Iterative Frequency Domain Equalization for Single-Carrier Wideband MIMO Channels

Single carrier frequency domain equalization (SC-FDE) is receiving considerable attention recently due to its comparable complexity and performance with OFDM. In this paper, an iterative SC-FDE with decision feedback in frequency domain is proposed for wideband multiple-input multiple-output (MIMO) channels and more general multipath vector channels as a generalization of previous works considering FDE with decision feedback for single-input single-output (SISO) systems. The proposed detector is based on iterative forward and backward filtering followed by a MIMO multi-stream detector that uses a priori log-likelihood ratios (LLR) of coded symbols. Forward and feedback filters are jointly optimized according to the minimum mean square error (MMSE) criterion to minimize both self inter-symbol-interference (ISI) and interference from other streams transmitted at different antennas. It has been observed that the proposed structure exploits the multi-path diversity sources of the channel effectively and a performance very close to MIMO-OFDM outage probability can be achieved. Therefore, our proposed iterative SC-FDE technique for MIMO wideband channels can be viewed as a strong alternative to MIMO-OFDM schemes with similar complexity.