车联网RSU单元下行流量的性能研究

基于802.11p/WAVE的车联网是一项涉及道路交通、无线通信、自组织系统等多学科综合性的技术领域,车联网中,RSU单元可作为AP,让在行驶的汽车中的人们可以随时随地接入Internet,其中,如何建立RSU单元的下行流量模型是一个关键问题.通过引入车辆密度概率质量函数,分析车联网MAC层车辆通过RSU设备访问Internet的信道竞争情形,提出了适用于高速公路交通场景的RSU单元网络吞吐量模型,并推导出RSU上行及下行流量的性能解析式.针对RSU单元通信范围有限、相邻RSU单元之间可能存在盲区的问题,提出了一种利用同向行驶的车辆协助数据下载的VCoDS方案,以达到提高某时间段RSU的下行流量的目标.仿真实验结果证实,VCoDS方案可有效提高RSU单元的下行流量.     

基于433MHz的DSRC技术在公交车自动报站的应用

针对因GPS卫星信号较差造成公交车无法准确自动报站,提出了使用专用短程通讯(DSRC)来提高自动报站精度的方法,设计了车载单元(OBU)和路旁单元(RSU)之间的通讯流程,开发了硬件电路,并进行实地测试.     

基于DSRC的ETC中RSU和OBU的优化配置分析

利用一个简单关系式描述RSU中接收模块接收到来自OBU中发射模块发射的上行信号强度大小.通过实际测试确定信号强度门限值,由cosn函数来模拟发射和接收方向图,可以计算出RSU接收到OBU发射的信号强度.从计算的接收信号强度和门限,分析了RSU和OBU的安装参数对可靠的通信区域的影响.同时也考虑了挡风玻璃对信号衰减的影响.借助于分析结果,很容易得到RSU和OBU的优化安装配置.     

IEEE802.11p/1609.4多信道协作机制改进研究

IEEE 802.11p/1609.4是车联网的专用接入访问控制协议。针对IEEE 802.11p/1609.4标准协议中多信道协作机制存在信道资源浪费、竞争信道拥塞等问题,在划分车载单元与路侧单元优先级的基础上,提出一种改进的多信道协作机制。将控制信道划分为注册时隙(RI)和轮询时隙(PI),RI节点利用服务信道提高空闲信道资源利用率,PI通过轮询列表在控制信道发布安全消息消除信道竞争。在Matlab和OMNET++的仿真环境下进行验证,结果表明改进机制在安全消息传输率、平均传输时延、服务信道吞吐量和消息丢失风险指数方面均有明显的性能提升,并且在高节点密度情况下,仍能保证消息传输效率。     

基于NCTUns的IEEE 802.11p MAC协议性能仿真

IEEE 802.11p对于车载自组网(VANET)的应用与部署具有重要作用。针对以往研究仿真场景不全面,且极少采用完整的WAVE通信方式等不足,在深入阐述IEEE 802.11p协议层次和NCTUns架构及仿真流程的基础上,利用NCTUns平台在不同应用场景下构建出逼真道路环境,使用完整的WAVE模式分别研究了节点密度、传输功率、传输距离以及车速对于网络性能的影响。仿真结果表明：节点密度、传输功率与传输距离对于分组接收概率和吞吐量有显著影响,而车速对节点吞吐量没有影响。基于仿真结果最后提出了一种通过动态联动调整分组接收概率以及竞争窗口大小来提高车载自组网MAC层性能的方法。     

一种可追溯的车载自组网隐私保护认证协议

利用标准模型下的单跳代理重签名技术,提出一个可追溯的车载自组网(VANET)隐私保护认证协议,其中,交通管理中心TRC授权路边单元RSU作为代理,将车载单元OBU签名的消息以TRC的名义进行代理重签名,从而防止根据签名追踪OBU,并能在TRC的协助和授权下,进一步通过RSU的配合准确快速地追溯消息签名的真实产生者。数字签名和时间戳技术的应用使协议能够抵御伪造消息和重放消息攻击。分析结果表明,该协议能够达到VANET条件隐私的目标,满足标准模型下代理重签名的安全性要求,与其他经典协议相比,存储开销更小,运行效率更高。     

