End-To-End Processing Delay; Table 7-5. Available Tpc Modes; Table 7-6. Turbo Product Coding Processing Delay Comparison - Comtech EF Data CDM-600L Installation And Operation Manual

CDM-600L Satellite Modem
Forward Error Correction Options
The Rate 7/8 TPC is extremely powerful, offering performance very close to the original
Rate 3/4 TPC, but using 15% less bandwidth. Note also that the Rate 0.95 TPC adds just
5% FEC overhead, but yields almost identical coding gain to Rate 1/2 Viterbi at a BER of
1 x 10
at April 2002:
Code Rate/Modulation
Rate 21/44 BPSK
Rate 5/16 BPSK
Rate 1/2 QPSK/Offset QPSK
Rate 3/4 QPSK/Offset QPSK
Rate 3/4 8-PSK
Rate 3/4 16-QAM
Rate 7/8 QPSK/Offset QPSK
Rate 7/8 8-PSK
Rate 7/8 16-QAM
Rate 0.95 QPSK/Offset QPSK
Rate 0.95 8-PSK
7.6.3

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 CDM-600L, the processing delays for the major FEC
types, including the three TPC modes:
Viterbi, Rate 1/2
Sequential, Rate 1/2
Viterbi Rate 1/2 + Reed Solomon
Sequential 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 0.95
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 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 less than or equal to Sequential
decoding.
* A larger block is used for the Rate 7/8 code, which increases decoding delay.
-7
. Below is a listing of all the available TPC modes and rates in the CDM-600L, as

Table 7-5. Available TPC Modes

4.8 kbps to 3.2 Mbps
4.8 kbps to 2.048 Mbps
4.8 kbps to 9.54 Mbps
7.2 kbps to 5.0 Mbps
10.8 kbps to 5.0 Mbps
14.4 kbps to 5.0 Mbps
8.4 kbps to 17.5 Mbps
12.6 kbps to 20 Mbps
16.8 kbps to 20 Mbps
9.1 kbps to 18.88 Mbps
13.6 kbps to 20 Mbps

Table 7-6. Turbo Product Coding processing delay comparison

FEC Mode (64 kbps data rate)
Data Rate Range
(to 4.77 Mbps with High Rate Turbo card)
(to 3.12 Mbps with High Rate option, but
currently unavailable)
(High Rate Turbo card only)
(to 15 Mbps with High Rate Turbo card)
(to 20 Mbps with High Rate Turbo card)
(to 20 Mbps with High Rate Turbo card)
(High Rate Turbo card only)
(High Rate Turbo card only)
(High Rate Turbo card only)
(High Rate Turbo card only)
(High Rate Turbo card only)
End-to-end delay, ms
7–7
Revision 0
MN/CDM600L.IOM
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