CDD-880 Multi Receiver
Router
MN-CDD880
Appendix H
Revision 2
H–3
H.3 VersaFEC ACM
The VersaFEC family of short-block LDPC MODCODs are designed specifically for low latency and
ACM applications. These MODCODS are equally well-suited to Constant Coding and Modulation
(CCM) applications. By comparison, they provide performance at or very close to DVB-S2 with
significantly reduced latency.
Table H-1
specifies the available VersaFEC short-block LDPC codes (MODCODs). The modulation
types include BPSK, QPSK, 8-QAM, and 16-QAM. This table shows that, in order to maintain a
constant number of symbols per block, the block size in bits (data + parity) must necessarily
change, depending on both the modulation type (which affects the number of bits per symbol)
and the code rate. For VersaFEC, the block size varies between 2k and 8.2k bits. At worst,
therefore, the VersaFEC codes are 50% shorter than the ‘short’ DVB-S2 codes.
Table H-1. The VersaFEC
MODCOD set
Modulation
(MODCOD
No.)
Code
Rate
Spectral
Efficiency
(bps/Hz)
Block
Size
(kbits)
Typical
Es/No for
BER = 5 x 10
-8
Typical
Eb/No for
BER = 5 x 10
-8
(dB)
Latency at
64 kbps
(in milliseconds)
Data Rate,
CCM Mode
Minimum
(kbps)
Maximum
(Mbps)
BPSK (00) 0.488
0.49
2
-0.70
2.4
26
16
2.2
QPSK (01) 0.533
1.07
4.1
2.49
2.2
53
17
4.81
QPSK (02) 0.631
1.26
4.1
3.70
2.7
59
20
5.67
QPSK (03) 0.706
1.41
4.1
4.89
3.4
62
22
6.34
QPSK (04) 0.803
1.61
4.1
5.87
3.8
66
25
7.24
8-QAM (05) 0.642
1.93
6.1
7.46
4.6
89
30
8.68
8-QAM (06) 0.711
2.13
6.1
8.48
5.2
93
34
9.58
8-QAM (07) 0.780
2.34
6.1
9.29
5.6
97
37
10.53
16-QAM (08) 0.731
2.93
8.2
11.17
6.3
125
46
13.18
16-QAM (09) 0.780
3.12
8.2
12.04
7.1
129
49
14.04
16-QAM (10) 0.829
3.32
8.2
12.91
7.7
131
53
14.94
16-QAM (11) 0.853
3.41
8.2
13.43
8.1
132
54
15.34
The VersaFEC
codes compared with the Shannon bound are shown in
Figure H-1.
It can be seen
that the performance of VersaFEC
at or near the DVB-S2 performance with 16 kbit blocks.
Note that SNR is used in place of Eb/No, a convention for comparing ACM MODCODs. SNR is
defined as
Eb/No + 10
log
(Spectral Efficiency)
.
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