Low-Complexity Beamforming Design for IRS-Aided NOMA Communication System with Imperfect CSI

TL;DR

This paper proposes a low-complexity, robust beamforming design for IRS-assisted NOMA systems with imperfect CSI, achieving near-optimal sum-rate performance and outperforming OMA under channel uncertainty.

Contribution

It introduces a novel iterative PDD-based algorithm for joint beamforming and passive reflection optimization with closed-form solutions, and a trellis-based method for discrete phase shift selection.

Findings

Algorithms achieve performance close to perfect CSI upper bound.

Proposed methods have lower computational complexity than existing schemes.

NOMA outperforms OMA in sum-rate under channel uncertainty.

Abstract

Intelligent reflecting surface (IRS) as a promising technology rendering high throughput in future communication systems is compatible with various communication techniques such as non-orthogonal multiple-access (NOMA). In this paper, the downlink transmission of IRS-assisted NOMA communication is considered while undergoing imperfect channel state information (CSI). Consequently, a robust IRS-aided NOMA design is proposed by solving the sum-rate maximization problem to jointly find the optimal beamforming vectors for the access point and the passive reflection matrix for the IRS, using the penalty dual decomposition (PDD) scheme. This problem can be solved through an iterative algorithm, with closed-form solutions in each step, and it is shown to have very close performance to its upper bound obtained from perfect CSI scenario. We also present a trellis-based method for optimal discrete phase shift selection of IRS which is shown to outperform the conventional quantization method. Our results show that the proposed algorithms, for both continuous and discrete IRS, have very low computational complexity compared to other schemes in the literature. Furthermore, we conduct a performance comparison from achievable sum-rate standpoint between IRS-aided NOMA and IRS-aided orthogonal multiple access (OMA), which demonstrates superiority of NOMA compared to OMA in case of a tolerated channel uncertainty.