Reduced-state BCJR-type algorithms

We propose a technique to reduce the number of trellis states in BCJR-type algorithms, i.e., algorithms with a structure similar to that of the well-known algorithm by Bahl, Cocke, Jelinek and Raviv (1974). This work is inspired by reduced-state sequence detection (RSSD). The key idea is the construction, during one of the recursions, of a “survivor map”, on a reduced-state trellis, to be used in the other recursion. Two examples of application of the proposed technique to iterative decoding structures are shown, namely coherent detection over intersymbol interference (ISI) channels and noncoherent detection based on an algorithm previously proposed by the authors