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1、 河北建筑工程學(xué)院 畢業(yè)設(shè)計(jì)（論文）外文資料翻譯 系別： 電氣系 專業(yè)： 電子信息工程 班級(jí)： 電子092班 姓名： 學(xué)號(hào)： 2009315213 外文出處： Wireless.Sensor.Networks： A.Networking.Perspective 附 件：1、外文原

2、文；2、外文資料翻譯譯文。 指導(dǎo)教師評(píng)語(yǔ)： 簽字： 年 月 日 1、 外文原文（復(fù)印件） 8.3 RANGING TECHNIQUES FOR WIRELESS SENSOR NETWORKS The RF location sensors operating in different environments can measure the RSS, AOA, phase of arrival (POA), TOA, and signature of the delay - power

3、profile as location metrics to estimate the ranging distance [4,7] . The deployment environment (i.e., wireless RF channel) will constrain the accuracy and the performance of each technique. In outdoor open areas, these ranging techniques perform very well. However, as the wireless medium becomes mo

4、re 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 nodes. For this reason, this chapter will focus i

5、ts 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 performance of ranging and localization is important.

6、In addition, range measurements using POA and AOA in indoor and urban areas are unreliable. Therefore, we will focus our discussion on two practical techniques,TOA and RSS.These two ranging techniques, which have been used traditionally in wireless networks, have a great potential for use in WSN loc

7、alization. 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 system bandwidth. This technique ha

8、s been implemented in GPS, PinPoint, WearNet, IEEE 802.15.3, and IEEE 802.15.4 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 and can work with

9、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 required.The RSS ranging has been used for WiFi positioning in systems, for example, Ekaha

10、u, 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 important to

11、 the understanding of the underlying issues in distance estimation, which is an important fundamental building block in WSN localization. 8.3.1 TOA Based Ranging In TOA based ranging, a sensor node measures the distance to another node by estimating the signal propagation delay in free spac

12、e, where radio signals travel at the constant speed of light. Figure 8.3 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 [4,14] . In its presence, for example, short distance line - of - sight

13、(LOS) conditions, accurate 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 [14,22] . These environments introduce several challenges. The first corrupts the TOA estimates

14、 due to the multipath components (MPCs), which 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 estim

15、ates. The third is the absence of the DP due to blockage, 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 clu

16、ttering the indoor environment. In order to analyze the behavior 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 ori

17、ginal signal with different amplitudes, phases, and delays. At the receiver, 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 arrival

18、s. For multipath channels, the impulse respons characterizes the arrival paths, their respective amplitudes, and delays. Mathematically, it can be represented as a summation of all the arriving multipath components or ， （8.1） where Lp is the number of MPCs, and , , and are amplitude, phase

19、, and propagation delay of the kth path, respectively [7,23] . Let and denote the DP amplitude and propagation 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

20、amplitude and propagation delay of the non - direct path (NDP) component given by and, respectively; resulting in a longer distance, where. For the receiver to identify the DP, the ratio of the strongest MPC to that of the DP given by ， （8.2） must be less than the receiver dynamic range k an

21、d the power of the DP must be greater than the receiver sensitivity . These constraints are given by ， （8.3a） , （8.3b） where. In general, ranging and localization accuracy is constrained by the ranging error, which is defined as the difference between the estimated and th

22、e actual distance; that is, . . （8.4） In an indoor environment, the node/MT will experience a varying error behavior depending on the availability of the DP and in the case of its absence on the characteristics of the DP blockage. It is possible to categorize the error based on the follo

23、wing ranging states [24] . In the presence of the DP, both (8.3a) and (8.3b) are met and the distance estimate is very accurate, yielding , （8.5a） where the random bias induced by the multipath, is the bias corresponding to the propagation delay caused by NLOS conditions, and z is a zero -

24、 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 obstacles.When the node experiences sudden blockage of the DP, Eq. (8.3a) is not met and the DP is shadowed by some o

25、bstacle, burying its power under the dynamic range of the receiver. In this situation, the ranging estimate experiences a larger error compared to Eq. (8.5a) . Emphasizing that ranging is achieved through the NDP component, the estimate is then given by , （8.6a） , （8.6b） where is

