Performance Evaluation of IRS Assisted OMA and NOMA Communication Systems with Coherent Phase Shift

Non-orthogonal multiple access (NOMA) is being recognized as a promising solution for the upcoming generation of wireless communication systems, attracting growing interest. Integrating NOMA with intelligent reflecting surfaces (IRS) offers a strategic approach, harnessing the distinct advantages of both technologies to enhance the overall performance and reliability of communication systems. This paper investigates the integration of an IRS in a downlink scenario with two users, focusing on evaluating outage probability (OP) in orthogonal multiple access (OMA) and NOMA systems. The study thoroughly examines the impact of coherent phase shift design on the performance and efficiency of IRS-assisted NOMA and OMA systems. It emphasizes that the precise alignment of reflected signals can boost system capacity, minimize OP, and enhance signal quality, providing key insights into the advantages of optimized phase shift control. Closed-form expressions for the OP have been obtained considering coherent-phase-shift design. The study investigates IRS-supported OMA and NOMA systems, comparing their performance under optimal and random phase shift designs with a focus on OP and sum-rate (SR). The simulation results demonstrate the superior performance of NOMA-IRS, emphasizing the significant impact of coherent-phase-shift optimization on enhancing overall system efficiency.