Umted States Patent [19]
`Kauser et a].
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,724,660
`Mar. 3, 1998
`
`[54] METHOD AND APPARATUS FOR LOCATING
`A MOBILE STATION BY COMPARING
`L
`ATI A A TH PS
`géoiglfgggsldoc ON RE WI G
`
`3/1994 Fukushima ....................... .. 364/449.95
`5,293,318
`5,365,447 11/1994 Dennis
`...... .. 342/357
`5,390,124
`2/1995 Kyrtsos
`464/4499
`5,390,339
`2/1995 Bruckert et a1. .
`.... .. 455/561
`5,422,813
`6/1995 Schuchman
`455/440
`
`
`
`[75] Inventors: Nicolas Kauser; Alan Denis MacDonald! both of Bellevue, Wash‘
`
`_
`
`,
`
`,
`
`
`
`
`
`' ' ' ' ' szchmdmmser' ' ‘ ' ‘ ' ' ' ............................ ..
`
`.
`
`.
`_
`[73] Asslgnce'
`
`.
`.
`tzfsielgsj Servlces’ Inc"
`
`Primary Examiner—Reinhard J. Eisenzopf
`Assistant Examiner—Lester G. Kincaid
`
`'
`
`[57]
`
`ABSTRACT
`
`[21] Ap p 1' No': 603’793
`[22] Filed:
`Feb. 20, 1996
`
`Related US. Application Data
`
`[63] cfm?llualio?-in-pa? of Sen NO- 472,032, Jun- 7, 1995.
`1 me 1.6 ........................... .. G01 2 00; 6015 3/02;
`[5 1
`C
`C 1,
`H0413 7 Q6
`[52] U S Cl
`455/456, 455/67 1_ 364/449 8_
`'
`'
`° """""""""" "
`’
`'
`’
`342/4'51’
`.
`[58] new of 81231767
`3‘79-'/59' 60 4’2/45'7’ 357’ 451’
`457
`45’2 45’0 463_ g 64/1149 1 44’9 8 449 9’
`’
`‘
`’
`' ’449
`'
`
`’
`
`'
`
`[5 6]
`
`.
`References Cited
`U.S. PATENT DOCUMENTS
`_
`22222;? as; insane.
`
`A method and apparatus for determining the location of a
`mobile telephone within the serving area of a mobile tele
`phone system. A mobile switching center analyzes the
`calling mobile telephone number and called telephone num
`ber to determine if a location function is required. Upon
`initiation of the location function by the mobile switching
`Center’ a “while 10°39” m°dule Calculates a1°°a?°n “ti
`mate of the mobile telephone. The mobile location module
`receives a list of signal strengths received by the mobile
`telephone from cell site antennas within the serving area.
`The distance between the mobile telephone and a plurality of
`cell site antennas is calculated using a technique which
`reduces the error component of the calculated distances.
`These reduced error distances are used to geometrically
`determine an estimate of the location area. In addition. the
`mobile telephone comprises a GPS receiver/processor for
`sending the most recent GPS coordinates of the mobile
`telephone which are within a predetermined con?dence level
`to the mobile location module. These GPS coordinates are
`compared with the calculated location area to increase the
`we mm
`
`.. 455/541
`5,055,851 10/1991 Sheffer ....... ..
