New decoder for STBC-OFDM multiuser system over time-frequency selective fading channels

The conventional zero forcing (ZF) and minimum mean squared error (MMSE) decoders for space-time block coded (STBC) multiuser (MU) system are based on the assumption that the channels are flat fading (FF) and quasistatic fading (QSF). By combining with orthogonal frequency division multiplexing (OFDM), S. Suthaharan et al. (2000) extend the MMSE decoder structure to frequency selective fading (FSF) channels. But an important assumption for the extension is that the channels remain constant over the length of two consecutive OFDM symbol block periods. Once the channels vary from one OFDM symbol interval to another, i.e., time selective fading (TSF), the decoder proposed by Suthaharan will exhibit intersymbol interference (ISI) for decoding one user's signals. In this paper, we propose a new decoder design scheme for STBC MU system over time-frequency selective fading, i.e., dual selective fading (DSF) channels. Finally, the performance of the new decoder are evaluated by computer simulation and the simulation results have revealed that significant gains can be achieved when the new decoder is operated in DSF channels.