REVISION RECORD
LTR

DESCRIPTIONDATEAPPROVED

NC

Initial Release

24 Nov 03

24 Nov 03

A

Incorporates GPSIIIA changes

8 Jun 2010

8 Jun 2010

N/A

SE&I Tech Pubs

29 July 2010

A

IRN-IS-705A-001 - RFC 00016B - Pseudorandom
Noise (PRN) Expansion

21 Sep 2011

8 Dec 2011

Incorporation of IRN-IS-705A-001 through IRN-IS705A-006

21 Sep 2011

8 Dec 2011

IRN-IS-705B-001

17 Apr 201217 Apr 2012

IRN-IS-705B-002 (RFC 139B – Public Signals-inSpace Updates

5 Sep 201231 Jan 2013

IRN-IS-705C-001 (L1C Data Predict Week Number

24 Sep 2013

21 Mar 2014

IRN-IS-705A-002 - RFC 00077B - PublicDocument Management (GPS III terminology andSpace Service Volume (SSV) group delay)
IRN-IS-705A-003 - RFC 00086 - User Range
Accuracy (URA) Definition
IRN-IS-705A-004 - RFC 00091A - Civil Navigation(CNAV) Durations
IRN-IS-705A-005 - RFC 00093 - Technical Note 36
IRN-IS-705A-006 - RFC 00097 - Pseudorange
Parameters
B

C(WNop)

IRN-IS-705C-002(Public
Requirements Disconnects)

D

Signalsin

Space

IRN-IS-705C-003 (CNAV Reference Times)
IRN-IS-705C-004(PRNs

211-1023

23 Jan 2014
MissionAssignments)

IRN-IS-705C-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. .................................................................................................... 3

3.2.1

Ranging Codes. ......................................................................................................... 4

3.2.2

NAV Data. ................................................................................................................ 4

3.2.3

L5 Signal Structure. .................................................................................................. 7

3.3

Interface Criteria. ............................................................................................................. 8

3.3.1

Composite Signal. ..................................................................................................... 8

3.3.2

PRN Code Characteristics....................................................................................... 11

3.3.3

Navigation Data. ..................................................................................................... 16

3.3.4

GPS Time and SV Z-Count. ................................................................................... 18

4

NOT APPLICABLE ............................................................................................................. 21

5

NOT APPLICABLE ............................................................................................................. 22

6

NOTES .................................................................................................................................. 23
6.1

Acronyms ....................................................................................................................... 23

6.2

Definitions. ..................................................................................................................... 26

6.2.1

User Range Accuracy. ............................................................................................ 26
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6.2.2

SV Block Definitions. ............................................................................................. 26

6.2.3

Operational Interval Definitions. ............................................................................ 26

6.2.4

GPS Week Number. ................................................................................................ 26

6.3

6.3.1

L5 Received Signals. .............................................................................................. 27

6.3.2

Integrated Phase Noise Characteristics. .................................................................. 27

6.3.3

Ellipticity Characteristics. ....................................................................................... 28

6.3.4

Additional PRN Sequences. .................................................................................... 28

6.4

10

Supporting Material........................................................................................................ 27

Operational Protocols ..................................................................................................... 33

6.4.1

Lower PRN Numbers Versus Upper PRN Numbers .............................................. 33

6.4.2

PRN Number Consistency ...................................................................................... 33

6.4.3

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

6.4.4

PRNs 33 through 63 ................................................................................................ 34

APPENDIX I. LETTERS OF EXCEPTION ....................................................................... 35
Scope. ......................................................................................................................... 35

10.2

Applicable Documents. .............................................................................................. 35

10.3

Letters of Exception.................................................................................................... 35

20

10.1

APPENDIX II. GPS NAVIGATION DATA STRUCTURE FOR L5 CNAV DATA, D5(t) .
............................................................................................................................................... 40
20.1

Scope. ......................................................................................................................... 40

20.2

Applicable Documents. .............................................................................................. 40

20.2.1Government Documents. ........................................................................................ 40

20.2.2

Non-Government Documents. ................................................................................ 40

20.3
20.3.1Requirements. ............................................................................................................. 40
Data Characteristics. ............................................................................................... 40

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20.3.2

Message Structure. .................................................................................................. 41

20.3.3Message Content. .................................................................................................... 41

20.3.4

Timing Relationships. ............................................................................................. 91

20.3.5

Data Frame Parity. .................................................................................................. 93v

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LIST OF FIGURES
Figure 3-1.

GPS Space Segment to User Segment Interfaces .................................................. 3

Figure 3-2.

Generation of Codes ............................................................................................. 12

Figure 3-3.

Modulation of Signals .......................................................................................... 13

Figure 3-4.

XA Shift Register Generator Configuration ........................................................ 15

Figure 3-5.

XB Shift Register Generator Configuration ......................................................... 15

Figure 3-6.

Relative Phases between the XA and XB Sequences .......................................... 16

Figure 3-7.

Convolution Encoder ........................................................................................... 17

Figure 3-8.

Convolution transmit/Decoding Timing Relationships ....................................... 18

Figure 3-9.

Time Line Relationship of a Six-Second Message .............................................. 20

Figure 6-1.

Carrier Phase Noise Spectral Density .................................................................. 27

Figure 10.3-1. Letters of Exception ............................................................................................. 36
Figure 10.3-2. Letters of Exception (continued). ........................................................................ 37
Figure 10.3-3. Letters of Exception (continued) ......................................................................... 38
Figure 10.3-4. Letters of Exception (continued) ......................................................................... 39
Figure 20-1.

Message type 10 - Ephemeris 1 ........................................................................... 42

Figure 20-2.

Message type 11 - Ephemeris 2 ........................................................................... 43

Figure 20-3.

Message type 30 - Clock, IONO & Group Delay ................................................ 44

Figure 20-4.

Message type 31 - Clock & Reduced Almanac ................................................... 45

Figure 20-5.

Message type 32 - Clock & EOP ......................................................................... 46

Figure 20-6.

Message type 33 - Clock & UTC ......................................................................... 47

Figure 20-7.

Message type 34 - Clock & Differential Correction ............................................ 48

Figure 20-8.

Message type 35 - Clock & GGTO ...................................................................... 49

Figure 20-9.

Message type 36 - Clock & Text.......................................................................... 50

Figure 20-10. Message Type 37 - Clock & Midi Almanac ........................................................ 51
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Figure 20-11. Message type 12 - Reduced Almanac .................................................................. 52
Figure 20-12. Message type 13 - Clock Differential Correction ................................................ 53
Figure 20-13. Message type 14 - Ephemeris Differential Correction ......................................... 54
Figure 20-14. Message type 15 – Text........................................................................................ 55
Figure 20-15: Sample Application of Correction Parameters..................................................... 75
Figure 20-16. Reduced Almanac Packet Content ....................................................................... 79
Figure 20-17. Differential Correction Data Packet ..................................................................... 85

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LIST OF TABLES
Table 3-Ia.

Code Phase Assignments (sheet 1 of 2) ................................................................. 5

Table 3-Ia.

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

Table 3-Ib.

Additional Code Phase Assignments (sheet 1 of 1) ............................................... 7

Table 3-II.

Composite L5 Transmitted Signal Phase** ........................................................... 9

Table 3-III.

Received Minimum RF Signal Strength.............................................................. 10

Table 3-IV.

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 .............................................................................................................. 10

Table 6-I.

Typical Ellipticity vs Off-Boresight Angle .......................................................... 28

Table 6-II.

Additional Code Phase Assignments (sheet 1 of 5) ............................................. 29

Table 6-II.

Additional Code Phase Assignments (sheet 2 of 5) ............................................. 30

Table 6-II.

Additional Code Phase Assignments (sheet 3 of 5) ............................................. 31

Table 6-II.

Additional Code Phase Assignments (sheet 4 of 5) ............................................. 32

Table 6-II.

Additional Code Phase Assignments (sheet 5 of 5) ............................................. 33

Table 20-I.

Message Types 10 and 11 Parameters (1 of 2)................................................... 61

Table 20-I.

Message Types 10 and 11 Parameters (2 of 2) .................................................. 62

Table 20-II.

Elements of Coordinate System (part 1 of 2) .................................................... 63

Table 20-II.

Elements of Coordinate System (part 2 of 2) .................................................... 64

Table 20-III.

Clock Correction and Accuracy Parameters ........................................................ 66

Table 20-IV.

Group Delay Differential Parameters **** ........................................................ 71

Table 20-V.

Midi Almanac Parameters .................................................................................. 77

Table 20-VI.

Reduced Almanac Parameters ............................................................................ 79

Table 20-VII.

Earth Orientation Parameters ............................................................................. 81

Table 20-VIII. Application of EOP Parameters .......................................................................... 82
Table 20-IX.

UTC Parameters ................................................................................................. 83
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Table 20-X.

Differential Correction Parameters ..................................................................... 86

Table 20-XI.

GPS/GNSS Time Offset Parameters .................................................................. 91

Table 20-XII.

Message Broadcast Intervals .............................................................................. 92

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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 5 (L5).
1.2 IS Approval and Changes.
The Interface Control Contractor (ICC) designated by the government is responsible for the basic
preparation, obtaining 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 isgoverned by the appropriate GPS Directorate Operating Instruction (OI). Military organizations
and contractors are represented at the CCB by their respective segment member. All civilorganizations and public interest are represented by the Department of Transportation
representative of the SMC/GP.
A proposal to change the approved version of this IS can be submitted by any ICWG
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 Revision 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 (US), and form a part ofthis IS to the extent specified herein.
Specifications
FederalNone

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Military
None
Other Government Activity
NoneStandards
FederalNone
Military
None
Other Publications
IS-GPS-200

Navstar GPS Space Segment / Navigation

current issue

User Interfaces

GP-03-001

GPS Interface Control Working Groupcurrent issue(ICWG) Charter

2.2 Non-Government Documents.
The following documents of the issue specified contribute to the definition of the interfaces
between the GPS SS and the GPS Navigation US and form a part of this IS to the extent
specified herein.
Specifications
None
Other Publications
International Earth Rotation and Reference Systems Service (IERS) Technical Note 36

3 REQUIREMENTS
3.1 Interface Definition.
The signal interface between the GPS SS and the GPS Navigation US includes three radio
frequency (RF) links: L1, L2 and L5. Figure 3-1 illustrates the interface between the SS and theusers. The L5 link is only available on Block IIF and the subsequent Blocks of SVs. Utilizing

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these links, the space vehicles (SVs) of the SS shall provide continuous earth coverage signalsthat provide to the users the ranging codes and the system data needed to accomplish the GPS
Navigation (NAV) mission. These signals shall be available to a suitably equipped user with RF
visibility to an SV, including users in terrestrial and near-terrestrial applications as well as users
in orbital applications up to geostationary altitude. The civil functions of the L1 and L2 RF links
are specified in IS-GPS-200. Only the L5 link and its relationship with the L1 and L2 links are
specified herein.

SPACE SEGMENT
L5*
BLOCK III and
FUTURE SVs

BLOCK IIF

L5

L5

L1 L2

L1 L2

BLOCK IIR

L1
L2

BLOCK IIA

L1

L2

USER SEGMENT* Illustration of minimum Signal-in-Space (SIS) components.
Future SVs may introduce additional signals beyond those shown.

Figure 3-1. GPS Space Segment to User Segment Interfaces
3.2 Interface Identification.
The carriers of the L5 are typically modulated by two bit trains in phase quadrature. One is acomposite bit train generated by the modulo-2 addition of a pseudo-random noise (PRN) ranging
code, a synchronization sequence (see paragraph 3.3.3.1.2), and the downlink system data
(referred to as L5 CNAV (civil navigation) data), and the second is modulated with a PRN
ranging code and synchronization sequence (see paragraph 3.3.2.3) that differ from those usedwith the L5 CNAV data.

