Research On 802.11-based Broadcast Protocols In Vehicular Ad Hoc Network

There are kinds of applications in VANET (Vehicular Ad Hoc Networks) which attracts more attentions. Broadcast is the main way to implement these applications. In VANET, due to the fast movement of the vehicle, the topology of the network changes rapidly that makes the traditional broadcast protocol low efficiency. What's more communication between vehicles is prevented by the buildings beside the roads in the city. So it needs to design a broadcast protocol adapted to the VANET.This paper proposes two kinds of 802.11-based broadcast protocols in VANET, using omni-antenna and directional-antenna respectively. Using omni-antenna, the far receiving node is responsible to forward the message. Besides, a fixed repeater at the intersection forwards the message. While using directional-antenna, the broadcast protocol adopts three different forwarding strategies; the basic principle is the node only forwards the message towards the direction where the message doesn't arrive. In addition, we also introduce several optimal methods such as making use of local nodes' density to evaluate the delay of forwarding, replacing the GPS device with the signal's strength and dividing the priority of the message.To improve the reality of mobility model, this paper generates a real mobility model SUVnet using more than 4000 taxis' GPS data in the processing of map matching, route determining, and interpolation. Besides, we verify the accuracy of SUVnet through the field test. Moreover a discrete-event based wireless simulator JWS is developed. Combining SUVnet and JWS, we compare the performance of the proposed protocols. The results show that the EDB performs better than others on the delivery ratio, end-to-end delay, and collisions, so it adapts to VANET best.