`5,272,483 12/1993 Kato ...................................... .. 342/357
`
`32 Claims, 6 Drawing Sheets
`
`CALCULATE
`ZONE 1
`ANI]
`ZONE 2
`
`I 1002
`
`LONGltn) 111mm
`
`LDNGlln) WITHIN
`ZONE 2
`YES
`
`LUCATION=
`LATltnl. LONE
`ltnl WITH
`HIGH CONFIDENCE
`
`J’ 1024
`
`1010~~k
`
`LU£ATION=
`ZONE 2 WITH
`MODERATE
`CONFIDENCE
`
`LUCATION=
`1U 1H1
`LATH?), LONGHH)‘
`HITH HDDERATE
`EMFIDENCE
`
`1005
`
`f 1022
`
`f 1003
`
`mats? f 1015
`
`EWFIDENEE
`
`T-Mobile / TCS / Ericsson EXHIBIT 1007
`T-Mobile / TCS / Ericsson v. TracBeam
`Page 1
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet‘ 1 of 6
`
`5,724,660
`
`FIG. 1
`
`FIG. 3
`
`CELL
`
`R531 1
`RS512
`H5513
`B3514
`B3515
`H3315
`
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`Page 2
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`

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`T-Mobile / TCS / Ericsson EXHIBIT 1007
`T-Mobile / TCS / Ericsson v. TracBeam
`Page 3
`
`

`
`U.S. Patent
`
`Mar. 3, 1998
`
`Sheet 3 0f 6
`
`5,724,660
`
`FIG. 4
`
`H531 (dBm)
`
`EIRP-A
`
`1 km
`
`dlkm)
`
`T-Mobile / TCS / Ericsson EXHIBIT 1007
`T-Mobile / TCS / Ericsson v. TracBeam
`Page 4
`
`

`
`US. Patent
`
`Mar. 3, 1998
`
`Sheet 4 of 6
`
`5,724,660
`
`FIG. 5
`
`E15
`
`T-Mobile / TCS / Ericsson EXHIBIT 1007
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`Page 5
`
`

`
`US. Patent
`
`Mar. 3, 1998
`
`Sheet 5 of 6
`
`5,724,660
`
`FIG. 9
`
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`Page 6
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`

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`T-Mobile / TCS / Ericsson EXHIBIT 1007
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`Page 7
`
`

`
`5,724,660
`
`1
`METHOD AND APPARATUS FOR LOCATING
`A MOBILE STATION BY COMPARING
`CALCULATED LOCATION AREA WITH GPS
`COORDINATES
`
`This application is a continuation-in-part of copending
`U.S. patent application Ser. No. 08/472,082 (attorney docket
`no. MacDonald 1), ?led Jun. 7, 1995, entitled Method And
`Apparatus For Determining The Location Of A Mobile
`Telephone.
`
`10
`
`FIELD OF THE INVENTION
`The present invention relates generally to mobile tele
`phone systems. More particularly, the present invention
`relates to determining the location of a mobile telephone
`within the geographic serving area of a mobile telephone
`system.
`
`25
`
`30
`
`35
`
`2
`mobile telephone can be determined by a geometric process
`such as triangulation.
`U.S. Pat. No. 4,891,650 describes a vehicle location
`system which determines an approximate vehicle location
`using a cellular telephone system. The location function is
`initiated when a vehicle transmits an alarm signal to nearby
`cell sites. The cell sites receiving this alarm signal analyze
`the received alarm signal to determine its signal strength.
`The cell sites then send signal strength information through
`the mobile telephone system to an alarm central station. The
`alarm central station then uses the signal strengths reported
`from various cells to determine an approximate location of
`the vehicle. A more accurate location is achieved by sending
`out actual tracking vehicles to the approximate location
`calculated by the central station. A disadvantage of this
`system is that each of the cell sites requires additional
`components which will generate and send an appropriate
`signal strength report message to a mobile telecommunica
`tions switching o?ice. The mobile telecommunications
`switching o?ice also needs special functionality to send
`appropriate information to a central tracldng station which
`will determine an approximate location of the vehicle using
`the signal strengths.
`U.S. Pat. No. 5,218,367 describes a vehicle tracking
`system which uses signal strengths received ?om nearby
`cells to calculate an approximate vehicle location. In this
`system, a special purpose mobile telephone determines
`signal strengths being received from nearby cells and gen
`crates and sends an appropriate alarm message, including
`signal strength information, to a central station via the
`mobile telephone system. The central station then uses ?iis
`information to determine an approximate location of the
`vehicle. The system can improve upon the accuracy of the
`approximate location if the cells are divided into sectors and
`particular information about the antennas in these sectors is
`used. Once an approximate location is found, a more accu
`rate location is achieved by sending out actual tracking
`vehicles to the approximate location calculated by the cen
`tral station.
