基于射频干涉的无线传感器网络目标节点定位与跟踪

Wireless sensor network (WSN) enables smart environments for cooperative sensing, distributed sampling and real-time processing. Localization is fundamental in WSNs,as the data collected by sensors should be associated with the locations where they carry out the measurements. It is a great challenge with respect to the physical layer of WSNs to accomplish accurate localization with low cost under harsh multipath environments. This project aims to design novel radio interferometric positioning systems. To be more specific, three aspects will be investigated in this project: 1) mitigate multipath effects. The multipath effects in harsh environments impose lots of difficulties on accurate ranging. We would explore how to design optimal signal waveforms to facilitate ranging, and make use of frequency, time and space diversities to be robust to multipath effects. 2) joint localization and synchronization. In phase, time, or frequency-based localization systems, synchronization is tightly coupled with localization. Joint localization and synchronization methods will be explored to relax stringent synchronization requirements of WSNs. 3) phase ambiguity problem. Due to the wrapping effect (phase ambiguity) of the phase estimate, the range estimate based on the estimated phase faces the integer ambiguity problem. It can be formulated as a nonlinear model with unknown real and integer parameters. This problem is theoretically difficult. We would investigate possible methods to efficiently solve it, in return to enrich the toolbox solving the similar problems. In general, this project focuses on the design of novel radio interferometric positioning systems, and elegantly solves the above problems using signal processing tools. It would provide solid theoretical fundamentals and feasible frameworks for localization in WSNs.

无线传感器网络(Wireless Sensor Network, WSN)的目标节点定位与跟踪是构建兼具分布式数据采集、协作感知和实时信息处理系统的关键。如何在复杂的多径环境中，实现低成本、高精度的定位与跟踪，对WSN物理层设计提出了新的挑战。本项目以提高定位与跟踪系统的精确度，降低系统的复杂度为目标，围绕射频干涉用于定位与跟踪系统存在的多径干扰，缺乏有效同步机制以及相位模糊的基本问题，从信号处理和信息融合的角度，探索射频干涉信号的收发新机制，同步定位联合估计的新方法以及非线性模型的近似优化求解。重点开展三方面研究内容：1）探索抗多径干扰的射频干涉信号设计；2）提出具有普适性的目标位置与时钟同步参数联合估计框架；3）解决基于整数与实数混合型非线性模型的定位释疑。为实现具有应用价值的射频干涉定位跟踪系统提供理论基础和科学方法。

目标节点的定位跟踪是无线传感器网络所提供的重要服务之一。目标节点的位置信息对于数据融合、网络拓扑、路由设计以及其他各类基于位置的应用服务来说必不可少。在GPS信号不可得、多径干扰严重的复杂环境中，如何实现低成本、高精度的定位与跟踪，是众所周知的一大挑战。本项目从信号处理和信息融合的角度入手，针对多径干扰，设计射频干涉信号的收发新机制和相位测距算法；针对不同的网络同步要求，研究同步定位联合估计的新算法；针对移动目标节点，提出射频干涉定位跟踪方案。主要的创新性成果如下：.1.双谐波射频干涉定位系统：在多个同步锚节点帮助下，提出基于双谐波射频干涉的相位测距方法，设计双谐波之间的频率间隔小于信道相干带宽，使得多径衰落可简化为平衰落，有效应对多径干扰；通过测量双谐波之间的相位差得到与距离和时钟相关的信息，提出了联合同步定位的估计算法；定位系统可分辨距离的增加简化了相位模糊问题求解。.2.基于移动锚节点的双谐波射频干涉定位系统：使用单个移动锚节点模拟多个静态锚节点的功能，降低了定位系统的同步要求；欠采样技术的采用进一步简化了双谐波射频干涉定位系统接收机结构，增加了信噪比，提高了定位精度；由多目标时钟差异引起的谐波频率偏移，通过信号子空间方法被估计出来并加以校正。.3.基于双谐波射频干涉的全异步网络目标定位跟踪：针对全异步网络，不对系统做任何同步假设，利用参考锚节点接收双谐波信号测量时钟参数进行校正；或者利用节点的移动性，将不同时刻接收到的信号相位做差分运算，以消除时钟影响；提出的联合同步跟踪算法，能对移动目标进行高精度跟踪。

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