Comtech EF Data CDM-IP 300L - Manual (Page 303)

CDM-IP 300L IP-Centric Satellite Modem Rev. 1
CD/CDMIP300L.IOM
277
9.3.2 M
OD
/D
EMOD
P
ROCESSING
D
ELAY
In many cases, FEC methods that provide increased coding gain do so at the expense of
increased processing delay. However, with TPC, this increase in delay is very modest.
Table 21 shows, the processing delays for the major FEC types, including the three TPC
modes:
Table 69. Turbo Product Coding processing delay comparison
FEC Mode (64 kbps data rate) Mod/Demod delay, ms
Viterbi, Rate 1/2 12
Sequential, Rate 1/2 74
Viterbi Rate 1/2 with Reed Solomon 266
Sequential Rate 1/2 with Reed Solomon 522
Turbo Product Coding, Rate 3/4, {O}QPSK 79
Turbo Product Coding, Rate 21/44, BPSK 64
Turbo Product Coding, Rate 5/16, BPSK 48
Note: In all cases, the delay is inversely proportional to data rate, so for 128 kbps, the delay
values would be half of those shown above. It can be clearly seen that the concatenated
Reed-Solomon cases increase the delay very significantly (due mainly to interleaving/de-
interleaving), while the TPC cases yield delays which are less than or equal to Sequential
decoding.