Concatenated soft-output equalization and TCM for wireless personal communications

In this paper, we will investigate the use of maximum a posteriori probability (MAP) algorithm to realize soft-output equalization in a concatenated equalization and trellis-coded modulation (TCM) based wireless communication system. Specifically, we will consider Lee´s (1974) MAP algorithm and propose a simplified version which does not require knowledge of the noise variance and can avoid the calculation of the nonlinear function which is involved in the probabilities. Furthermore, we use the square root Kalman filtering algorithm for real channel estimation. In order to improve the system performance, two-branch equal-gain combining diversity will be also considered. Finally, we compare the performance of the MAP algorithm based equalization with our previously proposed equalization scheme which combines decision feedback equalization and TCM