Performance Comparison of RIS - Aided Uplink NOMA and OMA Multiuser Networks

The combination of reconfigurable intelligent surface (RIS) and multiple access technologies is an efficient solution to improve spectrum efficiency and expand network coverage. However, due to the ability of RIS in reconfiguring the channel environment, it is unknown which access technology can obtain a superior transmission effect in the RIS-assisted wireless communication network. In this paper, a theoretical performance comparison between non-orthogonal multiple access (NOMA) and orthogonal multiple access technologies (OMA) including frequency division multiple access (FDMA) and time division multiple access (TDMA) in RIS-assisted Uplink communication is pursued, for which the theoretical maximum sum rate of all users under different multiple access are analyzed and compared, using the method of subtraction. Moreover, we propose reasonable methods to optimize discrete-phased RIS under three access technologies. The results show that in the RIS-assisted communication system the NOMA access scheme has no inherent superiority over the OMA access scheme, and a significant advantage can be obtained when the number of users and the channel difference are large enough.

I. Introduction

In wireless communication, by densely deploying the IRS and skillfully coordinating its reflections, it can enhance the coverage of signals and improve the spectral efficiency (SE) and energy efficiency (EE) of wireless communication networks [2], which has attracted widespread attention in the development of future 6G networks.