Versafec Extensions; B.1.1.1 Extended Ccm Codes; B.1.1.2 Ultra-Low-Latency (Ull) Codes; Table B-2. Extended Ccm Codes - Comtech EF Data CDM-425 Installation And Operation Manual

B.1.1

VersaFEC Extensions

B.1.1.1 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 (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.
Modulation
8-QAM
16-QAM

B.1.1.2 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 (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.
Code
Modulation
Rate
BPSK 0.493
QPSK 0.493
QPSK 0.654
QPSK 0.734
Appendix B

Table B-2. Extended CCM Codes

Spectral
Code Rate efficiency,
bps/Hz
0.576 1.73
0.644 2.58

Table B-3. ULL Codes

Typical
Spectral
efficiency,
Eb/No, for
bps/Hz
BER = 5 x 10
0.49 3.3 dB
0.99 3.3 dB
1.30 3.8 dB
1.47 4.3 dB
CDM-425 Advanced Satellite Modem
Typical Latency at
Eb/No, for 64 kbps, in
BER = 5 x 10 milliseconds
-8
4.5 dB 87
6.5 dB 121
Latency at Min. Data
64 kbps, in
milliseconds CCM mode
-8
18
19
21
23
B–4
Revision 0
Min. Data Max. Data
Rate, Rate,
CCM mode CCM mode
32 kbps 11 Mbps
47 kbps 11 Mbps
Max. Data
Rate, Rate,
CCM mode
18 kbps 5.7 Mbps
18 kbps 6 Mbps
24 kbps 9 Mbps
27 kbps 9 Mbps
MN-CDM-425