Wireless Power Transfer via Intelligent Reflecting Surface-Assisted Millimeter Wave Power Beacons

Wireless power transfer (WPT) can provide sustainable power supply to the distributed devices via electromagnetic (EM) waves. The narrow beams formed by millimeter wave (mmWave) beam can concentrate the transmission power and greatly improve the energy efficiency of WPT. However, the mmWave propagation is susceptible to blockage and suffers higher path-loss, resulting in low power intensity harvested by the devices in no line of sight (NLOS) state. In this paper, we propose a sectorized directional WPT scheme for wireless sensor network (WSN) assisted by the emerging intelligent reflecting surface (IRS), where power beacon (PB) transfers energy to the devices in selected charging sectors, and the IRS is deployed in each sector to achieve high passive beamforming gain and provide additional effective reflection paths to enhance WPT efficiency drastically. We aim to maximize the weighted sum-power received by devices via jointly optimizing the transmit precoders at the PB and reflect phase shifts at the IRS, subject to the individual energy harvesting constraints of each device. To solve this non-convex problem, an efficient algorithm to find a sub-optimal solution is proposed. Simulation results show that the proposed scheme can increase the weighted sum-power by 15% and 26% compared to the two baseline methods.