Outage Analysis of Uplink IRS-Assisted NOMA under Elements Splitting

TL;DR

This paper analyzes the outage performance of IRS-assisted NOMA uplink systems with elements split between two users, providing insights into optimal element configuration based on pathloss differences.

Contribution

It introduces a tractable outage probability analysis for IRS-assisted NOMA with element splitting and proposes a robust element split selection strategy.

Findings

Optimal split depends on pathloss differences between UEs.

Most IRS elements should boost the stronger UE for small pathloss differences.

Boosting the weaker UE is more beneficial for large pathloss differences.

Abstract

In this paper, we investigate the outage performance of an intelligent reflecting surface (IRS)-assisted non-orthogonal multiple access (NOMA) uplink, in which a group of the surface reflecting elements are configured to boost the signal of one of the user equipments (UEs), while the remaining elements are used to boost the other UE. By approximating the received powers as Gamma random variables, tractable expressions for the outage probability under NOMA interference cancellation are obtained. We evaluate the outage over different splits of the elements and varying pathloss differences between the two UEs. The analysis shows that for small pathloss differences, the split should be chosen such that most of the IRS elements are configured to boost the stronger UE, while for large pathloss differences, it is more beneficial to boost the weaker UE. Finally, we investigate a robust selection of the elements' split under the criterion of minimizing the maximum outage between the two UEs.