外文翻译--无线传感器网络的测距技术

1、外文翻译-无线传感器网络的测距技术 河北建筑工程学院毕业设计论文外文资料翻译系别 电气系 专业 电子信息工程 班级 电子092班 姓名 王成 学号 2021315213 外文出处 WirelessSensorNetworks ANetworkingPerspective 附 件1外文原文2外文资料翻译译文指导教师评语签字 年 月 日外文原文复印件83 RANGING TECHNIQUES FOR WIRELESS SENSOR NETWORKSThe RF location sensors operating in different environments can measure the

2、RSS AOA phase of arrival POA TOA and signature of the delay - power profile as location metrics to estimate the ranging distance 47 The deployment environment ie wireless RF channel will constrain the accuracy and the performance of each technique In outdoor open areas these ranging techniques perfo

3、rm very well However as the wireless medium becomes more complex for example dense urban or indoor environments the channel suffers from severe multipath propagation and heavy shadow fading conditions This finding in turn impacts the accuracy and performance in estimating the range between a pair of

4、 nodes For this reason this chapter will focus its ranging and localization discussion on indoor environments This is important because many of the WSN applications are envisioned for deployment in rough terrain and cluttered environments and understanding of the impact of the channel on the perform

5、ance of ranging and localization is important In addition range measurements using POA and AOA in indoor and urban areas are unreliable Therefore we will focus our discussion on two practical techniquesTOA and RSSThese two ranging techniques which have been used traditionally in wireless networks ha

6、ve a great potential for use in WSN localization The TOA based ranging is suitable for accurate indoor localization because it only needs a few references and no prior training By using this technique however the hardware is complex and the accuracy is sensitive to the multipath condition and the sy

7、stem bandwidth This technique has been implemented in GPS PinPoint WearNet IEEE 802153 and IEEE 802154 systems The RSS based ranging on the other hand is simple to implement and is insensitive to the multipath condition and the bandwidth of the system In addition it does not need any synchronization

8、 and can work with any existing wireless system that can measure the RSS For accurate ranging however a high density of anchors or reference points is needed and extensive training and computationally expensive algorithms are requiredThe RSS ranging has been used for WiFi positioning in systems for

9、example Ekahau Newbury Networks PanGo and Skyhook This section first introduces TOA based ranging and the limitations imposed by the wireless channel Then it will be compared with the RSS counterpart focusing on the performance as a function of the channel behavior What is introduced here is importa

10、nt to the understanding of the underlying issues in distance estimation which is an important fundamental building block in WSN localization831 TOA Based Ranging In TOA based ranging a sensor node measures the distance to another node by estimating the signal propagation delay in free space where ra

11、dio signals travel at the constant speed of light Figure 83 shows an example of TOA based ranging between two sensors The performance of TOA based ranging depends on the availability of the direct path DP signal 414 In its presence for example short distance line - of - sight LOS conditions accurate

12、 estimates are feasible 14 The challenge however is ranging in non - LOS NLOS conditions which can be characterized as site - specific and dense multipath environments 1422 These environments introduce several challenges The first corrupts the TOA estimates due to the multipath components MPCs which

13、 are delayed and attenuated replicas of the original signal arriving and combining at the receiver shifting the estimate The second is the propagation delay caused by the signal traveling through obstacles which adds a positive bias to the TOA estimates The third is the absence of the DP due to bloc

14、kage also known as undetected direct path UDP 14 The bias imposed by this type of error is usually much larger than the first two and has a significant probability of occurrence due to cabinets elevator shafts or doors that are usually cluttering the indoor environment In order to analyze the behavi

15、or of the TOA based ranging it is best to resort to a popular model used to describe the wireless channel In a typical indoor environment the transmitted signal will be scattered and the receiver node will receive replicas of the original signal with different amplitudes phases and delays At the rec

16、eiver the signals from all these paths combine and this phenomenon is known as multipath In order to understand the impact of the channel on the TOA accuracy we resort to a model typically used to characterize multipath arrivals For multipath channels the impulse respons characterizes the arrival pa

17、ths their respective amplitudes and delays Mathematically it can be represented as a summation of all the arriving multipath components or 81where Lp is the number of MPCs and and are amplitude phase and propagation delay of the kth path respectively 723 Let and denote the DP amplitude and propagati

