Cooperative Beacon Rate Adaptation for Vehicular Ad-hoc Network

Sammanfattning: In Vehicular Ad-hoc Networks (VANETs), the vehicles need to periodically exchange current mobility status information with neighboring vehicles through beacon messages. The mobility status includes, among others, speed, position, and direction of the vehicle, which help vehicles to keep awareness of neighboring vehicles for better traffic efficiency and safety. However, high rate of secured beacons results in higher communication overhead, which leads to channel congestion and packet loss in scenarios with large number of vehicles. Adaptive beacon rates (thus lower beacon rate when needed, e.g., in dense settings) can help relieving the communication overhead in the network. However, an optimized beacon rate without the consideration of possible packet loss could degrade the performance of the system. In this thesis, we propose a cooperative beacon rate adaptation scheme (CBA) for VANET. In this scheme, the vehicles adapt their beacon rate cooperatively instead of maintaining a default beacon rate of 10Hz (i.e., 10 safety beacons per second), which can reduce channel load. To be precise, the beacon rate of a vehicle increases when this vehicle detects packet loss for its beacons. When a packet is lost, the sender is notified by the scheme and broadcasts more frequently in the near future, so that the neighboring vehicles are able to maintain awareness of the vehicle mobility status. The notification is based on special acknowledgement included in beacons. We use OMNeT++, SUMO and Veins to simulate the performance of CBA in real world scenario. Using the simulation results, we show that our CBA scheme improves cooperative awareness while reducing network load.