LSBs; in addition, two noninformation bearing bits are provided as bits 23 and 24 of word ten in each page for parity
computation purposes. The data contained in the remaining bits of words three through ten of thevarious pages in subframes 4 and 5 are described in the following subparagraphs.
A brief summary of the various data contained in each page of subframes 4 and 5 is as follows:
SubframePage(s)Data

4

1, 6, 11, 16 and 21

Reserved

2, 3, 4, 5, 7, 8, 9 and 10

almanac data for SV 25 through 32 respectively

12, 19, 20, 22, 23 and 24

Reserved

13NMCT

14 and 15

Reserved for system use

17

Special messages

18

Ionospheric and UTC data

25

A-S flags/SV configurations for 32 SVs, plus SV health for SV 25
through 32

5

1 through 24

almanac data for SV 1 through 24

25

SV health data for SV 1 through 24, the almanac reference time, thealmanac reference week number

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20.3.3.5.1.1 Data ID and SV ID.
The two MSBs of word three in each page shall contain data ID. Data ID number two (denoted bybinary code 01) denotes the LNAV data structure of D(t) which is described in this Appendix and is
the only valid value.
As shown in Table 20-V, the data ID is utilized to provide one of two indications: (a) for thosepages which are assigned to contain the almanac data of one specific SV, the data ID defines thedata structure utilized by that SV whose almanac data are contained in that page; and (b) for allother pages, the data ID denotes the data structure of the transmitting SV.
The SV ID is given by bits three through eight of word three in each page as shown in Table 20-V.
Specific IDs are reserved for each page of subframes 4 and 5. The SV IDs are utilized in two
different ways: (a) for those pages which contain the almanac data of a given SV, the SV ID is thesame number that is assigned to the PRN code phase of that SV (reference Table 3-I), and (b) for
all other pages the SV ID assigned in accordance with Table 20-V serves as the "page ID". IDs 1
through 32 are assigned to those pages which contain the almanac data of specific SVs (pages 124 of subframe 5 and pages 2-5 and 7-10 of subframe 4). The "0" ID (binary all zeros) is assigned
to indicate a dummy SV, while IDs 51 through 63 are utilized for pages containing other thanalmanac data of a specific SV. The remaining IDs (33 through 50) are unassigned.
Pages which carry the same SV ID (e.g., in subframe 4, pages 1, 6, 11, 16 and 21 carry an ID of
57, while pages 12 and 24 are designated by an ID of 62) may not be considered to containidentical data. The data in the pages with the same SV ID can be different.

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Table 20-V. Data IDs and SV IDs in Subframes 4 and 5

Subframe 4

Subframe 5

Page

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

Data ID

SV ID*

Data ID

SV ID*

Note(2)
Note(1)
Note(1)
Note(1)
Note(1)
Note(2)
Note(1)
Note(1)
Note(1)
Note(1)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)

57
25
26
27
28
57
29
30
31
32
57
62
52
53
54
57
55
56
58 Note(3)59 Note(3)57
60 Note(3)61 Note(3)6263Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(2)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
51

* Use "0" to indicate "dummy" SV. When using "0" to indicate dummy SV, use the data ID of the transmitting
SV.
Note 1:
Note 2:
Note 3:

Data ID of that SV whose SV ID appears in that page.
Data ID of transmitting SV.
SV ID may vary (except for IIR/IIR-M/IIF/GPS III/ GPS IIIF SVs).

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20.3.3.5.1.2 Almanac Data.
Pages 1 through 24 of subframe 5, as well as pages 2 through 5 and 7 through 10 of subframe 4
contain the almanac data and a SV health word for up to 32 SVs (the health word is discussed inparagraph 20.3.3.5.1.3). The almanac data are a reduced-precision subset of the clock andephemeris parameters. The data occupy all bits of words three through ten of each page except
the eight MSBs of word three (data ID and SV ID), bits 17 through 24 of word five (SV health), andthe 50 bits devoted to parity. The number of bits, the scale factor (LSB), the range, and the unitsof the almanac parameters are given in Table 20-VI. The algorithms and other material related tothe use of the almanac data are given in paragraph 20.3.3.5.2.
The almanac message for any dummy SVs shall contain alternating ones and zeros with valid
parity.
Users are cautioned against attempting to track a dummy SV since the results are unpredictable.
The almanac parameters shall be updated by the CS at least once every 6 days while the CS isable to upload the SVs. If the CS is unable to upload the SVs, the accuracy of the almanac
parameters transmitted by the SVs will degrade over time.
For Block II and IIA SVs, three sets of almanac shall be used to span at least 60 days. The firstand second sets will be transmitted for up to six days each; the third set is intended to betransmitted for the remainder of the 60 days minimum, but the actual duration of transmission will
depend on the individual SV's capability to retain data in memory. All three sets are based on sixday curve fits that correspond to the first six days of the transmission interval.
For Block IIR/IIR-M, IIF, GPS III, and GPS IIIF SVs, five sets of almanac shall be used to span atleast 60 days. The first, second, and third sets will be transmitted for up to six days each; thefourth and fifth sets will be transmitted for up to 32 days; the fifth set is intended to be transmitted
for the remainder of the 60 days minimum, but the actual duration of transmission will depend on
the individual SV's capability to retain data in memory.
The first, second, and third sets are based on six day curve fits. The fourth and fifth sets are
based on 32 day curve fits.

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Table 20-VI. Almanac Parameters

Scale
Factor(LSB)

Valid Range***

Parameter

No. of
Bits**

e

16

2-21

0.0 to 0.03

dimensionless

toa

8

212

0 to 602,112

seconds

i****

16*

2-19



16*

2-38

-1.19E-07 to 0

semi-circles/sec

A

24

2-11

2530 to 8192

meters

Ω0

24*

2-23

semi-circles



24*

2-23

semi-circles

M0

24*

2-23

semi-circles

af0

11*

2-20

seconds

af1

11*

2-38

sec/secUnitssemi-circles* Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;** See Figure 20-1 for complete bit allocation in subframe;*** Unless otherwise indicated in this column, valid range is the maximum range attainable with indicated bit
allocation and scale factor;**** Relative to i0 = 0.30 semi-circles.

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20.3.3.5.1.3 SV Health.
Subframes 4 and 5 contain two types of SV health data: (a) each of the 32 pages which containthe clock/ephemeris related almanac data provide an eight-bit SV health status word regarding the
SV whose almanac data they carry, and (b) the 25th page of subframe 4 and of subframe 5 jointly
contain six-bit health status data for up to 32 SVs.
The three MSBs of the eight-bit health words indicate health of the LNAV data in accordance withthe code given in Table 20-VII. The six-bit words provide a one-bit summary of the LNAV data's
health status in the MSB position in accordance with paragraph 20.3.3.3.1.4. The five LSBs ofboth the eight-bit and the six-bit words provide the health status of the SV's signal components inaccordance with the code given in Table 20-VIII. A special meaning is assigned, however, to the"6 ones" combination of the six-bit health words in the 25th page of subframes 4 and 5: it indicatesthat "the SV which has that ID is not available and there may be no data regarding that SV in thatpage of subframes 4 and 5 that is assigned to normally contain the almanac data of that SV"(NOTE: this special meaning applies to the 25th page of subframes 4 and 5 only). The healthindication shall be given relative to the "as designed" capabilities of each SV (as designated by theconfiguration code -- see paragraph 20.3.3.5.1.4). Accordingly, any SV which does not have acertain capability will be indicated as "healthy" if the lack of this capability is inherent in its design
or it has been configured into a mode which is normal from a user standpoint and does not requirethat capability.
Additional SV health data are given in subframe 1. The data given in subframes 1, 4, and 5 of theother SVs may differ from that shown in subframes 4 and/or 5 since the latter may be updated at adifferent time.
The eight-bit health status words shall occupy bits 17 through 24 of word five in those 32 pages
which contain almanac data for individual SVs. The six-bit health status words shall occupy the 24
MSBs of words four through nine in page 25 of subframe 5 plus bits 19 through 24 of word 8, the24 MSBs of word 9, and the 18 MSBs of word 10 in page 25 of subframe 4.
The predicted health data will be updated at the time of upload when a new almanac has been
built by the CS. The transmitted health data may not correspond to the actual health of thetransmitting SV or other SVs in the constellation.

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Table 20-VII. LNAV Data Health Indications

Bit Position in Page
Indication
137

138

139

0

0

0

ALL DATA OK

0

0

1

PARITY FAILURE -- some or all parity bad

0

1

0

TLM/HOW FORMAT PROBLEM -- any departure from standard format (e.g.,preamble misplaced and/or incorrect, etc.), except for incorrect Z-count, asreported in HOW

0

1

1

Z-COUNT IN HOW BAD -- any problem with Z-count value not reflecting
actual code phase

1

0

0

SUBFRAMES 1, 2, 3 -- one or more elements in words three through ten of
one or more subframes are bad

1

0

1

SUBFRAMES 4, 5 -- one or more elements in words three through ten of one
or more subframes are bad

1

1

0

ALL UPLOADED DATA BAD -- one or more elements in words three
through ten of any one (or more) subframes are bad

1

1

1

ALL DATA BAD -- TLM word and/or HOW and one or more elements in any
one (or more) subframes are bad

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Table 20-VIII.

MSB

Codes for Health of SV Signal Components

LSB

00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111

Definition
All Signals OK
All Signals Weak*All Signals Dead
All Signals Have No Data Modulation
L1 P Signal Weak
L1 P Signal Dead
L1 P Signal Has No Data Modulation
L2 P Signal Weak
L2 P Signal Dead
L2 P Signal Has No Data Modulation
L1C Signal WeakL1C Signal Dead
L1C Signal Has No Data Modulation
L2C Signal WeakL2C Signal Dead
L2C Signal Has No Data Modulation
L1 & L2 P Signal Weak
L1 & L2 P Signal Dead
L1 & L2 P Signal Has No Data Modulation
L1 & L2C Signal Weak
L1 & L2C Signal Dead
L1 & L2C Signal Has No Data Modulation
L1 Signal Weak*
L1 Signal Dead
L1 Signal Has No Data Modulation
L2 Signal Weak*
L2 Signal Dead
L2 Signal Has No Data Modulation
SV Is Temporarily Out (Do not use this SV during current pass)**
SV Will Be Temporarily Out (Use with caution)*****One Or More Signals Are Deformed, However The Relevant URA Parameters Are Valid

More Than One Combination Would Be Required To Describe Anomalies (Not including thosemarked with “**”)*
3 to 6 dB below specified power level due to reduced power output, excess phase noise, SV attitude, etc.
** See definition above for Health Code 11111.
*** Note: Deformed means one or more signals do not meet the requirements in Section 3.

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20.3.3.5.1.4 Anti-Spoof (A-S) Flags and SV Configurations.
Page 25 of subframe 4 shall contain a four-bit-long term for each of up to 32 SVs to indicate the AS status and the configuration code of each SV. The MSB of each four-bit term shall be the A-Sflag with a "1" indicating that A-S is ON. The three LSBs shall indicate the configuration of each
SV using the following code:
Code SV Configuration000

No Information is available

001
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2 (e.g. Block II/Block IIA/IIR SV).
010
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2, M-code signal capability, L2C signal capability (e.g., Block IIR-M SV).
011
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2, M-code capability, L2C signal capability, L5 signal capability (e.g., Block IIF SV).
100
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2, M-code capability, L1C signal capability, L2C signal capability, L5 signal
capability, no SA capability (e.g., GPS III SVs).
101 A-S capability, plus flags for A-S and “alert” in HOW; memory capacity as described inparagraph 20.3.2, M-code capability, Regional Military Protection capability, L1C signal capability,
L2C signal capability, L5 signal capability, no SA capability (e.g., GPS IIIF SVs).
110, 111 Reserved in order to preserve future use of these values in a future revision of this IS.
Until such a revision, the User Segment developing to this version of this IS should interpret thesevalues as indicating that no information in this data field is presently usable as a means to identify
the actual SV configuration.
These four-bit terms shall occupy bits 9 through 24 of word three, the 24 MSBs of words four
through seven, and the 16 MSBs of word eight, all in page 25 of subframe 4.
Since the anti-spoof information is updated by the CS at the time of upload, the anti-spoof data
may not correspond to the actual anti-spoof status of the transmitting SV or other SVs in theconstellation.

20.3.3.5.1.5 Almanac Reference Week.
Bits 17 through 24 of word three in page 25 of subframe 5 shall indicate the number of the week
(WNa) to which the almanac reference time (t oa) is referenced (see paragraphs 20.3.3.5.1.2 and20.3.3.5.2.2). The WNa term consists of eight bits which shall be a modulo 256 binary
representation of the GPS week number (see paragraph 6.2.4) to which the t oa is referenced. Bits
9 through 16 of word three in page 25 of subframe 5 shall contain the value of t oa which isreferenced to this WNa.

20.3.3.5.1.6 Coordinated Universal Time (UTC) Parameters.
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The 24 MSBs of words six through nine plus the eight MSBs of word ten in page 18 of subframe 4
shall contain the parameters related to correlating UTC time with GPS time. The bit length, scale
factors, ranges, and units of these parameters are given in Table 20-IX. The related algorithms
are described in paragraph 20.3.3.5.2.4.
The UTC parameters shall be updated by the CS at least once every six days while the CS is able
to upload the SVs. If the CS is unable to upload the SVs, the accuracy of the UTC parameterstransmitted by the SVs will degrade over time.

20.3.3.5.1.7 Ionospheric Data.
The ionospheric parameters which allow the "L1 only" or "L2 only" user to utilize the ionosphericmodel (reference paragraph 20.3.3.5.2.5) for computation of the ionospheric delay are contained inpage 18 of subframe 4. They occupy bits 9 through 24 of word three plus the 24 MSBs of words
four and five. The bit lengths, scale factors, ranges, and units of these parameters are given in
Table 20-X.
The ionospheric data shall be updated by the CS at least once every six days while the CS is able
to upload the SVs. If the CS is unable to upload the SVs, the ionospheric data transmitted by theSVs may not be accurate.

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Table 20-IX. UTC Parameters

No. of
Bits**

Scale
Factor
(LSB)

A0

32*

2-30

seconds

A1

24*

2-50

sec/sec

 tLS

8*

1

seconds

tot

8

212

WNt

8

1

weeks

WNLSF

8

1

weeks

DN

8

1

 tLSF

8*

1

Parameter

*
**
***

Valid Range***0 to 602,112

1 to 7Units

seconds

days
seconds

Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;
See Figure 20-1 for complete bit allocation in subframe;
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicatedbit allocation and scale factor.

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Table 20-X. Ionospheric Parameters

Parameter

No. of
Bits**

Scale
Factor
(LSB)

0

8*

2-30

seconds

1

8*

2-27

sec/semi-circle

2

8*

2-24

sec/(semi-circle)2

3

8*

2-24

sec/(semi-circle)3

0

8*

211

seconds

1

8*

214

sec/semi-circle

2

8*

216

sec/(semi-circle)2

3

8*

216

sec/(semi-circle)3

Valid
Range***

Units*
Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;**
See Figure 20-1 for complete bit allocation in subframe;***
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicatedbit allocation and scale factor.

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20.3.3.5.1.8 Special Messages.
Page 17 of subframe 4 shall be reserved for special messages with the specific contents at thediscretion of the Operating Command. It shall accommodate the transmission of 22 eight-bit ASCII
characters. The requisite 176 bits shall occupy bits 9 through 24 of word three, the 24 MSBs ofwords four through nine, plus the 16 MSBs of word ten. The eight MSBs of word three shallcontain the data ID and SV ID, while bits 17 through 22 of word ten shall be reserved for systemuse. The remaining 50 bits of words three through ten are used for parity (six bits/word) and parity
computation (two bits in word ten). The eight-bit ASCII characters shall be limited to the following
set:
Alphanumeric Character

ASCII Character

Code (Octal)

A-Z

A-Z

101 - 132

0-9

0-9

060 - 071

+

+

053

-

-

055

. (Decimal point).

056' (Minute mark)'047° (Degree sign)

°

370

/

/

057

Blank

Space

040

:

:

072

" (Second mark)

"

042

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20.3.3.5.1.9 NMCT.
Page 13 of subframe 4 shall contain the NMCT data appropriate to the transmitting SV. Each
NMCT contains a two-bit availability indicator (AI) followed by 30 slots which may contain up to 30
valid six-bit ERD values. The layout of these 31 data items is as shown in Figure 20-1.
The two-bit AI in bits 9 and 10 of word three of page 13 of subframe 4 provide the user with thefollowing information.
AI

Navigation Message Correction Table Availability

00

The correction table is unencrypted and is available to both precise positioning service users and standard
positioning service users.

01

The correction table is encrypted and is available only to authorized users (normal mode).

10

No correction table available for either precise positioning service users or standard positioning service users.
Reserved in order to preserve future use of these values in a future revision of this IS. Until such a revision,
the User Segment developing to this version of this IS should interpret this value as indicating that nocorrection table is available for either precise positioning service users or standard positioning service users,
i.e. until such a revision, the User Segment developing to this version of this IS should interpret this value asfunctionally equivalent to an AI setting of 10.

11

Each one of the 30 six-bit ERD slots in bits 11 through 24 of word three, bits 1 through 24 of words
four through nine, and bits 1 through 22 of word ten of page 13 of subframe 4 will correspond to an
ERD value for a particular SV ID. There are 31 possible SV IDs that these ERD slots may
correspond to, ranging from SV ID 1 to SV ID 31. SV ID 32 is not a valid SV ID for any of the slots
in an NMCT.
The correspondence between the 30 ERD slots and the 31 possible SV IDs depends on the SV ID
of the particular transmitting SV in accordance with the following two rules:
1) The CS shall ensure via upload that no SV shall transmit an NMCT containing an ERD value
which applies to its own SV ID.
2) The CS shall ensure via upload that all ERD values shall be transmitted in ascending numericalslot order of the corresponding SV ID.
To illustrate: the SV operating as SV ID 1 will transmit (in order) ERD values which correspond to
SV ID 2 through SV ID 31 in ERD slots 1 through 30 respectively, while the SV operating as SV ID
31 will transmit ERD values which correspond to SV ID 1 through SV ID 30 in ERD slots 1 through30 respectively.
In addition, the CS shall ensure that the SV operating as SV ID 32 transmits an NMCT containing
an AI setting equal to "10" or "11."Each ERD value contained in an NMCT ERD slot shall be represented as a six-bit two’s
complement field with the sign bit occupying the MSB and an LSB of 0.3 meters for a valid rangeof 9.3 m. A binary value of “100000” shall indicate that no valid ERD for the corresponding SV ID
is present in that slot.
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20.3.3.5.2 Algorithms Related to Subframe 4 and 5 Data.
The following algorithms shall apply when interpreting Almanac, Coordinated Universal Time,
Ionospheric Model, and NMCT data in the LNAV message.

