Reduced-tree-based soft decoding for block-coded modulation

It is shown that soft maximum-likelihood decoding for block-coded modulation (BCM) can be performed using the code tree. It is easy to generate the code tree for any type of block code, linear as well as nonlinear. A reduced tree is obtained from the code tree. The trellis for a block code can be obtained from the reduced tree. Using this structure to perform computations in parallel, a scheme is proposed for the implementation of the soft decoder. Back tracking, necessary in a soft decoder using the Viterbi algorithm on a trellis, is eliminated