Hybrid-RIS-Aided Vehicular Wireless Sensing and Communication: Transmission Protocol and Performance Enhancement

The reconfigurable intelligent surface (RIS) enhances vehicle-to-everything (V2X) integrated sensing and communication (ISAC) by enabling more precise sensing and efficient communication. However, achieving low complexity and low overhead V2X ISAC remains challenging in time-varying channel conditions. To overcome this, we propose a distributed hybrid RIS (HRIS)-aided V2X ISAC system featuring a pre-designed transmission protocol that improves ISAC performance while minimizing channel estimation overhead and algorithmic complexity. In this system, the first sub-block of each coherence time block encompasses location sensing, beamforming and ISAC, along with a location prediction phase. At the same time, subsequent sub-blocks focus on the latter two phases. During the initial phase, two-dimensional multiple signal classification-based adaptive location sensing is performed by sensor elements in the distributed HRISs to obtain location information without requiring channel estimation. This information is then used to design optimal beams for enhanced ISAC performance in the subsequent phase. Finally, an extended Kalman filter-based location prediction method generates optimal beams for the following sub-blocks. Simulation results confirm the effectiveness of the proposed scheme, demonstrating its superiority over existing methods in terms of ISAC performance, computational complexity, overhead, and angle estimation accuracy.