基于IEEE802.11p标准的车载终端研究

在分析IEEE802.11p标准和车载自组网系统架构通信模式的基础上,结合GPS技术及车载自主网络通信技术,以车与车、车与路面单元之间互联,并进行实时有效数据传输与交换为目的,构建出车联网的网络通信架构模型。着重对移动车载终端模块设计提出一种具体的研究方案,为车联网的研究提供了参考。     

ETC中OBU电源系统的研究与实现

首先简述车载单元（OBU）的一种系统架构与实现，然后对其电源系统进行详细的仿真、分析与研究，归纳出其需求和核心参数的设计参考标准，最后针对市场需求和竞争，提出一套完整的、详细的OBU电源系统的架构和实现。     

基于速度与状态感知的车载网络接入退避算法

IEEE 802.11p协议是针对车载无线接入技术制定的MAC层和物理层标准,仍采用二进制指数退避算法,该算法不能根据车辆速度和密度作出调节,在V2I通信中,会造成严重的信道访问不公平和碰撞等现象,无法很好地适用于车载网络。针对上述问题,提出的算法在退避重传阶段,采用固定的最优竞争窗口,并能够根据车速和从路边单元获取的网络信息实时调整竞争窗口大小。模型分析和仿真实验表明,该算法可明显改善信道访问的吞吐量、公平性与可靠性。     

车载自组织网络中新颖的无加密匿名认证方案

针对车载自组织网(VANET)身份认证中的隐私信息保护问题,提出了一种新的基于线性方程组理论的匿名认证方案。该方案不使用传统的任何对称或非对称加密算法,而是利用线性方程组的求解理论,构建了一种匿名身份认证模型,在保证节点身份可认证的同时又防止了节点身份信息在非安全传输信道上泄露。此外,方案不仅满足了车辆单元节点(OBU)与路边单元节点(RSU)间的身份认证的需求,而且确保了车辆节点之间的身份认证。安全性和复杂性分析结果表明,所提方案安全可靠,且有较低的计算和通信开销。     

Augmenting Vehicle-to-Roadside connectivity in multi-channel vehicular Ad Hoc Networks

Vehicle-to-Roadside (V2R) wireless communication is a cornerstone for providing a wide plethora of intelligent transportation system (ITS) applications in the near future. Initial investment costs could discourage the deployment of a ubiquitous roadside infrastructure to support on-the-road networks; this would imply discontinuous coverage and short-lived connectivity.The purpose of this paper is to design techniques that make the best of sparse road-side unit (RSU) placement by supporting the spreading of network initialization advertisements from RSUs, when considering the multichannel features of the recently published IEEE 802.11p/IEEE 1609.4 standards for wireless access in vehicular environment (WAVE). The proposed techniques leverage time, space and channel diversity to improve efficiency and robustness of the network advertisement procedure in a urban scenario where obstructions to signal propagation due to buildings and traffic jam could hinder successful message spreading. Simulation under different RSU density, vehicular networking technology penetration rate, data rate, and packet size, aims at assessing effectiveness and efficiency of the proposed solutions.     

车载自组织网络中基于身份的匿名认证方案

针对于车载自组织网络中的身份认证问题,提出一种新颖的基于身份的匿名认证方案,该方案在保护了车辆的身份隐私信息的同时不仅满足了车辆节点与路边单元节点间的身份认证的需求,而且确保了车辆节点之间的身份认证。该方案利用基于身份的密码技术,减少了系统管理公钥证书的工作量和对节点证书认证的代价。最后通过安全性和复杂性分析,结果表明该方案不仅易于实现,而且安全可靠并具有较低的计算复杂度及通信开销。     

IEEE 802.11p协议MAC层自适应移动性改进研究

针对VANET环境下标准IEEE 802.11p协议的MAC层对车辆移动性因素支持不足的问题,对IEEE 802.11p协议MAC层自适应移动性机制进行了研究。首先,构建了一种VANET通信场景;然后,基于构建的通信场景,分别基于节点邻居数量和节点相对速度提出了一种P持续CSMA/CA机制和一种基于节点相对速度的动态优先级管理机制;最后,基于Veins仿真平台构建了测试场景,并对提出的改进机制进行了仿真测试。测试结果表明提出的两种机制能够有效增加系统吞吐量、减少丢包数量、降低平均数据传输延迟和平均数据重传次数,显著提升了VANET网络性能。     

