Making MLSD decisions by thresholding the matched filter output

Abstract

This paper presents an iterative detector that, by thresholding the output of the matched filter, gives maximum-likelihood sequence detector (MLSD) decisions on binary, antipodally modulated symbols that have been corrupted by intersymbol interference and additive Gaussian noise. The detector will make decisions on some, but often not all, of the symbols in a transmitted sequence, and those decisions will be the same decisions as the MLSD would have made. The number of symbols that are detected is stochastic, varying from sequence to sequence. The basis of the detector is a bound on a crossterm of the quadratic form in the log-likelihood function for the transmitted sequence. The detector is simple in structure, consisting of a matched filter and two variable threshold values for each symbol.