EXIT Chart Analysis of a Reduced Complexity Iterative MIMO-OFDM Receiver

The application of turbo principle in designing receivers for multiple-input multiple-output (MIMO) wireless systems not only achieves practical complexity receiver systems but also near optimal performances for many of the next generation systems. In particular, our recent research has shown that significant performance can be achieved by using a low complexity iterative soft interference cancellation minimum mean-squared error (SIC-MMSE) equalizer in various coded MIMO wireless channels including frequency-selective MIMO channels (S. Ahmed et al., 2006). This performance gain is due to an extrinsic information exchange process between the equalization and the channel decoding stages compared to a traditional system that treats these processes in isolation. However, the challenge faced with these iterative receivers is the understanding of their convergence behaviour. In this paper, to better understand the convergence behaviour of the proposed iterative receiver, we study the notion of extrinsic information transfer (EXIT) characteristics. Using simulations, we derive the extrinsic information trajectory on the EXIT chart at various E_b/N₀ ranges to confirm the convergence of the proposed equalizer.