蓝牙微微网对WLAN网络同频干扰的建模

由于同在2.4 GHz的ISM频段下工作,IEEE 802.11b局域网和蓝牙微微网不可避免地产生相互干扰,严重影响各自的网络性能。通过对基于CSMA/CA和RTS/CTS机制的IEEE 802.11b协议进行数学分析,剖析了其吞吐量降低与发送不同蓝牙数据包之间的内在关系,建立了一个蓝牙微微网对IEEE 802.11b局域网干扰影响的数学模型。仿真结果表明：该模型能较好地逼近IEEE 802.11b局域网在蓝牙微微网干扰下的吞吐量仿真曲线,在蓝牙DH1、DH3、DH5数据包干扰的情况下,平均相对误差分别为17.86%、10.39%和6.64%。根据该数学模型,提出了一个降低蓝牙微微网干扰的有效方案。该方案能快速、低成本、自适应地调整IEEE 802.11b发送帧长,有效提高其在蓝牙微微网干扰下的吞吐量。     

Design and evaluation of a novel MAC layer handoff protocol for IEEE 802.11 wireless networks

In recent years, the IEEE 802.11 wireless network family has become one of the most important set of standards in the wireless communications industry. IEEE 802.11 compliant devices are inexpensive and easier to configure and deploy than other wireless technologies. In an IEEE 802.11 wireless network, wireless terminals can move freely. As a result, when the wireless terminal moves away from its current access point, it must switch to another access point to maintain the active connection. This is known as the MAC layer handoff process. MAC layer handoff latency should be minimized to support real-time applications and to provide mobile devices with seamless roaming in IEEE 802.11 wireless networks. This paper proposes a novel MAC layer handoff protocol over IEEE 802.11 wireless networks by introducing advertisement messages sent from other mobile nodes and from which wireless terminals are able to receive the information of access points in their neighborhood. A mobile node can try to associate with access points based on the prediction before starting the probe process. The experimental results demonstrate that our solution can reduce MAC layer handoff latency to meet the requirements of real-time applications.     

Spectrally efficient emission mask shaping for OFDM cognitive radios

Orthogonal Frequency Division Multiplexing has been widely adopted in recent years due to its inherent spectral efficiency and robustness to impulsive noise and fading. For cognitive radio applications in particular, it can enable flexible and agile spectrum allocation, yet suffers from spectral leakage in the form of large side lobes, leading to inter-channel interference unless mitigated carefully. Hence, recent OFDM-based standards such as IEEE 802.11p for vehicular communication and IEEE 802.11af for TV whitespace reuse impose strict spectrum emission mask limits to combat adjacent channel interference. Stricter masks allow channels to operate closer together, improving spectral efficiency at the cost of implementation difficulty. Meeting these strict limits is a significant challenge for implementing both 802.11p and 802.11af, yet remains an important requirement for enabling cost-effective systems. This paper proposes a novel method that embeds baseband filtering within a cognitive radio architecture to meet the specification for the most stringent 802.11p and 802.11af masks, while allowing up to ten additional active 802.11af sub-carriers to occupy a single basic channel without violating SEM specifications. The proposed method, performed at baseband, relaxes otherwise strict RF filter requirements, allowing the RF subsystem to be implemented using much less stringent 802.11a designs, resulting in cost reductions.     

Mutual interference analysis of IEEE 802.15.4 and IEEE 802.11b

IEEE 802.15.4 and IEEE 802.11b, operating in the 2.4 GHz unlicensed industrial scientific medical (ISM) frequency band, may lead to signal interference and result in significant performance degradation when devices are collocated in the same environment. The main goal of this paper is to evaluate the effect of mutual interference on the performance of IEEE 802.15.4 and IEEE 802.11b systems. An analytic model for interference between IEEE 802.15.4 and IEEE 802.11b is suggested. The packet error rate (PER), transmission delay, and throughput are evaluated for IEEE 802.15.4 and IEEE 802.11b. The power spectral density of the IEEE 802.11b is considered in order to determine in-band interference power of the IEEE 802.11b to the IEEE 802.15.4. The simulation results by OPNET are shown to validate the numerical analysis.