Hindawi Publishing Corporation
Journal of Computer Networks and Communications
Volume2013,Article ID185138,12pages
dx.doi/10.1155/2013/185138
Review Article湖北大学专科
Recent Advances in Wireless Indoor Localization Techniques and System
Zahid Farid,Rosdiadee Nordin,and Mahamod Ismail
School of Electrical,Electronics&System Engineering,University Kebangsaan Malaysia(UKM),43600Bangi,
一般出国需要多少钱
Selangor,Malaysia
Correspondence should be addresd to Zahid Farid;
Received17May2013;Accepted17August2013
Academic Editor:Rui Zhang
Copyright©2013Zahid Farid et al.This is an open access article distributed under the Creative Commons Attribution Licen, which permits unrestricted u,distribution,and reproduction in any medium,provided the original work is properly cited.
The advances in localization bad technologies and the increasing importance of ubiquitous computing and context-dependent information have led to a growing business interest in location-bad applications and rvices.Today,most application requirements are locating or real-time tracking of physical belongings inside buildings accurately;thus,the demand for indoor localization rvices has become a key prerequisite in some markets.Moreover,indoor localization technologies address the inadequacy of global positioning system inside a clod environment,like buildings.Bad on this,though,this paper aims to provide the reader with a review of the recent advances in wireless indoor localization techniques and system to deliver a better understanding of state-of-the-art technologies and motivate new rearch efforts in this promising field.For this purpo,existing wireless localization position system and location estimation schemes are reviewed,as we also compare the related techniques and systems along with a conclusion and future trends.
1.Introduction
Location bad rvices(LBSs)[1]are a significant permissive technology and becoming a vital part of life.In this era, especially in wireless communication networks,LBS broadly exists from the short-range communication to the long-range telecommunication networks.LBS refers to the applications that depend on a ur’s location to provide rvices in various categories including navigation,tracking,healthcare,and billing.However,its demand is increasing with new ideas with the advances in the mobile phone market.The core of the LBSs is positioning technologies to find the motion activity of the mobile client.After detection,we pass the statistics to the mobile client on the move at the right time and the right location.So,the positioning technologies have a major influence on the performance,reliability,and privacy of LBSs, systems,and applications[2].
The basic components of LBS are software application (provided by the provider),communication network(mobile network),a content provider,a positioning device,and the end ur’s mobile device.There are veral ways to find the location of a mobile client indoors and outdoors.The most popular technology outdoors is global positioning system (GPS)[1].Location finding refers to a process of obtaining location information of a mobile client(MC)with respect to a t of reference positions within a predefined space. In the literature,many terms are ud for location finding like pos
ition location,geolocation,location nsing,or local-ization[3].Position system is a system arranged in such a way to find or estimate the location of an object.The aims of this paper are to provide the reader with fingerprinting bad wireless indoor localization techniques and systems for indoor applications.The authors hope that this paper will benefit rearchers working in this field,urs,and developers in terms of using the systems and will help them identify the potential rearch shortcoming and future application products in this emerging area.
1.1.Indoor versus Outdoor Positioning.Positioning system can be categorized depending on the target environment as either indoor,outdoor,or mixed type.For localization in an outdoor environment,global navigation satellite systems (GNSS)such as GPS have been ud in a wide range
of applications including tracking and ast management systems;transport navigation and guidance;synchronization of telecommunications networks;geodetic survey.GPS works extremely well in outdoor positioning.Unfortunately,GPS does not perform well in urban canyons,clo to walls, buildings,trees,indoors,and in underground environments as the signal from the GPS satellites is too weak to come across most buildings thus making GPS ineffective for indoor localization[4].
Indoor positioning[5]can be defined as any system that provides a preci position inside of a clod structure,such as a shopping mall,hospitals,airport,a subway,and university campus.By the complex nature of indoor environments, the development of an indoor localization technique is always associated with a t of challenges like smaller dimensions, high none line of sight(NLOS),influence of obstacles like walls,equipment,movement of human beings,doors, and other factors.Multipath effect signals are reflected and attenuated by walls and furniture and noi interference[6]. The challenges result mainly from the influence of obstacles on the propagation of electromagnetic waves.For getting good and accurate results,a positioning system must be able to handle the problems.Beside this,higher accuracy is also required indoors to locate a ur at least in the right room.One of the important aspects indoors is indoor signal property characteristics.A signal strength pattern around an access point interference is shown in Figure1.Some of the current indoor navigation technologies are listed in Figure2.
2.Performance Metrics
The performance criteria associated with localization systems can be classified into the following areas.