`The technique described in U.S. Pat. No. 4,891,650
`requires additional components in each of the cell sites in
`order to generate and send appropriate signal strength report
`messages. Since there are many such cells in a mobile
`telephone system, such additional components are undesir
`able. Thus, there is a need for a mobile telephone location
`system which does not require additional components at
`each cell site.
`Further, the location techniques described in the above
`patents does not calculate an accurate location of the mobile
`telephone. The accuracy of the location is improved by
`sending out actual tracking vehicles. However, the need for
`such vehicles makes these techniques very expensive. Thus,
`there is a need for a technique which will improve the
`accuracy of a location estimate calculated with signal
`strengths.
`
`BACKGROUND OF THE INVENTION
`Mobile telephone systems, also called cellular telephone
`systems, are becoming increasingly popular. These systems
`are generally made up of cell sites. each of which serves a
`coverage area, or cell. The cell site is the location within a
`cell which contains the required hardware (e.g. antenna(s)
`and radio base station) to communicate with the mobile
`telephones. A mobile telephone operating within a particular
`cell in the system communicates with the mobile telephone
`system through the cell site covering that cell. The various
`cell sites are connected to a mobile switching center which
`connects the mobile telephone system to the land-line tele
`phone network.
`One reason for the popularity of mobile telephones is that
`they can be used for emergencies when outside the home.
`For example, a motorist could use the mobile telephone to
`call for assistance in case of a disabled vehicle. Many areas
`provide a special emergency cellular telephone number. In
`other areas, users can dial 911, just as they would from a
`conventional land-line telephone.
`One of the problems with using the mobile telephone for
`emergencies stems from the mobility of the telephone.
`Public service providers. such as police, do not lmow the
`location of the mobile telephone calling the emergency
`number. In addition. users who call the emergency number
`often cannot provide enough location information to allow
`the public service provider to ?nd them. Thus, it is desirable
`to provide a mobile telephone system which can determine
`the location of a mobile telephone and provide that infor
`mation to public service providers, for example the police.
`Such a mobile telephone location service would be desir
`able in other contexts besides emergency responses. For
`example, a mobile telephone user who is lost may request
`location information from the mobile telephone system
`provider. The location information could be passed to the
`user from the system. Yet another user for such a system
`55
`would be companies which operate ?eets of vehicles. A
`home base for company operations could keep track of the
`locations of its vehicles by using a mobile telephone location
`service. Of course. there are many other applications for
`such a system.
`In known techniques for mobile telephone location, the
`distance between a mobile telephone and a mobile telephone
`system antenna in a cell site can be determined by analyzing
`the signal strength of a communication signal between the
`cell site antenna and the mobile telephone. If the distance
`between the mobile telephone and a number of cell site
`antennas is calculated, the approximate location of the
`
`45
`
`50
`
`SUlVHVlARY OF THE INVENTION
`The present invention provides a method and apparatus
`for accurately determining the location of a mobile tele
`phone within a mobile telephone system serving area.
`In accordance with one embodiment of the invention. the
`location of a mobile telephone is determined using a geo
`metric location technique in combination with GPS location
`coordinates produced by a GPS processor/receiver within
`the mobile telephone. A mobile location module within the
`mobile telephone system receives data representing the
`
`T-Mobile / TCS / Ericsson EXHIBIT 1007
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`

`
`3
`signal strengths of the signals surrounding the mobile
`telephone. which signals are being transmitted from cell site
`antennas of the mobile telephone system. The distances
`between the mobile telephone and each of these cell site
`antennas can be determined by using the signal strength
`data. In one embodiment. the accuracy of these distance
`calculations is improved by varying estimated values in the
`distance equation in order to reduce the error component of
`the calculated distances. These reduced error distances are
`then used to calculate a location area estimate. In addition,
`the mobile location module receives the most recent GPS
`coordinates calculated by the GPS receiver/processor which
`are within a predetermined con?dence level. These received
`GPS coordinates are compared with the calculated location
`area estimate to give a more accurate location area estimate.
