【作者】 赵静；

【导师】 冯军焕；

【作者基本信息】 西南交通大学 ， 计算机技术， 2013， 硕士

【摘要】 随着无线通信技术以及汽车工业的迅速发展,车载无线自组织网络技术(Vehicular Ad Hoc Network, VANET)已经成为人们研究的一个热点,VANET是一种特殊的移动自组织网络技术,它是未来智能交通系统的基础之一。车载无线通信网络是由车与车以及车与路边的基础设施之间的相互通信来构成,这样能够为驾驶者提供一系列的服务,如：Internet的接入,实时导航以及车载娱乐等,另外还能提供事故告警等信息,使交通网络更高效、安全。本文在研究移动Ad Hoc网络(Mobile Ad Hoc Networks, MANET)的MAC协议基础上进一步研究了VANET的MAC层协议的关键技术,主要贡献如下：第一,在二进制指数退避算法(Binary Exponential Backoff, BEB)的基础上,研究乘性增加线性减少退避算法(Multiple Increase Linear Decrease,指数增加指数减少退避算法(Exponential Increase Exponential Decrease, EIED),并在NS2软件平台上对上述三种算法进行仿真,比较其公平性,然后对后两种算法进行优化分别得到newMILD、newEIED退避算法,以提高网络的性能。并在newMILD算法的基础上进一步改进得到一种基于统计次数的退避算法,即当节点连续发送数据成功时,竞争窗口本应该减小,但是为了使竞争失败的节点接入信道,算法设定了一个门限值,当节点连续发送数据成功的次数超过此值时竞争窗口就变为最大,同理,当节点连续发送数据失败次数超过此值时,竞争窗口就降为最小。通过仿真分析,证明了此算法能够有效的降低隐藏节点的影响,提高了节点接入信道的公平性。第二,根据节点运动的特性,提出一种可用于评估车载网络冲突概率的模型,并仿真验证车载网络节点冲突概率与节点移动速度以及网络节点数量有关。然后提出一种基于相对距离的退避算法,本算法是基于相对距离和节点接入信道优先级成比例的基础上提出的。即节点根据自己与一跳邻居节点距离平均值的相对变化比例来调整竞争窗口的值。并利用Vanetmobisim软件模拟城市车辆运动场景图,然后利用其生成的脚本文件和cbrgen工具编写脚本代码来生成在NS2下的对应的场景图以实现仿真,仿真结果表明此算法能够有效的改善网络的性能。更多还原

【Abstract】 With the rapid development of wireless communication technology and the auto industry, Vehicular Ad Hoc Network has already become a hot topic of academic research, VANET is a particular kind of self-organizing network, which is the foundation of future intelligent transportation system. It communicates through Inter-vehicle (IVC) and Vehicle to Roadside (RVC). So that it can provide series of service for drivers. Such as Internet access, Real-time navigation and in-car entertainment, etc. In addition to that, it can provide the accident alarm information, so that it can make the traffic network more efficient and safer. This paper mainly researches the key technology of the VANET MAC layer protocol; the main contributions are as follows:First, MILD and EIED are researched on the basis of BEB, then the three kinds of algorithm are simulated with NS2and the fairness is compared. In order to improve network performance the latter two algorithms are optimized. And on the basis of newMILD a backoff algorithm which based on the statistical number are proposed. That is when the node sends success, the window of contention should be reduced, But in order to make the competition failed node could access channel, the algorithm sets a threshold value. When the number of nodes succeeding to send continuously is greater than the value, the contention window becomes the largest. Similarly, when the numbers of nodes failing to send continuously is greater than this value, the contention window will reduce to the minimum. Through the analysis of simulation, it is proved that the algorithm is effective to reduce the influence of hidden nodes and it has improved the fairness of node to access channel.Second, on the basis of the mobility characteristics of nodes, a model used to evaluate the VANET are proposed, and through simulating it has proved that the VANET node collision is based on the nodes speed and the number of the nodes. Then a backoff algorithm which is based on the relative distance is proposed. The algorithm is based on the relative distance and node access channel proportionally. It adjust the value of the contention window according to the average relative change of the distance that the node with it’s neighbor node. And city vehicle motion scene graph has been simulated using VanetMobiSim software, then the paper used the script that have generated and script made by cbrgen to generate scene in NS2. The simulation results show that the algorithm is effective to improve the preferment of network.更多还原