Secure Performance of RIS-Aided NOMA in Cognitive V2X Networks With Imperfect CSI over Double Rayleigh Fading

Cognitive non-orthogonal multiple access (NOMA) and reconfigurable intelligent surface (RIS) have been envisioned as two promising technologies for vehicle to everything (V2X) networks. This paper considers an RIS-aided V2X network with cognitive NOMA in the presence of a malicious eavesdropper while taking into account the imperfect channel information (ipCSI) due to the mobility of the vehicles. The new approximate and asymptotic outage probabilities (OP) and intercept probabilities (IP) expressions of the considered system are derived over double Rayleigh fading channels. The asymptotic OP and IP expressions are subsequently utilized to quantify the diversity orders achieved by vehicular users. Numerical and Monte Carlo simulation results are presented to corroborate the analysis. The simulation results show that ipCSI has significant but different impact on the OP and IP performance to the far user and the near user, which are also different under different number of reflecting units. We show that there is a trade-off between security and reliability, which can be improved by increasing the number of reflecting units of RIS. Specifically, the valuable finding is that the OP performance of the near user will not always be better than that of far user due to the impact of ipCSI, which shows that the power allocation needs to be reconsidered in order to serve the near user more better in the actual scenarios.