REVISION RECORDREVDESCRIPTIONDOCUMENTDATEAPPROVED

NC

Initial Release

25 Jan 1983

A

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

25 Sep 1984

B

Incorporates IRN-200A-001A

30 Nov 1987

C

Incorporates IRN-200B-001 thru IRN-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

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 L2 C signal, and otheradditional updates

7 Dec 2004

23 Nov 2004

Adds additional PRN sequences to Section 6

7 Mar 2006

9 Mar 2006

E

GPS IIIA Incorporations

8 Jun 2010

8 June 2010

N/A

SE&I Tech Pubs

29 July 2010F

IRN-IS-200E-001 (RFC 16B - Pseudorandom Noise(PRN) Expansion

21 Sep 2011

5 Mar 2012

IRN-IS-200F-001

21 Sep 201117 Apr 2012

IRN-IS-200F-002 (RFC 139B – Public Signals-inSpace Updates

5 Sep 201231 Jan 2013

D

IRN200D-001

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)

GiIS-GPS-200H
24 Sep 2013

Revision Record, Continued
REV

DESCRIPTIONDOCUMENTDATEAPPROVEDH

IRN-IS-200G-001 (L1C Data Predict Week Number(WNop)

24 Sep 2013

21 Mar 2014

IRN-IS-200G-002 (Public
Requirements Disconnects)

Signalsin

Space

IRN-IS-200G-003 (CNAV Reference Times)
IRN-IS-200G-004
Assignments)(PRNs

211-1023

23 Jan 2014
MissionIRN-IS-200G-005 (Clarification of CNAV Broadcast
Intervals)

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TABLE OF CONTENTS
1

2

3

INTRODUCTION .................................................................................................................. 1
1.1

Scope. ............................................................................................................................... 1

1.2

IS Approval and Changes................................................................................................. 1

APPLICABLE DOCUMENTS .............................................................................................. 1
2.1

Government Documents................................................................................................... 1

2.2

Non-Government Documents. ......................................................................................... 2

REQUIREMENTS .................................................................................................................. 2
3.1

Interface Definition. ......................................................................................................... 2

3.2

Interface Identification. .................................................................................................... 2

3.2.1

Ranging Codes. ......................................................................................................... 3

3.2.2

NAV Data. .............................................................................................................. 12

3.2.3

L1/L2 Signal Structure. ........................................................................................... 12

3.3Interface Criteria. ........................................................................................................... 13

3.3.1

Composite Signal. ................................................................................................... 13

3.3.2

PRN Code Characteristics....................................................................................... 19

3.3.3

Navigation Data. ..................................................................................................... 39

3.3.4

GPS Time and SV Z-Count. ................................................................................... 40

4

NOT APPLICABLE ............................................................................................................. 43

5

NOT APPLICABLE ............................................................................................................. 44

6

NOTES .................................................................................................................................. 45
6.1

Acronyms ....................................................................................................................... 45

6.2

Definitions ...................................................................................................................... 48

6.2.1

User Range Accuracy. ............................................................................................ 48

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6.2.2

SV Block Definitions. ............................................................................................. 49

6.2.3

Operational Interval Definitions. ............................................................................ 50

6.2.4

GPS Week Number. ................................................................................................ 50

6.2.5

L5 Civil Signal. ....................................................................................................... 50

6.3

6.3.1

Received Signals. .................................................................................................... 51

6.3.2

Extended Navigation Mode (Block II/IIA). ............................................................ 52

6.3.3

Block IIA Mode (Block IIR/IIR-M) and Extended Navigation Mode (Block II-F). ..
................................................................................................................................. 53

6.3.4

Extended Navigation Mode (GPS III). ................................................................... 54

6.3.5

Autonomous Navigation Mode. .............................................................................. 54

6.3.6

Additional PRN Code Sequences. .......................................................................... 55

6.3.7

Pre-Operational Use. ............................................................................................... 63

6.4

10

Supporting Material........................................................................................................ 51

Operational Protocols. .................................................................................................... 63

6.4.1

Lower PRN Numbers Versus Upper PRN Numbers. ............................................. 63

6.4.2

PRN Number Consistency. ..................................................................................... 64

6.4.3

PRNs 33 and 37. ..................................................................................................... 64

6.4.4

PRNs 33 through 63. ............................................................................................... 64

6.4.5

Health Code Setting of ‘11110’. ............................................................................. 64

APPENDIX I. LETTERS OF EXCEPTION ....................................................................... 65
10.1

Scope. ......................................................................................................................... 65

10.2

Applicable Documents. .............................................................................................. 65

10.3

Letters of Exception.................................................................................................... 65

20 APPENDIX II. GPS NAVIGATION DATA STRUCTURE FOR LNAV DATA, D(t), FOR
PRN 1-32 ...................................................................................................................................... 74
20.1

Scope. ......................................................................................................................... 74

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20.2
20.2.1Government Documents. ........................................................................................ 74

20.2.2

Non-Government Documents. ................................................................................ 74

20.3

30

Applicable Documents. .............................................................................................. 74

Requirements. ............................................................................................................. 75

20.3.1

Data Characteristics. ............................................................................................... 75

20.3.2Message Structure. .................................................................................................. 75

20.3.3Message Content. .................................................................................................... 87

20.3.4

Timing Relationships. ........................................................................................... 130

20.3.5

Data Frame Parity. ................................................................................................ 136

APPENDIX III. GPS NAVIGATION DATA STRUCTURE FOR CNAV DATA, DC(t) 139
30.1

Scope. ....................................................................................................................... 139

30.2

Applicable Documents. ............................................................................................ 139

30.2.1Government Documents. ...................................................................................... 139

30.2.2

Non-Government Documents. .............................................................................. 139

30.3

Requirements. ........................................................................................................... 139

30.3.1

Data Characteristics. ............................................................................................. 139

30.3.2Message Structure. ................................................................................................ 140

30.3.3Message Content. .................................................................................................. 140

30.3.4

Timing Relationships. ........................................................................................... 189

30.3.5

Data Frame Parity. ................................................................................................ 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 ............................................................................................................ 195v

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40.3.1

Data Characteristics .............................................................................................. 195

40.3.2Message Structure ................................................................................................. 195

40.3.3Message Content. .................................................................................................. 207

40.3.4

Timing Relationships. ........................................................................................... 213

40.3.5

Data Frame Parity. ................................................................................................ 213

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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 ........................................................ 24

Figure 3-4.

X2A Shift Register Generator Configuration........................................................ 25

Figure 3-5.

X2B Shift Register Generator Configuration ....................................................... 26

Figure 3-6.

P-Code Generation ................................................................................................ 28

Figure 3-7.

P-Code Signal Component Timing ....................................................................... 29

Figure 3-8.

G1 Shift Register Generator Configuration .......................................................... 32

Figure 3-9.

G2 Shift Register Generator Configuration .......................................................... 33

Figure 3-10:

Example C/A-Code Generation ............................................................................ 34

Figure 3-11.

C/A-Code Timing Relationships........................................................................... 35

Figure 3-12.

L2 CM-/L2 CL-Code Timing Relationships......................................................... 37

Figure 3-13.

L2 CM/L2 CL Shift Register Generator Configuration ........................................ 38

Figure 3-14.

Convolutional Encoder ......................................................................................... 40

Figure 3-15.

Convolutional transmit/Decoding Timing Relationships ..................................... 40

Figure 3-16.

Time Line Relationship of HOW Message ........................................................... 42

Figure 6-1.

User Received Minimum Signal Level Variations (Example, Block II/IIA/IIR) 52

Figure 10.3-1. Letters of Exception. ............................................................................................ 66
Figure 10.3-2. Letters of Exception (continued) .......................................................................... 67
Figure 10.3-3. Letters of Exception (continued) .......................................................................... 68
Figure 10.3-4. Letters of Exception (continued). ......................................................................... 69
Figure 10.3-5. Letters of Exception (continued) .......................................................................... 70
Figure 10.3-6. Letters of Exception (continued). ......................................................................... 71
Figure 10.3-7. Letters of Exception (continued). ......................................................................... 72

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Figure 10.3-8. Letters of Exception (continued). ......................................................................... 73
Figure 20-1.

Data Format (sheet 1 of 11)................................................................................. 76

Figure 20-1.

Data Format (sheet 2 of 11)................................................................................. 77

Figure 20-1.

Data Format (sheet 3 of 11)................................................................................. 78

Figure 20-1.

Data Format (sheet 4 of 11)................................................................................. 79

Figure 20-1.

Data Format (sheet 5 of 11)................................................................................. 80

Figure 20-1.

Data Format (sheet 6 of 11)................................................................................. 81

Figure 20-1.

Data Format (sheet 7 of 11)................................................................................. 82

Figure 20-1.

Data Format (sheet 8 of 11)................................................................................. 83

Figure 20-1.

Data Format (sheet 9 of 11)................................................................................. 84

Figure 20-1.

Data Format (sheet 10 of 11)............................................................................... 85

Figure 20-1.

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

Figure 20-2.

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

Figure 20-3.

Sample Application of Correction Parameters .................................................. 100

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 ................ 138

Figure 30-1.

Message Type 10 - Ephemeris 1 ....................................................................... 141

Figure 30-2.

Message Type 11 - Ephemeris 2 ....................................................................... 142

Figure 30-3.

Message Type 30 - Clock, IONO & Group Delay ............................................ 143

Figure 30-4.

Message Type 31 - Clock & Reduced Almanac ............................................... 144

Figure 30-5.

Message Type 32 - Clock & EOP ..................................................................... 145

Figure 30-6.

Message Type 33 - Clock & UTC ..................................................................... 146

Figure 30-7.

Message Type 34 - Clock & Differential Correction ........................................ 147

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Figure 30-8.

Message Type 35 - Clock & GGTO ................................................................. 148

Figure 30-9.

Message Type 36 - Clock & Text ..................................................................... 149

Figure 30-10. Message Type 37 - Clock & Midi Almanac ..................................................... 150
Figure 30-11. Message Type 12 - Reduced Almanac .............................................................. 151
Figure 30-12. Message Type 13 - Clock Differential Correction ............................................ 152
Figure 30-13. Message Type 14 - Ephemeris Differential Correction .................................... 153
Figure 30-14. Message Type 15 – Text ................................................................................... 154
Figure 30-15. Reduced Almanac Packet Content .................................................................... 177
Figure 30-16. Differential Correction Data Packet .................................................................. 183
Figure 40-1.

Data Format (sheet 1 of 11) .............................................................................. 196

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

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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 (III 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 (III 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) .. 16

Table 3-Va.

Received Minimum RF Signal Strength for Block IIA, IIR, IIR-M, IIF and
IIISatellites (20.46 MHz Bandwidth) ................................................................. 17

Table 3-Vb.

Received Minimum RF Signal Strength for GPS III (30.69 MHz Bandwidth) .. 17

Table 3-Vc.

Space Service Volume (SSV) Received Minimum RF Signal Strength for GPS
III and Subsequent Satellites over the Bandwidth Specified in 3.3.1.1–GEO
Based Antennas ................................................................................................... 18

Table 3-VII.

Final Code Vector States ..................................................................................... 31

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 1 of 5) ............................... 57

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 2 of 5) ............................... 58

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 3 of 5) ............................... 59

Table 6-I

Additional C/A-/P-Code Phase Assignments (sheet 4 of 5) ............................... 60

Table 6-I.

Additional C/A-/P-Code Phase Assignments (sheet 5 of 5) ............................... 61

Table 6-II.

Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 1 of 2) ................. 62

Table 6-II.

Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 2 of 2) ................. 63

Table 20-I.

Subframe 1 Parameters ........................................................................................ 95

Table 20-II.

Ephemeris Data Definitions .............................................................................. 102

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Table 20-III.

Ephemeris Parameters ....................................................................................... 103

Table 20-IV.

Elements of Coordinate Systems (sheet 1 of 2) ................................................ 104

Table 20-IV.

Elements of Coordinate Systems (sheet 2 of 2) ................................................ 105

Table 20-V.

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

Table 20-VI.

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

Table 20-VII. NAV 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) .......... 133
Table 20-XIII. Reference Times ................................................................................................ 136
Table 20-XIV. Parity Encoding Equations ................................................................................ 137
Table 30-I.

Message Types 10 and 11 Parameters (1 of 2) ................................................. 161

Table 30-I.

Message Types 10 and 11 Parameters (2 of 2) ................................................. 162

Table 30-II.

Elements of Coordinate System (part 1 of 2) ................................................... 163

Table 30-II.

Elements of Coordinate System (part 2 of 2) ................................................... 164

Table 30-III.

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

Table 30-IV.

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

Table 30-V.

Midi Almanac Parameters ................................................................................. 176

Table 30-VI.

Reduced Almanac Parameters ***** ................................................................ 177

Table 30-VII. Earth Orientation Parameters ............................................................................ 179
Table 30-VIII. Application of EOP Parameters ........................................................................ 180
Table 30-IX.

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

Table 30-X.

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

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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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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 andpublic 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
participating organization 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 the change paper as a Proposed Interface Revision Notice (PIRN) and is
responsible for coordination of 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 besubmitted to the ICC for consideration.

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.

1IS-GPS-200H
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Specifications
FederalNone

Military

None

Other Government Activity

NoneStandards
FederalNone

Military

None

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

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
normally is a composite generated by the modulo-2 addition of a pseudo-random noise (PRN)
ranging code and the downlink system data (referred to as NAV data).

