Comtech EF Data CDM-570A - Manual (Page 437)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix B Revision 2
B–9
B.6.1.2 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, limited to
BPSK and QPSK only (see Table B-5), use significantly shorter code blocks than ‘standard’
VersaFEC. 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-5. ULL Codes
Modulation
Code
Rate
Spectral
efficiency,
bps/Hz
Typical
Eb/No, for
BER = 5 x 10 -8
Latency at
64 kbps, in
milliseconds
Min. Data Rate
(kbps)
Max. Data Rate
(Mbps)
BPSK 0.493 0.49 3.3 dB 18 2.4 1.479
QPSK 0.493 0.99 3.3 dB 19 4.8 2.959
QPSK 0.654 1.30 3.8 dB 21 6.3 3.923
QPSK 0.734 1.47 4.3 dB 23 7.0 4.405