Comtech EF Data SDM-9000 - Manual (Page 205)

SDM-9000 Satellite Modem Options
Rev. 4 A–19
A.2.6 SYNC 1 Inversion and Scrambler/Descrambler
In compliance with the DVB specifications, and to ensure adequate binary transitions,
the payload data (187 bytes) in the transport packet is scrambled using a Pseudo Random
Binary Sequence (PRBS) generator.
The polynomial used for the PRBS is:
1 + X
14
+ X
15
The basic scrambler/descrambler is shown in Figure A-15.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
INITIALIZATION SEQUENCE
PRBS GENERATOR
ENABLE FROM
SYNC DETECT LOGIC
CLEAR/SCRAMBLED
DATA IN
SCRAMBLED/
DESCRAMBLED
DATA OUT
1 0 0 1 0 1 0 1 0 0 0 0 0 0 0
Figure A-15. Scrambler/Descrambler
At every eighth transport packet, the sequence “100101010000000” is loaded into the
PRBS registers. The inverted sync byte is used to initialize the PRBS generator.