CDM-625A Advanced Satellite Modem MN-CDM625A
Appendix B Revision 4
B–14
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 – reduction by a factor of 4.
The performance of the VersaFEC codes compared with the Shannon bound is shown in Figure B-2.
This puts the performance of VersaFEC at or near the DVB-S2 performance with 16 kbit blocks.
Figure B-2. VersaFEC Codes versus Shannon Capacity
Note that SNR is used in place of Eb/No – a convention for comparing ACM ModCods. SNR is
defined as Eb/No + 10
log
(Spectral Efficiency).
VersaFEC ACM requires the appropriate FAST code for the maximum operating
symbol rate.
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