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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 (AS) mode of operation 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-divisionmultiple-access techniques 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 anomalousnavigation signals. These two "incorrect" codes are termed non-standard C/A (NSC) and nonstandard 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 to protect 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 a chipping rate of 10.23 Mbps. The 7 day sequence is the modulo-2 sum of two sub-sequencesreferred 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
by SVs.)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.
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Additional PRN P-code sequences with assigned PRN numbers are provided in Section 6.3.6,
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 achipping 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, the G2i sequence is a G2 sequence selectively delayed by pre-assigned number ofchips, 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
accomplished by using the “Initial G2 Setting” as the initialization vector for the G2 shift registerof 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 6.3.6.1, 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
the X1 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 initialstates by SV ID number in Table 3-IIb. Additional PRN L2 CM-code sequence pairs areprovided in Section 6.3.6.3, Table 6-II.

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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 inlength 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 thesame code generator polynomial as the one used for CM,i(t). However, the CLi(t) sequence isshort cycled by resetting with a specified initial state every code count of 767250 chips.
Assignment of initial states by GPS PRN signal number is given in Table 3-IIa.
3.2.1.5.1 Expanded L2 CL-Code (GPS III and subsequent blocks).
An expanded set of 26 L2 CL-Code PRN sequences are identified with assignment of initialstates by SV ID number in Table 3-IIb. Additional PRN L2 CL-code sequence pairs areprovided in Section 6.3.6.3, Table 6-II.

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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

*

***

Table 3-Ia. Code Phase Assignments (sheet 1 of 2)
Code DelayFirst
Code Phase Selection
Chips
10 Chips
C/A(G2i)***
(X2i)
C/A
P
Octal*
C/A
2
3
4
5
1
2
1
2
3
2
3
5
6
7
8
9
1
2
3

⊕ 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

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

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

First
12 Chips
Octal
P
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).
**
C/A Codes for 34 and 37 are identical.
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

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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**

*

****

Table 3-Ia. Code Phase Assignments (sheet 2 of 2)
Code DelayFirst
Code Phase Selection
Chips
10 Chips
Octal*
C/A(G2i)****
(X2i)
C/A
P
C/A
4
5
6
1
4
5
6
7
8
1
2
3
4
5
4
1
2
4

⊕ 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

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

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

First
12 Chips
Octal
P
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 37are 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

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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

Table 3-Ib. Expanded Code Phase Assignments (III and subsequent blocks only)
Code Phase Selection
P-code
First
First
GPS
Relative
PRN
10 Chips
12 Chips
G2
Initial G2
X2
Advance
SignalDelay
Setting
Delay
Octal*
Octal(Hours) **No.
(Chips)(Octal)*(Chips)
C/A
P
38
67
0017
1
P1(t+24)
1760
3373
39
103
0541
2
P2(t+24)
1236
3757
40
91
1714
3
P3(t+24)0063
7545
P4(t+24)
41
19
1151
4
0626
5440
P5(t+24)
42
679
1651
5
0126
4402
P6(t+24)
43
225
0103
6
1674
4023
P7(t+24)
44
625
0543
7
1234
0233
P8(t+24)
45
946
1506
8
0271
2337
P9(t+24)
46
638
1065
9
0712
3375
P10(t+24)
47
161
1564
10
0213
3754
P11(t+24)
48
1001
1365
11
0412
3544
P12(t+24)
49
554
1541
12
0236
7440
P13(t-24)
50
280
1327
13
0450
1402
P14(t+24)
51
710
1716
14
0061
6423
P15(t+24)
52
709
1635
15
0142
1033
P16(t+-24)
53
775
1002
16
0775
2637
P17(t+24)
54
864
1015
17
0762
7135
P18(t+24)
55
558
1666
18
0111
5674
P19(t+24)
56
220
0177
19
1600
0514
P20(t+24)
57
397
1353
20
0424
6064
P21(t+24)
58
55
0426
21
1351
1210
P22(t+24)
59
898
0227
22
1550
6726
P23(t+24)
60
759
0506
23
1271
1171
P24(t+24)
61
367
0336
24
1441
6656
P25(t+24)
62
299
1333
25
0444
1105
63
1018
1745
26
P26(t+24)
0032
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

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SV
ID
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

Table 3-IIa. Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 1 of 2)
GPS
Initial Shift Register State (Octal)
End Shift Register State (Octal)
PRN
L2 CM
L2 CL
L2 CM *
L2 CL **
Signal
No.
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

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

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

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 future.

9

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Table 3-IIa. Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 2 of 2)
GPS
Initial Shift Register State (Octal)
End Shift Register State (Octal)
PRN
L2 CM
L2 CL
L2 CM *
L2 CL **
SignalNo.
2020120161274
266527765
365636111
641733155
2121044023533
006760703
143324657
730125345
22
22724744327
501474556
110766462
000316074
23
23045743577
743747443
602405203
171313614
24
24741201660
615534726
177735650
001523662
25
25
700274134
763621420
630177560
023457250
26
26010247261
720727474
653467107
330733254
27
27713433445
700521043
406576630
625055726
28
28
737324162
222567263
221777100
476524061
29
29311627434
132765304
773266673
602066031
30
30710452007
746332245
100010710
012412526
31
31722462133
102300466
431037132
705144501
32
32050172213
255231716
624127475
615373171
65
33500653703
437661701
154624012
041637664
66
34
755077436
717047302
275636742
100107264
6735136717361
222614207
644341556
634251723
68
36
756675453
561123307
514260662
257012032
6937435506112
240713073
133501670
703702423

SV
ID
No.

* 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 future.

10

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SV
ID
No.

Table 3-IIb.
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

Expanded Code Phase Assignments (III and subsequent blocks only)
Initial Shift Register State (Octal)
End Shift Register State (Octal)
L2 CM
L2 CL
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***

101232630
132525726
315216367
377046065
655351360
435776513
744242321
024346717
562646415
731455342
723352536
000013134
011566642
475432222
463506741
617127534
026050332
733774235
751477772
417631550
052247456
560404163
417751005
004302173
715005045
001154457

453413162
637760505
612775765
136315217
264252240
113027466
774524245
161633757
603442167
213146546
721323277
207073253
130632332
606370621
330610170
744312067
154235152
525024652
535207413
655375733
316666241
525453337
114323414
755234667
526032633
602375063

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

Short cycled period = 10230
Short cycled period = 767250.

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

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.

11

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3.2.2 NAV Data.
The NAV 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)- and C/A- codeson both the L1 and L2 channels. The content and characteristics of the NAV data, D(t), aregiven in Appendix II of this document for legacy NAV (LNAV) data transmitted by SVs
assigned to the lower set of PRN numbers (PRN 1-32) and Appendix IV of this document for
LNAV data transmitted 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, DC(t),also includes SV ephemerides, system time, SV clock behavior, status messages, etc. The DC(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 isused to modulate the L2 carrier. The content and characteristics of the CNAV data, DC(t), aregiven 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 NAV data, D(t), while the other is the modulo-2 sumof the C/A-code and the NAV 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 byground command. A third modulation mode is also selectable on the L2 channel by groundcommand: it utilizes the P(Y)-code without the NAV data as the modulating signal. For aparticular SV, all transmitted signal elements (carriers, codes and data) are coherently derived
from the same on-board 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 NAV 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 ofDC(t) is 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.
During the initial period of Block IIR-M SVs operation, prior to Initial Operational Capability of
L2 C signal, Block IIR-M may modulo-2 add the NAV data, D(t), to the L2 CM-code instead of
12

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24 Sep 2013

CNAV data, DC(t). In such configuration, the data rate of D(t) may be 50 bps (i.e. without
convolution encoding) or it may be 25 bps. The D(t) of 25 bps shall be convolutionally encoded
resulting in 50 sps.
The different configurations and combinations of codes/signals specified in this section are
shown in 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

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) = NAV 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
for the 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
the signal contained within two 20.46 MHz bands; one centered about the L1 nominal frequency
and the other centered about the L2 nominal frequency (see Table 3-Vb). For GPS III 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 other13

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centered about the L2 nominal frequency (see Table 3-Vc). The carrier frequencies for the L1
and L2 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 = 4.4647E-10, 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 (f0)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 recoveredin 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)

(III 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.
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 Pi(t) equals one, a 180-degree phasereversal of the P-carrier occurs; when Gi(t) equals one, the C/A carrier advances 90 degrees;
14

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when the Gi(t) equals zero, the C/A carrier shall be retarded 90 degrees (such that when Gi(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 beeither in phase quadrature or in the same phase (within ±100 milliradians) - see paragraph3.3.1.5.3 for additional information. The civil signal carrier component is modulated by any oneof 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 as well 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 in composite transmitted signal phase relationships other than the nominal special caseof Table 3-IV. 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 indicates that L2C and L2P(Y) are in-phase. If the CNAV message is not available, thenthe 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 indicatesthat 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 caused by signal modulation. Prior to health data being available on L2C,
satellites will be set unhealthy using the non-standard code.
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 thustransparent to the user segment. The minimum received power is measured at the output of a 3
dBi linearly polarized 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 offaxis relative power (referenced to peak transmitted power) shall not decrease by more than 2 dB
15

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from the 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 notdecrease by 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 monotonicallydecreasing fashion.
The GPS III SV shall provide L1 and L2 signals with the following characteristic: the L1 offaxis relative power (referenced to peak transmitted power) shall not decrease by more than 2 dBfrom the Edge-of-Earth (EOE) to nadir; the L2 off-axis power gain shall not decrease by morethan 2 dB from EOE to nadir; the power drop off between EOE and ±26 degrees shall be in amonotonically decreasing fashion. Additional related data is provided as supporting material inparagraph 6.3.1.
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.

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

ChannelP(Y)C/A or L2 C

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

III

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

ChannelP(Y)C/A or L2 C

L1-161.5 dBW-158.5 dBW

L2-161.5 dBW-158.5 dBW

III

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, inorder to meet the minimum levels specified in Table 3-Vc. The minimum received power ismeasured 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 are observed within the in-band allocation defined in paragraph. 3.3.1.1.

17IS-GPS-200H
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Table 3-Vc. Space Service Volume (SSV) Received Minimum RF Signal Strength for GPS III 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 L2 C

* 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; 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 NAV 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 meandifferential is defined 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 thetemperature and antenna effects during a vehicle orbital revolution. Corrections for the bias
components of the group delay differential are provided to the US in the NAV/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.

18

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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
no worse than 1.8 dB for Block IIR/IIR-M/IIF/GPS III SVs. L2 ellipticity shall be no worse than
3.2 dB for Block II/IIA SVs and shall be no worse than 2.2 dB for Block IIR/IIR-M/IIF and GPS
III 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 Pi(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 NAV bit train, D(t), which is clocked at 50 bps. The resultant composite bit trains arethen used to modulate 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 summationof 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.
19

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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 24 hours
after beginning of week). The list of expanded P-code PRN assignments is identified in Table 3Ib.
The linear Gi(t) pattern (C/A-code) is the modulo-2 sum of two 1023-bit linear patterns, G1 andG2i. The latter sequence is selectively delayed by an integer number of chips to produce manydifferent G(t) patterns (defined in Tables 3-Ia and 3-Ib).
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 CM,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 CL,i(t) patterns (defined in Tables 3IIa and 3-IIb).
For a given SV ID, two different initial states are used to generate different CL,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.

20

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EPOCH
DETECT

X1 EPOCH

EPOCH
RESET

20

50 Hz

Z-COUNT
1 KHz

ZCOUNTER

1.023
MHz

X1
GENERATOR

10GOLD 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

Figure 3-1.

CODE
SELECT
DEVICE

X2
GENERATOR

10.23 MHzFREQUENCY
SOURCED(t)DATA
ENCODER

Pi(t)

D(t)

Pi(t)

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

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 arecounted to 3750, the X1 epoch is generated. The X1 epoch occurs every 1.5 seconds after
15,345,000 chips of the X1 pattern have been generated. The polynomials for X1A and X1B, as
referenced to the shift 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, (b) the stage 12 value appears at the left followed by the values of the21

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24 Sep 2013

remaining states in order of descending stage numbers, and (c) the shift 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 thefirst 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 registercompletes its 3750th cycle (343 additional chips). The completion of the 3750th X1A cycle
establishes the next X1 epoch which re-initializes both the X1A and X1B shift registers starting a
new X1 cycle.

22

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POLYNOMIAL X1A:
1 + X 6 + X 8 + X 11 + X 12

STAGE
NUMBERS

0

1

2

3

4

5

6

7

8

9

10

11

12

0

0

0

1

0

0

1

0

0

1

0

0

1

2

3

4

5

6

7

INITIAL
CONDITIONS

8

9

10

11

OUTPUT

12

TAP
NUMBERSSHIFT DIRECTION

Figure 3-2.

X1A Shift Register Generator Configuration

23

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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

INITIAL
CONDITIONS

7

8

9

10

11

OUTPUT

12

TAP
NUMBERSSHIFT DIRECTION

Figure 3-3.

X1B Shift Register Generator Configuration

24

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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

0

1

2

3

4

5

6

7

8

9

10

11

12

1

0

1

0

0

1

0

0

1

0

0

1

1

2

3

4

5

6

7

INITIAL
CONDITIONS

8

9

10

11

OUTPUT

12

TAP
NUMBERSSHIFT DIRECTION

Figure 3-4.