26、 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

27、 defi ned as , （8.7a） , （8.7b） Figures 8.4 and 8.5 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 var

28、iance of TOA estimation is bounded by the CRLB [25] , （8.8） where 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 obtain

29、ed either by using spread spectrum technology or directly. 8.3.1.1 Direct Spread 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 pseudoran

30、dom (PN) sequence is transmitted and a receiver cross - correlates the received signal with 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

31、 of the processing gain of the correlation at the receiver, DSS ranging systems perform much 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

32、been applied successfully. Results have shown that these high - resolution algorithms can provide improved accuracy [25] . 8.3.1.2 Ultra - Wideband Ranging. A promising alternative to DSS systems is ultra - wideband (UWB) ranging [26] . According to Eq. (8.8) , it is clear that in multipath pro

33、pagation environments, the performance of TOA estimation is inversely related to the system bandwidth. Increasing the system bandwidth (i.e., narrower time - domain pulse) results in higher time resolution and thus better ranging accuracy. As a result, these systems have attracted considerable atten

34、tion in recent years [16,22,26] . For UWB applications, the FCC regulation allocated an unlicensed flat frequency band 3.1 – 10.6 GHz for which there are two proposals: direct sequence (DS) – UWB and multiband orthogonal frequency division multiplexing (MB – OFDM). The former is pulse based, which u

35、tilizes 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 their behaviors in the multipath channel. Sample measurements in indoor office environments are provided in Fig. 8.6 a for 500 - MHz systems, re

36、sembling the MB – OFDM channels and Fig. 8.6 b for 3 - GHz bandwidth, resembling the wider channel of the DS – UWB.The expected TOA between the transmitter and the receiver is 40.5 ns and the estimated arrival with 500 - MHz and 3 - GHz bands are 45.5 and 40.7 ns, respectively. The 5 - and 0.2 - ns

37、errors in TOA estimation results in 1.67 - m and 7 - cm errors, respectively, clearly illustrating the impact of a higher system bandwidth on accuracy. One important observation from these measurement results is that higher bandwidths improve time - domain resolution, which resolves the pulse into

38、 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. This means that the ranging coverage of 500 - MHz systems is larger than that of the 3 - GHz counterpart. Althoug

39、h 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 advance and cannot be mitigated through large bandwidths alone. Understanding of the error behavior in light of

40、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 DP blockage [27,28] . 2、外文資料翻譯譯文 8.3無(wú)線傳感器網(wǎng)絡(luò)的測(cè)距技術(shù) 射頻位置傳感器在不同的環(huán)境中運(yùn)行可測(cè)量RSS，AOA，階段的到來(lái)（POA），TOA，和作為位置的度量估計(jì)距離

41、延遲功率譜 [4,7]。這種部署環(huán)境（例如，無(wú)線射頻信道）將限制精度和每種技術(shù)的性能。在戶外空曠地區(qū)，這些測(cè)距技術(shù)執(zhí)行得很好。然而，隨著無(wú)線介質(zhì)而變得更加復(fù)雜，例如，密集的城市或室內(nèi)環(huán)境中，信道存在嚴(yán)重的多徑傳播和嚴(yán)重的陰影衰落環(huán)境。這一發(fā)現(xiàn)反過(guò)來(lái)說(shuō)明了在一對(duì)節(jié)點(diǎn)之間的距離估計(jì)對(duì)精度和性能的影響。為此，本章將重點(diǎn)討論在室內(nèi)環(huán)境中的測(cè)距和定位。這點(diǎn)很重要，因?yàn)樵S多WSN應(yīng)用程序設(shè)想在崎嶇的地形和雜亂的環(huán)境中部署傳感器，因此，對(duì)測(cè)距和定位性能的信道的影響的理解是很重要的。此外，采用POA和AOA在室內(nèi)和城市地區(qū)進(jìn)行測(cè)距是不可靠的。因此，我們將重點(diǎn)討論兩個(gè)實(shí)用技術(shù)，TOA和RSS。這兩種測(cè)距技術(shù)，已

