TANDBERG SM6610, Справочное руководство

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Equipment Description
Reference Guide: SM6610, SM6615, SM6620 and SM6625 Satellite Modulators Page 7-3
ST.RE.E10152.2
7.1 Scope of this Chapter
This chapter provides a simplified overview of the SM6600 range of
Satellite Modulators.
7.2 Basic DVB-S and DVB-DSNG Principles and
Techniques
7.2.1 DVB-S Modulation
The Modulators support QPSK modulation in accordance with ETSI
standard EN 300 421 (DVB-S). Additionally, they support BPSK modulation
in accordance with ETSI Technical Report TR 101 198. In the BPSK and
QPSK modulation schemes, each symbol represents 1 and 2 bits of data,
respectively. BPSK gives the lower bit-rate for a given symbol rate but is
the most rugged with respect to noise and interference.
Five convolutional code rates are available with BPSK and QPSK
modulations as follows:
1
⁄
2
,
2
⁄
3
,
3
⁄
4
,
5
⁄
6
, and
7
⁄
8.
These provide different
compromises between bit-rate and ruggedness.
Figure 7.1: BPSK and QPSK Constellations
7.2.2 DVB-DSNG Modulation
The Modulators optionally support 8PSK and 16QAM modulations in
accordance with ETSI standard EN 301 210 (DVB-DSNG). In the 8PSK and
16QAM modulation schemes, each symbol represents 3 and 4 bits of data,
respectively. 16QAM gives twice the bit-rate of QPSK for a given symbol
rate but is less rugged with respect to noise and interference.
For these modulations, pragmatic trellis coded modulation (PTCM) is used.
PTCM code rates of
2
⁄
3
,
5
⁄
6
and
8
⁄
9
are available with 8PSK modulation. PTCM
code rates of
3
⁄
4
and
7
⁄
8
are available with 16QAM modulation.
QPSK
2 bits
0 0
BPSK
1 bit
0 1