Project Number:
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`IST-2000-25382-CELLO
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`Project Title:
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`Cellular network optimisation based on mobile
`location
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`Cellular Location Technology
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`Contributors:
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`Heikki Laitinen (editor), Suvi Ahonen, Sofoklis Kyriazakos, Jaakko
`Lähteenmäki, Raffaele Menolascino, Seppo Parkkila
`CELLO-WP2-VTT-D03-007-Int
`CELLO-WP2-VTT-D03-007-Int.doc
`007
`VTT
`5.11.2001
`Deliverable
`PU
`
`Document Id:
`File Name:
`Version:
`Organization:
`Date:
`Document type:
`Security:
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`Abstract:
`This document contains a review of the current status of cellular location technology and
`near-future developments. Location methods based on cellular system signals (GSM and
`UMTS), and GPS are presented and evaluated in terms of their applicability for the purposes
`of CELLO project targets. The location-based applications of CELLO project, i.e. location-
`aided planning, location-aided handover, and location-aided mobility management, require a
`location method that gives fast response and accuracy to a fraction of cell radius, causes
`minimal amount of extra signalling, and has large capacity. These requirements are best met
`by methods that use standard measurement reports from mobile terminals. Changes to
`standards may be needed to retrieve the required measurements in GSM and UMTS.
`Keyword list:
`Location, positioning, GSM, UMTS, GPS
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`Apple Inc. Exhibit 1007 Page 1
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`

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`CELLULAR LOCATION TECHNOLOGY: CELLO-WP2-VTT-D03-007-Int
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`DOCUMENT HISTORY
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`
`Comments
`Version Status
`Date
`Initial TOC for partners’ comments
`07.03.2001 001
`Int
`Updated as agreed in Turin meeting
`03.05.2001 002
`Int
`First draft
`27.06.2001 003
`Int
`Second draft (some parts still missing)
`10.07.2001 004
`Int
`Full version
`30.08.2001 005
`Int
`Minor editorial corrections / version submitted to EC
`14.09.2001 007
`Apr
`Enhanced executive abstract
`05.11.2001 008
`Int.
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`CELLO Consortium (http://telecom.ntua.gr/cello): VTT Information Technology, Cosmote
`Mobile Telecommunications S. A., Center for PersonKommunikation, Elisa
`Communications Corporation, Motorola S.p.A, Institute of Communication and Computer
`Systems, Teleplan AS.
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`Copyright  2001 CELLO Consortium
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`CELLULAR LOCATION TECHNOLOGY: CELLO-WP2-VTT-D03-007-Int
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`TABLE OF CONTENTS
`1
`INTRODUCTION .............................................................................................................1
`2 CELLULAR LOCATION METHODS...........................................................................1
`2.1 CELL IDENTIFICATION .....................................................................................................3
`2.2 SIGNAL STRENGTH...........................................................................................................4
`2.3 ANGLE OF ARRIVAL.........................................................................................................4
`2.4 UPLINK TIME (DIFFERENCE) OF ARRIVAL .........................................................................5
`2.5 DOWNLINK OBSERVED TIME DIFFERENCES ......................................................................6
`2.5.1 Enhanced Observed Time Differences (E-OTD)....................................................7
`2.5.2 Observed Time Difference of Arrival (OTDOA) ....................................................8
`2.6 HYBRID METHODS ...........................................................................................................9
`2.6.1 Angle of Arrival + Round Trip Time (AOA+RTT) .................................................9
`2.6.2 OTDOA + AOA ......................................................................................................9
`2.7 DATABASE CORRELATION..............................................................................................10
`2.7.1 Generic location method ......................................................................................10
`2.7.2 Application to GSM ..............................................................................................11
`2.8 LOCALISATION IN 2/3 G SYSTEMS BASED ON SIGNAL PATTERN RECOGNITION ...............12
`2.8.1 Hidden Markov Models ........................................................................................12
`2.8.2 Training the Models..............................................................................................13
`1.1.3 Conclusions ..........................................................................................................16
`3 HANDSET-BASED GPS LOCATION OF MOBILE TERMINALS ........................17
`3.1 GPS OVERVIEW.............................................................................................................17
`3.2 DGPS............................................................................................................................19
`3.3 ASSISTED GPS...............................................................................................................21
`3.4 OTHER SATELLITE-POSITIONING SYSTEMS.....................................................................21
