Cross-Layer Design for Packet Routing in Vehicular Ad Hoc Networks

In this paper we present a cross-layer design between packet routing and medium access control (MAC) for a vehicular ad hoc network (VANET) in order to guarantee special quality of service (QoS) requirements. As precondition we consider vehicles equipped with driving-assistant-systems that exchange environmental object information through the VANET. The object information is collected by onboard sensors and gets obsolete after some time because of the fast changing surroundings. Therefore it should be distributed to other vehicles with a lower delay than the data gets outdated. This introduces a special low delay QoS requirement the VANET has to provide to the application. As a solution we propose a cross-layered combination of MAC and routing mechanisms. In detail we use advantages of a cluster-based forwarding mechanism and adapt them to the MAC. This helps to decrease collisions and to control packet forwarding. On the other hand the MAC protocol provides cluster and neighbor node information to the routing algorithm. We show that this QoS mechanism satisfies the required packet delay for a desired information propagation area. Finally VANET simulations of certain traffic scenarios validate the proposed cross-layer protocol and show the performance of this mechanism.