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Table B-1. Code phase assignments
Satellite ID
number
GPS
PRN signal
G2 delay
(chips)
First 10 chips
octal*
1 1 5 1440
2 2 6 1620
3 3 7 1710
4 4 8 1744
5 5 17 1133
6 6 18 1455
7 7 139 1131
8 8 140 1454
9 9 141 1626
10 10 251 1504
11 11 252 1642
12 12 254 1750
13 13 255 1764
14 14 256 1772
15 15 257 1775
16 16 258 1776
17 17 469 1156
18 18 470 1467
19 19 471 1633
20 20 472 1715
21 21 473 1746
22 22 474 1763
23 23 509 1063
24 24 512 1706
25 25 513 1743
26 26 514 1761
27 27 515 1770
28 28 516 1774
29 29 859 1127
30 30 860 1453
31 31 861 1625
32 32 862 1712
*** 33 863 1745
*** 34** 950 1713
*** 35 947 1134
*** 36 948 1456
*** 37** 950 1713
* In the octal notation for the first 10 chips of the C/A code as shown in this column, the first digit represents
a “1” for the first chip and the last three digits are the conventional octal representation of the remaining
9 chips (e.g. the first 10 chips of the C/A code for pseudo-random noise (PRN) signal assembly 1 are:
1100100000).
** C/A codes 34 and 37 are common.
*** PRN signal assemblies 33 through 37 are reserved for other uses (e.g. ground transmitters).
APP B-3 23/11/06
Annex 10 — Aeronautical Communications Volume I
3.1.1.2.5.2 Bit 19. Bit 19 shall be reserved.
3.1.1.2.5.3 Bits 20, 21 and 22. Bits 20, 21 and 22 of the HOW shall provide the identification (ID) of the subframe in
which that particular HOW is the second word. The ID code shall be as defined below:
ID Code
1 001
2 010
3 011
4 100
5 101
3.1.1.2.6 Satellite Z-count. Each satellite shall internally derive a 1.5-second epoch that shall contain a convenient unit
for precisely counting and communicating time. Time stated in this manner shall be referred to as a Z-count. The Z-count
shall be provided to the user as a 29-bit binary number consisting of two parts as follows.
3.1.1.2.6.1 Time-of-week (TOW) count. The binary number represented by the 19 LSBs of the Z-count shall be referred
to as the TOW count and is defined as being equal to the number of 1.5-second epochs that have occurred since the transition
from the previous week. The count shall be short-cycled such that the range of the TOW count is from 0 to 403 199
1.5-second epochs (equalling one week) and shall be reset to zero at the end of each week. The TOW count’s zero state shall
be the 1.5-second epoch that is coincident with the start of the present week. A truncated version of the TOW count,
consisting of its 17 MSBs, shall be contained in the HOW of the L1 downlink data stream. The relationship between the
actual TOW count and its truncated HOW version shall be as indicated in Figure B-5.
Note.— The above-mentioned 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.
3.1.1.2.6.2 Week count. The 10 MSBs of the Z-count shall be a binary representation of the sequential number assigned
to the present GPS week (Modulo 1024). The range of this count shall be from 0 to 1 023. Its zero state shall be that week
which starts with the 1.5-second epoch occurring at (approximately) the UTC zero time point (3.1.4). At the expiration of
GPS week number 1 023, the GPS week number shall roll over to zero. The previous 1 024 weeks in conversions from GPS
time to a calendar date shall be accounted for by the user.
3.1.1.3 DATA CONTENT
3.1.1.3.1 Subframe 1 — satellite clock and health data. The content of words 3 through 10 of subframe 1 shall contain
the clock parameters and other data as indicated in Table B-2. The parameters in a data set shall be valid during the interval
of time in which they are transmitted and shall remain valid for an additional period of time after transmission of the next
data set has started.
3.1.1.3.1.1 Week number. The 10 MSBs of word 3 shall contain the 10 MSBs of the 29-bit Z-count and shall represent
the number of the current GPS week at the start of the data set transmission interval with all zeros indicating week “zero.”
The GPS week number shall increment at each end/start of week epoch.
3.1.1.3.1.2 User range accuracy (URA). Bits 13 through 16 of word 3 shall provide the predicted satellite URA as
shown in Table B-3.
Note 1.— The URA does not include error estimates due to inaccuracies of the single-frequency ionospheric delay model.
Note 2.— The URA is a statistical indicator of the contribution of the apparent clock and ephemeris prediction
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