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Mobile Phone Tracking

ContentsArticles

Mobile phone tracking 1Multilateration 4Real-time locating system 12Location-based service 19Local positioning system 24

ReferencesArticle Sources and Contributors 26Image Sources, Licenses and Contributors 27

Article LicensesLicense 28

Mobile phone tracking 1

Mobile phone trackingMobile phone tracking refers to the attaining of the current position of a mobile phone, stationary or moving.Localization may occur either via multilateration of radio signals between (several) radio towers of the network andthe phone, or simply via GPS. To locate the phone using multilateration of radio signals, it must emit at least theroaming signal to contact the next nearby antenna tower, but the process does not require an active call. GSM isbased on the signal strength to nearby antenna masts.[1]

Mobile positioning, which includes location based service that discloses the actual coordinates of a mobile phonebearer, is a technology used by telecommunication companies to approximate where a mobile phone, and therebyalso its user (bearer), temporarily resides. The more properly applied term locating refers to the purpose rather than apositioning process. Such service is offered as an option of the class of location-based services (LBS).[2]

TechnologyThe technology of locating is based on measuring power levels and antenna patterns and uses the concept that amobile phone always communicates wirelessly with one of the closest base stations, so if you know which basestation the phone communicates with, you know that the phone is close to the respective base station.Advanced systems determine the sector in which the mobile phone resides and roughly estimate also the distance tothe base station. Further approximation can be done by interpolating signals between adjacent antenna towers.Qualified services may achieve a precision of down to 50 meters in urban areas where mobile traffic and density ofantenna towers (base stations) is sufficiently high. Rural and desolate areas may see miles between base stations andtherefore determine locations less precisely.GSM localization is the use of multilateration to determine the location of GSM mobile phones, usually with theintent to locate the user.[2]

Localization-Based Systems can be broadly divided into:• Network-based• Handset-based• SIM-based• Hybrid

Network-basedNetwork-based techniques utilize the service provider's network infrastructure to identify the location of the handset.The advantage of network-based techniques (from mobile operator's point of view) is that they can be implementednon-intrusively, without affecting the handsets.The accuracy of network-based techniques varies, with cell identification as the least accurate and triangulation asmoderately accurate, and newer "Forward Link" timing methods as the most accurate. The accuracy ofnetwork-based techniques is both dependent on the concentration of base station cells, with urban environmentsachieving the highest possible accuracy, and the implementation of the most current timing methods.One of the key challenges of network-based techniques is the requirement to work closely with the service provider,as it entails the installation of hardware and software within the operator's infrastructure. Often, a legislativeframework, such as E911, would need to be in place to compel the cooperation of the service provider as well as tosafeguard the privacy of the information.

Mobile phone tracking 2

Handset-basedHandset-based technology requires the installation of client software on the handset to determine its location. Thistechnique determines the location of the handset by computing its location by cell identification, signal strengths ofthe home and neighboring cells, which is continuously sent to the carrier. In addition, if the handset is also equippedwith GPS then significantly more precise location information is then sent from the handset to the carrier.The key disadvantage of this technique (from mobile operator's point of view) is the necessity of installing softwareon the handset. It requires the active cooperation of the mobile subscriber as well as software that must be able tohandle the different operating systems of the handsets. Typically, smart phones, such as one based on Symbian,Windows Mobile, Windows Phone, BlackBerry OS, iPhone, or Android, would be able to run such software.One proposed work-around is the installation of embedded hardware or software on the handset by themanufacturers, e.g. E-OTD. This avenue has not made significant headway, due to the difficulty of convincingdifferent manufacturers to cooperate on a common mechanism and to address the cost issue. Another difficultywould be to address the issue of foreign handsets that are roaming in the network.

SIM-basedUsing the SIM in GSM and UMTS handsets, it is possible to obtain raw radio measurements from the handset.[3] [4]

The measurements that are available can include the serving Cell-ID, round trip time and signal strength. The type ofinformation obtained via the SIM can differ from what is available from the handset. For example, it may not bepossible to obtain any raw measurements from the handset directly, yet still obtain measurements via the SIM.

HybridHybrid positioning systems use a combination of network-based and handset-based technologies for locationdetermination. One example would be some modes of Assisted GPS, which can both use GPS and networkinformation to compute the location. Both types of data are thus used by the telephone to make the location moreaccurate (ie A-GPS). Alternatively tracking with both systems can also occur by having the phone attain hisGPS-location directly from the satellites, and then having the information sent via the network to the person that istrying to locate the telephone. Services allowing such cellphone tracking are Mologogo, instaMapper, Buddyway andGoogle Latitude.[5] [6] [7]

Operational purposeIn order to route calls to a phone the cell towers listen for a signal sent from the phone and negotiate which tower isbest able to communicate with the phone. As the phone changes location, the antenna towers monitor the signal andthe phone is roamed to an adjacent tower as appropriate.By comparing the relative signal strength from multiple antenna towers a general location of a phone can be roughlydetermined. Other means is the antenna pattern that supports angular determination and phase discrimination.Newer phones may also allow the tracking of the phone even when turned on and not active in a telephone call-. Thisresults from the roaming procedures that perform hand over of the phone from one base station to another.[8]

Mobile phone tracking 3

Bearer interestA phone's location can be uploaded to a common web site where one's "friends and family" can view one's lastreported position. Newer phones may have built-in GPS receivers which could be used in a similar fashion, but withmuch higher accuracy.

PrivacyLocating or positioning touches upon delicate privacy issues, since it enables someone to check where a person iswithout the person's consent. Strict ethics and security measures are strongly recommended for services that employpositioning, and the user must give an informed, explicit consent to a service provider before the service providercan compute positioning data from the user's mobile phone.In Europe, where most countries have a constitutional guarantee on the secrecy of correspondence, location dataobtained from mobile phone networks is usually given the same protection as the communication itself. The UnitedStates however has no explicit constitutional guarantee on the privacy of telecommunications, so use of location datais limited by law.With tolling systems, as in Germany, the locating of vehicles is equally sensitive to the constitutional guarantee onthe secrecy of correspondence and thus any further use of tolling information beyond deducting the road fee isprohibited. Even obviously criminal intent may not be inferred by such means, although such a use is technicallypossible.Officially, the authorities (like the police) can obtain permission to position phones in emergency cases where people(including criminals) are missing. The U.S. Justice Department has argued that current laws allow them to tracksuspects without having probable cause to suspect a law is being violated.[9] In some instances law enforcement mayeven access a mobile phone's internal microphone to eavesdrop on local conversations while the phone is switchedoff.[10]

The Electronic Frontier Foundation is tracking some cases, including USA v. Pen Register [11], regardinggovernment tracking of individuals.[12]

Some "Free" tracking services allow the cellular telephone number being tracked to be added to telemarketers' lists.China has proposed using this technology to track commuting patterns of Beijing city residents.[13]

References[1] "Tracking a suspect by mobile phone: Tracking SIM and handset" (http:/ / news. bbc. co. uk/ 1/ hi/ technology/ 4738219. stm). BBC News.

2005-08-03. . Retrieved 2010-01-02.[2] "Location Based Services for Mobiles: Technologies and Standards“ (http:/ / to. swang. googlepages. com/

ICC2008LBSforMobilessimplifiedR2. pdf), Shu Wang, Jungwon Min and Byung K. Yi, IEEE International Conference on Communication(ICC) 2008 (http:/ / www. ieee-icc. org/ ), Beijing, China

[3] ETSI TS 102 223 V9.1.0 SIM standard[4] Vodafone Local Zone (http:/ / pcworld. co. nz/ pcworld/ pcw. nsf/ mobwire/ F41D663EAD41BC01CC2574B000133BB3) PC World.[5] InstaMapper (http:/ / www. instamapper. com/ )[6] Mologogo (http:/ / www. mologogo. com/ )[7] Buddyway (http:/ / www. buddyway. com/ )[8] "Roving Bug in Cell Phones Used By FBI to Eavesdrop on Syndicate" (http:/ / www. thechicagosyndicate. com/ 2006/ 12/

roving-bug-in-cell-phones-used-by-fbi. html). The Chicago Syndicate. .[9] Ryan Singel (May 8, 2006). "Cell-Phone Tracking: Laws Needed" (http:/ / www. wired. com/ politics/ security/ news/ 2006/ 05/ 70829).

