Non-Orthogonal Multiple Access (NOMA) With Multiple Intelligent Reflecting Surfaces

TL;DR

This paper investigates the use of multiple intelligent reflecting surfaces with discrete phase shifts to enhance NOMA network performance, deriving outage probability bounds and demonstrating near-optimal performance with low-resolution phase shifts.

Contribution

It introduces a novel analysis of NOMA networks assisted by multiple IRSs with discrete phase shifts, including outage performance and diversity order, showing minimal performance degradation with low-resolution phase shifts.

Findings

Discrete phase shifts do not reduce diversity order.

3-bit phase resolution achieves near-optimal outage performance.

IRSs outperform full-duplex relays in simulations.

Abstract

In this paper, non-orthogonal multiple access (NOMA) networks assisted by multiple intelligent reflecting surfaces (IRSs) with discrete phase shifts are investigated, in which each user device (UD) is served by an IRS to improve the quality of the received signal. Two scenarios are considered according to whether there is a direct link between the base station (BS) and each UD, and the outage performance is analyzed for each of them. Specifically, the asymptotic expressions for the upper and lower bounds of the outage probability in the high signal-to-noise ratio (SNR) regime are derived. Following that, the diversity order is obtained. It is shown that the use of discrete phase shifts does not degrade diversity order. More importantly, simulation results reveal that a 3-bit resolution for discrete phase shifts is sufficient to achieve near-optimal outage performance. Simulation results also imply the superiority of IRSs over full-duplex decode-and-forward relays.