A Cross-Layer Congestion Avoidance Routing Scheme in Vehicular Ad Hoc Networks

We propose a cross-layer congestion avoid-ance routing (CCAR) scheme for VANETs based on IEEE 802.11p/WAVE (wireless access in vehicular environment) protocol. Due to highly dynamic network topology, the forwarders are selected one by one. The CCAR scheme first adjust the number of candidates adaptively so that senders have high probability to find a candidate as the forwarder. Then it dynamically adjusts the selection probability of each service channel (SCH) based on traffic load of SCHs to make channel load balanced. Finally, the CCAR scheme takes the number of co-channel senders, the loads of each possible forwarder, and the vehicular moving direction into account to determine the most appropriate route for senders. Simulation results show that the proposed CCAR scheme achieves lower packet delay (higher system uplink through-put) than the conventional GyTAR and AODV schemes by amounts of 95% and 95.7%, (8.4% and 19.2%,) respectively, when the number of vehicles is 150.