20.3.3.5.2.1 Almanac.
The almanac is a subset of the clock and ephemeris data, with reduced precision. The user
algorithm is essentially the same as the user algorithm used for computing the precise ephemerisfrom the one subframe 1, 2, and 3 parameters (see Table 20-IV). The almanac content for one SV
is given in Table 20-VI. A close inspection of Table 20-VI will reveal that a nominal inclination
angle of 0.30 semicircles is implicit and that the parameter i (correction to inclination) is
transmitted, as opposed to the value computed by the user. All other parameters appearing in theequations of Tables 20-IV, but not included in the content of the almanac, are set to zero for SV
position determination. In these respects, the application of the Table 20-IV equations differs
between the almanac and the ephemeris computations.
The user is cautioned that the sensitivity to small perturbations in the parameters is even greaterfor the almanac than for the ephemeris, with the sensitivity of the angular rate terms over theinterval of applicability on the order of 10 14 meters/(semicircle/second). An indication of the URE
provided by a given almanac during each of the operational intervals is as follows:
Operational Interval

Almanac Ephemeris URE (estimated by analysis) 1 sigma (meters)

Normal900*

Short-term Extended

900 - 3,600*

Long-term Extended

3600 - 300,000** URE values generally tend to degrade quadratically over time. Larger errors may be encountered during eclipse
seasons and whenever a propulsive event has occurred.

20.3.3.5.2.2 Almanac Reference Time.
Within each upload, the CS shall ensure that all toa values in subframes 4 and 5 shall be the samefor a given almanac data set and shall differ for successive data sets which contain changes inalmanac parameters or SV health. In addition, the Block IIR/IIR-M SVs will also ensure that, basedon a valid CS upload, all toa values in subframes 4 and 5 will be the same for a given almanac data
set and will differ for successive data sets which contain changes in almanac parameters.
Note that cutover to a new upload may continue to indicate the same t oa values in subframes 4 and5 as prior to the cutover but the new almanac data set may contain changes in almanac
parameters or SV health. Note also that cutover to a new upload may occur between the almanac
pages of interest and page 25 of subframe 5 (reference paragraph 20.3.4.1), and thus there may
be a temporary inconsistency between t oa, in the almanac page of interest, and in word 3 of page
25 of subframe 5. The toa mismatch signifies that this WNa may not apply to the almanac ofinterest and that the user must not apply almanac data until the pages with identical values of t oa
are obtained.

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Normal and Short-term Extended Operations.
The almanac reference time, t oa, is some multiple of 212 seconds occurring approximately 70 hours
after the first valid transmission time for this almanac data set (reference 20.3.4.5). The almanac
is updated often enough to ensure that GPS time, t, shall differ from t oa by less than 3.5 days
during the transmission period. The time from epoch t k shall be computed as described in Table
20-IV, except that toe shall be replaced with toa.
Long-term Extended Operations.
During long-term extended operations or if the user wishes to extend the use time of the almanac
beyond the time span that it is being transmitted, one must account for crossovers into time spans
where these computations of tk are not valid. This may be accomplished without time ambiguity byrecognizing that the almanac reference time (t oa) is referenced to the almanac reference week
(WNa), both of which are given in word three of page 25 of subframe 5 (see paragraph20.3.3.5.1.5).

20.3.3.5.2.3 Almanac Time Parameters.
The almanac time parameters shall consist of an 11-bit constant term (af0) and an 11-bit first orderterm (af1). The applicable first order polynomial, which shall provide time to within 2 microsecondsof GPS time (t) during the interval of applicability, is given byt = tsv - tsv
where
t =

GPS system time (seconds),

tsv =effective SV PRN code phase time at message transmission time (seconds),

tsv = SV PRN code phase time offset (seconds).
The SV PRN code phase offset is given by
tsv = af0 + af1 tk
where the computation of tk is described in paragraph 20.3.3.5.2.2, and the polynomial coefficientsaf0 and af1 are given in the almanac. Since the periodic relativistic effect is less than 25 meters, itneed not be included in the time scale used for almanac evaluation. Over the span of applicability,
it is expected that the almanac time parameters will provide a statistical URE component of lessthan 135 meters, one sigma. This is partially due to the fact that the error caused by the truncationof af0 and af1 may be as large as 150 meters plus 50 meters/day relative to the t oa reference time.
During extended operations (short-term and long-term) the almanac time parameter may notprovide the specified time accuracy or URE component. Additionally, occasional CS actions tomanage clock offsets may also inhibit the ability to provide specified almanac time parameter
accuracies.

20.3.3.5.2.4 Coordinated Universal Time (UTC).
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Page 18 of subframe 4 includes: (1) the parameters needed to relate GPS time to UTC, and (2)notice to the user regarding the scheduled future or recent past (relative to LNAV message upload)
value of the delta time due to leap seconds (tLSF), together with the week number (WNLSF) and the
day number (DN) at the end of which the leap second becomes effective. "Day one" is the first day
relative to the end/start of week and the WNLSF value consists of eight bits which shall be a modulo
256 binary representation of the GPS week number (see paragraph 6.2.4) to which the DN isreferenced. The user must account for the truncated nature of this parameter as well as truncationof WN, WNt, and WNLSF due to rollover of full week number (see paragraph 3.3.4(b)). The CS
shall manage these parameters such that, when tLS and tLSF differ, the absolute value of thedifference between the untruncated WN and WNLSF values shall not exceed 127.
Depending upon the relationship of the effectivity date to the user's current GPS time, the following
three different UTC/GPS-time relationships exist:
a. Whenever the effectivity time indicated by the WN LSF and the DN values is not in the past(relative to the user's present time), and the user's present time does not fall in the time span
which starts at six hours prior to the effectivity time and ends at six hours after the effectivity time,
the UTC/GPS-time relationship is given by
tUTC=(tE - tUTC) [modulo 86400 seconds]

where tUTC is in seconds andtUTC =

tLS + A0 + A1 (tE - tot + 604800 (WN - WNt)), seconds;

tE

GPS time as estimated by the user after correcting t SV for factors=

described inparagraph 20.3.3.3.3 as well as for selective availability (SA) (dither) effects;
tLS=

delta time due to leap seconds;

A0 and A1 = constant and first order terms of polynomial;
tot=

reference time for UTC data (reference 20.3.4.5);

WN=

current week number (derived from subframe 1);

WNt=

UTC reference week number.

The estimated GPS time (tE) shall be in seconds relative to end/start of week. During the normal
and short-term extended operations, the reference time for UTC data, t ot, is some multiple of 212
seconds occurring approximately 70 hours after the first valid transmission time for this UTC dataset (reference 20.3.4.5). The reference time for UTC data (t ot) shall be referenced to the start ofthat week whose number (WNt) is given in word eight of page 18 in subframe 4. The WNt value
consists of eight bits which shall be a modulo 256 binary representation of the GPS week number(see paragraph 6.2.4) to which the t ot is referenced. The user must account for the truncatednature of this parameter as well as truncation of WN, WNt, and WNLSF due to rollover of full weeknumber (see paragraph 3.3.4(b)). The CS shall manage these parameters such that the absolutevalue of the difference between the untruncated WN and WN t values shall not exceed 127.
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b. Whenever the user's current time falls within the time span of six hours prior to the effectivity
time to six hours after the effectivity time, proper accommodation of the leap second event with apossible week number transition is provided by the following expression for UTC:
tUTC = W[modulo (86400 + tLSF - tLS)], seconds;
where
W = (tE - tUTC - 43200) [modulo 86400] + 43200, seconds;
and the definition of tUTC (as given in 20.3.3.5.2.4a above) applies throughout the transition
period. Note that when a leap second is added, unconventional time values of the form
23:59:60.xxx are encountered. Some user equipment may be designed to approximate UTC by
decrementing the running count of time within several seconds after the event, thereby promptly
returning to a proper time indication. Whenever a leap second event is encountered, the user
equipment must consistently implement carries or borrows into any year/week/day counts.
c. Whenever the effectivity time of the leap second event, as indicated by the WN LSF and DNvalues, is in the "past" (relative to the user's current time), and the user’s current time does not fallin the time span as given above in 20.3.3.5.2.4b, the relationship previously given for t UTC in
20.3.3.5.2.4a above is valid except that the value of tLSF is substituted for tLS. The CS will
coordinate the update of UTC parameters at a future upload so as to maintain a proper continuityof the tUTC time scale.

20.3.3.5.2.5 Ionospheric Model.
The "dual-frequency" (L1 and L2) user shall correct the time received from the SV for ionosphericeffect by utilizing the time delay differential between L1 and L2 (reference paragraph 20.3.3.3.3.3).
The "single-frequency" user, however, may use the model given in Figure 20-4 to make thiscorrection. It is estimated that the use of this model will provide at least a 50 percent reduction in
the single - frequency user's RMS error due to ionospheric propagation effects. During extended
operations, the use of this model will yield unpredictable results.

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20.3.3.5.2.6 NMCT Data.
For each SV, the ERD value in the NMCT is an estimated pseudorange error. Each ERD value iscomputed by the CS and represents the radial component of the satellite ephemeris error minus
the speed of light times the satellite clock error. The satellite ephemeris and clock errors arecomputed by subtracting the broadcast from current estimates. Therefore, the ERD value may be
used as follows to correct the user's measured pseudorange:
PRc = PR - ERD
where,
PRc = pseudorange corrected with the ERD value from the NMCT
PR = measured pseudorange.
Note that as described above, the ERD values are actually error estimates rather than differential
corrections and so are subtracted rather than added in the above equation.

126

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The ionospheric correction model is given by x 2 x 4 F  5.0  10  9  (AMP )1 , x  1.57
2
24 
Tiono   
 (sec)9, x  1.57 
F  5.0  10





where
Tiono is referred to the L1 frequency; if the user is operating on the L2 frequency, the correction term must be
multiplied by  (reference paragraph 20.3.3.3.3.2),

 3n
  n  m , AMP  0 
AMP  n  0if AMP  0, AMP  0



(sec)

x

2 t - 50400
PER(radians)

 3n  n  m , PER  72,000
PER  n  0if PER  72,000, PER  72,000



(sec)

F = 1.0 + 16.0 [0.53 - E]3and n and n are the satellite transmitted data words with n = 0, 1, 2, and 3.

Figure 20-4. Ionospheric Model (Sheet 1 of 3)

Other equations that must be solved are127

IS-GPS-200L
14 May 2020

m = i + 0.064cos(i - 1.617)(semi-circles) sinAcos  i(semi-circles) i  u i  

 i  0.416 if  i  0.416, then  i  0.416
if  i  0.416, then  i  0.416 u   cosA,

0.0137- 0.022E  0.11

t = 4.32 (104) i + GPS time(semi-circles)(semi-circles)

(sec)

where
0  t < 86400: therefore, if t  86400 seconds, subtract 86400 seconds;
if t < 0 seconds, add 86400 seconds.

Figure 20-4. Ionospheric Model (Sheet 2 of 3)

128

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The terms used in computation of ionospheric delay are as follows: Satellite Transmitted Terms
n-the coefficients of a cubic equation representing the amplitude of the verticaldelay (4 coefficients - 8 bits each)n-the coefficients of a cubic equation representing the period of the model(4 coefficients - 8 bits each) Receiver Generated Terms
E-

elevation angle between the user and satellite (semi-circles)A-azimuth angle between the user and satellite, measured clockwise positive fromthe true North (semi-circles)

u-user geodetic latitude (semi-circles) WGS 84

u-user geodetic longitude (semi-circles) WGS 84

GPS time-

receiver computed system timeX-

phase (radians)F-obliquity factor (dimensionless)t-local time (sec)m-geomagnetic latitude of the earth projection of the ionospheric intersection point

 Computed Terms(mean ionospheric height assumed 350 km) (semi-circles)
i-geodetic longitude of the earth projection of the ionospheric intersection point(semi-circles)

i-geodetic latitude of the earth projection of the ionospheric intersection point(semi-circles)-earth's central angle between the user position and the earth projection ofionospheric intersection point (semi-circles)

Figure 20-4. Ionospheric Model (Sheet 3 of 3)

129

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20.3.4 Timing Relationships.
The following conventions shall apply.

20.3.4.1 Paging and Cutovers.
At end/start of week (a) the cyclic paging of subframes 1 through 5 shall restart with subframe 1
regardless of which subframe was last transmitted prior to end/start of week, and (b) the cycling of
the 25 pages of subframes 4 and 5 shall restart with page 1 of each of the subframes, regardlessof which page was the last to be transmitted prior to the end/start of week. Cutovers to newly
updated data for subframes 1, 2, and 3 occur on frame boundaries (i.e., modulo 30 seconds
relative to end/start of week). Newly updated data for subframes 4 and 5 may start to betransmitted with any of the 25 pages of these subframes.

20.3.4.2 SV Time vs. GPS Time.
In controlling the SVs and uploading of data, the CS shall allow for the following timing
relationships:a.

Each SV operates on its own SV time;b.

All time-related data in the TLM word and the HOW shall be in SV-time;c.

All other data in the LNAV message shall be relative to GPS time;d.

The acts of transmitting the LNAV message shall be executed by the SV on SV time.

20.3.4.3 Speed of Light.
The speed of light used by the CS for generating the data described in the above paragraphs is
c = 2.99792458 x 108 meters per second
which is the official WGS 84 speed of light. The user shall use the same value for the speed oflight in all computations.

20.3.4.4 Data Sets.
The IODE is an 8 bit number equal to the 8 LSBs of the 10 bit IODC of the same CEI data set.
The following rules govern the transmission of IODC and IODE values in different CEI data sets:(1) The transmitted IODC will be different from any value transmitted by the SV during thepreceding seven days; (2) The transmitted IODE will be different from any value transmitted by the
SV during the preceding six hours. The range of IODC will be as given in Table 20-XI for Block
II/IIA SVs and Table 20-XII for Block IIR/IIR-M/IIF and GPS III/IIIF SVs.
Cutovers to new CEI data sets will occur only on hour boundaries except for the first CEI data setof a new CEI data sequence propagation. The first CEI data set may be cut-in (reference
paragraph 20.3.4.1) at any time during the hour and therefore may be transmitted by the SV forless than one hour. During short-term operations, cutover to 4-hour sets and subsequent cutovers
to succeeding 4-hour CEI data sets will always occur modulo 4 hours relative to end/start of week.
130

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Cutover from 4-hour CEI data sets to 6-hour CEI data sets shall occur modulo 12 hours relative toend/start of week. Cutover from 12-hour CEI data sets to 24-hour CEI data sets shall occur
modulo 24 hours relative to end/start of week. Cutover from a CEI data set transmitted 24 hours ormore occurs on a modulo 24-hour boundary relative to end/start of week.
The start of the transmission interval for each CEI data set corresponds to the beginning of thecurve fit interval for the CEI data set. Each CEI data set nominally remains valid for the duration of
its curve fit interval. A CEI data set may be rendered obsolete before the end of its curve fit
interval when it is superseded by the SV cutting over to new data.
The toe shall be equal to the toc of the same LNAV CEI data set.
Updates to parameters in Table 6-I-1 shall prompt changes in toe/toc/IODC/IODE. Any parameter
marked with NOTE1 may be changed with or without a change in t oe/toc/IODC/IODE.
Normal Operations.
The subframe 1, 2, and 3 CEI data sets are transmitted by the SV for periods of two hours. The
corresponding curve fit interval is four hours.
Short-term and Long-term Extended Operations.
The transmission intervals and curve fit intervals with the applicable IODC ranges are given in
Tables 20-XI and 20-XII.

131

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Table 20-XI. IODC Values and Data Set Lengths (Block II/IIA)

Days
SpannedTransmission Interval(hours)(Note 4)

Curve Fit
Interval(hours)

IODC Range(Note 1)

1
2-14
15-16
17-20
21-27
28-41
42-59
60-63

2
4
6
12
24
48
72
96

4
6
8
14
26
50
74
98

(Note 2)
(Note 2)240-247248-255, 496 (Note 3)497-503504-510511, 752-756
757

Note 1: For transmission intervals of 6 hours or greater, the IODC values shown will be transmitted inincreasing order.
Note 2: IODC values for blocks with 2- or 4-hour transmission intervals (at least the first 14 days after a
new CEI data sequence propagation) shall be any number in the range 0 to 1023 excluding thosevalues of IODC that correspond to IODE values in the range 240-255, subject to the constraints on
re-transmission given in paragraph 20.3.4.4.
Note 3: The ninth 12-hour data set may not be transmitted.
Note 4: The first CEI data set of a new CEI data sequence propagation may be cut-in at any time andtherefore the transmission interval may be less than the specified value.

132

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Table 20-XII. IODC Values and Data Set Lengths (Block IIR/IIR-M/IIF & GPS III/ IIIF)

Days
SpannedTransmission Interval(hours)(Note 5)

1
2-14
15-16
17-20
21-62

2 (Note 4)
4
6
12
24

Curve Fit
Interval(hours)

IODC Range

4
6
8
14
26

(Note 2)
(Note 2)240-247 (Note 1)
248-255, 496 (Note 1) (Note 3)497-503, 1021-1023

Note 1: For transmission intervals of 6 and 12 hours, the IODC values shown will be transmitted inincreasing order.
Note 2: IODC values for blocks with 1-, 2- or 4-hour transmission intervals (at least the first 14 days after
a new CEI data sequence propagation) shall be any number in the range 0 to 1023 excluding thosevalues of IODC that correspond to IODE values in the range 240-255, subject to the constraints on
re-transmission given in paragraph 20.3.4.4. The CS can define the GPS III and GPS IIIF SV timeof transition from the 4 hour curve fits into extended navigation (beyond 4 hour curve fits).
Following the transition time, the SV will follow the timeframes defined in the table, including
appropriately setting IODC values.
Note 3: The ninth 12-hour data set may not be transmitted.
Note 4: The first CEI data set of a new CEI data sequence propagation may be cut-in at any time andtherefore the transmission interval may be less than the specified value.

133

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20.3.4.5 Reference Times.
Many of the parameters which describe the SV state vary with true time, and must therefore be
expressed as time functions with coefficients provided by the Navigation Message to be evaluatedby the user equipment. These include the following parameters as functions of GPS time:a.

SV time,b.

Mean anomaly,c.

Longitude of ascending node,

d.

UTC,

e.

Inclination.

Each of these parameters is formulated as a polynomial in time. The specific time scale ofexpansion can be arbitrary. Due to the short data field lengths available in the Navigation
Message format, the nominal epoch of the polynomial is chosen near the midpoint of the
expansion range so that quantization error is small. This results in time epoch values which canbe different for each data set. Time epochs contained in the Navigation Message and the different
algorithms which utilize them are related as follows:
Epoch Application Algorithm Reference
toc

20.3.3.3.3.1

toe

20.3.3.4.3

toa

20.3.3.5.2.2 and 20.3.3.5.2.3

tot

20.3.3.5.2.4

Table 20-XIII describes the nominal selection which will be expressed modulo 604,800 seconds in
the Navigation Message.
The coefficients of expansion are obviously dependent upon choice of epoch, and thus the epoch
time and expansion coefficients must be treated as an inseparable parameter set. Note that a user
applying current navigation data will normally be working with negative values of (t-toc) and (t-toe) in
evaluating the expansions.
The CS (Block II/IIA/IIR/IIR M/IIF) and SS (GPS III and GPS IIIF) shall assure that the t oe value, forat least the first CEI data set transmitted by an SV from a new CEI data sequence propagation, isdifferent from that transmitted from the prior CEI data sequence propagation (see paragraph20.3.4.4). As such, when a new CEI data sequence propagation is cutover for transmission, theCS (Block IIA/IIR/IIR-M/IIF) and SS (GPS III and GPS IIIF) shall introduce a small deviation in the
toe resulting in the toe value that is offset from the hour boundaries (see Table 20 XIII). This offset
toe will be transmitted by an SV in the first CEI data set of the new CEI data sequence propagationand the second CEI data set, following the first CEI data set, may also continue to reflect the sameoffset in the toe.

