Statistical QoS-Aware Precoding Scheme for Downlink Multiuser MIMO Systems

In this paper, a downlink multi-user multiple-input multiple-output (MU-MIMO) system operating under statistical QoS constraints is investigated. Effective capacity, which is defined as the maximal constant arrival rate that can be supported by a given service process while satisfying the statistical queueing constraints, is adopted as the performance metric. Initially, perfect CSI is assumed at the base station (BS). An optimization problem is formulated to determine the optimal precoding matrix that maximizes the weighted sum effective capacity under total transmit power constraints at the BS. Then, an optimality condition that the optimal precoding matrix needs to satisfy is derived, which is proven to always have a feasible solution. Subsequently, fixed point iteration algorithms are designed to find a solution. Through extensive numerical results, the superiority of the proposed scheme is demonstrated under stringent delay constraints. Overall, this work provides an effective precoder design incorporating the statistical QoS constraints for the downlink MU-MIMO systems that outperforms existing strategies.