Space-time weighted nonbinary repeat-accumulate codes in frequency-selective MIMO channels

The so-called space-time weighted nonbinary repeat-accumulate (ST-WNRA) codes are capable of achieving full antenna diversity in single-user flat fading channels. In this paper, the performance of these codes is evaluated over a frequency-selective Rayleigh fading multiple-input multiple-output channel in a multiuser environment. Under this channel condition, the full antenna diversity supported by the ST-WNRA codes can no longer be achieved due to the presence of intersymbol interference and multiple access interference. Hence, in order to suppress these interferences, a turbo equalization technique based on the minimum mean square-error filtering with soft interference cancellation (SC-MMSE) is employed. The SC-MMSE detector is designed such that the diversity that can be gleaned from the multiple antennas as well as from the multipath components can be fully exploited. Computer simulations demonstrate that our proposed turbo-equalized system with ST-WNRA codes is capable of achieving the maximum diversity order and hence achieving an excellent bit error rate performance with a reasonable spectral efficiency at a low complexity cost.