Joint Power Waveforming and Beamforming for Wireless Power Transfer
In the Internet of Things, wireless devices need more easily accessible energy resources, which motivates the development of wireless power transfer (WPT) using radio frequency signals. Beamforming technique has been widely adopted by using multiple transmit antennas to form a sharp energy beam toward an intended receiver. However, few of them have considered the potential gain of multipath propagation. In this paper, we propose a joint power waveforming and beamforming in the time domain for WPT, in which the waveforms on multiple transmit antennas driven by a common reference signal are designed to maximize the gain of energy delivery efficiency. We consider both nonperiodic and periodic reference signals and propose low-complexity waveforms that can achieve near-optimal performance. It is found that the energy delivery efficiency gain of the proposed approach increases with the waveform length until saturation. We theoretically analyze the outage probability of the proposed approach under a uniform power delay channel profile, which quantifies the impact of the number of antennas and multipaths. Simulations are performed to validate the theoretic analysis and the effectiveness of the proposed joint power waveforming and beamforming approach.