On the Beneficial Roles of Fading and Transmit Diversity in Wireless Power Transfer with Nonlinear Energy Harvesting

TL;DR

This paper demonstrates that channel fading and a new transmit diversity technique significantly improve wireless power transfer efficiency by exploiting energy harvester nonlinearity, without requiring channel state information at the transmitter.

Contribution

The paper introduces a novel transmit diversity scheme that enhances WPT efficiency through channel fluctuations, independent of CSIT, and validates it with experiments and simulations.

Findings

Fading enhances RF-to-DC conversion efficiency.

Transmit Diversity boosts power transfer without CSIT.

Experimental results show 50% power gain with two antennas.

Abstract

We study the effect of channel fading in Wireless Power Transfer (WPT) and show that fading enhances the RFto- DC conversion efficiency of nonlinear RF energy harvesters. We then develop a new form of signal design for WPT, denoted as Transmit Diversity, that relies on multiple dumb antennas at the transmitter to induce fast fluctuations of the wireless channel. Those fluctuations boost the RF-to-DC conversion efficiency thanks to the energy harvester nonlinearity. In contrast with (energy) beamforming, Transmit Diversity does not rely on Channel State Information at the Transmitter (CSIT) and does not increase the average power at the energy harvester input, though it still enhances the overall end-to-end power transfer efficiency. Transmit Diversity is also combined with recently developed (energy) waveform and modulation to provide further enhancements. The efficacy of the scheme is analyzed using physics-based and curve fitting-based nonlinear models of the energy harvester and demonstrated using circuit simulations, prototyping and experimentation. Measurements with two transmit antennas reveal gains of 50%in harvested DC power over a single transmit antenna setup. The work (again) highlights the crucial role played by the harvester nonlinearity and demonstrates that multiple transmit antennas can be beneficial to WPT even in the absence of CSIT.