Wired. .[10] "FBI taps cell phone mic as eavesdropping tool" (http:/ / news. cnet. com/ 2100-1029_3-6140191. html). Cnet. December 1, 2006. .

Retrieved June 24, 2010. "Kaplan's opinion said that the eavesdropping technique "functioned whether the phone was powered on or off."Some handsets can't be fully powered down without removing the battery; for instance, some Nokia models will wake up when turned off if analarm is set."

[11] http:/ / www. eff. org/ legal/ cases/ USA_v_PenRegister/[12] Cell Tracking (http:/ / www. eff. org/ issues/ cell-tracking) Electronic Frontier Foundation

Mobile phone tracking 4

[13] Cecilia Kang (March 3, 2011). "China plans to track cellphone users, sparking human rights concerns" (http:/ / voices. washingtonpost. com/posttech/ 2011/ 03/ china_said_it_may_begin. html). The Washington Post. .

External links• privacyrights.org (http:/ / www. privacyrights. org/ fs/ fs2b-cellprivacy. htm#5) - Protecting Your Privacy in the

Age of the Super-Phone• Cell Reception (http:/ / www. cellreception. com/ towers/ ) - Google maps API to locate cell towers in the United

States• Cellphone Tracking Powers on Request (http:/ / www. washingtonpost. com/ wp-dyn/ content/ article/ 2007/ 11/

22/ AR2007112201444. html?hpid=topnews), washingtonpost.com• GSM Localization on Mobile Phones (http:/ / www. cs. toronto. edu/ ~walex/ papers/

are_gsm_phones_the_solution_for_localization_wmcsa2006. html)• OpenCellID: An OpenSource CellID database (http:/ / www. opencellid. org)• J2ME and Location-Based Services (http:/ / developers. sun. com/ techtopics/ mobility/ apis/ articles/ location/ )• Location API for J2ME (http:/ / www-users. cs. umn. edu/ ~czhou/ docs/ jsr179/ lapi/ )• openBmap: Map and tools for a free and open Cell ID database in GPL and Creative Common Licence (http:/ /

www. openBmap. org)

MultilaterationMultilateration, also known as hyperbolic positioning, is the process of locating an object by accurately computingthe time difference of arrival (TDOA) of a signal emitted from that object to three or more receivers. It also refers tothe case of locating a receiver by measuring the TDOA of a signal transmitted from three or more synchronisedtransmitters.Though based on the concept of triangulation, multilateration should not be confused with trilateration, which usesdistances or absolute measurements of time-of-flight from three or more sites, or with triangulation, which uses abaseline and at least two angles measured e.g. with receiver antenna diversity and phase comparison.

PrincipleMultilateration is commonly used in civil and military surveillance applications to accurately locate an aircraft,vehicle or stationary emitter by measuring the time difference of arrival (TDOA) of a signal from the emitter at threeor more receiver sites.If a pulse is emitted from a platform, it will arrive at slightly different times at two spatially separated receiver sites,the TDOA being due to the different distances of each receiver from the platform. In fact, for given locations of thetwo receivers, a whole set of emitter locations would give the same measurement of TDOA. Given two receiverlocations and a known TDOA, the locus of possible emitter locations is a one half of a two-sheeted hyperboloid.

Multilateration 5

Fig1. A two-sheeted hyperboloid

In simple terms, with two receivers at known locations, an emitter canbe located onto a hyperboloid[1] . Note that the receivers do not need toknow the absolute time at which the pulse was transmitted - only thetime difference is needed.

Consider now a third receiver at a third location. This would provide asecond TDOA measurement and hence locate the emitter on a secondhyperboloid. The intersection of these two hyperboloids describes acurve on which the emitter lies.If a fourth receiver is now introduced, a third TDOA measurement isavailable and the intersection of the resulting third hyperboloid withthe curve already found with the other three receivers defines a uniquepoint in space. The emitter's location is therefore fully determined in3D.In practice, errors in the measurement of the time of arrival of pulsesmean that enhanced accuracy can be obtained with more than four receivers. In general, N receivers provide N − 1hyperboloids. When there are N > 4 receivers, the N − 1 hyperboloids should, assuming a perfect model andmeasurements, intersect on a single point. In reality, the surfaces rarely intersect, because of various errors. In thiscase, the location problem can be posed as an optimization problem and solved using, for example, a least squaresmethod or an extended Kalman filter.

Additionally, the TDOA of multiple transmitted pulses from the emitter can be averaged to improve accuracy.

Reciprocal case: locating a receiver from multiple transmitter sitesMultilateration can also be used by a single receiver to locate itself, by measuring the TDOA of signals emitted fromthree or more synchronised transmitters at known locations. This can be used by navigation systems, an examplebeing the British DECCA navigation system, developed during World War II, which used the phase-difference oftwo transmitters, rather than the TDOA of a pulse, to define the hyperboloids. This allowed the transmitters tobroadcast a continuous wave signal. Phase-difference and time-difference can be considered the same fornarrow-band transmitters.

Multilateration 6

TDOA geometry

Fig 2. TDOA geometry.

Consider an emitter (E in Figure 2) atan unknown location vector

E = (x, y, z)which we wish to locate. The source iswithin range of N+1 receivers atknown locations

P0, P1, ..., Pm, ..., PN.The subscript m refers to any one ofthe receivers:

Pm = (xm, ym, zm)0 ≤ m ≤ N

The distance (R) from the emitter toone of the receivers in terms of thecoordinates is

(1)

The math is made easier by placing the origin at one of the receivers (P0), which makes its distance to the emitter

(2)

Multilateration 7

Measuring the Time Difference in a TDOA System

- Fig 3a. Pulse Signal

- Fig 3b. Wide-band Signal

Multilateration 8

- Fig 3c. Narrow-band SignalThe distance in equation 1 is the wave speed ( ) times transit time ( ). A TDOA multilateration systemmeasures the time difference ( ) of a wavefront touching each receiver. The TDOA equation for receivers m and0 is

(3)

Figure 3a is a simulation of the a pulse waveform recorded by receivers and . The spacing between , and is such that the pulse takes 5 time units longer to reach than . The units of time in Figure 3 arearbitrary. The following table gives approximate time scale units for recording different types of waves.

Type of wave Material Time Units

Acoustic Air 1 millisecond

Acoustic Water 1/2 millisecond

Acoustic Rock 1/10 millisecond

Electromagnetic Vacuum, air 1 nanosecond

The red curve in Figure 3a is the cross-correlation function . The cross correlation function slides onecurve in time across the other and returns a peak value when the curve shapes match. The peak at time = 5 is ameasure of the time shift between the recorded waveforms, which is also the value needed for Equation 3.Figure 3b is the same type of simulation for a wide-band waveform from the emitter. The time shift is 5 time unitsbecause the geometry and wave speed is the same as the Figure 3a example. Again, the peak in the cross correlationoccurs at .Figure 3c is an example of a continuous, narrow-band waveform from the emitter. The cross correlation function shows an important factor when choosing the receiver geometry. There is a peak at Time = 5 plus every increment of the waveform period. To get one solution for the measured time difference, the largest space between any two receivers must be closer than one wavelength of the emitter signal. Some systems, such as the LORAN C and Decca

Multilateration 9

mentioned at earlier (recall the same math works for moving receiver & multiple known transmitters), use spacinglarger than 1 wavelength and include equipment, such as a Phase Detector, to count the number of cycles that passby as the emitter moves. This only works for continuous, narrow-band waveforms because of the relation betweenphase ( ), frequency (f) and time (T)

.The phase detector will see variations in frequency as measured phase noise, which will be an uncertainty thatpropagates into the calculated location. If the phase noise is large enough, the phase detector can become unstable.