`3.5 INDUSTRY SUPPORT TO HANDSET-BASED SYSTEMS .......................................................22
`4 PRODUCTS AND TRIALS ...........................................................................................22
`4.1 RADIOLINJA...................................................................................................................22
`4.2 KSI................................................................................................................................23
`1.3 CAMBRIDGE POSITIONING SYSTEMS..............................................................................24
`1.4 VTT ..............................................................................................................................24
`1.5 US WIRELESS ................................................................................................................25
`1.6 BENEFON .......................................................................................................................27
`1.7 SNAPTRACK ..................................................................................................................27
`5 STANDARDISATION....................................................................................................28
`5.1 GSM STANDARDISATION...............................................................................................28
`5.2 GSM STANDARDISATION SUPPORT FOR CELLO APPLICATIONS ....................................29
`5.3 UMTS STANDARDISATION ............................................................................................31
`5.3.1 Location Architecture...........................................................................................31
`5.3.2 Location Measurements and Reporting................................................................32
`5.4 CELLO CONTRIBUTION TO STANDARD BODIES ............................................................34
`5.4.1 3rd Generation Partnership Project (3GPP) ........................................................34
`5.4.2 Location Interoperability Forum (LIF) ................................................................35
`5.4.3 Proposed Strategy.................................................................................................36
`6 COMPARISON OF DIFFERENT TECHNIQUES.....................................................36
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`6.1 LOCATION ACCURACY ...................................................................................................39
`7 CONCLUSIONS..............................................................................................................41
`ANNEX A
`REFERENCES .............................................................................................42
`
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`TERMS AND ACRONYMS
`2G
`Second generation cellular mobile system (GSM)
`3G
`Third generation cellular mobile system (UMTS)
`3GPP
`Third Generation Partnership Project
`AOA
`Angle of Arrival
`BCCH
`Broadcast Control Channel
`BS
`Base Station
`BSC
`Base Station Controller
`BTS
`Base Transceiver System
`CBC
`Cell Broadcast Centre
`CDMA
`Code Division Multiple Access (UMTS)
`CPICH
`Common Pilot Channel
`DCM
`Database Correlation Method
`DGPS
`Differential GPS
`DL
`Downlink
`E911
`Enhanced 911 (wireless Enhanced 911 emergency call service in United States)
`E-OTD
`Enhanced Observed Time Difference
`ETSI
`European Telecommunications Standards Institute
`FCC
`Federal Communications Committee
`FDD
`Frequency Division Duplex
`GDOP
`Geometrical Dilution of Precision
`GMLC
`Gateway Mobile Location Centre
`GPS
`Global Positioning System
`GSM
`Global System for Mobile communication
`HLR
`Home Location Register
`HMM
`Hidden Markov Model
`IPDL
`Idle Period Downlink
`LAH
`Location-Aided Handover
`LAM
`Location-Aided Mobility Management
`LAP
`Location-Aided Planning
`LCS
`Location Services
`LIF
`Location Interoperability Forum
`LMU
`Location Measurement Unit
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`LOS
`MGIS
`MLC
`MS
`MSC
`NLOS
`OTDOA
`PCF
`QoS
`RTD
`RTT
`SA
`SACCH
`SFN
`SIM
`SMLC
`SMS
`SPS
`SRNC
`TA
`TA-IPDL
`TDD
`TDMA
`TDOA
`TOA
`TS
`TSG
`UMTS
`UTRA
`UTRAN
`VLR
`VMSC
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`Line of Sight
`Mobile Geographical Information System
`Mobile Location Centre
`Mobile Station (Mobile phone)
`Mobile Switching Centre
`Non-Line of Sight
`Observed Time Difference of Arrival
`Position Calculation Function
`Quality of Service
`Real Time Difference
`Round Trip Time
`Selective Availability
`Slow Associated Control Channel
`System Frame Number
`Subscriber Identification Module
`Serving Mobile Location Centre
`Short Message Service
`Standard Positioning Service
`Serving Radio Network Controller
`Timing Advance
`Time Aligned-IPDL
`Time Division Duplex
`Time Division Multiple Access
`Time Difference of Arrival
`Time of Arrival
`Technical Specification
`Technical Specification Group
`Universal Mobile Telecommunication System (CDMA)
`UMTS Terrestrial Radio Access
`UMTS Terrestrial Radio Access Network
`Visitor Location Register
`Visited Mobile Switching Centre
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`EXECUTIVE SUMMARY
`This document contains a review of the current status of cellular location technology and
`near-future developments. Basic location techniques based on cellular system signals (GSM
`and UMTS), and satellite systems are presented. Cellular location techniques include methods
`based on cell identification, signal strength, angle-of-arrival, time delay, correlation with
`database and signal pattern recognition. An overview of Global Positioning System is given
`along with description of differential and assisted GPS positioning methods. Some trial
`systems and commercial products, based on different techniques, are described in order to
`give a general view on what is being developed and what is already available on the market.
