Furuno FELCOM 12 Service Manual

2-6
2.2 Signal Processing
1. Signal Processing Flow for Each Channel
Message are processed on each channel as below.
Scrambling
Convolutional
Encoding
Adding unique word
BPSK mod.
TX on SES
Signalling Channel
Scrambling
De-scrambling
Adding pre-amble
BPSK mod.
De-interleaving
Viterbi decoding
De-permuting
Detecting U.W.
(Frame synch.)
TX on SES
Message Channel
TX on NCS/CES
TDM Channel
RX on NCS/CES
TDM Channel
Adding unique word
Interleaving
Permuting
BPSK demod.
Message
Message Message
RX signal
TX signal
TX signal
Packet detection
Convolutional
Encoding
Convolutional
Encoding
Scrambling
Message
Adding unique word
Interleaving
Permuting
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.
LSB MSB
+
X0 X1
X2 X3 X4 X5 X6 X7
+
Data
G
DATA
OUT
G=X3+X4+X5+X7
Start state
: 1000000
(To encoder)
Modulo-2 adder
(exclusive OR)
Scrambling
Generator
(Shift Register)
Figure 2-6 Scrambling

Furuno FELCOM 12 Specifications

General

Brand	Furuno
Model	FELCOM 12
Category	Marine GPS System
Language	English