Comtech EF Data CDM-625 - Manual (Page 403)

CDM-625 Advanced Satellite Modem Revision 15
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