Table 7-5. Available Tpc/ Ldpc Modes - Comtech EF Data CDM-625 Installation And Operation Manual

CDM-625 Advanced Satellite Modem
Forward Error Correction Options
It is clear that, in order to provide the best possible performance over the range of code rates
from 1/2 to 0.95, both an LDPC and a TPC codec need to be offered.
In order to meet this requirement, Comtech EF Data has developed a combination LDPC/TPC
Codec module that can be added to the CDM-625 Modem. Table 7-5 outlines the operating
modes provided by this module.
Mode
TPC Rate 21/44 BPSK (aka 1/2)
Rate 5/16 BPSK
Rate 21/44 QPSK, OQPSK (aka 1/2)
Rate 3/4 QPSK, OQPSK
Rate 3/4 8-PSK , 8-QAM
Rate 3/4 16-QAM
Rate 7/8 QPSK, OQPSK
Rate 7/8 8-PSK , 8-QAM
Rate 7/8 16-QAM
Rate 0.95 QPSK, OQPSK (aka 17/18)
Rate 0.95 8-PSK , 8-QAM (aka 17/18)
LDPC Rate 1/2 BPSK
Rate 1/2 QPSK, OQPSK
Rate 2/3 QPSK, OQPSK
Rate 2/3 8-PSK , 8-QAM
Rate 3/4 QPSK, OQPSK
Rate 3/4 8-PSK , 8-QAM
Rate 3/4 16-QAM
This LDPC/TPC codec module may be installed in any existing CDM-625 as a simple field
upgrade, or it can be pre-installed in new modems ordered from the factory. It also requires the
appropriate FAST codes for enabling operation beyond the base data rate limit of 5 Mbps.
Contact a Comtech EF Data Sales representative during normal business hours for pricing and
delivery information.
Table 7-6 compares all TPC and LDPC modes available in Comtech EF Data's CDM-625, 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).

Table 7-5. Available TPC/ LDPC Modes

Code Rate/Modulation
7–8
Lower Data Rate Limit
(kbps)
18.0
18.0
18.0
27.0
40.0
54.0
31.5
48.0
63.0
34.2
52.0
18.0
18.0
24.0
36.0
27.0
40.5
54.0
Revision 13
MN-CDM625
Upper Data Rate Limit
(kbps)
5965.9
3906.2
11931.8
18750.0
25000.0
25000.0
21875.0
25000.0
25000.0
23611.1
25000.0
6250.0
12500.0
16666.6
25000.0
18750.0
25000.0
25000.0