Robust SLR-based beamformer for a multi-user SC-FDE-MIMO system

We address the problem of transmit beamforming under channel uncertainty for a multiuser (MU), single carrier frequency domain equalization multiple input multiple output (SC-FDE-MIMO) system. SC-FDE-MIMO scheme is effective solution with relative low complexity to combat inter -symbol interference (ISI) whilst exploiting multi antennas diversity gain. In our system, the signal to leakage ratio (SLR) criterion is used to design the transmit beamformer and the minimum mean square error (MMSE) criterion is employed for the receiver equalization and combining. Non-robust beamforming techniques require perfect channel state information (CSI) knowledge which is not available in practice. In this paper, we propose a robust transmit beamformer which can successfully tolerate CSI imperfection. Diagonal loading is employed to introduce robustness to channel state information errors. The novelty of this work, however, is the application of the robust beamforming in the context of downlink MU-SC transmission. Average bit error (BER) simulations are presented to verify the efficiency of the proposed method.