Covert Transmission and Secrecy Analysis of RS-RIS-NOMA-Aided 6G Wireless Communication Systems

In this work, we investigate a novel covert communication system, where the legitimate transmitter attempts to communicate with a covert user in the presence of a warden and the public user covertly. Specifically, the legitimate transmitter employs non-orthogonal multiple access (NOMA) and rate-splitting (RS) to communicate with users aided by a reconfigurable intelligent surface (RIS). In this context, we investigate key performance indicators of covert communication, namely the detection error probability and the covert communication rate. Meanwhile, we consider the physical layer security (PLS) of the proposed system in the presence of an eavesdropper, and derive the approximate secrecy outage probability (SOP) expression. Also, an asymptotic analysis of the SOP is also carried out. Various numerical results are presented that demonstrate the usefulness of the proposed analysis, which are complemented by simulated ones, verifying the correctness of the theoretical framework. From these results, it becomes evident that the use of RS, NOMA, and RIS can improve the performance of covert communication. Finally, it is also depicted that under the condition of high signal-to-noise ratio, the SOP of the system tends to be a constant value.