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Abstract

Reconfigurable Intelligent Surface (RIS) has been recognized as the core technology for 6G. However, transmission signals may be blocked by obstacles due to mobility and complex transmission in vehicular scenario. In order to solve the above issue, this paper researches the RIS assisted dual function radar communication system (DFRC) in the Internet of Vehicles (IoV), and proposes an alternating optimization algorithm, named joint guaranteed radar communication (JGRC) algorithm, with sensed power and semidefinite relaxation to maximize the spectral efficiency of the communication vehicle while simultaneously ensuring the radar sensing performance of the target vehicle. Specifically, the proposed JGRC algorithm can be divided into two stages. Stage one, active beamforming of Base Station (BS) transmission is optimized with the power constraint of the sensed target vehicle. Stage two, the optimized active beamforming is applied, and the phase shift matrix is optimized. Then, RIS phase shift optimization problem is transformed into Quadratically Constrained Quadratic Programming (QCQP), and rank-1 non-convex constraint is relaxed by semidefinite relaxation, which can be transformed into a standard semidefinite programming solved by Matlab toolbox. Simulation results demonstrate that compared to the RIS element random reflection, the proposed algorithm achieves higher spectral efficiency by 9.5%.