1、 Report ITU-R SM.2211(06/2011)Comparison of Time-Difference-of-Arrivaland Angle-of-Arrival Methods of Signal GeolocationSM SeriesSpectrum managementii Rep. ITU-R SM.2211 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio
2、-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Rad
3、iocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission o
4、f patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Reports (
5、Also available online at http:/www.itu.int/publ/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related
6、satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management Note: This ITU-R Report was approved
7、in English by the Study Group under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2011 ITU 2011 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R SM.2211 1 REPORT ITU-R SM.2211 Com
8、parison of Time-Difference-of-Arrival and Angle-of-Arrival Methods of Signal Geolocation (2011) Table of Contents Page 1 Introduction 1 2 Overview of TDOA Technology 1 3 Strengths and weaknesses of TDOA compared with traditional AOA 2 4 Summary . 6 5 References 7 1 Introduction This Report compares
9、the strengths and weaknesses of time-difference-of-arrival (TDOA) versus angle-of-arrival (AOA) methods of signal geolocation. While this Report focuses on TDOA, it should be noted that other geolocation techniques exist1. The AOA method determines the angle of arrival of a wave at a measurement poi
10、nt. AOA methods have been commonly used in many direction-finding applications, and have some advantages but also some disadvantages related to antenna requirements, for example. TDOA methods, on the other hand, compute the time difference of arrival of a wave at multiple measurement points, and cal
11、culate the source point based on timing and wave comparisons. TDOA methods have not been widely used in spectrum monitoring, but have become increasingly useful due to the availability of inexpensive and compact computing power, more advanced radio receiver technology, ready availability of data lin
12、ks, and accurate distributed timing signal availability. The paper will provide a short overview of TDOA technology and some comparison of the strengths and weaknesses of the TDOA method compared to more traditional AOA methods. 2 Overview of TDOA Technology The TDOA technique measures the time of a
13、rrival of an RF signal at several points in space and compares the time difference between each receiver. The traditional approach to estimating TDOA is to compute the cross-correlation of a signal arriving at two receivers. The TDOA estimate is the delay which maximizes the cross-correlation functi
14、on. By knowing the location of each receiver, an estimate of the location of the source of the emissions can then be deduced provided all receivers 1Received signal strength (RSS) uses the measured power ratio of a signal at multiple measurement points to compute the source point. RSS is often used
15、for indoor geolocation. Frequency-difference-of-arrival (FDOA) uses the frequency Doppler shift of a moving source (and/or multiple receivers) to calculate the source point. FDOA is often used in conjunction with TDOA for airborne applications. 2 Rep. ITU-R SM.2211 are time synchronized. The complem
16、ent to an AOA systems line-of-bearing (LoB) is a hyperbolic line of constant time difference of arrival referred to as an isochron or line-of-position (LoP). A more complete discussion of TDOA methods is contained in the ITU Handbook on Spectrum Monitoring, Edition 2011, Chapter 4.7.3.2. TDOA method
17、s have been used in radiolocation tasks in some defence applications, and more recently in some specific applications such as location of mobile cellular telephones for emergency responses (fire, ambulance, etc.) The main obstacle in the past to more pervasive civil deployment has been the required
18、nanosecond-level time synchronization. As electromagnetic radiation travels at approximately 30 cm/ns, any significant timing jitter between receivers will translate directly into the dilution of location accuracy. Today, the advent of satellite navigation systems (GPS, Galileo and GLONASS) provides
19、 one such accessible and inexpensive means of maintaining time synchronization. As a result, TDOA-based systems are now available today from several vendors in different countries around the world. 3 Strengths and weaknesses of TDOA compared with traditional AOA To better understand TDOA we present
20、a short comparative survey of its strengths and weaknesses with regard to AOA. It should be noted that TDOA and AOA are complementary techniques for geolocation. A geolocation system that combines both may outperform either alone 1. Also, having an alternate and confirming method of geolocation can
21、be crucial for spectrum enforcement actions. To simplify the discussion, we assume that the TDOA system uses cross-correlation based detection, and that measurement receivers relay sampled signals to a central server for TDOA processing. For most spectrum monitoring applications, this method will be
22、 preferred for both its location performance and flexibility. To further simplify the discussion, we compare TDOA against a correlative interferometer (CI) AOA system. Correlative interferometry is a widely implemented AOA technique in modern radio monitoring. The correlative interferometer is intro
23、duced and discussed in Chapter 4.7.2.2.5 of the ITU Handbook on Spectrum Monitoring, Edition 2011. (NOTE 1 “Chapter” references in Tables 3-1 and 3-2 refer to the ITU Handbook on Spectrum Monitoring, Edition 2011. Numbers in parentheses in Tables refer to References listed in 5.) TABLE 3-1 TDOA stre
24、ngths Simpler antenna requirements The antenna is low cost, low complexity, and may be small in size. TDOA receivers may employ a single simple antenna (such as a monopole or dipole). Unlike AOA systems, the antenna does not require high mechanical tolerances and electrical precision, and does not r
25、equire operational test and measurement for calibration. An added benefit is that the antenna may be made small in size and made inconspicuous. This is important when deploying monitoring systems in historical or architecturally restricted sites or when negotiating siting agreements with 3rdparties.
