Cooperative and Opportunistic Channel Access for Vehicle to Roadside (V2R) Communications

This paper focuses on vehicle to roadside (V2R) communications in vehicular networks based on the IEEE 802.11 DCF MAC protocol. In vehicular networks, roadside units (RSUs) are typically spaced apart along the road and each vehicle can be connected to an RSU only when the vehicle is within its transmission range. Due to the high relative speed between a moving vehicle and a stationary RSU, the residence time of the vehicle within the coverage of each RSU is very short. Thus it is hard for the system to reach a steady state. With multi-hop forwarding, in which a vehicle may be connected to an RSU through relaying over other vehicles, the connection time of each V2R access may be extended. But this is at the expense of introducing wireless interference among vehicles, which may dramatically degrade the system performance. To tackle these challenges, we propose a new mechanism called Proxy-based Vehicle to RSU access (PVR) for V2R communications. This protocol is designed to exploit cooperative and opportunistic forwarding between any two distant RSUs and to emulate back-to-back transmissions within the coverage of an RSU. As a result, it can shorten the access delay by taking advantage of opportunistic forwarding and mitigate the interference problem during the short residence time within the coverage of an RSU. The simulation results show that PVR achieves excellent performance and outperforms all existing solutions for V2R communications in vehicular networks.