2.1.Accuracy.Accuracy(or location error)of a system is the important ur requirement of positioning systems.Accuracy can be reported as an error distance between the estimated location and the actual mobile location.Sometimes,accuracy is also called the area of uncertainty;that is,the higher the accuracy is,the better the system is.
2.2.Responsiveness.The responsiveness determines how quickly the location estimate of a moving target is updated.
2.3.Coverage.The problem of determining the network coverage for a designated area is important when evaluating the effectiveness of a positioning system.Coverage is cloly related to accuracy.Coverage can be categorized as local cov-erage,scalable coverage,and global coverage.Local coverage is a small well-defined,limited area which is not extendable (e.g.,a single room or building).In this ca,the coverage size is ,(m),(m2),or(m3)).Scalable coverage means systems with the ability to increa the area by adding hardware,and global coverage means system performance worldwide or within the desired/specified area.
2.4.Adaptiveness.Environmental influence changes may affect the localization system performance.The ability of
the
Figure1:Signal strength
pattern.
technologies
宝贝我爱你英文Figure2:Indoor navigation technologies. localization system to cope with the changes is called its adaptiveness.A system that is able to adapt to environmental changes can provide better localization accuracy than systems that cannot adapt.An adaptive system can also prevent the need for repeated calibration.
2.5.Scalability.Scalability is a desirable property in almost any system that suggests how well the system performs when it operates with a larger number of location requests and a larger coverage.Poor scalability can result in poor system performance,necessitating the reengineering or duplication of systems.A scalable positioning system should be able to handle large numbers of tags without unnecessary strain. 2.6.Cost and Complexity.The cost gained from a positioning system can ari from the cost of extra infrastructure,addi-tional bandwidth,money,lifetime,weight,energy,and nature of deployed technology.The cost may include installation and survey time during the deployment period.If a positioning system can reu an existing communication infrastructure, some part of infrastructure,equipment,and bandwidth can be saved.The complexity of the signal processin
g and algorithms ud to estimate the location is another issue that needs to be balanced with the performance of positioning
systems.Tradeoffs between the system complexity and the accuracy affect the overall cost of the system.
3.Location Detection Techniques and Location Algorithms
Several different methods are ud for location techniques and algorithms in wireless bad localization.Location detec-tion techniques can be divided into three general categories: proximity,triangulation and scene analysis as shown in Figure3.
3.1.Proximity Detection(Connectivity Bad Positioning). Proximity detection or connectivity bad is one of the simplest positioning methods to implement.It provides sym-bolic relative location information.The position of mobile client is determined by cell of origin(CoO)method with known position and limited range[7].When more than one beacon detects the mobile target,it simply forwards the position nearest where the strongest signal is received. The accuracy of CoO relates to the density of beacon point deployment and signal range.This method is implemented with veral wireless positioning technologies,in particular, the system running infrared radiation(IR),radio freque
ncy identification(RFID)GSM(Cell-ID),bluetooth,and custom radio devices[3].
3.2.Triangulation.Triangulation us the geometric proper-ties of triangles to determine the target location.It has two derivations:lateration and angulation.Techniques bad on the measurement of the propagation-time ,TOA, RTOF,and TDOA)and RSS-bad and received signal pha methods are called lateration technique[8,9].The AOA estimation technique is also called an angulation technique.
3.2.1.Angle Bad Method
Angle of Arrival(AoA)/Angulation.The angle of arrival(AoA) technique determines the angle of arrival of the mobile signal coming from a known location at which it is received at multiple ba stations[3].To estimate position in a2D dimension plane,AoA approach requires only two beacons. To improve accuracy,three beacons or more are ud for location estimation(triangulation).For finding direction, it requires highly directional antennas or antenna arrays. Geometric relationships can then be ud to estimate the location of the interction of two lines of bearing(LoBs) from the known reference points as shown in Figure4.
AOA-bad techniques have their limitations.AOA requires additional antennas with the capacity to
measure the angles which increa the cost of the AOA system imple-mentation.In indoor environments,AOA-bad methods are affected by multipath and NLOS propagation of signals,along with reflections from walls and other objects,so it is not good for indoor implementation.Due to the factors,it can significantly change the direction of signal arrival and thus degrade the accuracy of an indoor AOA-bad positioning system[10
].
Figure3:Location detection bad classification.
Localization
Figure4:Angle-of-arrival positioning method.
3.2.2.Time Bad Methods
Lateration/Trilateration/Multilateration.All three terms (lateration/trilateration/multilateration)refer to a position determined from distance measurements.Lateration or trilateration determines the position of an object by measuring its distance from multiple reference points. Thus,it is also called range measurement technique.In trilateration,the“tri”says that at least three fixed points are necessary to determine a position.Techniques bad on the measurement of the propagation-time ,TOA, RTOF,and TDOA)and RSS-bad and received signal pha methods are called lateration techniques[5,11].