`In urban environment the best accuracy can be achieved by time delay and correlation based
`techniques.
`GSM and UMTS standardisation on location methods and services is covered. Different
`location methods are evaluated based on the requirements set by CELLO applications. It is
`concluded that the most applicable location methods are based on standard measurement
`reports that are continuously transmitted from the mobile station back to the network during a
`connection. Such methods in GSM are e.g. the signal strength method and database
`correlation method. To ensure the support for CELLO applications in GSM and UMTS,
`contribution to standardisation bodies may be needed.
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`CELLULAR LOCATION TECHNOLOGY
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`1 INTRODUCTION
`There is increasing interest towards location technologies and location based mobile services.
`One of the driving forces is the obligation set by the FCC (Federal Communications
`Committee) in the United States to provide enhanced 911 (E911) wireless services. According
`to the obligation, cellular systems will be able to locate a cellular phone in connection of an
`emergency, with certain schedules and accuracy requirements [11]. Also the European
`Commission has plans to implement a similar obligation, but probably without accuracy
`specifications. Another driving force is the wealth of foreseen location-based services. By
`summer 2001, some location-based services have already been introduced by GSM operators
`in Europe. Available location methods include cell identification and methods based on signal
`strength measurements. Also first GSM handsets with integrated GPS navigator are available
`on the market.
`There are two basic approaches for locating the mobile phone. The phone can either be
`located with the help of the cellular system's signals or the phone can be integrated with a
`GPS receiver, which takes care of the location function. Implementing location methods
`requires some modifications, either software or hardware or both, to the cellular phone and/or
`the network. These modifications create various amounts of costs and new signalling to the
`network. Also the achievable accuracy of location methods varies. The requirements set by
`the applications determine which location method is the best or most cost-effective.
`The location-based applications of CELLO project are location-aided planning (LAP),
`location-aided handover (LAH) and location-aided mobility management (LAM). They aim at
`performance enhancements in the cellular network by collecting location-dependent
`performance data (LAP) or by using the location of mobile users in real-time (LAH and
`LAM). The requirements for the location method to support these applications are demanding.
`Accuracy to a fraction of cell size is clearly needed. High capacity of the location system is a
`requirement, since a large number of users (preferably all!) with on-going call or data
`connection has to be located. LAH and LAM also need fast response, but for LAP this is not
`critical. The purpose of this document is to present the location methods that are available or
`being developed and to evaluate their applicability for LAP, LAH and LAM.
`The different location techniques using cellular system’s signals are described in Chapter 2.
`Chapter 3 contains an overview of Global Positioning System and its use as a stand-alone or
`network-assisted cellular location method. Some of the commercial products and reported
`location trials are reviewed in Chapter 4. A brief overview of the standardisation activities and
`their influence on CELLO project is given in Chapter 5. Different location methods are
`compared, in view of CELLO requirements, in Chapter 6.
`
`2 CELLULAR LOCATION METHODS
`Cellular location methods use the signals of the cellular system to find the location of a
`mobile station. Since cellular systems were not originally designed for positioning, the
`implementation of different location methods may require new equipment to make the
`necessary measurements for location determination and new signalling to transfer the
`measurement results to the location determination unit. Before presenting the cellular location
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`methods and their implementation aspects, some concepts that will be used to classify
`different methods based on the role of the mobile station (MS) and the network or on the
`location measurement principle are defined.