X2A Shift Register Generator Configuration25

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24 Sep 2013

POLYNOMIAL X2B:
2
3
4
8
9
12
1+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

INITIAL
CONDITIONS

7

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 X2i sequences is thenmodulo-2 added to the X1 sequence thereby producing up to 37 unique P(t) sequences.
The X2A and X2B shift registers, used to generate X2, operate in a similar manner to the X1A
and X1B shift registers. They are short-cycled, X2A to 4092 and X2B to 4093, so that they havethe same 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 laststate of 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.

26

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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 andprovide 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. 37 unique P(t) code phases. Signal component timing for these original P(t) code phases isshown in Figure 3-7, while the end-of-week reset timing and the final code vector states are
given in Tables 3-VI and 3-VII, respectively.

27

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10.23 MHz

X1
EPOCH

SET X1A EPOCH

C

R

I

REGISTER
6
12

1

A

4092
DECODE

6, 8, 11, 12

3750

RESUME

CLOCK
CONTROL

HALT

Z-COUNTER
403,200

CI
1

SET X1B
EPOCH

R

X1B
REGISTER

3749

B

12

7 DAY
RESET

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

REGISTERINPUTS

END/WEEK

CLOCK
CONTROL

HALT

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

3750
C
I
1

SET X2A
EPOCH

R

X2A
REGISTER

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

CLOCK
CONTROLCI

X2B
REGISTER
1 2
12

R

X2 i
SET X2B
EPOCH

3749

1
i

C

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

X2

SHIFT
REGISTER

P-Code Generation

28

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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

29

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Table 3-VI. P-Code Reset Timing(Last 400 µsec of 7-day period) **Code Chip
X1A-Code

X1B-Code

X2A-Code

X2B-Code

1

345

1070

967

•

•

•

•

•

•

•

•

•

•

•

•

3023

3367

•

•

•

•

•

•

•

•

•

•

•

•

3127

3471

4092

•

•

•

•

•

•

•

•

•

•

•

•

4092

4093

3749

4093

4092

3989

4093

•

•

•

•

•

•

•

•

•

•

•

•

4093

4092

4093

4092*

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

30

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Table 3-VII.
Code
X1A
X1B
X2A
X2B

Final Code Vector States

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.

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 (seeFigures 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 310). However, this two-tap coder implementation generates only a limited set of valid C/Acodes. Table 3-I contains a tabulation of the G2 shift register taps selected and theircorresponding P-code X2i and PRN signal numbers together with the first several chips of eachresultant PRN code. Timing relationships related to the C/A code are shown in Figure 3-11.

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POLYNOMIAL G1:
1 + X 3 + 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

OUTPUT

10

TAP
NUMBERSSHIFT DIRECTION

Figure 3-8.

G1 Shift Register Generator Configuration

32

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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

OUTPUT

10

TAP
NUMBERSSHIFT DIRECTION

Figure 3-9.

G2 Shift Register Generator Configuration

33

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3

10

X1 EPOCH
I
S
C

10.23 MHzG1

G1
REGISTER

SYNCH
10
2

I
C
S

SYNCH

20

3

G EPOCH
1 Kbps

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

Figure 3-10: Example C/A-Code Generation
Valid for C/A PRNs 1-37. For PRNs 38-63, the G1 Register should be XOR-ed directly to the G2 Register in orderto make Gi. These PRNs do not use the Phase Select Logic box for G2i generation.

34

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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

35

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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 a
specified initial state (defined in Table 3-II). CM,i(t) pattern is reset after 10230 chips resulting ina code 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 modulartype shift register generator.

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0

1
End/start ofweek

1.5 second

X1 Epoch @ 2/3
bps
767250767250 BIT L2 CL- Code @ 511.5 Chips
Kbps
4
73
1
2
3
74
10230
10230
10230 10230 10230 10230
10230 BIT L2 CM-Code@ 511.5
Kbps

etc.
75
10230

etc.

20
msec

Data @ 50
cps

L2 CM @ 511.5
Kbps

L2 CL @ 511.5
Kbps

L2 C @ 1023
Kbps
Figure 3-12.

L2 CM-/L2 CL-Code Timing Relationships

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Figure 3-13.

L2 CM/L2 CL Shift Register Generator Configuration

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3
2

3

3

2

4

5

6

9

11

13

16

19

21

24

27

2

3

SHIFT DIRECTION

1

1

1

3

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

3

POLYNOMIAL:

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

3

DELAY
NUMBERSOUTPUT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, DC(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 1/2
convolutional code. For Block IIR-M, the NAV bit train, D(t), can be selected to be
convolutionally encoded. 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 is selected 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 acontinuous process independent of message boundaries (i.e. at the beginning of each newmessage, the encoder 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 symbolthat 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), for which they must compensate to determine system time from the received signal.
This convolutional decoding delay and the various relationships with the start of the data blocktransmission and SV time are illustrated in Figure 3-15.

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G2 (133 OCTAL)OUTPUT SYMBOLS(50 SPS)DATA INPUT(25 BPS)(ALTERNATING G1/G2)

G1 (171 OCTAL)

Figure 3-14.

SYMBOL
CLOCK

Convolutional Encoder

ENCODED DATA BLOCKENCODEDDATA BLOCKDATA BLOCKDECODED BY
USER’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 in stating 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 correctedperiodically with an integer number of leap seconds. There also is an inherent but bounded drift

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rate between the UTC and GPS time scales. The OCS shall control the GPS time scale to bewithin one microsecond of UTC (modulo one second).
The NAV data contains the requisite data for relating GPS time to UTC. The accuracy of thisdata during the transmission interval shall be such that it relates GPS time (maintained by the
MCS of the CS) to UTC (USNO) within 90 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 forusers. Range error components (e.g. SV clock and position) contribute to the GPS time transfer
error, and under normal operating circumstances (two frequency time transfers from SV(s)whose navigation message indicates a URA of eight meters or less), this corresponds to a 97
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:a.
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) andis reset 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 occurrenceof the "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
such correction. To aid rapid ground lock-on to the P-code signal, a truncated version of the
TOW-count, consisting of its 17 most significant bits, is contained in the hand-over word (HOW)of the L1 and L2 NAV 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 thesequential number assigned to the current GPS week (see paragraph 6.2.4).

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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

100,799

0

1

2

3

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

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4 NOT APPLICABLE

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5 NOT APPLICABLE

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6 NOTES
6.1

Acronyms

AI-

Availability Indicator

AODO

-

Age of Data Offset

A-S-

Anti-Spoofing

Autonav-

Autonomous Navigation

BPSK

-

Bi-Phase Shift Key

CDC-

Clock Differential Correction

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, expressed in 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

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GNSS

-

Global Navigation Satellite System

GPS-

Global Positioning System

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

LSB-

Least Significant Bit

LSF-

Leap Seconds Future

L2 C

-

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

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OBCP

-

On-Board Computer Program

OCS-

Operational Control System

PPS-

Precise Positioning Service

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-

Week Number

WNe-

Extended Week Number

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6.2

Definitions

6.2.1 User Range Accuracy.
User Range Accuracy (URA) is a statistical indicator of the GPS ranging accuracy obtainablewith a 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 forwhich the Space 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 of integrity assurance). When the integrity status flag is 'on', 5.73 times URA
bounds the instantaneous 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 (multipliedby either 4.42 or 5.73 as appropriate) upper bound values of the URA index or to the scaled
composite of the upper bound values of all component URA indexes.
Note #1: URA applies over the transmission interval that is applicable to the NAV data fromwhich 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 NAV data
or by a composite of more than one index representing components of the total URA. Specific
URA indexes and formulae for calculating the total URA for each signal are defined in appendix
20 for the LNAV message and appendix 30 for the CNAV message.
Note #3: The URA is not required to bound the instantaneous URE when: (a) an alert is issued
to the 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 thiscontext, 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.
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 differentialuser range errors in the navigation data for that satellite. It includes all errors for which theSpace and Control Segments are responsible.

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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
and GPS III SVs. Characteristics of these SVs are provided below. Modes of operation for theseSVs and accuracy of positioning services provided are described in paragraphs 6.3.2 through6.3.4. 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 designatedas 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 aredesignated as 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, toprovide positioning service without contact from the CS for that period. (Contractual
requirements for these SVs specify transmission of correct data for only 14 days to support shortterm extended operations while in IIA mode.) The IIR SV will provide a minimum of 60 days of
positioning service without contact from the CS when operating in autonomous navigation(Autonav) mode.
6.2.2.2.4 Block IIR-M SVs.
The subset of operational replenishment SVs developed by Lockheed Martin which are“Modernized” configuration of “Block IIR” SVs are termed “Block IIR-M”.

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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 fromthe 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
block of operational SVs that transmit the L1C signal. These SVs will provide at least 60 daysof 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 lastnavigation 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 andthe 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 ofJanuary 5, 1980/ morning of January 6, 1980. The GPS week number continuously incrementsby one (1) at each end/start of week epoch without ever resetting to zero. Users must recognizethat the week number information contained in the Nav 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).
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.

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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 atmosphericpath loss. For Block II/IIA and IIR SVs, the maximum received signal levels as a result of thesefactors is not expected to exceed -155.5 dBW and -153.0 dBW, respectively, for the P(Y) andC/A components of the L1 channel, nor -158.0 dBW for either signal on the L2 channel. For
Block IIR-M and IIF SVs, the maximum received signal levels as a result of these factors is notexpected to exceed -155.5 dBW and -153.0 dBW, respectively, for the P(Y) and C/Acomponents of the L1 channel and L2 channel. In addition, due to programmable power output
capabilities of Block IIR-M and IIF SVs, under certain operational scenarios, individual signal
components of Block IIR-M/IIF SVs may exceed the previously stated maximum but are notexpected to exceed -150 dBW.

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-155.5

C/A - L1

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

P - L1-161.5

P - L2 or-164.5
C/A - L2

0o 5o

20o

40o

60o

80o

90o

100o

USER ELEVATION ANGLE (DEG)

Figure 6-1.

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

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 daysof navigation data to support a 60 day positioning service. Due to memory retention limitations,
the Block II SVs may not transmit correct data for the entire 60 days but are guaranteed totransmit correct data for at least 14 days to support short-term extended operations. Under

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normal conditions the CS will provide daily uploads to each SV, which will allow the SV tomaintain 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 tosupport a positioning accuracy of 16 meters spherical error probable (SEP). In addition, thealmanac data, UTC parameters and ionospheric data will be maintained current to meet theaccuracy specified in 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
defined in paragraphs 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As timefrom upload 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 is slow over the short-term extended operations interval, such that at the end of thisinterval (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, such that by the 180th day after the last upload, the positioning errors will havegrown 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 II-F).

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 theBlock IIA 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 short-term and long-term extended operations). (Contractual requirements for theseSVs 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 toeach 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
defined in paragraph 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As timefrom upload continues through these three operational intervals, the user range error (URE) of
the SV will increase, causing a positioning service accuracy degradation.

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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 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
defined in paragraph 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As timefrom 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 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 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
defined in paragraph 6.2.3.2 and 6.2.3.3, and as further described throughout this IS. As timefrom 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.
The Block IIR/IIR-M, Block IIF, and directional crosslink-capable GPS III SV in conjunction
with a sufficient number of other Block IIR/IIR-M, Block IIF or directional crosslink-capable
GPS III SVs, operates in an Autonav mode when commanded by the CS. Each Block IIR/IIRM/IIF/directional crosslink-capable GPS III SV in the constellation determines its own
ephemeris and clock correction parameters via SV-to-SV ranging, communication of data, andon-board data processing which updates data uploaded by the CS.
In the Autonav mode the Block IIR/IIR-M/IIF/directional crosslink-capable GPS III SV will
maintain normal operations as defined in paragraph 6.2.3.1 and as further described within thisIS, and will have a URE of no larger than 6 meters, one sigma for Block IIR/IIR-M. URE of 6
meters, one sigma, is expected to support 16 meter SEP accuracy under a nominal position
dilution of precision. If the CS is unable to upload the SVs, the Block IIR/IIR-M/IIF/directionalcrosslink-capable GPS III SVs will maintain normal operations for period of at least 60 days
after the last upload.

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In the Autonav mode, the almanac data, UTC parameters and ionospheric data are still calculated
and maintained current by the CS and uploaded to the SV as required. If the CS is unable to
upload the SVs, the almanac data, UTC parameters and ionospheric data will not be maintained
current and will degrade in accuracy from the time of the last upload.
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 registerof Figure 3-9. For higher order PRNs (>37) the two-tap output mask is not used and the outputof the G2 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
24 hours.
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 ofTable 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 ofTable 6-I.

56

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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
2111
5266
4711
4166
2251
5306
4761
2152
5247
5736
2575
3054
3604
3520
5472
4417
2025
3230
5736
4575
2054
3204
3720
5572
4457
4005
2220
3332
3777
3555

In the octal notation for the first 10 chips of the C/A-code or the initial 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 specific
P code phase, as shown above.

57

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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
2716
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 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 specific
P code phase, as shown above.

58

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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
7070
3616
7525

*

In the octal notation for the first 10 chips of the C/A-code or the initial 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 specific
P code phase, as shown above.

59

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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
3420
5432
0437
6035
1234

In the octal notation for the first 10 chips of the C/A-code or the initial 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 specific
P code phase, as shown above.

60

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Table 6-I.

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

PRN
SignalNo.

