Hybrid EM and KF receiver of MIMO OFDM systems in time-varying environments

In this paper, simultaneous channel estimation, carrier frequency offset (CFO) estimation, and data decision are considered for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. It is shown that the expectation maximization (EM) approach is complementary to the Kalman filter (KF) approach where the latter provides poor CFO estimation but good channel estimation and the former provides poor channel estimation but good CFO estimation. A hybrid combination of EM and KF approaches is proposed to take advantages of the strengths and avoid the weaknesses of both approaches. Numerical results have shown the hybrid combination is around 1.2 dB better than the non-hybrid approaches (EM or KF) in BER performances. The complexity of the hybrid approach is comparable to the KF approach and is much lower than the EM approach.