An Adaptive Minimum-BER Approach for Multi-User Detection in STBC-MIMO MC-CDMA Systems

In the recent years, MIMO MC-CDMA techniques have been proposed in order to increase system capacity over frequency-selective wireless channels. The key feature of MIMO MC-CDMA is the capability of exploiting diversity jointly in time, frequency and in the space domains. Very promising results have been achieved by STBC-MIMO MC-CDMA using receiver schemes targeted to maximize the signal-to-noise plus interference ratio (SINR) at the output of the diversity combiner. Such a concept turns on the minimum mean squared error (MMSE) combining criterion. Nevertheless, it is known by literature that MSE cost function is not always optimal in digital communications. In this work, we are proposing an adaptive multi-user detection approach based on a minimum-BER (M- BER) concept for a synchronous STBC-MIMO MC-CDMA system transmitting data over time-varying multipath fading channels. The practical implementation of the M-BER receiver relies on an adaptive least-mean-square (LMS)-like algorithm, periodically aided by a training sequence and working in decision-directed modality during a coherence time window. Experimental results have shown a performance improvement yielded by the proposed adaptive M-BER MUD with respect to MMSE adaptive MUD achieved by spending an affordable computational effort.