3-D SolutionEquation 3 is the hyperboloid described in the previous section, where 4 receivers (0 ≤ m ≤ 3) lead to 3 non-linearequations in 3 unknown values (x,y,z). The system must then solve for the unknown emitter location in real time.Civilian air traffic control multilateration systems use the Mode C SSR transponder return to find the altitude (z).Three or more receivers at known locations are used to find the other 2 dimensions (x, y).R. Bucher and D. Misra show the detailed algebra to locate 1 receiver with TDOA between 3 transmitters.[2] Theirsolution is a set of linear equations to find (x, y) and a quadratic for (z).Improving accuracy with a large number of receivers can be a problem for devices with small embedded processorsbecause of the time required to solve several simulatious, non-linear equations (1, 2 & 3). The TDOA problem canbe turned into a system of linear equations when there are 5 or more receivers, which can reduce the computationtime. Starting with equation 3, solve for Rm, square both sides, collect terms and divide all terms by :

(4)

Removing the 2 R0 term will eliminate all the square root terms. That is done by subtracting the TDOA equation ofreceiver m = 1 from each of the others (2 ≤ m ≤ N)

(5)

Focus for a moment on equation 1. Square Rm, group similar terms and use equation 2 to replace some of the termswith R0.

(6)

Combine equations 5 and 6, and write as a set of linear equations of the unknown emitter location x,y,z

Multilateration 10

(7)

Use equation 7 to generate the four constants from measured distances and time for eachreceiver 2 ≤ m ≤ N. This will be a set of N homogeneous linear equations.There are many robust linear algebra methods that can solve for the values of (x,y,z), such as Singular valuedecomposition or Gaussian Elimination. Chapter 15 in Numerical Recipes [3] describes several methods to solvelinear equations and estimate the uncertainty of the resulting values.

2-D SolutionFinding the emitter location in a two dimensional geometry can use any of the methods used for the 3-D geometry.The coordinate frame is typically defined to make the z dimension zero or constant. Examples of 2-D multilaterationare short wave radio long distance communications through the Earth's atmosphere, acoustic wave propagation in thesound fixing and ranging channel of the oceans and the LORAN navigation system.

AccuracyFor trilateration or multilateration, calculation is done based on distances, which requires the frequency and the wavecount of a received transmission. For triangulation or multiangulation, calculation is done based on angles, whichrequires the phases of received transmission plus the wave count.For lateration compared to angulation, the numerical problems compare, but the technical problem is morechallenging with angular measurements, as angles require two measures per position when using optical or electronicmeans for measuring phase differences instead of counting wave cycles.Trilateration in general is calculating with triangles of known distances/sizes, mathematically a very sound system.In a triangle, the angles can be derived if one knows the length of all sides, (see congruence), but the length of thesides cannot be derived based on all of the angles, not without knowing the length of at least one of the sides (abaseline) (see similarity).In 3D, when four or more angles are in play, locations can be calculated from n + 1 = 4 measured angles plus oneknown baseline or from just n + 1 = 4 measured sides.Multilateration is, in general, far more accurate for locating an object than sparse approaches such as trilateration,where with planar problems just three distances are known and computed. Multilateration serves for several aspects:• over-determination of an n-variable quadratic problem with (n + 1) + m quadratic equations• stochastic errors prohibiting a deterministic approach to solving the equations• clustering needs to segregate members of various clusters contributing to various models of solving, i.e. fixed

locations, oscillating locations and moving locationsAccuracy of multilateration is a function of several variables, including:• The antenna or sensor geometry of the receiver(s) and transmitter(s) for electronic or optical transmission.• The timing accuracy of the receiver system, i.e. thermal stability of the clocking oscillators.• The accuracy of frequency synchronisation of the transmitter oscillators with the receiver oscillators.

Multilateration 11

• Phase synchronisation of the transmitted signal with the received signal, as propagation effects as e.g. diffractionor reflection changes the phase of the signal thus indication deviation from line of sight, i.e. multipath reflections.

• The bandwidth of the emitted pulse(s) and thus the rise-time of the pulses with pulse coded signals intransmission.

• Inaccuracies in the locations of the transmitters or receivers when used as a known locationThe accuracy can be calculated by using the Cramér–Rao bound and taking account of the above factors in itsformulation.

Example applications• Decca Navigator System - A system used from the end of World War II to the year 2000, employing the

phase-difference of multiple transmitters to locate on the intersection of hyperboloids• OMEGA Navigation System - A worldwide system similar to Decca, shut down in 1997• GEE - British aircraft location technique from World War II, using accurate reference transmitters• LORAN-C - navigation system using TDOA of signals from multiple synchronised transmitters• Passive ESM multilateration systems, including Kopáč, Ramona, Tamara, VERA and possibly Kolchuga -

location of a transmitter using multiple receivers• Mobile phone tracking - using multiple base stations to estimate phone location (by either the phone itself, or the

phone network)• Reduced Vertical Separation Minima (RVSM) monitoring using Secondary Surveillance Radar - Mode C/S

transponder replies to calculate the position of an aircraft. Application to RVSM was first demonstrated by RokeManor Research Limited in 1992.

SimplificationFor applications where no need for absolute coordinates determination is assessed, the implementing of a moresimple solution is advantageous. Compared to multilateration as the concept of crisp locating, the other option isfuzzy locating, where just one distance delivers the relation between detector and detected object. This most simpleapproach is unilateration. However, such unilateration approach never delivers the angular position with reference tothe detector. Many solutions are available today [4] [5] [6] [7] [8] . Some of these vendors offer a position estimatebased on combining several laterations. This approach is often not stable, when the wireless ambience is affected bymetal or water masses. Other vendors offer room discrimination with a room-wise excitation, one vendor offers aposition discrimination with a contiguity excitation.

References• The Multilateration Executive Reference Guide [9] is an easy-to-read reference for air traffic management, airport

and airline professionals to learn more about this next-generation surveillance technology

Notes[1] In other words, given two receivers at known locations, one can derive a three-dimensional surface (characterized as one half of a

hyperboloid) for which any two points on said surface will have the same differential distance from said receivers, i.e., a signal transmittedfrom any point on the surface will have the same TDOA (measured by the receivers) as a signal transmitted from any other point on thesurface.Therefore, in practice, the TDOA corresponding to a (moving) transmitter is measured, a corresponding hyperbolic surface is derived, and thetransmitter is said to be "located" somewhere on the that surface.

[2] A Synthesizable VHDL Model of the Exact Solution for Three-dimensional Hyperbolic Positioning System (http:/ / www. hindawi. com/journals/ vlsi/ 2002/ 935925. abs. html), Ralph Bucher and D. Misra, VLSI Design, Volume 15 (2002), Issue 2, Pages 507-520.

[3] Numerical Recipes (http:/ / www. numerical-recipes. com/ ) official website[4] Sonitor Technologies, NO-0314 Oslo, Norway: SONITOR Ultra sound proprietary approach (http:/ / www. sonitor. com)

Multilateration 12

[5] RF Code, Austin, TX 78758, USA: RF Code 433 MHz proprietary approach (http:/ / www. rfcode. com)[6] ReadPost Bremerhaven Germany: TokLoc®, the Bluetooth® LowEnergy based approach (http:/ / www. tokloc. de/ tokloc/ tokloclocating/

mission/ mission. html)[7] Albis Zurich Switzerland: ZOMOFI Microwave proprietary approach (http:/ / www. albistechnologies. com/ products/ zone_monitoring/

index. php)[8] Location estimation in wireless telecommunication networks: Ekahau proprietary modified WLAN fuzzy locating approach (http:/ / www.

patentstorm. us/ patents/ 7228136. html)[9] http:/ / www. multilateration. com

Real-time locating systemReal-time locating systems (RTLS) are a type of local positioning system that allow to track and identify thelocation of objects in real time. Using simple, inexpensive badges or tags attached to the objects, readers receivewireless signals from these tags to determine their locations.[1] RTLS typically refers to systems that provide passiveor active (automatic) collection of location information.Location information usually does not include speed, direction, or spatial orientation. These additional measurementswould be part of a navigation, maneuvering or positioning system.

