无线传感器网络中基于粒子滤波的人员跟踪方法

人员跟踪是室内定位系统的一项重要任务。在无线传感器网络中利用信号强度实现人员跟踪,无需专门的测距设备,能够降低系统的复杂度和成本,成为研究的热点。但是,由于人体对信号传播产生比较大的影响,给人员跟踪带来困难。提出一种新的信道模型,描述有人环境下信号强度与距离的关系。跟踪算法根据该模型建立信号强度的测量模型,并结合人的运动特点建立状态转移模型,最后利用粒子滤波技术实现了对人员的跟踪。该方法以序贯方式估计人员的位置,计算过程简单,而且对信号强度的噪声不敏感。仿真和实验表明,该方法的跟踪效果良好。     

基于节点差异性的无线传感网恶意软件传播模型研究*

针对目前无线传感网络中恶意软件模型化工作的不足,在二维元胞自动机基础上提出了节点差异性的恶意软件传播模型。该模型引入了MAC无线信道争用机制和邻域通信距离因素,描述了节点差异度对恶意软件在无线传感网传播扩散的影响。分析仿真实验表明,大规模无线传感网络的节点差异度、无线信道争用机制都对传播行为产生了重要影响,降低了恶意软件的传播速度。与传统传播模型相比,该模型更能够准确描述恶意软件在无线传感网络环境下的传播行为,为无线传感网络安全防御研究提供基础。     

高速铁路环境下的MIMO信道建模及仿真

根据高速铁路环境下电波传播特性,基于多入多出(MIMO)无线散射信道模型,提出一种高速铁路无线环境下的MIMO无线信道模型,详细分析了其构建过程,并通过仿真得出MIMO信道的空域相关性随天线单元间距的增大而减小,拓展了MIMO信道衰落模型的研究。     

三维统计信道中的多普勒效应及其信号分析

在三维(3 Dimensional,3D)空间域无线通信信道建模中,针对不同环境中仰角(Elevation Angle,EA)分布的复杂性,提出一种指数型概率分布,然后对这种分布下的无线信道进行建模,最后对接收端的多普勒功率谱密度(Power Spectral Density,PSD)和信号特性进行分析与仿真。采用近似算法推导出多普勒PSD的解析式,同时对Rayleigh 衰落信道中接收信号包络、平方包络的功率谱及时延相位差的概率密度函数进行研究。实验结果表明,所提出的三维无线信道模型在进行参数估计时符合相关理论与实际经验,同时指数函数模型的单变量特性使其在适应不同实际信道环境时非常灵活,因此可以对多种无线信道环境下的信道特征进行参数估计。     

平坦地面无线信道的大尺度衰落特性

针对近地面无线信道缺乏大尺度衰落模型的现状,选取平坦地面环境为典型研究对象,进行了2.4GHz无线信号沿近地面传播的信号强度测量,通过测量数据的线性回归建立了该地面环境的路径损耗模型.统计参数分析表明,双斜率对数距离路径损耗模型适用于近地面无线信道的大尺度衰落特性表征,突变点位置取决于收发天线高度,路径损耗指数在突变点前小于2,突变点后在2.87～3.74之间.所得模型与传统模型进行了性能对比,结果表明传统模型不适用于近地面无线信道的传播特性表征,本文所建模型更具实际意义.     

Channel-Based Detection of Sybil Attacks in Wireless Networks

Due to the broadcast nature of the wireless medium, wireless networks are especially vulnerable to Sybil attacks, where a malicious node illegitimately claims a large number of identities and thus depletes system resources. We propose an enhanced physical-layer authentication scheme to detect Sybil attacks, exploiting the spatial variability of radio channels in environments with rich scattering, as is typical in indoor and urban environments. We build a hypothesis test to detect Sybil clients for both wideband and narrowband wireless systems, such as WiFi and WiMax systems. Based on the existing channel estimation mechanisms, our method can be easily implemented with low overhead, either independently or combined with other physical-layer security methods, e.g., spoofing attack detection. The performance of our Sybil detector is verified, via both a propagation modeling software and field measurements using a vector network analyzer, for typical indoor environments. Our evaluation examines numerous combinations of system parameters, including bandwidth, signal power, number of channel estimates, number of total clients, number of Sybil clients, and number of access points. For instance, both the false alarm rate and the miss rate of Sybil attacks are usually below 0.01, with three tones, pilot power of 10 mW, and a system bandwidth of 20 MHz.      

