基于无线传感器网络时钟同步的定位算法研究

讨论了在无线传感器定位节点(文中称为锚节点)位置已知条件下,基于信号到达时间差(TDOA)的时间同步算法。根据所有传感器定位节点彼此之间周期性地广播信号,测量信号到达时间(TOA)来估计时间频率的偏移。当信源发送信号,由于传感器钟差造成的初始TDOA误差可以通过一系列补偿计算来减少误差。在一个加性高斯白噪声模型里,通过卡尔曼滤波提高钟差和频差的估计精度。在此基础上改善标签节点的定位精度。     

基于传播时延测量值的定位技术研究

无线通信系统中的定位需要用到用于表征环境中某一特定位置的物理量测量值,因而要求这些测量值必须具备局部相关性。文章介绍三种基于信号传播时延测量值的无线通信系统定位技术:TOA(到达时间)、TDOA(到达时间差)、RTTOA(往返到达时间),给出每种定位技术的工作原理,分析每种定位技术的优缺点,并对圆形定位(TOA、RTTOA)和双曲线定位(TDOA)的性能进行比较。     

一种改进的TOA/AOA混合定位算法

在蜂窝网络中利用电波到达时间（TOA）对移动台（MS）进行定位估计时，也可利用服务基站（BS）提供较准确电波到达角（AOA）信息，以提高定位性能。为此，本文对Chan提出的电波到达时间差（TDOA）定位算法进行了改进，提出了一种既继承原算法的优点，又增加AOA测量值以提高定位性能的TOA/AOA混合定位算法，分析和仿真结果表明，只要AOA测量值达到一定精度，该算法就能取得比单纯TOA定位法更好的性能。     

基于TOA/TD0A的Ad hoc网络无线定位研究

基于802.11b协议,该文针对Ad hoc网络的特点,探讨适合Ad hoc网络的定位方案.用TOA法获得定位中需要的时间测量值,从而得到各信标台的距离差;并对所得信息进行分解、综合,用TDOA法得到移动台的位置估计.这在多点定位时降低了矩阵的阶数,加快了运算速度.在此基础上,用适合于运动对象的扩展Kalman滤波算法对位置估计进行了优化,使得定位精度更加准确.     

一种在非视距环境中的TDOA/AOA混合定位方法

提出了一种在非视距环境中的到达时间差/到达角混合定位方法。该方法使用了两步卡尔曼滤波。先用卡尔曼滤波器对到达时间测量值进行预处理,以消除TOA测量值中的NLOS误差。再把经过预处理的TOA测量值输入到用卡尔曼滤波器实现的TDOA/AOA混合定位器中进行定位。实验证明,该方法的定位误差性能优于单纯的TDOA定位方法及静态定位方法中泰勒级数展开法的误差性能。     

一种基于卡尔曼滤波的UWB定位算法

文中提出了一种基于卡尔曼滤波的UWB(Ultra Wide Band)定位算法,先用卡尔曼滤波算法对信号的到达时间测量值进行处理,以消除TOA(Time Of Arrival)测量值中的NLOS(Non.Line of Sight)误差,再对经过处理的TOA测量值进行TOA定位,理论分析和计算机仿真实验都表明:该方法的定位误差性能优于单纯的TDOA定位方法,具有较强的实用价值.     

无线传感器网络节点的辅助式定位方法

节点定位是无线传感器网络的一个重要研究内容。针对传感器网络内所有节点物理位置都未知的情况，文中提出一种利用已知的外界参考信号源来对网络内传感器节点进行定位的方法，并建立了基于TDOA、TOA及AOA的定位估计模型。尽管参数测量有误差，但所提出的方法能够提供有效的位置信息及一定的精度，而且基于AOA的定位模型并不增加传感器节点的成本和复杂度。仿真实验结果表明，该方法能对节点进行有效的定位。     

一种TDOA/AOA混合定位算法及其性能分析

在蜂窝移动通信系统中，智能天线阵列的应用使得服务基站（BS）能提供较准确的移动台（MS）电波到达角（AOA）测量值，从而可以用于对移动台的定位估计，文中对文献[1]的电波到达时间差（TDOA）定位算法进行了改进，提出了一种既能继承原算法的优良性能，又可充分利用AOA测量值信息提高定位性能的TDOA/AOA混合定位算法，该算法还具有解析表达式解。仿真结果表明，只要AOA测量值达到一定精度，该算法就能取得比文献[1]的单纯TDOA定位算法更好的性能。     