OriginThe term RTLS was created (circa 1998) to describe an emerging technology that not only provided the AutomaticIdentification capabilities of active RFID tags, but added the ability to see the physical location of the tagged asseton a computer screen. Although this capability had been utilized previously by military and government agencies,the technology had been too expensive for commercial purposes.By the early 1990s, commercialization began at two healthcare facilities in the United States (Foote Hospital inJackson, MI and Broward Children's Hospital in Pompano Beach, FL). These early adoptors are atrributed toreal-time locating industry innovator Precision Tracking (Versus Technology, Inc.) and were based on thetransmission and decoding of infrared light signals from actively transmitting tags.

System designsRTLS excludes passive RFID indexing (radio frequency transponder indexers) and Cellnet base station segmentlocators (location-based services) from the scope of the ISO/IEC approach to RTLS standardization as well as allbeacon systems, that ping without request. RTLS systems apply typically in confined areas, where the requiredreference points would be equipped with wireless anchor nodes.

OperationFor RTLS to function, the location of tagged items must be determined either by a central processor or by anembedded mobile computing facility. Locating is generally accomplished in one of the following ways• 1. ID signals from nodes are identifiable to a single reader in a sensory network thus indicating the coincidence of

reader and nodes.• 2. ID signals from nodes are picked up by a multiplicity of readers in a sensory network and a position is

estimated using one or more locating algorithms• 3. Location signals from signposts with identifiers are transmitted to the moving nodes and are then relayed,

usually via a second wireless channel, to a location processor.• 4. Mobile nodes communicate with each other and perform metering distances.Examples one (1) and three (3) have much of the same characteristics. They typically require that a node be assignedat a time to a single reader/signpost. Separation from overlapping readers/signposts is roughly provided by RSSI or

Real-time locating system 13

Physical Space Division (walls/floors/ceilings). Readers/signposts are often associated with highly stable locationboundaries (i.e. a room or room division). In these examples, locations are listed as "Current Location" or "LastKnown Location."Example two (2) requires that distances between nodes in the sensory network be determined in order to preciselylocate a node. In this instance, the determination of the location is called Localization. The location is calculatedthrough Trilateration or Multilateration from the determined distance between the nodes or through Triangulationfrom the determined angles between nodes. The determination of distances is called Ranging.

ApplicationRTLS serves in operational areas for logistics and other services,as for example stock grounds or storehouses, andfor servicing areas in clinics and industrial plants. Tasks done by a RTLS include:• to combine identity and location of any type of items or objects• to combine identity of items with location of lifter placing the items• to ensure permanent availability of proper information about temporary placement• to support notification of placing of items• to prove proper manning of operational areas• to prove consequent evacuation of endangered areas• to make marshalling staff dispensable

Standards

ISO/IECThe basic issues of RTLS are standardized by the International Organization for Standardization and theInternational Electrotechnical Commission, under the ISO/IEC 24730 series. In this series of standards, the basicstandard ISO/IEC 24730-1 identifies the terms describing a form of RTLS used by a set of vendors, but does notencompass the full scope of RTLS technology.Currently several standards are published or under discussion:• ISO/IEC FDIS 19762-5 Information technology AIDC techniques — Harmonized vocabulary, Part 5 — Locating

systems• ISO/IEC 24730-1:2006 Information technology real-time locating systems (RTLS) Part 1: Application program

interface (published).• ISO/IEC 24730-2:2006 Information technology real-time locating systems (RTLS) Part 2: 2,4 GHz Air interface

protocol (published, WhereNet/Zebra approach).• ISO/IEC WD 24730-5 Information technology real-time locating systems (RTLS) Part 5: (drafted ISO/IEC

standard out for balloting in 2008, Nanotron approach).The other proposals ISO/IEC 24730-3 and ISO/IEC 24730-4 had never left the stage of intention. For copies of thesedocuments see references.These standards do not stipulate any special method of computing locations, nor the method of measuring locations.This may be defined in specifications for triangulation or any hybrid approaches to trigonometric computing forplanar or spherical models of a terrestrial area.

Real-time locating system 14

ANSI standards• ANS/INCITS 371: Information Technology – Real-Time Locating Systems (RTLS).

RangingRanging, as a special term for measuring distance, is the prerequisite for locating. Measuring a bearing angle, i.e.angulating is the other alternative.Determining the distance may be either a non cooperative scanning process, as with RADAR or LIDAR, or acooperative direct distance measuring process, as with RTLS. A scanned beam may form an overall image as amodel of the whole scene. In all other cases the image of the scene is rather selective.The following step is extracting the distance information from the scanned image. Direct distance measurement witha single beam targets only the object to be measured, for example, with a laser. This method requires additionalinformation about the direction of the beam. The remaining method is omni-directional transmission with a signalcontaining an address code. Only the addressed object responds to the request. The time required for the signal toreach the object can be used to calculate the distance. After completing the distance measurement, the location maybe computed.There are two different principles when measuring travel time of radio waves:• Trilateration derives the travel time of a radio signal from a metering unit, and measures and computes the

distance with the relation of light speed in vacuum, the (Time of arrival concept).• Triangulation derives the travel time of a pair of synchronous radio signals from a metering unit with two

transmitters, and measures and computes the difference of distance with the relation of light speed in vacuum asan angle versus the baseline of the two transmitters (TDOA time difference of arrival concept).

All the terms named here just apply to measurement concepts. All information about location is for services appliedto mobile or portable or otherwise transportable objects. Location information may be relevant for managinginteraction of persons with services as well.• Angle of arrival (AoA)• Line-of-sight (LoS)• Time of arrival (ToA)• Multilateration (Time difference of arrival) (TDoA)• Time-of-flight (ToF)• Two-way ranging (TWR) according to Nanotron’s patents• Symmetrical Double Sided – Two Way Ranging (SDS-TWR)• Near-field electromagnetic ranging (NFER)

Privacy concernsRTLS may be seen a threat to privacy, if applied to persons, either directly or parasitically. The requirementtherefore is to describe the purpose and the conditions of operation to those affected and to advertise for expressedagreement. Recent adjustment of jurisdiction leads to more careful assessment of needs and options. The newlydeclared human right of informational self-determination de:Informationelle Selbstbestimmung, i.e. to prevent one'sidentity and personal data from disclosure to others, covers disclosure of locality as well. Base of discussion is verysimilar to disclosure of personal data for passing immigration at US airports: Balancing threat and burden [2].

Real-time locating system 15

Types of technologies usedThere is a wide variety of systems concepts and designs to provide real-time locating. A good choice is listed inRTLS for Dummies by Ajay Malik (Wiley 2009).[3] Methods include:• Active radio frequency identification (Active RFID)• Active radio frequency identification - infrared hybrid (Active RFID-IR)• Infrared (IR)• Optical locating,[4] [5]

• Low-frequency signpost identification• Semi-active radio frequency identification (semi-active RFID)• Radio beacon,[6] [7]

• Ultrasound Identification (US-ID) [8]

• Ultrasonic ranging (US-RTLS) [9]

• Ultra-wideband (UWB) [10]

• Wide-over-narrow band [11]

• Wireless Local Area Network (WLAN, Wi-Fi)[12]

• Bluetooth,[13] [14]

• Clustering in noisy ambience,[15] [16]

• Bivalent systems [17]

A general model for selection of the best solution for a locating problem has been constructed at the RadboudUniversity of Nijmegen.[18] Many of these references do not comply with the definitions given in internationalstandardization with ISO/IEC 19762-5 [19] and ISO/IEC 24730-1.[20] However, some aspects of real-timeperformance are served and aspects of locating are addressed in context of absolute coordinates.

Locating conceptsA lot of systems concepts sails under the label of real-time locating systems. However the qualification of theseapproaches is very different and offers a wide variation of cost-to-benefit ratio.

Locating at choke pointsThere is class of most simple locating which applies no physical measurement at all, but just communicates atcoincidence of transceiver and transponder as long as communication may happen. Then locating collapses to simpleapplication of RFID technologies according to the equivalent standard.[21] This is the only option to apply passiveRFID tags for locating. Then the reach of the RFID reader determines the choke point. Hence accuracy is defined bythe sphere spanned with the reach of the reader. The concept does not serve for discrimination of direction onpassage, unless the reader is enhanced with a two distant antenna inputs to determine a sequence of activation anddeactivation of the pair of antennae.

