Turbo equalization and an M-BCJR algorithm for strongly narrowband intersymbol interference

M-BCJR algorithms are proposed and tested over an AWGN channel with moderate to intense intersymbol interference (ISI). Two M-BCJR applications are evaluated, simple detection over the ISI channel and turbo equalization. The signaling is binary faster than Nyquist linear modulation. The ISI models tested correspond to transmission of increasingly many bits/Hz-s with a fixed signal spectra; the paper studies the range 2-8 bits/Hz-s, which implies ISI models as long as 32 taps. As a simple detector, the M-BCJR achieves the ML error rate with small computation, where the Viterbi algorithm is completely impractical. In turbo equalization, the M-BCJR needs somewhat more computation and a more careful design because it must produce accurate likelihoods.