A decoder for distorted trellis-encoded signals

Considers the decoding of trellis-encoded signals in the presence of intersymbol interference (ISI) and additive white Gaussian noise. An existing and practical arrangement at the receiver is to disregard the ISI present, in the channel, in the decoding process and to use a conventional adaptive linear (or nonlinear) equalizer to precede the corresponding soft-decision Viterbi algorithm (VA) decoder. The equalizer is used in this case to mitigate the effects of the ISI prior to the decoding process. However, extensive computer simulation tests have suggested that this arrangement might not yield a satisfactory level of performance for the higher data rates over severely distorted channels. An important question to raise at this stage is the following: `Can anything be gained by utilising the additional memory due to the channel (ISI) in the decoding process?´ A decoder is presented which attempts to incorporate the ISI present in the channel in the decoding process. The performance of this decoder is then examined for a range of distorted channel models. Finally two special cases of the decoder are examined