STAR-RIS-Enabled NOMA with Signal Constellation Adjustment for 6G LEO Satellite Networks

In this paper, we investigate a simultaneous transmitting and reflecting-reconfigurable intelligent surface-enabled non–orthogonal multiple access (STAR-RIS-NOMA) technique for 6G low earth orbit (LEO) satellite networks. In particular, we focus on the problem of similar channel gains of user equipment (UE) when a direct path between LEO and UEs cannot be formed due to the surrounding terrain and buildings. In this paper, we propose a novel signal constellation scaling and rotation for the STAR-RIS-NOMA technique in LEO satellite networks. In addition, we consider a joint maximum likelihood (JML) detector that can achieve optimal performance in terms of bit-error-rates (BER) rather than a sub-optimal successive interference cancellation (SIC) detector. Through extensive simulations, we show that the proposed technique significantly improves the BER performance of LEO satellite networks.