Symbol-level precoding in MISO broadcast channels for SWIPT systems

Abstract

This work investigates a problem for joint transmit beamforming and receive power splitting in multiple-input single-output downlink systems under quality of service and power transfer constraints. Rather than suppressing interference as in conventional schemes, this work takes advantage of constructive interference among users, inherent in the downlink, as a source of both useful information signal energy and electrical wireless energy. Specifically, we propose a new data-aided precoding design that minimizes the transmit power while guaranteeing the quality of service (QoS) and energy harvesting constraints for generic phase shift keying modulated signals. The QoS constraints are modified to accommodate constructive interference, based on the constructive regions in the signal constellation. Although the resulting problem is nonconvex, we propose second-order cone programming algorithms with polynomial complexity that provide upper and lower bounds to the optimal solution and establish the asymptotic optimality of these algorithms when the modulation order and signal to interference-plus-noise ratio threshold tend to infinity. Simulation results show significant power savings with the proposed data-aided precoding approach compared to the conventional precoding scheme.