RIS-Aided Uplink NOMA in the Presence of CCI

This paper investigates the co-channel interference (CCI) effects on the uplink non-orthogonal multiple access (NOMA) users. The investigation considers that two NOMA users communicate with the base station (BS). The NOMA user close to the BS has a line of sight with the BS, while the far user only communicates with the BS via passive and absorptive reconfigurable intelligent surface (RIS). The investigation also considers that BS is under the effect of the randomly deployed CCI and interfere the received signal from the NOMA users. Performance of the aforementioned system is measured by means of the outage probability performance metric. Analytical derivations are verified by means of the Monte Carlo-based computer simulations. The results indicate that increasing the number of RIS elements degrades the outage performance for the near user but enhances it for the far user. Furthermore, the findings reveal that CCI causes minor loss in coding gain for NOMA users when the RIS has a small number of elements. However, this negative impact of CCI diminishes as the number of RIS elements increases.