文章資訊


原始檔案

Journal/Conference: Communications Surveys & Tutorials, IEEE

Year:2009

Authors:

Units:

摘要


近年來,有許多類型的室內定位系統(Indoor Positioning Systems, IPSs)不斷地被設計來提供個人或裝置的定位資訊,提供室內的定位資訊能夠加強定位應用程式所涵蓋的範圍,尤其是個人網路(Personal Networks, PNs)這類型的應用程式,個人網路主要的功能是用來串聯起人類周邊不同類型的裝置及其所使用的通訊方式,使其能夠得到充分的整合以滿足使用者的需要。具有位置概念的服務是個人網入中不可或缺的部份,它能夠有效地改善人們的生活品質,在此篇文章中將會探討多種室內定位系統,包含已商業化的定位系統,以及尚在研究階段的定位系統。並且分別就系統的安全性、隱密性、成本、效能、自動化程度、複雜度、使用者喜好程度、商業化程度...等項目對這些室內定位系統進行評估,並從個人網路的角度來比較這些系統的差異。


看完心得

本篇文章對室內定位系統有很完整的研究與整理,作者從個人網路(Personal Network)這角度的觀點去探討IPS系統的需求、架構、既有系統之種類與各個項目之比較,對於我們研究如何將室內與室外之座標軸整合而言,這篇文章提供了我們許多關於室內定位系統的資訊,尤其是針對射頻類型的定位系統的研究內容更是有所幫助。

將可針對射頻類型的定位系統,例如WLAN、RFID與UWB的射頻技術繼續深入了解,例如:Ekahau,以找出適合國科會研究案所使用的定位技術與演算法。

認同之處


懷疑與問題


改進建議




介紹

願景與概念

欲解決的問題

  • The needs of users are highly addressed by the rapid development of integrated networks and services in personal networks (PNs) [7]. Much more attention has been paid to context-aware intelligent services for personal use, which make the persons’ behaviors more convenient and simple. Position information in indoor environments is of course an essential part of the contexts. The uncertainty in dynamic and changing indoor environments is reduced by the availability of position information. And valuable position-based applications and services for users in PNs are enabled by location context offered by IPSs in various places such as homes, offices, sports centers, etc
  • Global positioning system (GPS) [8] is the most widely used satellite-based positioning system, which offers maximum coverage. GPS capability can be added to various devices by adding GPS cards and accessories in these devices, which enable location-based services, such as navigation, tourism, etc. However, GPS can not be deployed for indoor use, because line-of-sight transmission between receivers and satellites is not possible in an indoor environment.
  • Comparing with outdoor, indoor environments are more complex. There are various obstacles, for example, walls, equipment, human beings, influencing the propagation of electromagnetic waves, which lead to multi-path effects. Some interference and noise sources from other wired and wireless networks degrade the accuracy of positioning. The building geometry, the mobility of people and the atmospheric conditions result in multi-path and environmental effects [9]. Considering these issues, IPSs for indoor applications raise new challenges for the future communications systems.
  • In this paper, we systematically introduce and explain various commercially available and research-oriented IPSs.We also discuss the advantages and disadvantages of these IPSs and compare them in terms of the services design for the users in PNs.

研究的內容

解決方案

N/A

研究方法

  • The remainder of this paper is organized as follows.
    • An overview of indoor positioning systems is presented in Section II.
    • In Section III, we describe 17 existing IPSs and classify them into 6 categories according to their main medium used
  • to sense location. The advantages and disadvantages of each of the IPSs are also included.
    • Section IV evaluates each of the IPSs from the viewpoint of PNs. Finally,
    • Section V summarizes our work and presents recommendations for future work.

研究過程

AN OVERVIEW OF INDOOR POSITIONING SYSTEM FOR PERSONAL NETWORKS

What is a Personal Network?

  • To meet the demands of users, personal networks (PNs) [7], interconnect various users’ personal devices at different places such as home, office, vehicle, etc., into one single network, which is transparent to the users, as shown in Figure 1.
Fig.1 Personal Network
Fig.1 Personal Network

Why does a PN require an Indoor Positioning System?

