Hybrid RF/VLC intelligent vehicular communications: a secrecy analysis

Abstract

Next generation intelligent transportation systems (ITS) are expected to use visible light communications (VLC) as a complementary technology to the existing radio frequency (RF)-based technologies in vehicle-to-everything (V2X) communication to provide secure and reliable transmission by exploiting the directivity and impermeability of light. Moreover, reconfigurable intelligent surfaces (RIS) are a promising solution to enhance the coverage and reliability of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications by modifying the phase, amplitude and polarization of incoming electromagnetic waves. Most previous works assumed double Rayleigh and Rayleigh fading channels for the RF links, with RIS-assisted setup lacking direct links between vehicles, and non-random distributions for vehicle movement in the VLC links. In this paper, we analyze the physical layer security performance of RIS-assisted hybrid RF/VLC links for both V2V and V2I scenarios. We also assume a direct line-of-sight (LoS) link between legitimate vehicles. In the existence of co-channel interference (CCI), an eavesdropper attempts to receive the information. We employ an accurate method to derive an exact expression for the cumulative distribution function (CDF) of RIS-assisted links combined with a direct link. More specifically, we derive closed-form expressions of secrecy outage probability (SOP), average secrecy capacity (ASC), probability of strictly positive secrecy capacity (PSPSC), effective secrecy throughput (EST), and intercept probability (IP). We assume double Nakagami-m fading for the V2V links, Nakagami-m channel for the V2I links, and log-Normal fading and uniform distribution for both longitude separation of Tx and Tx-Rx distance, leading to random path-loss. The correctness of the derivations is verified by using extensive Monte Carlo simulations for both V2V and V2I scenarios.