Iterative Receivers for MIMO-OFDM and Their Convergence Behavior

In this paper, we investigate two reduced-complexity iterative soft interference cancellation minimum mean square error (SIC-MMSE) receivers for frequency-selective multiple-input-multiple-output (MIMO) channels. In the first receiver, the extrinsic information is exchanged between the SIC-MMSE equalizer and the channel decoding stages at each iteration. In the second receiver, the extrinsic information obtained from the SIC-MMSE equalizer is fed back to itself only up to a certain number of iterations and then passed to the channel decoder at the end of the last iteration only to reduce the computational complexity. Moreover, to better understand the convergence behavior of the proposed iterative receivers, we study the notion of extrinsic information transfer (EXIT) characteristics. Using simulations, we derive the extrinsic information trajectory on the EXIT chart at various bit-energy-to-noise-spectral-density ratio (E-b/N-o) ranges to predict the number of iterations required to converge and the turbo cliff region. The predicted behavior of the proposed receivers is then confirmed by the bit-error-rate (BER) performance curves.