OTDOA Location Determining Technology for Universal Intelligent PositioningSystem (UIPS) Implementation in Malaysia

Keeratpal Singh, Mahamod IsmailDept. of Electrical, Electronics and System Engineering, Faculty of Engineering,

Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor D.E., MALAYSIATel: +603-89216322, Fax: +603-89216146, Email: singhjatt@hotmail.com, mahamod@eng.ukm.my

Abstract- Various location determining techniques havebeen proposed for Location Based Services (LBS) such asCell Identification (Cell ID), Observed Time Difference ofArrival (OTDOA), Enhanced Observed Time Difference (E-OTD), Network Multipath Analysis and Assisted GlobalPositioning System (A-GPS). This paper presents thedevelopment work by simulating OTDOA based locationdetermining technology (LDT) with integration to UniversalIntelligent Position System (UIPS) implementation inMalaysia's Telco network. The concept of UIPS for GSM andUMTS networks offers the key players of the entire mobileservices value chain in Malaysia to benefit through itsintegration. It is expected with the usage of UIPS, ContentProviders (CP) can connect easily to Telcos and offer varietyof LBS services. It is hope that with UILPS, major key playersto continuously promote LBS to make it a successfulconsolidated effort for navigation, information search andemergency tracking. Challenges faced on differentgeographical terrains calls for further study on random surveyto construct a trained database with noise/loss models foraccuracy improvement. This is to complement any fall backcontingency.

Keywords: Location Based Services, UMTS, 3G,Wireless Technology, OTDOA

I. INTRODUCTION

In Malaysia, the first LBS called Friend Finder waslaunched by Maxis in 2004. The accuracy and complexity toimplement each LDT within a Telco' s network is very crucialfor Telco's to launch the accurate Location Based Services.Table I illustrates the accuracy and complexity for each LDT.As part of improvement to the LBS, the design of UniversalIntelligent Positioning System (UIPS) offers any LocationDetermining Technology (LDT) such as AGPS, Cell ID, andOTDOA to be integrated under its Positioning DeterminingLayer in a real Telco's GSM/GPRS/EDGE, 3G or beyondnetwork [1. Figure 1 illustrates the concept. The OTDOALDT method will be chosen here to be simulated. OTDOA orhyperbolic method is based on the mobile measurements ofthe relative arrival times of pilot signal from at least 3 basestations.

TABLE 1. LDT COMPARISONSLDT Complexity AccuracyCell ID Simple-Telco use Base Low accuracy -20Gm(GSM/ station info to obtain (microcell in buildings) toUMTS) location of mobile phone 15km (rural or large cell

attached to the size).nearest/strongest BS

E-OTD Medium-Telco may need Medium accuracy- 10Gm(GSM) to implement LMU in to 500m in urban and few

network to synchronize km in rural. Need at leastclocking to obtain timning 3 BS.

OTDOA Medium-Telco may need Medium accuracy- lOOm(UMTS) to implement LMU in to 500m in urban and few

network to obtain km in rural. Need at leastaccurate time of arrival 3 BS.

Angle Of Medium -Telco may need Medium accuracy-I 0Gm toArrival to implement smart 500m in urban and up to(UMTS) antenna in network that few km in rural.

provides angle and timinginfo

A-GPS Medium- Telco need High accuracy-30m to(GSM/ AGPS server at base 300m. Need Line of SightUMTS) stations and users have to of GPS satellites for high

buy new AGPS phones accuracy.Database Medium-Require to Medium to High accuracy-Method construct database on area 50m in urban areas.(GSMI points, cell info related toUMTS) signals multipath /delay.

Minor software changesto base stations.

. ----_ _ _ _ __ __ _ _

Locations Content!Applications Layer ICPL----------

PositioninigiDetermining UIPS

, Layer , FutureL _ Work

$ OTDOA

Network GSM 3G L 4LLayerL

Malaysian Telcos: Maxis (2G,3G), Digi(2G), Celcom (2G,3G)

Figure 1. Concept of UIPS in 2G, 3G and 4G. For this research,OTDA is selected as the LDT technique

1-4244-0000-7/05/$20.00 02005 IEEE. 1057

A pair of base station defines the hyperbola and with 3 basestations, making 2 pairs, the intersection or convergence canbe obtained for the location coordinates [2]. This coordinateswill be translated to the grid plans in actual location thatTelco's already stored in their location database. Once thisfinal info is obtained, the UIPS will send to the CP therespective info in an agreed format. And content provider willoutput the feedback message to the requester while requestingUIPS to charge the Telco's billing mediation/network. Fromthis research, observations will be made to note the total timerequired for a simple round trip SMS query and servicefeedback message to the SMS requester.