G2 Delay(Chips)

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

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 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 specific
P code 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 inTables 3-IIa and 3-IIb. An additional set of 52 L2 CM-/L2 CL-code PRN sequence pairs are
selected and assigned with 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 not exist for numbers 64 through 158 for L2 CM-/L2 CL-code. Any

61

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assignment of a L2 CM-/L2 CL-code PRN number and its code sequence pair for any additional
SV and/or other L2 signal applications will be selected from the sequences of Table 6-II and will
be approved, controlled, and managed by the GPS Directorate.

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

Table 6-II. Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 1 of 2)
Initial Shift Register State (Octal)
End Shift Register State (Octal)
L2 CM
L2 CL
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***

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

62

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Table 6-II. Additional L2 CM-/L2 CL-Code Phase Assignments (sheet 2 of 2)
Initial Shift Register State (Octal)
End Shift Register State (Octal)
PRN Signal
L2 CM
L2 CL
L2 CM *
L2 CL **
No.
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210

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

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

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

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 not comply with all requirements of the relevant IS or ICD. For example, the preoperational broadcast of L2C signals from the IIR-M satellites did not include any NAV or
CNAV data as required by IS-GPS-200. Pre-operational use of any new signal or group of
signals is at the users own risk.
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
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 for

63

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modernized 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.

64

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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"
when authorized 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 10.3-8.

65

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Figure 10.3-1. Letters of Exception.

66

IS-GPS-200H
24 Sep 2013

Figure 10.3-2. Letters of Exception (continued)

67

IS-GPS-200H
24 Sep 2013

Figure 10.3-3. Letters of Exception (continued)

68

IS-GPS-200H
24 Sep 2013

Figure 10.3-4. Letters of Exception (continued).

69

IS-GPS-200H
24 Sep 2013

Figure 10.3-5. Letters of Exception (continued)

70

IS-GPS-200H
24 Sep 2013

Figure 10.3-6. Letters of Exception (continued).

71

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

72

IS-GPS-200H
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Figure 10.3-8. Letters of Exception (continued).

73

IS-GPS-200H
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20 APPENDIX II. GPS NAVIGATION DATA STRUCTURE FORLNAV DATA, 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, whentransmitted 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 is denoted 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 NAV data related interfaces and form a part of thisAppendix to the 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 NAV data related interfaces and form a part of thisAppendix to the extent specified herein.
Specifications
None
Other Publications

74

IS-GPS-200H
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None
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 shallbe subcommutated 25 times each, so that a complete data message shall require the transmissionof 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 followedby eight data 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 NAV data. However, the memory retention of these SVs will determine the durationof data transmission. Block IIR SVs have the capability, with current memory margin, to store atleast 60 days of uploaded NAV data in the Block IIA mode and to store at least 60 days of CS
data needed to generate NAV data on-board in the Autonav mode. GPS III SVs have thecapability to support operation for at least 60 days without contact from the CS. Alternating
ones and zeros will be transmitted in words 3 through 10 in place of the normal NAV datawhenever 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 theaffected words will be invalid, (b) the two trailing bits of word 10 will be zeros (to allow theparity of subsequent subframes to be valid -- reference paragraph 20.3.5), (c) if the problem isthe lack of a data element, only the directly related subframe(s) will be treated in this manner, (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 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 andNSY) which would preclude normal use by the US. Normal NAV data transmission will beresumed by the SV whenever a valid set of elements becomes available.

75

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Block II/IIA SVs are uploaded with a minimum of 60 days of NAV 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 repeatedwrite 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 isdesigned and guaranteed for at least 60 days.
The memory retentivity is guaranteed for at least 60 days for SVs subsequent to Block IIA.
Although the data content of the SVs will be temporarily reduced during the upload process, thetransmission of valid NAV 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

61
HOW

C P

22 BITS73 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

181

24 BITS***

P

16
BITS***

WORD 8197
T GD

MSB FIRST

3 SECONDS

WORD 7151

P

L2 P DATA FLAG - 1 BIT

DIRECTION OF DATA FLOW FROM SV

WORD 624 BITS***

WORD 9211 219241

P
16 BITS

271

af2

toc
P

8 BITS

WORD 10

8
BITS

af1
16 BITS

8 LSBs

P

a f0

t

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)

76

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

PAGE
NO.

WORD 2

1

WORD 3

31
TLM

2

61
HOW

C P

N/A

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

WORD 7

167

8
BITS

MSBs

WORD 8

181

P

211

24 BITSMSB FIRST

3 SECONDSP

C US
16 BITS

LSBs

WORD 9

227

8
BITS

WORD 10

241

P

271

24 BITS

287
toe

P

t

P

16 BITS

MSBs

LSBs

A - 32 BITS TOTALe - 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)

77

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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

61

TLM

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

MSBs

i0 - 32 BITS TOTAL

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 BITSΩP

24 BITS

MSBs

LSBs

P

LSBs

DIRECTION OF DATA FLOW FROM SV

151

8
BITS

16 BITSΩ 0 - 32 BITS TOTAL

WORD 6

137

LSBs

P

IODE
8
BITS

279
IDOT
14
BITS

t

P

ω - 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)

78

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

5

PAGE
NO.

MSB FIRST

3 SECONDS

WORD 2

WORD 3

WORD 4

WORD 5

61
1

31
TLM

1
THRU
24

63

69

HOW

e

C P

t

22 BITS

91

PP

22 BITS

16 BITS

t oa
8
BITS

99

121
δi

•

Ω

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

AP

24 BITS

WORD 9211Ω0

MSB FIRST

3 SECONDS

241
ω

P

24 BITS

WORD 10P
24 BITS

271
M0

P

279

290

t P

24 BITS

8 MSBs3 LSBs

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)

79

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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
CP

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

WORD 10271 277

16 BITS ** t P

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)

80

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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

WORD 10249

16
BITS***

271

P

22 BITS**t

P** 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)

81

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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**

WORD 10271

P

22 BITS**t

P** 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)

82

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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

18

t

22 BITS

77

α
α
0
1
8
8
BITS BITS

P

22 BITS

91

P

99

α
α
2
3
8
8
BITS BITS

107

121

β
0
8
BITS

β
β
β
1
2
3
8
8
8
BITS BITS BITS

P

129

137

P

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

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

418

WORD 8

181
A1

211

219

24 BITS

8
BITS

tot
WN t
8
8
BITS BITS

MSBs

LSBs

P

24 BITSMSB FIRST

3 SECONDSP

WORD 9

227

241

P

249

∆t
LS
8
8
BITS BITS

WORD 10

257

271

DN
8
BITS

∆t
P

279

LSF
8
BITS

14
BITS **

t

P

WNLSF

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)

83

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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 SECONDSt

22 BITS

121

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

25

91

A-SPOOF &SV CONFIGP

22 BITS

1

2

3

A- SPOOF &SV CONFIG

4

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

211

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

229

241

SV
25

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

A-SPOOF &SV CONFIGP

SV SV SV SV
29 30 31 32

P

2 BITS **271
SV HEALTH
6 BITS/SVSV SV SV
30 31
32

t P

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 20-1.

P

4 BITS **Data Format (sheet 9 of 11)

84

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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

WORD 10

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

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

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)

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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 20-1.

Data Format (sheet 11 of 11)

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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 wordin each 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 statusflag, one reserved bit, and six parity bits. The TLM message contains information needed by theprecise 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 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 upperbound value of the current broadcast URA index, for more than 5.2 seconds, without anaccompanying alert, is less than 1E-5 per hour. A "1" in bit-position 23 indicates that theconveying signal is provided with an enhanced level of integrity assurance. That is, theprobability that the instantaneous URE of the conveying signal exceeds 5.73 times the upperbound value of the current broadcast URA index, for more than 5.2 seconds, without anaccompanying 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 and content 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 countconsists 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).

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

ID Code

1

001

2

010

3

011

4

100

5

101

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

2

TLM Message

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

ParityLSB

9 10 11 12 131

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

Figure 20-2.

00

20 21 22 23 24 25 26 27 28 29 30

TLM and HOW Formats

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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 forparity computation purposes. The remaining 190 bits of words three through ten shall containthe clock parameters and other data described in the following.
The clock parameters describe the SV time scale during the period of validity. The parameters
are applicable during the time in which they are transmitted. The timing information forsubframes, pages, and 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 data set transmission interval (see paragraph 3.3.4(b)). The GPS week number
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 L2channel, as follows:

00 = Reserved,
01 = P code ON,
10 = C/A code ON.

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. Except for Block IIR/IIR-M SVs in the90

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Autonav mode, the URA index (N) is an integer in the range of 0 through 15 and has thefollowing 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.)

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),
91

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24 Sep 2013• 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.
For Block IIR/IIR-M SVs in the Autonav mode, the URA shall be defined to mean “no better
than X meters”, with “X” as defined above for each URA index.
The nominal URA value (X) is suitable for use as a conservative prediction of the RMS signalin-space (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: LSB representation/truncation error; the net effect of clock correction polynomial
error and code phase error in the transmitted signal for single-frequency L1C/A or singlefrequency L2C users who correct the code phase as described in Section 30.3.3.3.1.1.1; the net
effect of clock parameter, code phase, and inter-signal 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; 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 NAV data, where

0 = all NAV data are OK,
1 = some or all NAV 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).
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Accordingly, any SV which does not have a certain capability will be indicated as "healthy" if
the lack of this capability is inherent in its design or if it has been configured into a mode which
is normal 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 adifferent time.
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 convenientmeans of detecting any change in the correction parameters. Constraints on the IODC as well as
the relationship 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
to determine the actual fit interval of the 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 NAV data stream was commanded
OFF on the P-code 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, thenumber of bits, the scale factor of the LSB (which shall be the last bit received), the range, andthe units shall be as specified in Table 20-I.
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 "single
frequency" (L1 or L2) user to compensate for the effects of SV group delay differential (the user
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who utilizes both frequencies does not require this correction, since the clock parameters accountfor the induced effects), and (c) allow the "two frequency" (L1 and L2) user to correct for thegroup propagation delay due to ionospheric effects (the single frequency user may correct forionospheric effects as described in paragraph 20.3.3.5.2.5).

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Table 20-I. Subframe 1 Parameters
No. of
Bits**

Scale
Factor(LSB)

Code on L2

2

1

discretes

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

Parameter

*

Units

(see text)(see text)
604,784

seconds

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

Effective
Range***

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

Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor.

20.3.3.3.3.1 User Algorithm for SV Clock Correction.
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 theoffset apparent to the two-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 ofgroup 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)
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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, toc 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 µc 2 = - 4.442807633 (10)-10F =sec
meter ,

where
meters 32µ = 3.986005 x 1014 second =value of Earth's universal gravitational parameters

metersc = 2.99792458 x 10

8 second=

speed of light.

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Note that equations (1) and (2), as written, are coupled. While the coefficients af0, af1 and af2 are
generated by using GPS time as indicated in equation (2), sensitivity of tsv to t is negligible. Thisnegligible sensitivity will allow the user to approximate t by tSV in equation (2). The value of t
must account for beginning or end of week crossovers. That is, if the quantity t - toc is greaterthan 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 NAV parameters:
→

−

∆tr =

→

2 R •V
c2

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 - L2 Correction.
The L1 and L2 correction term, TGD, is initially calculated by the CS to account for the effect ofSV group delay differential between L1 P(Y) and L2 P(Y) based on measurements made by the
SV contractor during SV manufacture. The value of TGD for each SV may be subsequently
updated to reflect the actual on-orbit group delay differential. This correction term is only forthe benefit of "single-frequency" (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 paragraph20.3.3.3.3.1) are based on the effective PRN code phase as apparent with two frequency (L1
P(Y) and L2 P(Y)) ionospheric corrections. Thus, the user who utilizes the L1 P(Y) signal only
shall modify the code phase offset in accordance with paragraph 20.3.3.3.3.1 with the equation(∆tSV)L1P(Y) = ∆tSV - TGD

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where TGD is provided to the user as subframe 1 data. For the user who utilizes L2 P(Y) only,
the code phase modification is given by(∆tSV)L2P(Y) = ∆tSV - γTGD

where, denoting the nominal center frequencies of L1 and L2 as fL1 and fL2 respectively,γ = (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 valuethat represents the mean group delay differential multiplied by 1/(1- γ). That is,
1
1-γ

TGD =

(tL1P(Y) - tL2P(Y))

where tLiP(Y) is the GPS time the ith 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 two frequency (L1 P(Y) and L2 P(Y)) user shall correct for the group delay due toionospheric effects by applying the relationship:

PR =PR L2P(Y) - γ PR L1P(Y)
1 - γ

where

PR

=

pseudorange corrected for ionospheric effects,

PRi=

pseudorange measured on the channel indicated by the subscript,

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and γ is as defined in paragraph 20.3.3.3.3.2. The clock correction coefficients are based on "twofrequency" measurements and therefore account for the effects of mean differential delay in SV
instrumentation.
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 Figure20-3. 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 toin Figure 20-3 is discussed in paragraph 20.3.3.5.2.6 in conjunction with the related datacontained in page 13 of subframe 4.

