tracking and positioning of mobile system in telecommunication

8/8/2019 Tracking and Positioning of Mobile System in Telecommunication

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Tracking andTracking and

positioning ofpositioning of

mobile system inmobile system in

telecommunicationtelecommunication

Trackin

g andTracking and

positioning ofpositioning of

mobile system inmobile system in

telecommunicationtelecommunicationJENNY JOSEPH

ROLL:25


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Overview

Introduction to mobiletechnology

Need for geolocation

Technologies used for

geolocation

Location tracking curve method

Conclusion


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Configuration of a typical mobile

communication


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Description A mobile telecommunication network includes several

base stations(T1 to Tn) for providing service to a mobilesubscriber through a mobile telephone M1, base stationcontroller (BSC) that controls the base station,and amobile telephone switching office (MTSO) for

connecting the BSC to another BTS or a PSTN(Publicswitched Telephone network)

The whole service area is divided into a several coverageareas having having respective base stations(BS).EachBS coverage area is called a CELL.

Each BS is provided with a frequncy ranging between450 to 900MHz and more than one cell can use thesame frequency.


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Need for geolocation

The ability to obtain the geolocation of theMobile Telephone in the cellular systemsallows the network operators to facilitate newservices to the mobile users

The geoplocation of the mobile user couldprovide services like:

Emergency service for subscriber safety

Billing

Cellular fraud detectionIntelligent transport systems services

Efficient and effective networkperformance


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Architecture of geolocation

system


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Upon a request from a subscriber about an

MS,the service provider will contact a location

control centre enquiering the cordinates of

the MS.

The location control centre gather information

required to compute the MSs location.

This informations could be parameters such as

received signal strength,TOA of signal etc.

Depending upon the past information aboutthe MSs,a set of BS could be used to page the

MS, and directly or indirectly obtain the

location parameters


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Once this information is collected,the location

control centre can determine the location of

the mobile and convey information to the

service provider

These are sometimes called geolocation base

stations.

The service provider use this information to

visually display the MSs location to the

subscriber


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Technologies used forgeolocation

HANDSET BASED MOBILE POSITIOING AND

TRACKING

global positioning system

DIRECTION BASED GEO LOCATION

Angle of arrival method

DISTANCE BASED POSITIONINGTime of arrival method(TOA)

Time difference of arrival method(TDOA)


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Global positioningsystem(GPS)


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the A mobile telephone can be located by a

mobile telephone itself through a mobile

telecommunication networkTo locate the the mobile telephone by itself, the

mobile is provided with a GPS reciever to

calculate its location in latitude and longitude

cordinates based on the location information

received from satellite through receiver.

DISADVANTAGES

Higher price

Increased load

High power consumption


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Angleof arrivalmethod


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When a mobile user switches the system ON,it

receives signal from different BSIn this method,it measures the direction of

signal falling on the BS and measures the

angle of incidence with respect to a normal

and determines the position of the system

DISADVANTAGES

Change in angle of incidence due to any

obstacle

Inaccurate location when mobile is in

between stations


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Timeof arrivalmethod(TOA)

It is assumed that the mobile is located at theintersection point of three circles having radius ofthe mobile and the BS

Distance is calculated by:

Ri = C ti = sqrt ( (xi X ) 2 + (yi Y) 2 ) where, C propagation speed of electromagnetic wave,

ti propagation of time from the mobile telephone toith base station,

xi, yi -- location of ith base station, X, Y mobile position.


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Timedifferenceofarrivalmethod(TDOA)


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Here the mobile is assumed to be located in

the overlap area of circlesWhen atleast three circles are overlapped over

an area without meeting at one point,the

mobile is considered to exist at theintersection point of three common chords

This method is still not accurate because it is

applicable in case where the mobile is at

equal distance from the selected BS


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When the mobile is not at an equal distance

from BS:


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Locationtrackingcurvemethod


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Description


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This method is used when mobile position

cannot be determined by the common chordL1.

The two curves TR1 and TR2 have their middlepoints intersecting the line ST, which connects

the positions of the two BSs T1 and T2 and theparts of the two circles C1 and C2 drawn toconnect the two intersection points P1 and P2

Instead of the common chord L1,yhe location

data processor uses the curve TR1 for themobile telephone M1 and the curve TR2 for themobile telephone TR2


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Determinationof location

trackingcurve


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If the radio propogation environment between themobile and the BS is poor due to multi path fadingand the NLOS effects,the TOA of the received signal

has error.