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3.2.1 Ranging Codes.
Two PRN ranging codes are transmitted on L5: the in-phase code (denoted as the I5-code); andthe quadraphase code (denoted as the Q5-code). Code-division-multiple-access techniques allow
differentiating between the SVs even though they may transmit at the same L5 frequency. The
SVs shall transmit intentionally "incorrect" versions of the I5 and the Q5-codes when needed toprotect the users from receiving and utilizing anomalous NAV signals. These two "incorrect"
codes are termed non-standard I5 (NSI5) and non-standard Q5 (NSQ5) codes.
3.2.1.1 L5-Codes.
The PRN ranging codes I5i(t) and Q5i(t) for SV ID number i are independent, but timesynchronized, 1 millisecond in length, with a chipping rate of 10.23 Mbps. For each code, the 1millisecond sequences are the modulo-2 sum of two sub-sequences referred to as XA and XBi;
their lengths are 8,190 chips and 8,191 chips, respectively that restart to generate the 10,230 chipcode. The XBi sequence is selectively advanced, thereby allowing the basic code generation
technique to produce different code sequences of 1-millisecond in length. Of these, 32 pairs are
currently designated for use by SVs and 5 pairs are currently reserved. Assignment of these code
phase segments by SV ID number (or other use) is given in Table 3-I. SV ID and PRN numbers
are identical to those for the L1 and L2 signals as specified in IS-GPS-200.
The 74 codes (37 I5-codes and 37 Q5-codes) are a selected subset of over 4,000 possible codesthat could be generated using the selective advance. The remaining codes are available for future
use of additional SVs and/or other L5 signal applications such as Satellite-Based Augmentation
System (SBAS) satellite signals. Of the remaining codes, Section 6.3.4 provides a selected
subset of codes with assigned PRN numbers.
3.2.1.2 Non-Standard Codes.
The NSI5 and NSQ5 codes, used to protect the user from tracking anomalous navigation signals
are not for utilization by the user and, therefore, are not defined in this document. The SVs shallalso be capable of initiating and terminating the broadcast of NSI5 and/or NSQ5 code(s)independently of each other, in response to Control Segment (CS) command.
3.2.2 NAV Data.
The L5 CNAV data, D5(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 encoded
in a rate 1/2 convolution encoder. The resulting 100 symbols per second (sps) symbol stream ismodulo-2 added to the I5-code only; the resultant bit-train is used to modulate the L5 in-phase (I)carrier. The content and characteristics of the L5 CNAV data, D5(t), are given in Appendix II ofthis document. In general, the data content is very similar to that modulated on the L2 C channelof the SV.
The L5 quadraphase (Q5) carrier has no data.

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Table 3-Ia. Code Phase Assignments (sheet 1 of 2)
GPS PRN
Signal No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

XB Code Advance – Chips*
I5
Q5
266
365
804
1138
1509
1559
1756
2084
2170
2303
2527
2687
2930
3471
3940
4132
4332
4924
5343

1701
323
5292
2020
5429
7136
1041
5947
4315
148
535
1939
5206
5910
3595
5135
6082
6990
3546

Initial XB Code State**
I5Q50101011100100
1100000110101
0100000001000
1011000100110
1110111010111
0110011111010
1010010011111
1011110100100
1111100101011
0111111011110
0000100111010
1110011111001
0001110011100
0100000100111
0110101011010
0001111001001
0100110001111
1111000011110
1100100011111

1001011001100
0100011110110
1111000100011
0011101101010
0011110110010
0101010101001
1111110000001
0110101101000
1011101000011
0010010000110
0001000000101
0101011000101
0100110100101
1010000111111
1011110001111
1101001011111
1110011001000
1011011100100
0011001011011* - XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific
I5 and a specific Q5-code phase, as shown above.

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Table 3-Ia. Code Phase Assignments (sheet 2 of 2)
GPS PRN
Signal No.
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

XB Code Advance – Chips*
I5
Q5
5443
5641
5816
5898
5918
5955
6243
6345
6477
6518
6875
7168
7187
7329
7577
7720
7777
8057

1523
4548
4484
1893
3961
7106
5299
4660
276
4389
3783
1591
1601
749
1387
1661
3210
708

Initial XB Code State**
I5Q50110101101101
0010000001000
1110111101111
1000011111110
1100010110100
1101001101101
1010110010110
0101011011110
0111101010110
0101111100001
1000010110111
0001010011110
0000010111001
1101010000001
1101111111001
1111011011100
1001011001000
0011010010000

1100001110001
0110110010000
0010110001110
1000101111101
0110111110011
0100010011011
0101010111100
1000011111010
1111101000010
0101000100100
1000001111001
0101111100101
1001000101010
1011001000100
1111001000100
0110010110011
0011110101111
0010011010001* XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific
I5 and a specific Q5-code phase, as shown above.

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Table 3-Ib. Additional Code Phase Assignments (sheet 1 of 1)
PRN
Signal No.*
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
*

XB Code Advance – Chips**
I5
Q5
5358
4226
3550
5604
3412
6375
819
3056
4608
1772
3698
3662
962
4401
3001
5218
4441
2838
4937
6913
3717
1685
4730
1194
7291
6963
2279
5001
7613
6694
5723
991
7030
7489
1475
2441
2593
639
2904
2097
2056
2498
2757
6470
3756
2399
6205
242
5053
3768
6437
1186

Initial XB Code State***I5
Q50101100000110
1111110011101
1001001100101
0101010011111
1100111001010
1000110101010
0111011011001
0010111100100
0011101101100
1011000100000
0011011111010
0011001011001
1001011010001
1000100101000
1001010111111
0000001111110
0111000111101
0000000010011
0000001000100
0101110011110
1000101010001
0001001000111
0011010001001
0011110000100
1000111110001
0100101011100
1011100101001
0010100011111
0100101011010
1101110011001
0000001000010
0011111101111
0110001101110
1100100110111
0000011001110
1001001100110
1110111011110
0100010011001
0001000010011
0000000001011
0000010100001
0000001101111
0100001100001
0101101101111
0100101001001
0100100001101
0011110011110
1101100101011
1011000110001
1010111000100
0101111001011
0010001101001

PRN sequences 38 through 63 are reserved for GPS.

** XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
*** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of a
specific I5 and a specific Q5-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.

3.2.3 L5 Signal Structure.
The L5 consists of two carrier components that 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 I5-code, NAV data, and synchronization sequence while the other isthe Q5-code with no NAV data, but with another synchronization sequence. For a particular SV,

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all transmitted signal elements (carriers, codes, synchronization sequences, and data) are
coherently derived from the same on-board frequency source.
3.3 Interface Criteria.
The criteria specified in the following define the requisite characteristics of the L5 interface.
3.3.1 Composite Signal.
The following criteria define the characteristics of the composite L5 signal.
3.3.1.1 Frequency Plan.
The requirements specified in this document shall pertain to the signal contained within a 24
MHz band centered about the L5 nominal frequency. The carrier frequencies for the L1, L2 andL5 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 Δf/f = 4.4647E-10, equivalent to a change in the I5 and Q5-code chipping rate of 10.23 MHz offset by aΔf = -4.5674E-3 Hz. This is equal to 10.2299999954326 MHz. The nominal carrier frequency(f0) -- as it appears to an observer on the ground - shall be 1176.45 MHz, or 115 times 10.23
MHz.
3.3.1.2 Correlation Loss.
Correlation loss is defined as the difference between the SV power received in the bandwidthdefined in 3.3.1.1 (excluding signal combining loss) and the signal power recovered in an ideal
correlation receiver of the same bandwidth using an exact replica of the waveform within an
ideal sharp-cutoff filter bandwidth centered at L5, whose bandwidth corresponds to that specified
in 3.3.1.1 and whose phase is linear over that bandwidth. The correlation loss apportionment due
to SV modulation and filtering imperfections shall be 0.6 dB maximum.
3.3.1.3 Carrier Phase Noise.
The phase noise spectral density of the un-modulated 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 root mean square (RMS). See additional supporting material for phase noisecharacteristics in section 6.3.2.
3.3.1.4 Spurious Transmissions.
In-band spurious transmissions, from the SV, shall be at or below -40 dBc over the band
specified in 3.3.1.1. In-band spurious transmissions are defined as transmissions within the band
specified in 3.3.1.1 which are not expressly components of the L5 signal.

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3.3.1.5 Phase Quadrature.
The two L5 carrier components modulated by the two separate bit trains (I5-code plus data andQ5-code with no data) shall be in phase quadrature (within ±100 milliradians) with the Q5 signal
carrier lagging the I5 signal by 90 degrees. Referring to the phase of the I5 carrier when I5i(t)equals zero as the "zero phase angle," the I5 and Q5-code generator output shall control therespective signal phases in the following manner: when I5i(t) equals one, a 180-degree phasereversal of the I5-carrier occurs; when Q5i(t) equals one, the Q5 carrier advances 90 degrees;
when the Q5i(t) equals zero, the Q5 carrier shall be retarded 90 degrees (such that when Q5i(t)changes state, a 180-degree phase reversal of the Q5 carrier occurs). The resultant nominal
composite transmitted signal phases as a function of the binary state of the modulating signals
are as shown in Table 3-II.
3.3.1.6 Signal Power Levels.
The SV shall provide, at a minimum, worst-case I5 and Q5 navigation signal strength at end-oflife (EOL), in order to meet the levels specified in Table 3-III. The minimum received power ismeasured 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 paragraph 3.3.1.1. Additional
related data is provided as supporting material in paragraph 6.3.1.
The GPS III SV shall provide L5 signals with the following characteristic: the L5 off-axis
relative power (referenced to peak transmitted power) shall not decrease by more than 2 dB fromthe Edge-of-Earth (EOE) to nadir, and no more than 18 dB from EOE to 26 degrees off nadir; thepower drop off between EOE and ±26 degrees shall be in a monotonically decreasing fashion.
Table 3-II. Composite L5 Transmitted Signal Phase**
Code State

Nominal Composite L5
Signal Phase*

0°
-90°
+90°
180°
*
**

I5

Q5

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 L5 carrier components at the same power.

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Table 3-III. Received Minimum RF Signal Strength
SignalSV
I5

Q5

Block IIF

-157.9 dBW-157.9 dBW

GPS III-157.0 dBW-157.0 dBW

3.3.1.6.1 Space Service Volume (SSV) Received Signal Power Levels.
The SV shall provide, at a minimum, worst-case I5 and Q5 navigation signal strength at end-oflife (EOL), in order to meet the SSV levels specified in Table 3-IV. The minimum received
power is measured at the output of a 0 dBi right-hand circularly polarized (i.e. 0 dB axial ratio)user receiving antenna at normal orientation at the off-nadir angle of 26.0 degrees. The received
signal levels are observed within the in-band allocation defined in paragraph 3.3.1.1.
Table 3-IV. 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

GPS III and

I5

Q5-182.0 dBW-182.0 dBW

Subsequent Blocks

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 on L1/L2 P(Y) is of noconcern to users since it is included in the clock correction parameters relayed in the NAV data,and is therefore accounted for by user computations of system time (reference paragraphs
20.3.3.2.3, 20.3.3.3.2.3 and 20.3.3.3.2.4). The uncertainty (variation) of these delays as well as
the group delay differential between the signals of L1, L2, and L5 are defined in the following.
3.3.1.7.1 Group Delay Uncertainty.
The effective uncertainty of the group delays shall not exceed 3.0 nanoseconds (95%
probability).