  • In order to meet the user’s needs and offer adaptive and convenient personal services, the location information of the persons and their devices at different places such as home, office, etc., can be provided by the IPSs to any applications in PNs.
  • Although the GPS system can provide location information for users in outdoor environments, GPS can not give accurate positioning estimations for indoor use. Thus, IPS is required to support location-based services when the PN is located in indoor area.
  • Through the use cases, the location context awareness should be implemented in PN services, which offers comfort and efficiency to the end-user.

What is an Indoor Positioning System?

  • An indoor positioning system (IPS) considers only indoor environments such as inside a building. The location of users or their devices in PNs can be determined by an IPS by measuring the location of their mobile devices in an indoor environment.
  • Dempsey [13] defines an IPS as a system that continuously and in real-time can determine the position of something or someone in a physical space such as in a hospital, a gymnasium, a school, etc. [1].
  • An IPS can provide different kinds of location information for location-based applications required by the users.
    • The absolute location information is provided by some IPSs. Before the position can be estimated, the map of the locating area such as an office, a floor, a building, etc., should be available and saved in the IPS. With respect to the map, the absolute position of a target can be measured and displayed. Usually, the absolute position information with respect to the map of a coverage area is offered by indoor positioning tracking systems and indoor navigation systems, because tracking and guiding services need the exact positions of the targets.
    • The relative position information is another kind of outputs offered by the IPSs, which measure the motion of different parts of a target. For example, an IPS which tracks whether the door of a car is closed or not, needs to give the relative position information of the tracked point on the door with respect to the body of the car.
    • The third kind of position information is proximity location information, which specifies the place where a target is. Sometimes, IPSs do not need to provide absolute or relative position information. The position monitoring and tracking systems in hospitals are such examples. The IPS should provide the room where a patient is. Thus location-based applications in hospital can monitor whether the patient enters a correct room for diagnoses or operations.
  • The system architecture of the location-aware computing systems [17] is illustrated in the Figure 2, which includes 3 layers, the location sensing systems, the software location abstractions and the location-based applications.
    • At the location sensing systems layer, different location sensing technologies are used to perform measurements of the location of the users and their devices.
    • The software location abstractions layer converts the data reported from the location sensing systems layer into a required presentation of the locations [18]. An example of the software location abstractions layer is the Java location application programming interface (API) [19]. The Java location API can produce the location information of targets in a standard format and provide access to a database of landmarks....
    • Moreover, the location-based applications, such as navigation and geographical advertising [20], are implemented at the highest layer, which use the location context information measured and calculated by the lower layers.
Fig.2 Location-aware Computing System Architecture
Fig.2 Location-aware Computing System Architecture

Location Technologies, Location Techniques and Location Algorithms

  • As the need of IPS is to enable location-awareness in computing systems, a number of wireless technologies have been developed for indoor location sensing. These technologies include IR, ultra-sound, RFID, WLAN, Bluetooth, UWB, magnetic technology, etc.

  • There are four techniques for indoor position estimations. Triangulation, fingerprinting and vision analysis positioning techniques can provide absolute, relative and proximity position information. The proximity positioning technique can only offer proximity position information.


  • The basic principle of triangulation method for a 2-D position measurement is demonstrated in Figure 3. If the geographical coordinates (xi, yi) of three reference elements A, B, C are known, the absolute position E1 can be calculated by using either the length [10] or the directions [10] of R1, R2 and R3.
    • TOA is the most accurate technique, which can filter out multi-path effects in the indoor situations. However, it is complex to implement [10].
    • RSS and TOA need to know the position of at least three reference elements, such as A, B, C in Figure 3, to estimate the position of an object.
    • AOA only requires two position measuring elements to perform location estimation. However, when the target object to be located is far away, the AOA method may contain some errors, which will result in lower accuracy [21].
Fig.3 Triangulation Positioning Techniques
Fig.3 Triangulation Positioning Techniques

  • Fingerprinting positioning technique is proposed to improve the accuracy of indoor position measurements by using pre-measured location related data. Fingerprinting includes two phases:
    • offline training phase and
    • online position determination phase [50].

