MAP Receiver with Enhanced EM Channel Estimation for MIMOOFDM Systems

This paper investigates iterative channel estimation for multiple-input multiple-output (MIMO) systems with orthogonal frequency division multiplexing (OFDM) transmission technique. Using the candidate list obtained by the list sphere decoder (LSD), the soft information is calculated and fed back to the channel estimator which is based on the maximum a posteriori (MAP) version of the expectation-maximization (EM) algorithm. A soft symbol threshold was set to avoid the performance deterioration due to the unreliable detected symbols. With the aid of the decomposed component signals obtained at the E step, the soft symbols with low reliability are recalculated and the more accurate soft information is used in the channel estimation. Simulation results show that the newly proposed enhanced EM-MAP algorithm outperforms the conventional EM-ML and EM-MAP algorithms.