Electromagnetic characterization of a computational asymmetric analysis for wireless networks

While sensor networks research for terrestrial applications has made significant strides in the past few years, the literature has relatively few examples of papers that have validated the feasibility and reliability issue, for the performance of Wireless Sensor Networks (WSNs) for underground applications. The propagation characteristics of electromagnetic (EM) waves in soil, and significant differences from propagation in air, prevent straightforward characterization of the underground wireless channel. Fundamentals, such as the dielectric permittivity and magnetic permeability, are required to solve the propagation of EM waves in soil. To this end, in this paper, we proposed a new model, Asymmetric Mixture Homogenization, based on the representative volume element concept, to characterize the dielectric permittivity of soil according to the composition of soil, and layout the foundation for efficient communication in this new environment. Further, in this paper we validated that with the latest wireless network system being used for terrestrial applications, challenges exists for the WSN to be used for underground applications. Experiments are performed to examine the link-level quality and received signal strength parameter between under-soil and above soil sensor nodes. The theoretical analysis and the experimental results prove the feasibility for the realization of WSN in underground applications.     

高速移动下U型槽的时变信道建模

随着国内高速铁路建设的迅速发展,在高速铁路上要求移动办公、娱乐的客户需求与日俱增,而现有的蜂窝移动通信以及针对铁路的移动通信铁路全球系统（GSM-R）均不能很好地满足客户对宽带无线通信的服务质量（QoS）需求。高铁在实际的行驶过程中,会经历各种复杂的场景,U型槽是常见的场景,然而目前尚未有充分针对高速移动下U型槽的时变信道建模的研究。针对此问题,提出一种高速移动下U型槽的时变信道建模方法。首先,采用几何随机分布理论,针对高铁典型场景U型槽建立几何分布模型,分析散射体簇的变化规律,推导视距（LOS）分布、时变角度扩展、时变多普勒扩展等参数的表达式,并给出了信道冲击响应的闭式解。其次,分析了信道的时变空时域互相关函数、时变自相关函数以及时变空域多普勒功率谱密度的表达式。最后,对所提模型进行了统计性能的仿真,验证了该模型具有时变性以及较高的相关性,体现了高铁信道的非平稳性,满足高速无线信道的特性。     

蓝牙通信的室内建模与仿真

蓝牙设备经常是在室内应用,如办公室、居家、机场等平坦的二维环境.为了符合实际的应用场合,给出了适用于蓝牙室内传输的无线传播信道模型.从室内传输模型出发,根据通信的距离、噪声和发射功率,得出瞬时接收信噪比,并根据蓝牙射频GFSK调制特性求出瞬时位错误率.再根据蓝牙不同的数据分组类型求出ACL数据分组的平均丢包率和吞吐量以及SCO数据分组的位错误率.与实验测试结果进行了对比,比较结果显示了系统模型的有效性.研究工作对蓝牙在室内的通信性能有一定的借鉴意义.     

低空信道对无线传感器网络的影响分析

无线通信系统的性能很大程度上受到无线信道特性的影响.随着通信技术的发展,近地环境中电波传播特性的研究已成为研究无线通信系统的重要课题之一.本文在室外开阔地、天线低空架设的环境下,针对2.4GHz频段的无线信号传播特性进行了实测研究,并利用最小二乘法对数据进行了拟合分析.研究表明,地表无线信道同传统微蜂窝无线信道存在较大...     