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3.3.1.7.2 Group Delay Differential.
The group delay differential between the radiated L1 and L5 signals (i.e. L1 P(Y) and L5 I5; andL1 P(Y) and L5 Q5) 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 30.0 nanoseconds. The random plus non-random variations about the mean shallnot exceed 3.0 nanoseconds (95% probability), when including consideration of the temperature
and antenna effects during a vehicle orbital revolution. L1 and L2 group delay differential isdescribed in 3.3.1.7.2 of IS-GPS-200. Corrections for the bias components of the group delaydifferential are provided to the users in the NAV message using parameters designated as TGD(reference paragraph 20.3.3.3.3.2 of IS-GPS-200) and Inter-Signal Correction (ISC) (reference
paragraph 20.3.3.3.1.2).
3.3.1.7.3 Space Service Volume Group Delay Differential.
The group delay differential between the radiated L5 signal, with respect to the Earth Coverage
signal, for users of the Space Service Volume are provided in http://www.igs.org/products/ssv
3.3.1.8 Signal Coherence.
All transmitted signals on the same carrier for a particular SV shall be coherently derived fromthe same on-board frequency standard. On the L5 channel, the chip transitions of the twomodulating signals, L5I and L5Q, shall be such that the average time difference between them,and between each and the transitions of L1 P(Y), do not exceed 10 nanoseconds. The variable
time difference shall not exceed 1 nanosecond (95% probability), when including considerationof the temperature and antenna effect changes during a vehicle orbital revolution. Corrections forthe bias components of the group delay differential are provided to the users using parameters
designated as ISCs (reference paragraph 20.3.3.3.1.2).
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, L5 ellipticity shall be no worse than 2.4 dB. Nominal values are listed
in section 6.3.3.
3.3.2 PRN Code Characteristics.
The characteristics of the I5-codes and the Q5-codes are defined below in terms of their structure
and the basic method used for generating them. Figures 3-2 and 3-3 depict simplified block
diagrams of the scheme for generating the 10.23 Mbps I5i(t) and Q5i(t) patterns, and for modulo2 summing the I5 patterns with the NAV bit train, D5(t), which is rate 1/2 encoded and clocked at
100 sps. In addition, the 100 sps are modulated with a 10-bit Neuman-Hofman code that isclocked at 1 kHz. The resultant composite bit trains are then used to modulate the L5 in-phasecarrier. The Q5-code is modulated with a 20-bit Neuman-Hofman code that is also clocked at 1
kHz.

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3.3.2.1 Code Structure.
The I5i(t) pattern (I5-code) and the Q5i(t) pattern (Q5-code) are both generated by the modulo-2
summation of two PRN codes, XA(t) and XBIi(nIi, t) or XBQi(nQi, t), where nIi and nQi are
initial states of XBIi and XBQi for satellite i. There are over 4000 unique L5 codes generatedusing different initial states of which 128 are currently assigned and identified in Table 3-Ia andTable 3-Ib using the same basic code generator. Section 6.3.4 provides a selected subset of
additional L5-code sequences with assigned PRN numbers.
Exclusive OR
Reset to all 1s on next clock
1

2

3

4

5

6

7

8

9 10 11 12 13
Decode 1111111111101

All 1'sXA(t)XA CoderXBI State for SV i
Code Clock1 ms EpochXIi(t)XBI(t-niTC)

Initial XBI StateReset

XQi(t)

1

2

3

4

5

6

7

8

9 10 11 12 13
XBQ(t-niTC)

Exclusive OR
XBI Coder
XBQ State for SV i

Initial XBQ State

1

2

3

4

5

6

7

8

9 10 11 12 13

Exclusive OR
XBQ CoderFigure 3-2. Generation of Codes

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Figure 3-3. Modulation of Signals
3.3.2.2 Code Generation.
Each I5i(t) pattern (I5-code) and Q5i(t) pattern (Q5-code) are the modulo-2 sum of two extended
patterns clocked at 10.23 Mbps (XA and XBIi or XBQi). XA is an 8190 length code, with an
initial condition of all 1s, that is short cycled 1-chip before its natural conclusion and restarted to
run over a period of 1 millisecond (synchronized with the L1 frequency C/A-code) for a total of
10,230 chips. The XBIi and XBQi, with initial conditions indicated in Table 3-I, are 8191 length
codes that are not short cycled. They are restarted at their natural completion and run over a
period of 1 millisecond (synchronized with the XA code) for a total of 10,230 chips. The
polynomials for XA and XBIi or XBQi codes, as referenced to the shift register input, are:

XA: 1+ x9 + x10 + x12 + x13, andXBIi or XBQi: 1 + x + x3 + x4 + x6 + x7 + x8 + x12 + x13.
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 3-4 (XA code) and 3-5(XB code). In the case of the XB codes, the shift register can either be initialized with all 1s andadvanced ni states as specified in Table 3-I, or initialized with the state indicated in Table 3-I.
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 each stage of the register,
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(b) the stage 13 value appears at the right followed by the values of the remaining states in orderof descending stage numbers, and(c) the shift direction is from lower to higher stage number with stage 13 providing the current
output. This code vector convention represents the present output and 12 future outputs insequence. Using this convention, at each XA epoch (state 8190), the XA shift register is
initialized to the code vector 1111111111111, while at each XB epoch (state 8191), the XB shift
register is initialized to a code vector peculiar to the PRN number and phase. The XB code
vectors are as indicated in Table 3-I. Alternatively, the XB shift register is initialized to the code
vector 1111111111111 and advanced ni states as indicated in Table 3-I.
The natural 8191 chips of the XA sequence is shortened to 8190 chips to cause precession of thesecond XA sequence with respect to the natural 8191 chip XB sequence, as shown in Figure 3-6.
Re-initialization of the XA shift register produces a 10230-chip sequence by omitting the last
6151 chips of the second natural XA sequence, or reinitializing to all 1s at the 1 ms epoch. The
XB shift register is simply allowed to run its natural course until the next 1 ms epoch when it isreinitialized at its initial state, B0, based upon PRN number and phase. This results in the phaseof the XB sequence leading by one chip during the second XA sequence in the 1-millisecond
period. Depending upon the initial state of the XB sequence, a third 8191-chip sequence may be
started before the 10230-chip sequence is completed. Two different scenarios that may result are
shown in Figure 3-6.
In scenario a, the initial state of the XB sequence, B0, is less than State 6152. Thus, the second
natural XB sequence does not run to completion prior to the next 1 ms epoch. In scenario b, theinitial state of the XB sequence, B0, is greater than State 6151. Thus, the second natural XB
sequence runs to completion and a third natural sequence starts (except when B0 is State 6152)
prior to the next 1 ms epoch.

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POLYNOMIAL XA:

1+x9+x10+x12+x13
STAGE
NUMBERS

1
1

0

2
1

1

3
1

2

4
1

3

5
1

4

INITIAL
CONDITIONS

6
1

5

7
1

8
1

6

7

9
1

8

10
1

11
1

10

9

12
1

11

13
1

12

OUTPUT

13

TAP
NUMBERSSHIFT DIRECTION

Figure 3-4. XA Shift Register Generator Configuration
POLYNOMIAL XB:

1+x+x3+x4+x6+x7+x8+x12+x13
STAGE
NUMBERS

1

2

4

3

5

6

7

9

8

10

11

12

13
OUTPUT

0

1

2

3

4

5

6

7

INITIAL CONDITIONS ARE A FUNCTION
OF PRN AND PHASESHIFT DIRECTION

8

9

10

11

12

13

TAP
NUMBERS

Figure 3-5. XB Shift Register Generator Configuration

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1 ms = 10230
8190
1

81

XA CodeB0

91

XB Code1 = 1111111111111

8 = 1111111111101

21

9 = 1111111111110

2 = State 2040

B0a) B0 = Initial State at 1 ms (less than State 6152)
1 ms = 10230
8190
1

81

XA Code

21

8191
B0

91

XB Code1 = 1111111111111

8 = 1111111111101

9 = 1111111111110

91
2 = State 2040

B0b) B0 = Initial State at 1 ms (greater than State 6151)

Figure 3-6. Relative Phases between the XA and XB Sequences
3.3.2.3 Q5 Synchronization Sequence.
Each of the 1 ms Q5-code blocks is further encoded with a 20-bit Neuman-Hofman code. The 20
bits are modulo-2 added to the Q5 code chips at the PRN code epoch rate of 1 kHz. The code,
nh20(t), starting coincident with the 20 ms data epoch on the I5 channel, is as follows:
1st

Last

nh20(t) = 0 0 0 0 0 1 0 0 1 1 0 1 0 1 0 0 1 1 1 0

3.3.3

Navigation Data.

3.3.3.1 Navigation Data Modulation.
The L5 CNAV bit train, D5(t), is rate 1/2 convolution encoded and, thus, clocked at 100 symbols
per second (sps). In addition, the 100 sps symbols are modulated with a 10-bit Neuman-Hofman
code that is clocked at 1 kHz (reference paragraph 3.3.3.1.2). The resultant symbol sequence isthen modulo-2 added with I5 PRN code and used to modulate the L5 in-phase carrier.
3.3.3.1.1 Forward Error Correction.
The L5 CNAV bit train, D5(t), will always be rate 1/2 convolution encoded with a Forward Error
Correction (FEC) code. Therefore, the symbol rate is 100 sps. The convolution coding will be
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constraint length 7, with a convolution encoder logic arrangement as illustrated in Figure 3-7.
The G1 symbol is selected on the output as the first half of a 20-millisecond data bit period
coincident with the first bit of the 20-bit Q5 Neuman-Hofman code.
Six-second navigation messages broadcast by the SV are synchronized with every fourth of the
SV’s P(Y)-code X1 epochs. Although these epochs are not necessarily accessible to the L5 user,
they are used within the SV to define GPS time. However, message synchronization does
provide the L5 user an access to the time of every 4th P(Y)-code X1 epoch. The navigation
message is FEC encoded in a continuous process independent of message boundaries (i.e. at the
beginning of each new message, the encoder registers illustrated in Figure 3-7 contain the last six
bits of the previous message). Thus, herein, reference will continue to be made to these X1
epochs. See IS-GPS-200 for details.
The FEC encoding convolves successive messages. It is necessary to define which transmitted
symbol is synchronized to SV time as follows. The beginning of the first symbol that contains
any information about the first bit of a message will be synchronized to every fourth X1 epoch(referenced to end/start of week). The users’ convolution decoders will introduce a fixed delaythat 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 convolution
decoding delay and the various relationships with the start of the data block transmission and SV
timing are illustrated in Figure 3-8 for the L5 signal.
G2 (133 OCTAL)OUTPUT SYMBOLS(100 SPS)DATA INPUT(50BPS)(ALTERNATING G1/G2)

G1 (171 OCTAL)SYMBOL
CLOCK

Figure 3-7. Convolution Encoder

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ENCODED DATA BLOCK
TRANSMITTED ON L5

