Table 4-4. Available Tpc Modes; Table 4-5. Turbo Product Coding Processing Delay Comparison - Comtech EF Data SLM-7650 Installation And Operation Manual

SLM-7650 Satellite Modem
Theory of Operation
Comtech EF Data now offers a very broad range of TPC code rates, combined with the
entire range of modulation types, from BPSK to 16-QAM.
Table 4-4 is a listing of all the available TPC modes and rates in the modulator.
4.3.3.4.2 End-to-End Processing Delay
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 4-5 below shows the processing delays for the major FEC types, including three
TPC modes. Note that 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.
Viterbi, Rate 1/2
Viterbi Rate 1/2 + Reed Solomon
Turbo Product Coding, Rate 3/4, QPSK/OQPSK
Turbo Product Coding, Rate 21/44, BPSK
Turbo Product Coding, Rate 5/16, BPSK

Table 4-4. Available TPC Modes

Code Rate/Modulation
Rate 21/44 BPSK
Rate 5/16 BPSK
Rate 1/2 QPSK/OQPSK
Rate 3/4 QPSK/OQPSK
Rate 7/8 QPSK/OQPSK
Rate 17/18 QPSK/OQPSK
Rate 3/4 8PSK
Rate 7/8 8PSK
Rate 17/18 8PSK
Rate 3/4 16QAM
Rate 7/8 16QAM

Table 4-5. Turbo Product Coding processing delay comparison

FEC Mode (64 kbps data rate)
Data Rate Range
9.6 kbps to 4.772 Mbps
9.6 kbps to 3.125 Mbps
9.6 kbps to 9.54 Mbps
14.4 kbps to 15.0 Mbps
16.8 kbps to 17.5 Mbps
18.13 kbps to 18.88 Mbps
72.0 kbps to 20 Mbps
84.0 kbps to 20 Mbps
90.6 kbps to 20 Mbps
256.0 kbps to 20 Mbps
256.0 kbps to 20 Mbps
End-to-end delay, ms
12
266
79
64
48
4–8
Revision 4
MN/SLM7650.IOM