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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.
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 theirLSBs; in addition, two non-information bearing bits shall be provided as bits 23 and 24 of wordten of each subframe for parity computation purposes. Bits 288 through 292 of subframe 2 shallcontain the 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 of100

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those two subframes shall contain the ephemeris representation parameters of the transmittingSV.
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 for each 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 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 data will be accomplished with a simultaneous change inboth IODE words. The CS (Block II/Block IIA/IIR/IIR-M/IIF) and SS (GPS III) shall assurethat the toe value, for at least the first data set transmitted by an SV after an upload, is different
from that transmitted prior to the cutover (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 Timeω

Argument of Perigee•ΩRate 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) via a least squares curve fit of
the predicted 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, theresultant accuracy, and the applicable coordinate system are given in the following
subparagraphs.

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20.3.3.4.3.1 Curve Fit Intervals.
Bit 17 in word 10 of subframe 2 is a "fit interval" flag which indicates the curve-fit interval usedby the CS (Block II/Block IIA/IIR/IIR-M/IIF) and SS (GPS III) in determining the ephemeris
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.
Parameter

No. of Bits**

IODE

8

Ephemeris Parameters

Scale Factor (LSB)

Effective Range***Units(see text)-5

meters

Crs

16*

2

∆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

toe

16

24

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

ω

32*

2-31

semi-circles

24*

2

-43

semi-circles/sec

2-43

semi-circles/sec

•

Ω
IDOT
*
***

14*

0.03

dimensionlessradians
meters604,784

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, effective range is the maximum range attainable withindicated bit allocation and scale factor.

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Table 20-IV.
µ = 3.986005 x 1014 meters3/sec2

Elements of Coordinate Systems (sheet 1 of 2)
WGS 84 value of the earth's gravitational constant for
GPS user•Ω e = 7.2921151467 x 10-5 rad/sec
A=
n0 =

( A)

2

µ
A3

WGS 84 value of the earth's rotation rate
Semi-major axis
Computed mean motion (rad/sec)

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

Corrected mean motion

Mk = M0 + ntk

Mean anomaly

Mk = Ek - e sin Ek

Kepler's Equation for Eccentric Anomaly (may be solved by
iteration) (radians) sin ν k 
ν k = tan −1  cos ν k 

True Anomaly 1 − e 2 sin E / (1 − e cos E ) kk= tan −1 

(
)
(
cos
E
e
/
1
e
cos
E
−
−
k
k) 



*

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 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 tk. If tk is less than -302,400 seconds, add 604,800 seconds to tk.

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Table 20-IV. Elements of Coordinate Systems (sheet 2 of 2)
 e + cos ν k 
E k = cos −1 
1 + e cos ν k 

Eccentric AnomalyΦk = νk + ωArgument of Latitude}

δuk = cussin2Φk + cuccos2Φkδrk = crssin2Φk + crccos2Φkδik = cissin2Φk + ciccos2Φk

Argument of Latitude Correction
Radius Correction
Inclination Correction

Second Harmonic Perturbations

uk = Φk + δuk

Corrected Argument of Latitude

rk = A(1 - e cosEk) + δrk

Corrected Radius

ik = i0 + δik + (IDOT) tk

Corrected Inclinationxk′ = rkcosuk
yk′ = rksinuk}•

Positions in orbital plane.

••Ωk = Ω0 + ( Ω - Ω e ) tk - Ω e toe

Corrected longitude of ascending node.

xk = xk′cosΩk - yk′cosiksinΩkyk = xk′sinΩk + yk′cosikcosΩk

Earth-fixed coordinates.

zk = yk′sinik}

20.3.3.4.3.2 Parameter Sensitivity.
The sensitivity of the SV's antenna phase center position to small perturbations in mostephemeris parameters is extreme. The sensitivity of position to the parameters A , Crc and Crs isabout 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 1012
meters/semicircle/second. Because of this extreme sensitivity to angular perturbations, the valueof π used in the curve fit is given here. π is a mathematical constant, the ratio of a circle's
circumference to its diameter. Here π is taken as π = 3.1415926535898.
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:

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Origin*=Earth's center of mass

Z-Axis**=The direction of the IERS (International Earth Rotation andReference 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 =coordinate system

Completes a right-handed, Earth-Centered, Earth-Fixed orthogonal* 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 t0. The x, y, z coordinatesin the ECEF coordinate system at some other time t can be transformed to the x′, y′, z′coordinates in the selected ECI coordinate system of convenience by the simple** rotation:x′ = x cos(θ) - y sin(θ)
y′ = x sin(θ) + y cos(θ)
z′ = zwhere•θ = Ω 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 beneglected by most users for small values of (t - t0).
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)|106

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wheretT 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 tT,→r (tR) = position vector of the receiver in the selected ECI coordinate system at time tR.

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 NAV data from thetransmitting 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 (tnmct)
using the ephemeris toe 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 tnmct 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 tnmct 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 tnmct values for all visible and available
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SVs in order to find and use the NMCT with the latest tnmct. If the same latest (largest) tnmct isprovided by two or more visible and available SVs, then the NMCT from any SV with the latest
tnmct may be selected and used; however, the estimated range deviation (ERD) value provided by
the selected NMCT for the other SVs with the same tnmct shall be set to zero if those SVs are usedin 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 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 only when
operating in the IIA like mode of operation including the Autonav Test mode.
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
the various 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:

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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

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 (denotedby binary code 01) denotes the NAV data structure of D(t) which is described in this Appendix.
Future data IDs will be defined as necessary.
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 20V. 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 isthe same 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 1-24 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 than almanac 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: 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 SVs).

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),
and the 50 bits devoted to parity. The number of bits, the scale factor (LSB), the range, and theunits of the almanac parameters are given in Table 20-VI. The algorithms and other material
related to the use of the almanac data are given in paragraph 20.3.3.5.2.

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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 basedon six-day curve fits that correspond to the first six days of the transmission interval.
For Block IIR/IIR-M, IIF, and GPS III SVs, five sets of almanac shall be used to span at least 60
days. The first, second, and third sets will be transmitted for up to six days each; the fourth andfifth sets will be transmitted for up to 32 days; the fifth set is intended to be transmitted for theremainder of the 60 days minimum, but the actual duration of transmission will depend on theindividual 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

Parameter

No. of
Bits**

Scale
Factor
(LSB)

e

16

2-21

toa

8

212

δi****

16*

2-19

semi-circles

Ω

16*

2-38

semi-circles/sec

A

24

2-11

meters

Ω0

24*

2-23

semi-circles

ω

24*

2-23

semi-circles

M0

24*

2-23

semi-circles

af0

11*

2-20

seconds

af1

11*

2-38

sec/sec•

Effective
Range***

Units
dimensionless

602,112seconds* 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, effective range is the maximum range attainable withindicated bit allocation and scale factor;**** Relative to i0 = 0.30 semi-circles.

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 NAV data in accordance withthe code given in Table 20-VII. The six-bit words provide a one-bit summary of the NAV 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

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indicates that "the SV which has that ID is not available and there may be no data regarding that
SV in that page of subframes 4 and 5 that is assigned to normally contain the almanac data ofthat SV" (NOTE: this special meaning applies to the 25th page of subframes 4 and 5 only). The
health indication shall be given relative to the "as designed" capabilities of each SV (asdesignated 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 the lack of this capability isinherent in its design or it has been configured into a mode which is normal from a user
standpoint and does not require that capability.
Additional SV health data are given in subframe 1. The data given in subframes 1, 4, and 5 ofthe other SVs may differ from that shown in subframes 4 and/or 5 since the latter may be
updated at a different 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,
the 24 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.

NAV 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

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

*

Codes for Health of SV Signal Components
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
L1 C Signal Weak
L1 C Signal Dead
L1 C Signal Has No Data Modulation
L2 C Signal Weak
L2 C Signal Dead
L2 C Signal Has No Data Modulation
L1 & L2 P Signal Weak
L1 & L2 P Signal Dead
L1 & L2 P Signal Has No Data Modulation
L1 & L2 C Signal Weak
L1 & L2 C Signal Dead
L1 & L2 C 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.

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
A-S status and the configuration code of each SV. 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 ofeach SV using the following code:

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Code SV Configuration
000

Reserved

001 A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as
described in paragraph 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 in paragraph 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 in paragraph 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 in paragraph 20.3.2, M-Code capability, L1C signal capability, L2C signal
capability, L5 signal capability, no SA capability (e.g., GPS III SVs).

Additional codes will be assigned in the future, should the need arise.
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 (toa) 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 toa is referenced. Bits
9 through 16 of word three in page 25 of subframe 5 shall contain the value of toa which isreferenced to this WNa.
20.3.3.5.1.6 Coordinated Universal Time (UTC) Parameters.
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.
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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 theionospheric model (reference paragraph 20.3.3.5.2.5) for computation of the ionospheric delay
are contained in page 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 theseparameters 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)

Effective
Range***

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*

7

seconds

days
seconds

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

602,112

Units

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

Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor;****

Right justified.

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Table 20-X.

Ionospheric Parameters

Parameter

No. of
Bits**

Scale
Factor
(LSB)

α0

8*

2-30

seconds

α1

8*

2-27

sec/semi-circle

α2

8*

2-24

sec/(semi-circle)2

α3

8*

2-24

sec/(semi-circle)3

β0

8*

211

seconds

β1

8*

214

sec/semi-circle

β2

8*

216

sec/(semi-circle)2

β3

8*

216

sec/(semi-circle)3

*

Units

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

Effective
Range***

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

Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor.

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 of words four through nine, plus the 16 MSBs of word ten. The eight MSBs of word threeshall contain the data ID and SV ID, while bits 17 through 22 of word ten shall be reserved forsystem use. 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:

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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

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.

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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

Each one of the 30 six-bit ERD slots in bits 11 through 24 of word three, bits 1 through 24 ofwords four through nine, and bits 1 through 22 of word ten of page 13 of subframe 4 willcorrespond 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 thefollowing 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 uploadthat all ERD values shall be transmitted in ascending numerical slot order of the corresponding
SV ID. To illustrate: the SV operating as SV ID 1 will transmit (in order) ERD values whichcorrespond 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 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 an effective
range of ±9.3 m. A binary value of “100000” shall indicate that no valid ERD for thecorresponding SV ID is present in that slot.
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 NAV 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 δi (correction to
inclination) is transmitted, as opposed to the value computed by the user. All other parameters
appearing in the equations of Tables 20-IV, but not included in the content of the almanac, are

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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 1014 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.
†

After the CS is unable to upload the SVs, URE values for the SVs operating in the Autonav mode

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,based on 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 toa values in subframes 4
and 5 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 toa, 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 toa
are obtained.
Normal and Short-term Extended Operations. The almanac reference time, toa, is somemultiple 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 ensurethat GPS time, t, shall differ from toa by less than 3.5 days during the transmission period. The
time from epoch tk shall be computed as described in Table 20-IV, except that toe shall be
replaced with toa.

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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 mustaccount for crossovers into time spans where these computations of tk are not valid. This may be
accomplished without time ambiguity by recognizing that the almanac reference time (toa) is
referenced to the almanac reference week (WNa), both of which are given in word three of page
25 of subframe 5 (see paragraph 20.3.3.5.1.5).
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 firstorder term (af1). The applicable first order polynomial, which shall provide time to within 2
microseconds of 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
coefficients af0 and af1 are given in the almanac. Since the periodic relativistic effect is less than
25 meters, it need not be included in the time scale used for almanac evaluation. Over the spanof applicability, it is expected that the almanac time parameters will provide a statistical URE
component of less than 135 meters, one sigma. This is partially due to the fact that the error
caused by the truncation of af0 and af1 may be as large as 150 meters plus 50 meters/day relative
to the toa 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 NAV message upload)
value of the delta time due to leap seconds (∆tLSF), together with the week number (WNLSF) andthe day number (DN) at the end of which the leap second becomes effective. "Day one" is thefirst day relative to the end/start of week and the WNLSF value consists of eight bits which shallbe a modulo 256 binary representation of the GPS week number (see paragraph 6.2.4) to which
the DN is referenced. The user must account for the truncated nature of this parameter as well as
truncation of WN, WNt, and WNLSF due to rollover of full week number (see paragraph3.3.4(b)). The CS shall manage these parameters such that, when ∆tLS and ∆tLSF differ, theabsolute value of the difference 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, thefollowing three different UTC/GPS-time relationships exist:
a. Whenever the effectivity time indicated by the WNLSF 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 tSV for factors
described in paragraph 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, tot, is some multiple of 212
seconds occurring approximately 70 hours after the first valid transmission time for this UTC

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data set (reference 20.3.4.5). The reference time for UTC data (tot) shall be referenced to thestart of that 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 tot is referenced. The user must account for thetruncated nature of this parameter as well as truncation of WN, WNt, and WNLSF due to rolloverof full week number (see paragraph 3.3.4(b)). The CS shall manage these parameters such thatthe absolute value of the difference between the untruncated WN and WNt values shall not
exceed 127.
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 witha possible 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 WNLSF and DNvalues, is in the "past" (relative to the user's current time), and the user’s current time does not
fall in the time span as given above in 20.3.3.5.2.4b, the relationship previously given for tUTC 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 "two frequency" (L1 and L2) user shall correct the time received from the SV for
ionospheric effect by utilizing the time delay differential between L1 and L2 (reference
paragraph 20.3.3.3.3.3). The "one frequency" user, however, may use the model given in Figure20-4 to make this correction. 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

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effects. During extended operations, or for the SVs in the Autonav mode if the CS is unable to
upload the SVs, the use of this model will yield unpredictable results.
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
is computed 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.