42、經(jīng)有在無(wú)線網(wǎng)絡(luò)中使用的傳統(tǒng)，它們對(duì)于在無(wú)線傳感器網(wǎng)絡(luò)定位有著很大的潛力。 TOA測(cè)距適合于精確的室內(nèi)定位是因?yàn)樗恍枰苌俚奈墨I(xiàn)并且不需要事先訓(xùn)練。但是，通過(guò)使用這種技術(shù)，硬件會(huì)變得復(fù)雜、精度的多徑條件和系統(tǒng)帶寬會(huì)敏感。這種技術(shù)已經(jīng)被實(shí)施在GPS，PinPoint，wearnet，IEEE 802.15.3，和IEEE 802.15.4系統(tǒng)應(yīng)用上。另一方面，RSS測(cè)量實(shí)現(xiàn)簡(jiǎn)單，對(duì)多徑條件和系統(tǒng)的帶寬不敏感。此外，它不需要任何同步，可以與任何現(xiàn)有的無(wú)線系統(tǒng)協(xié)同工作，可以測(cè)量RSS。然而，對(duì)于準(zhǔn)確的測(cè)量，錨或參考點(diǎn)的高密度是必要的，并且廣泛的培訓(xùn)和昂貴的算法也是必需的。RSS測(cè)距已被用于在WiF

43、i定位系統(tǒng)中，比如Ekahau，Newbury Networks，Pango和Skyhook。 本章首先介紹了基于測(cè)距的TOA和所施加在無(wú)線通道的局限性。然后它與專注于信道行為函數(shù)的RSS的性能進(jìn)行比較。這里所介紹的在測(cè)距基本問(wèn)題上的認(rèn)識(shí)很重要，這是研究無(wú)線傳感器網(wǎng)絡(luò)定位的重要基礎(chǔ)。 8.3.1 TOA測(cè)距 在TOA測(cè)距中，傳感器節(jié)點(diǎn)到另一個(gè)節(jié)點(diǎn)間距離的測(cè)量是通過(guò)自由空間中的信號(hào)傳播時(shí)延來(lái)估計(jì)的，信號(hào)傳播在無(wú)線信號(hào)以光速為恒定速度。圖8.3展示了兩個(gè)節(jié)點(diǎn)間的TOA測(cè)距。 TOA測(cè)距的性能取決于直接路徑的可用性（DP）信號(hào)[ 14 ]。例如，在DP信號(hào)中，短距離的線的視線（LOS）的條件下

44、，準(zhǔn)確的估計(jì)是可行的[ 14 ]。然而，我們面臨的挑戰(zhàn)是，在非LOS（NLOS）表現(xiàn)為網(wǎng)站的特異性和密集多徑環(huán)境的條件下。這些環(huán)境提出了一些挑戰(zhàn)。 圖8.3 傳感器間的TOA測(cè)距 第一個(gè)由于多徑分量（MPC）所引起的腐化的TOA估計(jì)，這是原始信號(hào)延遲和衰減的復(fù)制品，到達(dá)和合并接收器的移動(dòng)估計(jì)。第二個(gè)是由信號(hào)穿過(guò)障礙物引起的傳播延遲，這增加了一個(gè)正向偏置的TOA估計(jì)。第三是由于堵塞的DP的缺失，也被稱為未發(fā)現(xiàn)的直接路徑（UDP）[ 14 ]。這種類型的錯(cuò)誤引起的偏壓通常是比前兩大得多，同時(shí)由于櫥柜，電梯，或通常在室內(nèi)門附近，也會(huì)引起更大出錯(cuò)的概率。 為了分析基于TOA測(cè)距的行為

45、,最好采取一個(gè)受歡迎的模型用來(lái)描述無(wú)線信道。在一個(gè)典型的室內(nèi)環(huán)境中,傳輸信號(hào)將被分散，接收者節(jié)點(diǎn)將收到與原始信號(hào)不同振幅、階段和延誤的副本信號(hào)。在接收機(jī),信號(hào)從所有這些路徑結(jié)合,這種現(xiàn)象稱為多徑。為了了解影響精度的渠道,我們常常借助于一個(gè)用于描述多路徑到達(dá)的模型。這個(gè)模型描述了多路徑通道,脈沖響應(yīng)特征路徑,到達(dá)各自的振幅和延誤。在數(shù)學(xué)上,它可以表示為一個(gè)求和的多路徑組件或到達(dá) ， （8.1） 其中，Lp代表MPCs的數(shù)量，，，分別是振幅，相位以及傳播延遲的路徑。讓和分別表示DP振幅和傳播延遲。傳感器節(jié)點(diǎn)之間的距離和RP或錨是,v是信號(hào)傳播的速度。在DP的缺席中,測(cè)距可以通過(guò),分別

