Position Based Handoff Scheme In VANETs

To keep pace with the requirement of communication quality in vehicular environment, VANETs is attracting more and more attentions. For one of the key technologies, handoff technology, there is no suitable algorithm for VANETs, whose distinguishing feature is high speed, frequent disconnection. For other words, it is not ideal for existing handoff scheme to deploy in VANETs. Consequently, from the sight of protocol designed, this article is to study how to make full use of the character of VANETs to meet the target of smooth and seamless handoff. That is, to maximize the reduction of handoff delay, while ensuring the quality of communication.Firstly, the advantages and disadvantages of kinds of existing handoff schemes are illustrated and compared. Then the position based handoff scheme(PHS), who is suitable for VANETs, is proposed based on the handoff scheme of the mature IEEE 802.11r standard in open system with over-the-air mode. After that, based on the the communication between vehicles and infrastructure on the free way, the system model is built. In this situation, do only consider the impact of large scale fading, ignoring other facts'effect.. Based on this model, the designment of frame for the key technology and communication in handoff scheme are fully detailed. In addition, to get the position information from GPS, an interface is added in MAC layer to complete the function of interworking between MAC and GPS.In the end, NS2 simulator plantform is used to build for VANETs communication system. Firstly of all, the simulation scenarios is established. In the case of the same simulation scenario, the handoff delay, system throughput, packet loss rate is compared between proposed PHS and 802.11 handoff scheme based on the open system model in over-the-air mode. From the simulation result, PHS's handoff delay is significantly less than the 802.11r handoff scheme, up to 30 percent, while the system throughput and packet loss rate are slightly better than the 802.11r handoff scheme. That is, on condition of QoS, the proposed PHS is satisfied with VANETs'handoff demand.