STAR-RIS Assisted NOMA with Receive Spatial Modulation

In this work, we have investigated the bit error rate (BER) performance of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted non-orthogonal multiple access (NOMA) with index modulation (IM) over the Rician fading channel in the downlink. Compared with the conventional reflecting-only RIS, STAR-RIS has been introduced to serve many users simultaneously. In the proposed system, STAR-RIS utilizes the mode-switching (MS) protocol to serve two non-orthogonal users on either side of the metasurface. To maintain fairness among NOMA users, equal RIS elements allocation has been adopted. Furthermore, to improve the spectral efficiency and reliability of the users, the concept of IM has been introduced with STAR-RIS. Monte Carlo simulations have been performed, which show that BER performance improves as we increase the number of RIS elements. Meanwhile, the optimal power allocation, the effect of an increase in receive antenna, and the effect of an increase in the Rician factor have also been studied.