DATA BLOCKDECODED BY
USER

ENCODEDDATA BLOCKRECEIVED BY
USER

USER’S DECODING DELAY
DOWNLINK DELAY

LATER

EARLY

SV 6 SECOND EPOCHS

Figure 3-8. Convolution transmit/Decoding Timing Relationships
3.3.3.1.2 Neuman-Hofman Code.
Each of the 100 sps symbols are further encoded with a 10-bit Neuman-Hofman code. The 10-bit
Neuman-Hofman code is defined to be 0000110101. The 10 bits are modulo-2 added to thesymbols at the PRN code epoch rate of 1 kHz starting at the 100 sps symbol transitions. The
result is that a "1" data symbol is replaced by 1111001010, and a "0" data symbol is replaced by
0000110101.
3.3.4 GPS Time and SV Z-Count.
GPS time is established by the Operational Control System (OCS) 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 ofJanuary 6, 1980. GPS time is the ensemble of corrected composite L1/L2 P(Y) SV times,
corrected via the clock corrections in the L1 and L2 NAV data and the relativity correction. The
largest unit used in stating GPS time is one week defined as 604,800 seconds, concatenated with
the GPS week number. GPS time may differ from UTC because GPS time is a continuous timescale, while UTC is corrected periodically with an integer number of leap seconds. There also is
an inherent but bounded drift rate between the UTC and GPS time scales. The OCS controls the
GPS time scale to be within one microsecond of UTC (modulo one second).
The L5 CNAV data contains the requisite data for relating GPS time to UTC. The accuracy ofthis data during the transmission interval will be such that it relates GPS time to UTC (USNO) to
within 20.0 nanoseconds (one sigma). This data is generated by the CS (or provided to the CS);

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therefore, the accuracy of these relationships may degrade if for some reason the CS is unable to
upload data to an SV.
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. A truncated version of the TOW-count, consisting of its 17 most significant
bits, is contained in each of the six-second messages of the L5 downlink data stream; therelationship between the actual TOW-count and its truncated message version is illustrated by
Figure 3-9.
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)
1.5 sec

X1 EPOCHS

0403,192

403,196

1

2

3

4

5

6

7

8

403,199
DECIMAL EQUIVALENTS
OF ACTUAL TOW COUNTSMESSAGE EPOCHS
6 sec

0

100,799

1

2

3

DECIMAL EQUIVALENTS OF MESSAGE TOW COUNTSNOTES:
1. THE TOW COUNT APPEARS IN EACH 6-SECOND MESSAGE
2.

THE 6-SECOND MESSAGE TOW COUNT CONSISTS OF THE 17 MSBs OF THE
ACTUAL TOW COUNT AT THE START OF THE NEXT MESSAGE.

3.

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

Figure 3-9. Time Line Relationship of a Six-Second Message

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4 NOT APPLICABLE

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5 NOT APPLICABLE

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6 NOTES
6.1

Acronyms

AFMC-

Air Force Materiel Command

AFSPC

-

Air Force Space Command

ASCII

-

American Standard Code for Information Interchangebps-

bits per second

BPSK

-

Bi-Phase Shift Key

C/A-

Course/Acquisition

CDC-

Clock Differential Correction

CNAV

-

Civil Navigation

CRC-

Cyclic Redundancy CheckCS-

Control SegmentdB-

DecibeldBc-

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

dBi-

Decibels with respect to isotropic antennadBW-

Decibels with respect to 1 Watt

DC-

Differential Correction

DoD-

Department of Defense

ECEF

-

Earth-Centered, Earth-Fixed

ECI-Earth Centered Inertial

EDC-

Ephemeris Differential Correction

EOL-

End of Life

FEC-

Forward Error Correction

GGTO

-

GPS/GNSS Time Offset

GNSS

-

Global Navigation Satellite System

GPS-

Global Positioning System

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GPSW

-

Global Positioning System Wing

Hz

-

Hertz

I5

-

In-phase Code on L5 Signal

ICC-Interface Control Contractor

ID-

Identification

IODC

-

Issue of Data, Clock

IS-

Interface Specification

ISC-

Inter-Signal Correction

LSB-

Least Significant Bit

MSB-

Most Significant Bit

NAV-Navigation

NSI5

-

Non-Standard I-Code

NSQ5

-

Non-Standard Q-Code

OCS-

Operational Control System

PIRN

-

Proposed Interface Revision Notice

PRN-

Pseudo-Random Noise

P(Y)

-

Precise (Anti-Spoof) Code

Q5-

Quadraphase code on L5 Signal

RF-Radio Frequency

RHCP

-

Right Hand Circular Polarization

RMS-

Root Mean Square

SBAS

-

Satellite Based Augmentation Systemsps-

Symbols per Second.

SIS-

Signal In SpaceSS-

Space Segment

SSV-Space Service Volume

SV-

Space Vehicle

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TBD

-

To Be DeterminedTBS-

To Be Supplied

TOW-

Time Of Week

URA-

User Range Accuracy

US-

User Segment

USNO

-

US 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.
See Section 6.2.1 of IS-GPS-200.
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-user interface.
6.2.2.1 Developmental SVs.
See paragraph 6.2.2.1 of IS-GPS-200.
6.2.2.2 Operational SVs.
The operational satellites are designated Block IIA, Block IIR, Block IIRM, Block IIF and GPS
III SVs. Characteristics of these SVs are provided below. These SVs transmit configuration
codes as specified in paragraph 20.3.3.5.1.4 of IS-GPS-200. The navigation signal provides nodirect indication of the type of the transmitting SV.
6.2.2.2.1 Block II SVs
See paragraph 6.2.2.2.1 of IS-GPS-200. These satellites do not broadcast the L5 signal.
6.2.2.2.2 Block IIA SVs.
See paragraph 6.2.2.2.2 of IS-GPS-200. These satellites do not broadcast the L5 signal.
6.2.2.2.3 Block IIR SVs.
See paragraph 6.2.2.2.3 of IS-GPS-200. These satellites do not broadcast the L5 signal.
6.2.2.2.4 Block IIR-M SVs.
See paragraph 6.2.2.2.4 of IS-GPS-200. These satellites do not broadcast the L5 signal.
6.2.2.2.5 Block IIF SVs.
See paragraph 6.2.2.2.5 of IS-GPS-200. The IIF operational SVs do broadcast the L5 signal.
6.2.2.2.6 GPS III SVs
See paragraph 6.2.2.2.6 of IS-GPS-200. The III operational SVs do broadcast the L5 signal.
6.2.3 Operational Interval Definitions.
See paragraph 6.2.3 of IS-GPS-200. There is no requirement for extended operations on L5.
6.2.4 GPS Week Number.
See paragraph 6.2.4 of IS-GPS-200 and paragraph 20.3.3.1.1.1.

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6.3

Supporting Material.

6.3.1 L5 Received Signals.
The guaranteed minimum user-received signal levels are defined in paragraph 3.3.1.6. Higher
received signal levels can be caused by such factors as SV attitude errors, mechanical antennaalignment errors, transmitter power output variations resultant of temperature variations, voltage
variations and power amplifier variations, and a variability in link atmospheric path loss. In
addition and for the purpose of establishing GPS user receiver dynamic range, the maximum
received signal level, as measured at the output of a 3 dBi linearly polarized receiver antenna, is
not expected to exceed -150.0 dBW in each L5 signal channel.
6.3.2 Integrated Phase Noise Characteristics.
As an aid to user equipment receiver designers, a plot is provided (Figure 6-1) of a typical GPS
Block IIF phase noise spectral density for the un-modulated L5 carrier. A plot of a typical GPS
III phase noise spectral density will be added TBD.

Figure 6-1. Carrier Phase Noise Spectral Density

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6.3.3 Ellipticity Characteristics.
As an aid to user equipment receiver designers, a table is provided (Table 6-I) of a typical GPS
Block IIF and GPS III ellipticity as a function of off-boresight angle.
Angle (deg)GPS BlockIIF Ellipticity(dB)
GPS III
Ellipticity
(dB)

±0
1.5
0.8

Table 6-I. Typical Ellipticity vs Off-Boresight Angle
±2
±4
±6
±8
±10
1.5
1.5
1.5
1.5
1.5
0.8

0.8

1.1

1.3

1.4

±12
1.5

±14.3
2.0

1.4

1.3

6.3.4 Additional PRN Sequences.
Among all unique L5-code sequences that could be generated using different initial states as
described in Section 3.2.1.1, 126 sequences (63 I5 and 63 Q5) are selected and assigned in Table
3-Ia and Table 3-Ib. An additional 294 sequences (147 I5 and 147 Q5) are selected and assignedwith PRN numbers in the below Table 6-II. Any assignment of an L5 PRN number and its code
sequence for any additional SV and/or other L5 signal applications, such as Satellite Based
Augmentation System (SBAS) satellite signals, will be selected from the sequences of Table 6II. PRN sequences numbered 211-1023 are reserved for internal system use and are therefore notprovided in this section.

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Table 6-II. Additional Code Phase Assignments (sheet 1 of 5)
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
96
97
98
99

XB Code Advance – Chips**
I5
Q5
7789
5246
2311
4259
7432
5907
5155
3870
1593
3262
5841
7387
5014
3069
1545
2999
3016
7993
4875
7849
2119
4157
229
5031
7634
5986
1406
4833
4506
5739
1819
7846
7580
898
5446
2022
6053
7446
7958
6404
5267
155
2956
7862
3544
7795
1277
6121
2996
4840
1758
6585
3360
429
2718
6020
3754
200
7440
1664
2781
1499
6756
7298
7314
1305
208
7323
5252
7544
696
4438

Initial XB Code State***I5Q51000100010001
1001101001111
0001000101111
0001100100010
0001100111111
0000111111000
1010101100001
0011100100111
0101011111001
0000001010010
0101101100001
1100111111001
1000101111011
0111111110010
0111011001111
0101011111111
0001011011000
1100001111011
1110000111000
1110100110101
0111010010001
1010010110101
0001101111000
0101111101111
1111001010100
1010110110010
1011101110100
1101110110001
0000100110000
1010000100100
1100010000111
0100110101010
0001101111111
1000011100011
1100110101101
1100111011010
1101011001011
0010110001111
1100001101100
1101101110110
1011110110001
1101111001001
0111010110101
1100100000000
1100101101101
1001101000100
1100111011111
1111011010001
1011111111011
0110101110111
1110100100111
0000100111111
1111110010100
1101101001110
0101001111110
1100111001011
0010100100101
1010111000011
0001111000011
1110110010110
1100111000000
1110100011111
1110010101000
0001101100011
0111000101001
0001011010110
1111101010101
0000001000111
1010111001101
1010011000000
1100101001011
1000111101101** XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
*** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific
I5 and a specific Q5-code phase, as shown above.

29

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Table 6-II. Additional Code Phase Assignments (sheet 2 of 5)
PRN
Signal No.
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
126
127
128
129

XB Code Advance – Chips**
I5
Q5
527
2485
1399
3387
5879
7319
6868
1853
217
5781
7681
1874
3788
7555
1337
2132
2424
6441
4243
6722
5686
1192
1955
2588
4791
2188
492
297
1518
1540
6566
4138
5349
5231
506
4789
113
659
1953
871
2797
6837
934
1393
3023
7383
3632
611
1330
4920
4909
5416
4867
1611
1183
2474
3990
118
6217
1382

Initial XB Code State***I5Q50010100000110
1101101011100
1101000010001
1000010110011
0111011010011
0010001110001
1101110101111
0010100100110
0111011011111
0100000111111
1010101001100
1000001111101
1011010000011
1010101111010
0101100000000
1111010101010
0000111101000
1101010111100
0110000111011
1111100001010
1101100100000
1111000010001
0011011101111
1101111011101
1001111101100
0010000100001
0100011000110
1100100111100
0111000101110
1100111100011
0100010110000
1001100001111
0110111100100
1110011001001
0001110010010
0111110110011
1110110110101
1111011010110
1101110111100
1000111011110
1101001100010
1101001011001
1100011001100
0010001111001
1000011000101
1111110011111
1111011011011
1000110000001
0000001100100
0000111100011
1101110000101
0111011011100
1100001000010
0101101010100
0001101001101
0000101010111
1010100101011
1010111101101
1111011110100
0100010000010** XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
*** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific
I5 and a specific Q5-code phase, as shown above.

