Soft-output equalization with TCM for wireless communications

Abstract

This paper investigates the use of soft-output equalization methods that are based on Bahl's (1974) MAP algorithm along with a modified version of such algorithm which does not require knowledge of the noise variance. We use both algorithms to realize soft-output detection in a concatenated equalization and trellis-coded modulation (TCM) decoding based wireless communication system. Further, the effect of using different detection block lengths in the modified MAP algorithm is studied and the use of two-branch equal-gain combining and selection diversity is also considered. Finally, we compare the performance of the MAP algorithm based equalization with our previously proposed equalization scheme which combines decision feedback equalization (DFE) and TCM.