Iterative Biased MMSE Detections for DSTTD-OFDM Systems over Time-Varying Multipath Channels

In this paper, we propose iterative biased minimum-mean-squared-error (BMMSE) detection schemes for double space-time transmit diversity (DSTTD)-orthogonal frequency division multiplexing (OFDM) systems over time-varying multipath channels. The time-varying effects cause intercarrier interference (ICI) and destroy the orthogonality of each STTD unit, considerably degrading system performance. To mitigate these impairments, we first estimate all transmitted symbols temporarily using sorted-QR-decomposition (SQRD)-based decision-feedback detection (DFD) considering the partial ICIs. Next, the significantly dominant ICI terms are eliminated with the help of the estimated symbols in the previous step. Finally, the SQRD-based DFD with the only desired subcarriers is performed. In each detection steps, we employ a biased MMSE criterion, which considers ICIs as well as noise. Numerical results demonstrate that the system performance of the proposed algorithms is greatly enhanced in comparison to the conventional schemes.