30

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Table 6-II. Additional Code Phase Assignments (sheet 3 of 5)
PRN
Signal No.
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
156
157
158
159

XB Code Advance – Chips**
I5
Q5
1224
1092
1733
7950
2319
7223
3928
1769
2380
4721
841
1252
5049
5147
7027
2165
1197
7897
7208
4054
8000
3498
152
6571
6762
2858
3745
8126
4723
7017
5502
1901
4796
181
123
1114
8142
5195
5091
7479
7875
4186
330
3904
5272
7128
4912
1396
374
4513
2045
5967
6616
2580
6321
2575
7605
7961
2570
2598

Initial XB Code State***I5
Q51111111101100
1010111011111
0000010000111
0110001000010
1111110000010
1011000011010
0011100111011
1000100000111
1101100010101
1001011110110
0101011111011
1000001011000
0001100011011
0000110010111
0001101110111
0010101101011
1110011110000
0011100001100
0111100011111
0100011001011
0011101110000
1010101001111
1111001001000
0100001000101
0001101110010
0000001111100
0101100111100
1101001110111
0010010111101
1110111110001
1101110110011
1110111010001
0011110011111
0001010110011
1001010101111
0111111000101
0111111101111
0100010011100
0000100100001
1110000010011
1110001101011
0110010101000
1111010010001
0000100000100
1011010111101
0100100101011
0001101110000
1000010001111
0000010111100
1110101000010
0100101111100
1110000111011
1110110111010
1110110010010
1101110101011
1001001001000
1101000110001
0011100001101
0100100010100
0000111101110** XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
*** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific
I5 and a specific Q5-code phase, as shown above.

31

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Table 6-II. Additional Code Phase Assignments (sheet 4 of 5)
PRN
Signal No.
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

XB Code Advance – Chips**
I5
Q5
2419
4508
1234
2090
1922
3685
4317
7748
5110
684
825
913
958
5558
1089
2894
7813
5858
6058
6432
7703
3813
6702
3573
1714
7523
6371
5280
2281
3376
1986
7424
6282
2918
3201
5793
3760
1747
1056
7079
6233
2921
1150
2490
2823
4119
6250
3373
645
977
2401
681
1639
4273
2946
5419
7091
5626
923
1266

Initial XB Code State***I5Q51110100011001
0100001001100
1101000100111
0010111011110
0101101110111
0110011011010
0010111010000
1101011000010
0000111011000
1100010001101
1001110111011
1010111011001
0110100011111
0100001001010
0111011111100
0111000111010
1010010011010
0000000110000
0010011010110
1100101111100
0111100110011
0001100100111
0000011011011
0011010111001
1001010011010
0001000011100
1101010101111
1100101010110
1110111001010
1101110010010
0010011110110
1111111111001
0011110101001
0110000001010
1111010000111
0100101001010
0010010010100
1111110100100
0100101110010
1100010101011
1101110110000
1100110000001
1000111111011
0111111011010
0101101110000
0111000011101
0001110101011
1110010010110
1111000100010
0011111111000
0101001000011
0010001101101
0011101111100
0001100110011
1011010111010
0100111011011
0000001010011
0110111000101
0010011111101
1101011100011** XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
*** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific
I5 and a specific Q5-code phase, as shown above.

32

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Table 6-II. Additional Code Phase Assignments (sheet 5 of 5)
PRN
Signal No.
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210

XB Code Advance – Chips**
I5
Q5
7045
5804
6493
2414
1706
6444
5836
4757
926
427
6086
5452
950
5182
5905
6606
3240
6531
6675
4268
3197
3115
1555
6835
3589
862
4555
4856
5671
2765
6948
37
4664
1943
2086
7977
5950
2512
5521
4451
1515
4071

Initial XB Code State***I5
Q51111100011000
1001110110001
1101101101100
0001100110110
1101010010110
1101101010111
0110000101110
1001110000111
0110010011111
0110100111010
1000111001100
0110001100110
1111101110001
0000100001100
0011111100001
0101000101101
0000001110001
1000001010111
1010110100100
0011001110001
0100001110110
0100011100110
0111110100011
0100101100101
0001111001011
1110001010111
1010100011011
1010110110100
1001101110011
1111101101000
0010111000001
1000001110100
1101100001111
1000010101100
1110111101001
1100001001101
0110110101101
1111111000011
0111110110010
0001011110011
1000101110111
1001000100001** XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.
*** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns. The rightmost bit is the first bit out. Since the initial state of the XA Code is all
1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.
NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific
I5 and a specific Q5-code phase, as shown above.

6.4

Operational Protocols

6.4.1 Lower PRN Numbers Versus Upper PRN Numbers
See IS-GPS-200.
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
See IS-GPS-200.

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6.4.4 PRNs 33 through 63
See IS-GPS-200.

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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,
10.3-2, 10.3-3, and 10.3-4.

35

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Figure 10.3-1. Letters of Exception

36

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Figure 10.3-2. Letters of Exception (continued).

37

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Figure 10.3-3. Letters of Exception (continued)

38

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Figure 10.3-4. Letters of Exception (continued)
39

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20 APPENDIX II. GPS NAVIGATION DATA STRUCTURE FOR
L5 CNAV DATA, D5(t)20.1 Scope.
This appendix describes the specific GPS L5 civil navigation (CNAV) data structure denoted by,
D5(t).
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 CNAV data related interfaces and form a part of thisAppendix to the extent specified herein.
Specifications
NoneStandards
None
Other Publications
None
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 CNAV data related interfaces and form a part of thisAppendix to the extent specified herein.
Specifications
None
Other Publications
None
20.3 Requirements.
20.3.1 Data Characteristics.
The L5 channel data stream mostly contains the same data as the L2 C channel. The data stream
shall be transmitted by the SV on the L5 channel at the rate of 50 bps with rate 1/2 FEC resulting
in 100 sps.

40

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20.3.2 Message Structure.
As shown in Figures 20-1 through 20-14, the L5 CNAV message structure utilizes a basic formatof six-second 300-bit long messages. Each message contains a Cyclic Redundancy Check(CRC) parity block consisting of 24 bits covering the entire six-second message (300 bits)(reference Section 20.3.5).
Message type 0 (zero) is defined to be the default message. In the event of message generation
failure, the SV shall replace each affected message type with the default message type. In theevent that a particular message is not assigned (by the CS) a particular message type forbroadcast, 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 IIF SVs have the capability of storing at least 48 hours of CNAV navigation data, withcurrent memory margins, to provide CNAV positioning service without contact from the CS forthat 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.
20.3.3 Message Content.
Each message starts with an 8-bit preamble - 10001011, followed by a 6-bit PRN number of
the transmitting SV, a 6-bit message type ID with a range of 0 (000000) to 63 (111111), andthe 17-bit 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 6-second message. An“alert” flag, when raised (bit 38 = “1”), indicates to the user that the signal URA components
may be worse than indicated in the associated message types and that he shall use at his own
risk. For each default message (Message Type 0), bits 39 through 276 shall be alternating ones
and zeros and the message shall contain a proper CRC parity block.

41

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9

1

15

21

PRN
8
BITS

6
BITS

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

6
BITS

MESSAGETOW COUNT*
17 BITSMESSAGE TYPE ID"ALERT" FLAG - 1 BIT

PREAMBLE

WN n

top

13 BITS

11 BITS

5BITS

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

71

82
toe

∆A

11 BITS

19 MSBs

URA ED INDEXDIRECTION OF DATA FLOW FROM SV
100 BITS
2 SECONDS
101

150

133

108

MSB FIRST

173

∆A

•
A

∆n 0

•
∆n 0

M 0-n

7 LSBs25 BITS

17 BITS

23 BITS

28 MSBs

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 SECONDSMSB FIRST
272

201

206

M 0-n

5 LSBs

277

239
en

ωn

CRC

33 BITS

33 BITS

24 BITSINTEGRITY STATUS FLAG – 1 BIT
L2C PHASING – 1 BIT
RESERVED – 3 BITS

* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6 SECOND MESSAGE

Figure 20-1. Message type 10 - Ephemeris 1

42

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1

15

9
PRN
6
BITS

8 BITS

6BITS

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 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
2 SECONDS
101

133

116
i0-n

•
∆Ω

15 LSBs

17 BITS

•
i0-n

148

164

15 BITS

180

cis-n

cic-n

crs-n

16 BITS

16 BITS

21 MSBs

MSB FIRST

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

228

270

249

crc-n

cus-n

cuc-n

24 BITS

21 BITS

21 BITS

crs-n - 3 LSBs

277
CRC

7 BITS

24 BITSRESERVED* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-2. Message type 11 - Ephemeris 2

43

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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
2 SECONDS
101

128

118
af1-n

af2-n

17 LSBs

10 BITS

141

154

167

α1
8 BITs

209

217
α2

225
α3

8 BITS

8 BITS

β0
8 BITS

180

193

TGD

ISCL1C/AISCL2CISCL5I5

ISCL5Q5

α013 BITS

13 BITS

13 BITS

13 BITS

13 BITS

8 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 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
2 SECONDS
38
50
55 58 61
39

233

241
β1

8 BITS

257

249
β2

8 BITS

265

277

β3

WNOP

RESERVED

8 BITS

8 BITS

12 BITS

CRC
24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-3. Message type 30 - Clock, IONO & Group Delay

44

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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
2 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

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 SECONDS
201

10 LSBs

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
2 SECONDS
38
50
55 58 6139

211

21 MSBs

MSB FIRST

273 277

242
Reduced Almanac
Packet 3

Reduced Almanac
Packet 4

31 BITS

31 BITS

Reduced Almanac Packet 2

Reduced Almanac
Packet 2

CRC
4
BITS

24 BITSRESERVED* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-4. Message type 31 - Clock & Reduced Almanac

45

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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
2 SECONDS
101

17 LSBs

144

128

118
af1-n

af2-n

tEOP

10 BITS

16 BITS

165

180

PM-X

•
PM-X

PM-Y

21 BITS

15 BITS

21 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 SECONDS
201

15 BITS

266

247

216
•
PM-Y

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
2 SECONDS
38
50
55 58 61
39

277

∆UT1

•
∆UT1

RESERVEDCRC

31 BITS

19 BITS

11 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-5. Message type 32 - Clock & EOP

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1

9

21

15

PRN
6
BITS

8 BITS

6BITS

MESSAGETOW COUNT*

top

17 BITS

11 BITS

5BITS

URANED0
INDEX"ALERT" FLAG - 1 BIT

toc

af0-n

11 BITS

26 BITSMSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 SECONDS
101

128

118

144

98

72

URANED2 INDEX - 3 BITS
URANED1 INDEX - 3 BITS
af1-n – 3 MSBs

MESSAGE TYPE ID
PREAMBLEMSB FIRST

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

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
2 SECONDS

WNLSF
13 BITS

277

226

214 218201

MSB FIRST∆tLSF
4BITS 8 BITS
DN

RESERVEDCRC

51 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-6. Message type 33 - Clock & UTC

47

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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
af1-n
17 LSBs

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
2 SECONDS
38
50
55 58 61
39

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

MSB FIRST

185

af2-n

top-D

tOD

CDC

EDC

10 BITS

11 BITS

11 BITS

34 BITS

16 MSBs

DC DATA TYPE – 1 BIT

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 SECONDSMSB FIRST

277

201
EDC

CRC

76 LSBs

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE
CDC = Clock Differential Correction
EDC = Ephemeris Differential Correction

