The Research Of Handoff Algorithms On MAC Layer Of Vehicular Heterogeneous Networks

Currently vehicular network is a good solution of Intelligent Transportation System. It can make the information exchanging between vehicles, road, infrastructure and smart mobile terminal. So it can reduce the ratio of traffic accident effectively, increase the road passing efficiency. With the development of networks, people hope that they can connect to the Internet when driving. But Traditional vehicular networks based on the ad-hoc network cannot provide a variety of service with different Qos, so the vehicular heterogeneous networks are the future of VANET. When a car moves, it may pass through the coverage of different networks and there will be a handoff of network. But handoff will lead to transmission delay and packet loss of communication. So how to realize the handoff of vehicular heterogeneous networks, reduce the times of handoff, handoff delay, ensure the quality of communication and improve the performance of the system is very important.This paper is researching on the handoff technology on MAC layer of vehicular heterogeneous networks based on VANET and 3G. Mainly about the vertical handoff algorithms on MAC layer of vehicular heterogeneous networks and the horizontal handoff on MAC layer of vehicle ad-hoc network based on the protocol of WAVE. At last, I designed a horizontal handoff scheme. The man jobs in this paper are showed in follow:Firstly, I introduced the architecture of WAVE and the protocol stack. After that I compared the protocol of 802.11 a and 802.11 p. Then I gave an overview of the physical parameters and the new features of 802.11 p.Secondly, as wireless signal fades fast in the traffic environment, I chose the RSSI as the index of handoff and carried on a MATLAB simulation of the vertical handoff algorithm based on relative RSSI and the algorithm based on relative RSSI with a threshold. The results indicate that the algorithm based on relative RSSI will lead to the handover back and forth. The algorithm with a threshold can reduce the number of handoff efficiently in the traffic environment.Thirdly, this paper adopted the handoff decision algorithm based on the relative signal strength RSSI with a threshold and designed a handoff scheme on MAC layer of vehicle ad-hoc network based on WAVE protocol. Referring to the open source code of Wireless Tools provided by Linux, I completed the horizontal handoff program.Finally I took a test of the handoff scheme in the real road traffic scenarios through the 802.11 p on-board communication platform designed by our laboratory. And the success rate of the handoff is 70%, the average delay is 465 ms and the number of average packet loss is 160. The results demonstrate that the horizontal handoff scheme on MAC layer of vehicular ad-hoc network based on the WAVE protocol works well.