`These and other advantages of the invention will be
`apparent to those of ordinary skill in the art by reference to
`the following detailed description and the accompanying
`drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows the geographic serving area of a mobile
`telephone system.
`FIG. 2 shows a mobile telephone system in accordance
`with one embodiment of the present invention.
`FIG. 3 shows an example MAHO list.
`FIG. 4 illustrates the Hata propagation loss model.
`FIG. 5 illustrates a location area as the intersection of
`circles where the radii of the circles are overestimates.
`FIG. 6 illustrates a location area as the intersection of
`circles where the radii of the circles are underestimates.
`FIG. 7 illustrates a location point as the intersection of
`circles where the radii of the circles are accurately estimated.
`FIG. 8 illustrates the basis for the technique for reducing
`the error components of computed distances in accordance
`with the present invention.
`FIG. 9 shows a graph of the latitude and longitude
`coordinates calculated by a GPS receiver/processor over a
`time interval.
`FIG. 10 is a ?ow diagram of the steps for calculating the
`location of a mobile telephone.
`
`DETAILED DESCRIPTION
`
`FIG. 1 shows the geographic serving area 100 of a mobile
`telephone system. The serving area 100 is shown having 7
`hexagonal cells numbered 1-7. Cell 7 is shown in the center,
`surrounded by adjacent cells 1-6. The serving area 100 of a
`mobile telephone system would typically contain more than
`7 cells. however. for ease of reference. only 7 cells are
`shown in FIG. 1. Each cell 1-7 contains an antenna 101-107
`which is used to transmit signals to. and receive signals
`from. mobile telephones. e.g. mobile telephone 120. within
`the mobile telephone system serving area 100.
`A mobile telephone system 200 in accordance with one
`embodiment of the present invention is shown in FIG. 2.
`Cell 7 is shown containing antenna 107 connected to a radio
`base station (RBS) 214. The mobile telephone 120 shown
`within cell 7 communicates with the mobile telephone
`system 200 via an air interface 202. In an advantageous
`embodiment. the mobile telephone 120 is a digital mobile
`telephone which operates according to the Noah American
`Time Division Multiple Access (T DMA) system IS-55
`standard. and the air interface is described by the 15-54 and
`18-136 standards. See. TIA/EIA Interim Standard IS-SS-A.
`
`4
`“Recommended Minimum Performance Standards of 800
`MHz Mode Mobile Stations”, September 1993; EIA/I‘IA
`Interim Standard IS-54-B “Cellular System Dual-Mode
`Mobile Station—Basestation Compatibility Standard”,
`April. 1992; BIA/TIA Interim Standard IS-l36 “Cellular
`System Dual-Mode Mobile Station—Basestation: Digital
`Control Channel Compatibility Standard”. April, 1995;
`which are incorporated by reference herein. In addition. a
`GPS (global positioning satellite) receiver/processor unit
`125 is required as a component in the mobile telephone 120
`which is to be located. This use of the GPS receiver/
`processor 125 in the mobile telephone 120 will be described
`in further detail below. Each cell 1-7 within the mobile
`telephone system serving area 100 contains an antenna
`connected to a RBS. Each RBS is connected to the mobile
`switching center (MSC) 220.
`Each cell 1-7 has assigned to it a plurality of voice
`channels for transmitting and receiving voice signals. and
`one control channel for transmitting and receiving control
`data signals. Referring to FIGS. 1 and 2. consider mobile
`telephone 120 which is operating in cell 7. The mobile
`telephone 120 is communicating over the air interface 202
`with the mobile telephone system 200 via antenna 107 and
`RBS 214. Voice signals are communicated between the
`mobile telephone 120 and the antenna 107 via one of the
`cell’s voice channels, and control data signals are commu
`nicated between mobile telephone 120 and the antenna 107
`via the cell’s control channel. In such a situation. cell 7 is the
`serving cell since the voice data is being communicated
`through that cell. In addition to the communication with the
`serving cell. the mobile telephone 120 also monitors the
`control channels of nearby cells. The mobile telephone 120.