Real-time locating system 16

Locating in relative coordinatesMany references describe locating at relative coordinates. Such coordinates may be radial distances compared withreference to known locations and no angular directions. There is no exact metrics required, unless the relation to thereference points is intelligible. This is a valuable support for many operational needs, whereas the precision of theterm RTLS is widely diluted to arbitrary interpretation. Such solutions may be referred as fuzzy locating.

Locating in absolute coordinatesThe high precision of satellite navigation systems led to some snugness in setting the requirements for locating ofobjects. generally the determining of absolute coordinates is the most challenging approach. Such solutions may bereferred as crisp locating. The difference to the qualities of relative coordinates may be easily understood with indoorsensor operations, where satellites are not commonly available for referring to global coordinates and when always amultiplicity of errors applies. The most challenging problem with modern modulation concepts still is multi-pathpropagation, which causes ambiguous results of erratic measurement.A sound escape from electromagnetics and surface effects is found with ultra short pulse communications, as withUWB indoor approaches. However, many such concepts often do not serve results for the paid price when the targetsmove. This may be assessed by the vast number of publications and the very small references on installed solutions

Locating in contiguityA newer approach for locating defines a location just as the contiguous ambience of the person looking forsomething to be located. That is very similar to choke point locating. However, the accuracy may be much bettertuned, as the reach is not influenced by the steady illumination of the tag with the reader, but just by the tunedtransmission power level of an active RFID tag as an itermittent beacon.This is the easy option to apply graded active RFID tags for economised locating. Then the reach of the RFIDreceiver determines the base point. Hence operational suitability is defined by the algorithm for varying theminimum reach of transmission of the beacon. Solutions are available as very simple electronic leashes or in morecomplex designs. A very common application is with electronic wireless lock solutions. More advanced applicationscombine the tag operation with autonomously operating software agents, e.g. in smartphones for monitoringmanually controlled systems and services.[22]

Erratic effects in locating systemsReal-time locating is affected by a variety of errors. The major reasons are physical and may not be reduced byimproving the technical equipment. The only escape is mathematical intelligence to improve.None or no direct responseMany RTLS systems have a very mundane requirement: they require direct and clear wireless visibility. For thosesystems, where there is no visibility on the path from mobile tags to resident nodes there will be no result or a nonvalid result from locating engine. This applies to satellite locating as well as other RTLS systems such as angle ofarrival and time of arrival. Fingerprinting is a way to overcome the visibility issue: If the locations in the trackingarea contain distinct measurement fingerprints, line of sight is not necessarily needed. For example, if each locationcontains a unique combination of signal strength readings from transmitters, the location system will functionproperly. This is true, for example, with some Wi-Fi based RTLS solutions. However, having distinct signal strengthfingerprints in each location typically requires a fairly high saturation of transmitters.False locationThe measured location may appear entirely faulty. This is a generally result of simple operational models tocompensate for the plurality of error sources. It proves impossible to serve proper location after ignoring the errors.

Real-time locating system 17

Locating backlogReal time is no registered branding and has no inherent quality. A variety of offers sails under this term. As motioncauses location changes, inevitably the latency time to compute a new location may be dominant with regard tomotion. Either an RTLS system that requires waiting for new results is not worth the money or the operationalconcept that asks for faster location updates does not comply with the chosen systems approach.Temporary location errorLocation will never be reported exactly, as the term real-time and the term precision directly contradict in aspects ofmeasurement theory as well as the term precision and the term cost contradict in aspects of economy. That is noexclusion of precision, but the limitations with higher speed are inevitable.Steady location errorRecognizing a reported location steadily apart from physical presence generally indicates the problem of insufficientover-determination and missing of visibility along at least one link from resident anchors to mobile transponders.Such effect is caused also by insufficient concepts to compensate for calibration needs.Location jitterNoise from various sources has an erratic influence on stability of results. The aim to provide a steady appearanceincreases the latency contradicting to real time requirements.Location jumpAs objects containing mass have limitations to jump, such effects are mostly beyond physical reality. Jumps ofreported location not visible with the object itself generally indicate improper modeling with the location engine.Such effect is caused by changing dominance of various secondary responses.Location creepLocation of residing objects gets reported moving, as soon as the measures taken are biased by secondary pathreflections with increasing weight over time. Such effect is caused by simple averaging and the effect indicatesinsufficient discrimination of first echoes.

External links• International Standardization in Engineering [23]

• International Standardisation in Industry and Science [24]

• Search Page for ISO standards concerning RTLS [25]

• A real-time location search primer [26]

• International Standardisation in Electrical Engineering [27]

• International Standardisation in Communications [28]

• International Lobbying in Automatic Identification [29]

• US American Lobbying in Automatic Identification [30]

• Statement of International Lobbying on Real-Time Locating [31]

• ISO JTC1 (TC122) SC31 WG5 Homepage on RTLS [32]

• ISO JTC1 (TC122) SC31 WG5 Homepage on MIIM [32]

• Company driving international standardisation on e.g. RFID and RTLS in US [33]

• Schedule and actual scope of RTLS standardisation in ISO JTC1, TC122 and SC31 [34]

• Car-to_Car communications programme funding of the European Union [35]

• RT Non-Line-of-Sight Localization System by CMR@UNSW [36]

• the RTLS Blog [37]

Real-time locating system 18

Literature[1] ISO/IEC 19762-5 (http:/ / www. iso. org)[2] http:/ / www. hasbrouck. org/ articles/ PNR. html[3] Malik, Ajay (2009). RTLS For Dummies. Wiley. pp. 336. ISBN 978-0-470-39868-5.[4] Laserscannersteuerung für FTF HG 43600 (http:/ / www. goetting. de/ de/ multimedia/ bilder/ produkte/ laser/ )[5] Auswerter zur optischen Spurführung (http:/ / www. goetting. de/ de/ produkte/ optisch/ 73840)[6] RFID Technology from Texas Instruments and RF Code Helps Kids Play it Safe (http:/ / www. rfidjournalevents. com/ live2005/

press_releases/ RF Code. pdf)[7] RFID Technology from Texas Instruments and RF Code Brings Service and Safety to Guests (http:/ / www. rfidjournalevents. com/ live2005/

press_releases/ RF Code. pdf)[8] (http:/ / www. sciam. com/ article. cfm?id=indoor-positioning-system)[9] (http:/ / www. sonitor. com/ news/ ITNfiles/ HospitNews08HospitalDecisi. pdf)[10] UWB RTLS Vendor Improves Sensitivity, Lowers Cost (http:/ / www. timedomain. com/ news/ RFIDUpdate072308. pdf)[11] Essensium LOST system for RTLS combining benefits of UWB and Narrowband (http:/ / www. essensium. com/ lost_system. html)[12] (http:/ / www. nortel. com/ solutions/ wlan/ collateral/ nn120920. pdf)[13] Enhancing Accuracy Performance of Bluetooth Positioning (http:/ / ieeexplore. ieee. org/ xpl/ freeabs_all. jsp?arnumber=4224751)[14] "Real-Time Location Systems" (http:/ / www. clarinox. com/ docs/ whitepapers/ RealTime_main. pdf). clarinox. . Retrieved 2010-08-04.[15] Collaborative Localization (http:/ / mll. csie. ntu. edu. tw/ papers/ collaboration_pervasive2006. pdf)[16] WLAN location determination via clustering and probability distributions (http:/ / ieeexplore. ieee. org/ xpl/ freeabs_all.

