Optimum and sub-optimum detection of coded data disturbed by time-varying intersymbol interference [applicable to digital mobile radio receivers]

The MLSE (maximum-likelihood sequence-estimation) approach is applied to the concatenation of an equalizer and a channel decoder. An equalization algorithm which yields the optimal soft-decision information for the channel decoder in the case of ideal interleaving is presented. This equalization algorithm is applicable to digital mobile radio receivers which comprise an equalizer, a channel decoder, and some means for interleaving in between. The optimum equalization algorithm for computing bit-by-bit soft-decision information turns out to be a trellis-based algorithm, which minimizes the bit error probability (rather than the sequence error probability). Suboptimum variants which are simpler to implement and perform nearly as well as the optimum are derived. The complexity of the suboptimum variant is less than that of the soft-decision output Viterbi algorithm (SOVA), since no extra memory and operations for the path history are required