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ssociated integer number of chips as illustrated in Table B-23. Each of the G1 and G2 sequences shall be defined as the output
ter, where the input to the shift register is the Modulo-2 addition of the following stages of
e shift register:
a) G1: stages 3 and 10; and
b) G2: stages 2, 3, 6, 8, 9 and 10.
The initial state for the G1 and G2 shift registers shall be “1111111111”.
3.5.2.3 Spurious emissions. Spurious emissions shall be at least 40 dB below the unmodulated carrier power over all
frequencies.
3.5.2.4 Code/carrier frequency coherence. The short-term (less than 10 seconds) fractional frequency difference
between the code phase rate and t –11
(lm
tiplying the number of code chips by 1 540, and the change in the broadcast carrier phase, in cycles, shall be within one
carrier cycle (standard deviation).
Note.— This applies to the output of the satellite transmit antenna and does not include code/carrier divergence due to
ionospheric refraction in the downlink propag
3.5.2.5 Correlation loss. The loss in the recovered signal power due to imperfections in the signal modulation and
waveform distortion shall not exceed 1 dB.
Note.— The loss in signal power is the difference between the broadcast power in a 2.046 MHz bandwidth and the signal
power recovered by a noise-free, loss-free receiver with 1-chip correlator spa
3.5.2.6 Maximum code phase deviation. The maximum uncorrected code phase of the broadcast signal shall n
fr –20
3.5.2.7 Code/data coherence. Each 2-millisecond symbol shall be synchronous with every o
3.5.2.8 Message synchronization. The leading edge of the first symbol that depends on the first bit of the current
message shall be broadcast from the SBAS satellite synchronous with a 1-second epoch of SNT.
3.5.
a
arrangement shall be as illustrated in Figure B-11 with the G3 output selected for the first half of each 4-millisecond data bit
period.
3.5.2.10 Pseudo-random noise (PRN) codes. Each PRN code shall be a 1 023-bit Gold code which is itself the Modulo-2
addition of two 1
a
of stage 10 of a 10-stage shift regis
th
23/11/06 APP B-34
Appendix B Annex 10 — Aeronautical Communications
Table B-23. SBAS PRN
cod er
G2 delay
(
(Leftm
trans ary)
codes
PRN
e numb chips)
First 10 SBAS chips
ost bit presents first
mitted chip, bin
re
120 145 110111001
121 175 101011110
122 52 1
1
1 10 0
137 68 111111000
138 386 1011010111
101001000
123 21 1101100101
124 237 110000
125 235 111000001
126 886 1011
127 657 1000110000
128 634 10100101
129 762 101010111
130 355 1100011110
131 012 1001011
132 176 1010101111
133 603 100110
134 130 1000111001
135 359 101110001
136 595 1000011111
3.5.3.1 Format summary. All messages shall consist of a message type identifier, a preamble, a data field and a cyclic
3.5.3.2 Preamble. The preamble shall consist of the sequence of bits “01010011 10011010 11000110”, distributed over
3.5.3.3 Message type identifier. The message type identifier shall be a 6-bit value identifying the message type (Types
3.5.3.4 Data field. The data field shall be 212 bits as defined in 3.5.6. Each data field parameter shall be transmitted
SB
e CRC code shall be calculated in accordance with 3.9.
4 bits.
3.5.3.5.2 The CRC
G(x) = x24 + x23 + x + x + x + x + x + x + x + x4 + x3 + x + 1
3.5.3 DATA STRUCTURE
redundancy check as illustrated in Figure B-12.
three successive blocks. The start of every other 24-bit preamble shall be synchronous with a 6-second GPS subframe epoch.
0 to 63) as defined in Table B-24. The message type identifier shall be transmitted MSB first.
M first.
3.5.3.5 Cyclic redundancy check (CRC). The SBAS messag
3.5.3.5.1 The length of the CRC code shall be k = 2
generator polynomial shall be:
18 17 14 11 + x10 7 6 5
APP B-35 23/11/06
Annex 10 — Aeronautical Communications Volume I
Table B-24. Broadcast mes es
Message type
sage typ
Contents
0 “Do Not Use” (SBAS test mode)
2
y information
nging function parameters
offset parameters
13 6
tellite almanacs
19 3
ror corrections
corrections
service message
meris covariance matrix
29 1
62 Reserved
63 Null message
1 PRN mask
to 5 Fast corrections
6 Integrit
7 Fast correction degradation factor
8 Spare
9 GEO ra
10 Degradation parameters
11 Spare
12 SBAS network time/UTC
to 1 Spare
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