New reduced state space BCJR algorithms for the ISI channel

A critical component in detection under intersymbol interference (ISI) and in turbo equalization is the BCJR algorithm. We combine three approaches to reducing its computation. First, energy seen by the receiver is focused by a phase-maximizing all pass filter; an improvement on this older idea is proposed. Then the state used by the BCJR is broken into an offset state and a main state. Finally, some reduced-state BCJR procedures are evaluated. These receivers are tested by ISI detection and turbo equalization over strongly bandlimited channels.