Estimation of channel statistics for iterative detection of OFDM signals

Maximum likelihood sequence detection for OFDM transmissions over unknown multipath fading channels is a challenging task for lack of efficient methods to maximize the likelihood function. A feasible solution to this problem based on the expectation-maximization (EM) algorithm has been recently proposed in the context of space-time block-coded OFDM. The resulting detector operates iteratively and exploits knowledge of the channel statistics and the operating signal-to-noise ratio (SNR). In this work we address the problem of estimating the above quantities in a recursive fashion. Simulations indicate that the EM detector employing the estimated SNR and channel statistics has better performance than other existing schemes that operate in a mismatched mode. Also, the performance loss with respect to a system with perfect channel knowledge is negligible at SNR values of practical interest.