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CDM-600L Satellite Modem
Forward Error Correction Options
This new LDPC/TPC codec module may be installed in any existing CDM-600L, as a simple
field upgrade, or already installed in new modems ordered from the factory. It requires Firmware
Version 1.3.0 (or higher) to be installed.
Please contact the Sales Department at Comtech EF Data for pricing and delivery information.
The table that follows compares all TPC and LDPC modes available in Comtech EF Data's
CDM-600L, and shows Eb/No performance and spectral efficiency (occupied bandwidth) for
each case. This information will be of particular interest to satellite operators wishing to
simultaneously balance transponder power and bandwidth. The large number of modes offered
will permit, in the majority of cases, significant power and/or bandwidth savings when compared
with existing schemes such as concatenated Viterbi/Reed-Solomon, or the popular 8-
PSK/Trellis/Reed-Solomon (Intelsat IESS-310)
7.7.3 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. Table 7-6
shows, for the CDM-600L, the processing delays for the major FEC types, including the three
TPC modes:
FEC Mode (64 kbps data rate)
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, O/QPSK
Turbo Product Coding, Rate 21/44, BPSK
Turbo Product Coding, Rate 5/16, BPSK
Turbo Product Coding, Rate 7/8, O/QPSK
Turbo Product Coding, Rate 0.95, O/QPSK
LDPC Coding, Rate 1/2
LDPC Coding, Rate 2/3, O/QPSK
LDPC Coding, Rate 2/3, 8-PSK, 8-QAM
LDPC Coding, Rate 3/4, O/QPSK
LDPC Coding, Rate 3/4, 8-PSK, 8-QAM, 16-QAM
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.
Table 7-6. Turbo Product Coding Processing Delay Comparison
End-to-end delay, ms
12
74
266
522
47
64
48
245 *
69
248
296
350
321
395
7–9
Revision 2
MN/CDM600L.IOM
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