Downlink Multi-User MIMO Precoding Design Via Signal-Over-Leakage Capacity

We study the linear precoder design problem in downlink multiuser MIMO (MU-MIMO). We first analyze the leakage-based precoder design under a full multiplexing constraint, which maximizes the signal-to-leakage-and-noise ratio (SLNR) for each individual user. We prove that the SLNR-optimal multistream precoder always maximizes the SLNR via essentially concentrating all the available transmit power on a single data stream, regardless of the rank constraint. We then propose a novel design criterion, called signal-over-leakage capacity (SLC), which corresponds to the achievable rate difference between a virtual signal-only link and a virtual interference-only link, for each individual user. We completely solve the SLC maximization problem and provide a closed-form optimal solution, which distributes the transmit power among multiple data streams, and thus better utilizes the available spatial degrees of freedom in an MU-MIMO system. Numerical experimental results are provided to corroborate the analysis.