134

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When the toe, immediately prior to a new CEI data sequence propagation cutover, already reflects
a small deviation (i.e. a new CEI data sequence propagation cutover has occurred in the recentpast), then the CS (Block II/IIA/IIR/IIR-M/IIF) and SS (GPS III and GPS IIIF) shall introduce anadditional deviation to the toe when a new CEI data sequence propagation is cutover fortransmission.
A change from the broadcast reference time immediately prior to cutover is used to indicate achange of values in the CEI data set. The user may use the following example algorithm to detect
the occurrence of a new CEI data sequence propagation cutover:
DEV = toe [modulo 3600]
If DEV ≠ 0, then a new CEI data sequence propagation cutover has occurred within past 4
hours.
Table 20-XIII.

Reference Times

Hours After First Valid Transmission TimeFit Interval (hours)

Transmission
Interval (hours)

toc(clock)toe(ephemeris)

4

2*

2

2

6

4

3

3

8

6

4

4

14

12

7

7

26

24

13

13

50

48

25

25

74

72

37

37

98

96

49

49

122

120

61

61

146

144

73

73

144 (6 days)> 144 (6 days)*

toa(almanac)

tot
(UTC)

144

70

70

> 144

70

70

Some SVs will have transmission intervals of 1 hour per paragraph 20.3.4.4.

20.3.5 Data Frame Parity.
The data signal shall contain parity coding according to the following conventions.
135

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20.3.5.1 SV/CS Parity Algorithm.
This algorithm links 30-bit words within and across subframes of ten words using the (32,26)
Hamming Code described in Table 20-XIV.

20.3.5.2 User Parity Algorithm.
As far as the user is concerned, several options are available for performing data decoding anderror detection. Figure 20-5 presents an example flow chart that defines one way of recovering
data (dn) and checking parity. The parity bit D30* is used for recovering raw data. The parity bits
D29* and D30*, along with the recovered raw data (d n) are modulo-2 added in accordance with theequations appearing in Table 20-XIV for D25 . . . D30, which provide parity to compare withtransmitted parity D25 . . . D30.
Table 20-XIV.

D1=

d1  D30

D2
D3

=
=

d2  D30
d3  D30









Parity Encoding Equations



D24
D25

=
=



d24  D30
D29  d1  d2  d3  d5  d6  d10  d11  d12  d13  d14  d17  d18  d20  d23

D26=

D30  d2  d3  d4  d6  d7  d11  d12  d13  d14  d15  d18  d19  d21  d24

D27=

D29  d1  d3  d4  d5  d7  d8  d12  d13  d14  d15  d16 d19  d20  d22

D28=

D30  d2  d4  d5  d6  d8  d9  d13  d14  d15  d16  d17  d20  d21  d23

D29
D30
Where

=
=

D30  d1 d3 d5 d6 d7 d9  d10  d14  d15  d16  d17  d18  d21  d22 d24
D29  d3  d5  d6  d8  d9  d10  d11  d13  d15  d19  d22  d23  d24

d1, d2, ..., d24 are the source data bits;
the symbol  is used to identify the last 2 bits of the previous word of the subframe;
D25, D26, ..., D30 are the computed parity bits;
D1, D2, ..., D29, D30 are the bits transmitted by the SV; is the "modulo-2" or "exclusive-or" operation.

136

IS-GPS-200L
14 May 2020ENTERCOMPLEMENT
D1 . . . D24
TO OBTAIN
d1 . . . d24

YES* = 1?
IS D30NO

DO NOTCOMPLEMENT
D1 . . . D24
TO OBTAIN
d1 . . . d24

SUBSTITUTE d1 . . . d24,
* & D * INTO
D29
30
PARITY EQUATIONS(TABLE 20-XIV)NO

ARE COMPUTED
D25 . . . D30
EQUAL TO CORRESPONDING
RECEIVED
D25 . . . D30?

YES

PARITY CHECKFAILSPARITY CHECKPASSES

FAIL
EXIT

PASS
EXIT

Figure 20-5. Example Flow Chart for User Implementation of Parity Algorithm137

IS-GPS-200L
14 May 2020

30 APPENDIX III. GPS NAVIGATION DATA STRUCTURE FOR CNAVDATA, DC(t)30.1 Scope.
This appendix describes the specific GPS CNAV data structure denoted as DC(t).

30.2 Applicable Documents.
30.2.1 Government Documents.
In addition to the documents listed in paragraph 2.1, the following documents of the issue specified
contribute to the definition of the CNAV data related interfaces and form a part of this Appendix tothe extent specified herein.
Specifications
NoneStandards
None
Other Publications
None

30.2.2 Non-Government Documents.
In addition to the documents listed in paragraph 2.2, the following documents of the issue specified
contribute to the definition of the CNAV data related interfaces and form a part of this Appendix tothe extent specified herein.
Specifications
None
Other Publications
None

30.3 Requirements.
30.3.1 Data Characteristics.
The CEI data set provided in the CNAV data, DC(t), is a higher precision representation andnominally contains more accurate data than the CEI data set provided in the LNAV data, D(t),described in Appendices II and IV. Also, the CNAV data stream uses a different parity algorithm.

138

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Users are advised that the CEI data sets provided in the CNAV data, D C(t), described in thisappendix and the CEI data sets provided in the LNAV data, D(t), described in Appendices II andIV, should not be mixed in any user algorithms or applications. Each of the two data sets shouldbe treated as a set and used accordingly.

30.3.2 Message Structure.
As shown in Figures 30-1 through 30-14, the CNAV message structure utilizes a basic format oftwelve-second 300-bit long messages. Each message contains a Cyclic Redundancy Check(CRC) parity block consisting of 24 bits covering the entire twelve-second message (300 bits)(reference Section 30.3.5). Message Type 0 (zero) is defined to be the default message. In theevent of message generation failure, the SV shall replace each affected Message Type with thedefault Message Type. In the event that a particular message is not assigned (by the CS) a
particular Message Type for broadcast, the SV shall generate and broadcast the default Message
Type in that message slot.
Currently undefined and unused Message Types are reserved for future use.
Block IIR-M and IIF SVs have the capability of storing at least 48 hours of CNAV navigation data,with current memory margins, to provide CNAV positioning service without contact from the CS forthat period. GPS III and GPS IIIF SVs have the capability of providing up to 60 days of CNAV
positioning service without contact from the CS. The timeframe is defined by the CS.

30.3.3 Message Content.
Each message starts with an 8-bit preamble - 10001011, followed by a 6-bit PRN number of thetransmitting SV, a 6-bit Message Type ID with a range of 0 (000000) to 63 (111111), and the 17-bit
message time of week (TOW) count. When the value of the message TOW count is multiplied by
6, it represents SV time in seconds at the start of the next 12-second message. An “alert” flag,
when raised (bit 38 = “1”), indicates to the users that the signal URA components may be worse
than indicated in the associated Message Types and that the users may use at their own risk. For
each default message (Message Type 0), bits 39 through 276 shall be alternating ones and zeros
and the message shall contain a proper CRC parity block.

139

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1

21

15

9
PRN
6
BITS

8 BITS

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
52 55
66
39

6
BITS

MESSAGETOW COUNT*WN

17 BITS

13 BITsMESSAGE TYPE ID"ALERT" FLAG - 1 BIT

PREAMBLEMSB FIRST

t oe

A

11 BITS

19 MSBst op
11 BITS

5BITS

L1 HEALTH - 1 BIT
L2 HEALTH - 1 BIT
L5 HEALTH - 1 BIT

URAED INDEXMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

133

108

A


A

7 LSBs25 BITS

82

71

150

173

 n0


 n0

M0-n

17 BITS

23 BITS

28 MSB s

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
272
201

206

M0-n

277

239

en

n

CRC

33 BITS

33 BITS

24 BITs

Integrity Status Flag – 1 BIT
5 LSBsL2C Phasing – 1 BIT
RESERVED – 3 BITs

* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12 SECONDMESSAGE

Figure 30-1. Message Type 10 - Ephemeris 1

140

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1

9

15

PRN
6
BITS

8 BITS

6BITS

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
39

21

83

MESSAGETOW COUNT*

toe

0-n

i0-n

17 BITS

11 BITS

33 BITS

18 MSBs

MESSAGE TYPE ID
PREAMBLE"ALERT" FLAG - 1 BITMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

133

116

148

164

180

i0-n




i0-n - DOT

cis-n

cic-n

crs-n

15 LSBs

17 BITS

15 BITS

16 BITS

16 BITS

21 MSBs

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
201
204

228

270

249

crc-n

cus-n

cuc-n

24 BITS

21 BITS

21 BITS

crs-n - 3 LSBs

277
CRC

7 BITSRESERVED* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-2. Message Type 11 - Ephemeris 2

141

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14 May 2020

1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5
BITS"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

128

118

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 61
39

141

154

167

180

193

af1-n

af2-n

TGD

ISCL1C/AISCL2CISCL5I5

ISCL5Q5017 LSBs

10 BITS

13 BITS

13 BITS

13 BITS

13 BITS

13 BITS

8 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
201

209

217

225

233

241

257

249

265

277

1

2

3

0

1

2

3

WNOP

RESERVEDCRC

8 BITs

8 BITS

8 BITS

8 BITS

8 BITS

8 BITS

8 BITS

8 BITS

12 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-3. Message Type 30 - Clock, IONO & Group Delay

142

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1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5
BITS"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

128

118

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 61
39

141

149

180

af1-n

af2-n

WNa-n

toa

Reduced Almanac
Packet 1

Reduced Almanac
Packet 2

17 LSBs

10 BITS

13 BITS

8 BITS

31 BITS

21 MSBs

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
201

10 LSBs

211

MSB FIRST

273 277

242
Reduced Almanac
Packet 3

Reduced Almanac
Packet 4

31 BITS

31 BITS

Reduced Almanac Packet 2

CRC
4
BITS
RESERVED* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-4. Message Type 31 - Clock & Reduced Almanac

143

24 BITSIS-GPS-200L
14 May 2020

1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5
BITS"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

144

128

118

165

180

af1-n

af2-n

tEOP

PM_X


PM_X

17 LSBs

10 BITS

16 BITS

21 BITS

15 BITS

266

247

216

PM_Y

UTGPSUTGPS

15 BITS

31 BITS

19 BITS

21 BITS

277

RESERVED

CRC

11 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-5. Message Type 32 - Clock & EOP

144

PM_Y

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
201

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 6139

IS-GPS-200L
14 May 2020

1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5
BITS"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

128

118

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 61
39

144

157

164

172

188

af1-n

af2-n

A0-n

A1-n

A2-n

tLS

tot

WNot

17 LSBs

10 BITS

16 BITS

13 BITS

7 BITS

8 BITS

16 BITS

13 BITS

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS

WNLSF
13 BITS

tLSF
4BITS 8 BITS
DN

277

226

214 218201

MSB FIRST

RESERVEDCRC

51 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-6. Message Type 33 - Clock & UTC

145

IS-GPS-200L
14 May 2020

1

9

21

15

PRN
8 BITS

6
BITS

6
BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS"ALERT" FLAG - 1 BIT

101

128

118

5
BITS

98

72
toc

af0-n

11 BITS

26 BITS

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 61
39

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
150
139
151

MSB FIRST

185

af1-n

af2-n

top-D

tOD

CDC

EDC

17 LSBs

10 BITS

11 BITS

11 BITS

34 BITS

16 MSBs

DC DATA TYPE – 1 BIT

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS

277

201

*

MSB FIRST

EDC

CRC

76 LSBs

24 BITSMESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

CDC = Clock Differential Correction
EDC = Ephemeris Differential Correction

Figure 30-7. Message Type 34 - Clock & Differential Correction146

IS-GPS-200L
14 May 2020

1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5
BITS"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITS

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

128

118

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 6139

144

157 160MSB FIRST

189

176

196

af1-n

af2-n

tGGTO

WNGGTOA0GGTOA1GGTOA2GGTO

17 LSBs

10 BITS

16 BITS

13 BITS

16 BITS

13 BITS

7 BITS 5 BITS

RESERVEDGNSS ID – 3 BITS

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDSMSB FIRST

277

201
RESERVEDCRC

76 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-8. Message Type 35 - Clock & GGTO

147

IS-GPS-200L
14 May 2020

1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5
BITS"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 61
39

128

118
af1-n

af2-n

TEXT MESSAGE (18 8-BIT CHAR)

17 LSBs

10 BITS

73 MSBs

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
272

201

276
277

TEXT MESSAGE (18 8-BIT CHAR)

CRC
4
BITS

71 LSBs
TEXT PAGE

24 BITSRESERVED – 1 BIT* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-9. Message Type 36 - Clock & Text

148

IS-GPS-200L
14 May 2020

1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5
BITS"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101

128

118

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs
URANED0 INDEXMESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
50
55 58 61
39

141

af1-n

af2-n

WNa-n

toa

17 LSBs

10 BITS

13 BITS149

155 158

180

191

e

i




11 BITS

11 BITS

11 BITSPRNa

8 BITS 6 BITS

169

A
10 MSBs

L1 HEALTH – 1 BIT
L2 HEALTH – 1 BIT
L5 HEALTH – 1 BITMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
201

240

224

208

256

277

267

A

0



M0

af0

af1

CRC

7 LSBs16 BITS

16 BITS

16 BITS

11 BITS

10 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-10.

Message Type 37 - Clock & Midi Almanac

149

IS-GPS-200L
14 May 2020

1

15

9
PRN

8 BITS

6
BITS

6
BITS

21

91

MESSAGETOW COUNT*

WNa-n

toa

Reduced Almanac
Packet 1

17 BITS

13 BITS

8 BITS

31 BITS

10 MSBs

Reduced Almanac Packet 2

MESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
60
52
39

"ALERT" FLAG - 1 BIT

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
122

101

153

Reduced Almanac
Packet 2
21 LSBs

184

Reduced Almanac
Packet 3

Reduced Almanac
Packet 4

Reduced Almanac
Packet 5

31 BITS

31 BITS

17 MSBs

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
215

201

MSB FIRSTMSB FIRST

277

246

Reduced Almanac
Packet 5

Reduced Almanac
Packet 6

Reduced Almanac
Packet 7

CRC

14 LSBs

31 BITS

31 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-11.

Message Type 12 - Reduced Almanac

150

IS-GPS-200L
14 May 2020

1

21

15

9
PRN

8 BITS

6
BITS

6
BITS

96
97

MESSAGETOW COUNT*

top-D

tOD

CDC

17 BITS

11 BITS

11 BITS

34 BITSDC DATA TYPE – 1 BIT

MESSAGE TYPE ID
PREAMBLEMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
61
38
50
39
62

DC DATA TYPE – 1 BIT
CDC - 4 MSBs

"ALERT" FLAG - 1 BITMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
131
166
132
167

101
CDC

CDC

CDC

30 LSBs

34 BITS

34 BITSDC DATA TYPE – 1 BIT

DC DATA TYPE – 1 BIT

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
236
237

201
202
CDC

271

277

CDC

34 BITSDC DATA TYPE – 1 BITMSB FIRST

34 BITSDC DATA TYPE – 1 BIT

6
BITS

CRC
24 BITSRESERVED* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE
CDC = Clock Differential Correction

Figure 30-12.

Message Type 13 - Clock Differential Correction151

IS-GPS-200L
14 May 2020

1

15

9
PRN

8 BITS

6
BITS

6
BITS

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
61
50
39
62

21

MESSAGETOW COUNT*

top-D

tOD

EDC

17 BITS

11 BITS

11 BITS

39 MSBs

DC DATA TYPE – 1 BIT

MESSAGE TYPE ID
PREAMBLEMSB FIRST"ALERT" FLAG - 1 BIT

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDSMSB FIRST

154
155

101
EDC

EDC

53 LSBs

46 MSBs
DC DATA TYPE – 1 BIT

201

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDSMSB FIRST

247

277

EDC

RESERVEDCRC

46 LSBs

30 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE
EDC = Ephemeris Differential Correction

Figure 30-13.

Message Type 14 - Ephemeris Differential Correction152

IS-GPS-200L
14 May 2020

1

15

9
PRN

8 BITS

6
BITS

6
BITS

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
38
39

21

MESSAGETOW COUNT*TEXT MESSAGE (29 8-BIT CHAR)

17 BITS

62 MSBs

MESSAGE TYPE ID
PREAMBLE"ALERT" FLAG - 1 BITMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
101
TEXT MESSAGE (29 8-BIT CHAR)
BITS 63-162

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
4 SECONDS
271

201

275
277

TEXT MESSAGE (29 8-BIT CHAR)

CRC
4
BITS

70 LSBs
TEXT PAGE

24 BITSRESERVED – 2 BITS

* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 12-SECOND MESSAGE

Figure 30-14.

Message Type 15 – Text

153

IS-GPS-200L
14 May 2020

30.3.3.1 Message Type 10 and 11 Ephemeris and Health Parameters.
30.3.3.1.1 Message Type 10 and 11 Ephemeris and Health Parameter Content.
The contents of the SV health, ephemeris representation and accuracy parameters in Message
Types 10 and 11 are defined below, followed by material pertinent to the use of the data. Message
Type 10 in conjunction with Message Type 11, provides users with the requisite data to calculate
SV position. The general format of Message Types 10 and 11 consists of data fields for referencetime tags, a set of gravitational harmonic correction terms, rates and rate corrections to quasiKeplerian elements, and an accuracy indicator for ephemeris-related data.
The ephemeris parameters in the Message Type 10 and type 11 describe the orbit of thetransmitting SV during the curve fit interval of three hours. The nominal transmission interval is
two hours, and shall coincide with the first two hours of the curve fit interval. The predicted periodof applicability for ephemeris data coincides with the entire three-hour curve fit interval. Table 30-I
gives the definition of the orbital parameters using terminology typical of Keplerian orbitalparameters; it is noted, however, that the transmitted parameter values are expressed such thatthey provide the best trajectory fit in Earth-Centered, Earth-Fixed (ECEF) coordinates for eachspecific fit interval. The user shall not interpret intermediate coordinate values as pertaining to any
conventional coordinate system.
The toe term shall provide the user with a convenient means for detecting any change in theephemeris representation parameters. The t oe is provided in both Message Type 10 and 11 for the
purpose of comparison with the toc term in Message Type 30 - 37. Whenever these three terms do
not match, a CEI data set cutover has occurred and new data must be collected. The timing of thetoe and constraints on the toc and toe are defined in paragraph 30.3.4.4.
Any change in the Message Type 10 and 11 ephemeris data will be accomplished with asimultaneous change in the toe value. The CS (Block IIR-M/IIF) and SS (GPS III and GPS IIIF) willassure that the toe value, for at least the first CEI data set transmitted by an SV from a new CEI
data sequence propagation, is different from that transmitted from the prior CEI data sequence
propagation (reference paragraph 30.3.4.5 for additional information regarding t oe).
The CNAV messages contain information that allows users to take advantage of situations when
integrity is assured to the enhanced level. This is accomplished using a composite integrity
assured URA value in conjunction with an integrity status flag. The composite integrity assured
URA (IAURA) value is the RSS of an elevation-dependent function of the upper bound value of the
URAED component and the upper bound value of the URANED component. The composite IAURA
value is assured to the enhanced level only when the integrity status flag is “1”; otherwise the
IAURA value is assured to the legacy level.
Bit 272 of Message Type 10 is the Integrity Status Flag (ISF). A "0" in bit position 272 indicatesthat the conveying signal is provided with the legacy level of integrity assurance. That is, theprobability that the instantaneous URE of the conveying signal exceeds 4.42 times the current
broadcast IAURA value, for more than 5.2 seconds, without an accompanying alert, is less than
1E-5 per hour. A "1" in bit-position 272 indicates that the conveying signal is provided with anenhanced level of integrity assurance. That is, the probability that the instantaneous URE of the154

IS-GPS-200L
14 May 2020

conveying signal exceeds 5.73 times the current broadcast IAURA value, for more than 5.2
seconds, without an accompanying alert, is less than 1E-8 per hour. The probabilities associatedwith the nominal and lower bound values of the current broadcast URA ED index, URANED indexes,
and related URA values are not defined.
In this context, an "alert" is defined as any indication or characteristic of the conveying signal, as
specified elsewhere in this document, which signifies to users that the conveying signal may beinvalid or should not be used, such as the health bits not indicating operational-healthy,
broadcasting non-standard code parity error, etc.
Bit 273 of Message Type 10 indicates the phase relationship between L2C and P(Y) as specified in
section 3.3.1.5.1 of IS-GPS-200.

