Optimal Downlink Transmission in Massive MIMO Enabled SWIPT Systems with Zero-Forcing Precoding

This paper investigates the downlink transmission of massive multiple-input-multiple-output (MIMO) simultaneous wireless information and power transfer (SWIPT) systems. The base station (BS) is equipped with large scale antenna array to provide users with concurrent information and energy supplies. Considering the short communication range between users and the BS in SWIPT systems, the transmission channels are modeled as Rician fading channels to capture both the line-of-sight (LOS) and non-LOS propagations. The approximate and asymptotic expressions of the achievable rate are first derived, and a sum achievable rate optimization problem is formulated based on the asymptotic expression subject to the quality-of-service (QoS) and transmit power constraints. An iterative optimization framework is proposed to solve the original non-linear non-convex problem, and iterative successive convex approximation (SCA) method is introduced in the framework to transmit the non-convex subproblem into convex form. The convergence and effectiveness of the proposed framework are analyzed and proved through analysis and intensive simulations. Results show that the proposed framework can achieve the optimal system performance as the exhaustive search method does.