Turbo multi-user receiver for asynchronous multi-user OFDM systems

This paper proposes a low complexity turbo multi-user receiver for the coded asynchronous multi-user orthogonal frequency division multiplexing (OFDM) signal over multipath fading channels. While asynchronous multi-user multiplexing with antenna diversity accommodates high speed applications and achieves the high spectral efficiency in communication systems, the multiple access interference deteriorates the quality of signal detection. In order to effectively suppress the interference and amplify a performance gain from channel coding, we employ a turbo equalization technique. Based on the asynchronous OFDM signal model and the corresponding linear minimum mean squared error (MMSE) estimator, an iterative space-time MMSE multi-user detector with a parallel soft interference canceller is developed. Simulation results demonstrate that iterative joint demodulation of the asynchronous multi-user OFDM signal achieves a significant performance gain even with a reduced complexity equalizer and a few iterations.