IRS-Assisted Secure OFDMA With Untrusted Users

Abstract

Intelligent reflecting surfaces (IRSs) have recently started gaining research attention for improving the performance of next generation wireless communication systems. Considering the potential of physical layer security, in providing secure communication, this paper investigates an IRS assisted Orthogonal Frequency-Division Multiple Access (OFDMA) based downlink secure communication system in the presence of untrusted users. More specifically, we consider the joint optimization of subcarrier allocation, power allocation, and IRS reflection coefficients, and present a low complexity solution. After obtaining optimal subcarrier allocation, the problem is decoupled into two individual optimization problems namely, power allocation for a known reflection coefficients, and reflection coefficients optimization for a known power allocation, which are solved in closed form. The joint optimization is achieved through alternating optimization using these individual optimizations. The proposed scheme is shown to outperform the benchmarks through extensive numerical results, which further highlight design insights for IRS-assisted OFDMA based secure communication system. © 2022 IEEE.