Joint estimation of path delay and complex gain for coded systems using the EM algorithm

In this paper, we investigate the performance of a turbo estimation scheme based on the expectation maximization (EM) algorithm for M-PSK modulation and a convolutionally coded system. Estimates of the path delay and the complex gain are updated jointly by combining the training sequence and the soft information provided by the MAP channel decoder. Initial estimates may be obtained through either a data aided or a non data aided algorithm. We show through computer simulation that the iterative process between turbo detection and estimation leads to performances close to those obtained for perfect channel state information in terms of bit error rate (BER). On the other hand, the mean square estimation errors (MSEE) of path delay and the complex gain reach the classical modified Cramer-Rao bound. Comparisons with conventional estimation schemes are carried out.