IMU辅助的TDOA室内定位

室内环境下,当无线信号受到多径和非视距干扰时,传统的基于到达时间差（Time Difference of Arrival,TDOA）的测距模型定位精度不满足室内定位精度要求。为此,提出利用TDOA与低成本的惯性测量单元（Inertial Measurement Unit,IMU）相结合的定位方法。在视距情况下,只有TDOA系统工作,但在信号受到干扰时,利用IMU能够在短时间内提供一个准确的相对位置信息的特性,采用TDOA算法对其进行辅助定位,并利用卡尔曼滤波器对它们的数据进行预处理,最后使用扩展卡尔曼滤波器对数据进行处理融合。实验结果表明,提出的算法比传统的TDOA定位具有更高的精度。     

无线自组网同步实现方案的研究

无线自组网是一种无中心、全分布式的无线分组网络。同所有的分布式系统一样,网络各节点的时钟同步是Ad Hoc网络技术研究中的一个重要问题。本文针对在Ad Hoc网络中实现高精度的时钟同步提出了解决方案,将PTP协议（Precise Time Protocol）引入到Ad Hoc网络中,并在FPGA开发板上加以验证。在本文的设计中使用了软件和硬件相结合的实现方案,充分利用了软件的灵活性和硬件的快速性等特点,实现了PTP节点应有的功能,并且通过硬件获取时间戳使同步精度大大提高。     

Sensor Allocation for Source Localization With Decoupled Range and Bearing Estimation

The source localization accuracy is known to be affected by the placement of sensors. This paper addresses the problem of optimum sensor allocation for decoupled range and bearing estimation, as well as position estimation of an emitting source, under the constraint that all sensors must be confined within a certain area. The source is assumed to be distant and has a curved wavefront when arriving at the sensors. The optimization criterion is the minimum estimation variance defined by the Cramer–Rao lower bound that is derived under Gaussian noise model. A geometric approach is employed to arrive at the optimum geometries and no complicated optimization technique is required. The optimum sensor allocations for time difference of arrival (TDOA), angle of arrival (AOA), and time of arrival (TOA) positionings are derived and their estimation accuracies are contrasted. The optimum geometries belong to the generic structure of a ring array plus some sensors at the center. TDOA and TOA are found to have identical optimum geometries for bearing estimation and yield the same accuracy, although the position localization accuracy of TDOA is known to be worse than that of TOA. Simulations are included to confirm the theoretical development and illustrate the improvement of using an optimum array compared to a random sensor placement array.      

位置指纹定位技术

在室内利用无线网络对移动目标定位,可用的技术有基于波达时间(TOA/TDOA)、基于波达角度(AOA)、以及基于接收信号强度(RSS)的技术等。比较而言,基于接收信号强度(RSS)的位置指纹(LF)技术更适合于复杂的室内环境。对该技术目前的研究情况进行比较全面和详细的介绍。     

The Cramer-Rao bounds of hybrid TOA/RSS and TDOA/RSS location estimation schemes

The Cramer-Rao bound (CRB) on location estimation accuracy of two different hybrid schemes, time of arrival/received signal strength (TOA/RSS) and time difference of arrival/received signal strength (TDOA/RSS), is computed. For short-range networks, the hybrid schemes offer improved accuracy with respect to conventional TOA and TDOA schemes, particularly in the proximity of the reference devices.     

Localization via ultra-wideband radios: a look at positioning aspects for future sensor networks

UWB technology provides an excellent means for wireless positioning due to its high resolution capability in the time domain. Its ability to resolve multipath components makes it possible to obtain accurate location estimates without the need for complex estimation algorithms. In this article, theoretical limits for TOA estimation and TOA-based location estimation for UWB systems have been considered. Due to the complexity of the optimal schemes, suboptimal but practical alternatives have been emphasized. Performance limits for hybrid TOA/SS and TDOA/SS schemes have also been considered. Although the fundamental mechanisms for localization, including AOA-, TOA-, TDOA-, and SS-based methods, apply to all radio air interface, some positioning techniques are favored by UWB-based systems using ultrawide bandwidths.     

