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CGS-2 764 C
2.5 h
ow
the
tps
module
works
After decoding QPSK- or 8PSK-modulated signals, the demodulated data
streams can be accessed via the integrated TPS module. These data streams,
also called transport streams, contain several stations with all their compo-
nents (video, audio, data and service information), which can be changed
using the TPS module.
s
tation
filter
Individual stations can be deleted. This reduces the data rate and, conse-
quently, the output data rate.
C
hanging
the
t
r ansport
strea m
and
orgnet-id
The transport stream ID can be changed. If the stations of a transponder are
split into the transport streams of different channel strips, a new identification
must be allocated to the "new" transport streams to realise the channel search
of the settop boxes connected without mistakes.
If the ORGNET-ID is changed a new NIT must be generated.
C
hanging
the
nit
The transport stream contains data in the form of tables which the receivers
evaluate and require for convenient use. The TPS module can adjust the "Net-
work Information Table" (NIT) to accommodate the new stations output data
(incl. LCN). The "NIT" contains data which is required by the set-top boxes
connected to the cable network for the automatic search feature.
2.6 e
xpl anation
of
the
ter m
"
symbol
r ate
"
Modulation schemes such as QPSK and QAM transmit multiple bits simultane-
ously. These are referred to as symbols. In addition to the user data flow which
transmits video and audio information, error correction bits are transferred.
The FEC number states the ratio of user bits to the complete transmitted bits.
The output symbol rate is calculated as follows:
256-QAM:
SR (A)
= FEC x
1
/
4
x SR (E)
128-QAM:
SR (A)
= FEC x
2
/
7
x SR (E)
64-QAM:
SR (A)
= FEC x
1
/
3
x SR (E)
32-QAM:
SR (A)
= FEC x
2
/
5
x SR (E)
16-QAM:
SR (A)
= FEC x
1
/
2
x SR (E)
4-QAM:
SR (A)
= FEC x
1
/
1
x SR (E)
