Joint Design of Transmit Waveform and Reflection Phase for Intelligent Reflecting Surface Aided Wireless Power Transfer

Abstract

In this paper, we consider an intelligent reflecting surface (IRS)-aided wireless power transfer (WPT) system in multipath channel environments. The IRS can configure a favorable wireless propagation environment for the WPT by shifting the phases of the incident signals using passive reflecting elements. To improve energy transfer performance using the IRS, a joint design of the transmitter and the IRS is crucial. In this paper, we maximize harvested energy at an energy receiver with a non-linear energy harvester (EH) by jointly optimizing the transmit waveform and the IRS reflection coefficients. We first formulate an optimization problem for the system as non-convex due to the coupling of the optimization variables. To handle the non-convexity of the problem, we adopt an assumption based on the non-linear energy conversion characteristic of the EH and propose the suboptimal solution. As a result, a time-reversal (TR) waveform and reflection coefficients obtained by singular value decomposition (SVD) are derived as the solution. Furthermore, a performance analysis and simulation results are provided to verify the effectiveness of the proposed system showing considerable enhancement on harvested energy over the non IRS-aided system.