【作者】 孙琳；

【导师】 徐敬东；

【作者基本信息】 南开大学 ， 计算机应用技术， 2012， 博士

【摘要】 车载无线自组网络（Vehicular Ad hoc NETworks, VANETs）近年来在高速公路安全应用场景中显示出巨大的研究潜力和应用价值，成为智能交通系统乃至物联网系统的重要组成部分，受到学术界和工业界的广泛关注。在高速公路上，车-车（Vehicle-to-vehicle，V2V）通信和车-路（Vehicle-to-infrastracture，V2I）通信是安全信息传输的两种实现方式。路边单元RSU（Road Side Unit）是一种高速公路基础设施，通过V2V和V2I相结合的传输方式能够实现RSU高效收集道路交通信息的目的。RSU能够将收集的信息进行集中处理和反馈。一方面，这些信息能够用于车辆运行状态的实时监控。当RSU通过对数据特征的挖掘发现潜在交通异常后，能够及时为车辆提供预警，防止交通事故的大规模发生。另一方面，如果已经出现交通事故等特殊状况，RSU获取信息后能够尽早提出应对策略，为事故救援和恢复正常通行争取宝贵的时间。因此，研究高速公路安全应用场景中的信息传输机制具有重要的科研价值和实用价值。本文即围绕这个目标对高速公路VANETs关键技术展开研究，对车辆之间以及车辆和RSU之间的信息传输性能和效率进行深入的研究和探讨，主要工作包括以下几个方面：第一，本文通过数学模型和理论分析的方法，根据高速公路上车辆速度服从正态分布这一事实，推导出相邻簇头节点之间保持稳定通信的概率公式和一维簇头链状网络保持稳定通信的概率公式。分析结果为后续簇头选择协议和中断恢复协议奠定了坚实的理论基础。第二，本文以数学分析作为基本出发点，提出一种RSU辅助簇头选择协议。该协议以RSU作为簇头选择过程的发起者和执行者，从自身的信息传输范围内依次选择速度最接近于高速公路平均速度的车辆作为簇头节点，进而形成稳定性更高的一维簇头链状网络，实现RSU的高效信息传输和信息采集。仿真实验结果证明，相对于随机簇头选择方式，该协议能够使RSU对于探测数据包的接收率具有最高19.00%的提升，信息收集范围能够实现900米的延长。第三，为了提高一维簇头链状网络通信的稳定性并扩展RSU的信息收集范围，本文提出一种与簇头选择协议相适应的中断恢复协议。在中断发生时，检测到中断的簇头节点将发起中断恢复流程，并在合理范围内选择速度最接近于高速公路平均速度的车辆作为新的后备簇头节点。通过对中断恢复等待时间进行合理的设置，该协议能够实现RSU信息收集范围2800米的延长，并将中断恢复的错误率维持在较低的数值水平上。第四，本文提出一种自适应的探测数据包重传方案，以提高簇头节点的信息接收率进而提升RSU对于探测数据包的接收率。该协议能够根据无线信道环境的动态变化计算并设置探测数据包重传的概率。仿真实验结果证明，以中断恢复等待时间2秒为例，该协议能够使得RSU对于探测数据包的接收率具有平均7.11%和最高22.53%的提升。第五，本文对高速公路安全应用场景中需要收集的信息按照其属性和处理方式进行了详细的归类。进而根据信息类型和重要程度的不同提出基于优先级的探测数据包传输协议和概率式带宽节约方案，以降低高优先级探测数据包到RSU的传输时间延迟和带宽消耗。仿真实验结果表明，基于优先级的探测数据包传输协议能够有效降低高优先级探测数据包的传输时间延迟，当事故发生的地点距离RSU4000米时，该事故信息能够在0.18秒之内被RSU所获取。同时，本文提出的概率式带宽节约方案能够有效降低未经数据融合的高优先级探测数据包总数，同不采用该方案相比，在保证RSU的探测数据包接收率的前提条件下，仿真实验结果证明该方案能够减少72.73%包含相同事故信息的冗余高优先级探测数据包，实现了带宽等网络资源的节约。更多还原