A data fusion architecture for enhanced position estimation inwireless networks

The problem of position determination of a mobile user in a wireless network has been studied extensively-particularly in the context of military operations and emergency 911 service in cellular networks. The Global Positioning System (GPS) and network-based angle of arrival (AOA), time difference of arrival (TDOA), and time of arrival (TOA) techniques offer solutions to the position estimation problem. However, each method has limitations that prevent its adoption as a universal solution. Data fusion is a collection of methods and techniques for merging disparate types of information. We present a data fusion model for the enhanced accuracy of position estimates within wireless networks. We illustrate our model with several examples and conclude with recommendations for future research directions     

A Novel Wireless Positioning System for Seamless Internet Connectivity based on the WLAN Infrastructure

Nowadays, several positioning systems are available for outdoor localization, such as the global positioning system (GPS), assisted GPS (A-GPS), and other systems working on cellular networks, for example, time difference of arrival (TDOA), angle of arrival (AOA) and enhanced observed time difference of arrival (E-OTD). However, with the increasing use of mobile computing devices and an expansion of wireless local area networks (WLANs), there is a growing interest in indoor wireless positioning systems based on the WLAN infrastructure. Wireless positioning systems (WPS) based on this infrastructure can be used for indoor localization to determine the position of mobile users. In this paper, we present a novel wireless positioning system, based on the IEEE 802.11b standard, using a novel access point (AP) with two transceivers to improve the performance of WPS in terms of accuracy of the location estimation and to avoid service connectivity interruption. In our proposed system, the novel AP uses the second transceiver to find information from neighboring mobile stations (STAs) in the transmission range and then sends information in advance to associated APs, which estimate the location of the STA based on an internal database. We also use a TDOA technique to estimate the location of the STA when there is not enough information in the database (in this case, the STA moves into a new area where the system has not run the calibration phase). Using TDOA, the database can be generated and updated automatically. The initial results from our simulations show that the proposed system provides higher accuracy of location estimation than other related work and does not interrupt the Internet connection for end users in contrast with other proposed schemes.

Joint TOA/AOA Positioning Scheme with IP-OFDM Systems

In this paper, a new positioning scheme with impulse postfix OFDM (IP-OFDM) systems is proposed for estimating the positional information of a user within a wireless local area network. In the proposed scheme, the channel information is estimated by the IP of the IP-OFDM symbol in the time domain, and then the round-trip time and the angle of signal arrival from a wireless terminal to an access point equipped with a uniform linear antenna array are investigated for time-of-arrival (TOA) and angle-of-arrival (AOA) estimation for a user. The position of the wireless terminal is finally estimated by combining the estimated TOA and AOA information. The performance of the proposed scheme is evaluated with computer simulations, and the error characteristics are analyzed with respect to the TOA error, and the AOA error influence on the positioning error. According to the simulation results, the positioning error of the proposed scheme can be reduced to some centimeters for high signal-to-noise ratio (SNR). The major influence on the positioning error comes from the TOA error in low SNR, while the AOA error has more influence on the positioning error in high SNR.     

Exact and approximate maximum likelihood localization algorithms

Sensors at separate locations measuring either the time difference of arrival (TDOA) or time of arrival (TOA) of the signal from an emitter can determine its position as the intersection of hyperbolae for TDOA and of circles for TOA. Because of measurement noise, the nonlinear localization equations become inconsistent; and the hyperbolae or circles no longer intersect at a single point. It is now necessary to find an emitter position estimate that minimizes its deviations from the true position. Methods that first linearize the equations and then perform gradient searches for the minimum suffer from initial condition sensitivity and convergence difficulty. Starting from the maximum likelihood (ML) function, this paper derives a closed-form approximate solution to the ML equations. When there are three sensors on a straight line, it also gives an exact ML estimate. Simulation experiments have demonstrated that these algorithms are near optimal, attaining the theoretical lower bound for different geometries, and are superior to two other closed form linear estimators.     

TDOA定位系统的无线电监测网工程应用探讨

随着无线电监测事业的发展,在如何扩大无线电监测网的覆盖范围,提升监测能力等方面越来越得到无线电监测人员的重视,文中主要探讨了TDOA无源定位方法在无线电监测网中的应用问题。本文首先从TDOA定位原理入手,介绍了到达时间差估计的相关函数获取法,比较了双曲线方程组的两种求解算法,由此分析TDOA定位的关键技术与定位优点。文中还以云南省无线电监测网为例,从定位流程出发,进行系统设计,探讨TDOA定位系统的工程应用,进而提出能全面提升监测网监测能力的TDOA定位方案。