Reduced-Complexity BCJR Algorithm for Turbo Equalization

We present innovative techniques to reduce the complexity of the well known BCJR detection algorithm applied on channels affected by intersymbol interference. On a general channel with mixed phase, we independently perform two reduced trellis searches in the forward and backward recursions, and propose a modified completion stage for combining them. When iterative detection/decoding is performed, the reduced searches are defined on the basis of a probabilistic criterion which provides a noticeable performance improvement with respect to the other reduced-complexity algorithms. On the other hand, for channels with minimum phase, we show that the simplified backward recursion can operate on the same set of paths selected during the forward search. Computer simulations confirm the effectiveness of the proposed algorithms in various turbo equalization schemes.