Abstract: A symbol based communications system involves symbol detection at a receiver in the system. The symbol detection involves determining a set of symbols likely to be present on a sequence of received data. A symbol detector provided to fulfil this role includes means for performing a forward backward recursion means on the basis of a reduced set of active states, to determine state probabilities in a hidden Markov model state trellis. The symbol detector further comprises forward message determination means operable to determine a reduced set of forward messages associated with a set of the available states for performance of the reduced state forward recursion, and backward message determination means operable, independently of the forward message determination means, to determine a reduced set of backward messages associated with a backward message determination means for performance of the reduced state backward recursion.

Abstract: This invention generally relates to methods, apparatus and computer program code for decoding signals, and more particularly to trellis-based decoding using a variant of a BCJR procedure.