The Research Of A Fast Handoff Scheme Based On The VANET In MAC Layer

In recent years,with the rapid development of internet technology,intelligent transportation system has become a hot topic of research,bringing the hope for solving the increasingly serious traffic congestion,traffic safety and a series of problem.Vehicular Ad Hoc Network(VANET)is an important application of mobile ad hoc network(MANET)in ITS.The WAVE(Wireless Access Vehicular Environment)protocol stack that issued by American Society of Electrical and Electronics Engineers is dedicated to vehicular network communication and will gradually become the international standard of ITS communication technology.However,the rapid movement of the vehicle and the complex road environment result in the variation of network topology in VANET more fast than MANET.The handoff between OBU(On Board Unit)and RSU(Road-Side Unit)is more frequent and the requirement for handoff delay is relatively high in VANET.The traditional IEEE802.11 protocol-based handoff scheme is not applicable for communication in VANET.This thesis proposes an improved fast handoff scheme based on the WAVE protocol stack,which makes full use of the driving characteristics of the vehicle and combines the design advantages of the WAVE protocol stack.The main work of this thesis is as follows:(1)In-depth studying the architecture of the WAVE protocol stack,especially the IEEE802.11 p protocol,the 1609.4 protocol and the 1609.3 protocol are analyzed in depth,and analyzing the handoff mechanism of the IEEE802.11 protocol and illustrating some new features of IEEE802.11 p protocol in handoff mechanism.(2)Extensively studing the improved fast handoff scheme based on the traditional IEEE802.11 protocol,on this basis and based on the characteristics of VANET,this thesis proposes a improved fast handoff scheme based on the WAVE protocol stack,which fully combines the position,speed and received signal strength of the vehicle.This handoff scheme focuses on the improvement of the MAC layer of the WAVE protocol stack and the choice of the best handoff position.(3)The FCM(Fuzzy c-means)algorithm for the optimal handoff position selection in the fast handoff scheme proposed in this thesis is simulated and compared with the K-means algorithm.Finally,the process of the whole handoff scheme is simulated under the condition of highway scene and urban scene respectively,and compared with the handoff scheme based on the neighbor graph method and the handoff scheme based on the WAVE protocol stack.The comparison and analysis of the simulation results show that the fast handoff scheme proposed in this thesis has a great improvement in reducing the handoff delay,reducing the packet loss rate and preventing the ping-pong effect.