It is important to take into account the various LDT to beused in future as some requires more computations thanothers and this translates to a lot of query time between theUTRAN (BSS in GSM) and the UE (Mobile phone). 3GPPTS 25.215 version 6.0 .0 Release 6 [3], defines UMTSPhysical layer Measurements for FDD networks, whichincludes UE or network side carrier received signal strengthindicator (RSSI), UE transmitted power, observed timedifference, GPS code phase, Signal to interference ratio,round trip time, propagation delay during PRACHJPCPCHaccess and others. Therefore for this research, OTDOA wasutilized where in Release '99 of UMTS, all local Telcos haveimplemented this specifications with the availability ofOTDOA-IPDL (Observed Time Difference Of Arrival-IdlePeriod Downlink). This specification is to avoid the near-farproblems that are introduced along with the UMTS network,where during the idle period; the UE mobile could receive theneighbor station's pilot signal even though the best pilotsignal on same frequency is strong from another base station.Location measurement unit (LMU) will be utilized in basestations so the network (Node B towards RNC) can calculatethe UE (mobile) location in relative to transmission times ofpilot signals from the neighbor or adjacent stations.

In this research the scope is assumed to have 3 best pilotsignal at all times and that all UE are within the line of sight,which in ideal conditions may not typically be available.Study is being pursued to generate a trained databasetopology where propagation delays i.e. path loss will beadded to the timing calculations to generate better accuracy insurveyed metropolitan areas.

II. METHODOLOGY

In this research the development and performance will bediscussed as part of the design with the OTDOA simulationin a 7 hexagon cell settings, assuming LOS of UEs inrelations to the 7 Node Bs. Work is in progress to develop theinterface from CP (Content Provider) ApplicationProgramming interface (API) towards Core Network, MSC,HLR, SGSN, GGSN, BSS, and UTRAN and its integration tothe respective location determining technology (under UIPSposition determining layer).

Figure 2 shows the Flowchart of the testing as initiatedby the UE. The user sends an SMS message requesting for alocation based service pertaining to his/her location to anadvertised shortcode number, for example 22222. From theTelco' s SMSC, the message is then forwarded to therespective owner of the shortcode number, which is theContent Provider. The Content Provider's Server/Engine willthen communicate via VPN network /dedicated lease linewith UIPS. Since the format of the UIPS has been preset bythe API used between Telcos and CP, the QoS associatedwith it and the billing charges are sent along to the Telcoupon successful feedback.

UIPS will then route the request to UTRAN or BSSbased on the user's telephone network details as interrogatedfrom the HLR. Since for this example, the UE is for 3Gnetwork, the RNC will be requested for timing measurementsfrom all adjacent Node Bs (base stations).

Once the hyperbolic timing are calculated from LMUinputs at Node Bs (3 node B are required to generate 2 pair ofhyperbolic equations), the coordinates of the convergence willbe calculated.

Figure 3 illustrates an example of 7 Node Bs with 5 UEspresent in the selected zone. Based on the example, Node Bstation 6, 7 and 1 provides the intersection or convergencepoint. This coordinate for the particular zone is sent to thedatabase location server where relation of actual location inlongitude and latitude is sent back to the content provider.

If the service was to request for bookstores, the data sentback to the CP will have latitude and longitude information soCPs will do the building/places mappings themselves. Oncethe request has been sent by UIPS to CP, and successfulacknowledgement flag has been received by CP and hasforwarded the message back to the user ("the nearestbookstore is Menara ABC"), the charging request will also besent to Telco's billing mediation for further charging on theuser's phone number.

From experience, and adding the simulation result time,this whole process approximately takes about 40-50 secondsfor each location transactions and this is consideredacceptable since other infotainment based requests like monoringtone and picture message request via SMS takes about 20seconds to 50 seconds (during peak hours) to receive requestsat times. The chunk of time is due to heavy numericalcalculations done by the LMU (simulation) and sending thecoordinates to the database location server.

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3000 r

2000

1000[

0

-1000

-2000

-3000 -2000 -1000 0

Figure 2. Process Flow of UIPS for SMS request example which isgenerated by UE and terminates as feedback SMS location based

service to the requester/originator

1000 2000 3000

Figure 3. 7 cells with each node B centrally located in each cell.This example shows the circle convergence ofUE at 3 cells (6, 7 and

1). Each x and y axis represents coordinates in meters.

III. RESULTS FROM SIMULATING OTDOA INUIPS

For this study, Matlab was used as the simulationenvironment for generating a cluster of 7 neighbor cell, wherein each cell one Node B is located. The UE will be generatedrandomly across any of the 7 hexagon cells. 3 base stationcalculations are required to obtain the 2 pair of hyperbolicequations. Based on IPDL, the measurements are generatedto support the nearest 3 Node Bs. With the timinginformation, the distance is calculated for the interested UE (3circle convergence). This info is then passed back to UIPS tosend to CP.

The aim to generate at least 15% of location based trafficat peak hours within a zone of 7 hexagon cells wasimplemented. 100 UEs were generated that requested forlocation based services. Since the location of the UEs wereknown, and to check whether the OTDOA algorithm workedwithin a tolerable line of sight performance, the simulationoutputs the reversible results to re-identify the locations ofeach of the 100 UEs. Table 2 shows the properties of thesimulation.

