Comtech EF Data ODM-840 - Manual (Page 173)

ODM/R-840 Outdoor Remote Router Revision 0
Appendix B MN-ODM840
B–3
Shannon bound – has resulted in the development of a set of VersaFEC codes with two distinct
purposes:
1) To provide an expanded choice of combinations of modulation and coding that significantly
reduces latency without compromising coding gain performance.
2) To provide combinations of modulation and coding (MODCODs) that are not only suitable for
Constant Coding and Modulation (CCM) applications, but are also the basis for a patent‐
pending Adaptive Coding and Modulation (ACM) system.
(ACM will be available in future
releases of the ODM/R‐840.)
VersaFEC is offered with a sufficient range of code rates and modulation types that optimize link
performance under most conditions. The performance of the VersaFEC codes compared with the
Shannon bound is shown in Figure B‐1.
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).
Figure B-1. The VersaFEC Codes versus Shannon Capacity
There are 12 MODCODs in the VersaFEC set (Table B‐1). The modulation types (BPSK, QPSK, 8‐
QAM and 16‐QAM) and the code rates have been chosen to give a continuous progression of