30.3.3.1.1.1 Transmission Week Number.
Bits 39 through 51 of Message Type 10 shall contain 13 bits which are a modulo-8192 binary
representation of the current GPS week number at the start of the CEI data set transmissioninterval (see paragraph 6.2.4).

30.3.3.1.1.2 Signal Health (L1/L2/L5).
The three, one-bit, health indication in bits 52 through 54 of Message Type 10 refers to the L1, L2,and L5 carrier of the transmitting SV. These health indication bits only apply to codes and data as
defined in IS-GPS-200, IS-GPS-705, and IS-GPS-800. The health of each carrier is indicated by:
0 = Some or all codes and data on this carrier are OK,
1 = All codes and data on this carrier are bad or unavailable.
The health bit indication shall be given relative to the capabilities of each SV as designated by theconfiguration code in the LNAV message (see paragraph 20.3.3.5.1.4). Accordingly, the health bit
for any SV which does not have a certain capability will be indicated as "healthy" if the lack of thiscapability is inherent in its design or if it has been configured into a mode which is normal from auser standpoint and does not require that capability; however, the Operating Command may
choose to set the health bit "unhealthy" for an SV without a certain capability. Single-frequency
L2C users or users who have not recieved or choose not to use configuration code should assume
that every signal is available on every SV. The predicted health data will be updated at the time of
upload when a new CEI data set has been built by the CS. Therefore, the transmitted health data
may not correspond to the actual health of the transmitting SV. For more information about user
protocol for interpreting health indications see paragraph 6.4.6.
Additional SV health data are given in the almanac in messages types 12, 31, and 37. The data
given in Message Type 10 may differ from that shown in other messages of the transmitting SV
and/or other SVs since the latter may be updated at a different time.

30.3.3.1.1.3 CEI Data Sequence Propagation Time of Week.

155

IS-GPS-200L
14 May 2020

Bits 55 through 65 of Message Type 10 shall contain the CEI data sequence propagation time ofweek (top). The top term provides the epoch time of week of the state data utilized for satellite CEI
data. Users are cautioned to avoid using this parameter to compute age of data for any SV.

30.3.3.1.1.4 Elevation-Dependent (ED) Accuracy
Bits 66 through 70 of Message Type 10 shall contain the elevation-dependent (ED) component
User Range Accuracy (URAED) index for the standard positioning service user. The URA ED index
shall provide the ED-related URA index or the current ephemeris curve fit interval. While the EDrelated URA may vary over the ephemeris curve fit interval and over the satellite footprint, the
URAED index (N) in Message Type 10 shall correspond to the maximum URA ED expected over theentire ephemeris curve fit interval for the worst-case location within the SV footprint (i.e., nominally
two points at the edge of the SV footprint). At the best-case location within the SV footprint (i.e.,
nominally directly below the SV along the SV nadir vector), the corresponding URA ED is zero.
The URAED index is a signed, two’s complement integer in the range of +15 to -16 and has thefollowing relationship to the ED URA:
URAED Index

URAED (meters)

15

6144.00< URAED(or no accuracy prediction is available)

143072.00< URAED≤6144.00

13

1536.00< URAED≤

3072.00

12

768.00< URAED≤1536.00

11

384.00< URAED≤768.0010

192.00< URAED≤384.00996.00< URAED≤

192.008

48.00< URAED

≤

96.00

7

24.00

< URAED

≤

48.00

6

13.65

< URAED

≤

24.00

5

9.65

< URAED

≤

13.65

4

6.85

< URAED

≤

9.65

3

4.85

< URAED

≤

6.85

2

3.40

< URAED

≤

4.85

1

2.40

< URAED

≤

3.40

0

1.70

< URAED

≤

2.40

-1

1.20

< URAED

≤

1.70

-2

0.85

< URAED

≤

1.20

156

IS-GPS-200L
14 May 2020

-3

0.60

< URAED

≤

0.85

-4

0.43

< URAED

≤

0.60

-5

0.30

< URAED

≤

0.43

-6

0.21

< URAED

≤

0.30

-7

0.15

< URAED

≤

0.21

-8

0.11

< URAED

≤

0.15

-9

0.08

< URAED

≤

0.11

-10

0.06

< URAED

≤

0.08

-11

0.04

< URAED

≤

0.06

-12

0.03

< URAED

≤

0.04

-13

0.02

< URAED

≤

0.03

-14

0.01

< URAED

≤

0.02

URAED

≤

0.01

-15
-16

No accuracy prediction available-use at own risk

For each URAED index (N), users may compute a nominal URAED value (X) as given by:• If the value of N is 6 or less, but more than -16, X = 2(1 + N/2),• If the value of N is 6 or more, but less than 15, X = 2 (N - 2),• N = -16 or N = 15 shall indicate the absence of an accuracy prediction and shall advise thestandard positioning service user to use that SV at his own risk.
For N = 1, 3, and 5, X should be rounded to 2.8, 5.7, and 11.3 meters, respectively.
The nominal URAED value (X) is suitable for use as a conservative prediction of the RMS ED range
errors for accuracy-related purposes in the pseudorange domain (e.g., measurement deweighting,
RAIM, FOM computations). Integrity properties of the IAURAED are specified with respect to thescaled (multiplied by either 4.42 or 5.73 as appropriate) upper bound values of the broadcast
URAED index (see 30.3.3.1.1).
For the nominal URAED value and the IAURAED value, users may compute an adjusted URAED
value as a function of SV elevation angle (E), for E ≥ 0, as follows:
Adjusted Nominal URAED
Adjusted IAURAED= Nominal URAED (sin(E+90 degrees))= IAURAED (sin(E+90 degrees))

URAED and IAURAED account for SIS contributions to user range error which include, but are notlimited to, the following: CNAV LSB representation/truncation error, CNAV alongtrack ephemeris
errors, and crosstrack CNAV ephemeris errors. URAED and IAURAED do not account for user
157

IS-GPS-200L
14 May 2020

range error contributions due to the inaccuracy of the broadcast ionospheric data parameters usedin the single-frequency ionospheric model or for other atmospheric effects.

30.3.3.1.2 Message Type 10 and 11 Ephemeris Parameter Characteristics.
For each ephemeris parameter contained in Message Types 10 and 11, the number of bits, thescale factor of the least significant bit (LSB) (which is the last bit received), the range, and the units
are as specified in Table 30-I. See Figures 30-1 and 30-2 for complete bit allocation in Message
Types 10 and 11.

30.3.3.1.3 User Algorithm for Determination of SV Position.
The user shall compute the ECEF coordinates of position for the SV’s antenna phase center (APC)
utilizing a variation of the equations shown in Table 30-II. The ephemeris parameters are
Keplerian in appearance; however, the values of these parameters are produced by the CS (Block
IIR-M/IIF) and SS (GPS III and GPS IIIF) via a least squares curve fit of the propagated ephemerisof the SV APC (time-position quadruples: t, x, y, z expressed in ECEF coordinates). Particulars
concerning the applicable coordinate system are given in Sections 20.3.3.4.3.3 and 20.3.3.4.3.4.
The user can compute velocity and acceleration for the SV, if required, utilizing a variation of theequations shown in Table 30-II Part 3 and 4.
The sensitivity of the SV’s position to small perturbations in most ephemeris parameters isextreme. The sensitivity of position to the parameters A, C rc-n, and Crs-n is about one meter/meter.
The sensitivity of position to the angular parameters is on the order of 10 8 meters/semi-circle, andto the angular rate parameters is on the order of 10 12 meters/semi-circle/second. Because of thisextreme sensitivity to angular perturbations, the value of  used in the curve fit is given here.  is amathematical constant, the ratio of a circle’s circumference to its diameter. Here  is taken as
3.1415926535898.

158

IS-GPS-200L
14 May 2020

Table 30-I.

Message Types 10 and 11 Parameters (1 of 2)

Parameter

No. of
Bits**

Scale
Factor(LSB)
1

WN

Data Sequence
Propagation Week Number

13

URAED Index

ED Accuracy Index

5*

Signal health(L1/L2/L5)

Valid
Range***

Units
weeks

(see text)

3

1(see text)
0 to 604,500

top

CEI Data sequence
propagation time of week

11

300

ΔA ****

Semi-major axis difference
at reference time

26*

2-9

metersA

Change rate in semi-major
axis

25*

2-21

meters/sec

Δn0

Mean Motion difference
from computed value atreference time

17*

2-44

semi-circles/sec

Δn0Rate of mean motion
difference from computed
value

23*

2-57

semi-circles/sec2

M0-n

Mean anomaly at reference
time

33*

2-32

semi-circles

enEccentricity

33

2-34

n

Argument of perigee

33*

2-32





*
**
***
****

0.0 to 0.03

seconds

dimensionlesssemi-circles

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figure 30-1 for complete bit allocation in Message Type 10;
Unless otherwise indicated in this column, valid range is the maximum range attainable withindicated bit allocation and scale factor.
Relative to AREF = 26,559,710 meters.

Table 30-I.

Message Types 10 and 11 Parameters (2 of 2)
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No. of
Bits**

Scale
Factor(LSB)

Ephemeris data reference time of week

11

300

Longitude of Ascending Node of Orbit
Plane at Weekly Epoch

33*

2-32

semi-circles

ΔΩ****

Rate of right ascension difference

17*

2-44

semi-circles/sec

i0-nInclination angle at reference time

33*

2-32

semi-circles

i0-n –DOT

Rate of inclination angle

15*

2-44

semi-circles/sec

Cis-n

Amplitude of the sine harmoniccorrection term to the angle of inclination

16*

2-30

radians

Cic-n

Amplitude of the cosine harmoniccorrection term to the angle of inclination

16*

2-30

radians

Crs-n

Amplitude of the sine correction term to
the orbit radius

24*

2-8

metersCrc-n

Amplitude of the cosine correction term
to the orbit radius

24*

2-8

metersCus-nAmplitude of the sine harmoniccorrection term to the argument oflatitude

21*

2-30

radians

Cuc-n

Amplitude of the cosine harmoniccorrection term to the argument oflatitude

21*

2-30

radians

Parameter
toe

0-n


Valid
Range***
0 to
604,500

Units
seconds******

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figure 30-1 and Figure 30-2 for complete bit allocation in Message Types 10 and 11;
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicatedbit allocation and scale factor.

****

Relative to REF = -2.6 x 10-9 semi-circles/second.



Table 30-II. Broadcast Navigation User Equations (sheet 1 of 4)160

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Description

Element/Equation
 = 3.986005 x 1014 meters3/sec2


WGS 84 value of the earth’s gravitational constant for GPS usere = 7.2921151467 x 10-5 rad/sec

WGS 84 value of the earth’s rotation rate

A0 = AREF + A *Semi-Major Axis at reference timeSemi-Major Axis

Ak = A0 + (A) tk

n0 =



Computed Mean Motion (rad/sec)

A03

tk = t – toe **Time from ephemeris reference timenA = n0 +½ ∆n0 tk

Mean motion difference from computed valuenA = n0 + nA

Corrected Mean Motion

Mk = M0 + nA tk

Mean Anomaly
Kepler’s equation ( 𝑀𝑘 = 𝐸𝑘 − 𝑒 sin 𝐸𝑘 ) may be solved forEccentric Anomaly (𝐸𝑘 ) by iteration:– Initial Value (radians)

E0 = Mk
𝐸𝑗 = 𝐸𝑗−1 +𝑀𝑘 −𝐸𝑗−1 +𝑒 sin 𝐸𝑗−1
1−𝑒 cos 𝐸𝑗−1

Ek = Ej
k = 2 tan-1

*

(

1+𝑒
1−𝑒

tan

𝐸𝑘
2

)

– Refined Value, minimum of three iterations, (j=1,2,3)–Final Value (radians)

True Anomaly (unambiguous quadrant)

AREF = 26,559,710 meters** t is GPS system time at time of transmission, i.e., GPS time corrected for transit time (range/speed of light).
Furthermore, tk shall be the actual total difference between the time t and the epoch time toe, and must accountfor beginning or end of week crossovers. That is if tk is greater than 302,400 seconds, subtract 604,800 seconds
from tk. If tk is less than -302,400 seconds, add 604,800 seconds to tk.

Table 30-II. Broadcast Navigation User Equations (sheet 2 of 4)

Element/Equation *Description161

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k = k + n

Argument of Latitude

uk = Cus-nsin2k + Cuc-ncos2k

Argument of Latitude Correctionrk = Crs-nsin2k + Crc-ncos2k

Radial Correction

ik = Cis-nsin2k + Cic-ncos2kInclination Correction

uk = k + uk

Second Harmonic
Perturbations

Corrected Argument of Latituderk= Ak(1 – en cos Ek) + rk

Corrected Radiusik= io-n + (io-n-DOT)tk + ik

Corrected Inclination

xk' = rk cos uk

Positions in orbital planeyk' = rk sin uk = REF + ∆ ***Rate of Right Ascensionk = 0-n + (  − e ) tk – e toe

Corrected Longitude of Ascending Nodexk = xk' cos k  yk' cos ik sin kyk = xk' sin k + yk' cos ik cos kEarth-fixed coordinates of SV antenna phase centerzk = yk' sin ik• REF = 2.6 x 10-9 semi-circles/second.
*** 

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Table 30- II. Broadcast Navigation User Equations (sheet 3 of 4)
Element/Equation

Description

SV Velocity
Ėk = n/ (1 – e cos Ek)

Eccentric Anomaly Ratev̇k = Ėk √1 − 𝑒 2 /(1 − 𝑒 cos 𝐸𝑘 )True Anomaly Rate

(dik / dt) = (IDOT) + 2 v̇k (cis cos 2ɸk – cic sin 2ɸk)

Corrected Inclination Angle Rateu̇k = v̇k + 2v̇k (cus cos 2ɸk – cuc sin 2ɸk)

Corrected Argument of Latitude Rateṙk = eAĖk sin Ek + 2v̇k (crs cos 2ɸk – crc sin 2ɸk)

Corrected Radius RateΩ̇k = Ω̇ - Ω̇eLongitude of Ascending Node Rate

ẋ′𝑘 = ṙk cos uk – rk u̇k sin uk

In- plane x velocity

𝑦̇ 𝑘′ = ṙk sin uk + rk u̇k cos uk

In- plane y velocity𝑥̇ k = -𝑥𝑘′ Ω̇k sin Ωk + 𝑥̇ 𝑘′ cos Ωk – 𝑦̇ 𝑘′ sin Ωk cos ik–𝑦𝑘′ (Ω̇k cos Ωk cos ik – (dik / dt) sin Ωk sin ik)

Earth- Fixed x velocity (m/s)

𝑦̇ k = 𝑥𝑘′ Ω̇k cos Ωk + 𝑥̇ 𝑘′ sin Ωk + 𝑦̇ 𝑘′ cos Ωk cos ik–𝑦𝑘′ (Ω̇k sin Ωk cos ik + (dik / dt) cos Ωk sin ik)

Earth- Fixed y velocity (m/s)

𝑧̇ k = 𝑦̇ 𝑘′ sin ik + 𝑦𝑘′ (dik / dt) cos ik

Earth- Fixed z velocity (m/s)

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Table 30-II. Broadcast Navigation User Equations (sheet 4 of 4)
Element/Equation

Description

SV Acceleration
RE = 6378137.0 meters

WGS 84 Earth Equatorial Radius

J2 = 0.0010826262

Oblate Earth Gravity CoefficientF = - (3/2) J2 (µ/ 𝑟𝑘2 ) (RE / rk)2

Oblate Earth acceleration Factor

𝑥̈ 𝑘 = - µ (𝑥𝑘 / 𝑟𝑘3 ) + F [(1 – 5 (𝑧𝑘 / 𝑟𝑘 )2 )(𝑥𝑘 / 𝑟𝑘 ) ]+2𝑦̇ 𝑘 Ω̇𝑒 + 𝑥𝑘 Ω̇2𝑒Earth- Fixed x acceleration (m/s2)

𝑦̈ 𝑘 = - µ (𝑦𝑘 / 𝑟𝑘3 ) + F [(1 – 5 (𝑧𝑘 / 𝑟𝑘 )2 )(𝑦𝑘 / 𝑟𝑘 ) ]–2𝑥̇ 𝑘 Ω̇𝑒 + 𝑦𝑘 Ω̇2𝑒Earth- Fixed y Acceleration (m/s2)𝑧̈𝑘 = - µ (𝑧𝑘 / 𝑟𝑘3 ) + F [(3 – 5 (𝑧𝑘 / 𝑟𝑘 )2 )(𝑧𝑘 / 𝑟𝑘 ) ]Earth- Fixed z Acceleration (m/s2)

30.3.3.2 Message Types 30 Through 37 SV Clock Correction Parameters.
30.3.3.2.1 Message Type 30 Through 37 SV Clock Correction Parameter
Content.
The clock parameters in any one of Message Types 30 through 37 describe the SV time scale
during the period of validity. The parameters are applicable during the time in which they aretransmitted. Beyond that time, they are still applicable, however, the most recent CEI data set
should be used since the accuracy degrades over time.
The general format of Message Types 30 through 37 includes data fields for SV clock correction
coefficients. Any one of Message Types 30 through 37 in conjunction with Message Types 10 and
11 provides users with the requisite data to correct SV time and to calculate SV position precisely.
In general, any Message Type 30’s (i.e. 30-39) will provide SV clock correction parameters as
described in this section.