    • For example, in an IPS [23], WLAN technology is used in the position estimation. In Figure 4 (a), three access points (APs)are fixed in the different places in an area of 25 m x 25 m. In the offline phase, a laptop equipped with a WLAN card was moved to various sample points to measure the strength of the signals received from different APs, as shown in Figure 4 (a). These pre-measured signal strength values are used to make the fingerprinting maps of the area with respect to different APs. Figure 4 (b) shows the received signal strength from AP1 with respect to various sample points in the IPS working area. In the online position determination phase, based on the fingerprinting maps of the area, the IPS [23] uses the knearest-neighbours location algorithm [22] to locate the target node.

Fig.4(a)
Fig.4(a)
Fig.4(b)
Fig.4(b)

  • The proximity location sensing technique examines the location of a target object with respect to a known position or an area. The proximity location technique needs to fix a number of detectors at the known positions. When a tracked target is detected by a detector, the position of the target is considered to be in the proximity area marked by the detector.
    • As shown in the Figure 5, E2 and E3 are the tracked targets. A proximity area of the detector D is specified and shown by the dotted square in the Figure 5.

Fig.5
Fig.5


  • The vision analysis estimates a location from the image received by one or multiple points [10] as shown in Figure 6. Vision positioning [84]-[87] brings the comfort and efficiency to the users, since no extra tracked devices are needed to be carried by the tracked persons.

INDOOR POSITIONING SYSTEMS FOR PERSONAL NETWORKS

Infrared (IR) Positioning Systems(紅外線定位系統)

<因與研究較無相關故省略跳過>

Ultra-sound Positioning Systems(超音波定位系統)

<因與研究較無相關故省略跳過>

Radio Frequency (RF) Positioning Systems(射頻定位系統)

  • Radio frequency (RF) technologies [49], [50] are used in IPSs, which provide some advantages as follows.
    • Radio waves can travel through walls and human bodies easier, thus the positioning system has a larger coverage area and needs less hardware comparing to other systems.
    • RF-based positioning systems can reuse the existing RF technology systems such as APs in WLAN. Triangulation and fingerprinting techniques are widely used in RF-based positioning systems.

  • Radio Frequency Identification (RFID):The radio frequency identification (RFID) is a means of storing and retrieving data through electromagnetic transmission to an RF compatible integrated circuit [51].
    • The RFID positioning systems are commonly used in complex indoor environments such as office, hospital, etc. RFID as a wireless technology enables flexible and cheap identification of individual person or device [52]. There are two kinds of RFID technologies,
      • passive RFID and
      • active RFID [51]-[53].
    • In this section, positioning systems [54]-[56] based on active RFID technology is explained in detail.
      • WhereNet: WhereNet positioning system [54], [55] is offered by Zebra Technology Company to provide various equipment to support indoor and outdoor real-time positioning.
        • WhereNet IPS uses sophisticated differential time of arrival (DTOA) algorithm [55] to calculate the locations of these tags.
        • WhereNet IPS produces absolute location information of tags, which can be used by a number of location-based applications.
        • WhereNet’s Real Time Locating System (RTLS) [54], [55] consists of the following parts: tags, location antennas, location processors, servers, and Where Ports, which are shown in Figure 11.
        • WhereNet tag III, which is a kind of tags [55] used in WhereNet IPS, is a small and convenient device for users. It has the size of 6.6 cm × 4.4 cm × 2.1 cm and the weight of 53 g. The tags are powered by batteries, which can last up to 7 years depending on the transmission rate of the tags.