基于中继器的无线侧信道分析方法

随着物联网时代的来临,通信设备的安全变得越来越重要.2018年出现的无线侧信道分析技术揭露了无线电安全中存在的漏洞,对物联网安全构成了很大的威胁.然而,无线侧信道分析方法极易受到噪声的干扰.在有噪声环境下,采集到的无线侧信道信号波形往往会出现畸变,导致后续分析失败.为了改善信号波形、提高无线侧信道的分析效率,本文提出了...     

基于TTIB技术的无线数据传输系统研究

TTIB是一种可抵抗无线信道中多径时延及多谱勒频移而引起信号衰落的一种高效的频谱技术。在文献[1]原有的两位数字信号的基础上,使用VHDL硬件编程语言建模、仿真,并基于FPGA硬件平台实现了一个八位数字信号的TTIB处理系统。结果表明,有效的实现了TTIB处理。     

In-plane detection of scattered light from a minute particle using a resin-based light waveguide incorporated with a microfluidic channel

An optical sensor combined total analysis system (TAS) is thought to be one of the most powerful functional elements needed to realize a “ubiquitous human healthcare” system. In accordance with this concept, we have proposed a fundamental structure of detecting side scattered light from a minute cell or particle running along a microfluidic channel, partially utilizing the channel filled with water or saline solution as a light waveguide. Based on this concept, we have fabricated a trial-manufactured optical TAS chip and carefully evaluated its side scattered light measuring performance in in-plane direction, supplying and detecting visible laser power by using multiple optical fibers and their precise positioning mechanisms. We have successfully obtained experimental results of both transmitted light power change and that of side scattered light, and we confirmed that there was a strong relationship between their signal waveforms. Furthermore, we have developed a hybrid numerical calculation method on the basis of the finite-difference time-domain method, in addition to the beam propagation method. Based on this hybrid method, we tried to compare results between the experimental inverse pulse of transmitted light and a pulse of side scattered light, and those based on numerical calculations. Excellent qualitative accordance was obtained between the inverse pulse of numerical and experimental results. In contrast, the experimental pulse of side scattered light indicated a considerably spread base in comparison to the numerical results.     

一种VANET信道丢包率模型

车载自组网（Vehicular Ad hoc Network,VANET）信道建模对车辆间通信具有重要意义。分析了2.4 GHz通信频段两车在武汉市内通信实测丢包率数据,提出了信道丢包率模型FVPM（Fresnel theory based VANET Propagation Model）,考虑了实际传输中车辆和街道环境对丢包率影响,以及丢包率随距离变化的概率分布。最后的模型检验结果表明,FVPM比经典Two-Ray、Shadowing模型更加准确地描述了VANET信道特征,对VANET信道研究具有借鉴意义。     

超宽带多径信道的频域建模与仿真

对于超宽带室内多径信道,由于信号传播的成簇特性,一般常采用较多参数描述的修正的S-V模型,而近年来频域自回归（AR）模型以其独有的特点得到大家的重视。针对频域AR模型,着重讨论了在超宽带室内多径信道的计算机仿真中,如何利用零极点分布进行频域AR建模的方法,并结合实例给出了仿真结果,说明了频域AR模型只需要很少的模型参数就可得到一个比较精确的信道描述,是超宽带信道建模比较理想的选择。     

煤矿井巷无线信道相干带宽的计算

基于矿井巷道电磁波传播多波模理论和射线传播理论,建立了煤矿井巷中无线信号的信道模型。综合考虑传播距离、巷道截面尺寸、载波频率、天线极化、天线位置、介质电参数等影响信道相干带宽的重要参数,推导了煤矿井巷中无线信道相干带宽的公式。在宽为4m、高为3m的矩形巷道仿真上述参数对相干带宽的影响,得出了如下结论:煤矿井巷内的相干带宽与频率成正比,与传播距离、巷道截面尺寸和介质电参数成反比,改变天线在巷道截面的位置对相干带宽影响不大。     