`Based on the functions of the MS and the network, implementation of a location method
`belongs to one of the following categories:
`• Network-based
`• Mobile-based
`• Mobile-assisted
`In network-based implementation one or several base stations (BSs) make the necessary
`measurements and send the measurement results to a location centre where the position is
`calculated. Network-based implementation does not require any changes to existing handsets,
`which is a significant advantage compared to mobile-based or most mobile-assisted solutions.
`However, the MS must be in active mode to enable location measurements and thus
`positioning in idle mode is impossible.
`In mobile-based implementation the MS makes measurements and position determination.
`This allows positioning in idle mode by measuring control channels which are continuously
`transmitted. Some assisting information, e.g. BS coordinates, might be needed from the
`network to enable location determination in the MS. Mobile-based implementation does not
`support legacy handsets
`The third category, mobile-assisted implementation, includes solutions where the MS makes
`measurements and sends the results to a location centre in the network for further processing.
`Thus, the computational burden is transferred to a location centre where powerful processors
`are available. However, signalling delay and signalling load increase compared to a mobile-
`based solution, especially if the location result is needed at MS. Although mobile-assisted
`solutions typically do not support legacy handsets, it is possible to use the measurement
`reports (see section 2.8.2) that are continuously sent by GSM handsets to the network in
`active mode. Techniques that use these measurement reports, e.g. signal strength
`measurements, are often classified as network-based since they do not require any changes to
`existing handsets. Nevertheless, it is the MS that makes the measurements and therefore these
`techniques will be called mobile-assisted in the following.
`The requirements set by different applications may favour different kinds of implementations.
`For example, emergency call location requires high reliability and it is highly desirable to
`locate these calls from legacy phones as well as new phones. Applications that use continuous
`tracking, e.g. route directions, require high accuracy and fast location with a fixed update rate.
`Since the location result is needed at MS in this case, these requirements are best met with a
`mobile-based solution. Some applications, e.g. traffic monitoring and location-aided network
`planning (LAP), require mass location capability at network. These requirements can only be
`met by network-based or mobile-assisted implementations.
`Another classification is based on the measurement principle [35]. The measurement principle
`of each method belongs to one of three categories:
`• Multilateral
`• Unilateral
`• Bilateral
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`In multilateral techniques, several BSs make simultaneous (or almost simultaneous)
`measurements. Multilateral measurement principle leads to network-based implementation.
`Unilateral means that the MS measures signals sent by several BSs and thus leads to mobile-
`based or mobile-assisted implementation. For bilateral techniques multiple measurements are
`not needed: either MS measures signal from a single BS or one BS measures signal from MS.
`This does not exclude any of the three implementation categories. Since multilateral
`techniques require co-ordination of simultaneous measurements at multiple sites, unilateral
`techniques are generally better for capacity and signalling load. Bilateral techniques are
`optimal for rural coverage since only one BS is involved.
`
`2.1 Cell Identification
`The simplest method for locating a mobile phone is based on cell identification. Since this is
`an inherent feature of all cellular systems, minimal changes to existing systems are needed.
`The cell ID only has to be associated with location, i.e. the coordinates of the BSs must be
`known (see Figure 1). This is a bilateral location principle that can be implemented as a
`network-based or mobile-based technique. In mobile-based implementation, the network
`would have to continuously transmit the coordinates on a control channel.
`
`x,y
`
`variable cell size:
`50 m (indoors) --> 30 km (rural areas)
`
`
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`Figure 1. Positioning based on cell identification.
`Another advantage of this method is that no calculations are needed to obtain location
`information. Thus, cell ID based location is fast and suitable for applications requiring high
`capacity. The drawback is that accuracy is directly dependent on cell radius, which can be
`very large especially in rural areas. In dense urban areas location accuracy is considerably
`better due to the small cell radius of micro- and picocells. Nevertheless, this method is not
`accurate enough for the purposes of CELLO project, since LAP, LAH and LAM all require
`sub-cell position accuracy. Accuracy can be improved using information of cell coverage area
`(e.g. sector cells) and timing advance (TA) in GSM or round trip time (RTT) in UMTS. Even
`with these enhancements the accuracy is probably too low for CELLO applications.
