Partial-response-channel precoding

DETAILED DESCRIPTION In the HDTV system shown in FIG.
1, binary input data in the form of an HDTV signal is generated by an HDTV signal source 11.
Illustratively, source 11 includes a television signal source encoder which converts an originally generated analog television signal into digital form and compresses that signal using any of a variety of well-known techniques.
The resulting signal is then applied to a broadcast transmitter, which includes a channel encoder 12.
The latter adds redundant bits to the received signal in order to achieve a measure of forward error correction.
As such, encoder 12 may implement Reed-Solomon or other classic error correction codes, coded modulation, or combinations of these.
Encoder 12 may also include an interleaver which, in known fashion, reorders the coded bits in such a way as to enhance the overall system performance in the presence of bursty noise, the latter arising from such sources as various elements within the transmitter itself, the TV channel and/or various elements within the receiver.
The latter elements, in particular, may include the comb filter and/or adaptive equalizer described below.
Illustratively, source 11 delivers q bits per signaling (baud) interval of T seconds to channel encoder 12 and the latter outputs m bits per signaling interval, m>q, onto lead 13.
In turn, those bits--referred to herein as the "present input bits"--are applied to precoder 14.
(Each group of m present input bits comprises a subset of the data applied to precoder 14 and may also be thought of as a binary data word.
) The function of precoder 14 is to process the present input bits in such a way that forced intersymbol interference introduced by the receiver is compensated for.
That is, the effects of the forced ISI are countered.
The output of precoder 14 is again comprised of m bits per signaling interval.
These bits are applied to constellation mapper 17 which outputs on lead 18 for each different group of m bits on lead 15 a different transmit symbol from a predetermined transmit constellation