Comtech EF Data CDM-625A Installation And Operation Manual page 517

Advanced satellite modem (18 kbps – 25 mbps)

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CDM-625A Advanced Satellite Modem

VersaFEC Extensions

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 (Rate 0.576 8-QAM and Rate 0.644 16-QAM) ) 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.

Ultra-Low-Latency (ULL) Codes

Four additional ultra-short block LDPC codes address the needs of users with applications

requiring even lower latency than the 'standard' VersaFEC code set. These codes (which are

limited to BPSK and QPSK only) use significantly shorter code blocks than 'standard' VersaFEC,

and as a result, the coding gain is slightly reduced. However, in terms of latency, the

performance is exceptional – far lower than any other FEC method ever offered, with the

exception of Viterbi.

Table B-10. Extended CCM Codes

Table B-11. ULL Codes

BER = 5 x 10

BER = 5 x 10

milliseconds

milliseconds

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