Comtech EF Data CDM-625 - Table 17-1. the Versafec Modcod Set; Figure 17-2. Versafec Codes Vs. Constrained Capacity

CDM-625 Advanced Satellite Modem Revision 13
Adaptive Coding and Modulation (ACM) MN-CDM625
17–7
Table 17-1. 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
Min.
Data Rate,
CCM mode
Max.
Data Rate,
CCM mode
BPSK
0.488
0.49
2k
2.4 dB
26
18 kbps
5.7 Mbps
QPSK
0.533
1.07
4.1k
2.2 dB
53
20 kbps
10 Mbps
QPSK
0.631
1.26
4.1k
2.7 dB
59
23 kbps
10 Mbps
QPSK
0.706
1.41
4.1k
3.4 dB
62
26 kbps
10 Mbps
QPSK
0.803
1.61
4.1k
3.8 dB
66
28 kbps
12 Mbps
8-QAM
0.642
1.93
6.1k
4.6 dB
89
35 kbps
12 Mbps
8-QAM
0.711
2.13
6.1k
5.2 dB
93
39 kbps
12 Mbps
8-QAM
0.780
2.34
6.1k
5.6 dB
97
43 kbps
12 Mbps
16-QAM
0.731
2.93
8.2k
6.3 dB
125
53 kbps
12 Mbps
16-QAM
0.780
3.12
8.2k
7.0 dB
129
57 kbps
14 Mbps
16-QAM
0.829
3.32
8.2k
7.5 dB
131
60 kbps
14 Mbps
16-QAM
0.853
3.41
8.2k
8.0 dB
132
62 kbps
16 Mbps
The VersaFEC
codes compared with the Shannon bound are shown below in Figure 17-2. 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 17-2. VersaFEC Codes vs. Constrained Capacity