Sparsening Filter Design for Iterative Soft-Input Soft-Output Detectors

A large body of research exists around the idea of channel shortening, where a prefilter is designed to reduce the effective channel impulse response to some smaller number of contiguous taps. This idea was originally conceived to reduce the complexity of Viterbi-based maximum-likelihood equalizers. Here, the authors consider a generalization of channel shortening which the authors term "Channel sparsening". In this case, a prefilter is designed to reduce the effective channel to a small number of nonzero taps which do not need to be contiguous. When used in combination with belief-propagation-based Maximum A Posteriori (MAP) detectors, an analogous complexity reduction can be realized.