The NLOS has been compared with LOS and thevariances of the TOAs of a signal transmitted fromthe mobile are higher in NLOS

By knowing this,appropriate curves can be selectedby comparison between the variances of a TOAs ofthe signal

That is,the mobile is nearer from the chord L1 to the

one with larger variances out of the two BSThat is the mobile neaarer to the BS1 will have a

larger variance compared to BS2


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Therefore the BS with the smaller variances shouldbe selected to draw reference circle

Since the mobile telephone is nearer to BS1 wrt

common chord L1,the variances of the TOAs of asignal transmoitted from the mobile at the first BS T1will be larger than those of the signal at the BS2

Therfore reference circles TR1 to TR4 are drawn withrespect to the BS2 with smaller variances

Selecting the centre of the reference circle issignificant as the mobile telephone is located on thereference circle.

The location data processor selects the desired

curves with respect to several BSs selected forlocation tracking

In figure,as the real location of the mobile telephonedeviates farther from the circle C2 with the BS2 at itscentre,the centre of the reference circle is fartherfrom the BS2


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Referencecircleselection

If the TOAs of the signal at the first BS1 frompropagation paths is t1, the first BS1 calculates thevariances W of t1

The location data processor compares the variances

calculated by the BS1 with the variances calculatedby BS2 and considers that the mobile telephone isnear to that BS with the larger variances.

With the larger variances, the center of a referencecircle gets farther to the right from the center of BS2.

In order to select the desired curve, the location dataprocessor initializes the reference circles withpredetermined radii and the variances of TOAs of asignal transmitted located and compare the presetvariances with real variance measurements.


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The location data processor sets a several referencecircles based on the distances between the mobile

telephone and the BS with the smaller variances , as an example, the first to the fourth reference

circles TR1 to TR4 have radii twice, three times, fourtimes, and five times, respectively, of that of BS T2.

The variances of the second BS T2 smaller thanthose of the first BS T1 are used as a criterion forselecting an optimal reference circle.

Therefore, the location data processor

predetermines the reference variances for the first tothe fourth reference circles TR1 to TR4 to becompared with respect to the second BS T1.


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It is assumed in the following description that W 1, W2, and W 3 are reference variances and

W 1< W 2< W 3

The location data processor selects the base stationwith smaller variances as a reference point to drawthe reference circle. If the selected variances (thoseof the second BS T2) are W, the location data

processor compares the selected variancesW

, withthe preset reference variances W 1, W 2, and W 3.

IfW


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, the location data processor selects the optimalcurve (reference circle) for the two BSs among the

several BSs, and selects another optimal circle foranother BS pair, and so on. When curves are selectedfor all selected BS pairs, the location data processorobtains the intersection points among the selected

curves as shown in Figure However, as the selected curves do not intersect at

one point due to the multi-path fading or the NLOSeffects, the midpoint of these intersection points isdetermined as the location of the mobile telephone.


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The location data processor selects a first optimalcurve TR1 for BSs T1 and T2, a second optimal curve

TR2 for the second and the third BSs, and a thirdoptimal curve TR3 for the first and third BSs. As thethree intersection points M1 (xA, yA), M2 (xB, yB),and M3 (xC, yC) are defined by the three curves TR1to TR3, the location data processor considers the

mobile telephone to be located at (x, y). After the location of the mobile telephone, that is,

the intersection points among the curves areobtained, the location data processor represents the

intersection points in the latitude and the longitudecoordinates and transmits the position coordinatesto the network (BS/BSC/MSC) and the mobiletelephone.


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ConclusionOur proposal is advantageous in that the

location of a mobile telephone can be accuratelytracked even in the multi-path fading and the NLOSenvironment, by using more accurate tracking curvesconnecting the intersection points among circleswith the radii being the distances between

corresponding BSs and the mobile telephone in acellular mobile communication system. We havedescribed about accurate positioning of mobiletelephones, which can be used for severalapplications. The important considerations to be

undertaken while selecting a location basedtechnology are location accuracy, implementationcost, reliability, increasing functionality.


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References

J. Caffery, and G. Stuber Jr, Vehiclelocation and tracking for IVHS in CDMA micro-cells, Proc. IEEE PIMRC, 1994

G. Morley, and W. Grover, Improvedlocation estimation with pulse-ranging inpresence of shadowing and multi-path excess-delay effects, Electronics Letters, vol.31,No.18, 1995

www.ieeexplore.ieee.org

gp.espacenet.com


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Thankyou

tracking and positioning of mobile system in telecommunication

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