车辆自组织网络MAC层协议的研究

发布时间：2020-03-17 13:31

【摘要】：Vehicular Ad Hoc Network (VANET) is an application of Mobile Ad Hoc (MANET) for road traffic. VANET has the characteristics of high moving speed, frequent changing topology, and different node densities. In this dissertation, according to the characteristics of VANET, it is aimed to improve the performance of MAC layer and provide reliable and real-time communications between vehicles. Modeling and analysis of periodic broadcast, modeling and analysis of broadcast in control channel, dynamic contention window scheme, MAC delay based clustering algorithm and cluster based time division multiple access are studied in detail.The main research contributions are as follows.(1) Modeling of periodic broadcast and dynamic contention window scheme in VANETA 1-D Markov model is proposed to analyze the performance of periodic broadcast in VANET. In this model, a new idle state is introduced under non-saturated condition when there is no message to send in the buffer of a node. The freezing of backoff time counter in backoff process is also considered in this model and a discrete time D/M/l queue is established to model the buffer of each node. Theoretical analysis show when vehicle density increases the performance of periodic broadcast decreases accordingly. Dynamic contention window scheme is proposed according to the changing of node density. Simulation results show the collision probability of DCW scheme is lower than that of fixed-contention window broadcast in IEEE 802.11 p. Simulation results also verify the accuracy of the Markov model.(2) Modeling of priority access to control channel in VANETAccording to the characteristics of messages with different priorities accessing to control channel, discrete time queue D/M/1 and M/M/1 are proposed to model periodic messages and emergent messages, respectively. Priority analysis is added to this model which is based on the previous 1-D Markov model. Packet collision probability, access delay of periodic message and emergent message and performance of DCW scheme in control channel are analyzed. Simulation results show DCW scheme could reduce the collision probability, which is suitable for control channel with different priority messages.(3) MAC delay based clustering algorithmThe performance of MAC protocol decreases in high vehicle density scenario. A MAC delay based adaptive (MDBA) clustering algorithm is proposed. Under the restriction of MAC delay, speed, acceleration, position and destination are considered in cluster head election algorithm. Cluster maintenance algorithm adaptively adjusts cluster according to changes of network topology. Traffic simulation software VISSIM is used to verify the proposed algorithm, and simulation results show that MDBA clustering algorithm performs better than classic clustering algorithms in wireless sensor network and mobile Ad Hoc network, which is more suitable for VANET.(4) Cluster based time division multiple access in VANETIn dense vehicle scenario, time slots are not available for all nodes in TDMA based access scheme. To solve this problem, a cluster based time division multiple access method is proposed. In this method, position based segment time slot allocation is employed. Cluster members are divided into two teams and allocated to two time segments. Moreover, slot reservation scheme is proposed to reduce collision and transmit emergent messages as soon as possible which lowers the access delay of emergent messages. Simulation results show the proposed method could reduce the collision probability and access delay of emergent messages in small traffic flow, compared with traditional TDMA scheme in VANET.
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交通事故,数据统计