30.3.3.2.1.1 SV Clock Correction.
Any one of Message Types 30 through 37, Figure 30-3 through Figure 30-10, contains theparameters needed by the users for apparent SV clock correction. Bits 61 to 71 contain t oc , clock
data reference time of week. Bits 72 to 127 contain SV clock correction coefficients. The related
algorithm is given in paragraph 20.3.3.3.3.1.

30.3.3.2.1.2 CEI Data Sequence Propagation Time of Week.
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Bits 39 through 49 of Message Types 30 through 37 shall contain the CEI data sequence
propagation time of week (t op). The top term provides the epoch time of week of the state datautilized for propagating the SV clock correction coefficients forward in time. Users are cautioned to
avoid using this parameter to compute age of data for any SV.

30.3.3.2.2 Clock Parameter Characteristics.
The number of bits, the scale factor of the LSB (which is the last bit received), the range, and theunits of clock correction parameters shall be as specified in Table 30-III.

30.3.3.2.3 User Algorithms for SV Clock Correction Data.
The algorithms defined in paragraph 20.3.3.3.3.1 allow all users to correct the code phase timereceived from the SV with respect to both SV code phase offset and relativistic effects. However,since the SV clock corrections of equations in paragraph 20.3.3.3.3.1 are estimated by the CS
using dual frequency L1 and L2 P(Y) code measurements, the single-frequency L1 or L2 user andthe dual-frequency L1 C/A - L2C users must apply additional terms to the SV clock correction
equations. These terms are described in paragraph 30.3.3.3.1.

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Table 30-III. Clock Correction and Accuracy Parameters

No. of
Bits**

Scale
Factor(LSB)

Valid
Range***

Units

11

300

0 to 604,500

seconds

300

0 to 604,500

seconds

top

Parameter
CEI Data Sequence Propagation Timeof Week

toc

Clock Data Reference Time of Week

11

URANED0
Index

NED Accuracy Index

5*(see text)

URANED1Index

NED Accuracy Change Index

3(see text)

URANED2
Index

NED Accuracy Change Rate Index

3(see text)

af2-n

SV Clock Drift Rate Correction
Coefficient

10*

2-60

sec/sec2

af1-n

SV Clock Drift Correction
Coefficient

20*

2-48

sec/sec

af0-n

SV Clock Bias Correction Coefficient

26*

2-35

seconds******

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figure 30-3 through 30-10 for complete bit allocation in Message Types 30 to 37;
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicatedbit allocation and scale factor.

30.3.3.2.4 Non-Elevation-Dependent (NED) Accuracy Estimates.
Bits 50 through 54, 55 through 57, and 58 through 60 of Message Types 30 through 37 shallcontain the non-elevation-dependent (NED) component URANED0 Index, URANED1 Index, and
URANED2 Index, respectively, of the SV (reference paragraph 6.2.1) for the standard positioning
service user. The following equations, together with the broadcast URA NED0 Index, URANED1 Index,
and URANED2 Index, shall give the non-elevation dependent user range accuracy of IAURANED overthe current clock/ephemeris fit interval. While the actual NED related URA may vary over thesatellite footprint, the IAURANED calculated using the parameters in Message Type 10 at each
instant during the current clock/ephemeris fit interval shall bound the maximum IAURA NED
expected for the worst-case location within the satellite footprint at that instant.
The user shall calculate the NED-related URA with the equation (in meters);
IAURANED = URANED0 + URANED1 (t - top + 604,800*(WN - WNop))
for t - top + 604,800*(WN - WNop) ≤ 93,600 seconds
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IAURANED = URANED0 + URANED1*(t - top + 604,800*(WN - WNop)) + URANED2*(t - top +604,800*(WN - WNop) - 93,600)2
for t - top + 604,800*(WN - WNop) > 93,600 seconds
where
t is the GPS system time
The CS shall derive URANED0, URANED1, and URANED2 indexes which, when used together in theabove equations, results in the minimum IAURANED that is greater than the predicted IAURANED
during the clock/ephemeris fit interval.
Non-elevation dependent URA (URANED) accounts for signal-in-space contributions to user range
error that include, but are not limited to, the following: the net effect of clock parameter and code
phase error in the transmitted signal for single-frequency L1C/A or single-frequency L2C users
who correct the code phase as described in Section 30.3.3.3.1.1.1, as well as the net effect ofclock parameter, code phase, and intersignal correction error for dual-frequency L1/L2 and L1/L5
users who correct for group delay and ionospheric effects as described in Section 30.3.3.3.1.1.2.
The user shall use the broadcast URANED0 index to derive the URANED0 value. The URANED0 index
is a signed, two’s complement integer in the range of +15 to -16 and has the following relationshipto the URANED0 value:

URANED0 Index

URANED0 (meters)

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156144.00< URANED0(or no accuracy prediction is available)

143072.00< URANED0≤6144.00

13

1536.00< URANED0≤3072.00

12

768.00< URANED0≤

1536.00

11

384.00< URANED0≤

768.0010

192.00< URANED0≤

384.00996.00< URANED0≤

192.008

48.00< URANED0

≤

96.00

7

24.00

< URANED0

≤

48.00

6

13.65

< URANED0

≤

24.00

5

9.65

< URANED0

≤

13.65

4

6.85

< URANED0

≤

9.65

3

4.85

< URANED0

≤

6.85

2

3.40

< URANED0

≤

4.85

1

2.40

< URANED0

≤

3.40

0

1.70

< URANED0

≤

2.40

-1

1.20

< URANED0

≤

1.70

-2

0.85

< URANED0

≤

1.20

-3

0.60

< URANED0

≤

0.85

-4

0.43

< URANED0

≤

0.60

-5

0.30

< URANED0

≤

0.43

-6

0.21

< URANED0

≤

0.30

-7

0.15

< URANED0

≤

0.21

-8

0.11

< URANED0

≤

0.15

-9

0.08

< URANED0

≤

0.11

-10

0.06

< URANED0

≤

0.08

-11

0.04

< URANED0

≤

0.06

-12

0.03

< URANED0

≤

0.04

-13

0.02

< URANED0

≤

0.03

-14

0.01

< URANED0

≤

0.02

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-15
-16

URANED0≤

0.01

No accuracy prediction available-use at own risk

For each URANED0 index (N), users may compute a nominal URANED0 value (X) as given by:• If the value of N is 6 or less, but more than -16, X = 2(1 + N/2),• If the value of N is 6 or more, but less than 15, X = 2 (N - 2),• N = -16 or N = 15 shall indicate the absence of an accuracy prediction and shall advise thestandard positioning service user to use that SV at his own risk.
For N = 1, 3, and 5, X should be rounded to 2.8, 5.7, and 11.3 meters, respectively.
The nominal URANED0 value (X) shall be suitable for use as a conservative prediction of the RMS
NED range errors for accuracy-related purposes in the pseudorange domain (e.g., measurement
de-weighting RAIM, FOM computations). Integrity properties of the IAURA NED are specified withrespect to the scaled (multiplied by either 4.42 or 5.73 as appropriate) upper bound values of the
URANED0 index, URANED1 index, and URANED2 index (see 30.3.3.1.1).
URANED0 accounts for zeroth order SIS contributions to user range error which include, but are notlimited to, the following: CNAV LSB representation/truncation error; the net effect of CNAV clock
correction polynomial error and code phase error in the transmitted signal for single-frequency L2C
users who correct the code phase as described in Section 30.3.3.3.1.1.1; the net effect of clockparameter, code phase, and inter-signal correction error for dual-frequency L1 C/A and L2C users
who correct for group delay and ionospheric effects as described in Section 30.3.3.3.1.1.2; radial
ephemeris error; anisotropic antenna errors; and signal deformation error. URA NED0 does notaccount for user range contributions due to the inaccuracy of the broadcast ionospheric data
parameters used in the single-frequency ionospheric model or for other atmospheric effects.
The transmitted URANED1 index is an integer value in the range 0 to 7. The URANED1 index has thefollowing relationship to the URANED1 value:

1
N
URANED1 = 2 (meters/second)where
N = 14 + URANED1 Index
The transmitted URANED2 index is an integer value in the range 0 to 7. URANED2 index has thefollowing relationship to the URANED2:

1N
URANED2 = 2 (meters/second2)
where
N = 28 + URANED2 Index.
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30.3.3.3 Message Type 30 Ionospheric and Group Delay Correction
Parameters.
30.3.3.3.1 Message Type 30 Ionospheric and Group Delay Correction
Parameter Content.
Message Type 30 provides SV clock correction parameters (ref. Section 30.3.3.2) and ionosphericand group delay correction parameters. Bits 128 through 192 of Message Type 30 provide thegroup delay differential correction terms for L1, L2, and L5 signal users. Bits 193 through 256
provide the ionospheric correction parameters for single frequency users. The following algorithms
shall apply when interpreting the correction parameters in the message.
The broadcast group delay differential correction terms apply to the pseudorange measurements
produced by an ideal correlation receiver with a bandwidth of 20.46 MHz centered at the reference
waveform nominal frequency whose phase is linear over that bandwidth using an exact replica of
the reference waveform in an early-late discriminator having a correlator spacing of 97.75
nanoseconds. The group delay differential correction terms may not apply to pseudorange
measurements produced by different methods due to potential distortion of the transmitted
waveform. Users employing pseudorange measurement methods different from the defined
method must account for the potential inapplicability of the group delay differential correction
terms.

30.3.3.3.1.1 Estimated L1-L2 Group Delay Differential.
The group delay differential correction terms, T GD, ISCL1C/A, ISCL2C for the benefit of single
frequency L1 P, L1 C/A, L2 P, L2C users and dual frequency L1/L2 users are contained in bits 128
through 166 of Message Type 30 (see Figure 30-3 for complete bit allocation). The bit length,
scale factors, ranges, and units of these parameters are given in Table 30-IV. The bit string of“1000000000000” shall indicate that the group delay value is not available. The related algorithm
is given in paragraphs 30.3.3.3.1.1.1 and 30.3.3.3.1.1.2.

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Table 30-IV. Group Delay Differential Parameters ****

*
**
***
****

Parameter

No. of
Bits**

Scale Factor
(LSB)

Valid
Range***

TGD

13*

2-35

seconds

ISCL1C/A

13*

2-35

seconds

ISCL2C13*

2-35

seconds

ISCL5I513*

2-35

seconds

ISCL5Q513*

2-35

seconds

Units

Parameters so indicated are two’s complement with the sign bit (+ or -) occupying the MSB;
See Figure 30-3 for complete bit allocation in Message Type 30;
Valid range is the maximum range attainable with indicated bit allocation and scale factor;
The bit string of “1000000000000” will indicate that the group delay value is not available.

30.3.3.3.1.1.1 Inter-Signal Correction.
The correction terms, TGD, ISCL1C/A and ISCL2C, are initially provided by the CS to account for theeffect of inter-signal biases between L1 P(Y) and L2 P(Y), L1 P(Y) and L1 C/A, and between L1
P(Y) and L2C, respectively, based on measurements made by the SV contractor during SV
manufacture. The values of TGD and ISCs for each SV may be subsequently updated to reflect theactual on-orbit group delay differential. For maximum accuracy, the single frequency L1 C/A user
must use the correction terms to make further modifications to the code phase offset in paragraph20.3.3.3.3.2 with the equation:(tSV)L1C/A = tSV - TGD + ISCL1C/A
where TGD (see paragraph 20.3.3.3.3.2) and ISCL1C/A are provided to the user as Message Type 30
data, described in paragraph 30.3.3.3.1.1. For the single frequency L2C user, the code phaseoffset modification is given by:(tSV)L2C = tSV - TGD + ISCL2C
where, ISCL2C is provided to the user as Message Type 30 data.
The values of ISCL1C/A and ISCL2C are measured values that represent the mean SV group delaydifferential between the L1 P(Y)-code and the L1 C/A- or L2C-codes respectively as follows,
ISCL1C/A = tL1P(Y) - tL1C/A
ISCL2C = tL1P(Y) - tL2C

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where, tLix is the GPS time the i th frequency x signal (a specific epoch of the signal) is transmitted
from the SV antenna phase center.

30.3.3.3.1.1.2 L1 /L2 Ionospheric Correction.
The dual-frequency (L1 C/A and L2C) user shall correct for the group delay and ionospheric effects
by applying the relationship:PR ( PRL 2C   12 PRL1C / A )  c ( ISCL 2C   12 ISCL1C / A ) c TGD
1   12

where,
PR = pseudorange corrected for ionospheric effects,
PRi = pseudorange measured on the channel indicated by the subscript,
ISCi = inter-signal correction for the channel indicated by the subscript (see paragraph30.3.3.3.1.1),
TGD = see paragraph 20.3.3.3.3.2,
c = speed of light,
and where, denoting the nominal center frequencies of L1 and L2 as f L1 and fL2 respectively,
12 = (fL1/fL2)2 = (1575.42/1227.6)2 = (77/60)2.

30.3.3.3.1.2 Ionospheric Data.
The ionospheric parameters which allow the “L1 only” or “L2 only” user to utilize the ionosphericmodel for computation of the ionospheric delay are contained in Message Type 30. The “singlefrequency” user should use the model given in paragraph 20.3.3.5.2.5 to make this correction for
the ionospheric effects. The bit lengths, scale factors, ranges, and units of these parameters are
given in Table 20-X.
The ionospheric data shall be updated by the CS at least once every six days while the CS is able
to upload the SVs. If the CS is unable to upload the SVs, the ionospheric data transmitted by theSVs may not be accurate.

30.3.3.3.1.3 CEI Data Sequence Propagation Week Number.
Bits 257-264 of Message Type 30 shall indicate the CEI Data Sequence Propagation Week
Number (WNop) to which top is referenced (see 30.3.3.1.1.3 and 30.3.3.2.1.2). The WN op term
consists of eight bits which shall be a modulo 256 binary representation of the GPS week number
to which the top is referenced. The user must account for the truncated nature of WN op in all
calculations in which WNop is used. The combination of the epoch time of state data (t op, WNop) fora valid CEI data sequence propagation will be in the past relative to the time of broadcast.

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30.3.3.4 Message Types 31, 12, and 37 Almanac Parameters.
The almanac parameters are provided in any one of Message Types 31, 37, and 12. Message
Type 37 provides Midi almanac parameters and the reduced almanac parameters are provided ineither Message Type 31 or type 12. The SV shall broadcast both Message Types 31 (and/or 12)
and 37. However, the reduced almanac parameters (i.e. Message Types 31 and/or 12) for thecomplete set of SVs in the constellation will be broadcast by a SV using shorter duration of timecompared to the broadcast of the complete set of Midi almanac parameters (i.e. Message Type37). The parameters are defined below, followed by material pertinent to the use of the data.

30.3.3.4.1 Almanac Reference Week.
Bits 39 through 51 of Message Type 12, and bits 128 through 140 of Message Types 31 and 37
shall indicate the number of the week (WNa-n) to which the almanac reference time (t oa) is
referenced (see paragraph 20.3.3.5.2.2). The WN a-n term consists of 13 bits which shall be amodulo-8192 binary representation of the GPS week number (see paragraph 6.2.4) to which the t oa
is referenced. Bits 52 through 59 of Message Type 12, and bits 141 to 148 of Message Types 31
and 37 shall contain the value of toa, which is referenced to this WNa-n.

30.3.3.4.2 Almanac Reference TimeSee paragraph 20.3.3.5.2.2.

30.3.3.4.3 SV PRN Number.
Bits 149 through 154 of Message Type 37 and bits 1 through 6 in each packet of reduced almanac
shall specify PRN number of the SV whose almanac or reduced almanac, respectively, is provided
in the message or in the packet.

30.3.3.4.4 Signal Health (L1/L2/L5).
The three, one-bit, health indication in bits 155, 156, and 157 of Message Type 37 and bits 29, 30
and 31 of each packet of reduced almanac refers to the L1, L2, and L5 carrier of the SV whose
PRN number is specified in the message or in the packet. These health indication bits only apply tocodes and data as defined in IS-GPS-200, IS-GPS-705, and IS-GPS-800.
The health of each carrier is indicated by:
0 = Some or all codes and data on this carrier are OK,
1 = All codes and data on this carrier are bad or unavailable.
The health bit indication shall be given relative to the capabilities of each SV as designated by theconfiguration code in the LNAV message (see paragraph 20.3.3.5.1.4). Accordingly, the health bit
for any SV which does not have a certain capability will be indicated as "healthy" if the lack of thiscapability is inherent in its design or if it has been configured into a mode which is normal from auser standpoint and does not require that capability; however, the Operating Command may
choose to set the health bit "unhealthy" for an SV without a certain capability. Single-frequency
L2C users or users who have not recieved or choose not to use configuration code should assume173

IS-GPS-200L
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that every signal is available on every SV. The predicted health data will be updated at the time of
upload when a new CEI data set has been built by the CS. Therefore, the transmitted health data
may not correspond to the actual health of the transmitting SV. For more information about user
protocol for interpreting health indications see paragraph 6.4.6.

30.3.3.4.5 Midi Almanac Parameter Content.
Message Type 37, Figure 30-10, provides Midi almanac data for a SV whose PRN number is
specified in the message. The number of bits, the scale factor (LSB), the range, and the units of
the almanac parameters are given in Table 30-V. The user algorithm is essentially the same as
the user algorithm used for computing the precise ephemeris as specified in Table 20-IV. Other
parameters appearing in the equations of Table 20-IV, but not provided by the Midi almanac withthe reference values, are set to zero for SV position determination. See paragraph 20.3.3.5.2.3 foralmanac time parameters.

30.3.3.4.6 Reduced Almanac Parameter Content.
Message Type 31, Figure 30-4, provides SV clock correction parameters (ref. Section 30.3.3.2)
and reduced almanac data packets for 4 SVs. Message Type 12, Figure 30-11, contains reduced
almanac data packets for 7 SVs.

30.3.3.4.6.1 Reduced Almanac Data.
Message Type 31 or 12 contains reduced almanac data and SV health words for SVs in theconstellation. The reduced almanac data of a SV is broadcast in a packet of 31 bits long, as
described in Figure 30-15. The reduced almanac data are a subset of the almanac data which
provide less precise ephemeris. The reduced almanac data values are provided relative to prespecified reference values. The number of bits, the scale factor (LSB), the range, and the units of
the reduced almanac parameters are given in Table 30-VI. The algorithms and other material
related to the use of the reduced almanac data are given in Section 30.3.3.4.6.2.
The reduced almanac parameters shall be updated by the CS at least once every 3 days while the
CS is able to upload the SVs. If the CS is unable to upload the SVs, the accuracy of the reduced
almanac parameters transmitted by the SVs will degrade over time.
A 6-bit value of “000000” in the PRNa field shall indicate that there is no data in the reduced
almanac packet. In this event, all subsequent bits through the last bit of the last packet in themessage (bit 272 for MT 31, bit 276 for MT 12) shall be filler bits, i.e., alternating ones and zeros
beginning with one.

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30.3.3.4.6.2 Reduced Almanac Packet.
The following shall apply when interpreting the data provided in each packet of reduced almanac(see Figure 30-15).