46、由和給出的使用振幅和傳播延遲的非直接的路徑(NDP)組件來(lái)達(dá)到;這導(dǎo)致了長(zhǎng)的距離,其中。為使接收機(jī)識(shí)別DP,最大的MPC與DP信號(hào)的比例如下 ， （8.2） 它必須低于接收機(jī)動(dòng)態(tài)范圍k的能力并且DP必須大于接收機(jī)靈敏度。這些約束條件如下 ， （8.3a） , （8.3b） 其中。 一般來(lái)說(shuō),測(cè)距和定位精度受到測(cè)距誤差的限制,其被定義為估計(jì)和實(shí)際的距離的差異;那就是 （8.4） 在室內(nèi)環(huán)境中,節(jié)點(diǎn)/MT將會(huì)體驗(yàn)一種取決于可用性的DP不同的錯(cuò)誤行為和具有DP堵塞特征對(duì)于的缺席。它可能是基于以下測(cè)距狀態(tài)[24] 的錯(cuò)

47、誤分類。在DP下, (8.3a)和(8.3 b)得到滿足和距離的估計(jì)是非常準(zhǔn)確的。 ， （8.5a） 其中，是在隨機(jī)偏差引起的多路徑, 是由NLOS引起的傳播延時(shí)的偏置, z是一個(gè)零,意味著添加劑測(cè)量噪聲。它已被證明的確是一個(gè)函數(shù)的帶寬和信號(hào)噪聲比(信噪比)[14],而bpd是依賴于介質(zhì)的障礙。當(dāng)節(jié)點(diǎn)經(jīng)歷突然DP,Eq阻塞,(8.3 a)不滿足和DP被一些障礙所阻擋,它將它的能量放在在動(dòng)態(tài)范圍的接收機(jī)。在這種情況下,同Eq(8.5 a)相比，測(cè)距估計(jì)將會(huì)有一個(gè)更大的誤差范圍。其中值得強(qiáng)調(diào)的是，測(cè)距是通過(guò)NDP組件來(lái)實(shí)現(xiàn)的,然后由以下給出 圖8.4 寬帶在200MHz范圍的

48、TOA估計(jì) ， （8.6a） ， （8.6b） 是一個(gè)堵塞性質(zhì)的確定性偏置。與多路徑偏置不同,但類似于由于傳播延遲引起的偏置，取決于系統(tǒng)帶寬的，并且信噪比都有自己的局限性上報(bào)信息[14]。一般來(lái)說(shuō)，這些測(cè)距狀態(tài)可以被定義為 ， （8.7a） ， （8.7b） 圖8.4和8.5提供樣品通道配置文件的這兩個(gè)測(cè)距情況[24]。 基于TOA測(cè)距的性能范圍可以由最大下界(CRLB)確定,它已廣泛地用于研究現(xiàn)有系統(tǒng)。TOA測(cè)距中的估計(jì)由CRLB[25]確定 ， （8.8） 圖8.5 在寬帶為200MHz范圍內(nèi)的NDP的

