Multi-User Energy Beamforming for Different Energy Requests

Energy beamforming takes center stage in radio frequency (RF)-enabled wireless energy transfer (WET) systems. In this letter, we study multi-user energy beamforming to minimize the overall charging time for energy harvesting users (EHUs) with different energy requirements. In order to lessen the cost and power consumption by reducing the required RF chains, it is of consequence to figure out low-rank optimal energy beamforming. By analyzing an upper bound on the rank of a minimum-rank solution, we develop a method to figure out low-rank optimal energy beamforming from the formulated semi-definite programming problem. Our simulation results exhibit the proposed energy beamforming considerably reduces the charging time required until all the requests are met. We also reveal that the capacity achieving precoder for multicasting transmission is a special case of the proposed energy beamforming solution.