Capacity Analysis of Reconfigurable Intelligent Surface-assisted in Overlay/Underlay Vehicular Networks

Reconfigurable Intelligent Surface (RIS), as a cost-effective and potential technology, has been visualized to improve transmission capacity in wireless communication. In this paper, we analyze the transmission capacity of RIS-assisted vehicular networks in both overlay and underlay modes. Dedicated spectrum resources are allocated to device-to-device involved vehicle-to-vehicle (D2D-V2V) user communication in the overlay mode, whereas D2D-V2V users reuse the same spectrum resources with cellular-vehicle users (C-VUs) in the underlay mode. Specifically, we build a three-dimensional (3D) system model which includes one RIS on building surfaces and D2D-V2V user pairs on the ground. Based on stochastic geometry theory, C-VUs, D2D-V2V users, and RIS are modeled as Poisson Point Process (PPP) with different densities in vehicular networks. To obtain the transmission capacity, the RIS existence probability and the successful transmission probability of each D2D-V2V user communication are derived. Therefore, the transmission capacities of D2D-V2V communication assisted by RIS in both overlay and underlay modes are deduced. Simulation results verify the benefits of introducing RIS for enhancing the transmission capacity, as well as the impacts of D2D-V2V transmission capacity, including RIS density, user density, transmission power, and the number of RIS reflecting elements, are given in the D2D-V2V communication systems.