Space-Time Scheduled Energy Beamforming in Distributed Random-Beamforming Wireless Energy Transfer

A space-time scheduled energy beamforming scheme is described for a distributed random-beamforming (RB) wireless energy transfer system to accommodate a large number of battery-less devices. As a dedicated energy beamforming (DEB) technique designed to be compatibly embedded into the RB-based system, we propose a semi-random DEB scheme based on opportunistic search for a sub-optimum beamformer by feeding back a time slot index in which the received signal strength indicator is maximized. To handle a large number of devices, we also propose a simple space-time scheduler to easily and efficiently schedule those devices to time-domain subframes by spatially multiplexing DEB using different antenna subsets in the same subframe. Our simulation results demonstrated that DEB achieved higher energy transfer efficiency than RB and that the space-time scheduler efficiently multiplexed multiple sets of DEB to increase periodical energy transfer efficiency.