jsp?arnumber=1192736)[17] services for elderly and disabled people (http:/ / portal. acm. org/ citation. cfm?id=1354947. 1355184Location-based)[18] "Positioning techniques : A general model" (http:/ / www. positioningtechniques. eu). Radboud University of Nijmegen. .[19] Information technology – Automatic identification and data capture (AIDC) techniques – Harmonized vocabulary – Part 5: Locating

systems (http:/ / www. iso. org/ iso/ iso_catalogue/ catalogue_tc/ catalogue_detail. htm?csnumber=50718)[20] Information technology – Real-time locating systems (RTLS) – Part 1: Application program interface (API) (http:/ / www. iso. org/ iso/

iso_catalogue/ catalogue_tc/ catalogue_detail. htm?csnumber=38840)[21] ISO/IEC 19762-3 (http:/ / www. iso. org)[22] Method and Components for Controls of Unblocking Systems or Services (http:/ / depatisnet. dpma. de/ DepatisNet/

depatisnet?action=bibdat& docid=DE102009039879A1)[23] http:/ / www. iec. ch/[24] http:/ / www. iso. org/[25] http:/ / www. iso. org/ iso/ search. htm[26] http:/ / www. promotionworld. com/ se/ articles/ article/ 100531-Real-Time-Location-Search-Primer[27] http:/ / www. ieee. org/[28] http:/ / www. ietf. org/[29] http:/ / www. aimglobal. org/[30] http:/ / www. aimusa. org/[31] http:/ / www. aimglobal. org/ technologies/ rtls/[32] http:/ / www. autoid. org/ SC31/ wg5. htm/[33] http:/ / www. qed. org/[34] http:/ / www. autoid. org/ SC31/ wg5. htm[35] http:/ / www. car-to-car. org/[36] http:/ / cmr. mech. unsw. edu. au/ research_areas?q=node/ 23[37] http:/ / www. theRTLSBlog. com

Malik, Ajay (2009). RTLS For Dummies. Wiley. pp. 384. ISBN 978-0-470-39868-5.• Indoor Geolocation Using Wireless Local Area Networks (Berichte Aus Der Informatik), Michael Wallbaum

(2006)• Local Positioning Systems: LBS applications and services, Krzysztof Kolodziej & Hjelm Johan, CRC Press Inc

(2006)

Real-time locating system 19

References

Location-based serviceA Location-Based Service (LBS) is an information or entertainment service, accessible with mobile devices throughthe mobile network and utilizing the ability to make use of the geographical position of the mobile device [1] [2] [3]

.[4]

LBS can be used in a variety of contexts, such as health, indoor object search[5] , entertainment[6] , work, personallife, etc. .[7]

LBS include services to identify a location of a person or object, such as discovering the nearest banking cashmachine or the whereabouts of a friend or employee. LBS include parcel tracking and vehicle tracking services. LBScan include mobile commerce when taking the form of coupons or advertising directed at customers based on theircurrent location. They include personalized weather services and even location-based games. They are an example oftelecommunication convergence.This concept of location based systems is not compliant with the standardized concept of real-time locating systemsand related local services (RTLS), as noted in ISO/IEC 19762-5 [8] and ISO/IEC 24730-1.[9]

HistoryResearch forerunners of today's location-based services are the infrared Active Badge system (1989–1993), TheEricsson-Europolitan GSM LBS trial ran during 1995 by Jörgen Johansson and the master thesis written by Nokiaemployee Timo Rantalainen, in 1994.In 1996 the US Federal Communication Commission (FCC) issued rules requiring all US mobile operators to locateemergency callers. This rule was a compromise resulting from US mobile operators seeking the support of theemergency community in order to obtain the same protection from law suits relating to emergency calls as fixed-lineoperators already had.In 1997 Christopher Kingdon, of Ericsson, handed in the Location Services (LCS) stage 1 description to the jointGSM group of the European Telecommunications Standard Institute(ETSI) and the American National StandardsInstitute (ANSI). As a result the LCS sub-working group was created under ANSI T1P1.5. This group went on toselect positioning methods and standardize Location Services (LCS), later known as Location Based Services (LBS).Nodes defined include the Gateway Mobile Location Centre (GMLC), the Serving Mobile Location Centre (SMLC)and concepts such as Mobile Originating Location Request (MO-LR), Network Induced Location Request (NI-LR)and Mobile Terminating Location Request (MT-LR).In 2000, after approval from the worlds 12 largest telecom operators, Ericsson, Motorola and Nokia jointly formedand launched the Location Interoperability Forum Ltd (LIF). This forum first specified the Mobile Location Protocol(MLP), an interface between the telecom network and an LBS application running on a server in the InternetDomain. Then, much driven by the Vodafone group, LIF went on to specify the Location Enabling Server (LES), a"middleware", which simplifies the integration of multiple LBS with an operators infrastructure. In 2004 LIF wasmerged with the Open Mobile Association (OMA). A LBS work group was formed within the OMA.The first consumer LBS-capable mobile web device was the Palm VII, released in 1999.[10] Two of the in-the-boxapplications made use of the ZIP code-level positioning information and share the title for first consumer LBSapplication: the Weather.com app from The Weather Channel, and the[11] TrafficTouch app from Sony-Etak / MetroTraffic.The first LBS services were launched during 2000 by TeliaSonera in Sweden (friendfinder, yellow pages,houseposition, emergency call location etc.) and by EMT in Estonia (emergency call location, friend finder, TV

Location-based service 20

game). TeliaSonera and EMT based their services on the Ericsson Mobile Positioning System (MPS).Other early LBS include friendzone, launched by swisscom in Switzerland in May 2001, using the technology ofvalis ltd. The service included friend finder, LBS dating and LBS games.[12] The same service was launched later byVodafone Germany, Orange Portugal and Pelephone in Israel[11] . Microsoft's Wi-Fi-based indoor location systemRADAR (2000), MIT's Cricket project using ultrasound location (2000) and Intel's Place Lab with wide-arealocation (2003).[13]

The first commercial LBS service in Japan was launched by DoCoMo, based on triangulation for pre-GPS handsetsin July 2001, and by KDDI for the first mobile phones equipped with GPS in December 2001.[14] Mobile handsetmakers have tended to take 'upstream initiative' to embed LBS in their mobile equipment. Originally, LBS wasdeveloped by mobile carriers in partnership with mobile content providers.In May 2002, go2 and AT&T launched the first (US) mobile LBS local search application that used AutomaticLocation Identification (ALI) technologies mandated by the FCC. go2 users were able to use AT&T’s ALI todetermine their location and search near that location to obtain a list of requested locations (stores, restaurants, etc.)ranked by proximity to the ALI provide by the AT&T wireless network. The ALI determined location was also usedas a starting point for turn-by-turn directions.The main advantage is that mobile users don't have to manually specify ZIP codes or other location identifiers to useLBS, when they roam into a different location. GPS tracking is a major enabling ingredient, utilizing access tomobile web.In 2010, location-based services power Mobile Local Search to enable the search and discovery of persons, places,and things within an identifiable space defined by distinct parameters. These parameters are evolving. Today theyinclude social networks, individuals, cities, neighborhoods, landmarks, and actions that are relevant to the searcher'spast, current, and future location. These parameters provide structure to vertically deep and horizontally broad datacategories that can stand alone or are combined to form searchable directories.[15]

Locating methods

Control Plane LocatingSometimes referred to as positioning, with control plane locating the service provider gets the location based on theradio signal delay of the closest cell-phone towers (for phones without GPS features) which can be quite slow as ituses the 'voice control' channel.[4] In the UK, networks do not use trilateration; LBS services use a single basestation, with a 'radius' of inaccuracy, to determine a phone's location. This technique was the basis of the E-911mandate and is still used to locate cellphones as a safety measure. Newer phones and PDAs typically have anintegrated A-GPS chip.In order to provide a successful LBS technology the following factors must be met:• Coordinates accuracy requirements that are determined by the relevant service;• Lowest possible cost;• Minimal impact on network and equipment.Several categories of methods can be used to find the location of the subscriber.[2] [16] The simple and standardsolution is GPS-based LBS. Sony Ericsson's "NearMe" is one such example. It is used to maintain knowledge of theexact location, however can be expensive for the end-user, as they would have to invest in a GPS-equipped handset.GPS is based on the concept of trilateration, a basic geometric principle that allows finding one location if oneknows its distance from other, already known locations.