浏览的意思Time of Arrival(ToA)/Time of Flight(ToF).Time of Arrival (ToA)systems are bad on the accurate synchronization of the arrival time of a signal transmitted from a mobile device to veral receiving beacons as shown in Figure5.In ToA, the mobile device transmits a time stamped signal towards receiving beacons.When it is received,the distance between the mobile node and the receiving beacons is calculated from the transmission time delay and the corresponding speed of the signal.
Figure5:Positioning bad on TOA/RTOF measurements.
ToA method needs preci knowledge of the transmission start time(s).Due to this,all receiving beacons along with mobile devices are accurately synchronized with a preci time source.ToA is the most accurate technique ud in indoor environment which can filter out multi-path effects [4].One of the disadvantages of TOA approach is the require-ment for preci time synchronization of all the devices. For time delay measurement,an additional rver will be needed which will increa the cost of the system.Along with this,incread delay can also be propagated by a denr environment,in terms of more people.
Time Difference of Arrival(TDoA).Time Difference of Arrival (TDoA)techniques are measured between multiple pairs of reference points with known locations and u relative time measurements at each receiving node in place of absolute time measurements illustrated in Figure6.TDoA does not need the u of a synchronized time source of transmission in order to resolve timestamps and find the location.With TDoA,a transmission with an unknown starting time is received at various receiving nodes,with only the receivers requiring time synchronization[5].Each difference of arrival time measurement produces a hyperbolic curve in the local-ization space on which the location of the mobile node lies. The interction of multiple hyperbolic curves specifies the possible locations of the client.Localization using TDOA is called multilateration.
Round Trip Time(RTT)/Round-Trip Time of Flight(RToF). It measures the time of flight of the signal pul traveling from the transmitter to the measuring unit and back[3].In TOA,calculating the delay is by using two local clocks in both nodes,while in RTT,it us only one node to record the transmitting and arrival times.Becau of this advantage, this technology solves the problem of synchronization to some extent.One of the drawbacks of this method is range measurements to multiple devices that need to be carried out concutively which may cau precarious latencies for applications where devices move quickly.
3.2.3.Signal Property Bad Method.The majority of wireless localization systems compute the distance to the
positioning
Figure6:Time difference of arrival(source[31]). device using either timing information or angle bad.In both scenarios,they are influenced by the multipath effect. Due to this,the accuracy of estimated location can be decread.The substitute method is to estimate the distance of unknown node to reference node from some ts of mea-suring units using the attenuation of emitted signal strength [3,12].This method can only be possible with radio signals. Mostly wireless localization systems positioning device using properties of the received signal,with received signal strength indicator(RSSI)being the most widely ud signal-related feature.RSSI measurement estimations depend heavily on the environmental interference,and they are also nonlinear. The methods work with the WiFi technology.As this system needs a rver for implementation,this technique can work using only access points which are cheaper than Wi-Fi routers.
3.3.Dead Reckoning(DR).Dead reckoning is the process of estimating known current position bad on last determined position and incrementing that position bad on known or estimated speeds ove
消防器材管理制度r elapd time.An inertial navigation system which provides very accurate directional information us dead reckoning and is very widely applied[13].One of the disadvantages of dead reckoning is that the inaccuracy of the process is cumulative,so the deviation in the position fix grows with time.The reason is that new positions are calculated entirely from previous positions.Rearch has been carried out[13,14]in indoor localization using dead reckoning.
factory是什么意思3.4.Map Matching(MM).This method is bad on the theory of pattern recognition[15]which combines electronic map with locating information to obtain the real position of vehicles in a road network.The u of maps is an efficient alternative to the installation of additional hardware.MM techniques include topological analys,pattern recognition, or advanced techniques such as hierarchical fuzzy inference algorithms.The authors of[16,17]prent a recent rearch work on map matching algorithm bad on indoor and LBS, respectively.
4.Position Systems
This ction prents a review of most prominent state-of-the-art wireless positioning systems as shown in Figure7. Our main focus is put on the radio bad systems especially in wireless local area network(WLAN)positioning(Table1).
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Global positioning system(GPS)is the most popular and worldwide radio navigation system to find the location and the position of the objects especially for outdoor environment [18].However,it does not work well in indoor tups becau the prence of obstacles in the line of sight between the satellite and the receiver and electromagnetic waves is spread and attenuated by the buildings and outdoor obstacles[8]. As people spend most of their time in a clod environment (indoors),GPS is not well suited for indoor positioning tracking(Table3).
