Joint symbol detection and channel tracking for MIMO-OFDM systems via the variational bayes EM algorithm

In this paper, a new joint symbol detection and channel tracking algorithm is proposed for the coded MIMO-OFDM systems over time-varying frequency-selective fading channels. The iterative detection/decoding and channel estimation are iteratively employed based on the Variational Bayes expectation-maximization (VBEM) algorithm to improve the system performance. A modified list sphere decoder (LSD) is derived to make the data detection feasible for large systems, which takes into account the statistical information about the channel uncertainty and provides soft symbols for channel estimation. With the autoregressive process channel model and the soft symbols calculated from detector, the time-varying channel impulse responses are tracked by the Kalman smoother. The VBEM iterations are embedded in the turbo-processing of the receiver for incorporation of the coding constraints. Simulation results demonstrate that the proposed algorithm has robust performance over time-varying channels.