1、 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： 2009315213 外文出处： Wireless.Sensor.Networks： A.Networking.Perspective 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 1、 外文原文（复印件） 8.3 RANGING TECHNIQUES FOR WIRELESS SENSOR NETWORKS The RF location sensors operating in different envir
2、onments can measure the RSS, AOA, phase of arrival (POA), TOA, and signature of the delay - power 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 op
3、en areas, these ranging techniques perform 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 perform
4、ance in estimating the range between a pair of 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 understa
5、nding of the impact of the channel on the performance 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 techniques,TOA and RSS.These two ranging techniques, wh
6、ich have been used traditionally in wireless networks, have 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 th
7、e accuracy is sensitive to the multipath condition and the system bandwidth. This technique has 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
8、 bandwidth of the system. In addition, it does not need any synchronization 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
9、are required.The RSS ranging has been used for WiFi positioning in systems, for 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 th
10、e performance as a function of the channel behavior. What is introduced here is important to 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 t
11、he distance to another node by estimating the signal propagation delay in free space, 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 (
12、DP) signal 4,14 . In its presence, for example, short distance line - of - sight (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 envi
13、ronments introduce several challenges. The first corrupts the TOA estimates 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
14、 traveling through obstacles, which adds a positive bias to the TOA estimates. 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 occ
15、urrence due to cabinets, elevator shafts, or doors that are usually cluttering 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 wil
16、l be scattered and the receiver node will receive replicas of the original 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