49、TOA測(cè)距 其中T是信號(hào)的觀測(cè)時(shí)間, 是信噪比、是運(yùn)作的頻率,w是系統(tǒng)帶寬。 在實(shí)踐中,可以通過(guò)測(cè)量獲得長(zhǎng)遠(yuǎn)的到達(dá)時(shí)間一個(gè)寬帶窄脈沖來(lái)獲得TOA,也可以通過(guò)使用或直接擴(kuò)頻技術(shù)。 8.3.1.1直接擴(kuò)頻 一種基于直接擴(kuò)頻(DSS)寬帶信號(hào)的TOA測(cè)距技術(shù)已經(jīng)應(yīng)用于GPS和其他測(cè)距系統(tǒng)許多年了。在這樣一個(gè)系統(tǒng),一個(gè)由已知的偽隨機(jī)(PN)序列編碼的信號(hào)是用來(lái)傳播的和一個(gè)交叉關(guān)聯(lián)的接收器接收信號(hào)的與本地PN序列生成使用滑動(dòng)相關(guān)器或一個(gè)匹配濾波器。發(fā)射機(jī)和接收機(jī)之間的距離是由到達(dá)時(shí)間的第一個(gè)相關(guān)峰確定。因?yàn)樘幚碓鲆娴南嚓P(guān)性在接收機(jī)、DSS測(cè)距系統(tǒng)在同一頻帶的性能遠(yuǎn)遠(yuǎn)好于競(jìng)爭(zhēng)的系統(tǒng)抑制干擾

50、其他無(wú)線電系統(tǒng)操作。在這些有限的系統(tǒng)中,超級(jí)分辨率技術(shù)已經(jīng)成功應(yīng)用于TOA測(cè)距。結(jié)果表明,這些高分辨率算法可以提供改善的準(zhǔn)確性[25]。 8.3.1.2超寬頻帶范圍。 一個(gè)有前途的可以用來(lái)替代DSS系統(tǒng)是超寬帶(UWB)測(cè)距[26]系統(tǒng)。很明顯,根據(jù)Eq. (8.8)，在多徑傳播環(huán)境,TOA測(cè)距的性能估計(jì)是逆相關(guān)系統(tǒng)帶寬。通過(guò)增加系統(tǒng)帶寬(即更窄的時(shí)間-域脈沖)導(dǎo)致更高的時(shí)間分辨率,從而有更好的測(cè)距精度。因此, 近年來(lái)這些系統(tǒng)已經(jīng)引起了相當(dāng)大的關(guān)注。對(duì)于超寬頻應(yīng)用,FCC規(guī)定分配一個(gè)無(wú)照平頻帶3.1 - 10.6 GHz,有兩個(gè)建議:直接序列(DS)——超寬頻和多頻帶正交頻分復(fù)用(MB -

51、 OFDM)。前者是基于脈沖,利用大帶寬,例如,3 GHz,而后者占有帶寬為528 MHz。這些系統(tǒng)的準(zhǔn)確性的評(píng)估可以通過(guò)他們?cè)诙鄰叫诺赖男袨閬?lái)檢查。在室內(nèi)辦公環(huán)境的測(cè)量由圖8.6a的500 - MHz系統(tǒng)提供,類似于MB - OFDM渠道。8.6 b為3 GHz帶寬,類似于更廣泛的DS - UWB信道。在發(fā)射機(jī)和接收機(jī)預(yù)計(jì)到達(dá)時(shí)間是40.5 ns，500 - MHz和3 – GHz的估計(jì)到達(dá)分別是45.5和40.7 ns。5 – 和0.2 - ns錯(cuò)誤在TOA估計(jì)中分別導(dǎo)致1.67米和7 -厘米誤差,這清晰說(shuō)明的影響系統(tǒng)精度更高的帶寬。 一個(gè)重要的發(fā)現(xiàn)是這些測(cè)量結(jié)果是高帶寬的改善時(shí)間-域分辨率,它解決了到各自組件的脈沖,從而提高精度。然而,反過(guò)來(lái)看，高分辨率便意味著較低的能量,這意味著MPC更高機(jī)率的DP堵塞。這意味著范圍覆蓋500 - MHz系統(tǒng)比3 – GHz更廣。雖然超寬頻可以顯著減少過(guò)度傳播延遲引起的多徑,，但是UDP因?yàn)檠舆t變得更加具有挑戰(zhàn)性和屏蔽材料的類型是無(wú)法提前知道的，并且它不能獨(dú)自通過(guò)大帶寬來(lái)減輕。根據(jù)這些主要的誤差貢獻(xiàn)來(lái)理解錯(cuò)誤的行為,對(duì)于實(shí)現(xiàn)有效的超寬頻測(cè)距是很有必要的。特別指出的是，無(wú)線傳感器網(wǎng)絡(luò)定位算法必須分析信道統(tǒng)計(jì)和試著識(shí)別、減輕DP堵塞(27、28]。