GALILEO - Understanding GPS: Principles and Applications - page 575

0 10 ms 20 ms

4ms 100 ms

1ms

Symbol
Sec. code
Pri. code

d 0

d 1

E5a-d 18 19 0 1

0123456 7 89

0123456 7 89

0 1

Sec. code
Pri. code

98 99

E5a-p

Symbol
Sec. code
Pri. code

d 0

d 1 d 2

E5b-d 0123456 7 89

Sec. code
Pri. code

0123456 7 89 9899 0 1

E5b-p

d 0 d 1 d 2 d 3 d 4 d 5 d 6 d 7 d 8 d 9

Symbol
Pri. code

E6C-d

0 1 2 3 4 49 0

Sec. code
Pri. code

E6C-p

d 0

d 1

Symbol
Pri. code

d 2

L1F-d

0 1

Sec. code
Pri. code

24 0

L1F-p

d k n One time primary code

period (N

Secondary code nth chip

Message stream kth symbol

chips length)

p

Figure 10.6 On-board synchronization between code subcarrier waveforms, code chips, and

data symbols.

the GALILEO frame structure, aiming at increasing the transmission rate efficiency
for the E5b and L1F signals in particular.
The subframe synchronization field is a fixed pattern (UW) that allows the
receiver to achieve synchronization to the data field boundaries. The synchroniza-
tion pattern is applied as uncoded data symbols at the transmitter.
The navigation message bit train, excluding the synchronization word, is rate
1/2 convolutional encoded with a FEC code. Therefore, the symbol rate is twice the
original data rate. The convolutional coding has constraint length 7 and is charac-
terized by polynomials G 1 = 171 (octal) and G 2 = 133 (octal), with a convolutional

logic arrangement as illustrated in Figure 10.8.
As shown in Figure 10.7, each subframe contains a CRC parity block consisting
of 24 bits covering the frame data field (excluding the synchronization pattern and
the tail bits). To compute the CRC, the subframe is written as a polynomial in x ,