Figure 20-7. Message type 34 - Clock & Differential Correction

48

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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
2 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
2 SECONDS
38
50
55 58 61
39

144

af1-n

af2-n

tGGTO

17 LSBs

10 BITS

16 BITS

157 160MSB FIRST

189

176

196

WNGGTOA0GGTOA1GGTOA2GGTO

13 BITS

16 BITS

13 BITS

7 BITS 5 BITS

RESERVEDGNSS ID – 3 BITS

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 SECONDSMSB FIRST

277

201
RESERVEDCRC

76 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-8. Message type 35 - Clock & GGTO

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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
2 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
2 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
2 SECONDS

276
277

272

201
TEXT MESSAGE (18 8-BIT CHAR)

CRC
4
BITS

71 LSBs
TEXT PAGE

24 BITSRESERVED – 1 BIT* MESSAGE TOW COUNT = 17 MSBs OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-9. Message type 36 - Clock & Text

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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
2 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
2 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
2 SECONDS
201

A
7 LSBs

240

224

208

256

277

267

Ω0

ω

M0

af0

af1

CRC

16 BITS

16 BITS

16 BITS

11 BITS

10 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSBs OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-10. Message Type 37 - Clock & Midi Almanac

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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
2 SECONDS
38
60
52
39

"ALERT" FLAG - 1 BIT

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 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
2 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 MSBs OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE

Figure 20-11. Message type 12 - Reduced Almanac

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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
2 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
2 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
2 SECONDS
236
237

201
202

MSB FIRST

271

277

CDC

CDC

34 BITS

34 BITS

6
BITS

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

RESERVED* MESSAGE TOW COUNT = 17 MSBs OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE
CDC = Clock Differential Correction

Figure 20-12. Message type 13 - Clock Differential Correction

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1

15

9
PRN

8 BITS

6
BITS

6
BITS

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 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
2 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
2 SECONDSMSB FIRST

247

277

EDC

RESERVEDCRC

46 LSBs

30 BITS

24 BITS* MESSAGE TOW COUNT = 17 MSBs OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGE
EDC = Ephemeris Differential Correction

Figure 20-13. Message type 14 - Ephemeris Differential Correction

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1

15

9
PRN

8 BITS

6
BITS

6
BITS

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 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
2 SECONDS
101
TEXT MESSAGE (29 8-BIT CHAR)
BITS 63-162

MSB FIRST

DIRECTION OF DATA FLOW FROM SV
100 BITS
2 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 6-SECOND MESSAGE

Figure 20-14. Message type 15 – Text

55

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20.3.3.1 Message Types 10 and 11 Ephemeris and Health Parameters.
20.3.3.1.1 Message Types 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 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 defined
method must account for the potential inapplicability of the group delay differential correction
terms.
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 20.3.4.4.
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 andSS 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 20.3.4.5 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 an enhanced levelof integrity assurance. That is, the probability that the instantaneous URE of the conveying
signal exceeds 5.73 times the current broadcast IAURA value, for more than 5.2 seconds,
without an accompanying alert, is less than 1E-8 per hour. The probabilities associated with thenominal and lower bound values of the current broadcast URAED index, URANED indexes, andrelated 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.
20.3.3.1.1.1 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 of IS-GPS-200).
20.3.3.1.1.2 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 message types 12, 31, and 37. The data
given in message type 10 may differ from that shown in the other messages of the transmitting
SV and/or other SVs since the latter may be updated at a different time.

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20.3.3.1.1.3 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.
20.3.3.1.1.4 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 for 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< URAED (or no accuracy prediction is available)

143072.00< URAED ≤6144.00

13

1536.00< URAED ≤3072.00

12

768.00< URAED ≤1536.00

11

384.00< URAED ≤768.0010

192.00< URAED ≤384.00996.00< URAED ≤192.008

48.00< URAED ≤

96.00

7

24.00

< URAED ≤

48.00

6

13.65

< URAED ≤

24.00

5

9.65

< URAED ≤

13.65

4

6.85

< URAED ≤

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3

4.85

< URAED ≤

6.85

2

3.40

< URAED ≤

4.85

1

2.40

< URAED ≤

3.40

0

1.70

< URAED ≤

2.40

-1

1.20

< URAED ≤

1.70

-2

0.85

< URAED ≤

1.20

-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 URA index (N), users may compute a nominal URA value (X) as given by:• If the value of N is 6 or less, X = 2(1 + N/2),• If the value of N is 6 or more, but less than 15, X = 2(N - 2),

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• N = 15 shall indicate the absence of an accuracy prediction and shall advise the standard
positioning service user to use that SV at his own risk.
For N = 1, 3, and 5, X should be rounded to 2.8, 5.7, and 11.3 meters, respectively.
The nominal 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 withrespect to the scaled (multiplied by either 4.42 or 5.73 as appropriate) upper bound values of thebroadcast URAED index (see 20.3.3.1.1).
For the nominal URAED value and the IAURAED value, users may compute an adjusted URAED
value as a function of SV elevation angle (E), for E ≥ 0, as follows:

Adjusted Nominal URAED = Nominal URAED (sin(E+90 degrees))
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.
20.3.3.1.2 Message Types 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 20-I. See Figures 20-1 and 20-2 for complete bit allocation inmessage types 10 and 11.
20.3.3.1.3 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 20-II. The ephemeris parameters are
Keplerian in appearance; the values of these parameters, however, are produced by the CS(Block IIF) or the SV (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 20.3.3.4.3.4of IS-GPS-200.

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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.
Table 20-I. Message Types 10 and 11 Parameters (1 of 2)
Parameter
SymbolWN

Parameter Description
Week No.

No. of
Bits**
13

URAED INDEXED accuracy

5*

Signal health(L1/L2/L5)

Scale
Factor(LSB)
1

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

semicircles/sec∆n0•Rate of mean motion difference
from computed value

23*

2-57

semicircles/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 20-1 for complete bit allocation in message type 10;***

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

****

Relative to AREF = 26,559,710 meters.

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Table 20-I. Message Types 10 and 11 Parameters (2 of 2)
No. of
Bits**
11

Scale
Factor(LSB)
300

Longitude of Ascending Node of Orbit
Plane at Weekly Epoch

33*

2-32

semi-circles•∆ Ω****

Rate of right ascension difference

17*

2-44

semi-circles/sec

i0-nInclination angle at reference time

33*

2-32

semi-circles•
i0-nRate 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 sine harmonic correction
term to the argument of latitude

21*

2-30

radians

Parameter
SymboltoeΩ0-nParameter Description
Ephemeris data reference time of week

Effective
Range***
604,500

Units
seconds*

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

See Figure 20-1 and Figure 20-2 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 20-II. Elements of Coordinate System (part 1 of 2)
Element/Equationµ = 3.986005 x 1014 meters3/sec2

DescriptionΩe = 7.2921151467 x 10-5 rad/sec

WGS 84 value of the earth’s gravitational constant for GPSuser
WGS 84 value of the earth’s rotation rate

A0 = AREF + ∆A *Semi-Major Axis at reference time••

Ak = A0 + (A) tk
n0 =

µ
A03

Semi-Major Axis
Computed Mean Motion (rad/sec)

tk = t – toe **Time from ephemeris reference time∆nA = ∆n0 +½ ∆n•0 tk

Mean motion difference from computed valuenA = n0 + ∆nA

Corrected Mean Motion

Mk = M0 + n A t k

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.

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Table 20-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) + δrkik= io-n + (io-n )tk + δik

Corrected Radius•Corrected Inclination

xk' = rk cos uk

Positions in orbital planeyk' = rk sin uk•••

Rate of Right AscensionΩ = ΩREF + ∆Ω ***•••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***• = −2.6 x 10-9 semi-circles/second.
Ω
REF

20.3.3.2 Message Types 30 through 37 SV Clock Correction Parameters.
20.3.3.2.1 Message Types 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 provide users with the requisite data to correct SV time and to calculate SV position precisely.

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In general, any message of type 30 to 39 will provide SV clock correction parameters as
described in this section.
20.3.3.2.1.1 SV Clock Correction.
Any one of message types 30 through 37, Figure 20-3 through Figure 20-10, 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 20.3.3.2.3.
20.3.3.2.1.2 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.
20.3.3.2.2 Clock Parameter Characteristics.
The number of bits, the scale factors of the LSB (which is the last bit received), the range, andthe units of clock correction parameters shall be as specified in Table 20-III.
20.3.3.2.3 User Algorithms for SV Clock Correction Data.
The algorithms defined in paragraph 20.3.3.3.3.1 of IS-GPS-200 allow all users to correct thecode phase time received 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 of ISGPS-200 are estimated by the CS using dual frequency L1 and L2 P(Y) code measurements, thesingle-frequency L5 user and the dual-frequency L1 and L5, and L2 and L5 users must apply
additional terms to the SV clock corrections equations. These terms are described in paragraph20.3.3.3.1.

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Table 20-III. Clock Correction and Accuracy Parameters
Parameter
Symboltoc

No. of
Bits**
11

Parameter Description
Clock Data Reference Time of Week

Scale
Factor(LSB)
300

Effective
Range***
604,500

Units
seconds

URANED0 Index

NED Accuracy Index

5*(see text)

URANED1 Index

NED Accuracy Change Index

3(see text)

URANED2 Index

NED Accuracy Change Rate Index

3(see text)

SV Clock
Coefficient

10*

2-60

sec/sec2

20*

2-48

sec/sec26*

2-35

seconds

af2-n

Drift

Rate

Correction

af1-n
SV Clock Drift Correction Coefficient
af0-n
SV Clock Bias Correction Coefficient
*
**
***

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figures 20-3 through 20-10 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.

20.3.3.2.4 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 unauthorized user.
The following equations together with the broadcast URANED0 Index, URANED1 Index, and
URANED2 Index shall give the clock-related 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 instantduring 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))

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

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IAURANED = URANED0 + URANED1*(t - top + 604,800*(WN - WNop)) + URANED2*(t - top +604,800*(WN - WNop) - 93,600)2

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

where

t is the GPS system time

The CS shall derive URANED0, URANED1, and URANED2 indexes which, when used together in
the above equations, results in the minimum IAURANED that is greater than the predicted
IAURANED during the ephemeris fit interval.
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:

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

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5

9.65

< URANED0

≤

13.65

4

6.85

< URANED0

≤

9.65

3

4.85

< URANED0

≤

6.85

2

3.40

< URANED0

≤

4.85

1

2.40

< URANED0

≤

3.40

0

1.70

< URANED0

≤

2.40

-1

1.20

< URANED0

≤

1.70

-2

0.85

< URANED0

≤

1.20

-3

0.60

< URANED0

≤

0.85

-4

0.43

< URANED0

≤

0.60

-5

0.30

< URANED0

≤

0.43

-6

0.21

< URANED0

≤

0.30

-7

0.15

< URANED0

≤

0.21

-8

0.11

< URANED0

≤

0.15

-9

0.08

< URANED0

≤

0.11

-10

0.06

< URANED0

≤

0.08

-11

0.04

< URANED0

≤

0.06

-12

0.03

< URANED0

≤

0.04

-13

0.02

< URANED0

≤

0.03

-14

0.01

< URANED0≤0.02

URANED0

≤

0.01

-15
-16

No accuracy prediction available-use at own risk

Integrity properties of the URA are specified with respect to the upper bound values of the URA
index (see 20.3.3.1.1).

