交通CPS环境下车辆主动式安全通信性能分析与协议优化

发布时间：2018-05-14 07:20

本文选题：交通信息物理融合系统 + 车载无线自组网　；参考：《西北工业大学》2015年博士论文

【摘要】：道路交通事故一直以来是全球性最重要的公共安全问题之一，给人类社会带来了巨大的生命和财产损失。为了避免交通事故的发生，在过去三十多年中，各大汽车研究机构都在积极研发车辆主动式安全应用，以提高行车安全。由于传统交通系统的计算过程和物理环境之间缺乏广泛的互连互通，大多数主动安全技术还是基于单一车辆实现，使得交通系统安全控制未达到充分的整体协调优化。而信息物理融合系统（Cyber PhysicalSystem, CPS）概念的出现，为上述问题开辟了新的解决途径。交通信息物理融合系统（Transportation Cyber Physical System, T-CPS）是CPS在交通领域的应用，通过将传感、计算、控制和通信等技术，有效集成运用于交通运行管理系统，形成信息化、智能化、人性化的新型交通运输系统。为了达到交通信息系统和交通物理系统的深度融合，需要一种适用于道路环境下的通信技术来实现两者的广泛互连互通。在这种需求背景下，车载无线自组网（VehicularAd Hoc Network, VANET）应运而生。通过车与车（Vehicle-to-Vehicle, V2V）和车与路边基础设施（Vehicle-2-Infrastructure, V2I）两种通信方式，使得驾驶者可以及时获取视野范围外的潜在威胁信息并作出预判。研究表明，车载无线自组网能够提供比传统安全技术更为全面和有效的安全保障。因此，各国政府、研究机构和汽车厂商都开始致力于研究基于车载无线自组网的车辆主动式安全通信（Vehicle Safety Communication, VSC）技术。由于车辆主动式安全应用对于通信性能的要求较高，因此，现有协议是否能够满足此类应用的实时性和稳定性需求，是协议设计和参数制定的关键问题。本文采用数理分析模型的方法，建立了基于IEEE802.11p的车载无线自组网在典型行车环境下的协议模型，并提出了协议实时性与稳定性分析方法。结合模型分析结果，进一步讨论与协议兼容的优化方案，设计了车辆主动式安全通信环境下自适应速率控制协议以提高通信的稳定性。本文的主要贡献如下：第一，本文结合车辆主动式安全通信的特点，考虑高速公路环境下车辆分布、信道衰落等影响，运用数学模型分析的方法，建立了车辆主动式安全通信网络综合模型。与大多数无线通信网络模型仅仅只对通信环节中单一层级进行建模不同，本文研究的模型涵盖了环境模型、信道模型、IEEE802.11p协议的物理层模型以及MAC层模型，并详细刻画了隐藏节点、虚拟冲突、非饱和网络状态等问题，更接近真实的通信环境。该模型是目前车辆主动式安全通信环境下较为有效的综合模型，对于深层次理解协议存在的问题、分析网络各项性能指标和协议改进与优化提供了很好的研究基础；第二，提出了车辆主动式安全通信实时性与稳定性分析方法。考虑到通信节点缓存能力限制，本文研究了有限队列长度下的协议性能指标。建立M/G/1/K队列模型，分析了标准IEEE802.11p协议在典型行车环境下的平均延时，并采用区域划分的分析方法估算了平均丢包率。仿真结果证明，本文提出的实时性与稳定性分析模型的理论值与仿真值基本一致，平均计算误差小于5%，具有较高的准确性。进而采用该模型详细分析了各种外部因素、系统参数对于通信实时性与稳定性的影响。分析结果表明标准IEEE802.11p协议可以很好的满足车辆主动式安全通信实时性需求，但不能达到其对稳定性的要求；第三，设计和实现了适合车载环境下主动安全应用的自适应通信协议VSCRA。目前，尚无针对单跳广播的自适应速率控制协议相关研究，本文率先提出了适用于单跳广播的自适应速率控制跨层协议框架。该优化协议解决了车辆主动式安全通信环境下自适应速率控制的两个重要问题：第一，在单跳广播通信缺乏反馈信息的条件下，发送节点如何在本地进行信道状态估计；第二，在车流密度较大的环境中，节点间相互干扰造成的丢包严重，如何区分信道衰落丢包和信道干扰丢包造成的影响，并选择最优传输速率。针对这两个问题，本文分别提出了基于信道对称性理论的本地丢包估计方法和基于节点间相对距离的信道衰落丢包估计，并设计了基于自组织模糊神经网络的自适应速率选择算法。仿真结果证明，优化协议能够在车流密度变化的环境中大大提高通信稳定性；第四，基于实际的DSRC车载无线通信单元搭建了实验平台，验证基于节点相对距离的信道衰落丢包估计。实验结果表明，，相同距离下的丢包率偏移值均小于4%，变化比较平稳，说明相对距离能够很好的估算大尺度信道衰落造成的丢包。同时，本文基于NS2设计了VSCRA仿真平台，进行大规模仿真，主要验证不同行车环境下，所提出理论模型和优化协议的正确性和有效性。仿真结果表明VSCRA较之固定速率传输模式3Mbps，6Mbps和12Mbps，其丢包率平均降低了34.16%，43.07%和60.76%。综上所述，本文的工作采用建立模型的方式分析了车载无线自组网在车辆主动式安全通信中的缺陷，并基于理论分析提出了有效的协议优化方案。论文的研究有助于车载环境下标准协议的制定与性能改善。
[Abstract]:Road traffic accident has always been one of the most important public safety problems in the world, which has brought great loss of life and property to human society. In order to avoid the occurrence of traffic accidents, in order to avoid the occurrence of traffic accidents, in the past thirty years, various automobile research institutions have actively developed vehicle active safety applications in order to improve traffic safety. There is a lack of extensive interconnection and intercommunication between the computing process of the traffic system and the physical environment. Most active safety technologies are based on a single vehicle, which makes the safety control of the traffic system not fully integrated and optimized. The emergence of the concept of Cyber PhysicalSystem (CPS) has opened up a new problem for the above problems. The transportation information physical fusion system (Transportation Cyber Physical System, T-CPS) is the application of CPS in the traffic field. Through the technology of sensing, computing, control and communication, it is effectively integrated into the traffic operation management system to form a new type of transportation system with information, intelligence and humanization.
In order to achieve the depth fusion of traffic information system and traffic physical system, a communication technology suitable for the road environment is needed to realize the wide interconnection and intercommunication between the two. In this context, the VehicularAd Hoc Network (VANET) has come into being. Through the vehicle and vehicle (Vehicle-to-Vehicle, V2V) and the road and road Vehicle-2-Infrastructure (V2I) is the two communication mode that enables the driver to obtain the potential threat information outside the field of vision and make a prejudgement. The research shows that the vehicle wireless ad hoc network can provide more comprehensive and effective security than the traditional security technology. Therefore, governments, research institutions and automobile factories are provided. Businesses are working on Vehicle Safety Communication (VSC) technology based on vehicular ad hoc networks.
Due to the high requirement of vehicle active safety application for communication performance, it is the key problem for the design of protocol and the formulation of parameters whether the existing protocols can meet the real-time and stability requirements of such applications. In this paper, a vehicle based vehicle wireless ad hoc network based on IEEE802.11p is established by means of mathematical analysis model. Based on the protocol model in the environment, the method of protocol real-time and stability analysis is proposed. Combined with the result of the model analysis, the optimization scheme compatible with the protocol is discussed, and the adaptive rate control protocol is designed to improve the stability of the communication in the vehicle active security communication environment. The main contributions of this paper are as follows:
First, considering the characteristics of vehicle active safety communication, considering the influence of vehicle distribution and channel fading under the environment of the expressway, the integrated model of vehicle active safety communication network is established by mathematical model analysis. And most of the wireless communication network models only model the single level of the communication link. In the same way, this model covers the environment model, channel model, the physical layer model of IEEE802.11p protocol and the MAC layer model, and depicts the hidden nodes, the virtual conflict, the unsaturated network state and so on, which is closer to the real communication environment. This model is a more effective comprehensive model in the current vehicle active security communication environment. It provides a good foundation for further understanding of the problems in the deeper understanding of the protocol, analyzing the performance indicators and improving and optimizing the protocols.
Second, the real time and stability analysis method of vehicle active safety communication is proposed. Considering the limitation of the communication node caching capability, this paper studies the performance index of the protocol under the finite queue length. The M/G/1/K queue model is set up, the average delay of the standard IEEE802.11p protocol under the typical driving environment is analyzed, and the regional partition is used. The analysis method estimates the average packet loss rate. The simulation results show that the theoretical value of the real time and stability analysis model is basically consistent with the simulation value. The average calculation error is less than 5% and has a high accuracy. Then the model is used to analyze the various external factors in detail, and the system parameters have a shadow on the real-time and stability of communication. The analysis results show that the standard IEEE802.11p protocol can meet the real-time requirement of vehicle active safety communication, but it can not meet the requirement of stability.
Third, the adaptive communication protocol VSCRA. suitable for active safety application in vehicle environment is designed and implemented. There is no related research on adaptive rate control protocol for single hop broadcasting. This paper first proposes an adaptive rate control cross layer protocol frame for single hop broadcasting. The optimization protocol solves the vehicle active security. Two important problems of adaptive rate control in communication environment: first, under the condition of lack of feedback information for single hop broadcast communication, how to estimate the channel state of the transmission node locally; second, in the environment with large traffic density, the loss of packet caused by mutual interference between nodes is serious, and how to distinguish the channel fading packet loss and channel dry. In this paper, the local packet loss estimation method based on the theory of channel symmetry and the channel fading estimation based on relative distance between nodes are proposed, and the adaptive rate selection algorithm based on self organizing fuzzy neural network is designed for these two problems. The simulation results are proved to be proved by the simulation results. Obviously, the optimization protocol can greatly improve the communication stability in the environment of changing vehicle density.
Fourth, based on the actual DSRC vehicle wireless communication unit, an experimental platform is built to verify the channel fading loss estimation based on the relative distance of the nodes. The experimental results show that the loss rate of the packet loss rate under the same distance is less than 4%, and the change is relatively stable, which shows that the relative distance can be used to estimate the packet loss caused by the large scale channel fading. Based on NS2, this paper designs a VSCRA simulation platform for large-scale simulation, which mainly validating the correctness and effectiveness of the proposed theoretical model and optimization protocol under different driving environments. The simulation results show that the packet loss rate of VSCRA is reduced by 34.16%, 43.07% and 60.76%., compared with the fixed rate transmission mode 3Mbps, 6Mbps and 12Mbps.
To sum up, this paper analyzes the defects of vehicle wireless ad hoc network in vehicle active security communication by establishing model, and proposes an effective protocol optimization scheme based on theoretical analysis. The research of this paper is helpful to the formulation and performance improvement of the standard protocol under the vehicle environment.

【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：U495

【参考文献】