Power Waveforming: Wireless Power Transfer Beyond Time Reversal
This paper explores the idea of time-reversal (TR) technology in wireless power transfer to propose a new wireless power transfer paradigm termed power waveforming (PW), where a transmitter engages in delivering wireless power to an intended receiver by fully utilizing all the available multipaths that serve as virtual antennas. Two power transfer-oriented waveforms, energy waveform and single-tone waveform, are proposed for PW power transfer systems, both of which are no longer TR in essence. The former is designed to maximize the received power, while the latter is a low-complexity alternative with small or even no performance degradation. We theoretically analyze the power transfer gain of the proposed power transfer system over the direct transmission scheme, which can achieve about 6 dB gain, under various channel power delay profiles and show that the PW is an ideal paradigm for wireless power transfer because of its inherent ability to recollect all the power that is possible to harvest from the surrounding environment. In addition, the outage performances in harvesting power of the PW system and the conventional multiple-input multiple-output (MIMO) system are derived. It reveals that the PW system can achieve the same outage performance of the MIMO system as long as the number of resolvable multipaths is sufficiently large. Simulation results validate the analytical findings and experimental results demonstrate the effectiveness of the proposed PW technique.