17. SatLink and DVB-S2
The DVB-S2 standard has become the most widely used standard for Forward Link transmission in
VSAT satellite communication systems. Advances in the field of digital coding and modulation
techniques have made possible a technology upgrade of the legacy DVB-S standard. In the DVB-S2
standard, there are primarily four features that directly translate to improved performance:
Higher order modulation
Reduced carrier roll-off filtering
Coding – LDPC-BCH with performance close to the Shannon limit
Adaptive Coding and Modulation (ACM)
The following provides further information on the features of the DVB-S2 standard supported by the
VSATs.
17.1 DVB-S2 Modulation
The SatLink IDUs support the following modulation schemes:
QPSK
8PSK
16APSK
Figure 38 shows the modulation constellations for QPSK, 8PSK, and 16APSK. With QPSK, two FEC-
coded bits are transmitted per modulation symbol, while with 8PSK and 16APSK three and four FEC-
coded bits, respectively, are transmitted per modulation symbol.
DVB-S2 may be operated with three different roll-off factors for the pulse shaping filter: 0.35, 0.25, and
0.2.
Figure 38: QPSK, 8PSK, and 16APSKConstellations
17.2 DVB-S2 Coding
DVB-S2 uses advanced LDPC code concatenated with outer BCH codes. This coding scheme results in a
performance that is only 0.7-1.0 dB short of the theoretical Shannon bound indicated by the dotted red
line in Figure 39 below. This translates to an improvement in coding gain of close to 2 dB compared to
DVB-S systems using concatenated Reed Solomon and Convolutional FEC.
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 39 below. This translates to an improvement
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