QoS Optimization Of Dedicated Short-Range Communications(DSRC) Protocol In Vehicle Ad-hoc Network

In order to effectively solve the problem of traffic congestion, traffic safety and other issues, the technologies from ITS(Intelligent Transport System) and Io V(Internet of Vehicle) have been vigorously promoted around the world. In this background, academic world in this field pay great attention on VANET(vehicle adhoc network), which is a part of the Io V. VANET protocol do not have any widely favorable standard in this stage. At present, DSRC is the protocol with most influence(dedicated short range communications). With the help of DSRC protocol, data exchange between vehicles and roadside infrastructures are achieved, and then the safe driving and intelligent traffic management will come true later.DSRC protocol uses the IEEE 802.11 p protocol in MAC layer. To solve the QoS problem of VANET application, the protocol uses the enhanced distributed channel mechanism(EDCA). The emergency data are set with high priority so that the dataset can be accessed within wireless medium and be transmitted above all. The other dataset, which is not sensitive to the delay, is set with a lower priority. In other word, dataset with lower priority will be transmitted until the one with high priority is completely transmitted. DSRC protocol can generally cover the requirements of the QoS of VANET. However, when the vehicle network density and network traffic become overload, the end to end delay, channel access delay and network throughput will turn into serious problems obviously. Therefore, we need to optimize DSRC protocol and guarantee acceptable QoS performance of VANET in the context of high vehicle density and network traffic.In this thesis, the author proposes a scheme to optimize DSRC protocol in order to guarantee the QoS performance of VANET. This scheme is mainly consisted of multistage classifier, multi-level scheduler, traffic shaping and adaptive EDCA parameter adjustment. With the classifier, the author divides more fine in the AC queues, combining with the multilevel scheduler and reduce end to end delay. Traffic shaping, which is based on the source address of IP packets, classifies non-security service messages and ensures fairness when passing channel. Traffic shaping algorithm is modified and optimised based on WF2 Q algorithm. Adaptive EDCA parameter adjustment referred from the packet collision rate is determined by loading to adjust the contention window.