18、on delay respectively The distance between the sensor node and the RP or anchor is where v is the speed of signal propagation In the absence of the DP ranging can be achieved using the amplitude and propagation delay of the non - direct path NDP component given by and respectively resulting in a lon

19、ger distance where For the receiver to identify the DP the ratio of the strongest MPC to that of the DP given by 82must be less than the receiver dynamic range k and the power of the DP must be greater than the receiver sensitivity These constraints are given by 83a 83bwhere In general ranging and l

20、ocalization accuracy is constrained by the ranging error which is defined as the difference between the estimated and the actual distance that is 84 In an indoor environment the nodeMT will experience a varying error behavior depending on the availability of the DP and in the case of its absence on

21、the characteristics of the DP blockage It is possible to categorize the error based on the following ranging states 24 In the presence of the DP both 83a and 83b are met and the distance estimate is very accurate yielding 85awhere the random bias induced by the multipath is the bias corresponding to

22、 the propagation delay caused by NLOS conditions and z is a zero - mean additive measurement noise It has been shown that is indeed a function of the bandwidth and the signal to noise ratio SNR 14 while bpd is dependant on the medium of the obstaclesWhen the node experiences sudden blockage of the D

23、P Eq 83a is not met and the DP is shadowed by some obstacle burying its power under the dynamic range of the receiver In this situation the ranging estimate experiences a larger error compared to Eq 85a Emphasizing that ranging is achieved through the NDP component the estimate is then given by 86a8

24、6bwhere is a deterministic additive bias representing the nature of the blockage Unlike the multipath biases but similar to the biases induced by the propagation delay the dependence of on the system bandwidth and SNR has its own limitations as reported in Ref 14 Formally these ranging states can be

25、 defi ned as87a87bFigures 84 and 85 provide sample channel profiles of these two ranging situations 24 The performance of TOA based ranging can be determined by the Cramer-Rao lower bound CRLB which has been studied extensively for existing systems The variance of TOA estimation is bounded by the CR

26、LB 25 88where T is the signal observation time is the SNR is the frequency of operation and w is the system bandwidth In practice TOA can be obtained by measuring the arrival time of a wide-band narrow pulse which can be obtained either by using spread spectrum technology or directly 8311 Direct Spr

27、ead Spectrum One TOA estimation technique based on the direct spread spectrum DSS wideband signal has been used in GPS and other ranging systems for many years In such a system a signal coded by a known pseudorandom PN sequence is transmitted and a receiver cross - correlates the received signal wit

28、h a locally generated PN sequence using a sliding correlator or a matched filter The distance between the transmitter and the receiver is determined from the arrival time of the first correlation peak Because of the processing gain of the correlation at the receiver DSS ranging systems perform much

29、better than competing systems in suppressing interference from other radio systems operating in the same frequency band In these band - limited systems super- resolution techniques for TOA estimation have been applied successfully Results have shown that these high - resolution algorithms can provid

30、e improved accuracy 25 8312 Ultra - Wideband RangingA promising alternative to DSS systems is ultra - wideband UWB ranging 26 According to Eq 88 it is clear that in multipath propagation environments the performance of TOA estimation is inversely related to the system bandwidth Increasing the system

31、 bandwidth ie narrower time - domain pulse results in higher time resolution and thus better ranging accuracy As a result these systems have attracted considerable attention in recent years 162226 For UWB applications the FCC regulation allocated an unlicensed flat frequency band 31 106 GHz for whic

32、h there are two proposals direct sequence DS UWB and multiband orthogonal frequency division multiplexing MB OFDM The former is pulse based which utilizes large bandwidths for example 3 GHz while the latter occupies a bandwidth of 528 MHz The accuracy of these systems can be evaluated by examining t

33、heir behaviors in the multipath channel Sample measurements in indoor office environments are provided in Fig 86 a for 500 - MHz systems resembling the MB OFDM channels and Fig 86 b for 3 - GHz bandwidth resembling the wider channel of the DS UWBThe expected TOA between the transmitter and the recei

34、ver is 405 ns and the estimated arrival with 500 - MHz and 3 - GHz bands are 455 and 407 ns respectively The 5 - and 02 - ns errors in TOA estimation results in 167 - m and 7 - cm errors respectively clearly illustrating the impact of a higher system bandwidth on accuracy One important observation f

