Comtech EF Data CDM-570A User Manual
Page 597
CDM-570A/570A Satellite Modem with Optional Packet Processor
MN-CDM570A
Appendix P
Revision 2
P–7
Table P-1. The VersaFEC ModCod Set
Modulation
Code Rate
Spectral
efficiency,
bps/Hz
Block size, bits
Typical
Eb/No, for
BER = 5 x 10
-8
Latency at
64 kbps, in
milliseconds
BPSK
0.488
0.49
2k
2.4 dB
26
QPSK
0.533
1.07
4.1k
2.2 dB
53
QPSK
0.631
1.26
4.1k
2.7 dB
59
QPSK
0.706
1.41
4.1k
3.4 dB
62
QPSK
0.803
1.61
4.1k
3.8 dB
66
8-QAM
0.642
1.93
6.1k
4.6 dB
89
8-QAM
0.711
2.13
6.1k
5.2 dB
93
8-QAM
0.780
2.34
6.1k
5.6 dB
97
16-QAM
0.731
2.93
8.2k
6.3 dB
125
16-QAM
0.780
3.12
8.2k
7.0 dB
129
16-QAM
0.829
3.32
8.2k
7.5 dB
131
16-QAM
0.853
3.41
8.2k
8.0 dB
132
The VersaFEC
codes compared with the Shannon bound are shown below in Figure P-2. It can be
seen that the performance of VersaFEC
at or near the DVB-S2 performance with 16 kbit blocks.
Note that SNR is used in place of Eb/No, a convention for comparing ACM ModCods. SNR is
defined as
Eb/No + 10log (Spectral Efficiency).
Figure P-2. VersaFEC Codes vs. Constrained Capacity