Impact of Orthogonal Multiple Access and Non Orthogonal Multiple Access for the Performance of IRS-Aided Downlink Systems

The rapid expansion of communicating devices has brought with a need of higher capacity, low latency wireless communication systems. Which has led to interest in advanced multiple access techniques such as NOMA. The NOMA technique allows multiple users to transmit over the same channel using power-domain multiplexing and SIC approach. This allows for an increase inconnectivity and spectral efficiency over traditional OMA. However, NOMA suffers from inter-user interference and a decline in performance in multipath environments. In order to eliminate such constraints, IRS emerged as a potential solution. This paper examines, how the IRS can be applied in conjunction with NOMA. Specifically, what effect does it have on user data rates. The Simulation is done for the cases of direct NOMA, IRS-Aided NOMA and OMA with varying number of Reflecting Elements. The results show improvements in data rates, in comparison with conventional NOMA and OMA schemes. Simulation also shows improvement in data rates with increase in Reflecting Elements. Moreover, this paper outlines some crucial research gaps and future directions.

I. Introduction

Demand for high-capacity, low-latency communication in today’s wireless networks has seen much interest in advanced multiple-access techniques. NOMA is most important technique of upcoming networks for its feature of facilitating many users simultaneously over the same frequency channel. NOMA uses PD multiplexing and successive interference cancellation (SIC). The use of NOMA increases data rates in comparison with the classical scheme OMA. Particularly, this feature becomes paramount when there is high population of users and high diversity on the quality of service (QoS) [1], [2], [3]. While NOMA can still be effective in increasing resource’s efficiency, its performance can still be much affected by inter-user interference as well as channel conditions, especially in multipath environments [4]. To mitigate some of these issues, the recent advancement of another technology known as Intelligent Reflecting Surface (IRS) appears to be a game changer, as it can modify the wireless landscape. Adjusting the phase shifts of signals that have been reflected by IRS, NOMA can improve the signal quality, system energy consumption, and interference [5], [6], [7]. IRS uses passive elements, and does not require massive power, has bright future in complementing communication systems like NOMA [8], [9].