Comtech EF Data CDD-562AL - Manual (Page 213)

CDD-562AL/564A/L Multi-Channel Demodulator Revision 0
Forward Error Correction MN-CDD562AL564AL
A–5
A.3.1 VersaFEC Extensions
A.3.1.1 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 (see Table A-2) 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.
Table A-2. Extended CCM 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,
CCM Mode
(kbps)
Max. Data Rate,
CCM Mode (Mbps)
8-QAM 0.576 1.73 4.5 dB 87 16.0 5.179
16-QAM 0.644 2.58 6.5 dB 121 16.0 7.726
A.3.1.2 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 A-3), 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 A-3. 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 16.0 1.479
QPSK 0.493 0.99 3.3 dB 19 16.0 2.959
QPSK 0.654 1.30 3.8 dB 21 16.0 3.923
QPSK 0.734 1.47 4.3 dB 23 16.0 4.405