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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 mustbe multiplied by γ (reference paragraph 20.3.3.3.3.2), 3n α n φ m , AMP ≥ 0 
AMP = n = 0if AMP < 0, AMP = 0

∑

(sec)

x=

2π (t - 50400 )PER(radians) 3n
 β n φ m , PER ≥ 72,000PER = n = 0
 (sec)if PER < 72,000, PER = 72,000

∑

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

Figure 20-4.

Ionospheric Model (Sheet 1 of 3)

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Other equations that must be solved are
φm = φi + 0.064cos(λi - 1.617)(semi-circles)ψ sinAcos φ i(semi-circles)

λ i = λu +φi = 

φ i ≤ 0.416 if φ i > +0.416, then φ i = +0.416
if φ i < −0.416, then φ i = −0.416 
φ u + ψ cosA,ψ=

0.0137- 0.022E + 0.11

t = 4.32 (104) λi + 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)

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The terms used in computation of ionospheric delay are as follows:• Satellite Transmitted Terms
αn-the coefficients of a cubic equation representing the amplitude of the verticaldelay (4 coefficients - 8 bits each)βn-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)

φu-user geodetic latitude (semi-circles) WGS 84

λu-user geodetic longitude (semi-circles) WGS 84

GPS time-

receiver computed system timeX-

phase (radians)F-obliquity factor (dimensionless)t-local time (sec)φm-geomagnetic latitude of the earth projection of the ionospheric intersection• Computed Terms

point (mean ionospheric height assumed 350 km) (semi-circles)
λi-

geodetic longitude of the earth projection of the ionospheric intersection point(semi-circles)

φi-geodetic latitude of the earth projection of the ionospheric intersection point(semi-circles)ψ-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)

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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 cyclingof the 25 pages of subframes 4 and 5 shall restart with page 1 of each of the subframes,
regardless of 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 NAV message shall be relative to GPS time;d.

The acts of transmitting the NAV 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 data set. The
following rules govern the transmission of IODC and IODE values in different data sets: (1) The
transmitted IODC will be different from any value transmitted by the SV during the preceding
seven days; (2) The transmitted IODE will be different from any value transmitted by the SV

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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 SVs.
Cutovers to new data sets will occur only on hour boundaries except for the first data set of a
new upload. The first 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 for less than one hour. During short-term
operations, cutover to 4-hour sets and subsequent cutovers to succeeding 4-hour data sets will
always occur modulo 4 hours relative to end/start of week. Cutover from 4-hour data sets to 6hour data sets shall occur modulo 12 hours relative to end/start of week. Cutover from 12-hourdata sets to 24-hour data sets shall occur modulo 24 hours relative to end/start of week. Cutover
from a data set transmitted 24 hours or more occurs on a modulo 24-hour boundary relative toend/start of week.
The start of the transmission interval for each data set corresponds to the beginning of the curve
fit interval for the data set. Each data set nominally remains valid for the duration of its curve fit
interval. A data set may be rendered invalid before the end of its curve fit interval when it issuperseded by the SV cutting over to new data.
Normal Operations. The subframe 1, 2, and 3 data sets are transmitted by the SV for periods of
two hours. The corresponding curve fit interval is four hours. SVs operating in the Autonav
mode will deviate. They will transmit subframe 1, 2, and 3 data sets for periods of one hour.
The corresponding curve-fit interval will be 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.

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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
upload) shall be any numbers in the range 0 to 1023 excluding those values 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 data set of a new upload may be cut-in at any time and therefore the transmission interval
may be less than the specified value.

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Table 20-XII.

IODC Values and Data Set Lengths (Block IIR/IIR-M/IIF & GPS III)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
upload) shall be any numbers in the range 0 to 1023 excluding those values 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 SV time of transition from the 4 hour
curve fits into extended navigation (beyond 4 hour curve fits). Following the transition time, theSV 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: SVs operating in the Autonav mode will have transmission intervals of 1 hour per paragraph20.3.4.4.
Note 5: The first data set of a new upload may be cut-in at any time and therefore the transmission interval
may be less than the specified value.

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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 beevaluated by 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 thedifferent 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 (ttoe) in evaluating the expansions.

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The CS (Block II/IIA/IIR/IIR-M/IIF) and SS (GPS III) shall assure that the toe value, for at least
the first data set transmitted by an SV after a new upload, is different from that transmitted prior
to the cutover (see paragraph 20.3.4.4). As such, when a new upload is cutover for transmission,
the CS (Block IIA/IIR/IIR-M/IIF) and SS (GPS III) 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 data set after a new upload cutover and the second
data set, following the first data set, may also continue to reflect the same offset in the toe.
When the toe, immediately prior to a new upload cutover, already reflects a small deviation (i.e. a
new upload cutover has occurred in the recent past), then the CS (Block II/IIA/IIR/IIR-M/IIF)
and SS (GPS III) shall introduce an additional deviation to the toe when a new upload is cutover
for transmission.
A change from the broadcast reference time immediately prior to cutover is used to indicate achange of values in the data set. The user may use the following example algorithm to detect theoccurrence of a new upload cutover:
DEV = toe [modulo 3600]
If DEV ≠ 0, then a new upload cutover has occurred within past 4 hours.

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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.
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 (dn) are modulo-2 added in accordance with the136

IS-GPS-200H
24 Sep 2013equations appearing in Table 20-XIV for D25 . . . D30, which provide parity to compare withtransmitted parity D25 . . . D30.
Table 20-XIV.
D1=

d1 ⊕ D30

D2=

d2 ⊕ D30

D3=d3 ⊕ D30

•

•

•

•

•

•

•

•

Parity Encoding Equations

D24=

d24 ⊕ D30

D25=

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 ⊕ d1⊕ d3⊕ d5⊕ d6⊕ d7⊕ d9 ⊕ d10 ⊕ d14 ⊕ d15 ⊕ d16 ⊕ d17 ⊕ d18 ⊕ d21 ⊕ d22⊕ d24

D30=

D29 ⊕ d3 ⊕ d5 ⊕ d6 ⊕ d8 ⊕ d9 ⊕ d10 ⊕ d11 ⊕ d13 ⊕ d15 ⊕ d19 ⊕ d22 ⊕ d23 ⊕ d24

Whered1, 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.

137

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ENTERCOMPLEMENT
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 Algorithm

138

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30 APPENDIX III. GPS NAVIGATION DATA STRUCTURE FOR
CNAV DATA, 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 thisAppendix to the 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 thisAppendix to the extent specified herein.
Specifications
None
Other Publications
None
30.3 Requirements.
30.3.1 Data Characteristics.
The CNAV data, DC(t), is a higher precision representation and nominally contains moreaccurate data than the NAV data, D(t), described in Appendix II. Also, the CNAV data stream
uses a different parity algorithm.
139

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Users are advised that the CNAV data, DC(t), described in this appendix and the NAV data, D(t),described in Appendix II, should not be mixed in any user algorithms or applications. Each of
the two data sets should be 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 fromthe CS for that period. GPS III 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 17bit message time of week (TOW) count. When the value of the message TOW count ismultiplied 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 theirown 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.

140

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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 n

17 BITS

13 BITsMESSAGE TYPE ID"ALERT" FLAG - 1 BIT

PREAMBLEMSB FIRST

82

71
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

173

150
∆ 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

ωn

CRC

33 BITS

33 BITS

24 BITs

Integrity Status Flag – 1 BIT
5 LSB sL2C 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

141

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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

Ω0-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

•
∆Ω

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
24 BITS

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

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
4 SECONDS
100 BITS
38
50
55 58 61
39

141

167

154

180

193

af1-n

af2-n

TGD

ISCL1C/AISCL2CISCL5I5

ISCL5Q5α017 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

α1

α2

α3

β0

β1

β2

β3

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

143

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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

141

149

180

af1-n

af2-n

WNa-n

toa

Reduced Almanac
Packet 1

17 LSBs

10 BITS

13 BITS

8 BITS

31 BITS

10 LSBs

211

21 MSBs

273 277

242
Reduced Almanac
Packet 3

Reduced Almanac
Packet 4

31 BITS

31 BITS

Reduced Almanac Packet 2

Reduced Almanac
Packet 2

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 61
39

CRC
4
BITS

24 BITSRESERVED* 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

144

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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

144

128

118

165

180

af1-n

af2-n

tEOP

PM-X

•
PM-X

17 LSBs

10 BITS

16 BITS

21 BITS

15 BITS

15 BITS

21 BITS

277

266

247

216
•
PM-Y

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 61
39

∆UT1

•
∆UT1

RESERVEDCRC

31 BITS

19 BITS

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

145

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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

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
214 218201

DN

13 BITS

4
BITS 8 BITS

277

226

∆tLSF

WNLSF

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

146

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1

9

21

15

PRN
6
BITS

8 BITS

6BITS

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 Correction

147

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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 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
55 58 6150
39

157 160

144

MSB 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

148

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1

21

15

9
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

149

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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

af1-n

af2-n

WNa-n

17 LSBs

10 BITS

13 BITStoa

149

155 158

180

191

e

δi

•
Ω

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

Ω0

ω

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

150

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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
Reduced Almanac
Packet 2
21 LSBs

153

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

151

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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 BITSMESSAGE TYPE ID
PREAMBLEMSB FIRST

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

DC DATA TYPE – 1 BIT

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

MSB FIRST

271

277

CDC

34 BITS

34 BITS

6
BITS

CRC
24 BITSDC DATA TYPE – 1 BIT
DC DATA TYPE – 1 BIT

RESERVED* 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 Correction

152

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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

MESSAGE TYPE ID
PREAMBLEMSB FIRSTDC DATA TYPE – 1 BIT"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 Correction

153

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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

154

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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 tocalculate SV position. The general format of message types 10 and 11 consists of data fields forreference time tags, a set of gravitational harmonic correction terms, rates and rate corrections toquasi-Keplerian 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 predictedperiod of 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
orbital parameters; it is noted, however, that the transmitted parameter values are expressed suchthat 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 aspertaining 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 toe 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 data set cutover has occurred and new data must be collected. The timing of the toe
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 will assure the toe value for Block IIR-M/IIF and SS
will assure the toe value for GPS III, for at least the first data set transmitted by an SV after an
upload, is different from that transmitted prior to the cutover. See Section 30.3.4.5 for additional
information regarding toe.
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 ofthe 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.

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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 theconveying 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 URAED 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 data set transmission interval(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 signals of the transmitting SV. The health of each signal is indicated by:
0 = Signal OK,
1 = Signal bad or unavailable.
The predicted health data will be updated at the time of upload when a new data set has been
built by the CS. The transmitted health data may not correspond to the actual health of thetransmitting SV.
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.

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30.3.3.1.1.3 Data Predict Time of Week.
Bits 55 through 65 of message type 10 shall contain the data predict time of week (top). The top
term provides the epoch time of week of the state estimate utilized for the prediction of satellitequasi-Keplerian ephemeris parameters.
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 URAED
index shall provide the ED-related URA index or the current ephemeris curve fit interval. While
the ED-related 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 URAED
expected over the entire 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), thecorresponding URAED 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< URAED143072.00< 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

157

(or no accuracy prediction is available)

IS-GPS-200H
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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

-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),

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• 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 the scaled (multiplied by either 4.42 or 5.73 as appropriate) upper bound valuesof 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:= Nominal URAED (sin(E+90 degrees))

Adjusted Nominal URAED
Adjusted IAURAED= IAURAED (sin(E+90 degrees))

URAED and IAURAED account for SIS contributions to user range error which include, but are
not limited to, the following: LSB representation/truncation error, alongtrack ephemeris errors,
and crosstrack ephemeris errors. URAED and IAURAED do 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 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 theunits are as specified in Table 30-I. See Figures 30-1 and 30-2 for complete bit allocation inmessage 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) via a least squares curve fit of the predicted ephemeris of 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.
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The sensitivity of the SV’s position to small perturbations in most ephemeris parameters isextreme. The sensitivity of position to the parameters A, Crc-n, and Crs-n is about one
meter/meter. The sensitivity of position to the angular parameters is on the order of 108
meters/semi-circle, and to the angular rate parameters is on the order of 1012 meters/semicircle/second. Because of this extreme sensitivity to angular perturbations, the value of π used in
the curve fit is given here. π is a mathematical constant, the ratio of a circle’s circumference toits diameter. Here π is taken as 3.1415926535898.

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Table 30-I. Message Types 10 and 11 Parameters (1 of 2)

Parameter

No. of
Bits**

Scale
Factor(LSB)
1

WN

Week No.

13

URAED Index

ED Accuracy Index

5*

Signal health(L1/L2/L5)

Effective
Range***

Units
weeks
(see text)

3

1(see text)

top

Data predict time of week

11

300

∆A ****

Semi-major axis difference atreference time

26*

2-9

metersA

Change rate in semi-major
axis

25*

2-21

meters/sec∆n0Mean Motion difference fromcomputed value at reference
time

17*

2-44

semi-circles/sec∆n0Rate 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

ωn

Argument of perigee

33*

2-32

•

•

*
***

604,500

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, effective range is the maximum range attainable withindicated bit allocation and scale factor.
****
Relative to AREF = 26,559,710 meters.