也给道路交通带来了挑战，城市交通拥堵、道路交通事故Ｗ及恶劣天气下道路交逡逑通安全成了亟待解决的问题。根据统计数据显示Ｗ，近年来我国交通事故次数２５万次逡逑左右，死亡人数为５万人左右，直接经济损失在１０亿元左右，如图１．１所示。而根据逡逑世界卫生组织公布的数据，我国交通事故的致死率为２７．３％，居世界首位，美国作为一逡逑个被世界公认为＂车轮上行走的国家＂，交通事故的致死率仅为１．３％，曰本只有０．９％。逡逑可见，近年来随着我国汽车数量的不断增加，关系到广大人民群众生命财产安全的道路逡逑交通安全管理的工作非常严峻。逡逑３５ｒｔ逦逦逦逦逦：逡逑３０邋＾ｒ￣ｎ逦；逡逑Ｉ口巧灥次数（方次）逡逑—Ｕ；逦—逦＼＿＿邋｜＿逦＾＿＿逦＿＿逦—逦＿＿＾画死亡人数（方人）逡逑巧＇ｒ邋＾逦｜￣邋—－邋一逦；邋——￣＾逦□巧巧人数（乃人）逡逑ｉ0Ｔ三１—邋Ｌ逦Ｔ逦Ｔ逦￣邋ｎ邋■邋Ｉ□经济损失（亿元）逡逑Ｐ邋ｍ邋ＩＨ１１邋□邋１１Ｄ１１０逡逑２００８逦２００９逦２０１０逦２０１１逡逑图１．１近年来我国交通事故数据统计逡逑作为智能交通系统（Ｉｎｔｅｌｌｉｇｅｎｔ邋Ｔｒａｎｓｐｏｒｔａｔｉｏｎ邋Ｓｙｓｔｅｍ，邋ＩＴＳ）邋口－Ｓ］重要组成部分的车逡逑辆自组织网络（Ｖｅｈｉｃｕｌａｒ邋Ａｄ邋Ｈｏｃ邋Ｎｅｔｗｏｒｋ，ＶＡＮＥＴ）就是在此背景下提出的，成为保逡逑障行车安全和提高交通效率的关键技术。ＶＡＮＥＴ是将无线通信技术应用于车辆间通信逡逑的自组织网络，车辆与车辆之间通过无线通信实现消息的传递。车辆在获取本车行驶数逡逑据（车辆位置、速度、加速度、行驶方向等）后可Ｗ将自己的行驶信息发送给周围的其逡逑他车辆

状态图,车辆,车载单元,基本架构

个用多重数组（矩阵）表示的信息描述模型。根据这个理论模型比较容易得到网络的拓逡逑扑结构进而研究其体系结构。例如，若＆，７取设备所在位置的经、韩度，并将其按照大逡逑小顺序在图２．１中排列时，通过适当的运算即可得到一张两维的所有车辆位置图；如果逡逑考虑到车辆的移动（速度和方向等）Ｗ及道路状况，可Ｗ通过改变及Ｊ数纪的类型和数逡逑值，把图２．１映射为状态和状态转移，从而得到状态图和状态转移图；同理可＾＾＾将通信逡逑模式（包括通信设备特征、所属子网等）、联网状态（包括车辆间通信状态、车辆内设逡逑备协同工作状态、与外部网络的连接情况等）、优先等级、紧急情况标识、节点切换方逡逑法等等，，用这种多重数组表征，从而进行定量的分析。逡逑用所提出的多维多层的理论模型进行ＶＡＮＥＴ体系结构的研究能够提供高度的可扩逡逑展性，同时做到灵活、方便，使得组网变得容易。逡逑ＶＡＮＥＴ的网络架构主要分为两大部分：一是车辆间的通信，二是车辆与固定设施逡逑（即路边节点）之间的通信，如图２．２所示。逡逑Ｉｎｔｅｒｎｅｔ邋网络逡逑Ｊ逦＾邋ｒｒ逡逑ｆ逦Ｉ邋信息发布逡逑１＾邋／邋Ｉ邋＼一逡逑＼0／＾４ｗｉＳ？＾￣。逦Ｉ路边单兀［路边单凡逡逑Ｉ逦逦Ｉ邋Ｌ邋」逦Ｌ邋ｊｓ己邋Ｊ逡逑Ｉ削平心型Ｌ逡逑Ｉ逦＼逦巧逡逑Ｉ车辆状态参数采集逦输入输出设备Ｉ逦＾巾元服Ｕ｜逡逑图２．２邋ＶＡＮＥＴ基本架构逡逑图中，车辆上装载有车载单元（化ＢｒｏａｄＵｎｉｔ，ＯＢＵ），车辆通过车载单元ＯＢＵ与外逡逑界通信；固定设施主要是指在道路边缘设置的路边单元（Ｒｏａｄ邋Ｓｉｄｅ邋Ｕｎｉｔ
【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN929.5;U495

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