An Analysis with interplay of NOMA and RSMA for RIS-aided System

Reconfigurable intelligent surface (RIS) has emerged as a potential technology for future-generation wireless communication by enhancing its signal quality and providing broader coverage network area. In this work, we provide an analytical framework of a RIS-assisted multi-user downlink system where the base station (BS) transmits a superimposed signal to multiple users with the aid of a RIS using non-orthogonal multiple access (NOMA) and rate splitting multiple access (RSMA) transmission technique. First, we discuss the statistical characteristics and evaluate the probability density function (PDF) of the different channels involved in the transmission. We then evaluate the system performance utilizing the PDF and obtain the analytical expressions of the outage probability through the application of NOMA and RSMA transmission techniques and verify the preciseness of the derived closed-form expressions using Monte-Carlo (MC) simulations. Moreover, to gain some useful insights about the system, we also highlight the impact of transmit power availability at the BS, imperfect channel state information (CSI) on the outage probability of each user, effect of number of RIS elements on outage probability. Lastly, we demonstrate the superiority of RSMA over NOMA on the performance of the system.