移动信道差错序列的分布概率模拟法及门限电平的讨论

采用了一种新方法产生移动信道的差错序列。即用计算机产生(0,1)均匀分布伪随机数,通过公式变换,产生Rayleigh分布随机数,加以适当门限,使模拟量量化,形成差错序列{Ei}、统计无误串分布G(K),并与实测G(K)曲线比较分析。由计算机模拟结果可知:概率模拟法是一种行之有效的方法。通过门限电平的讨论,发现此门限电平具有自适应特性。     

网络业务流的自相似性

对通信网络的大量研究表明,网络业务本质是自相似的(相关函数上表现为长相关特性)。网络业务的统计自相似性主要是指在不同时间尺度上观测到的业务流量序列具有相同的统计特性。讨论了当前网络业务流的特性;分析了现有的自相似业务流模型。为在线测量网络中的高速业务流,根据实测时间序列数据建立合适模型提供了参考。     

VANET网络中小尺度衰落信道仿真

车载网络（VANET）是智能交通系统的核心部分,能够提高道路交通的安全性与高效性。分析电波在VANET网络中的传播特点,着重分析该网络中双移动节点间的小尺度衰落信道,包括多普勒功率谱模型和用成型滤波器法仿真VANET网络中小尺度衰落信道特性,给出经历该信道后接收信号的包络。仿真结果表明,随着移动车辆速度比增大,接收信号衰落更深。该结果对于VANET网络下无线多媒体业务性能评估有着重要的作用。     

宽带卫星移动信道特性分析及仿真

信道模型是无线通信系统设计的基础,本文描述了宽带卫星移动信道的统计特性,分析了S频道基于幅度变化的抽头延迟线信道模型,对其特性进行了仿真,并与德国航空太空中心的农村、郊区、城市不同环境下实测数据统计特性进行对比,结果表明文章中的信道模型特性与真实宽带卫星移动传输环境的实测信道统计特性基本吻合,这对于解决未来宽带移动卫星移动信道模拟和通信系统设计具有重要的现实意义.     

车载自组织网络中的关键技术与应用研究

随着人们对驾驶的安全性和舒适性的要求越来越高,车载自组织网络(VANET)作为移动自组织网络在交通领域的一个应用,也受到越来越多的关注。VANET实现了车辆间通信,它创造性的把自组织网络与交通工具结合起来,利用全球定位系统(GPS)和无线通信技术,为处于高速运动中的车辆提供目视范围之外的交通信息,同时提供自动收费、车载娱乐等服务。本文研究了车载网络底层标准的确定、框架结构的建立以及快衰落的信道,对实现VANET的关键技术进行了探讨。最后对链路性能进行了测试,给出不同的信道参数对链路性能的影响。     

车载自组织网络关键技术

车载自组织网络(VANET)是一种自组织、结构开放的车辆间通信网络,随着无线通信技术与交通业联系的日益密切,VANET得到了大力发展。本文从VANET的基本概念和发展进程出发,综述VANET的关键技术。首先介绍VANET的网络模型、主要特点及体系结构,然后对VANET的物理层、MAC层、路由协议及应用层的研究内容和研究现状进行了系统阐述,最后对VANET今后的研究方向和应用前景进行了展望。     

三维开阔区车辆间通信的无线信道模型

车载自组网络-VANET（Vehicle Ad Hoc Network）作为移动自组网和传感器网络在道路交通领域的应用,节点具有对等性、高速移动等特点,这导致了VANET无线信道与无线蜂窝网络信道有着显著区别。文中主要研究开阔区域中车辆间通信的无线信道模型：在三维多径散射场景下,考虑配备定向天线的车辆终端,推导VANET双移动通信节点之间无线衰落信道的自相关函数与多普勒功率谱密度函数的解析表达式。该结果对于VANET网络下无线多媒体业务性能评估有着重要的作用。     

一个表示移动信道的Gilbert模型

移动信道是一典型的长突发信道,有其特殊的性质,所以将移动信道表示成一个Gilbert模型在工程上具有一定的实用价值。本文从一移动信道实测曲线R出发,利用非线性最小二乘拟合算法,得出二状态Markov模型各参数,推导出信道无误串分布G(m)的解析表达式,进而得到信道概率转移矩阵P;在此基础上将P代入Gilbert模型中求出模型的三个主要参数P、p、h,并由此推导出其差错统计指标:G(k)、Pe、p(n,m);最后讨论了h取不同值时对模型精度的影响,及h参数的优化设计问题。     

