IRS-based Secrecy Rate Analysis in Presence of an Energy Harvesting Eavesdropper

In this paper, we investigate an intelligent reflecting surface (IRS) based wireless system wherein an untrusted energy harvesting node wiretaps the legitimate signal. The achievable secrecy rate and the harvested energy are derived as functions of IRS phase coefficients. Then to maximize the secrecy rate while meeting the minimum required harvested energy, the non-convex optimization problem is analyzed. By utilizing the Charnes-Cooper transformation and semidefinite relaxation technique, the optimization problem is transformed into a convex one. Finally, the numerical results are presented to clarify the effects of size of the IRS and optimizing its phase elements on enlarging the secrecy rate-energy harvesting region.