Secure wireless communications for STAR‐RIS‐assisted millimetre‐wave NOMA uplink networks

This paper explores the potential application of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) in improving physical layer security (PLS) millimetre wave (mmWave) non-orthogonal multiple access (NOMA) uplink communications. In particular, legitimate users on both sides STAR-RIS send confidential information to base station (BS) while keeping it secret from eavesdroppers near BS by exploiting proactively regulate electromagnetic propagation environment. By jointly designing transmit power, active beamforming at BS, reflecting/transmitting coefficients STAR-RIS, authors' goal is maximize minimum secrecy capacity subject successive interference cancellation decoding order constraints. Due non-convexity formulated problem, an efficient algorithm proposed capitalizing alternating optimization, a penalty-based approach, convex approximation, semi-definite relaxation. Firstly, two-layer iterative based penalty for joint optimization sub-problem proposed. Then, non-convex problem transformed into positive programming power sub-problem. Numerical simulation results reveal that STAR-RIS-aided system has more tremendous advantages effectiveness PLS mmWave NOMA communication compared with benchmark schemes.