A novel APP-based soft-output adaptive equalizer. Exploiting non-linear MMSE fixed-lag smoothed estimates of the transmitted symbols

Non-linear minimum mean square error (NL-MMSE) estimators have seldom been used in practice because of the intrinsic analytic difficulties that arise in their development. However, it has been shown by Galli (2000) that the a posteriori probabilities (APPs) of the states of the ISI channel can be efficiently used to generate NL-MMSE filtered and fixed-lag smoothed estimates of the transmitted symbols. On the basis of this new result, a novel soft-output adaptive receiver is presented for TDMA-based cellular land-mobile radio communications. The proposed receiver uses NL-MMSE fixed-lag smoothed estimates of the transmitted symbols for channel estimation and tracking and exploits the APPs for the computation of the branch metrics of the Viterbi algorithm (VA). Simulations have shown that, in some situations, gains of at least 14 dB over the conventional hard-decision driven receivers are obtainable