Location-based service 21

GSM LocalizationGSM localization is the second option. Finding the location of a mobile device in relation to its cell site is anotherway to find out the location of an object or a person. It relies on various means of multilateration of the signal fromcell sites serving a mobile phone. The geographical position of the device is found out through various techniqueslike time difference of arrival (TDOA) or Enhanced Observed Time Difference (E-OTD).

OthersAnother example is Near LBS (NLBS), in which local-range technologies such as Bluetooth, WLAN, infrared and/orRFID/Near Field Communication technologies are used to match devices to nearby services. This application allowsa person to access information based on their surroundings; especially suitable for using inside closed premises,restricted/ regional areas.Another alternative is an operator- and GPS-independent location service based on access into the deep leveltelecoms network (SS7). This solution enables accurate and quick determination of geographical coordinates ofmobile phone numbers by providing operator-independent location data and works also for handsets that are notGPS-enabled.Many other Local Positioning Systems are available, especially for indoor use. GPS and GSM don't work very wellindoors, so other techniques are used, including Bluetooth, UWB, RFID and Wi-Fi[17] . But which techniqueprovides the best solution for a specific LBS problem? A general model for this problem has been constructed at theRadboud University of Nijmegen.[18]

Further information: Mobile phone tracking

LBS applicationsSome examples of location-based services are [2] :• Recommending social events in a city[1]

• Requesting the nearest business or service, such as an ATM or restaurant• Turn by turn navigation to any address• Locating people on a map displayed on the mobile phone• Receiving alerts, such as notification of a sale on gas or warning of a traffic jam• Location-based mobile advertising• Asset recovery combined with active RF to find, for example, stolen assets in containers where GPS wouldn't

work• Games where your location is part of the game play, for example your movements during your day make your

avatar move in the game or your position unlocks content.• Real-time Q&A revolving around restaurants, services, and other venuesMore examples are listed in.[2]

For the carrier, location-based services provide added value by enabling services such as:• Resource tracking with dynamic distribution. Taxis, service people, rental equipment, doctors, fleet scheduling.• Resource tracking. Objects without privacy controls, using passive sensors or RF tags, such as packages and train

boxcars.• Finding someone or something. Person by skill (doctor), business directory, navigation, weather, traffic, room

schedules, stolen phone, emergency calls.• Proximity-based notification (push or pull). Targeted advertising, buddy list, common profile matching (dating),

automatic airport check-in.• Proximity-based actuation (push or pull). Payment based upon proximity (EZ pass, toll watch).

Location-based service 22

In the U.S. the FCC requires that all carriers meet certain criteria for supporting location-based services (FCC94-102). The mandate requires 95% of handsets to resolve within 300 meters for network-based tracking (e.g.triangulation) and 150 meters for handset-based tracking (e.g. GPS). This can be especially useful when dialing anemergency telephone number - such as enhanced 9-1-1 in North America, or 112 in Europe - so that the operator candispatch emergency services such as Emergency Medical Services, police or firefighters to the correct location.CDMA and iDEN operators have chosen to use GPS location technology for locating emergency callers. This led torapidly increasing penetration of GPS in iDEN and CDMA handsets in North America and other parts of the worldwhere CDMA is widely deployed. Even though no such rules are yet in place in Japan or in Europe the number ofGPS-enabled GSM/WCDMA handset models is growing fast. According to the independent wireless analyst firmBerg Insight the attach rate for GPS is growing rapidly in GSM/WCDMA handsets, from less than 8 percent in 2008to 15 percent in 2009.[19]

European operators are mainly using Cell-ID for locating subscribers. This is also a method used in Europe bycompanies such as Podsystem [20] that are using cell based LBS as part of systems to recover stolen assets. In the UScompanies such as Rave Wireless in New York are using GPS and triangulation to enable college students to notifycampus police when they are in trouble. Rave Wireless and other companies with location based offerings arepowered by a variety of companies, including Skyhook Wireless and Xtify.

Mobile messagingMobile messaging plays an essential role in LBS. Messaging, especially SMS, has been used in combination withvarious LBS applications, such as location-based mobile advertising. SMS is still the main technology carryingmobile advertising / marketing campaigns to mobile phones. A classic example of LBS applications using SMS isthe delivery of mobile coupons or discounts to mobile subscribers who are near to advertising restaurants, cafes,movie theatres. The Singaporean mobile operator MobileOne carried out such an initiative in 2007 that involvedmany local marketers, what was reported to be a huge success in terms of subscriber acceptance.Companies offering location-based messaging (sometimes referred to as 'geo-messaging') include The Coupons App[21](US), Centrl [22](International), Zhiing (international), BluePont (US),[23] Loopt (US), Dodgeball (US) andGeoMe [24](Spain).

Privacy issuesWith the passing of the Can Spam Act in 2005, it became illegal in the United States to send any message to the enduser without the end user specifically opting-in. This put an additional challenge on LBS applications as far as'carrier-centric' services were concerned. As a result, there has been a focus on user-centric location-based servicesand applications which give the user control of the experience, typically by opting in first via a website or mobileinterface (such as SMS, mobile Web, and Java/BREW applications).The European Union also provides a legal framework for data protection that may be applied for location-basedservices, and more particularly several European directives such as: (1) Personal data: Directive 95/46/EC); (2)Personal data in electronic communications: Directive 2002/58/EC; (3) Data Retention: Directive 2006/24/EC.However the applicability of legal provisions to varying forms of LBS and of processing location data is unclear.[25]

One implication of this technology is that data about a subscriber's location and historical movements is owned andcontrolled by the network operators, including mobile carriers and mobile content providers.[26]

A critical article by Dobson and Fisher[27] discusses the possibilities for misuse of location information.Beside the legal framework there exist several technical approaches to protect privacy using privacy-enhancing technologies (PETs). Such PETs range from simplistic on/off switches [28] to sophisticated PETs using anonymization techniques,[29] e.g., related to k-anonymity. Today, only few LBS offer such PETs, e.g., Google Latitude offers an on/off switch and allows to stick one's position to a free definable location. Additionally, it is an

Location-based service 23

open question how users perceive and trust in different PETs. The only study that addresses user perception of stateof the art PETs is.[30] . Another set of techniques included in the PETs are the Location obfuscation techniques,which slightly alter the location of the users in order to hide their real location while still bein able to represent theirposition and receive services from their LBS provider.

Industry ValueIn 1999, analysts predicted that the industry would be worth USD 20 billion annually by 2005.[31]

Further reading• Werbach, Kevin (June 28, 2000). "Location-Based Computing: Wherever You Go, There You are" [32]. Esther

Dyson's Monthly Report (edventure.com) 18 (10): 1–6. Archived from the original [33] on 20011-05-04. Retrieved2011-05-04.

References[1] "Recommending Social Events from Mobile Phone Location Data" (http:/ / www. cl. cam. ac. uk/ ~dq209/ publications/

recommending10quercia. pdf), Daniele Quercia, et al., ICDM 2010[2] "Foundations of Location Based Services" (http:/ / sourceforge. net/ projects/ jump-pilot/ files/ w_other_freegis_documents/ articles/

lbs_lecturenotes_steinigeretal2006. pdf/ download), Stefan Steiniger, Moritz Neun and Alistair Edwardes, University of Zurich[3] "Permanent Reference Document SE.23: Location Based Services“ (http:/ / www. gsmworld. com/ documents/ se23. pdf), GSM Association[4] "Location Based Services for Mobiles: Technologies and Standards“ (http:/ / to. swang. googlepages. com/

ICC2008LBSforMobilessimplifiedR2. pdf), Shu Wang, Jungwon Min and Byung K. Yi, IEEE International Conference on Communication(ICC) 2008 (http:/ / www. ieee-icc. org/ ), Beijing, China

[5] B. Guo, S. Satake, M. Imai. Home-Explorer: Ontology-based Physical Artifact Search and Hidden Object Detection System (http:/ / www.ayu. ics. keio. ac. jp/ members/ bingo/ pic/ research/ sixth-sense/ homeexplorer-j-guo. pdf). Mobile Information Systems, Vol. 4 No.2 (2008),81-103, IOS Press, 2008.