26、 Simpler siting and calibration requirements Siting requirements are less restrictive than AOA and require little to no calibration. This allows more flexibility in choosing TDOA sites. As a result, TDOA installations are faster to deploy. In urban installations, additional TDOA receivers may be pla
27、ced to overcome the shadowing effects of tall structures. In contrast, AOA sites must be chosen to minimize wave front distortion due to re-emanation from local obstacles, ground reflections, and ground conductivity changes. Some AOA antenna arrays must be calibrated after site installation to minim
28、ize the resulting frequency and direction dependent errors. Antenna array calibration is one of the most important performance limiting issues in AOA 2. AOA siting issues are discussed in further detail in Chapters 4.7.2.3.1.2 and 2.6.1.3. Rep. ITU-R SM.2211 3 TABLE 3-1 (continued) Wideband, low SNR
29、 signals, and short duration signals TDOA performs well for new and emerging signals with complex modulations, wide bandwidths, and short durations. AOA typically performs well on narrow-band signals, but advanced AOA methods can be applied for locating any signals including wideband, complex, and s
30、hort duration. TDOA performance is a strong function of signal bandwidth. AOA performance is roughly independent of signal bandwidth provided that the FFT channel spacing is similar to the signal bandwidth. TDOA performance generally improves as signal bandwidth increases. Both TDOA and AOA perform
31、better on higher SNR signals and with longer integration times. The processing gain from correlation allows TDOA techniques to detect and locate low (and even negative) SNR signals. In addition, the correlation processing gain enables additional TDOA receivers to participate in a geolocation althoug
32、h they may have very low or negative SNR. Basic AOA techniques cannot detect and locate negative SNR signals, and may have issues locating low SNR signals. Advanced AOA techniques such as advanced resolution or data aided correlative AOA techniques (reference DF) can process these signals. Although
33、basic AOA does not benefit from processing gain by signal correlation, it benefits to some degree from the system gain which comes from the use of multiple antenna elements and receiver channels. Geolocation of short duration signals requires coordinated receivers, time synchronized to a fraction of
34、 the inverse signal bandwidth. This capability is fundamental to TDOA systems. In addition, TDOA can geolocate using very short duration measurements on longer duration signals. If AOA antenna elements are commutated, then the required integration duration will be decreased. System complexity The TD
35、OA receiver and antenna are less complex than the typical AOA antenna array and dual or multi-channel receiver. A TDOA receiver requires at least one real time RF channel for gap free processing and highest probability of signal interception(1). This may result in a less complex receiver in simple r
36、adio environments. Advanced TDOA processing techniques are necessary when using a simple receiver in complex radio environments. Efficient methods for time synchronization (GPS) and data link interfaces are readily available. Rejection of uncorrelated noise and interference The correlation processin
37、g used in TDOA can suppress co-channel, time coincident noise and interfering signals that are uncorrelated between sites. This property enables the system to geolocate signals with low signal to interference + noise ratios (low SINR). Time coordinated measurements are made at all receivers. Signals
38、 that are not common to two or more receivers are suppressed. With advanced processing, a TDOA system may geolocate using only correlations with the best observation of the emitted signal. A related application of cross correlation techniques for interference analysis is given in Chapter 4.8.5.5. Ad
39、vanced AOA systems may mitigate the effects of uncorrelated time coincident co-channel interference through the use of correlation with reference signals. Other advanced processing techniques such as MUSIC can be robust to uncorrelated noise and interference. However, such techniques are computation
40、ally expensive and not widely used for spectrum monitoring. Indoor, stadium, and campus geolocation With advanced processing techniques, TDOA may be used to geolocate high bandwidth signals indoors and outdoors at short range ( 100 m on a side) and in high multipath environments 4. AOA systems typic
41、ally do not perform well under these conditions. The challenge of accurate indoor timing synchronization may be overcome with IEEE-1588 compatible Ethernet switches and TDOA receivers. It should be noted that an alternate geolocation technique using received signal strength (RSS), generally outperfo
42、rms TDOA in high multipath, short range environments, especially for narrowband signals. 4 Rep. ITU-R SM.2211 TABLE 3-1 (end) Mitigates coherent co-channel interference (multipath) under certain conditions Both AOA and TDOA methods are compromised by multipath, also known as coherent co-channel inte
43、rference. Each method is impacted differently by the position of the sensor in relation to the multipath reflections. With sufficient signal bandwidth, TDOA is less sensitive to wave front distortion from local obstacles (local multipath). TDOA may require advanced signal processing to resolve locat
44、ion ambiguities caused by distant obstacles (distant multipath). Advanced processing can further filter the correlation pairs used in the TDOA geolocation to improve results under high multipath conditions. With advanced TDOA processing, time resolved multipath between sites can be suppressed 5, res
45、ulting in good performance in dense urban environments(2). Geometry considerations Both TDOA and AOA are most precise when the signal source is centred within a perimeter of measurement sites. Geolocation precision in TDOA is determined by geometric dilution of precision (GDOP), time synchronization
46、 quality, and TDOA estimation quality. The location uncertainty is not directly related to the baseline distance between TDOA receivers 6. This can be advantageous under certain conditions. In contrast, the precision of AOA methods is directly related to the distance between the source and each AOA
47、receiver. AOA position uncertainty is a function of bearing angle uncertainty and distance from the receiver to estimated position. When the source is far outside the perimeter, TDOA approximates a line of position similar to AOAs line of bearing. In this situation, the uncertainty in location and b
48、earing grows similarly with distance for both methods. Well suited to use in RF sensor networks For both TDOA and AOA, more receivers lead to better results through proximity gain and improved statistics. TDOA is well suited to multiple receiver deployments due to its lower complexity, size, power,
49、simpler antenna, and simplified siting requirements. A higher density of remote monitoring stations, referred to as RF sensors above, brings the monitoring receiver closer to the signal of interest. The resulting reduction in path loss, sometimes referred to as proximity gain, improves detection and geolocation performance 7. In addition, the processing gain from correlation in TDOA techniques enables additional sensors to participate in a geolocation although they may have very low or negative SNR. Full offline analysis possible at central server TDOA systems can s
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1