Digital Signal Processing Reference
In-Depth Information
the other one is the low priority path (LP). Since the two FEC stages are
completely identical with the FEC of the DVB-S satellite standard, dis-
cussed in the relevant chapter (Chapter 14), they do not need to be dis-
cussed in detail here.
Mem1
IQ
mod.
IFFT
D
A
IF
RF
RF
Mem2
Mem1
D
A
D D
A
IQ
mod.
IQ
mod.
IFFT
RF
RF
D
A
D D
A
Direct modulation
Mem2
Fig. 20.11.
Possible implementations of a DVB-T modulator
The modulator locks to the transport stream, present at the transport
stream input, in the baseband interface. It uses for this the sync byte which
has a constant value of 0x47 at intervals of 188 bytes. To carry also long-
term time stamps in the transport stream, every eighth sync byte is then in-
verted and becomes 0xB8. This is followed by the energy dispersal stage
which is synchronized by these inverted sync bytes both at the transmitting
end and at the receiving end. Following this, initial error control is per-
formed in the Reed Solomon encoder. The TS packets are now expanded
by 16 bytes error protection. After this block coding, the data stream is in-
terleaved in order to be able to break up error bursts during the de-
interleaving at the receiver end. In the convolutional encoder, additional
error protection is added which can be reduced again in the puncturing
stage.
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