`in accordance with the 15-54 and 18-136 standards. mea
`sures the signal strengths of these control channels of nearby
`cells. These control channel signal strength measurements
`are sent to the MSC 220 as described in further detail below.
`In addition. the mobile telephone 120 measures the signal
`strength of the voice signal it is receiving from the serving
`cell site antenna. ‘This voice channel signal strength mea
`surement is periodically sent by the mobile telephone 120 to
`the MSC 220 via the serving cell’s reverse voice channel.
`As the mobile telephone 120 travels within the geographic
`serving area 100, the signal strength of the voice channel
`signal between the antenna 107 and the mobile telephone
`120 will vary. As the mobile telephone 120 enters another
`cell, for example adjacent cell 5. the signal strength of the
`control channel signal from antenna 105 will become stron
`ger than the signal strength of the voice channel signal from
`antenna 107. At this point. it is desirable for the mobile
`telephone 120 to terminate communication over the voice
`channel with cell 7 and to initiate communication via a voice
`channel of cell 5. This operation is called a hand-01f. and is
`used to change the serving cell while the mobile telephone
`' 120 is traveling within the geographic serving area 100 so
`that the mobile telephone 120 maintains voice channel
`55
`communication via the antenna with the strongest signal.
`This hand-off operation is well known in the art of mobile
`telephone systems. and the details of the operation will not
`be discussed herein.
`In mobile telephones which work with the 13-54 and
`18-136 air protocols. this hand-o? operation is assisted by
`the mobile telephone itself. Such a function is called mobile
`assisted hand-o?.D (MAHO). The mobile telephone 120 main
`tains a MAHO list which contains the signal strengths of the
`signals that the mobile telephone 120 is receiving over the
`control channels of nearby cells. Each cell site has a pre
`de?ned MAHO list. The MSC 220 stores these MAHO lists
`
`5,724,660
`
`IO
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`20
`
`25
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`30
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`35
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`45
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`6
`The location of a mobile telephone 120 within the geo
`graphic service area 100 is determined, in one embodiment,
`by the MLM 230 as follows. The MSC 220 passes the
`following information to the MLM 230:
`the MAHO list 300 sent by the mobile telephone 120
`containing RSSI1_6;
`identi?cation of the cell site which is currently serving the
`mobile telephone 120; and
`the signal strength of the voice channel signal from the
`serving cell site, represented as (RSSIv), which is
`measured. and sent. by the mobile telephone 120.
`The MLM processor 232 then executes computer program
`code 238 stored in memory 234. The computer program
`code 238 describes the location algorithm to be performed
`by the processor 232. This algorithm is shown in the flow
`diagram of FIG. 10. The ?rst step 1002 is to calculate two
`location zones, zone 1 and zone 2. Zone 1 is de?ned by the
`geographic coverage area of the cell currently serving the
`mobile telephone 120. For example, if the serving cell was
`cell 7 (see FIG. 1) then zone 1 would be the geographic
`coverage area included in cell 7. Zone 2 is calculated by the
`MLM 230 as described below in conjunction with FIGS.
`4-8.
`The ?rst step in calculating zone 2 is to evaluate RSSIV
`and RSSI1_6 to determine the three strongest signal
`strengths. For the present example, assume that cell 7 is the
`serving cell and the strongest signal strengths are the voice
`channel signal strength (RSSIV) being communicated over
`antenna 107, the signal strength associated with the control
`channel for cell 2 (RS812) being communicated over antenna
`102, and the signal strength associated with the control
`channel for cell 4 (RSSI4) being communicated over antenna
`104.
