STAR-IOS Assisted NOMA Networks With EMI: Outage Analysis and Optimization

Integrating simultaneous reflecting and transmitting intelligent omini-surfaces (STAR-IOS) with non-orthogonal multiple access (NOMA) brings necessary spatial 360$^{\circ }$ coverage and high spectral efficiency for wireless communication networks. However, electromagnetic interference (EMI) inevitably exists in such networks, and its impact on system performance is often overlooked. In this paper, we investigate a downlink STAR-IOS-assisted NOMA network with EMI, and derive closed-form expressions for the outage probability of paired NOMA devices based on three STAR-IOS protocols, namely, the energy splitting protocol, the time switching protocol, and the mode switching protocol. Moreover, to further enhance performance, we employ a gradient projection method to mitigate the impact of EMI. The numerical results show that the EMI negatively impacts the outage performance of devices, especially for the near device in the NOMA pair. In addition, the gradient projection method improves outage performance by adjusting the phase of STAR-IOS based on EMI statistics.