Performance of STAR-RIS assisted NOMA networks in Nakagami-m fading channels

The concept of simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) has been proposed to overcome the limitation of conventional reflecting-only RISs, which only allow users to be located on the same side of the RIS. This novel STAR-RIS technology can serve all users on both sides of the space surrounding the RIS by reflecting and transmitting the incident wireless signal. Future wireless networks can improve their energy and spectrum efficiencies by combining STAR-RISs with the promising multiple access candidate non-orthogonal multiple access (NOMA). This paper analyzes the performance of STAR-RISs-assisted NOMA networks in terms of outage probability (OP) and bit error rate (BER). First, the closed-form OP expression is derived for each NOMA user in Nakagami- fading channels. Next, the asymptotic OP expression in a high signal-to-noise ratio (SNR) region is obtained to express the behavior of the network with diversity and array gains. Then, the BER expression is also derived in closed form. The accuracy of the theoretical analysis is finally verified through Monte Carlo simulation.