30.3.3.4.6.2.1 Reduced Almanac.
The reduced almanac data is provided in bits 7 through 28 of each packet. The data from a packet
along with the reference values (see Table 30-VI) provide ephemeris with further reduced
precision. The user algorithm is essentially the same as the user algorithm used for computing the
precise ephemeris from the parameters of the Message Types 10 and 11 (see paragraph30.3.3.1.3 and Table 30-II). Other parameters appearing in the equations of Table 30-II, but notprovided by the reduced almanac with the reference values, are set to zero for SV position
determination.
Table 30-V. Midi Almanac Parameters

Parameter

No. of
Bits**

Scale
Factor(LSB)

Valid
Range***

Units

toa

8

212

0 to 602,112

seconds

e

11

2-16

0.0 to 0.03

dimensionlessi****

11*

2-14



11*

2-33

-1.19E-07 to 0

semi-circles/sec

A

17

2-4

2530 to 8192

meters

Ω0

16*

2-15

semi-circles



16*

2-15

semi-circles

M0

16*

2-15

semi-circles

af0

11*

2-20

seconds

af1

10*

2-37

sec/secsemi-circles* Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;** See Figure 30-10 for complete bit allocation in Message Type 37;*** Unless otherwise indicated in this column, valid range is the maximum range attainable with indicated bit
allocation and scale factor;**** Relative to i0 = 0.30 semi-circles.

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31 BITS

1

7

PRN a
6 BITS

15

22

29 30

A

0

0

8 BITS

7 BITS

7 BITS

31

L1 HEALTH
L2 HEALTH*

See Figures 30 -4 and 30 -11 for complete bit allocation in therespective messages.

Figure 30-15.

L5 HEALTH

Reduced Almanac Packet Content

Table 30-VI. Reduced Almanac Parameters *****

Parameter

No. of Bits

Scale Factor (LSB)

Valid Range **UnitsA ***

8*

2+9

**

meters

0

7*

2-6

**

semi-circles

0 ****

7*

2-6

**

semi-circles*

Parameters so indicated shall be two’s complement with the sign bit (+ or -) occupying the MSB;**

Valid range is the maximum range attainable with indicated bit allocation and scale factor;***

Relative to Aref = 26,559,710 meters;****

0 = Argument of Latitude at Reference Time = M0 + ;*****

Relative to following reference values:e=0
i = +0.0056 semi-circles (i = 55 degrees)• = -2.6 x 10-9 semi-circles/second.

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30.3.3.5 Message Type 32 Earth Orientation Parameters (EOP).
The earth orientation parameters are provided in Message Type 32. The parameters are defined
below, followed by material pertinent to the use of the data.

30.3.3.5.1 EOP Content.
Message Type 32, Figure 30-5, provides SV clock correction parameters (ref. Section 30.3.3.2)
and earth orientation parameters. The EOP message provides users with parameters to construct
the ECEF and ECI coordinate transformation (a simple transformation method is defined in Section
20.3.3.4.3.3.2). The number of bits, scale factors (LSBs), the range, and the units of all EOP fields
of Message Type 32 are given in Table 30-VII.

30.3.3.5.1.1 User Algorithm for Application of the EOP.
The EOP fields in the Message Type 32 contain the EOP data needed to construct the ECEF-toECI coordinate transformation. The user computes the ECEF position of the SV antenna phasecenter using the equations shown in Table 30-II. The full coordinate transformation for translating
to the corresponding ECI SV antenna phase center position may be accomplished in accordancewith the computations detailed in Chapter 5 of IERS Technical Note 36: IERS Conventions (2010)
and equations for UT1, xp and yp as documented in Table 30-VIII. For UT1, Table 30-VIII
documents the relationship between GPS time and UT1 with ΔUTGPS and ΔU̇TGPS. Users who
may need ΔUT1 (UT1-UTC) as detailed in Chapter 5 of IERS Technical Note 36: IERS
Conventions (2010) can calculate this parameter from UT1-UTC, or more accurately as (UT1GPS) + (GPS-UTC), using intermediate quantities (UT1-GPS) and (GPS-UTC) which are produced
during calculation of UT1 and UTC. Figure 5.1 on page 73 of that document depicts thecomputational flow starting from GCRS (Geocentric Celestial Reference System) to ITRS
(International Terrestrial Reference System). Ongoing WGS 84 re-adjustment at NGA andincorporating the 2010 IERS Conventions, are expected to bring Earth based coordinateagreement to within 2 cm. In the context of the Conventions, the user may as a matter ofconvenience choose to implement the transformation computations via either the "Celestial
Intermediate Origin (CIO) based approach” or the “Equinox based approach”. The EOPs are used
to calculate UT1 (applied in the "Rotation to terrestrial system" process) and the polar motion
parameters, xp and yp (applied in the "Rotation for polar motion" process). Details of the calculation
are given in Table 30-VIII. Users are advised that the broadcast Message Type 32 EOPs alreadyaccount for the following effects and should not be further applied by the user:(1) zonal, diurnal and semi-diurnal effects (described in Chapter 8 of the IERS Conventions (2010))(2) A0-n, A1-n, A2-n and the leap second count in Message Type 33
EOPs that are not updated by the CS will degrade in accuracy over time.
The relevant computations utilize elementary rotation matrices R i(α), where α is a positive rotation
about the ith-axis ordinate, as follows:

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1R     0
1

0

0
cos( )
 sin ( )sin ( ) cos( )0

cos( ), R    02 sin( ) cos ( )R       sin( )
3

 0

sin( )
cos( )
00
10

 sin( )
0 
cos( ) 

0

0

1

The Inertial-to-Geodetic rotation matrix shall be calculated in accordance with the computations
detailed in Chapter 5 of IERS Technical Note 36: IERS Conventions (2010) and equations for UT1,
xp and yp as documented in Table 30-VIII.

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Table 30-VII. Earth Orientation Parameters

Parameter

No. of
Bits**

Scale
Factor(LSB)

Valid
Range***

Units

0 to 604,784

secondstEOP

EOP Data Reference Time

16

24

PM_X †, ††††

X-Axis Polar Motion Valueat Reference Time.

21*

2-20

arc-seconds

PM_X ††††

X-Axis Polar Motion Drift at
Reference Time.

15*

2-21

arc-seconds/day

PM_Y ††, ††††

Y-Axis Polar Motion Valueat Reference Time.

21*

2-20

arc-seconds

PM_Y ††††

Y-Axis Polar Motion Drift at
Reference Time.

15*

2-21

arc-seconds/day

UTGPS †††UT1-GPS Difference at
Reference Time.

31*

2-23

seconds

Rate of UT1-GPS
Difference at Reference
Time.

19*

2-25

seconds/day







UTGPS †††

*
**
***

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figure 30-5 for complete bit allocation in Message Type 32;
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicatedbit allocation and scale factor.

†

Represents the predicted angular displacement of instantaneous Celestial Intermediate Pole with respect
to semi-minor axis of the reference ellipsoid along Greenwich meridian.

††Represents the predicted angular displacement of instantaneous Celestial Intermediate Pole with respect
to semi-minor axis of the reference ellipsoid on a line directed 90 west of Greenwich meridian.

†††

Already account for zonal, diurnal, and semi-diurnal tides and should not be further applied by the user.

††††

Already account for diurnal and semi-diurnal tides and should not be further applied by the user.

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Table 30-VIII.

Application of EOPs

Element/Equation

Description

tdiff = (t – tEOP + 604800(WN - WNot))[seconds]

Compute difference between GPS
time and EOP reference time•
UT1 = t + 604800*WN + ΔUTGPS + ΔUTGPS*tdiff/86400[seconds]

Compute UT1 at GPS time•
xp = PM_X + PM_X*t
diff/86400[arc-seconds]

Polar Motion in the x-axis•
yp = PM_Y + PM_Y*t
diff/86400[arc-seconds]

Polar Motion in the y-axis

GPS system time (t) is expressed in seconds since start of current GPS week, and WN is the current week number expressedin number of weeks since GPS epoch.
The divisor 86400 converts rates per day to rates per second.

When calculating UT1, xp, and yp in Table 30-VIII, the week number for tEOP is equal to the WNot
value in Message Type 33 when both criteria are met:
 tEOP in Message Type 32 is equal to the tot in Message Type 33
 top in Message Type 32 is equal to the top in Message Type 33
If both criteria are not met, the data between the two message types may be inconsistent with eachother and should not be used in the calculations in Table 30-VIII.

30.3.3.6 Message Type 33 Coordinated Universal Time (UTC) Parameters.
Message Type 33, Figure 30-6 contains the UTC parameters. The contents of Message Type 33
are defined below, followed by material pertinent to the use of the UTC data.

30.3.3.6.1 UTC Parameter Content.
Message Type 33 provides SV clock correction parameters (ref. Section 30.3.3.2) and also, shallcontain the parameters related to correlating UTC (USNO) time with GPS Time. The bit lengths,
scale factors, ranges, and units of these parameters are given in Table 30-IX. See Figure 30-6 forcomplete bit allocation in Message Type 33.
The parameters relating GPS time to UTC (USNO) shall be updated by the CS at least once every
three days while the CS is able to upload the SVs. If the CS is unable to upload the SVs, theaccuracy of the UTC parameters transmitted by the SVs will degrade over time.

30.3.3.6.2 UTC and GPS Time.
Message Type 33 includes: (1) the parameters needed to relate GPS Time to UTC (USNO), and(2) notice to the user regarding the scheduled future or recent past (relative to Nav message
upload) value of the delta time due to leap seconds (tLSF), together with the week number (WNLSF)
and the day number (DN) at the end of which the leap second becomes effective. Information

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required to use these parameters to calculate t UTC is in paragraph 20.3.3.5.2.4 except the following
definition of tUTC shall be used.
tUTC = tLS + A0-n + A1-n (tE - tot + 604800 (WN - WNot)) + A2-n (tE - tot + 604800 (WN WNot)) seconds
2

Table 30-IX. UTC Parameters

Parameter

No. of
Bits**

Scale
Factor(LSB)

Valid
Range***

Units

A0-n

Bias coefficient of GPS time scale
relative to UTC time scale

16*

2-35

Seconds

A1-n

Drift coefficient of GPS time scale
relative to UTC time scale

13*

2-51

sec/sec

A2-nDrift rate correction coefficient of
GPS time scale relative to UTC
time scale

7*

2-68

sec/sec2

ΔtLS

Current or past leap second count8*

1

seconds

tot

Time data reference Time of Week

16

24

WNot

Time data reference Week Number

13

1

weeks

WNLSF

Leap second reference Week
Number

13

1

weeks

DN

Leap second reference Day Number

4

1

ΔtLSF

Current or future leap second count8*

1

0 to 604,784

1 to 7seconds

days
seconds****

Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;**
See Figure 30-6 for complete bit allocation;
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicated bit
allocation and scale factor.

30.3.3.7 Message Types 34, 13, and 14 Differential Correction Parameters.
Differential Correction (DC) parameters are provided either in Message Types 34 or in types 13
and 14. These parameters provide users with sets of correction terms that apply to the clock andephemeris data transmitted by other SVs. DC parameters are grouped in packets, as described in
the next sections. The availability of these Message Types is subject to the control anddetermination of the CS.

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30.3.3.7.1 Differential Correction Parameters Content.
Message Type 34 provides SV clock correction parameters (ref. Section 30.3.3.2) and also, shallcontain DC parameters that apply to the clock and ephemeris data transmitted by another SV.
One Message Type 34, Figure 30-7, shall contain 34 bits of clock differential correction (CDC)parameters and 92 bits of ephemeris differential correction (EDC) parameters for one SV otherthan the transmitting SV. Bit 150 of Message Type 34 shall be a DC Data Type indicator thatindicates the data type for which the DC parameters apply. Zero (0) signifies that the corrections
apply to CNAV data, Dc(t), and one (1) signifies that the corrections apply to LNAV data, D(t).
Message Types 13 and 14 together also provide DC parameters. Message Type 13, Figure 30-12,
shall contain CDC parameters applicable to 6 SVs and Message Type 14, Figure 30-13, shallcontain EDC parameters applicable to 2 SVs. There shall be a DC Data Type indicator preceding
each CDC or EDC packet. The content of an individual data packet is depicted in Figure 30-16.
The number of bits, scale factors (LSB), the range, and the units of all fields in the DC packet are
given in Table 30-X.

30.3.3.7.2 DC Data Packet.
Each DC data packet contains: corrections to SV clock polynomial coefficients provided in any
one of the Message Types 30 to 37 of the corresponding SV; corrections to quasi-Keplerianelements referenced to tOD of the corresponding SV; and User Differential Range Accuracy
(UDRA) and UDRA indices that enable users to estimate the accuracy obtained after corrections
are applied. Each DC packet is made up of two different segments. The first segment contains 34
bits for the CDC parameters and the second segment contains 92 bits of EDC parameters totaling
126 bits. The CDC and EDC parameters form an indivisible pair and users must utilize CDC and
EDC as a pair. Users must utilize CDC and EDC data pair of same t op-D and of same tOD.

30.3.3.7.2.1 Differential Correction Data Predict Time of Week.
The DC data predict time of week (t op-D) provides the epoch time of week, in increments of 300
seconds (i.e. five minutes), at which the prediction for the associated DC data was performed.

30.3.3.7.2.2 Time of Differential Correction Data.
The time of DC data, tOD, specifies the reference time of week, in increments of 300 seconds (i.e.,
five minutes) relative to the GPS week, for the associated CDC and EDC data.

30.3.3.7.2.3 SV PRN Identification.
The PRN ID of both CDC and EDC of Figure 30-16 identifies the satellite to which the subject 126bit differential correction packet data applies (by PRN code assignment). A value of all ones
“11111111” in any PRN ID field shall indicate that no DC data is contained in the remainder of thedata block. In this event, the remainder of the data block shall be filler bits, i.e., alternating ones
and zeros beginning with one.

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CDC = Clock Differential Correction

MSB
1

9

LSB

22

30

34

PRN ID

af0

af1

UDRA

.
8 BITS.
13 BITS.
8 BITS.
5 BITS

EDC = Ephemeris Differential Correction

MSB
1

LSB

23

9

36

PRN IDΔ

Δ

.
8 BITS.
14 BITS.
14 BITS

LSB

MSB
52

37

63

Δ

Δi

.
15 BITS.
12 BITS

.

LSB

MSB
88

76

64

92

Δ

ΔA


UDRA

12 BITS

12 BITS

5 BITS

Figure 30-16.

Differential Correction Data Packet

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Table 30-X. Differential Correction Parameters

Parameter
PRN IDNo. of
Bits**

Scale
Factor(LSB)

Valid
Range***

8Units
see text

top-D

DC data predict time of week

11

300

0 to 604,500

seconds

tOD

time of DC data

11

300

0 to 604,500

seconds

af0

SV Clock Bias Correction

13*

2-35

seconds

af1

SV Clock Drift Correction

8*

2-51

seconds/second

UDRA

User Differential Range
Accuracy Index

5*Alpha Correction to Ephemeris
Parameters

14*

2-34

dimensionless

Beta Correction to Ephemeris
Parameters

14*

2-34

dimensionlessGamma Correction to Ephemeris
Parameters

15*

2-32

semi-circles

iAngle of Inclination Correction

12*

2-32

semi-circles

Angle of Right Ascension
Correction

12*

2-32

semi-circles

A

Semi-Major Axis Correction

12*

2-9

metersUDRA

Change Rate of User Differential
Range Accuracy Index.

5*



*
**
***

see text

see text

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figure 7, 11 and 12 for complete bit allocation in Message Types 34, 13 and 14;
Unless otherwise indicated in this column, valid range is the maximum range attainable with indicated bit
allocation and scale factor.

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30.3.3.7.3 Application of Clock-Related DC Data.
The SV PRN code phase offset, uncorrected by clock correction coefficient updates, is given byequation 2 in paragraph 20.3.3.3.3.1 (see para. 30.3.3.2.3). If the matched pair of DC data for the
subject SV is available, the user may apply clock correction coefficient update values by;tsv = (af0 + af0) + (af1 + af1)(t  toc) + af2(t  toc )2 + tr,
where af0 and af1, (see Table 30-X), are given in Message Types 34 or 13, and all other terms
are as stated in paragraph 20.3.3.3.3.1. Clock-related DC data shall not be applied to any SVtransmitting clock correction parameters message(s) containing a t op value greater than the top-D
value of Message Types 34 or 13 containing the clock-related DC data.

30.3.3.7.4 Application of Orbit-Related DC Data.
The DC data packet includes corrections to parameters that correct the state estimates forephemeris parameters transmitted in the Message Types 10 and 11 (broadcast by the SV to which
the DC data packet applies). The user will update the ephemeris parameters utilizing a variation of
the algorithm expressed in the following equations. The user will then incorporate the updated
quasi-Keplerian element set in all further calculations of SV position, as represented by theequations in Table 30-II (see para. 30.3.3.1.3). Ephemeris-related DC data shall not be applied to
any SV transmitting Message Types 10 and 11 containing a t op value greater than the top-D value of
Message Types 34 or 14 containing the ephemeris-related DC data.
The user will construct a set of initial (uncorrected) elements by:
Ai

=

A0

ei

=

en

ii

=

i0-n

i

=

 0-n

i

=

en cos(n)i=

en sin(n)i=M0-n + nwhere A0, en, i0-n,  0-n, n and M0-n are obtained from the applicable SV’s Message Types 10 and
11 data. The terms i, i, and i form a subset of stabilized ephemeris elements which aresubsequently corrected by ,  and the values of which are supplied in the Message Types
34 or 14 - as follows:c=i + 

c=

i + 

c=

i + 

The quasi-Keplerian elements are then corrected by
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Ac=

Ai + Aec=(c2 + c2)1/2

ic=

ii + ic= i + c=tan-1 (c/c)

M0-c

=

c  c + M0

where A, i and  are provided in the EDC data packet of the Message Type 34 or 14 and M0
is obtained from1

 3    2  A0 
t oe  WN oe * 604,800  t OD  WN * 604,800
M 0 
2  A0 3   A0 
where WN(oe) is the week number associated with the t(oe) and WN is the current week number.
The corrected quasi-Keplerian elements above are applied to the user algorithm for determinationof antenna phase center position in Section 30.3.3.1.3, Table 30-II.

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30.3.3.7.5 SV Differential Range Accuracy Estimates.


