An Opportunistic Forwarding Protocol with Relay Acknowledgement for Vehicular Ad-hoc Networks

Robust and efficient data delivery in vehicular ad hoc networks (VANETs) with a high mobility is a challenging issue due to unstable wireless links and dynamic topology changes. In this vehicular environment, the exchanges of topology information and discoveries of routing paths on an end-to-end basis are not desired, because the network topology changes rapidly and the information is out-of-date in short. In this paper, we propose a contention based forwarding mechanism, which locally exploits geographic location information to achieve robustness of data delivery for vehicular communications. A node that is closer to the destination node has a higher priority in competing for the wireless channel, and forwards packets as a relay node earlier than other adjacent nodes. When a packet is forwarded by a relay node, its preceding node informs adjacent nodes that it has been already relayed to prevent the duplications of packet delivery. Through ns-2 simulations, we show that the proposed scheme can significantly improve the network performance in terms of the packet delivery ratio and the end-to-end delay in various synthetic and trace-based realistic VANET scenarios with a wide range of vehicle speed and density.