A combined adaptive equalizer and TCM-decoder for fast time-variant ISI-degraded Rayleigh radio channels

A new adaptive coherent receiver for decoding trellis-coded-modulated (TCM) signals transmitted over randomly time-variant frequency-selective fast-fading mobile radio-links is presented. The main novelty is that the equalization, decoding and channel estimation tasks are optimally combined. The first two tasks are jointly carried out by a symbol-by-symbol (SbS) equalizer/decoder which delivers not only the low-delayed hard decisions but also the more informative soft-statistics constituted by the a posteriori probabilities (APPs). The APPs sequence directly feeds an “ad hoc” developed non-linear Kalman-type estimator which tracks the channel variations. The use of soft-statistics in place of the usual hard-decoded data for channel estimation purposes constitutes the novel attractive feature of the presented receiver. In this way, the channel estimator is able to fully exploit the error-correcting properties of the TCM code, thus enhancing its tracking capabilities