Waveform Design for Wireless Power Transfer

TL;DR

This paper investigates the design of transmit waveforms for far-field wireless power transfer, emphasizing the importance of non-linear rectenna modeling to optimize power delivery and demonstrating significant gains over linear models through simulations.

Contribution

It introduces a non-linear rectenna model for waveform design, showing that multi-frequency waveforms outperform narrowband ones, and derives scaling laws highlighting the benefits of CSI and non-linear modeling.

Findings

Non-linear models favor multi-frequency waveforms for better power transfer.

Waveforms based on non-linear models outperform linear model designs.

Scaling laws demonstrate the advantages of CSI and multi-antenna configurations.

Abstract

Far-field Wireless Power Transfer (WPT) has attracted significant attention in recent years. Despite the rapid progress, the emphasis of the research community in the last decade has remained largely concentrated on improving the design of energy harvester (so-called rectenna) and has left aside the effect of transmitter design. In this paper, we study the design of transmit waveform so as to enhance the DC power at the output of the rectenna. We derive a tractable model of the non-linearity of the rectenna and compare with a linear model conventionally used in the literature. We then use those models to design novel multisine waveforms that are adaptive to the channel state information (CSI). Interestingly, while the linear model favours narrowband transmission with all the power allocated to a single frequency, the non-linear model favours a power allocation over multiple frequencies. Through realistic simulations, waveforms designed based on the non-linear model are shown to provide significant gains (in terms of harvested DC power) over those designed based on the linear model and over non-adaptive waveforms. We also compute analytically the theoretical scaling laws of the harvested energy for various waveforms as a function of the number of sinewaves and transmit antennas. Those scaling laws highlight the benefits of CSI knowledge at the transmitter in WPT and of a WPT design based on a non-linear rectenna model over a linear model. Results also motivate the study of a promising architecture relying on large-scale multisine multi-antenna waveforms for WPT. As a final note, results stress the importance of modeling and accounting for the non-linearity of the rectenna in any system design involving wireless power.