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`2.2 Signal strength
`Using signal strength measurements from the control channels of several BSs, the distances
`between the MS and the BSs can be estimated. Assuming two-dimensional geometry, an
`omnidirectional BS antenna, and free-space propagation conditions, signal level contours
`around BSs are circles. If signal levels from three different BSs are known, the location of the
`MS can be determined as the unique intersection point of the three circles. However, practical
`propagation conditions especially in urban areas are far from free-space propagation.
`Therefore, an environment-dependent propagation model for the dependence of received
`signal level on BS-MS distance should be used. In urban areas the received signal level
`generally decreases more rapidly with distance than in open areas.
`Multipath fading and shadowing poses a problem for distance estimation based on signal
`level. The instantaneous, narrowband signal level may vary by as much as 30-40 dB over a
`distance of only a fraction of the wavelength. Random variations of this order of magnitude
`cause very large errors in distance estimates. However, fast fading can be smoothed out by
`averaging the signal strength over time and frequency band. Time-averaging only has a minor
`effect, due to the motion in the surrounding environment, if the MS is stationary. Contrary to
`fast fading, the random variations caused by shadowing can not be compensated. Thus, the
`variations in antenna orientation and local shadowing conditions around the MS (indoors,
`inside a vehicle etc.) are seen as random errors in distance estimates and consequently in
`position estimate. Location accuracy also depends on the accuracy of the propagation model
`and the number of available measurements.
`Signal strength method is unilateral and can be implemented as mobile-assisted or mobile-
`based method. Mobile-based implementation requires that BS coordinates are transmitted to
`the MS. Signal strength method is easy to implement in GSM, based on measurement reports
`(see Table 1, p. 15) that are continuously transmitted from the MS back to the network in
`active mode. Therefore, it does not require any changes to existing phones, and is often called
`a network-based method although it is the MS that performs the measurements. An alternative
`implementation is to modify the MSs to enable sending measurement reports in idle mode
`also. GSM phones with this capability are already available. Signal strength is an easy and
`low-cost method to enhance the accuracy of pure cell ID based location (see also Section 4.1).
`However, it is questionable whether the accuracy is adequate for CELLO applications.
`In UMTS DL the BSs send the common pilot channel (CPICH) with constant power of 33
`dBm (10% of the max power). CPICH is unique in each cell and always present in the air.
`Before any other transmission each MS monitors the CPICH. Thus, each MS is able to
`measure the power levels of the nearest BSs common pilot channels. In UMTS, signal
`strength measurements may be slightly more reliable due to the wider bandwidth, which
`allows better smoothing of fast fading. On the other hand, the hearability problem prevents
`measurements of as many neighbouring BSs as it is possible in GSM.
`
`2.3 Angle of Arrival
`Signal angle of arrival (AOA) information, measured at the BS using an antenna array, can be
`used for positioning. Assuming two-dimensional geometry, angle of arrival measurement at
`two BSs is sufficient for unique location. This is illustrated in Figure 2, where the user
`location is determined as the point of intersection of two lines drawn from the BSs. It is seen
`that AOA technique requires line of sight between the MS and the BSs for accurate results.
`Also, the uncertainty in AOA measurement causes a position uncertainty that increases with
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`MS-BS distance. Achieved accuracy depends on the number of available measurements,
`geometry of BSs around the MS and multipath propagation also.
`
`
`
`Figure 2. Positioning with angle of arrival measurements.
`Since AOA method needs line-of-sight propagation conditions to obtain correct location
`estimates, it is clearly not the method of choice in dense urban areas where line of sight to two
`BSs is seldom present. In [32], an rms location error of approximately 300 m with two BSs
`and 200 m with three BSs in an urban environment was observed. However, the AOA
`technique could be used in rural and suburban areas where the attainable accuracy is better
`and it is an advantage to be able to locate a MS which can only be measured by two BSs.
`A major barrier to implement AOA method in existing 2G networks is the need for an antenna
`array at each BS. It would be very expensive to build an overlay of AOA sensors to existing
`cellular network. However, since it is a network-based method and supports legacy handsets,
`it is developed by several companies as an E911 solution. In 3G systems AOA measurements
`may become available without separate hardware if adaptive BS antennas (arrays) are widely
`deployed.
