Modified leakage-based transmit filter designs for multi-user MIMO systems

This paper proposes two modified definitions of signal-to-leakage-plus-noise ratio (mSLNR) as criteria for linear transmit filter design in Multi-User MIMO systems. The proposed criteria incorporate receiver structures and priority weight matrices into the precoder design, which can effectively exploit unused receive signal spaces, in the case that available eigenmodes are not fully transmitted, and can potentially prioritise users’ data streams. Iterative SLNR (iSLNR) precoding algorithms based on the proposed mSLNR definitions are also presented. Further, the variations of the iSLNR algorithms are thoroughly studied. In particular, the impact of the mSLNR definitions, choices of receive filters and iteration types on the convergence property and sum-rate performance is discussed. Moreover, the effect of weight matrices on users’ prioritisation is elaborated. For extreme weight values, the proposed algorithms are shown to converge to either eigenbeamforming or null-space decomposition techniques. Further, a robust design of the proposed schemes for the case of imperfect channel state information (CSI) is presented. It is shown that adequate knowledge of effective receive subspaces can be attained by simply assuming matched filters (MF) in the iterative precoding process, while further improvement can be obtained by an actual implementation of interference-mitigation-capable receivers.