external image %25E6%259C%25AA%25E5%2591%25BD%25E5%2590%258D.jpg


  • WLAN: WLAN technology is very popular and has been implemented in public areas such as hospitals, train stations, universities, etc. WLAN-based positioning systems reuse the existing WLAN infrastructures in indoor environments, which lower the cost of indoor positioning. The accuracy of location estimations based on the signal strength of WLAN signals is affected by various elements in indoor environments such as movement and orientation of human body, the overlapping of APs, the nearby tracked mobile devices, walls, doors, etc. The influence of these sources and their impacts have been discussed and analyzed in the literature [57]-[61]. In this section, some WLAN-based IPSs are introduced and discussed.
    • RADAR: RADAR [57] positioning system was proposed by a Microsoft research group as an indoor position tracking system, which uses the existing WLAN technology.
      • RADAR system employs signal strength and signal-to-noise ratio with the triangulation location technique.
      • The multiple nearest neighbors in signal space (NNSS) location algorithm was proposed, which needs a location searching space constructed by a radio propagation model. The RADAR system can provide 2-D absolute position information and thereby enable location-based applications for users.
      • The major advantages of RADAR system are that the existing indoor WLAN infrastructures are reused and it requires few base stations to perform location sensing.
      • the RADAR system suffers from the limitations of RSS positioning methodology [50].
    • Ekahau:The Ekahau positioning system [58] uses the existing indoor WLAN infrastructures to continually monitor the motion of WiFi devices and tags.
      • The triangulation positioning techinique is used for locating any WiFi enabled device in Ekahau positioning system.
      • The received signal strength indication (RSSI) values of the transmitted RF signals recorded at different APs are used to determine the targets.
      • The Ekahau system consists of three parts: site survey, WiFi location tags and positioning engines as shown in Figure 12.
        • Site survey is a software tool, which provides site calibration before the real-time position estimations, and demonstrates the network coverage area, signal strength, SNR, data rate and overlapping of the WLAN network in users social and professional places.
        • Another part is WiFi location tag, which can be attached to any tracked object to enable real-time positioning. The tags transmit RF signals. APs measure signal strength of the received RF signals.
        • The measured data is forwarded via WLAN to the third part, which is a positioning engine, a software tool, offering real-time positioning to any device such as laptop, PDA, etc., using WLAN technology.
      • Combining signal strength and site calibration done by site survey, the positioning engine calculates and displays the locations of WiFi location tags mounted on devices on the map of the local place.
    • COMPAS: The COMPASS system [61] takes advantages of WLAN infrastructures and digital compasses to provide low cost and relative high accurate positioning services to locate a user carrying a WLAN-enabled device. Position estimations are based on the signal strength measured by different APs.
      • The COMPASS system uses fingerprinting location technique and a probabilistic positioning algorithm to determine the location of a user [61].

  • Bluetooth: Bluetooth, the IEEE 802.15.1 standard, is a specification for WPAN. Bluetooth enables a range of 100 m (Bluetooth 2.0 Standards) communication to replace the IR ports mounted on mobile devices. In Bluetooth-based positioning systems [62]- [73], various Bluetooth clusters are formed as infrastructures for positioning.
    • Topaz: The Topaz location system [74] uses Bluetooth technology to locate tags in indoor environments. Topaz can only provide 2-D location information with an error range of around 2 m, which is not sufficient to provide room level accuracy in a multi-obstacle indoor environment.
      • Thus the Topaz system combines the Bluetooth-based positioning with IR-based positioning technique, where IR location techonology is suitable for this aim. Figure 13 shows the system components and the architecture of Topaz indoor location system. In the system, tags are located by numerous Bluetooth and IR enabled APs fixed in different places.

