Figure 15-4. Reed-Solomon Code Page Format - Comtech EF Data SNM-1001L Installation And Operation Manual

SNM-1001L Satellite Modem
Reed-Solomon Codec
Since errors from the Viterbi decoder usually occur in bursts, a block interleaver with a depth of
four is used in accordance with the INTELSAT-308 Rev. 6B specification. The interleaver has
the effect of spreading out the errors across blocks of data instead of concentrating the errors in
a single block of data. Since there are fewer errors in any given block, there is a greater chance
that the Reed-Solomon decoder can correct the errors on the receiving end of the satellite link.
To allow the decoder to synchronize to the data, four unique words are inserted in the last two
bytes of the last two pages at the end of each page of data.
Once the data passes through the interleaver, it is fed through a parallel/serial converter and sent
back to the interface PCB. After further processing by the interface PCB, the data is sent to the
modulator PCB.
1 RSWORD
'RSWORD'
n BYTES
k BYTES
OF DATA

Figure 15-4. Reed-Solomon Code Page Format

15–4
TERRESTRIAL
DATA RATE
1544 (1640)
2048 (2144)
2+t
CHECK BYTES
1 RS PAGE
UNIQUE WORD BYTES
GO INTO THESE BYTES
Revision 1
MN/SNM1001L.OM
RS CODE
(n,k,t)
225, 205, 10
219, 201, 9
RS SYNCH
PERIOD