【作者】 张良；

【导师】 谢胜利；

【作者基本信息】 广东工业大学 ， 模式识别与智能系统， 2014， 硕士

【摘要】 VANET (Vehicle Ad Hoc Network,车载Ad Hoc网络)作为一种特殊的Ad Hoc网络,是现在智能交通系统的重要组成部分。VANET既有一般Ad Hoc网络的通性,也有其自身特性：节点高速移动、网络拓扑频繁多变、通信链路不稳定,同时网络内部节点的运动轨迹又有规律可循,会受到静态道路的限制,这些特征使原有针对传统Ad Hoc的路由协议在VANET网络中表现不佳。因此根据VANET自身特点,结合相关信息,快速建立高效稳定的路由,使之应用到实际车载环境中具有重要的意义。本文首先介绍了车载自组网的研究背景以及国内外研究现状,接下来简要介绍了Ad Hoc网络,VANET的基本概念、特点、应用以及VANET的路由技术和分类。文中详细介绍了AODV(Ad Hoc On-demand Distance Vector routing)路由协议的两大组成部分：路由寻找和路由维护,分析了其设计原理、处理流程及其不足。同时针对现在大多数AODV改进只考虑移动车辆部分的局限性,在原AODV算法的基础上,结合实际的VANET特性,提出了基于路侧单元辅助路由的AODV改进设计——RUAR-AODV (Roadside Unit Assist Routing based AODV)。RUAR-AODV主要从路由寻找和路由维护两个方面进行改进：(1)RSU(Road Side Unit,路侧单元)辅助寻路。路由寻找阶段,把实际VANET中另一重要组成部分的RSU考虑进来,提出了辅助RSU路由寻找和传统AODV路由寻找相结合的方式,提高了路由寻找的效率；同时在备用路由的设计部分,提出选择路由维持时间最长的两条路由分别做主路由和备用路由,提高了通信路径的持续性和稳定性。(2)提前切换和修复。路由维护阶段,对用来通信的路由设定阈值,监听路由状态,在达到阈值时,就进行路由切换和路由修复。这种提前切换和修复机制提高了通信的持续性、稳定性,避免因路由重启而产生的大量网络开销。在文章的最后,我们采用现在比较流行的网络仿真工具NS2对AODV和RUAR-AODV进行仿真模拟。在设定的网络环境下,通过仿真结果对两种路由协议的路由跳数、丢包率、端到端延迟、协议开销这四个代表性的指标进行分析,衡量二者的整体性能。实验结果表明,RUAR-AODV在平均路由跳数、丢包率、端到端延迟都方面表现出了良好的优势,更加适用于VANET。更多还原

【Abstract】 VANET (Vehicle Ad Hoc Network) as a special Ad Hoc networks, is now an important part of the Intelligent Transportation System, which provides the infrastructure for the communication in vehicle or between vehicle and roadside equipment. VANET not only has common features of general Ad Hoc network, but also has its own characteristics:high-speed mobile nodes, frequently changing network topology, the not stable communication link, at the same time the trajectory of nodes within the network is regular, and always restricted by the static road. These characteristics make the existing routing protocols for Ad Hoc not have a good performance, not be suitable for VANET. Therefore, according to the VANET’s own characteristics, combined with relevant information, creating a stable and efficient routing quickly, which can be applied in the actual vehicle environment, is of great significance.First of all, this paper introduces the research background and overseas and domestic research status. And then there is a brief introduction to the Ad-Hoc, the basic concepts of VANET, VANET’s features and applications, and VANET’s routing technology and classification. In the paper we describe the AODV (Ad Hoc On-demand Distance Vector routing) routing protocol in detail, represent its two components-its route discovery and maintenance, analyze its design principle and the process flow, and point out its insufficiency. Nowadays most of the research on improving AODV protocol only just consider the part of moving vehicle. In our paper, we propose AODV’s improvement based on Roadside Unit assists in routing on the basis of the AODV algorithm, combining with the actual characteristics of VANET. RUAR-AODV (Roadside Unit Assist Routing based AODV) maintains two major improvements in route discovery and maintenance:(1)RSU (Road Side Unit) assists in routing. In the route discovery phase, we put RSU, another important component of the actual VANET, into the modified algorithm. The algorithm proposes RSU assisted in routing, combining traditional AODV’s route discovery, can improve the efficiency of routing; while we propose to find and choose two longest maintained routes, one named the main route while another used the alternate route. This mechanism can improve the continuity and stability of communication between nodes.(2) Switch and repair advanced. During maintenance phase, we set threshold to the using route, listening routing state. When the threshold is reached, switch to alternate route and repair the main route advanced. Such a mechanism can improve the continuity and stability of communication, and avoid network overhead caused by the routing restart.In the end of the paper, we use NS2, a popular network simulation tool, to simulate AODV and RUAR-AODV. Under the set of network environment, we measure the overall performance of two protocols, by analyzing the simulation results and comparing the four representative indicators of both:the hop count, the loss rate, the end to end delay and the protocol’s overhead. Experimental results show that, RUAR-AODV with help of RSU in routing, combining with the design of alternate routes can establish a stable and longer maintained route quickly. Advanced switching and repairing mechanism, to some extent, can extend the communication time, improve the stability of the route, and reduce network overhead caused by the routing restart. RUAR-AODV shows a good advantage in the hop count, the loss rate and the end to end delay. So the improved protocol can be more suitable for VANET.更多还原