35、rom these measurement results is that higher bandwidths improve time - domain resolution which resolves the pulse into respective components resulting in improved accuracy The trade - off however is that higher resolution implies lower energy per MPC which means a higher probability of DP blockage T

36、his means that the ranging coverage of 500 - MHz systems is larger than that of the 3 - GHz counterpart Although UWB can reduce multipath significantly combating the excess propagation delay and UDP becomes challenging because the amount of delay and the type of blocking material are not known in ad

37、vance and cannot be mitigated through large bandwidths alone Understanding of the error behavior in light of these major error contributors is necessary to enable effective UWB ranging Specifi cally WSN localization algorithms must analyze the channel statistics and attempt to identify and mitigate

38、DP blockage 2728 2外文资料翻译译文83无线传感器网络的测距技术射频位置传感器在不同的环境中运行可测量RSSAOA阶段的到来POATOA和作为位置的度量估计距离延迟功率谱 47这种部署环境例如无线射频信道将限制精度和每种技术的性能在户外空旷地区这些测距技术执行得很好然而随着无线介质而变得更加复杂例如密集的城市或室内环境中信道存在严重的多径传播和严重的阴影衰落环境这一发现反过来说明了在一对节点之间的距离估计对精度和性能的影响为此本章将重点讨论在室内环境中的测距和定位这点很重要因为许多WSN应用程序设想在崎岖的地形和杂乱的环境中部署传感器因此对测距和定位性能的信道的影响的理解是很重

39、要的此外采用POA和AOA在室内和城市地区进行测距是不可靠的因此我们将重点讨论两个实用技术TOA和RSS这两种测距技术已经有在无线网络中使用的传统它们对于在无线传感器网络定位有着很大的潜力TOA测距适合于精确的室内定位是因为它只需要很少的文献并且不需要事先训练但是通过使用这种技术硬件会变得复杂精度的多径条件和系统带宽会敏感这种技术已经被实施在GPSPinPointwearnetIEEE 802153和IEEE 802154系统应用上另一方面RSS测量实现简单对多径条件和系统的带宽不敏感此外它不需要任何同步可以与任何现有的无线系统协同工作可以测量RSS然而对于准确的测量锚或参考点的高密度是必要的

40、并且广泛的培训和昂贵的算法也是必需的RSS测距已被用于在WiFi定位系统中比方EkahauNewbury NetworksPango和Skyhook本章首先介绍了基于测距的TOA和所施加在无线通道的局限性然后它与专注于信道行为函数的RSS的性能进行比拟这里所介绍的在测距根本问题上的认识很重要这是研究无线传感器网络定位的重要根底831 TOA测距在TOA测距中传感器节点到另一个节点间距离的测量是通过自由空间中的信号传播时延来估计的信号传播在无线信号以光速为恒定速度图83展示了两个节点间的TOA测距 TOA测距的性能取决于直接路径的可用性DP信号 14 例如在DP信号中短距离的线的视线LOS的条件

41、下准确的估计是可行的 14 然而我们面临的挑战是在非LOSNLOS表现为网站的特异性和密集多径环境的条件下这些环境提出了一些挑战图83 传感器间的TOA测距第一个由于多径分量MPC腐化的TOA估计这是原始信号延迟和衰减的复制品到达和合并接收器的移动估计是由信号穿过障碍物引起的传播延迟这增加了一个正向偏置的TOA估计第三是由于堵塞的DP的缺失也被称为未发现的直接路径UDP 14 这种类型的错误偏压通常是比前两大得多由于橱柜电梯或通常在室内门为了分析基于的行为最好采取一个受欢送的模型用来描述无线信道在一个典型的室内环境中传输信号将被分散接收者节点将收到与原始信号不同振幅阶段和延误副本在接收机信号从所有这些路径结合这种现象称为多径为了了解影响精度渠道我们助于一个用于描述多路径到达模型多路径通道脉冲响应特征路径到达各自的振幅和延误在数学上它可以表示为一个求和的多路径组件或到达其中Lp代表MPCs的数量分别是振幅相位以及传播延迟的路径让和表示DP振幅和传播延迟传感器节点之间的距离和RP或锚是v是信号传播的速度在的缺席测距可以通过分别和给出使用振幅和传播延迟的非直接的路径 NDP 组件这导致长的距离为接收机识别DP最的MPCDP信号的比例如下82它必须低于接收机动态范围k的能力DP必须大于接收机灵敏度这些约束条