Turbo Receiver Design with EM-Based Frequency Synchronization for MIMO-OFDM Systems

A maximum-likelihood estimator (MLE) based on the expectation-maximization (EM) algorithm is presented to estimate the carrier frequency offset (CFO) in multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. This MLE estimator is also capable to accommodate any space-time coded (STC)-OFDM transmission. Then by incorporation of proposed ML estimator into the initialization step of conventional turbo receiver, a novel turbo receiver with CFO estimation/compensation capability is developed for MIMO-OFDM systems. Simulation results are presented which clearly show the application of the proposed MLE estimator into the turbo receiver structure leads to a bit-error rate (BER) that is only slightly higher than that of a perfectly synchronized system, making it highly applicable.