Waveform Design for Wireless Power Transfer with Power Amplifier and Energy Harvester Non-Linearities

TL;DR

This paper develops waveform optimization strategies for wireless power transfer that account for both power amplifier and energy harvester nonlinearities, improving harvested power under various operational regimes.

Contribution

It introduces two novel multi-carrier waveform designs optimized at the HPA input, considering nonlinearities, and analyzes their performance in different channel conditions.

Findings

HPA non-linearity degrades harvested power, while EH non-linearity can enhance it.

Optimal waveform shifts from multi-carrier to single-carrier depending on non-linearity dominance.

Proposed waveforms outperform traditional designs, especially in frequency-flat channels.

Abstract

Waveform optimization has shown its great potential to boost the performance of far-field wireless power transfer (WPT). Current research has optimized transmit waveform, adaptive to channel state information (CSI), to maximize the harvested power in WPT while accounting for energy harvester (EH)'s non-linearity. However, the existing transmit waveform design disregards the non-linear high power amplifiers (HPA) at the transmitter. Driven by this, this paper optimizes the multi-carrier waveform at the input of HPA to maximize the harvested DC power considering both HPA's and EH's non-linearities. Two optimization models are formulated based on whether the frequencies of the multi-carrier waveform are concentrated within the transmit pass band or not. Analysis and simulations show that, while EH's non-linearity boosts the power harvesting performance, HPA's non-linearity degrades the harvested power. Hence, the optimal waveform shifts from multi-carrier that exploits EH's non-linearity to single-carrier that reduces HPA's detrimental non-linear distortion as the operational regime of WPT becomes more sensitive to HPA's non-linearity and less sensitive to EH's non-linearity (and inversely). Simultaneously, operating towards HPA's non-linear regime by increasing the input signal power benefits the harvested power since HPA's DC power supply is better exploited, whereas the end-to-end power transfer efficiency (PTE) might decrease because of the increasing non-linear degradation. Throughout the simulations, the proposed waveforms show significant gain over those not accounting for HPA's non-linearity, especially in frequency-flat channels. We also compare the two proposed waveforms and show that the severity of HPA's non-linearity dictates which of the two proposed waveforms is more beneficial.