SatLink VSAT User Guide
Publication no. 101557
Copyright © 2009 – STM Group, Inc.
Page 79 (160)
DVB-S2 uses advanced LDPC codes concatenated with BCH codes. Together, these coding schemes
result in a performance (indicated by the solid blue lines) that is only 0.7-1.0 dB from the theoretical
Shannon limit (indicated by the dotted red lines), see Figure 33 below. This translates to an improvement
in coding gain of close to around 2 dB in C/N compared to DVB-S (indicated by the solid black lines) at
the same bandwidth efficiency and a 30% increase in bandwidth efficiency at the same C/N.
The code rate may be varied in small steps for each modulation, thus yielding both a high granularity and
wide range of possible C/N-bandwidth efficiency operational points.The STM SatLink VSATs support
the following combinations of Modulation and FEC rates in DVB-S2 mode, denoted MODCODs:
MODCOD Modulation FEC Code
Rate
QPSK-1/4 QPSK 1/4
QPSK-1/3 QPSK 1/3
QPSK-2/5 QPSK 2/5
QPSK-1/2 QPSK 1/2
QPSK-3/5 QPSK 3/5
QPSK-3/5 QPSK 2/3
QPSK-3/4 QPSK 3/4
QPSK-4/5 QPSK 4/5
QPSK-5/6 QPSK 5/6
QPSK-8/9 QPSK 8/9
QPSK-9/10 QPSK 9/10
8PSK-3/5 8PSK 3/5
8PSK-2/3 8PSK 2/3
8PSK-3/4 8PSK 3/4
8PSK-5/6 8PSK 5/6
8PSK-8/9 8PSK 8/9
8PSK-9/10 8PSK 9/10
16APSK-2/3 16APSK 2/3
16APSK-3/4 16APSK 3/4
16APSK-4/5 16APSK 4/5
16APSK-5/6 16APSK 5/6
16APSK-8/9 16APSK 8/9
16APSK-9/10 16APSK 9/10
The SatLink IDUs support two options for FEC frame size: 64 kbits (normal frame) and 16 kbits (short
frame) The LDPC+BCH codes are slightly more effective when used on the longer (normal) FEC frame,
i.e. the required SNR is 0.2 dB lower for normal frame than for short frame However, the short FEC
frame is useful in several circumstances, e.g. for reducing delay when the forward link information rate is
low.
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