Reconfigurable Intelligent Surface Aided MIMO Wireless Power Transfer With Multiple Energy Harvesting Requirements

In this correspondence, a reconfigurable intelligent surface (RIS) assisted wireless power transfer system where a multi-antenna energy station (ES) transmits energy beams to multi-antenna energy receivers (ERs) is considered. We aim at optimizing the ES beamforming and the RIS beamforming to minimize the transmit power of the ES under individual energy harvesting constraints for ERs. To handle the beamforming optimization problem, we develop an algorithm where an alternating direction method of multipliers based scheme is put forward for the RIS beamforming optimization. Compared with the counterpart which relies on semidefinite relaxation to optimize the RIS beamforming, the complexity of the proposed beamforming optimization algorithm is significantly reduced. Simulation results illustrate that the proposed algorithm performs close to the counterpart, which implies that the complexity reduction is achieved at very limited expense of performance.