Energy Efficient SWIPT Systems in Multi-cell MISO Networks

This paper studies beamforming design problems for multi-cell multi-user downlink networks with simultaneous wireless information and power transfer (SWIPT). In this system, multi-antenna base stations (BSs) concurrently transfer information and energy to multiple single-antenna information decoding (ID) and energy harvesting (EH) users. We aim to maximize energy harvesting efficiency (EHE), which is defined as the ratio of the harvested energy at the EH users to the amount of energy consumption at the BSs, while guaranteeing quality-of-service constraint for each ID user. The EHE metric quantifies the efficiency of the power transfer capability of the SWIPT network. For the EH operation, both an ideal linear model and a practical non-linear model are individually investigated. We optimally solve this non-convex problem in two different scenarios according to the cooperation level among the BSs. First, for the centralized case where global channel state information (CSI) is available at all BSs, we propose a centralized beamforming method based on the semi-definite relaxation and the successive convex approximation techniques. Next, in order to reduce the backhaul signaling overhead, decentralized algorithms are presented where each BS computes its beamforming vector by only using local CSI. Simulation results show that the proposed SWIPT beamforming algorithms offer a significant EHE performance gain over conventional schemes.