End-To-End Processing Delay; Table 6-4. Available Tpc Modes; Table 6-5. Turbo Product Coding Processing Delay Comparison - Comtech EF Data CDM-Qx Installation And Operation Manual

CDM-Qx Satellite Modem
Forward Error Correction Options
6.5.3

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.
The table below shows, for the Modem, the processing delays for the major FEC types,
including the three TPC modes.
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 seen that the concatenated
Reed-Solomon cases increase the delay significantly (due mainly to interleaving/de-
interleaving) while the TPC cases yield delays, which are much less.
A larger block is used for the Rate 7/8 code, which increases decoding delay.
*

Table 6-4. Available TPC Modes

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

Table 6-5. Turbo Product Coding processing delay comparison

FEC Mode (64 kbps data rate)
Viterbi, Rate 1/2
Viterbi Rate 1/2 + Reed-Solomon
Turbo Product Coding, Rate 3/4
Turbo Product Coding, Rate 21/44, BPSK
Turbo Product Coding, Rate 5/16, BPSK
Turbo Product Coding, Rate 7/8
Turbo Product Coding, Rate 17/18
Data Rate Range
32 kbps to 4.772 Mbps
32 kbps to 3.125 Mbps
32 kbps to 10 Mbps
32 kbps to 15 Mbps
288 kbps to 20 Mbps
384 kbps to 20 Mbps
32 kbps to 17.5 Mbps
336 kbps to 20 Mbps
448 kbps to 20 Mbps
32 kbps to 18.88 Mbps
362.7 kbps to 20 Mbps
End-to-end delay, ms
6–6
Revision 6
MN/CDMQx.IOM
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