Infrared radiation(IR)positioning systems are one of the most common positioning systems that u wireless technology.The spectral region of infrared has been ud in various ways for detection or tracking of objects or persons and available in various wired and wireless devices such as mobile phone,PDAs,and TV[19].Most IR bad wireless devices us line-of-sight(LOS)communication mode between transmitter and receiver without interference from strong light sources[20].The main advantage of using IR bad system devices is being small,lightweight,and easy to carry out.The IR systems undertake an indoor positioning determination in a preci way.Besides the,IR bad indoor positioning systems have some disadvantages like curity and privacy issues.IR signals have some limitations for location determination,like interference from fluorescent light and sunlight[4].Beside this,the IR bad indoor system has expensive system hardware and maintenance cost.
Radio frequency technologies[21]are commonly ud in location position systems becau of some advantages;for example,radio waves can penetrate through obstacles like building walls and human bodies easily.Due to this,the positioning system in RF bad has a larger coverage area and needs less hardware comparing to other systems.In addition, RF bad technologies are further divided into narrow band bad technologies(RFID,bluetooth,WLAN,and FM)and wide band bad technologies(UWB)[19].RADAR[22] by Microsoft Rearch was the first RF bad technique for location determination and ur tracking.
Radio frequency identification(RFID)has been recog-nized as the next promising technology in rving the posi-tioning system for locating objects or people.RFID enables a one way wireless communication using a noncontact and advanced automatic identification technology that us radio signals that put an RFID tag on people or objects,for the purpo of automatic identification,tracking,and manage-ment.Tracking the movements of objects in RFID is done through a network of radio enabled scanning devices over a distance of veral meters.RFID technology is ud in a wide range of applications including people,automobile asmbly industry,warehou management,supply chain network,and asts without the need of line of sight contact[9].
Bluetooth is a wireless standard for wireless personal area networks(WPANs).Almost every WiFi ena
bled mobile device,such as mobile phone or computer,also has an embed-ded bluetooth module.Bluetooth operates in the2.4GHz ISM band.The benefit of using bluetooth for exchanging information between devices is that this technology is of high curity,low cost,low power,and small size.Each bluetooth tag has a unique ID,which can be ud for locating the Bluetooth tag.There are veral recent rearch works dedicated to bluetooth bad localization systems[23,24]. One of the drawbacks of using bluetooth technology in localization is that,in each location finding,it runs the device discovery procedure;due to this,it significantly increas the localization latency(10–30s)and power consumption as well. That is why bluetooth device has a latency unsuitable for real-time positioning applications.
Ultrawideband(UWB)is a radio technology for short-range,high-bandwidth communication holding the proper-ties of strong multipath resistance.Widespread u of UWB in a variety of localization applications requiring higher accuracy20–30cm than achievable through conventional wireless ,radio frequency identification (RFID),wireless local area networks(WLAN),etc.)[25].A typical UWB tup structures stimulus radio wave generator and receivers which capture the propagated and scattered wave.Moreover,UWB hardware is expensive,making it costly for wide-scale u.托福中国官网
The FM radio bad system is popular through the ages. It is widely available across the globe especially in most houholds and in cars.FM radio us the frequency-division multiple access(FDMA)approach which splits the band into a number of parate frequency channels that are ud by stations.FM band ranges and channel paration distances vary in different regions.There are only a few works dedicated to FM radio bad positioning.Recently[26,27]prented rearch that worked on indoor positioning using FM radio signals.
The ZigBee technology is an emerging wireless technol-ogy standard which provides solution for short and medium range communications due to its numerous benefits[28].It is mainly designed for applications which require low-power consumption but do not require large data throughput.The signal range coverage of a ZigBee in indoor environments is typically20m to30m.Distance calculation between two ZigBee nodes is usually carried out from RSSI values.ZigBee is open to interference from a wide range of signal types using the same frequency which can disrupt radio communication becau it operates in the unlicend ISM bands.Hu et al.[7] deployed a ZigBee bad localization algorithm for indoor environments.Beside this,Fern´a ndez et al.[29]propod a way to improve the position determination in an indoor location system(ILS)bad on the power levels(RSSI)of an ad hoc ZigBee network.
中国日报双语版Hybrid positioning systems are defined as systems for determining the location of a mobile client combining v-eral different positioning technologies[30].Many location technologies are ud to estimate the position of mobile client in a space or grid,bad on some mathematical models.The local positioning systems fail to work outdoors,whereas the GPS bad positioning systems do not work inside buildings due to the abnce of line of sight to the satellites.So,there
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