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24 Sep 2013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 20.3.3.1.1).
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
20.3.3.3.1.1.1; 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 20.3.3.3.1.1.2; radial ephemeris error; anisotropic antenna errors; and signal
deformation error. URANED does not account for user range contributions due to the inaccuracyof 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 URA NED1 index has
the following relationship to the URA NED1 value:
1
N
URANED1 = 2 (meters/second)
where

N

= 14 + URANED1 Index.

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The transmitted URANED2 index is an integer value in the range 0 to 7. URANED2 index has thefollowing relationship to the URANED2:URANED2

1N= 2 (meters/second/second)

where

N

= 28 + URANED2 Index.

20.3.3.3 Message Type 30 Ionospheric and Group Delay Correction Parameters.
20.3.3.3.1 Message Type 30 Ionospheric and Group Delay Correction Parameter Content.
Message type 30 provides SV clock correction parameters (ref. Section 20.3.3.2) 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 user. The following
algorithms shall apply when interpreting the correction parameters in the message.
20.3.3.3.1.1 Estimated L1-L2 Group Delay Differential.
The group delay differential correction terms, TGD, ISCL1C/A, ISCL2C are contained in bits 128
through 166 of message type 30. See paragraph 30.3.3.3.1.1 of IS-GPS-200. The bit lengths,
scale factors, ranges, and units of these parameters are given in Table 20-IV. These group delaydifferential correction terms are also used for the benefit of single frequency L5-I5 and L5-Q5
users and dual frequency L1/L5 and L2/L5 users.
20.3.3.3.1.1.1 L1/L2 Inter-Signal Group Delay Differential Correction.
See paragraph 30.3.3.3.1.1.1 of IS-GPS-200.
20.3.3.3.1.2 Estimated L5 Group Delay Differential
The group delay differential correction terms, TGD, ISCL5I5 and ISCL5Q5, for the benefit of single
frequency L5-I5 and L5-Q5 users and dual frequency L1/L5 and L2/L5 users are contained inbits 128 through 140 and 167 through 192 of message type 30 (see Figure 20-3 for complete bit
allocation). The bit lengths, scale factors, ranges, and units of these parameters are given in
Table 20-IV. The bit string of “1000000000000” shall indicate that the group delay value is notavailable. The related algorithms are given in paragraphs 20.3.3.3.1.2.1, 20.3.3.3.1.2.2, and20.3.3.3.1.2.3.

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Table 20-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 20-3 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.

20.3.3.3.1.2.1 L1/L5 Inter-Signal Correction.
The L5 correction terms, TGD, ISCL5I5 and ISCL5Q5 are provided by the CS to account for theeffect of inter-signal biases between L1 P(Y) and L2 P(Y), L1 P(Y) and L5 I5, and between L1
P(Y) and L5 Q5, respectively. These values are initially based on measurements made by the SVcontractor during SV manufacture. The values of TGD and ISC’s for each SV may besubsequently updated to reflect the actual on-orbit group delay differential. For maximum
accuracy, the single frequency L5 I5 user must use the correction terms to make further
modifications to the code phase offset in paragraph 20.3.3.3.3.1 of IS-GPS-200 with theequation:(∆tSV)L5I5 = ∆tSV − TGD + ISCL5I5
where TGD (see paragraph 20.3.3.3.3.2 of IS-GPS-200) and ISCL5I5 (described in paragraph20.3.3.3.1.2) are provided to the user as message type 30 data. For maximum accuracy, thesingle frequency L5 Q5 user must use the correction terms to make further modifications to thecode phase offset given by:(∆tSV)L5Q5 = ∆tSV − TGD + ISCL5Q5

where ISCL5Q5 (described in paragraph 20.3.3.3.1.2) is provided to the user as message type 30
data.

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The values of ISCL5I5 and ISCL5Q5 are measured values that represent the mean SV group delaydifferential between the L1 P(Y)-code and the L5 I5-code or L5 Q5-code respectively as follows.
ISCL5I5 = tL1P(Y) − tL5I5
ISCL5Q5 = tL1P(Y) − tL5Q5
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.
20.3.3.3.1.2.2 L1/L5 Ionospheric Correction.
The two frequency (L1 C/A and L5 I5) user shall correct for the group delay and ionosphericeffects by applying the relationship:
PR =(PR L5I5 − γ 15 PR L1C / A ) + c(ISC L5I5 - γ 15 ISC L1C / A )− cTGD
1 − γ 15

The two frequency (L1 C/A and L5 Q5) user shall correct for the group delay and ionosphericeffects by applying the relationship:

PR =(PR L5Q5 − γ 15 PR L1C / A ) + c(ISC L5Q5 - γ 15 ISC L1C / A )1 − γ 15

− cTGD

wherePR= pseudorange corrected for ionospheric effects,

PRi= pseudorange measured on the channel indicated by the subscript;

ISCi =
inter-signal correction for the channel indicated by the subscript (seeparagraph 20.3.3.3.1.2),
TGD= see paragraph 20.3.3.3.3.2 of IS-GPS-200,c= speed of light (see paragraph 20.3.4.3),

and where, denoting the nominal center frequencies of L1 and L5 as fL1 and fL5 respectively,

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γ15 = (fL1/fL5)2 = (1575.42/1176.45)2 = (154/115)2.
20.3.3.3.1.2.3 L2/L5 Ionospheric Correction.
The two frequency (L2 C and L5 I5) user shall correct for the group delay and ionosphericeffects by applying the relationship:

PR =(PR L5I5 − γ 25 PR L 2C ) + c(ISC L5I5 - γ 25 ISC L 2C )− cTGD
1 − γ 25

The two frequency (L2 C and L5 Q5) user shall correct for the group delay and ionosphericeffects by applying the relationship:

PR =(PR L5Q5 − γ 25 PR L 2C ) + c(ISC L5Q5 - γ 25 ISC L 2C )1 − γ 25

− cTGD

wherePR= pseudorange corrected for ionospheric effects,

PRi= pseudorange measured on the channel indicated by the subscript,

ISCi =
inter-signal correction for the channel indicated by the subscript (seeparagraph 20.3.3.3.1.2),
TGD= see paragraph 20.3.3.3.3.2 of IS-GPS-200,c= speed of light (see paragraph 20.3.4.3).

and where, denoting the nominal center frequencies of L2 and L5 as fL2 and fL5 respectively.
γ25 = (fL2/fL5)2 = (1227.6/1176.45)2 = (24/23)2
20.3.3.3.1.3 Ionospheric Data.
The ionospheric parameters which allow the “L5 only” user to utilize the ionospheric model forcomputation of the ionospheric delay are contained in message type 30. The “one frequency”
user should use the model given in Figure 20-4 of IS-GPS-200 to make this correction. The
calculated value of Tiono (Tiono = ionospheric correction parameter) in the model is referred to the73

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L1 frequency; if the user is operating on the L5 frequency, the correction term must be
multiplied by γ15 (reference paragraph 20.3.3.3.1.2.2). 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 toionospheric propagation effects. The bit lengths, scale factors, ranges, and units of theseparameters are given in Table 20-X of IS-GPS-200 (See Figure 20-3 for complete ionospheric bit
allocation).
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. During extended operations or in the Autonav mode, if the CS isunable to upload the SVs, the use of this model will yield unpredictable results.
20.3.3.3.1.4 Example Application of Correction Parameters.
A typical system application of the correction parameters for a user receiver is shown in Figure20-15. The ionospheric model referred to in Figure 20-15 is discussed in paragraph 20.3.3.3.1.3.

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TGD*, ISCL1C/A**, ISCL2C**, ISCL5I5* , ISCL5Q5*

ESTIMATE OF SV
TRANSMISSION TIME

af0, af1, af2, toc

CLOCK
CORRECTIONPOLYNOMIAL

∆tr

∆tSV
TROPOSPHERIC
MODEL
CODE PHASE OFFSET- TRUE SV CLOCK EFFECTS- EQUIPMENT GROUP DELAY
DIFFERENTIAL EFFECTS- RELATIVISTIC EFFECTS

TtropoIONOSPHERIC
MODEL

Tiono

αn, β nFILTER AND
COORDINATECONVERTER

GPS TIME PATH DELAY- GEOMETRIC- TROPOSPHERIC- IONOSPHERIC*PSEUDORANGEDIVIDED BY THE
SPEED OF LIGHT
USER CLOCK BIAS

USER POSITION,VELOCITY and
TIME (CLOCK BIAS)- RANGE DATA FROMOTHER SATELLITES- CALIBRATION DATA- AUXILIARY SENSOR* SINGLE FREQUENCY AND DUALFREQUENCY (L1/L5 AND L2/L5)
USERS

GPS TIME** DUAL FREQUENCY USERS ONLY

Figure 20-15: Sample Application of Correction Parameters20.3.3.3.1.5 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 20.3.3.1.1.3 and 20.3.3.2.1.2). The
WNOP term consists of eight bits which shall be a modulo 256 binary representation of the GPS
week number to which the top is referenced. The user must account for the truncated nature of
WNop in all calculations in which WNop is used.

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20.3.3.4 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.
20.3.3.4.1 Almanac Reference Week.
Bits 39 through 51 of message types 12, and bits 128 through 140 of message type 31 and 37
shall indicate the number of the week (WNa-n) to which the almanac reference time (toa) is
referenced (see paragraph 20.3.3.4.2). 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 thetoa is referenced. Bits 52 through 59 of message types 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.
20.3.3.4.2 Almanac Reference Time. See paragraph 20.3.3.5.2.2 of IS-GPS-200.
20.3.3.4.3 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.
20.3.3.4.4 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.
20.3.3.4.5 Midi Almanac Parameter Content.
Message type 37, Figure 20-10, 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 20-V. The user algorithm is essentially the same as
the user algorithm used for computing the precise ephemeris as specified in Table 20-IV of ISGPS-200. Other parameters appearing in the equations of Table 20-IV of IS-GPS-200, but notprovided by the Midi almanac with the reference values, are set to zero for SV position
determination. See paragraph 20.3.3.5.2.3 of IS-GPS-200 for almanac time parameters.
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Table 20-V. Midi Almanac Parameters

Parameter

No. of
Bits**

Scale
Factor(LSB)

Effective
Range***

toa

8

212

602,112

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•Unitsseconds* Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;** See Figure 20-10 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.

20.3.3.4.6 Reduced Almanac Parameter Content.
Message type 31, Figure 20-4, provides SV clock correction parameters (ref. Section 20.3.3.2)
and reduced almanac data packets for 4 SVs. Message type 12, Figure 20-11 contains reduced
almanac data packets for 7 SVs.
20.3.3.4.6.1 Reduced Almanac Data.
Message types 31 or 12 contain reduced almanac data and SV health words for SVs in theconstellation. The reduced almanac data of a SV is broadcast in a packet 31 bits long, as
described in Figure 20-16. 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 ranges, and the units

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of the reduced almanac parameters are given in Table 20-VI. The algorithms and other material
related to the use of the reduced almanac data are given in Section 20.3.3.4.6.2.
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.
20.3.3.4.6.2 Reduced Almanac Packet.
The following shall apply when interpreting the data provided in each packet of reduced almanac(see Figure 20-16).
20.3.3.4.6.2.1 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 20-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 paragraph20.3.3.1.3 and Table 20-II). Other parameters appearing in the equations of Table 20-II, but notprovided by the reduced almanac with the reference values, are set to zero for SV position
determination.

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31 BITS

1

7

15
δA

PRNa

22

29 30 31Ω0

Φ0

L1 HEALTH
L2 HEALTH*

See Figures 20-4 and 20-11 for complete bit allocation in therespective messages.