  • Sensor Networks: Sensors are devices exposed to a physical or environmental condition including sound, pressure, temperature, light, etc., and generate proportional outputs. Sensors are typically divided into two kinds: active sensors and passive sensors. Active sensors can interact with the environment such as radars. Passive sensors only receive information from the outside world. The sensor-based positioning systems consist of a large number of sensors fixed in predefined locations [75]. Positioning methods using sensor networks were discussed in [76].
    • Online Person Tracking (OPT) System: Online Person Tracking (OPT) system [77] is designed to provide location information to the context-aware applications in PNs. OPT uses cheap and small sensors called T-mote [78]. The sensors are employed and mounted at fixed positions in the OPT system. These sensors take advantages of RSSI to measure the distance between a transmitter sensor and a receiver sensor. Based on these determined distances, triangulation location technique with a weighted minimum mean square error (W-MMSE) location algorithm [77] is used.
      • OPT system gives a low cost location sensing solution that reuses the sensors deployed at fixed positions in the indoor environments. However, the accuracy of the system varies from 1.5 m to 3.8 m, which is not very accurate to offer room level location information. And installing sensors in fixed locations and maintaining numerous sensors in OPT system is complex.

  • UWB: The RF positioning systems suffer from the multi-path distortion of radio signals reflected by walls in indoor environments. The ultra-wideband (UWB) [79] pulses having a short duration (less than 1 ns) make it possible to filter the reflected signals from the original signal, which offer higher accuracy. Using UWB technology in positioning systems has been a popular way of improving the positioning accuracy [80].
    • Ubisense: The Ubisense Company, which is funded by engineers from AT&T Cambridge, provides a new real-time positioning system based on UWB technology [81].
      • The triangulation locating technique, which takes advantages of both the time difference of arrival (TDOA) and AOA techniques, is employed in the system to provide flexible capability of location sensing.
      • Since Ubisense can measure signal angles and difference in arrival times, and complex indoor environments including walls and doors do not significantly influence the performance [81], the accuracy offered by Ubisense is about tens of centimeters.
      • The Ubisense system consists of three parts:
        • the sensors,
        • the tracked tags and
        • the Ubisense software platform as shown in Figure 15.
      • Comparing with the other RF-based positioning systems, the Ubisense system results in a higher accuracy of about 15 cm in 3-D. The time delay of the position estimations is short and the sensing rate can be up to 20 times per second.
      • The Ubisense sensors are organized into cells. In each cell, there are at least four sensors, which cover an area of up to 400 m2.
      • UWB technology offers various advantages over other positioning technologies used in the IPSs: no line-of-sight requirement, no multipath distortion, less interference, high penetration ability, etc. Thus using UWB technology provides a higher accuracy. Furthermore, the UWB sensors are cheap, which make the positioning system a cost-effective solution. In addition, the large coverage range of each sensor results in that the UWB-based positioning system is scalable.

Magnetic Positioning System(磁感應定位系統)

<因與研究較無相關故省略跳過>

Vision-based Positioning System(視覺影像定位系統)

<因與研究較無相關故省略跳過>

Audible Sound Positioning System(聲音定位系統)

<因與研究較無相關故省略跳過>

研究成果
後續
  • In future research, a combination of different existing communications technologies and location information from different sources should be considered to increase the scalability and availability of location estimation services [97].

後續的工作

N/A
後續的挑戰
N/A

總結

  • None of the technologies can satisfy the system requirements of performance and cost. Instead of using a single medium to estimate the locations of the targets, combining some positioning technologies can improve the quality of positioning services [91].
    • For example, the SVG system [92] combines the advantages of WLAN and UWB based positioning technologies, where WLAN technology can provide positioning services covering large area and UWB can give highly accurate position estimated in some small required areas.



相關資料


相關專案

  • A project named ”Development of Location Centric Networks” [94] is undertaken by Mitsubishi Electric Research Laboratories (MERL) to estimate the location of transceivers in an UWB impulse radio network. Currently, the location system proposed by this project can determine the location of an object with an accuracy of 15 centimetres and cover large area.
  • Another on-going research project is ”Indoor position location technology project” [95] taken by the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia. The aim of the project is to improve the accuracy of location estimation, at the same time, reduce the cost of indoor tracking systems.
  • The third project is a ”Real-Time Location System (RTLS) Healthcare”, which is undertaken by AeroScout Company [96], an industry leader of WiFi-based active RFID solutions. The project focuses on patients care in digital hospitals to propose advanced locating technologies and methods.

相關研究

N/A

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