基于NS2的无线地下网络信道模型仿真

受限于复杂的地下通讯环境,对无线地下传感器网络的大多研究还停留在理论阶段。主流仿真平台所提供的信道模型都只适用于地上无线通信的仿真,没有合适的模型能反映电磁信号在地下环境能量严重损耗的情况。为解决以上问题,给无线地下网络研究提供仿真实验平台,本文采用双径模型为基础叠加多径瑞利衰落的信道模型,在NS2上加以实现并在实现的平台上进行仿真实验。分析吞吐率和单位有效比特能量消耗这2个性能指标在不同含水量下的变化规律。结果表明,所采用的模型能很好地反映地下通讯情况,验证了双径叠加多瑞利分布模型用于地下环境仿真的可行性,为以后的无线地下网络研究提供参考。      

Analysis of low power wireless links in smart grid environments

Recently, wireless sensor networks (WSNs) have been used in various smart grid applications, including remote power system monitoring and control, power fraud detection, wireless automatic metering, fault diagnostics, demand response, outage detection, overhead transmission line monitoring, load control, and distribution automation. However, harsh smart grid environment propagation characteristics cause great challenges in the reliability of WSN communications in smart grid applications. To this end, the analysis of wireless link reliability and channel characterizations can help network designers to foresee the performance of the deployed WSN for specific smart grid propagation environments, and guide the network engineers to make design decisions for the channel modulation, encoding schemes, output power, and frequency band. This paper presents a detailed analysis of low power wireless link reliability in different smart grid environments, such as 500 kV outdoor substation environment, indoor main power control room, and underground network transformer vaults. Specifically, the proposed analysis aims to evaluate the impact of different sensor radio parameters, such as modulation, encoding, transmission power, packet size, as well as the channel propagation characteristics of different smart grid propagation environments on the performance of the deployed sensor network in smart grid. Overall, the main objective of this paper is to help network designers quantifying the impact of the smart grid propagation environment and sensor radio characteristics on low power wireless link reliability in harsh smart grid environments.     

基于Ptolemy的通用CPM调制器的建模与仿真

连续相位调制（CPM）是一类具有良好频谱利用率和恒包络特性的调制方式，非常适合应用于带宽及功率都受限的无线环境中，然而建模与仿真工具的缺乏大大限制了这类调制方式的应用。文中采用递归的方法，在ADS Ptolemy环境下定制出CPM调制器的核心模块——通用相位产生模块，并结合库中已有模块，实现了对一个通用CPM调制器的建模，最后给出了不同调制参数下CPM信号的频谱及与测试仪表协同仿真的结果。从仿真得出的频谱和仪表观察的波形可以看出，模型具有良好的通用性，适合对各种CPM调制方式的建模和仿真。     

FM radio for indoor localization with spontaneous recalibration

The position of mobile users has become highly important information in pervasive computing environments. Indoor localization systems based on Wi–Fi signal strength fingerprinting techniques are widely used in office buildings with an existing Wi–Fi infrastructure. Our previous work has proposed a solution based on exploitation of a FM signal to deal with environments not covered with Wi–Fi signal or environments with only a single Wi–Fi access point. However, a general problem of indoor wireless positioning systems pertains to signal degradation due to the environmental factors affecting signal propagation. Therefore, in order to maintain a desirable level of localization accuracy, it becomes necessary to perform periodic calibrations of the system, which is either time consuming or requires dedicated equipment and expert knowledge. In this paper, we present a comparison of FM versus Wi–Fi positioning systems and a combination of both systems, exploiting their strengths for indoors positioning. We also address the problem of recalibration by introducing a novel concept of spontaneous recalibration and demonstrate it using the FM localization system. Finally, the results related to device orientation and localization accuracy are discussed.