Figure 4 illustrates the error distance for 100 UEs ascompared to the actual position of the simulated UE. Thestatistical result for median is 1.6460m for distance (inmeters) of actual to predicted by OTDOA simulation. Thisshows that the hyperbolic equation [41 is very tolerable if lineof sight is in place. The maximum inaccuracy is 1l.9mbetween predicted and actual UE location and the minimum is0.0193m.

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TABLE 2. SIMULATION PARAMETERSNo. Description ParametersI Cell Size 1000 meters

(homogeneous cell size)2 7 cluster area size 5000 meters3 Numbers of Request 100 UEs (Mobile phones

requesting for LBSservices)

4 LDT method OTDOA based on 3 circlesconvergence

5 Secondary LDT Cell ID based on strongestand nearest BTS used asfall back

6 Terrain Environment 2 dimension flat surfacewith Good line of Sight

09

08

0.7

0.6

xoD 5

0-4

0.3

02

0.1

Empincal CDF

0 2 4 6 8 10 12

Figure 4. Cumulative Distribution Function of comparing the real100 UE locations vs. the corresponding predicted 100 UE location as

obtained from OTDOA algorithm

Another simulation parameter, Secondary LDT, which isbased on Cell ID' s strongest and nearest signal of a fewneighbor BTS (Node B) was added to ensure the algorithmcompares final iteration distance in order to obtain the leastdistance errors. This acts as the control limit for the simulation.On going simulations on noisy environment are in progress toimprove the initial location tracking algorithm.

IV. CHALLENGES FACED AND FURTHERSTUDIES

In cities, ideal cases are not always observed due to timingdelay from propagation and object mutipath losses [4]. It istherefore, recommended to develop a trained database withnoise/loss table for interpolating the calculated distances. Thiswill be done during site survey of few random locations and thetable will be populated accordingly to mimic the random trends.Similar studies have been conducted for Database correlationMethod for GSM location [5]. Work in this area is in progress.

The simulated result distance error was less than 12m but inaverage cases, the inaccuracy could be more than lOOm due tonon line of sight of Node Bs or additional time delay frommultipath losses. Where there are no 3 adjacent stations,especially on straight highways, it is inappropriate to useOTDOA, and other location determining technology need to beconsidered for this case. Of course Cell ID or signal strengthbased technology is the easiest one to fall back to, but theaccuracy will be lower i.e. 500m difference from the actual UEdistance. It is crucial for OTDOA to be complemented with CellID in the event there are no proper alignments of 3 Node Bs.

It is also very important that the site survey data bepopulated at certain random locations pertaining to which LDTto use at which sites. This will then be populated at the UIPSdatabase server.

V. CONCLUSION

In this paper, the scope of UIPS integration work wasdiscussed. An example of SMS request LBS service by an UEuser was illustrated. To perform the OTDOA LDT, a Matlabprogram was simulated to work hand in hand with UIPS. Thisprogram simulates 100 UE in a 7 cell cluster and verifies itsaccuracy to detect the corresponding 100 UEs with theparameters of UTRAN as queried based on relative time from 3base stations. The calculation of convergence or intersectionpoint of the 2 hyperbolic pairs denotes the location of themobile UE. This info will be sent to UIPS location mapping,which will be pushed back to CP and finally the mobilerequester. From the experiment and experience, a 40-50 secsresponse time is considered acceptable if this testbed were to beput on a live environment. But at times when the environmentis not ideal, complement of LDT is required and adjustment tothe location calculation should be made by random survey toconstruct a trained database with noise/loss models. Work inthis area is in progress.

In general, CPs Location based services are dependent onhow accurate Telco's LDT is and when Telco's role out plan forCP to interface with Telco's network. Therefore it is expectedwith the usage of UIPS, CPs can connect easily to Telcos viathe LBS API and offer variety of LBS services.

ACKNOWLEDGEMENT

This work is supported by IRPA grant 04-02-02-0062-EA289

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REFERENCES

[11 Keeratpal Singh, Mahamod Ismail, "Location BasedServices for GSM and 3G in Malaysia: Perspective,Challenges and Promises", Proceedings for M2USIC2004 Conference, Putra Jaya, Malaysia, 7fh-8h October2004, Document No. TS4C-5, pp. 17-20

[21 Harri Holma, Antti Toskala, "WCDMA for UMTS RadioAccess for Third Generation Mobile Communications",John Wiley & Sons Ltd, Third Edition, 2004, pp. 40-44

[31 3GPP TS 25.215, "Technical Specification UniversalMobile Telecommunications System (UMTS); PhysicalLayer; Measurements (FDD) (3GPP TS25.215 version6.0.0 Release 6)", V6.0.0 (2003-12), pp. 1-19

[41 M.A. Spirito, "Accuracy of Hyperbolic Mobile StationLocation in Cellular Networks", Electronics Letters, vol.37, No. 11, 2001, pp. 708-710

[51 H. Laitinen, J. Lahteenmaki, T. Nordstrom, "Databasecorrelation method for GSM location", Proc. of IEEE53rd VTC Spring 2001, pp.2504-2508

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