Table 7-4. Available Tpc And 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 7-4 outlines the operating
modes provided by this module:
TPC Code Rate/Modulation
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 Code Rate/Modulation
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 new LDPC/TPC codec module may be installed in any existing CDM-625 as a simple field
upgrade, or 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.
Please contact the Sales Department at Comtech EF Data for pricing and delivery information.
Table 7-5 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 7-4. Available TPC and LDPC Modes

Lower Data Rate Limit
Lower Data Rate Limit
MN-0000036 (Ref MN/CDM625.IOM)
(kbps)
18.0
18.0
18.0
27.0
40.0
54.0
31.5
48.0
63.0
34.2
52.0
(kbps)
18.0
18.0
24.0
36.0
27.0
40.5
54.0
7–7
Revision 1
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
Upper Data Rate Limit
(kbps)
6250.0
12500.0
16666.6
25000.0
18750.0
25000.0
25000.0