Waveform Design for Wireless Power Transfer with Limited Feedback

TL;DR

This paper introduces limited feedback strategies for waveform design in wireless power transfer, improving energy harvesting efficiency over frequency-selective channels by optimizing codebooks with novel algorithms.

Contribution

It proposes two limited feedback waveform strategies and develops algorithms for codebook optimization, enhancing WPT performance without perfect channel knowledge.

Findings

Limited feedback strategies outperform baselines in harvested energy.

Proposed algorithms effectively optimize codebooks in space and frequency.

Strategies adapt waveform precoders based on minimal feedback, improving efficiency.

Abstract

Waveform design is a key technique to jointly exploit a beamforming gain, the channel frequency-selectivity and the rectifier nonlinearity, so as to enhance the end-to-end power transfer efficiency of Wireless Power Transfer (WPT). Those waveforms have been designed assuming perfect channel state information at the transmitter. This paper proposes two waveform strategies relying on limited feedback for multi-antenna multi-sine WPT over frequency-selective channels. In the waveform selection strategy, the Energy Transmitter (ET) transmits over multiple timeslots with every time a different waveform precoder within a codebook, and the Energy Receiver (ER) reports the index of the precoder in the codebook that leads to the largest harvested energy. In the waveform refinement strategy, the ET sequentially transmits two waveforms in each stage, and the ER reports one feedback bit indicating an increase/decrease in the harvested energy during this stage. Based on multiple one-bit feedback, the ET successively refines waveform precoders in a tree-structured codebook over multiple stages. By employing the framework of the generalized Lloyd's algorithm, novel algorithms are proposed for both strategies to optimize the codebooks in both space and frequency domains. The proposed limited feedback-based waveform strategies are shown to outperform a set of baselines, achieving higher harvested energy.