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Table 30-I. Message Types 10 and 11 Parameters (2 of 2)

Parameter

No. of
Bits**

Scale
Factor(LSB)

Effective
Range***

Units

604,500

seconds

toe

Ephemeris data reference time of week

11

300

Ω0-n

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 harmonic correction
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 harmonic correction
term to the argument of latitude

21*

2-30

radians

Cuc-n

Amplitude of the cosine harmoniccorrection term to the argument of latitude

21*

2-30

radians•*
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, effective range is the maximum range attainable withindicated bit allocation and scale factor.
****•

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

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Table 30-II. Elements of Coordinate System (part 1 of 2)
Element/Equationµ = 3.986005 x 1014 meters3/sec2•

Description
WGS 84 value of the earth’s gravitational constant for GPS userΩe = 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 =µComputed 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

Mk = Ek – en sin Ek

Kepler’s equation for Eccentric Anomaly (radians)(may be solved by iteration)

 sin ν k 
νk = tan-1  cos ν k 

True Anomaly 1 − e 2 sin E / (1 − e cos E ) 

n
k
n
k 
= tan-1 

(
)
(
−
−
cos
E
e
/
1
e
cos
E
k
n
n
k) 


 e + cos ν k 
Ek = cos-1  n1 + e n cos ν k *

Eccentric Anomaly

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.

163

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Table 30-II.

Elements of Coordinate System (part 2 of 2)

Element/Equation *Φk = νk + ωn

Description
Argument of Latitude

δuk = Cus-nsin2Φk + Cuc-ncos2Φk

Argument of Latitude Correctionδrk = Crs-nsin2Φk + Crc-ncos2Φk

Radial Correction

δik = Cis-nsin2Φk + Cic-ncos2ΦkInclination Correction

uk = Φk + δuk

Second Harmonic
Perturbations

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

Corrected Radiusik= io-n + (io-n-DOT)tk + δik

Corrected Inclination

xk' = rk cos uk

Positions in orbital planeyk' = rk sin uk•••Ω = ΩREF + ∆Ω ***••Rate of Right Ascension•Ωk = Ω0-n + ( Ω − Ωe ) tk – Ωe toe

Corrected Longitude of Ascending Nodexk = xk' cos Ωk − yk' cos ik sin Ωkyk = xk' sin Ωk + yk' cos ik cos ΩkEarth-fixed coordinates of SV antenna phase centerzk = yk' sin ik•*** ΩREF = −2.6 x 10-9 semi-circles/second.

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 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.

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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 toc , 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 Data Predict Time of Week.
Bits 39 through 49 of message types 30 through 37 shall contain the data predict time of week(top). The top term provides the epoch time of week of the state estimate utilized for theprediction of SV clock correction coefficients.
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 and the dual-frequency L1 C/A - L2 C 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

Parameter

No. of
Bits**

Scale
Factor(LSB)

Effective
Range***

300

604,500

toc

Clock Data Reference Time of Week

11

URANED0
Index

NED Accuracy Index

5*

URANED2
Index
af2-n

af1-n

af0-n

NED Accuracy Change Index

3

NED Accuracy Change Rate Index

10*

2-60

20*

2-48

26*

2-35

SV Clock Drift Rate Correction
Coefficient

secon
ds
(see
text)

3
URANED1
Index

Units

(see
text)

SV Clock Drift Correction
Coefficient

(see
text)
sec/sec2
sec/sec

SV Clock Bias Correction Coefficient
secon
ds

*
***

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, effective range is the maximum range attainable withindicated bit allocation and scale factor.

30.3.3.2.4 Non-Elevation-Dependent (NED) Accuracy Estimates.
Bits 50 through 54, and 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 URANED0 Index, URANED1
Index, and URANED2 Index shall give the non-elevation dependent user range accuracy of
IAURANED over the current clock/ephemeris fit interval. While the actual NED related URA
may vary over the satellite 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
IAURANED 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))

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for t - top + 604,800*(WN - WNop) ≤ 93,600 seconds

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
the above 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 parameterand 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 of clock 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
relationship to the URANED0 value:

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URANED0 Index

URANED0 (meters)

15

6144.00< 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

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-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

URANED0

≤

0.01

-15
-16

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 IAURANED
are specified with respect to the scaled (multiplied by either 4.42 or 5.73 as appropriate) upperbound 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
not limited to, the following: LSB representation/truncation error; the net effect of clock
correction polynomial error 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; the net effect of clock parameter, code phase, and inter-signal correction error fordual-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; radial ephemeris error; anisotropic antenna errors; and signal
deformation error. URANED0 does not account for user range contributions due to the inaccuracy
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of the broadcast ionospheric data parameters used in the single-frequency ionospheric model orfor other atmospheric effects.
The transmitted URANED1 index is an integer value in the range 0 to 7. The URANED1 index has
the following 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.
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 thereference 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 defined170

IS-GPS-200H
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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, TGD, ISCL1C/A, ISCL2C for the benefit of single
frequency L1 P, L1 C/A, L2 P, L2 C 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
Table 30-IV.

Group Delay Differential Parameters ****

No. of
Bits**

Scale Factor
(LSB)

TGD

13*

2

-35

seconds

ISCL1C/A

13*

2-35

seconds

ISCL2C13*

2-35

seconds

ISCL5I513*

2-35

seconds

ISCL5Q513*

2-35

seconds

Parameter

Effective
Range***

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;***
Effective 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
the effect of inter-signal biases between L1 P(Y) and L2 P(Y), L1 P(Y) and L1 C/A, andbetween L1 P(Y) and L2 C, 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 the actual 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 paragraph 20.3.3.3.3.1 with the equation:(∆tSV)L1C/A = ∆tSV - TGD + ISCL1C/A

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where TGD (see paragraph 20.3.3.3.3.2) and ISCL1C/A are provided to the user as Message Type30 data, described in paragraph 30.3.3.3.1.1. For the single frequency L2 C 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 L2 C-codes respectively as follows,

ISCL1C/A = tL1P(Y) - tL1C/A
ISCL2C = tL1P(Y) - tL2C

where, tLix is the GPS time the ith 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 two frequency (L1 C/A and L2 C) user shall correct for the group delay and ionosphericeffects by applying the relationship:PR =( PRL 2C − γ 12 PRL1C / A ) + c ( ISC L 2C − γ 12 ISC L1C / A )− c TGD
1 − γ 12

where,
PR = pseudorange corrected for ionospheric effects,
PRi = pseudorange measured on the channel indicated by the subscript,

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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 fL1 and fL2 respectively,
γ12 = (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 theionospheric model for computation of the ionospheric delay are contained in Message Type 30.
The “one frequency” user should use the model given in paragraph 20.3.3.5.2.5 to make thiscorrection for the ionospheric effects. The bit lengths, scale factors, ranges, and units of theseparameters 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 Data Predict Week Number.
Bits 257-264 of Message Type 30 shall indicate the Data Predict Week Number (WNop) to which
the Data Predict Time of Week (top) is referenced (see 30.3.3.1.1.3 and 30.3.3.2.1.2). The WNop
term consists of eight bits which shall be a modulo 256 binary representation of the GPS weeknumber to which the top is referenced. The user must account for the truncated nature of WNop in
all calculations in which WNop is used.
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 in either
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 the complete setof SVs in the constellation will be broadcast by a SV using shorter duration of time compared tothe broadcast of the complete set of Midi almanac parameters (i.e. message type 37). 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 (toa) is
referenced (see paragraph 20.3.3.5.2.2). The WNa-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

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toa 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 Time.
See 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, isprovided 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 signals of the SV whose
PRN number is specified in the message or in the packet. For each health indicator, a “0”signifies that all signals on the associated frequency are okay and “1” signifies that some or all
signals on the associated frequency are bad. The predicted health data will be updated at thetime of upload when a new reduced almanac has been built by the CS. The transmitted healthdata may not correspond to the actual health of the transmitting SV or other SVs in theconstellation.
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
with the reference values, are set to zero for SV position determination. See paragraph20.3.3.5.2.3 for almanac 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

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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 no further Status Words arecontained in the remainder of the data block. In this event, all subsequent bits in the data block
field shall be filler bits, i.e., alternating ones and zeros beginning with one.
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 apacket 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.

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Table 30-V. Midi Almanac Parameters

Parameter

No. of
Bits**

Scale
Factor(LSB)

Effective
Range***

Units

toa

8

212

602,112seconds

e

11

2-16

dimensionlessδi****

11*2-14

semi-circles

Ω

11*

2-33

semi-circles/sec

A

17

2-4

meters

Ω0

16*

2-15

semi-circles

ω

16*

2-15

semi-circles

M0

16*

2-15

semi-circles

af0

11*

2-20

seconds

af1

10*

2-37

sec/sec•* 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, effective range is the maximum range attainable withindicated bit allocation and scale factor;**** Relative to i0 = 0.30 semi-circles.

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31 BITS

1

7

15

29 30

δA

Ω0

Φ0

8 BITS

7 BITS

7 BITSPRN a
6 BITS

22

31

L1 HEALTH
L2 HEALTH*

See Figures 30 -4 and 30 -11 for complete bit allocation in therespective messages.

L5 HEALTH

Figure 30-15. Reduced Almanac Packet Content

Table 30-VI.
Parameter

Reduced Almanac Parameters *****

No. of Bits

Scale Factor (LSB)

Effective Range **UnitsδA ***

8*

2

+9

**

meters

Ω0

7*

2-6

**

semi-circles

7*

-6

**

semi-circles

Φ0 ****

2*

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

Effective range is the maximum range attainable with indicated bit allocation and scale factor;***

Relative to Aref = 26,559,710 meters;****

Φ0 = Argument of Latitude at Reference Time = M0 + ω;*****

Relative to following reference values:e=0
δi = +0.0056 semi-circles (i = 55 degrees)•Ω = -2.6 x 10-9 semi-circles/second.

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.

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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 fortranslating to the corresponding ECI SV antenna phase center position may be accomplished inaccordance 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. Figure
5.1 on page 73 of that document depicts the computational flow starting from GCRS (Geocentric
Celestial Reference System) to ITRS (International Terrestrial Reference System). Ongoing
WGS 84 re-adjustment at NGA and incorporating the 2010 IERS Conventions, are expected tobring Earth based coordinate agreement to within 2 cm. In the context of the Conventions, theuser may as a matter of convenience choose to implement the transformation computations via
either the Celestial Intermediate Origin (CIO) based approach” or the “Equinox based
approach”. The EOP parameters for ΔUT1 are to be applied within the “Rotation to terrestrial
system” process, and the parameters for xp and yp are applied in the “Rotation for polar motion”
process. Users are advised that the broadcast message type 32 EOP parameters already accountfor zonal, diurnal and semidiurnal effects (described in Chapter 8 of the IERS Conventions(2010)), so these effects should not be further applied by the user.
The relevant computations utilize elementary rotation matrices Ri(α), where α is a positive
rotation about the ith-axis ordinate, as follows:1=R1 ( α ) 000
cos(α )− sin (α )sin (α ) cos(α )0

 cos (α )R3 ( α ) =  − sin(α ) 0cos(α ), =R2 ( α )  0 sin(α )sin(α )
cos(α )
00
1
0

− sin(α )
0 
cos(α ) 

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)

Effective
Range***

Units

tEOP

EOP Data Reference Time

16

24

604,784

seconds

PM_X †

X-Axis Polar Motion Valueat Reference Time.

21*

2-20

1

arc-seconds

PM_X

X-Axis Polar Motion Drift at
Reference Time.

15*

2-21

7.8125 x 10-3

arc-seconds/day

PM_Y ††

Y-Axis Polar Motion Valueat Reference Time.

21*

2-20

1

arc-seconds

PM_Y

Y-Axis Polar Motion Drift at
Reference Time.

15*

2-21

7.8125 x 10-3

arc-seconds/day∆UT1 †††

UT1-UTC Difference at
Reference Time.

31*

2-24

64

seconds

Rate of UT1-UTC
Difference at Reference
Time

19*

2-25

7.8125 x 10-3

seconds/day

•

•

•

∆UT1 †††****

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, effective range is the maximum range attainable withindicated bit allocation and scale factor.

†

Represents the predicted angular displacement of instantaneous Celestial Ephemeris Pole with respect tosemi-minor axis of the reference ellipsoid along Greenwich meridian.

††Represents the predicted angular displacement of instantaneous Celestial Ephemeris Pole with respect tosemi-minor axis of the reference ellipsoid on a line directed 90° west of Greenwich meridian.
†††With zonal tides restored.

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Table 30-VIII.
Element/Equation•

UT 1 = UTC + ∆UT 1 + ∆ UT 1 (t − t EOP ) *Application of EOP Parameters
Description
Compute Universal Time at time t•

x p = PM _ X + PM X (t − t EOP ) *Polar Motion in the x-axis•

y p = PM _ Y + PM Y (t − t EOP ) *Polar Motion in the y-axis*t is GPS system time at time of transmission, i.e., GPS time corrected for transit time (range/speed of light).
Furthermore, the quantity (t-tEOP) shall be the actual total time difference between the time t and the epoch timetEOP, and must account for beginning or end of week crossovers. That is, if (t-tEOP) is greater than 302,400
seconds, subtract 604,800 seconds from (t-tEOP). If (t-tEOP) is less than -302,400 seconds, add 604,800 seconds
to (t-tEOP).

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 Figure30-6 for complete 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,
the accuracy 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 required to use these parameters to calculate tUTC 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

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Table 30-IX.

Parameter

UTC Parameters

No. of
Bits**

Scale
Factor(LSB)

Effective
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

days

ΔtLSF

Current or future leap second count8*

1

seconds

604,784

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, effective range is the maximum range attainable with indicatedbit allocation and scale factor;****
Right justified.

