Comtech EF Data DMD-2050E - Manual (Page 95)

DMD2050E Universal Satellite Modem Theory of Operation
MN-DMD2050E Revision 2 3–53
It can be seen from this graph that, for Code Rates above 3/4, Comtech’s TPCs are very close
(1-1.5 dB) to the Shannon Limit. However, at 3/4 and below, LDPCs are performing 0.7-1.2 dB
better than TPCs.
Figure 3-19. TPC & LDPC Modes Performance (Relative to Shannon Limit)
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 DMD2050E Modem. Table 3-2 outlines the operating
modes provided by this module.
Table 3-2. Available TPC and LDPC Modes
Mode Code Rate/Modulation
Lower Data Rate Limit
(kbps)
Upper Data Rate Limit
(kbps)
TPC Rate 21/44 BPSK (aka 1/2) 18.0 5965.9
Rate 5/16 BPSK 18.0 3906.2
Rate 21/44 QPSK, OQPSK (aka 1/2) 18.0 11931.8
Rate 3/4 QPSK, OQPSK 27.0 18750.0
Rate 3/4 8-PSK , 8-QAM 40.0 25000.0
Rate 3/4 16-QAM 54.0 25000.0
Rate 7/8 QPSK, OQPSK 31.5 21875.0
Rate 7/8 8-PSK , 8-QAM 48.0 25000.0