车载网中信息局部存储时间的研究

车载自组织网络(VANET)中车辆节点既是网络终端也是路由器,可以实现自组织和自管理,它不需要基础设施的帮助,仅仅通过车辆间的通信就能够在一段时间内把信息存储在一个给定的地理区域内。本文针对城市环境和高速公路环境这两种不同的交通模式来分析估算消息在VANET的局部存储时间。在高速公路环境中,我们研究VANET的参数对该时间的影响;在城市环境中,我们将它的结果与随机路径模型(Random Way Point)的模拟结果进行比较。结果显示在高速公路环境下,节点的传输半径能极大的影响局部信息的存储时间;在城市环境下,我们选取存储信息的地理区域的大小决定了该区域内信息的存储时间。     

移动信道Markov模型的Stateflow仿真技术

针对具有长突发误码特性的无线信道特征,根据移动通信系统的仿真要求,基于简单分群马尔科夫（Markov）信道模型,提出了利用stateflow技术的信道仿真方法,并生成移动信道的差错序列.仿真结果表明,该信道模型能够有效地描述无线移动信道的统计特性,并具有可视化、流程化和层次化的特点,在无线移动通信系统的软件仿真中具有实用性.     

一种基于VANET的数字城市网络

针对数字城市建设和发展的需求,提出了一种基于车载自组网(VANET)的数字城市网络的组网方案.作为一种特殊的移动Ad hoc网络,VANET应用于数字城市可发挥灵活、高效优势.首先提出了数字城市的网络体系结构,并基于概率模型,分析了VANET的网络连通性,进一步在NS2网络仿真平台中建立了VANET的网络模型,仿真评估...     

基于局部梯度场的VANET路由研究

车载自组织网络(VANET,Vehicular Ad hoc Network)近几年受到高度关注,同时多跳安全消息路由成为VANET应用的核心问题之一。试图借助梯度场的方法,研究VANET网络安全消息的定向、受限空间及拓扑动态变化条件的传播机制,以达到快速准确地传播安全消息的目的。提出了一种局部梯度场的路由协议(LGFR,Local Gradient Field Routing),并与城市场景下的贪婪边界无状态路由(GPSR,Greedy Perimeter Stateless Routing)和无线自组网按需平面距离矢量路由(AODV,Ad hoc On-DemandDistance Vector Routing)进行了对比。仿真结果表明,LGFR在数据包丢包率、数据包端到端平均时延和全局数据吞吐量方面具有较好的性能。     

TFRC协议在Ad Hoc网络中的改进及仿真

由于TFRC协议不适合Ad hoc网络环境,这将限制TFRC协议在Ad hoc络中的应用。针对TFRC协议在Ad hoc网络中存在的问题,本文在TFRC算法的基础上提出了一种基于丢包区分机制的TFRC拥塞控制策略,它不仅考虑到了差错误码,切换、连接中断引起的丢包对传输的影响,而且还考虑到了实际的链路本身的差错控制导致的乱序包对算法性能的影响,解决TTFRC算法在Ad hoc网络中因不能正确区分拥塞丢包和误码丢包而造成性能下降的问题,改善TTFRC在Ad hoc网络中的性能。仿真结果表明改进协议的性能优于TFRC。     

A dynamic timing-storage covert channel in vehicular ad hoc networks

Vehicular Ad hoc Network (VANET) enables high speed vehicles to communicate with each other. This kind of communication can provide road safety and passengers’ comfort. Covert channels are used to transmit information secretly over the network. Network covert channel is not only used as a hacking tool, but also used to convey secret information such as private keys. Unlike wired and conventional wireless networks, few studies are conducted on covert communication in VANET. The goal of this paper is to develop a hybrid (timing and storage) covert channel in VANET. In the timing part, covert messages are sent by altering the timing pattern of the service and control packets. The proposed covert timing algorithm is dynamically changed based on the vehicular traffic volume in the transmitter’s radio range. This dynamism is used to achieve better covert capacity with an acceptable error rate. On the other hand, some fields of the periodic status messages, sent in the control channel, are utilized in the storage part. An encoding algorithm is also proposed to embed the covert data in the mentioned covert timing and storage opportunities. The encoding algorithm provides a high embedding capacity, even if the number of opportunities’ possible values is not any power of two. Finally, the transmitted secret data volume, the packet loss ratio, the channel error rate and the effect of the proposed method on other vehicles’ throughput are evaluated in a simulation process.     

DCDS: Data centric dispatcher selection protocol for cellular enabled VANET communication