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.
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)

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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 NAV 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 top-D and of sametOD.
30.3.3.7.2.1 Differential Correction Data Predict Time of Week.
The DC data predict time of week (top-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
126-bit 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 theremainder of the data 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

δaf0

δaf1

UDRA

.
8 BITS.
13 BITS.
8 BITS.
5 BITS

EDC = Ephemeris Differential Correction

MSB
1

LSB

23

9

36

PRN IDΔαΔβ.
8 BITS.
14 BITS.
14 BITS

LSB

MSB
52

37

63

Δi

Δγ

.
12 BITS.
15 BITS

.

LSB

MSB
88

76

64

92

ΔΩ

ΔA

•
UDRA

12 BITS

12 BITS

5 BITS

Figure 30-16. Differential Correction Data Packet

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Table 30-X.

Parameter
PRN ID

Differential Correction Parameters
No. of
Bits**

Scale
Factor(LSB)

8Effective
Range***

Units
see text

δaf0

SV Clock Bias Correction

13*

2-35

seconds

δaf1

SV Clock Drift Correction

8*

2-51

seconds/second

UDRA

User Differential Range
Accuracy Index

5*∆αAlpha Correction to Ephemeris
Parameters

14*

2-34

dimensionless∆β

Beta Correction to Ephemeris
Parameters

14*

2-34

dimensionless∆γ

Gamma Correction to Ephemeris
Parameters

15*

2-32

semi-circles∆iAngle of Inclination Correction

12*

2-32

semi-circles∆Ω

Angle of Right Ascension
Correction

12*

2-32

semi-circles∆A

Semi-Major Correction

12*

2-9

metersChange Rate of User Differential
Range Accuracy Index.

5*

•
UDRA

see text

see text*

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;**
See Figure 30-7 , 11 and 12 for complete bit allocation in Message types 34, 13 and 14;***
Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor.

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 + δaf0) + (af1 + δaf1)(t − toc) + af2(t − toc )2 + ∆tr,
where δaf0 and δaf1, (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 SV

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transmitting clock correction parameters message(s) containing a top value greater than the top-D
value of messages 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 variationof the algorithm expressed in the following equations. The user will then incorporate theupdated quasi-Keplerian element set in all further calculations of SV position, as represented by
the equations in Table 30-II (see para. 30.3.3.1.3). Ephemeris-related DC data shall not beapplied to any SV transmitting message types 10 and 11 containing a top 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

Ωi

=

Ω0-n

αi

=

en cos(ωn)βi=

en sin(ωn)γi=M0-n + ωnwhere A0, en, i0-n, Ω0-n, ωn and M0-n are obtained from the applicable SV’s message types 10 and
11 data. The terms αi, βi, and γi form a subset of stabilized ephemeris elements which aresubsequently corrected by ∆α, ∆β and ∆γthe values of which are supplied in the message types
34 or 14 - as follows:αc=

αi + ∆αβc=βi + ∆βγc=γi + ∆γ185

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The quasi-Keplerian elements are then corrected byAc=

Ai + ∆Aec=(αc2 + βc2)1/2

ic=

ii + ∆iΩc=Ωi + ∆Ω

ωc=tan-1 (βc/αc)

M0-c

=

γc − ωc + ∆M0

where ∆A, ∆i and ∆Ω are provided in the EDC data packet of the message type 34 or 14 and∆M0 is obtained from1

− 3  µ  2  ∆A0 
[(t oe + WN oe * 604,800 ) − (t OD + WN * 604,800 )]∆M 0 =
2  A0 3   A0 
where WNoe is the week number associated with the toe and WN is the current week number.
The corrected quasi-Keplerian elements above are applied to the user algorithm fordetermination of antenna phase center position in Section 30.3.3.1.3, Table 30-II.
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:186

IS-GPS-200H
24 Sep 2013•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
3072.00
UDRAop-D ≤ 6144.00
1536.00
UDRAop-D ≤ 3072.00
768.00
UDRAop-D ≤ 1536.00
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 ≤UDRAop-D ≤
0.43
0.30
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
UDRAop-D ≤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)
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.

187

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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 for other systems.

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.
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.

188

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Table 30-XI.

GPS/GNSS Time Offset Parameters
No. of
Bits**

Parameter

Scale
Factor(LSB)

Effective

Units

Range***-35

seconds

A0GGTO

Bias coefficient of GPS time scale
relative to GNSS time scale

16*

2

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

3604,784

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, effective range is the maximum range
attainable with indicated 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.
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

189

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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;b.

All time-related data (TOW) in the messages shall be in SV-time;c.

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

The acts of transmitting the Nav messages shall be executed by the SV on SV
time.

190

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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 data set. The following rules govern thetransmission of toe and toc values in different data sets: (1) The transmitted toc will be different
from any value transmitted by the SV during the preceding seven days; (2) The transmitted toe
will be different from any value transmitted by the SV during the preceding six hours.
Cutovers to new data sets will occur only on hour boundaries except for the first data set of a
new upload. The first data set may be cut-in (reference paragraph 30.3.4.1) at any time during
the hour and therefore may be transmitted by the SV for less than one hour.
The start of the transmission interval for each data set corresponds to the beginning of the curve
fit interval for the data set. Each data set remains valid for the duration of its transmissioninterval, and nominally also remains valid for the duration of its curve fit interval. A data set isrendered invalid before the end of its curve fit interval when it is superseded by the SV cutting
over to the first data set of a new upload.
Normal Operations. The message type 10, 11, and 30-37 data sets are transmitted by the SV for
periods of two hours. The corresponding curve fit interval is three hours.
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 beevaluated by the user equipment. These include the following parameters as functions of GPS
time:
a. SV time,b. Semi-major axis,
c. Mean anomaly,d. Longitude of ascending node,e. Inclination,
f. UTC,

191

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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 that quantization error is small. This results in time epoch values which can be different foreach 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 (ttoe) in evaluating the expansions.

192

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The CS (Block IIR-M/IIF) and SS (GPS III) shall assure that the toe value, for at least the firstdata set transmitted by an SV after a new upload, is different from that transmitted prior to thecutover (see paragraph 30.3.4.4). As such, when a new upload is cutover for transmission, the CS(Block IIR-M/IIF) and SS (GPS III) shall introduce a small deviation in the toe resulting in the toe
value that is offset from the nominal location of 1.5 hours into the fit interval (see Table 30XIII). This offset toe will be transmitted by an SV in the first data set after a new upload cutover
and the second data set, following the first data set, may also continue to reflect the same offset
in the toe.
When the toe, immediately prior to a new upload cutover, already reflects a small deviation (i.e. a
new upload cutover has occurred in the recent past), then the CS (Block IIR-M/IIF) and SS (GPSIII) shall introduce an additional deviation to the toe when a new upload is cutover fortransmission.
For CNAV data, the user may use the following example algorithm to detect the occurrence of a
new upload cutover:
DEV = toe [modulo 7200]
If DEV ≠ 5400, then a new upload cutover has occurred within the past 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 a probability 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

193

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24 Sep 2013

whereg i = 1 for i = 0,1,3, 4,5,6,7,10,11,14,17,18, 23, 24= 0 otherwise

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 + X 8 + X 7 + X 5 + X 3 + 1

When, by the application of binary polynomial algebra, the above g(X) is divided into m(X)X24,
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 pi, 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

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40 APPENDIX IV GPS NAVIGATION DATA STRUCTURE FORLNAV DATA, 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, whentransmitted 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 is denoted 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

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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

61
HOW

C P

22 BITS73 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

WORD 10241
t oc

16 BITS

P

a f2
8
BITS

8 LSBs271
af1
16 BITS

a f0

P

t

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

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

PAGE
NO.

WORD 2

1

WORD 3

31
TLM

2

61
HOW

C P

N/A

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

287
toe

P

t

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

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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

61

TLM

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

MSBs

i0 - 32 BITS TOTAL

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 BITSΩP

24 BITS

MSBs

LSBs

P

LSBs

DIRECTION OF DATA FLOW FROM SV

151

8
BITS

16 BITSΩ 0 - 32 BITS TOTAL

WORD 6

137

LSBs

P

IODE
8
BITS

279
IDOT
14
BITS

t

P

ω - 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

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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
δi

•

Ω

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 BITSP

WORD 9211Ω0

MSB FIRST

3 SECONDS

241
ω

P

24 BITS

WORD 10P
24 BITS

271
M0

P

279

290

t P

24 BITS

8 MSBs3 LSBs

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

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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
65 66 67 68
69 70 71 72

HOW
CP

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

WORD 10271 277

16 BITS ** t P

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

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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

WORD 10249

16
BITS***

271

P

22 BITS**t

P** 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

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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**

WORD 10271

P

22 BITS**t

P** 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)

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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

18

t

22 BITS

77

α
α
0
1
8
8
BITS BITS

P

22 BITS

91

P

99

α
α
2
3
8
8
BITS BITS

107

121

β
0
8
BITS

β
β
β
1
2
3
8
8
8
BITS BITS BITS

P

129

137

P

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

DIRECTION OF DATA FLOW FROM SV
150 BITS
WORD 6

WORD 7151

418

WORD 8

181
A1

211

219

24 BITS

8
BITS

tot
WN t
8
8
BITS BITS

MSBs

LSBs

P

24 BITSMSB FIRST

3 SECONDSP

WORD 9

227

241

P

249

∆t
LS
8
8
BITS BITS

WORD 10

257

271

DN
8
BITS

∆t
P

279

LSF
8
BITS

14
BITS **

t

P

WNLSF

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)

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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

HOW
C P

25

t

22 BITS

91

A-SPOOF &SV CONFIGP

SV SV SV SV
65 66 67 68

22 BITSP

121
A- SPOOF &SV CONFIG

SV SV SV SV SV SV
69 70 71 72 73 74

P

A- SPOOF &SV CONFIG
SV SV SV SV SV SV
75 76 77 78 79 80

P

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
81 82 83 84 85 86

P

211

A- SPOOF &SV CONFIG
SV SV SV SV SV SV
87 88 89 90 91 92

P

SV SV SV
93 94 95 ****** 2 BITS*** Reserved Bits

229

241

SV
89

SV HEALTH
6 BITS/SVSV SV SV SV
90 91 92 93

A-SPOOF &SV CONFIG

P

271

P

SV HEALTH
6 BITS/SV
SV SV
94 95
***

t P

*** 2 BITS

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
4 BITS **Figure 40-1. Data Format (sheet 9 of 11)

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

PAGE
NO.

WORD 2

63

71

HOW
C P

13

t

22 BITS

WORD 4

WORD 5

69

31
TLM

4

WORD 361

1

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

WORD 10

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

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

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)

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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)

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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.
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
the various 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:

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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

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(denoted by binary code 01) denotes the LNAV data structure of D(t) which is described in thisAppendix. Future data IDs will be defined as necessary.
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 agiven SV, the SV ID is equal to 32 plus the number that is assigned to the PRN code phase ofthat SV (reference Tables 3-Ia and 3-Ib), and (b) for all other pages the SV ID assigned inaccordance with Table 40-V serves as the "page ID". IDs 65 through 95 are assigned to thosepages which contain the almanac data of specific SVs (pages 1-24 of subframe 5 and pages 2-5
and 7-9 of subframe 4). 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.

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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)
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 / and GPS III 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),
and the 50 bits devoted to parity. The number of bits, the scale factor (LSB), the range, and theunits of the almanac parameters are given in Table 20-VI. The algorithms and other material
related to the 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 dependon the individual SV's capability to retain data in memory. All three sets are based on six-day
curve fits that correspond to the first six days of the transmission interval. For Block IIR/IIR-M,
IIF and GPS III 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 accordancewith the 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 40.3.3.3.1.4. The five
LSBs of both the eight-bit and the six-bit words provide the health status of the SV's signal
components in accordance 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 indicates that "the SV which has that ID is not available and there may be no data
regarding that SV in that page of subframes 4 and 5 that is assigned to normally contain thealmanac data of that SV" (NOTE: this special meaning applies to the 25th page of subframes 4

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and 5 only). The health indication shall be given relative to the "as designed" capabilities ofeach SV (as designated by the configuration code -- see paragraph 40.3.3.5.1.4). Accordingly,
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 it has been configured into a mode which is normal from auser standpoint and does not require that capability.
Additional SV health data are given in subframe 1. The data given in subframes 1, 4, and 5 ofthe other SVs may differ from that shown in subframes 4 and/or 5 since the latter may be
updated at a different 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,
the 24 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
A-S status and the configuration code of each SV transmitting with a PRN number in the rangeof 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

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/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 SV).

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Additional codes will be assigned in the future, should the need arise.
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.
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 tousers (normal mode).

precise positioning service

10 No correction table available for either precise positioning service users or standard
positioning service users.
11 Reserved.

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Each one of the 30 six-bit ERD slots in bits 11 through 24 of word three, bits 1 through 24 ofwords four through nine, and bits 1 through 22 of word ten of page 13 of subframe 4 willcorrespond 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 slots and the 31 possible SV IDs depends on the SV ID of the particulartransmitting SV in accordance with the following two rules: 1) the CS shall ensure via uploadthat 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 the corresponding 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 an effective
range of ±9.3 m. A binary value of “100000” shall indicate that no valid ERD for thecorresponding 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 Appendix 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.

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