A High-Capacity MAC Protocol for UAV-Enhanced RIS-Assisted V2X Architecture in 3-D IoT Traffic

With the development of Internet of Things (IoT) technology and its wide application in urban traffic, the next-generation Vehicle-to-Everything (V2X) communication network should support high-capacity, ultrareliable, and low-latency massive information exchange to provide unprecedentedly diverse user experiences. The development of the sixth-generation (6G) mobile communication technology will pave the way for realizing this vision. Reconfigurable intelligent surfaces (RISs), a critical 6G technology, is expected to make a big difference in V2X communications when used in conjunction with unmanned aerial vehicles (UAVs), allowing for extremely increased communication capacity and reduced latency. We propose an UAV-enhanced RIS-assisted V2X communication architecture (UR-V2X) suitable for urban 3-D IoT traffic and design an adapted MAC protocol UR-V2X MAC protocol (UR-V2X-MAC) to accomplish communication resource allocation and scheduling. The UAVs are used as access points and resource allocation centers, while the RISs are used as passive relays to assist V2X communication in proposed architecture. To improve the performance of UR-V2X-MAC, we use a distributed optimization algorithm in the message report phase of the protocol to maximize the system capacity by allocating the transmit power and alternately optimizing the RIS phase shift matrix. We analyze the delay and system capacity characteristics under different parameter settings through theoretical derivation and protocol performance simulation. Analysis and simulation results are presented to demonstrate that UR-V2X-MAC achieves a reduction in communication delay and a significant increase in system capacity through detailed design and alternate optimization compared to the existing V2X MAC protocol and no-RIS case.