Table of Contents
Advertisement
CDM-625 Advanced Satellite Modem
Forward Error Correction Options
7.8.1 VersaFEC Extensions
VersaFEC Extensions require Firmware Version 1.5.4 (or higher)
7.8.1.1 Extended CCM Codes
In Firmware Version 1.5.4 and later, two additional rates have been added to 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 new 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
7.8.1.2 Ultra-Low-Latency (ULL) Codes
Four new ultra-short block LDPC codes have been added to address the needs of users with
applications requiring even lower latency than the 'standard' VersaFEC code set. These new
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.
Modulation
BPSK
QPSK
QPSK
QPSK
Table 7-10. Extended CCM Codes
Spectral
Code Rate
efficiency,
bps/Hz
0.576
1.73
0.644
2.58
Table 7-11. ULL Codes
Spectral
Code
efficiency,
Eb/No, for
Rate
bps/Hz
BER = 5 x 10
0.493
0.49
0.493
0.99
0.654
1.30
0.734
1.47
Typical
Latency at
Eb/No, for
64 kbps, in
BER = 5 x 10
milliseconds
-8
4.5 dB
6.5 dB
Typical
Latency at
64 kbps, in
milliseconds
-8
3.3 dB
18
3.3 dB
19
3.8 dB
21
4.3 dB
23
7–13
Min. Data
Rate,
CCM mode
87
32 kbps
121
47 kbps
Min. Data
Max. Data
Rate,
CCM mode
CCM mode
18 kbps
5.7 Mbps
18 kbps
6 Mbps
24 kbps
9 Mbps
27 kbps
9 Mbps
Revision 13
MN-CDM625
Max. Data
Rate,
CCM mode
11 Mbps
11 Mbps
Rate,
Advertisement
Table of Contents