L5 HEALTH

Figure 20-16. Reduced Almanac Packet Content

Parameter*****

Table 20-VI. Reduced Almanac Parameters
No. of Bits
Scale Factor (LSB)
Effective Range **UnitsδA ***

8*

2

Ω0

7*

2-6

**

semi-circles

7*

-6

**

semi-circles

Φ0 ****+9**meters2*

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

20.3.3.5 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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20.3.3.5.1 EOP Content.
Message type 32, Figure 20-5, provides SV clock correction parameters (ref. Section 20.3.3.2)
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 of IS-GPS-200). The number of bits, scale factors (LSBs), the ranges, andthe units of all EOP fields of message type 32 are given in Table 20-VII.
20.3.3.5.1.1 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 20-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 20-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

0

0



sin (α ) cos(α )0cos(α )− sin (α )cos(α ), =R2 ( α )  0 sin(α ) cos (α )R3 ( α ) =  − sin(α )

 0

80

sin(α )
cos(α )
00
1
0

− sin(α )
0 
cos(α ) 

0

0

1

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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 20-VIII.
Table 20-VII. Earth Orientation Parameters

Parameter Symbol

Parameter Description

No. of

Scale
FactorEffective

Bits**(LSB)

Range***

Units4

604,784

secondstEOP

EOP Data Reference Time

16

2

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
Reference Time.

at

31*

2-24

64

seconds

UT1-UTC
Reference

19*

2-25

7.8125 x 10-3

seconds/day

•

•

•

∆UT1 †††

RateofDifference at
Time

*
**
***

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figure 20-5 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 20-VIII. Application of EOP Parameters
Element/Equation•

UT 1 = UTC + ∆UT 1 + ∆ UT 1 (t − t EOP )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).

20.3.3.6 Message Type 33 Coordinated Universal Time (UTC) Parameters.
Message type 33, Figure 20-6, contains the UTC parameters. The contents of message type 33
are defined below, followed by material pertinent to the use of the UTC data.
20.3.3.6.1 UTC Parameter Content.
Message type 33 provides SV clock correction parameters (ref. Section 20.3.3.2) 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 20-IX. See Figure20-6 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.
20.3.3.6.2 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 (and define) tUTC is in paragraph20.3.3.5.2.4 of IS-GPS-200 except the following definition of ∆tUTC shall be used.
∆tUTC = ∆tLS + A0-n + A1-n (tE - tot + 604,800 (WN - WNot)) + A2-n (tE - tot + 604,800 (WN WNot))2 seconds

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Table 20-IX. UTC Parameters

Parameter
SymbolParameter Description

No. of

Scale
FactorEffective

Bits**(LSB)

Range***-35

Seconds

Units

A0-n

Bias coefficient of GPS time scale
relative to UTC time scale

16*

2

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 of UTC
time scale

7*

2-68

sec/sec2∆tLS

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
Number

8

1

weeks

4****

1

days

8*

1

seconds

reference

Week

DN

Leap second reference Day Number∆tLSF

Current or future leap second count

*
**
***
****

604,784

seconds

Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;
See Figure 20-6 for complete bit allocation
Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor;
Right justified.

20.3.3.7 Message Types 34, 13, and 14 Differential Correction Parameters.
Differential Correction (DC) parameters are provided either in message type 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.
20.3.3.7.1 Differential Correction Parameters Content.
Message type 34 provides SV clock correction parameters (ref. Section 20.3.3.2) and also, shallcontain DC parameters that apply to the clock and ephemeris data transmitted by another SV.
One message type 34, Figure 20-7, shall contain 34 bits of clock differential correction (CDC)83

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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 L5 CNAV data, D5(t), and one (1) signifies that the corrections apply to NAV data, D(t),described in Appendix II of IS-GPS-200.
Message types 13 and 14 together also provide DC parameters. Message type 13, Figure 20-12,
shall contain CDC parameters applicable to 6 SVs and message type 14, Figure 20-13, 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 20-17. The number of bits, scale factors (LSB), the ranges, and the units of all fields inthe DC packet are given in Table 20-X.
20.3.3.7.2 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; User Differential Range Accuracy (UDRA)•

and UDRA indices that enable users to estimate the accuracy obtained after corrections areapplied. 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 pairs of the same top-D (top-D =DC data
predict time of week) and of the same tOD.
20.3.3.7.2.1 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.
20.3.3.7.2.2 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.
20.3.3.7.2.3 SV PRN Identification.
The PRN ID of both CDC and EDC of Figure 20-17 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 20-17. Differential Correction Data Packet

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Table 20-X. Differential Correction Parameters
Scale
Factor(LSB)Parameter
SymbolPRN ID

Parameter Description

No. of
Bits**
8

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*

Alpha Correction to Ephemeris
Parameters

14*

Beta Correction to Ephemeris
Parameters

14*

∆α
∆β
∆γ

Gamma Correction to Ephemeris
Parameters∆iAngle of Inclination Correction∆A•

Change Rate of User Differential
Range Accuracy Index

UDRA
*
**
***

see text

dimensionless

2-34

dimensionless

15*

2-32

semi-circles

12*

2-32

12*

-32

semi-circles

12*
Semi-Major Correction

Units
see text

2-34

Angle of Right Ascension
Correction∆Ω

Effective
Range***

2

2-9

5*

semi-circles

meterssee text

Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;
See Figures 20-7, 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 with indicatedbit allocation and scale factor.

20.3.3.7.3 Application of Clock-Related Differential Correction Data.
The SV PRN code phase offset, uncorrected by clock correction coefficient updates, is given byequation 2 in 20.3.3.3.3.1 of IS-GPS-200 (see paragraph 20.3.3.2.3). If the matched pair of DC
data for the subject SV is available, the user may apply clock correction coefficient update valuesby;∆tsv = (af0 + δaf0) + (af1 + δaf1)(t − toc) + af2(t − toc )2 + ∆tr

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where δaf0 and δaf1, (see Table 20-X), are given in message types 34 or 13, and all other terms
are as stated in 20.3.3.3.3.1 of IS-GPS-200. Clock-related DC data shall not be applied to any
SV 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.
20.3.3.7.4 Application of Orbit-Related Differential Correction 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 20-II (see para. 20.3.3.1.3). 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 + ∆γThe quasi-Keplerian elements are then corrected by

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Ac=

Ai + ∆Aec=(αc2 + βc2)1/2

ic=

ii + ∆iΩc=Ω i + ∆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 
The corrected quasi-Keplerian elements above are applied to the user algorithm fordetermination of antenna phase center position in Section 20.3.3.1.3, Table 20-II.
20.3.3.7.5 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 have the following relationship:•

Index Value

UDRA (10-6 m/sec)

UDRAop-D (meters)

15

6144.00 <UDRAop-D

6144.00

143072.00 <UDRAop-D≤ 6144.00

3072.00

13

1536.00 <UDRAop-D≤ 3072.00

1536.00

12

768.00<

UDRAop-D≤ 1536.00

768.0011

384.00<

UDRAop-D≤ 768.00

384.0088

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10

192.00 <UDRAop-D≤ 384.00

192.00996.00 <

UDRAop-D≤ 192.00

96.00

8

48.00 <

UDRAop-D≤ 96.00

48.00

7

24.00 <

UDRAop-D≤ 48.00

24.00

6

13.65 <

UDRAop-D≤ 24.00

13.65

5

9.65

<

UDRAop-D≤ 13.65

9.65

4

6.85

<

UDRAop-D≤ 9.65

6.85

3

4.85

<

UDRAop-D≤ 6.85

4.85

2

3.40

<

UDRAop-D≤ 4.85

3.40

1

2.40

<

UDRAop-D≤ 3.40

2.40

0

1.70

<

UDRAop-D≤ 2.40

1.70

-1

1.20

<

UDRAop-D≤ 1.70

1.20

-2

0.85

<

UDRAop-D≤ 1.20

0.85

-3

0.60

<

UDRAop-D≤ 0.85

0.60

-4

0.43

<

UDRAop-D≤ 0.60

0.43

-5

0.30

<

UDRAop-D≤ 0.43

0.30

-6

0.21

<

UDRAop-D≤ 0.30

0.21

-7

0.15

<

UDRAop-D≤ 0.21

0.15

-8

0.11

<

UDRAop-D≤ 0.15

0.11

-9

0.08

<

UDRAop-D≤ 0.11

0.08

-10

0.06

<

UDRAop-D≤ 0.08

0.06

-11

0.04

<

UDRAop-D≤ 0.06

0.04

-12

0.03

<

UDRAop-D≤ 0.04

0.03

-13

0.02

<

UDRAop-D≤ 0.030.02

89IS-GPS-705D
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-14

0.01

-15
-16

<

UDRAop-D

≤

0.02

0.01

UDRAop-D

≤

0.01

0.005

No accuracy prediction available-use at own risk

For any time, tk, other than top-D, UDRA is found by,•

UDRA = UDRAop-D + UDRA (tk - top-D)
20.3.3.8 Message Type 35 GPS/GNSS Time Offset.
Message type 35, Figure 20-8, 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.
20.3.3.8.1 GPS/GNSS Time Offset Parameter Content.
Message Type 35 provides SV clock correction parameters (ref. Section 20.3.3.2) 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 ranges, and the units of the GGTO parameters
are given in Table 20-XI. See Figure 20-8 for complete bit allocation in message type 35.
20.3.3.8.2 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)90

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where tGNSS is in seconds, tE and WN are as defined in Section 20.3.3.5.2.4 of IS-GPS-200, andthe remaining parameters are as defined in Table 20-XI.
Table 20-XI. GPS/GNSS Time Offset Parameters

Parameter
SymbolParameter Description

No. of

Scale
FactorEffective

Bits**(LSB)

Range***-35

seconds

Units

A0GGTO

Bias coefficient of GPS timescale relative to GNSS time scale

16*

2

A1GGTO

Drift coefficient of GPS timescale 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

13

20

WNGGTOTime data reference Week
NumberGNSS 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 20-8 for complete bit allocation;***

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

20.3.3.9 Message Types 36 and 15 Text Messages.
Text messages are provided either in message type 36, Figure 20-9, or type 15, Figure 20-14.
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 in paragraph 20.3.3.5.1.8
of IS-GPS-200.
20.3.4 Timing Relationships.
The following conventions shall apply.
20.3.4.1 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 24 seconds. Allother messages shall be broadcast in-between, not exceeding the maximum broadcast interval in

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Table 20-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 20-XII.

Message Broadcast Intervals

Message Type Number

Maximum Broadcast Intervals †Ephemeris

10 & 1124 secClock

Type 30’s

24 sec30*

144 sec

31* or 12

10 min**,****

Midi Almanac

37*

60 min**EOP

32*

15 min****

UTC

33*

144 sec

34* or 13 & 14

15 min***,****

GGTO

35*

144 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.

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 (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.

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
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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 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 20.3.4.1) 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.
20.3.4.5 Reference Times
The CNAV reference time information may be found in paragraph 30.3.4.5 in IS-GPS-200.
20.3.5 Data Frame Parity.
The data signal contains parity coding according to the following conventions.
20.3.5.1 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 x 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.

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24

g ( X ) = ∑ gi X i
i =0

where
g i = 1 for i = 0, 1, 3, 4, 5, 6, 7, 10, 11, 14, 17, 18, 23, 24= 0 otherwise
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 + X 17 + X 13 + X 12 + X 11 + 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 ) = mk + mk −1 X + mk − 2 X 2 + ⋅ ⋅ ⋅ + m1 X 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.

94

IS-GPS-705D
24 Sep 2013

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.

95

IS-GPS-705D
24 Sep 2013