`In addition to financial issues, AOA method may have a capacity problem. Multilateral
`measurement principle (measurement at several BSs) requires the co-ordination of almost
`simultaneous measurements at several BS sites, and it is difficult to serve a large number of
`users.
`
`2.4 Uplink time (difference) of arrival
`Signal time of arrival (TOA) measurements, performed either at the BSs or at the MS, can be
`used for positioning. If the BSs and the MS are fully synchronised, TOA measurements are
`directly related to the BS-MS distances and three measurements are needed for unique 2D
`location. However, if the network is not synchronised, such as GSM and UMTS FDD
`networks, TOA measurements can only be used in differential manner. Even in this case, a
`common time reference for the BSs is needed. Two TOA measurements then define a
`hyperbola, and four measurements are needed for unambiguous 2D location.
`If the measurements are performed at BSs, it is a network-based multilateral technique. This
`technique has two drawbacks compared to downlink method: it is only possible to perform the
`measurements in dedicated mode and there may be capacity problems due to the multilateral
`measurement principle. The advantage is that due to the network-based implementation,
`uplink TOA supports legacy phones. It was taken into GSM standardisation as a candidate
`E911 solution [21]. In GSM implementation of uplink TOA technique, a common time
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`reference, e.g. GPS receiver, is needed at each BS site. The location of an MS with call on is
`accomplished by forcing the MS to request a handover to several neighbouring BSs. The MS
`then sends access bursts at full power, and TOA measurements are made from these bursts.
`
`2.5 Downlink observed time differences
`In the downlink time difference techniques, the MS observes time differences of signals from
`several BSs. These signals are typically control channel signals and therefore the MS can
`perform the measurements in idle mode as well as in dedicated mode. The clock differences
`of the BSs can be solved by having a reference receiver at known location continuously
`measuring the observed time differences. This is much simpler and more economical than
`synchronising the BS transmissions.
`The accuracy of all time difference based techniques (uplink as well as downlink) depend on
`several factors. The accuracy of an individual time difference measurement depends on signal
`bandwidth and multipath channel. This is illustrated in Figure 3 with an error margin for each
`time difference measurement. In an urban area the error margin is typically larger, since
`heavy multipath makes it more difficult to detect the time of arrival of the first echo. If there
`is no line of sight between the MS and the BSs involved, the location estimates will be biased
`away from the BSs with no line of sight to the MS (see Figure 3). This is a problem especially
`in urban areas. In open areas the geometry of the BS configuration around the MS may
`introduce an additional error, which is described by geometrical dilution of precision
`(GDOP). A favourable geometry is a uniform distribution of BSs around the MS. Also the
`number of available measurements has an effect on accuracy: generally it is better to have as
`many measurements as possible.
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`Figure 3. Positioning based on time difference measurements in open (left) and urban
`environment (right).
`UMTS bandwidth is 5 MHz and it operates at a high chip rate 3.84 Mcps/s, which contributes
`to the better resolution in timing measurements compared to GSM. The timing resolution in
`UMTS with one sample per chip is ∼0.26 µs which corresponds to the propagation distance of
`∼78 m. In GSM (bit rate 270.8 kBits/s) the bit duration is 3.69 µs and the corresponding
`propagation distance is ∼1100 m. Thus, the finite timing advance (TA) allows to represent
`absolute distances with a resolution of 554 m. Oversampling of four times the chip rate is
`often used in the receiver [33]. For UMTS and GSM that means sampling with a rate of
`4⋅3.84Mcps and 4⋅270.8kBit/s respectively. Thus the timing resolutions are improved to
`
`Copyright  2001 CELLO Consortium
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`6 of 44
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`CELLO-WP2-VTT-D03-007-Int
`25/10/2001 5:34 PM
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`Apple Inc. Exhibit 1007 Page 13
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`

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`CELLULAR LOCATION TECHNOLOGY: CELLO-WP2-VTT-D03-007-Int
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`values ∼65 ns in UMTS and ∼923 ns in GSM corresponding to propagation distances ∼19,5 m
`and ∼277 m respectively. In timing techniques for obtaining the needed accuracy level of the
`MS position estimates, oversampling will be quite mandatory. With advanced technology, it
`should be possible to achieve higher sampling rates. Thus, the sampling resolution in UMTS
`will also affect the timing accuracy in measurements. However, the bandwi