Energy-Efficiency-Oriented Charge Scheduling and Beamforming for a Two-Tier Wireless Powered Network

Abstract

Long-range radio-frequency wireless charging has received more and more attention in recent years. Unlike the literature that focuses on the mobile charging scenario, which is formulated as a path-planning problem, we consider a static network that consists of a power beacon (PB) and multiple wireless powered user nodes. Each user node is equipped with a rechargeable battery and harvests energy only from the PB. We assume that all user nodes are either in charge or work mode. Under this assumption, we first propose a charge scheduling scheme that achieves the system’s maximal energy efficiency. We then further investigate the system’s improvement with a multiantenna PB using the energy beamforming technique. Next, we extend our scheduling scheme to a two-tier network architecture, where a first-tier PB first transfers energy to the second-tier sub-PBs, and then those sub-PBs deliver energy to the user nodes which belong to their clusters. It is shown that energy beamforming with multiple antennas brings a significant improvement to the system’s performance. Moreover, the two-tier architecture is shown to be superior to the one-tier architecture in terms of the energy transfer efficiency and the system’s realization complexity. Finally, the simulation results demonstrate our theoretical findings.