Signal Processing; Signal Processing Flow For Each Channel - Furuno FELCOM 12 Service Manual

2.2 Signal Processing

1. Signal Processing Flow for Each Channel

Message are processed on each channel as below.
TX on SES
Signalling Channel
Message
Scrambling
Convolutional
Encoding
Adding unique word
BPSK mod.
TX signal
Scrambling
Data is scrambled by exclusive ORing original data with scramble generator output bit
by bit. Scrambling prevents 0 from continuing excessively; if 0 continues, clock
recovery would be reduced at the BPSK modulator. The scramble generator consists
of an eight step shift register and polynomial G.
TX on SES
Message Channel
Message
Scrambling
Convolutional
Encoding
Adding unique word
Interleaving
Permuting
Adding pre-amble
BPSK mod.
TX signal
Scrambling
Generator
+
G=X3+X4+X5+X7
LSB
X0 X1
X2 X3 X4
Start state
: 1000000
Figure 2-6 Scrambling
TX on NCS/CES
TDM Channel
Message
Scrambling
Convolutional
Encoding
Adding unique word
Interleaving
Permuting
BPSK mod.
TX signal
Data
DATA
+
G
Modulo-2 adder
(exclusive OR)
MSB
(Shift Register)
X5 X6 X7
2-6
RX on NCS/CES
TDM Channel
RX signal
BPSK demod.
Detecting U.W.
(Frame synch.)
De-permuting
De-interleaving
Viterbi decoding
De-scrambling
Packet detection
Message
OUT
(To encoder)