The UDRAop-D and UDRA shall give the differential user range accuracy for the SV. It must be
noted that the two parameters provide estimated accuracy after both clock and ephemeris DC areapplied. The UDRAop-D and UDRA indices are signed, two’s complement integers in the range of+15 to -16 and has the following relationship:Index Value
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
-13
-14
-15
-16

UDRAop-D (meters)
6144.00
3072.00
1536.00
768.00384.00
192.00
96.00
48.00
24.00
13.65
9.65
6.85
4.85
3.40
2.40
1.70
1.20
0.85
0.60
0.43
0.30
0.21
0.15
0.11
0.08
0.06
0.04
0.03
0.02
0.01

<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<

UDRA (10-6 m/sec)

UDRAop-D
6144.00
UDRAop-D6144.00
3072.00
UDRAop-D

3072.00
1536.00
UDRAop-D
1536.00
768.00
UDRAop-D
768.00384.00
UDRAop-D
384.00
192.00
UDRAop-D
192.0096.00
UDRAop-D

96.00
48.00
UDRAop-D

48.00
24.00
UDRAop-D

24.00
13.65
UDRAop-D

13.65
9.65
UDRAop-D

9.65
6.85
UDRAop-D

6.85
4.85
UDRAop-D

4.85
3.40
UDRAop-D

3.40
2.40
UDRAop-D

2.40
1.70
UDRAop-D

1.70
1.20
UDRAop-D

1.20
0.85
UDRAop-D

0.85
0.60
UDRAop-D

0.60
0.43
UDRAop-D

0.43
0.30
UDRAop-D

0.30
0.21
UDRAop-D

0.21
0.15
UDRAop-D

0.15
0.11
UDRAop-D

0.11
0.08
UDRAop-D

0.08
0.06
UDRAop-D

0.06
0.04
UDRAop-D

0.04
0.03
UDRAop-D

0.03
0.02
UDRAop-D

0.02
0.01
UDRAop-D

0.01
0.005
No accuracy prediction available—use at own risk

For any time, tk, other than top-D, UDRA is found by,

UDRA = UDRAop-D + UDRA (tk - top-D)

187

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14 May 2020

30.3.3.8 Message Type 35 GPS/GNSS Time Offset.
Message Type 35, Figure 30-8, contains the GPS/Global Navigation Satellite System (GNSS)Time Offset (GGTO) parameters. The contents of Message Type 35 are defined below. The
validity period of the GGTO shall be 1 day as a minimum.

30.3.3.8.1 GPS/GNSS Time Offset Parameter Content.
Message Type 35 provides SV clock correction parameters (ref. Section 30.3.3.2) and also, shallcontain the parameters related to correlating GPS time with other GNSS time. Bits 157 through159 of Message Type 35 shall identify the other GPS like navigation system to which the offset
data applies. The three bits are defined as follows;
000 = no data available,
001 = Galileo,
010 = GLONASS,
011 through 111 = Reserved in order to preserve use of these values in a future revision of this IS.
Until such a revision, the User Segment developing to this version of this IS should interpret thesevalues as indicating that the GPS/GNSS Time Offset Parameter data, to which the GNSS Type ID
applies, is presently unusable.
The number of bits, the scales factor (LSB), the range, and the units of the GGTO parameters are
given in Table 30-XI. See Figure 30-8 for complete bit allocation in Message Type 35.

188

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14 May 2020

30.3.3.8.2 GPS and GNSS Time.
The GPS/GNSS-time relationship is given by,
tGNSS = tE - (A0GGTO + A1GGTO (tE - tGGTO + 604800 (WN - WNGGTO)) + A2GGTO (tE - tGGTO + 604800(WN - WNGGTO))2)
where tGNSS is in seconds, tE and WN are as defined in Section 20.3.3.5.2.4, and the remaining
parameters are as defined in Table 30-XI.
Table 30-XI. GPS/GNSS Time Offset Parameters

No. of
Bits**

Parameter

Scale
Factor
(LSB)

Valid

Units

Range***-35

A0GGTO

Bias coefficient of GPS time scale
relative to GNSS time scale

16*

2

seconds

A1GGTO

Drift coefficient of GPS time scale
relative to GNSS time scale

13*

2-51

sec/sec

A2GGTO

Drift rate correction coefficient of
GPS time scale relative to GNSS
time scale

7*

2-68

sec/sec2

tGGTO

Time data reference Time of Week

16

24

WNGGTOTime data reference Week Number

13

20

GNSS ID

GNSS Type ID

3

*
**
***

0 to 604,784

seconds
weeks
see text

Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the
MSB;
See Figure 30-8 for complete bit allocation;
Unless otherwise indicated in this column, valid range is the maximum range attainable withindicated bit allocation and scale factor.

30.3.3.9 Message Types 36 and 15 Text Messages.
Text messages are provided either in Message Type 36, Figure 30-9, or type 15, Figure 30-14.
The specific contents of text message will be at the discretion of the Operating Command.
Message Type 36 can accommodate the transmission of 18 eight-bit ASCII characters.
Message Type 15 can accommodate the transmission of 29 eight-bit ASCII characters.
The requisite bits shall occupy bits 39 through 274 of Message Type 15 and bits 128 through 275
of Message Type 36. The eight-bit ASCII characters shall be limited to the set described inparagraph 20.3.3.5.1.8.

189

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30.3.4 Timing Relationships.
The following conventions shall apply.

30.3.4.1 Paging and Cutovers.
Broadcast system of messages is completely arbitrary, but sequenced to provide optimum user
performance. Message Types 10 and 11 shall be broadcast at least once every 48 seconds. Allother messages shall be broadcast in-between, not exceeding the maximum broadcast interval in
Table 30-XII. Message Type 15 will be broadcast as needed, but will not reduce the maximum
broadcast interval of the other messages. Type 15 messages that are longer than one page will
not necessarily be broadcast consecutively.
Table 30-XII. Message Broadcast Intervals

Message Type Number

Maximum Broadcast Intervals †Ephemeris

10 & 1148 secClock

Type 30’s

48 sec30*

288 sec

31* or 12

20 min**,****

Midi Almanac

37*

120 min**,****

EOP

32*

30 min****

UTC

33*

288 sec

34* or 13 & 14

30 min***,****

GGTO

35*

288 sec****Text

36* or 15

As needed****Message Data

ISC, IONOReduced Almanac

Diff Correction

*
**
***
****
†

Also contains SV clock correction parameters.
Complete set of SVs in the constellation.
When Differential Corrections are available.
Optional (interval applies if/when broadcast).

The intervals specified are maximum. As such, the broadcast intervals may be shorter than thespecified value.

30.3.4.2 SV Time vs. GPS Time.
In controlling the SVs and uploading of data, the CS shall allow for the following timing
relationships:a.

Each SV operates on its own SV time;190

IS-GPS-200L
14 May 2020b.

All time-related data (TOW) in the messages shall be in SV-time;c.

All other data in the CNAV message shall be relative to GPS time;d.

The acts of transmitting the CNAV messages shall be executed by the SV on SV

time.

30.3.4.3 Speed of Light.
The speed of light used by the CS for generating the data described in the above paragraphs is
c = 2.99792458 x 108

meters per second

which is the official WGS 84 speed of light. The user shall use the same value for the speed oflight in all computations.

30.3.4.4 Data Sets
The toe shall be equal to the toc of the same CNAV CEI data set. top does not have to match toe/toc.
As a redundant check, top in Message Type 10 and 11 will match with the t op term in Message Type
30-37 for a valid CEI data set. The following rule governs the transmission of t oe and toc values indifferent data sets: The transmitted toe/toc will be different from any value transmitted by the SV
during the preceding six hours. Cutovers to new CEI data sets will occur only on hour boundaries
except for the first data set of a new CEI data sequence propagation. The first CEI data set may
be cut-in (reference paragraph 30.3.4.1) at any time during the hour and therefore may betransmitted by the SV for less than one hour.
The start of the transmission interval for each CEI data set corresponds to the beginning of thecurve fit interval for the CEI data set. Each CEI data set remains valid for the duration of its
transmission interval, and nominally also remains valid for the duration of its curve fit interval. A
CEI data set is rendered obsolete before the end of its curve fit interval when it is superseded by
the SV cutting over to the first CEI data set of a new CEI data sequence propagation.
Normal Operations. The Message Type 10, 11, and 30-37 CEI data sets are transmitted by the SV
for periods of two hours. The corresponding curve fit interval is three hours.
Updates to parameters in Table 6-I-1 shall prompt changes in toe/toc. Any parameter marked with
NOTE1 may be changed with or without a change in t oe/toc.

30.3.4.5 Reference Times
Many of the parameters which describe the SV state vary with true time, and must therefore be
expressed as time functions with coefficients provided by the Navigation Message to be evaluatedby the user equipment. These include the following parameters as functions of GPS time:a. SV time,b. Semi-major axis,
c. Mean anomaly,191

IS-GPS-200L
14 May 2020

d. Longitude of ascending node,e. Inclination,
f. UTC,g. URANED,h. EOP,i. Differential corrections,j. GGTO.
Each of these parameters is formulated as a polynomial in time. The specific time scale ofexpansion can be arbitrary. Due to the short data field lengths available in the Navigation Message
format, the epoch of the polynomial is chosen near the midpoint of the expansion range so thatquantization error is small. This results in time epoch values which can be different for each data
set. Time epochs contained in the Navigation Message and the different algorithms which utilize
them are related as follows:
Epoch Application Algorithm Reference
toc

20.3.3.3.3.1

toe

20.3.3.4.3

toa

20.3.3.5.2.2 and 20.3.3.5.2.3

tot

20.3.3.5.2.4 and 30.3.3.6.2

top

30.3.3.2.4

tEOP

30.3.3.5.1

tOD

30.3.3.7

tGGTO 30.3.3.8.2
For those parameters for which fit interval and transmission interval are relevant, Table 30-XIII
specifies the fit interval, the nominal transmission interval, and the nominal selection of the fit point(which will be expressed modulo 604,800 seconds in the Navigation Message).
The coefficients of expansion are obviously dependent upon choice of epoch, and thus the epoch
time and expansion coefficients must be treated as an inseparable parameter set. Note that a user
applying current navigation data will normally be working with negative values of (t-toc) and (t-toe) in
evaluating the expansions.
The CS (Block IIR-M/IIF) and SS (GPS III and GPS IIIF) shall assure that the t oe value, for at least
the first CEI data set transmitted by an SV after a new CEI data sequence propagation, is different
from that transmitted prior to the cutover (see paragraph 30.3.4.4). As such, when a new CEI data
sequence propagation is cutover for transmission, the CS (Block IIR-M/IIF) and SS (GPS III and
GPS IIIF) shall introduce a small deviation in the t oe resulting in the toe value that is offset from the192

IS-GPS-200L
14 May 2020

nominal location of 1.5 hours into the fit interval (see Table 30-XIII). This offset toe will betransmitted by an SV in the first data set after a new CEI data sequence propagation cutover andthe second CEI data set, following the first CEI data set, may also continue to reflect the sameoffset in the toe.
When the toe, immediately prior to a new CEI data sequence propagation cutover, already reflects
a small deviation (i.e. a new CEI data sequence propagation cutover has occurred in the recentpast), then the CS (Block IIR-M/IIF) and SS (GPS III/IIIF) shall introduce an additional deviation to
the toe when a new CEI data sequence propagation is cutover for transmission.
For CNAV data, the user may use the following example algorithm to detect the occurrence of a
new CEI data sequence propagation cutover:
DEV = toe [modulo 7200]
If DEV ≠ 5400, then a new CEI data sequence propagation cutover has occurred within thepast 4 hours.
Table 30-XIII. Reference Times

Fit Interval
Transmission(hours)Interval (hours)3*2*
144 (6 days)
144=144 (6 days)=144* Defined in Section 30.3.3.1.1

Hours After First Valid Transmission Time
toc
toe
toa
tot
(clock)(ephemeris)(almanac)
(UTC)
1.5
1.5
70
70
70
70

30.3.5 Data Frame Parity.
The data signal contains parity coding according to the following conventions.

30.3.5.1 Parity Algorithm.
Twenty-four bits of CRC parity will provide protection against burst as well as random errors with aprobability of undetected error  2-24 = 5.9610-8 for all channel bit error probabilities  0.5. The
CRC word is calculated in the forward direction on a given message using a seed of 0. The
sequence of 24 bits (p1,p2,...,p24) is generated from the sequence of information bits
(m1,m2,...,m276) in a given message. This is done by means of a code that is generated by thepolynomial
24gX    g i X i
i 0

where
g i  1 for i  0,1,3, 4,5,6,7,10,11,14,17,18, 23, 24
 0 otherwise

193

IS-GPS-200L
14 May 2020

This code is called CRC-24Q. The generator polynomial of this code is in the following form (using
binary polynomial algebra):g X   1  X pX 

where p(X) is the primitive and irreducible polynomialpX   X 23  X17  X13  X12  X11  X 9  X8  X 7  X 5  X 3  1

When, by the application of binary polynomial algebra, the above g(X) is divided into m(X)X 24,
where the information sequence m(X) is expressed asmX   m k  m k 1X  m k  2 X 2      m1X k 1

The result is a quotient and a remainder R(X) of degree < 24. The bit sequence formed by thisremainder represents the parity check sequence. Parity bit p i, for any i from 1 to 24, is thecoefficient of X24-i in R(X).
This code has the following characteristics:
1) It detects all single bit errors per code word.
2) It detects all double bit error combinations in a codeword because the generator polynomial g(X)has a factor of at least three terms.
3) It detects any odd number of errors because g(X) contains a factor 1+X.
4) It detects any burst error for which the length of the burst is  24 bits.
5) It detects most large error bursts with length greater than the parity length r = 24 bits. The
fraction of error bursts of length b > 24 that are undetected is:a) 2-24 = 5.96  10-8, if b > 25 bits.
b) 2-23 = 1.19  10-7, if b = 25 bits.

194

IS-GPS-200L
14 May 2020

40 APPENDIX IV GPS NAVIGATION DATA STRUCTURE FOR LNAVDATA, D(t), FOR PRN 33-63
40.1 Scope
This appendix describes the specific legacy navigation (LNAV) data structure denoted by data ID
number 2 for the upper set of PRN numbers (PRN 33-63). This data ID number, when transmitted
as part of the LNAV data, shall be represented by the two-bit binary notation as 01. Data ID
number 1 is no longer in use. The LNAV data structure for the upper set of PRN numbers isdenoted as LNAV-U. The LNAV data structure for the lower set of PRN numbers (LNAV-L) is
described in Appendix II.

40.2 Applicable Documents
Applicable documents shall be as specified in Appendix II, Section 20.2.

40.3 Requirements
40.3.1 Data Characteristics
The data characteristics shall be as specified in Appendix II, Section 20.3.1.

40.3.2 Message Structure
The message structure shall be as specified in Appendix II, Section 20.3.2 except as indicated by
Figure 40-1.

195

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 571
SUBFRAME
NO.

PAGE
NO.

1

N/A

1

31
TLM
22 BITS

61
HOW

C P

73 77 83

91

121

WN
t

22 BITS

P

P

10
BITS

23 BITS***C/A OR P ON L2 - 2 BITS
URA INDEX - 4 BITS
SV HEALTH - 6 BITSP

2 MSBs150 BITSIODC - 10 BITS TOTAL

1

N/A

24 BITS***

P

181

197

16
BITS***

8 BITST GDMSB FIRST

3 SECONDS

WORD 7151

P

L2 P DATA FLAG - 1 BIT

DIRECTION OF DATA FLOW FROM SV

WORD 624 BITS***

WORD 8WORD 9211 219

P

241

t oc
16 BITS

P

a f2
8
BITS

8 LSBs271

af1
16 BITS

a f0

P

22 BITSIODC - 10 BITS TOTAL*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 1 of 11)

196

WORD 10tP

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

2

N/A

WORD 2

1

WORD 3

31
TLM

61
HOW

C P

t

22 BITSMSB FIRST

3 SECONDSP

22 BITS

WORD 4

69

IODE
8
BITS

91

WORD 5

107

121

n

C rs
P
16 BITS

8BITS

16 BITSP

24 BITS

MSBs

P

LSBs

M0 - 32 BITS TOTAL

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6
151

C UC
2

N/A

16 BITS

8
BITS

MSBs
e - 32 BITS TOTAL

WORD 7

167

WORD 8

181

P

211

24 BITSMSB FIRST

3 SECONDS

C US

P

16 BITS

LSBs

WORD 9

227

8
BITS

WORD 10

241

P

271

24 BITS

toe

P

16 BITS

MSBs

LSBs

A - 32 BITS TOTALFIT INTERVAL FLAG - 1 BIT
AODO - 5 BITS

P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 2 of 11)

197

287

t

P

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

3

N/A

WORD 2

1

WORD 3

31
TLM

61
HOW

WORD 4

77

WORD 5

91

121

Cic

C P

t

22 BITSMSB FIRST

3 SECONDS

C is

P

22 BITS

8BITS

16 BITSP

24 BITSP
16 BITSMSBs

150 BITSMSB FIRST

3 SECONDS

WORD 7

WORD 8181

WORD 9211

WORD 10

241

271


3

N/A

24 BITSP

C rc
16 BITS

8BITS

P24 BITSP

24 BITS

MSBs

LSBs

P

i0 - 32 BITS TOTAL

DIRECTION OF DATA FLOW FROM SV

151

8
BITS

LSBs

 - 32 BITS TOTAL
0

WORD 6137

LSBs

 - 32 BITS TOTAL

i 0 - 32 BITS TOTAL

P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 3 of 11)

198

P

IODE
8
BITS

279

IDOT
14
BITS

t

P

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

5

1
THRU
24

MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63

69

HOW

e

C P

t

22 BITS

91

PP

22 BITS

16 BITS

t oa
8
BITS

99

121
i





P

16 BITS

16 BITS

8BITS

PDATA ID - 2 BITS

SV ID - 6 BITS

SV HEALTHDIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7

151

5

1
THRU
24

WORD 8181

A
24 BITS

WORD 9

211


P

0

MSB FIRST

3 SECONDS

241


P

24 BITS

WORD 10P
24 BITS

271

M0

P

290

t P

24 BITS

8 MSBs
af0 - 11 BITS TOTAL
af1 - 11 BITS TOTAL
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVEDNOTE: PAGES 2, 3, 4, 5, 7, 8, 9 & 10 OF SUBFRAME 4 HAVE THE SAME FORMAT AS PAGES 1 THROUGH 24 OF SUBFRAME 5

Figure 40-1. Data Format (sheet 4 of 11)

199

279

3 LSBsIS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31

63

TLM
5

MSB FIRST

3 SECONDS

22 BITS

91

121

SV HEALTHSV HEALTH
toa WNa
6 BITS/SV
6 BITS/SVPPP88SV SV SV SV
SV SV SV SV
BITS BITS
65 66 67 68
69 70 71 72

HOW
C P

25

69

t P
22 BITSDATA ID- 2 BITS

SV (PAGE) ID- 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6151

525

WORD 7181

MSB FIRST

3 SECONDS
WORD 8211

WORD 9241

SV HEALTHSV HEALTHSV HEALTHSV HEALTH
6 BITS/SV
6 BITS/SV
6 BITS/SV
6 BITS/SVPPPPSV SV SV SV
SV SV SV SV
SV SV SV SV
SV SV SV SV
73 74 75 76
77 78 79 80
81 82 83 84
85 86 87 88
6 BITS ***** RESERVED FOR SYSTEM USE*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 5 of 11)

200

WORD 10271 277

16 BITS ** t P

IS-GPS-200L
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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

1, 6, 11,16 & 21MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69

91

121

HOW
C P

t

22 BITS

P

16
BITS***

22 BITSP

24 BITS***P

24 BITS***PDATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

4

1, 6, 11,16 & 21

WORD 8181

24 BITS***P

WORD 9211

24 BITS***MSB FIRST

3 SECONDSP

241

24 BITS***

P

8***
BITS

249

16
BITS***** RESERVED FOR SYSTEM USE*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 6 of 11)

201

WORD 10271

P

22 BITS**tP

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

12, 19, 20,
22, 23 & 24

MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69

91

121

HOW
C P

t

22 BITS

P

16
BITS***

22 BITSP

24 BITS***P

24 BITS***PDATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

412, 19, 20,
22, 23 & 24

WORD 8181

24 BITS***P

WORD 9211

24 BITS***MSB FIRST

3 SECONDSP

24 BITS***

P

241

249

8***
BITS

16 BITS**** RESERVED FOR SYSTEM USE*** RESERVED
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 7 of 11)

202

WORD 10271

P

22 BITS**tP

IS-GPS-200L
14 May 2020

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

18

MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69



0
1
8
8
BITS BITS

HOW
C P

t

22 BITS

77

P

22 BITS

P

91

99

107


2
8
BITS


3
8
BITS


0
8
BITS

121

P

129

137



1
2
8
8
BITS BITS


3
8
BITS

P

DATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7

151

18

WORD 8

181

A
1
4

211

219

24 BITS

8
BITS

t
WN
ot
t
8
8
BITS BITS

MSBs

LSBs

P

24 BITSMSB FIRST

3 SECONDSP

WORD 9

227

241

P

249

257

t
LS
8
8
BITS BITS

DN
8
BITS

WORD 10
271

t
P

279

LSF
8
BITS

14
BITS **WN
LSF

A 0 - 32 BITS TOTAL** RESERVED FOR SYSTEM USE
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 8 of 11)

203

t

P

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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31

63 69

TLM
4

MSB FIRST

3 SECONDS

25t

22 BITS

121
A- SPOOF &SV CONFIG

65 66 67 68

69 70 71 72 73 74

A- SPOOF &SV CONFIG
P SV SV SV SV SV SV P SV SV SV SV SV SV P
SV SV SV SV

HOW
C P

91

A-SPOOF &SV CONFIGP

22 BITS75 76 77 78 79 80

DATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6MSB FIRST

3 SECONDS

WORD 7

WORD 8WORD 9WORD 10

227
151

4

25

181

211

A- SPOOF &SV CONFIG

A- SPOOF &SV CONFIG

A-SPOOF &SV CONFIG

81 82 83 84 85 86

87 88 89 90 91 92

93 94 95 ***P SV SV SV SV SV SV P SV SV SV
SV SV SV SV SV SV*** 2 BITS*** Reserved Bits

229

SV
89

241

271

SV HEALTH
6 BITS/SVP
SV SV SV SV
90 91 92 93

P

SV HEALTH
6 BITS/SV
SV SV
94 95
***

*** 2 BITS

2 BITS **SV HEALTH - 6 BITS** RESERVED FOR SYSTEM USE
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 9 of 11)

204

4 BITS **t P

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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUB
FRAME
NO.

