Comtech EF Data SDM-9000, Installation And Operation Manual

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SDM-9000 Satellite Modem Options
Rev. 4 A–23
A.2.8 Depth 12 Interleaver/De-interleaver
Conceptually, the interleaver is composed of I = 12 branches, cyclically connected to the
input byte stream by the input switch. Each branch is a FIFO shift register, with
depth = 17 x branch index. The cells of the FIFO contain 1 byte, and the input and output
branches are synchronized. For synchronization purposes, the sync bytes and inverted
sync bytes are always routed in branch 0 of the interleaver, corresponding to a null delay.
The de-interleaver is similar in principle to the interleaver, but the branch indexes are
reversed (i.e., branch 0 corresponds to the longest delay). De-interleaver synchronization
is accomplished by routing the first recognized sync byte to branch 0.
Figure A-18 shows the interleaver/de-interleaver block diagram.
17
17x2
17x3
17x11
0
1
2
3
11
0
1
2
3
11
17x11
0
0
17x3
8 8
17x2
9 9
17
10 10
11
11
•
•
•
•
•
•
INTERLEAVER
SYNC BYTE ROUTE
DE-INTERLEAVER
17 BYTE FIFO SHIFT REGISTER
SYNC BYTE ROUTE
Figure A-18. Interleaver/De-interleaver