Furuno FELCOM 12 Service Manual page 38

Convolutional Encoding
The end of scrambled bit stream data of 120 bits is affixed with 6 bits of continuous
flash bits and sent to the half-rate convolutional encoder which consists of a 7 bits
shift register (constraint length-7) and two polynomials. 126 bits of signalling packet
input are encoder to 252 symbols. The first state of the shift register is all zeroes.
G1=X0+X2+X3+X5+X6
Formatted
(Scrambled) data
Start state
: 0 0 0 0 0 0
G2=X0+X1+X2+X3+X6
Unique Word
The 252 symbols from the encorder is affixed with an unique word (uw) to be used for
bit synchronization at the recorder. The uw is 64 bits in length on the SES signalling
channel and 64 × 2 bits on the NCS/CES TDM channel.
Interleaving and Permuting Encoder
The figure below shows the interleave matrix, consisting of 64 rows by 162 columns.
Symbol data comes in column by column. Note that columns 0 and 1 are filled with
unique words.
Row
UW 64bits UW 64bits
+
X0 X1 X2 X3
+
Figure 2-7 Encoding
Interleaving and
Permuting Encoder
Figure 2-8 UW
Column
0 1 2 ....................................161
0
1 65
1
2 66
2
3 67
62
63 127
63
64 128
1 2 3 ...
Figure 2-9 Interleave Matrix
exclusive OR
G1
X4 X5 X6
G2
exclusive OR
symbol UW
(added)
10177
10177
10177
10239
10240
64 65 ... 128 ..................
2-7
Coded symbols
(To interleaver)
(Half-rate: Output of 2 bits
with input of 1 bit)
BPSK modulator
or
interleaver
Interleave Matrix
Bit stream
10177 ... 10240