PAGE
NO.

WORD 231
TLM

4

WORD 3

61
1

71

HOW
t

22 BITS

WORD 4

WORD 5

69
63

C P

13

MSB FIRST

3 SECONDSP

22 BITS

91

E
R
D
1

E
R
D
2

E
R
D
3

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

121

E
R
D
3

E
R
D
4

E
R
D
5

E
R
D
6

E
R
D
7

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

E
R
D
7

E
R
D
8

E
R
D
9

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

E
R
D
1
0

E
R
D
1
1

6
B
I
T
S

2
M
S
B
S

P

DATA ID - 2 BITS
SV (PAGE) ID - 6 BITS

AVAILABILITY INDICATOR - 2 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

413

WORD 8

181

E
R
D
1
1

E
R
D
1
2

E
R
D
1
3

E
R
D
1
4

E
R
D
1
5

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

MSB FIRST

3 SECONDS
WORD 9

211

E
R
D
1
5

E
R
D
1
6

E
R
D
1
7

E
R
D
1
8

E
R
D
1
9

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

241

E
R
D
1
9

E
R
D
2
0

E
R
D
2
1

E
R
D
2
2

E
R
D
2
3

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P

271

E
R
D
2
3

E
R
D
2
4

E
R
D
2
5

E
R
D
2
6

E
R
D
2
7

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

2
M
S
B
S

P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 10 of 11)

205

WORD 10

P

E
R
D
2
7

E
R
D
2
8

E
R
D
2
9

E
R
D
3
0

4
L
S
B
S

6
B
I
T
S

6
B
I
T
S

6
B
I
T
S

t

P

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DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 1
SUBFRAME
NO.

PAGE
NO.

4

14, 15& 17**MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

63 69

91

121

HOW
C P

t

22 BITS

P

16
BITS**

22 BITSP

24 BITS**P

24 BITS**PDATA ID - 2 BITS

SV (PAGE) ID - 6 BITS

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

14, 15& 17**

4

WORD 8181

24 BITS**P

WORD 9211

24 BITS**MSB FIRST

3 SECONDSP

WORD 10241

24 BITS**P

271

24 BITS**P

22 BITS**

t

P

**

THE INDICATED PORTIONS OF WORDS 3 THROUGH 10 OF PAGES 14 AND 15 ARE RESERVED FOR SYSTEM USE, WHILE
THOSE OF PAGE 17 ARE RESERVED FOR SPECIAL MESSAGES PER PARAGRAPH 20.3.3.5.1.8
P = 6 PARITY BITS
t = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)
C = TLM BITS 23 AND 24. BIT 23 IS THE INTEGRITY STATUS FLAG AND BIT 24 IS RESERVED

Figure 40-1. Data Format (sheet 11 of 11)

40.3.3 Message Content
The format and contents of the TLM word and the HOW, as well as those of words three throughten of each subframe/page, are described in the following subparagraphs. The timing of thesubframes and pages is covered in Section 40.3.4.

40.3.3.1 Telemetry Word
The TLM word shall be as specified in Appendix II, Section 20.3.3.1.

40.3.3.2 Handover Word (HOW)The HOW shall be as specified in Appendix II, Section 20.3.3.2.

40.3.3.3 Subframe 1
Subframe 1 shall be as specified in Appendix II, Section 20.3.3.3.

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40.3.3.4 Subframes 2 and 3
Subframes 2 and 3 shall be as specified in Appendix II, Section 20.3.3.4.

40.3.3.5 Subframes 4 and 5
Both subframe 4 and 5 are subcommutated 25 times each; the 25 versions of these subframes arereferred to as pages 1 through 25 of each subframe. With the possible exception of "reserved forsystem use" pages and explicit repeats, each page contains different specific data in words three
through ten. As shown in Figure 40-1, the pages of subframe 4 utilize seven different formats,while those of subframe 5 use two. The content of words three through ten of each page is
described below, followed by algorithms and material pertinent to the use of the data.

40.3.3.5.1 Content of Subframes 4 and 5
Words three through ten of each page contain six parity bits as their LSBs; in addition, two noninformation bearing bits are provided as bits 23 and 24 of word ten in each page for parity
computation purposes. The data contained in the remaining bits of words three through ten of thevarious pages in subframes 4 and 5 are described in the following subparagraphs.

A brief summary of the various data contained in each page of subframes 4 and 5 is as follows:

SubframePage(s)Data

4

1, 6, 11, 16 and 21

Reserved

2, 3, 4, 5, 7, 8, and 9

Almanac data for SV ID 89 through 95 (PRN 57 through 63) respectively

10

Reserved

12, 19, 20, 22, 23 and 24

Reserved

13NMCT

14 and 15

Reserved for system use

17

Special messages

18

Ionospheric and UTC data

25

A-S flags/SV configurations for 31 SVs, plus SV health for SV ID 89
through 95 (PRN 57 through 63)

5

1 through 24

Almanac data for SV ID 65 through 88 (PRN 33 through 56)

25

SV health data for SV ID 65 through 88 (PRN 33 through 56), thealmanac reference time, the almanac reference week number

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40.3.3.5.1.1 Data ID and SV ID
The two MSBs of word three in each page shall contain the data ID. Data ID number two (denotedby binary code 01) denotes the LNAV data structure of D(t) which is described in this Appendix
and is the only valid value.
As shown in Table 40-V, the data ID is utilized to provide one of two indications: (a) for thosepages which are assigned to contain the almanac data of one specific SV, the data ID defines thedata structure utilized by that SV whose almanac data are contained in that page; and (b) for allother pages, the data ID denotes the data structure of the transmitting SV.
The six LSBs of the SV ID are given by bits three through eight of word three in each page asshown in Table 40-V. Specific IDs are reserved for each page of subframes 4 and 5. The SV IDs
are utilized in two different ways: (a) for those pages which contain the almanac data of a given
SV, the SV ID is equal to 32 plus the number that is assigned to the PRN code phase of that SV(reference Tables 3-Ia and 3-Ib), and (b) for all other pages the SV ID assigned in accordance with
Table 40-V serves as the "page ID". IDs 65 through 95 are assigned to those pages which containthe almanac data of specific SVs (pages 1-24 of subframe 5 and pages 2-5 and 7-9 of subframe4). The "0" ID (binary all zeros) is assigned to indicate a dummy SV, while IDs 115 through 127
are utilized for pages containing other than almanac data of a specific SV. IDs 116 through 126
have the same data as LNAV-L IDs 52 through 62. ID 115 is the LNAV-U analog of ID 51 in
LNAV-L, while ID 127 is the LNAV-U analog of ID 63 in LNAV-L.
Pages which carry the same SV ID (e.g., in subframe 4, pages 1, 6, 11, 16 and 21 carry an ID of
121, while pages 12 and 24 are designated by an ID of 126) may not be considered to containidentical data. The data in the pages with the same SV ID can be different. Pages 1, 6, 11, 16
and 21 reference Appendix II. Pages 12, 19, 20, 22, 23 and 24 reference Appendix II. Pages 14
and 15: (Reference Appendix II)

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Table 40-V. Data IDs and SV IDs in Subframes 4 and 5

Subframe 4
Page

Data ID

Subframe 5

SV ID*

Data ID(Note 4)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

Note(2)
Note(1)
Note(1)
Note(1)
Note(1)
Note(2)
Note(1)
Note(1)
Note(1)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)
Note(2)

121
89
90
91
92
121
93
94
95
0
121
126
116
117
118
121
119
120
122 Note(3)123 Note(3)121124 Note(3)125 Note(3)126127

SV ID*(Note 4)Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(1)
Note(2)

65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
115

* Use "0" to indicate "dummy" SV. When using "0" to indicate dummy SV, use the data
ID of the transmitting SV.
Note 1:
Data ID of that SV whose SV ID appears in that page.
Note 2:
Data ID of transmitting SV.
Note 3:
SV ID may vary (except for IIR/IIR-M/IIF/GPS III/GPS IIIF SVs).
Note 4:For almanac data pages, the SV ID relationship to PRN ID is defined inTable 3-Ia and Table 3-Ib

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40.3.3.5.1.2 Almanac Data
Pages 1 through 24 of subframe 5, as well as pages 2 through 5 and 7 through 9 of subframe 4
contain the almanac data and a SV health word for up to 31 SVs (the health word is discussed inparagraph 40.3.3.5.1.3). The almanac data are a reduced-precision subset of the clock andephemeris parameters. The data occupy all bits of words three through ten of each page except
the eight MSBs of word three (data ID and SV ID), bits 17 through 24 of word five (SV health), andthe 50 bits devoted to parity. The number of bits, the scale factor (LSB), the range, and the unitsof the almanac parameters are given in Table 20-VI. The algorithms and other material related tothe use of the almanac data are given in paragraph 40.3.3.5.2.
The almanac message for any dummy SVs shall contain alternating ones and zeros with valid
parity.
The almanac parameters shall be updated by the CS at least once every 6 days while the CS isable to upload the SVs. If the CS is unable to upload the SVs, the accuracy of the almanac
parameters transmitted by the SVs will degrade over time.
For Block IIA SVs, three sets of almanac shall be used to span at least 60 days. The first andsecond sets will be transmitted for up to six days each; the third set is intended to be transmitted
for the remainder of the 60 days minimum, but the actual duration of transmission will depend on
the individual SV's capability to retain data in memory. All three sets are based on six-day curvefits that correspond to the first six days of the transmission interval. For Block IIR/IIR-M, IIF, GPS
III, and GPS IIIF SVs, multiple sets of almanac parameters shall be uploaded to span at least 60
days.

40.3.3.5.1.3 SV Health
Subframes 4 and 5 contain two types of SV health data: (a) each of the 31 pages which containthe clock/ephemeris related almanac data provide an eight-bit SV health status word regarding the
SV whose almanac data they carry, and (b) the 25th page of subframe 4 and of subframe 5 jointly
contain six-bit health status data for up to 31 SVs.
The three MSBs of the eight-bit health words indicate health of the LNAV data in accordance withthe code given in Table 20-VII. The six-bit words provide a one-bit summary of the LNAV data's
health status in the MSB position in accordance with paragraph 20.3.3.3.1.4. The five LSBs ofboth the eight-bit and the six-bit words provide the health status of the SV's signal components inaccordance with the code given in Table 20-VIII. A special meaning is assigned, however, to the"6 ones" combination of the six-bit health words in the 25th page of subframes 4 and 5: it indicatesthat "the SV which has that ID is not available and there may be no data regarding that SV in thatpage of subframes 4 and 5 that is assigned to normally contain the almanac data of that SV"(NOTE: this special meaning applies to the 25th page of subframes 4 and 5 only). The healthindication shall be given relative to the "as designed" capabilities of each SV (as designated by theconfiguration code -- see paragraph 40.3.3.5.1.4). Accordingly, any SV which does not have acertain capability will be indicated as "healthy" if the lack of this capability is inherent in its design
or it has been configured into a mode which is normal from a user standpoint and does not requirethat capability.

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Additional SV health data are given in subframe 1. The data given in subframes 1, 4, and 5 of theother SVs may differ from that shown in subframes 4 and/or 5 since the latter may be updated at adifferent time.
The eight-bit health status words shall occupy bits 17 through 24 of word five in those 31 pages
which contain almanac data for individual SVs. The six-bit health status words shall occupy the 24
MSBs of words four through nine in page 25 of subframe 5 plus bits 19 through 24 of word 8, the24 MSBs of word 9, and the 12 MSBs of word 10 in page 25 of subframe 4.
The predicted health data will be updated at the time of upload when a new almanac has been
built by the CS. The transmitted health data may not correspond to the actual health of thetransmitting SV or other SVs in the constellation.

40.3.3.5.1.4 Anti-Spoof (A-S) Flags and SV Configurations
Page 25 of subframe 4 shall contain a four-bit-long term for each of up to 31 SVs to indicate the AS status and the configuration code of each SV transmitting with a PRN number in the range of 33
through 63. The MSB of each four-bit term shall be the A-S flag with a "1" indicating that A-S is
ON. The three LSBs shall indicate the configuration of each SV using the following code:
Code SV Configuration
000
Reserved in order to preserve future use of these values in a future revision of this IS. Until
such a revision, the User Segment developing to this version of this IS should interpret thesevalues as indicating that no information in this data field is presently usable as a means to identify
the actual SV configuration.
001
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2 (e.g. Block II/Block IIA/IIR SV).
010
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2, M-code signal capability, L2C signal capability (e.g., Block IIR-M SV).
011
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2, M-code capability, L2C signal capability, L5 signal capability (e.g., Block IIF SV).
100
A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described inparagraph 20.3.2, M-code capability, L1C signal capability, L2C signal capability, L5 signal
capability, no SA capability (e.g., GPS III SVs).
101, 110, 111 Reserved in order to preserve future use of these values in a future revision ofthis IS. Until such a revision, the User Segment developing to this version of this IS shouldinterpret these values as indicating that no information in this data field is presently usable as ameans to identify the actual SV configuration.
These four-bit terms shall occupy bits 9 through 24 of word three, the 24 MSBs of words four
through seven, and the 12 MSBs of word eight, all in page 25 of subframe 4.

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Since the anti-spoof information is updated by the CS at the time of upload, the anti-spoof data
may not correspond to the actual anti-spoof status of the transmitting SV or other SVs in theconstellation.

40.3.3.5.1.5 Almanac Reference Week
The almanac reference week shall be as specified in Appendix II, paragraph 20.3.3.5.1.5.

40.3.3.5.1.6 Coordinated Universal Time (UTC) Parameters
The UTC parameters shall be as specified in Appendix II, paragraph 20.3.3.5.1.6.

40.3.3.5.1.7 Ionospheric Data.
The ionospheric data shall be as specified in Appendix II, paragraph 20.3.3.5.1.7.

40.3.3.5.1.8 Special Messages
The special messages shall be as specified in Appendix II, paragraph 20.3.3.5.1.8.

40.3.3.5.1.9 NMCT
Page 13 of subframe 4 shall contain the NMCT data appropriate to the transmitting SV. Each
NMCT contains a two-bit availability indicator (AI) followed by 30 slots which may contain up to 30
valid six-bit ERD values. The layout of these 31 data items is as shown in Figure 40-1.
The two-bit AI in bits 9 and 10 of word three of page 13 of subframe 4 provide the user with thefollowing information.

AI

Navigation Message Correction Table Availability

00

The correction table is unencrypted and is available to both precise positioning service users and standard
positioning service users.

01

The correction table is encrypted and is available only to authorized users (normal mode).

10

No correction table available for either precise positioning service users or standard positioning service users.

11

Reserved in order to preserve future use of these values in a future revision of this IS. Until such a revision,
the User Segment developing to this version of this IS should interpret this value as indicating that nocorrection table is available for either precise positioning service users or standard positioning service users,
i.e. until such a revision, the User Segment developing to this version of this IS should interpret this value asfunctionally equivalent to an AI setting of 10.

Each one of the 30 six-bit ERD slots in bits 11 through 24 of word three, bits 1 through 24 of words
four through nine, and bits 1 through 22 of word ten of page 13 of subframe 4 will correspond to an
ERD value for a particular SV ID. There are 31 possible SV IDs that these ERD slots may
correspond to, ranging from SV ID 65 to SV ID 95. The correspondence between the 30 ERD
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IS-GPS-200L
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slots and the 31 possible SV IDs depends on the SV ID of the particular transmitting SV inaccordance with the following two rules: 1) the CS shall ensure via upload that no SV shall transmit
an NMCT containing an ERD value which applies to its own SV ID, and 2) the CS shall ensure via
upload that all ERD values shall be transmitted in ascending numerical slot order of thecorresponding SV ID. To illustrate: the SV operating as SV ID 65 will transmit (in order) ERD
values which correspond to SV ID 66 through SV ID 95 in ERD slots 1 through 30 respectively,
while the SV operating as SV ID 95 will transmit ERD values which correspond to SV ID 65
through SV ID 94 in ERD slots 1 through 30 respectively.
Each ERD value contained in an NMCT ERD slot shall be represented as a six-bit two’s
complement field with the sign bit occupying the MSB and an LSB of 0.3 meters for a valid range
of ±9.3 m. A binary value of “100000” shall indicate that no valid ERD for the corresponding SV ID
is present in that slot.

40.3.3.5.2 Algorithms Related to Subframe 4 and 5 Data
The algorithms related to subframe 4 and 5 data shall be as specified in ppendix II, Section
20.3.3.5.2.

40.3.4 Timing Relationships
The timing relationships shall be as specified in Appendix II, Section 20.3.4.

40.3.5 Data Frame Parity
The data frame parity shall be as specified in Appendix II, Section 20.3.5.

213