Wireless MIMO switching: Sum rate optimization

This paper addresses relay design for a wireless multiple-input-multiple-output (MIMO) switching scheme that enables data exchange among multiple users. Here, a multi-antenna relay linearly precodes the received (uplink) signals from multiple users before forwarding the signal in the downlink, where the purpose of precoding is to let each user receive its desired signal with interference from other users suppressed. The problem of optimizing the precoder based on sum-rate maximization criteria is typically non-convex and difficult to solve. The main contribution of this paper is that we show the sum-rate maximization problem can be converted to an equivalent weighted sum-MSE minimization problem and can therefore be solved using an iterative algorithm proposed in our previous work. Asymptotic analysis reveals that, with properly chosen initial values, the proposed iterative algorithms are asymptotically optimal in both high and low signal-to-noise-ratio (SNR) regimes for MIMO switching, either with or without self-interference cancellation (a.k.a., physical-layer network coding). Numerical results show that the optimized MIMO switching scheme based on the proposed algorithms significantly outperforms existing approaches in the literature.