【Abstract】 Recently, VANETs (Vehicular Ad hoc NETworks) have shown great potentialand application value in safety related scenarios on the highway. VANETs havebecome important parts of ITS (Intelligent Transportation System) and the system ofIoT (Internet of Things), and got widely attentions by the academic and industrialcircles. On the highway, the communications of V2V (Vehicle-to-vehicle) and V2I(Vehicle-to-infrastructure) are two important ways to transmit safety-relatedinformation. The RSU (Road Side Unit) is one of the highway infrastructures. It cancollect traffic and environmental information through V2V and V2I communications.The information gathered by the RSU will be centrally prcessed and reported to thedrivers. For one thing, the information can be used for real-time monitoring ofvehicle’s moving state. If the RSU tests the unusual activities in the traffic throughdata mining, it can provide warning services to the drivers and prevent large scaletraffic accidents. For another, if there has already been an accident in a fixed place,the RSU can put forward the corresponding countermeasures as soon as possible tosave valuable time for the accident rescue and normal traffic recovery. Therefore, theresearch on the information transmission mechanism in highway safety-relatedscenario has great scientific values and practical values. This dissertation focuses onthe research on important technologies of VANETs in highway situations. It willdiscuss the efficiency and performance of the information transmission betweenvehicles and the RSU, which includes the following contributions:First, based on the fact that the speed of each vehicle on the highway followsnormal distribution, this dissertation uses mathematical models and analysis toobtain the probabilities of stable communication between two consecutive CHs(cluster heads) and between CHs in one-dimensional and multi-hop CH chain. Theanalytical results will become theoretical basis of our protocols in followingchapters.Second, we propose an RSU-assisted CH selection protocol in this dissertation using analytical results in Chapter2. In that protocol, the RSU is the initiator andoperator of the CH selection process. It will choose the vehicle with the speedclosest to the average speed on the highway as a CH within CH selection range oneby one to form a one-dimensional and multi-hop CH chain to collect traffic andenvironmental information. The simulation results show that our protocol can makethe RSU’s reception rate of the probing packet has at most19.00%improvement,and make the RSU’s information collection range has900meters extension.Third, in order to improve the stability of one-dimensional and multi-hop CHchain and enlarge the RSU’s information collection range, we propose a backupprotocol in this dissertation. The CH who detects the interruption between itself andits previous CH will launch the backup process, and choose the vehicle with thespeed closest to the average speed on the highway as a new backup CH withinreasonable range. In our simulation, the protocol can achieve2800meters extensionof the RSU’s information collection range with proper configuration. The error rateis low accordingly.Forth, we propose a self-adaptive retransmission protocol to improve the RSU’sreception rate of the probing packets. The protocol can automatically change theretransmission probability of the probing packet in each CH according to thevariation of wireless conditions. When the backup waiting time Tbackupis2s, thesimulation results show that our protocol can improve the RSU’s reception rate ofthe probing packet with7.11%on average and22.53%at most.Fifth, we analyze important information to be obtained by the RSU on thehighway and sort the information into four kinds according to its nature and way ofprocessing. Then we propose a priority based transmission protocol and aprobability bandwidth reserve method based on the information types and theirimportance to reduce the transmission delay of urgent probing packets and thebandwidth consumption. The simulation results show that, the priority basedtransmission protocol can effectively lower the transmission delay of the urgentprobing packet. When an accident happens at4000m in front of the RSU, theaccident information can be obtained within0.18s on average. At the same time, wealso propose a probability bandwidth reserve method to reduce the total number of the urgent probing packet without data aggregation. Under the condition ofmaintaining the RSU’s reception rate, the simulation results show that the totalnumber of the redundant urgent probing packet can be lower at72.73%corresponding to the result not using the method.更多还原