Versafec Extensions; Extended Ccm Codes; Table B-4. Extended Ccm Codes - Comtech EF Data CDM-570A Installation And Operation Manual

As a comparison, looking at LDPC Rate 2/3 8-QAM and VersaFEC Rate 0.642 8-QAM essentially
identical spectral efficiency and Eb/No performance. However, at 64 kbps, the latency has been
reduced from 350 milliseconds to 89 milliseconds – a factor of 4 reduction.
The performance of the VersaFEC codes compared with the Shannon bound is shown in Figure B-1.
This puts the performance of VersaFEC at or near the DVB-S2 performance with 16 kbit blocks.
Note that SNR is defined as Eb/No + 10
B.6.1

VersaFEC Extensions

B.6.1.1

Extended CCM Codes

Two additional rates are available with the VersaFEC family of codes. Note that these are CCM
(Constant Coding and Modulation) only – they are NOT included in the ACM set of ModCods.
These two codes (see Table B-4) have been added to fill in perceived gaps in the progression of
spectral efficiency versus SNR. They do not, in fact, provide any discernible improvement in
Eb/No performance (compared with their nearest neighbors in the initial VersaFEC family), but
exhibit a modest SNR improvement.
Code
Modulation
Rate
8-QAM 0.576
16-QAM 0.644
FEC (Forward Error Correction) Options
CDM-570A/570AL Satellite Modem with Optional Packet Processor
Figure B-1. VersaFEC Codes versus Shannon Capacity
(Spectral Efficiency).
log

Table B-4. Extended CCM Codes

Typical
Spectral efficiency,
Eb/No, for
bps/Hz
BER = 5 x 10
1.73 4.5 dB
2.58 6.5 dB
Latency at
Min. Data Rate,
64 kbps, in
CCM Mode (kbps)
milliseconds
-8
87
121
B–8
Revision 5
Max. Data Rate, CCM
Mode (Mbps)
8.3 5.179
12.4 7.726
MN-CDM570A