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CDD-562AL/564A/L Multi-Channel Demodulator
Forward Error Correction
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.
Code
Modulation
Rate
8-QAM 0.576
16-QAM 0.644
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.
Code
Modulation
Rate
BPSK
0.493
QPSK
0.493
QPSK
0.654
QPSK
0.734
Table A-2. Extended CCM Codes
Typical
Spectral
efficiency,
Eb/No, for
bps/Hz
BER = 5 x 10
1.73
4.5 dB
2.58
6.5 dB
Table A-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
Latency at
Min. Data Rate,
64 kbps, in
CCM Mode
-8
milliseconds
87
121
Latency at
Min. Data Rate
64 kbps, in
-8
milliseconds
18
19
21
23
A–5
Revision 0
MN-CDD562AL564AL
Max. Data Rate,
CCM Mode (Mbps)
(kbps)
16.0
16.0
Max. Data Rate
(kbps)
(Mbps)
16.0
16.0
16.0
16.0
5.179
7.726
1.479
2.959
3.923
4.405
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