[6] B. Guo, R. Fujimura, D. Zhang, M. Imai. Design-in-Play: Improving the Variability of Indoor Pervasive Games (http:/ / www. springerlink.com/ content/ c50217p160272h44/ ). Multimedia Tools and Applications, Springer, 2011

[7] Deuker, André (2008), "Del 11.2: Mobility and LBS" (http:/ / www. fidis. net/ resources/ deliverables/ mobility-and-identity/ ), FIDISDeliverables 11 (2),

[8] ISO/IEC 19762-5 (http:/ / www. iso. org/ iso/ en/ iso_catalogue/ catalogue_ics/ catalogue_detail_ics. htm?csnumber=50718& ICS1=35&ICS2=40) Information technology -- Automatic identification and data capture (AIDC) techniques -- Harmonized vocabulary -- Part 5:Locating systems

[9] ISO/IEC 24730-1 (http:/ / www. iso. org/ iso/ iso_catalogue/ catalogue_tc/ catalogue_detail. htm?csnumber=38840) Information technology-- Real-time locating systems (RTLS) -- Part 1: Application program interface (API)

[10] Newsweek - "The World in Your Hand" (http:/ / www. newsweek. com/ id/ 88432)[11] http:/ / www. tarif4you. de/ news/ n10079. html[12] portal.acm.org/ft_gateway.cfm?id=1052394&type=pdf[13] Anind Dey, Jeffrey Hightower, Eyal de Lara, Nigel Davies (2010): Location-Based Services. Pervasive Computing 1/2010, 11-12[14] "Location Based Services FAQ (LBS-FAQ)" (http:/ / www. eurotechnology. com/ market_reports/ LBS/ ), Location Based Services FAQ

(LBS-FAQ)[15] "Mobile Local Search Saturates Profit over LBS Vendors, Advertisers, and Search Application Developers" (http:/ / www. directionsmag.

com/ press. releases/ ?duty=Show& id=44939)[16] LBS Positioning Methods http:/ / www. navigationevent. com/ pdf/ tyntec_kunz. pdf[17] "Precise Indoor Localization Using Smart Phones" (http:/ / www. icsi. berkeley. edu/ pubs/ speech/ preciseindoor10. pdf) E. Martin, O.

Vinyals, G. Friedland, R. Bajcsy, ACM Multimedia 2010, 787-790[18] "Positioning techniques : A general model" (http:/ / www. positioningtechniques. eu). Radboud University of Nijmegen. .[19] Berg Insight - GPS and Mobile Handsets (http:/ / www. berginsight. com/ ReportPDF/ ProductSheet/ bi-gps4-ps. pdf)[20] http:/ / www. podsystem. com[21] http:/ / www. thecouponsapp. com[22] http:/ / www. centrl. com[23] Mobile Technology provided by BluePont allows you to find last minute workout buddy (http:/ / www. snewsnet. com/ cgi-bin/ snews/

13748. html/ ) SNEWSNET reviews BluePont - a Location based service in US[24] http:/ / www. geo-me. com

Location-based service 24

[25] Cuijpers, Colette; Roosendaal, Arnold; Koops, Bert-Jaap (2007), "Del 11.5: The legal framework for location-based services in Europe"(http:/ / www. fidis. net/ resources/ deliverables/ mobility-and-identity/ ), FIDIS Deliverables 11 (5),

[26] "WhyGeo" (http:/ / whygeo. com/ questions/ 26/ what-are-the-downsides-of-using-location-based-services), What are the downsides ofusing location-based services?,2010

[27] "Geoslavery" (http:/ / dusk. geo. orst. edu/ virtual/ 2005/ geoslavery. pdf), J.E. Dobson and P.F. Fisher, IEEE Technology and SocietyMagazine, 2003

[28] Barkhuus; Dey (2003), ".: Location-based services for mobile telephony: A study of users' privacy concerns", CHI INTERACT[29] Mokbel; Chow; Aref (2006), ".: The new casper: query processing for location services without compromising privacy", VLDB[30] Burghardt, Thorben; Buchmann, Erik; Mueller, Jens; Boehm, Klemens (2009), ".: Understanding User Preferences and Awareness: Privacy

Mechanisms in Location-Based Services", Coopis[31] "SnapTrack's Personal Location Technology to be Available for Microsoft Mobile Explorer Phone Platform". Sinocast (Westlaw).

December 14, 1999.[32] http:/ / www. webcitation. org/ 5yQd8VpVd[33] http:/ / cdn. oreilly. com/ radar/ r1/ 06-00. pdf

Local positioning systemA local positioning system (LPS) is a navigation system that provides location information in all weather, anywherewithin the coverage of the network, where there is an unobstructed line of sight to three or more signaling beacons ofwhich the exact position on earth is known. A special type of LPS is the Real-time locating system; which alsoallows real-time tracking of an object or person.

UseUnlike GPS or other global navigation satellite systems, local positioning systems don't provide global coverage.Instead, they use (a set of) beacons which have a limited range, hence requiring the user to be near these. Beaconsinclude celllular base stations, Wi-Fi access points (used by the Skyhook Wireless system), and radio broadcasttowers.In the past, long-range LPS's have been used for navigation of ships and aircraft. Examples are the Decca NavigatorSystem and LORAN.Nowadays, local positioning systems are often used as complementary (and in some cases alternative) positioningtechnology to GPS, especially in areas where GPS does not reach or is weak, for example, inside buildings, or urbancanyons.Local positioning systems using cellular broadcast towers are also heavily used to determine the current position of aperson (carrying a cellphone without GPS-capability), ie for a wide array of services. See Mobile phone tracking

TechniquesAn LPS can either use:• triangulation• trilateration or• multilaterationto calculate the position of an object.

Local positioning system 25

Commercial systemsCommercial systems on the market and/or in progress include[1] :• Microsoft's RADAR [2]

• Ekahau's RTLS [3]

• Zebra Technologies Corporation RTLS WhereLAN [4]

• Awarepoint RTLS [5]

• Skyhook Wireless

References[1] Elektor magazine February 2011, Geolocalisatie zonder GPS[2] http:/ / research. microsoft. com/ en-us/ projects/ radar/ default. aspx[3] http:/ / www. ekahau. com/[4] http:/ / zes. zebra. com/ products/ rtls/ index. jsp[5] http:/ / www. awarepoint. com/

Article Sources and Contributors 26

Article Sources and ContributorsMobile phone tracking  Source: http://en.wikipedia.org/w/index.php?oldid=448545069  Contributors: -

Multilateration  Source: http://en.wikipedia.org/w/index.php?oldid=440042794  Contributors: -

Real-time locating system  Source: http://en.wikipedia.org/w/index.php?oldid=448872987  Contributors: -

Location-based service  Source: http://en.wikipedia.org/w/index.php?oldid=443244741  Contributors: -

Local positioning system  Source: http://en.wikipedia.org/w/index.php?oldid=445792034  Contributors: -

Image Sources, Licenses and Contributors 27

Image Sources, Licenses and ContributorsFile:HyperboloidOfTwoSheets.png  Source: http://en.wikipedia.org/w/index.php?title=File:HyperboloidOfTwoSheets.png  License: GNU Free Documentation License  Contributors: -Image:TDOA Geometry.png  Source: http://en.wikipedia.org/w/index.php?title=File:TDOA_Geometry.png  License: Creative Commons Attribution-Sharealike 3.0  Contributors: TinyPebbleImage:CrossCorr_Pulse.png  Source: http://en.wikipedia.org/w/index.php?title=File:CrossCorr_Pulse.png  License: Creative Commons Attribution-Sharealike 3.0  Contributors: TinyPebbleImage:CrossCorr_Wideband.png  Source: http://en.wikipedia.org/w/index.php?title=File:CrossCorr_Wideband.png  License: Creative Commons Attribution-Sharealike 3.0  Contributors:TinyPebbleImage:CrossCorr_Narrowband.png  Source: http://en.wikipedia.org/w/index.php?title=File:CrossCorr_Narrowband.png  License: Creative Commons Attribution-Sharealike 3.0  Contributors:TinyPebble

License 28

LicenseCreative Commons Attribution-Share Alike 3.0 Unportedhttp:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/