Outage Performance of Downlink IRS-Assisted NOMA Systems

Abstract

In this paper, a downlink non-orthogonal multiple access (NOMA) system is studied, in which an intelligent reflecting surface (IRS) is deployed to enhance the coverage by assisting a cell-edge user device (UD) to communicate with the base station (BS). To characterize system performance, new channel statistics for the BS-IRS-UD link with Nakagami-m fading are investigated. Based on the new channel statistics, the closed-form expression for the outage probability is derived. To gain further insight into the problem, the diversity order is obtained according to the asymptotic approximation in the high signal-to-noise ratio (SNR) regime. It is demonstrated that the diversity order is affected by the number of IRS elements and Nakagami fading parameters. Simulation results validate our analysis and reveal the superiority of the IRS over the full-duplex decode-and-forward relay in the high-SNR regime.