TANDBERG SM6610, Справочное руководство

Страница: 15 / 200

Introduction
Reference Guide: SM6610, SM6615, SM6620 and SM6625 Satellite Modulators Page 1-7
ST.RE.E10152.2
1.3.7 Forward Error Correction Coding
Noise and interference can cause some bits to be received in error.
Therefore, Forward Error Correction (FEC) consisting of Reed-Solomon
(RS) coding followed by convolutional coding is used to add extra bits to
the transmitted signal. This allows a large number of errors at the receiver
to be corrected by Viterbi decoding followed by RS decoding.
Five convolutional code rates are available with BPSK and QPSK
modulations:
1
⁄
2
,
2
⁄
3
,
3
⁄
4
,
5
⁄
6
and
7
⁄
8.
These provide different compromises
between bit-rate and ruggedness. For 8PSK and 16QAM 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.
Data are interleaved between the outer RS Encoder and the inner
convolutional or PTCM Encoder in order to aid error correction techniques
at the receiver.
1.3.8 Modulation Schemes
BPSK and QPSK modulations are available as standard on each base unit
model. Additionally, 8PSK and 16QAM modulations are available with the
SM66XX/SWO/HOM option.
1.3.9 Symbol Rate Range
Each base unit model has a symbol rate range of 1 to 48 Msymbol/s as
standard. An extended symbol rate range of 0.2 to 66 Msymbol/s is
available with the SM66XX/SWO/HS option.