Convergence analysis of turbo equalization in ST block-coded MIMO systems

We investigate the probabilistic convergence behavior of minimum mean square error (MMSE) turbo equalization in space-time (ST) block-coded multiple-input multiple-output (MIMO) systems with finite block lengths. For this purpose, the extrinsic information transfer characteristics (EXIT)-band chart technique, which was originally proposed for analyzing turbo decoding of parallel concatenated codes is applied. The impact on the convergence behavior and performance due to the use of ST block coding is analyzed through the EXIT-band characteristics. The convergence behaviors of the exact and approximate implementations of MMSE equalization are compared. We show that in the hybrid equalization schemes, the EXIT-band chart analysis can be used to determine the number of iterations that should be performed using the exact implementation. Our results clearly demonstrate the usefulness of the EXIT-band chart technique as a simple tool to analyze the convergence behavior of turbo equalization in systems with finite block lengths.