Performance of combined equalization and TCM decoding for Rayleigh fading channels

We describe a power and bandwidth efficient transmission scheme for Rayleigh fading channels and a suitable low complexity combined equalization and decoding system. The transmission system is based on an orthonormal transform (fast Hadamard transform) combined with trellis-coded modulation (TCM). The receiver uses an iterative block decision feedback equalizer and a Viterbi algorithm to decode the TCM. It is shown that the equalizer transforms the Rayleigh fading channel asymptotically into a set of parallel AWGN subchannels. Therefore, the decoder of each subchannel "sees" an AWGN channel. Hence, coding gains comparable to the coding gains in an AWGN environment can be achieved. The results are considerably better than the performance of TCM codes designed for the Rayleigh fading channel with the same power and bandwidth efficiency. The conclusions of channel capacity considerations support the potential of the proposed transmission and reception scheme. The theoretical findings are furthermore supported by simulation results.