The Vehicular Ad‐hoc Network (VANET) is one of the emerging research areas in recent days, in which accomplishing the robustness and security are the demanding tasks. To obtain these objectives, various offloading‐based techniques are developed in the traditional works. Still, it remains with the limitations of high mobility, no assurance for data acceptance, and limited applicability for multiple data exchange units. Thus, this paper aims to develop a Data Centric Dispatcher Selection (DCDS) algorithm based on data offloading for a secure information exchange in VANET. It aims to enable the cellular‐based VANET connection by using the application layer protocol without taking the Pending Interest (PI)‐based information. Also, the Content Centric Network (CCN) concept is utilized to exchange the data between for upcoming internet. In this environment, the position of own vehicle and neighboring vehicle are known to each vehicle by using the Global Positioning System (GPS) and security messages. Moreover, the communication does not depend on the device's name, but it depends on the content name in CCN. Because of the availability of multiple interfaces in CCN, there is no content loss in the network. During simulation, various performance measures are used to evaluate the performance of the proposed technique, which includes throughput, packet loss rate, average end‐to‐end delay, total Satisfied Interest Packet (SIP), Forwarded Interest Packet (FIP), and average Interest Satisfactory Delay (ISD). Also, the superiority of this paper is proved by comparing it with some existing techniques such as Internet Protocol Television Quality of Service (IPTV‐QoS), Michael Oche (MO), and RobUst Forwarder Selection (RUFs).     

Cognitive Agent Based Critical Information Gathering and Dissemination in Vehicular Ad hoc Networks

Next generation vehicles will have capability of sensing, computing, and communicating capabilities. Different components in a vehicle have to constantly exchange available information with other vehicles on the road and cooperate for the purpose of ensuring safety and comfort using a Vehicular Ad hoc Network (VANET). Critical information like navigation, cooperative collision avoidance, lane-changing, speed limit, accident, obstacle or road condition warnings, etc. play a significant role for safety-related applications in VANET. Such kind of critical information gathering and dissemination is challenging, because of their delay-sensitive nature. This paper proposes an agent based model that consists of heavy-weight static cognitive (based on Belief Desire Intention : BDI) and light-weight mobile agents. Proposed model executes push (gather/store and disseminate) and pull (gather/store) operations on information gathered based on information relevance, criticalness and importance. The simulation results show that BDI based information gathering and dissemination scheme performs better than the reliable broadcast scheme in terms of bandwidth utilization, packet delivery ratio, push latency (information saturation time) and push/pull decision latency.     

车载Ad Hoc网络数据收集方法研究

车载Ad Hoc网络(VANET)是基于车辆－车辆(V2V)、车辆－基础设施(V2I)和混合架构的快速移动且自组织的网络,由于VANET中具有节点快速移动和拓扑结构动态变化等特点,文中针对如何在安全应用中收集到安全、可靠和实时的数据进行了研究,归纳论述了基于随车/随身设备的数据收集方法、基于路由协议的数据收集方法、提取式数据收集方法的技术进展,分析了各方法特点,指出了各方法主要研究方向,并对各方法应用和性能进行了对比分析。     

高速公路场景中车用自组织网络的节点度

该文基于大尺度路径损耗无线传播模型将高速公路场景中的车用自组织网络(VANET)建模为几何随机图,提出了VANET有效组网面积的概念,分析说明了VANET的准线性拓扑特点,并基于交通流理论关于自由流条件下的车头时距分布,推导得出了无线传输范围内至少存在k个邻居的概率计算方法。实验结果表明:该文提出的概率描述思想是一种适合计算高速公路场景中车辆网络节点度的有效方法。     

城市场景下基于速度信息的VANET路由协议的改进

车载自组网络(Vehicular Ad Hoc Networks,VANET)是指道路上由车辆搭载的无线通信装置构成的一种特殊的多跳无线移动自组织网络。VANET在实现多种智能交通方面应用的同时,还能满足用户在乘车时的娱乐等舒适性的需求,近些年来已成为无线自组网络研究的新热点。总结了近些年来出现的主要VANET路由协议的核心路由机制及其优缺点,并分析了各种技术对路由协议性能的影响。其后给出了一种基于速度信息的VANET路由协议改进方法,并通过实验验证了将改进方法与GPSR协议结合可以提高路由路径的稳定性,减少了端到端的平均时延,降低了VANET网络中拓扑的高动态性对路由协议性能的影响。     

SDR: A Stable Direction-Based Routing for Vehicular Ad Hoc Networks

A stable and reliable routing mechanism for vehicular ad hoc networks (VANETs) is an important step toward the provision of long data transmission applications, such as file sharing and music download. Traditional mobile ad hoc network (MANET) routing protocols are not suitable for VANET because the mobility model and environment of VANET are different from those of traditional MANET. To solve this problem, we proposed a new stable routing algorithm, called stable directional forward routing. The novelty of the proposed routing protocol is its combining direction broadcast and path duration prediction into ad hoc on-demand distance vector routing protocols, which including: (1) Nodes in VANET are grouped based on the position, only nodes in a given direction range participating in the route discovery process to reduce the frequency of flood requests, (2) Route selection is based on the link duration while not the hops or other metrics to increase the path duration, (3) Route discovery is executed before the path expiration in order to decrease the end to end delay. The performance of the new scheme is evaluated through extensive simulations with Qualnet. Simulation results indicate the benefits of the proposed routing strategy in terms of decreasing routing control packet, reducing the number of link-breakage events, improving the packet delivery ratio and decreasing the end-to-end delay.