`Using these signal sn'engths, it is possible to estimate the
`distance of the mobile telephone 120 from each of the
`antennas 102, 104, 107 using the following equation:
`
`20
`
`25
`
`5
`for each cell site and sends the appropriate list to the mobile
`telephone 120, depending on the serving cell site. These
`de?ned MAHO lists generally consist of the cells adjacent to‘
`the serving cell. For example, assuming that cell 7 is the
`serving cell, an example MAHO list 300 is shown in FIG. 3.
`The list of channels to measure and to include in the MAHO
`list is communicated to the mobile telephone 120 by the
`MSC 2220. The list 300 contains an entry for each of the
`adjacent cells 1-6 in this illustration. with a corresponding
`signal strength (RSSI) which represents the signal strengths
`of the control channels broadcast by cells 1-6 as received by
`mobile telephone 120. Thus, RSSI1 represents the control
`channel signal strength being received by the mobile tele
`phone 120 from the antenna 101 in cell 1; RSSI2 represents
`the control channel signal strength being received by the
`mobile telephone 120 from the antenna 102 in cell 2; etc.
`MAHO measurements are periodically sent from the
`mobile telephone 120 to the MSC 220 via the serving cell’s
`reverse voice channel. The contents of the MAHO list are
`determined by the IS-54 standard, and thus all digital mobile
`telephones which comply with this air protocol will maintain
`a MAHO list.
`As discussed in the background of the invention, it is
`often desirable to determine the speci?c geographic location
`of a mobile telephone 120 within the geographic serving
`area 100. In accordance with one embodiment of the
`invention, a mobile location module (MLM) 230 is added to
`the mobile telephone system 200 to provide this function.
`The MLM 230 contains a processor 232 and a memory 234.
`The MLM 230 is connected to the MSC 220. and the
`location function of the MLM 230 is initiated by the MSC
`220 as follows.
`Upon initiation of a telephone call by the mobile tele
`phone 120. the RES 214 sends the MSC 220 the telephone
`number of the mobile telephone (the A number) and the
`telephone number of the telephone being called by the
`mobile telephone (the B number). For each call handled by
`the MSC 220. the MSC 220 is con?gured to perform anA/B
`number analysis to determine whether a location function is
`to be performed. For example, the MSC 220 can initiate the
`location function each time a mobile telephone dials 911. In
`addition. the mobile telephone system provider can offer this
`location function as a service to its customers. In this
`situation. if the user of the mobile telephone 120 dials a
`certain number, the MSC 220 can initiate the location
`function and the location of the mobile telephone could be
`communicated to the mobile telephone user. Further, the
`MSC 220 can determine whether a location function is
`required by referring to a user pro?le stored in the MSC 220.
`For example. a company which uses a ?eet of vehicles may
`want a location function performed each time a call is
`initiated from one of its mobile telephones. As seen by these
`examples, by performing an A/B number analysis. the MSC
`220 can initiate a location function based on various criteria.
`One skilled in the art would recognize that various otherA/B
`number analyses could be performed to determine whether
`initiation of the location function is required. Ifthe MSC 220
`determines that a location function is required it initiates the
`location function in the MLM 230. Whether or not a location
`function is initiated. the voice portion of the signal is sent to
`the appropriate destination. For example, if the mobile
`telephone 120 called a land line telephone, then the voice
`signal is sent to the public switch telephone network
`(PSTN). Thus. calls which result in the initiation of a
`location function do not need to terminate at the MLM 230.
`Voice information may be transmitted to the appropriate
`location based upon the number dialed.
`
`40
`
`45
`
`50
`
`(1)
`RSSI(dBrn)=ElRP(dBm)-Propagation Loss(dB).
`In the above equation, RSSI is the known signal strength
`being received by a mobile telephone from an antenna. EIRP
`~ is the effective isotropic radiated power of the antenna, and
`it depends on the power of the transmitter (TxPower) and the
`gain of the antenna (Antenna Gain), such that EIRP (dBm)
`=TxPower(dBm)+Antenna Gain(dBi). For each antenna
`102, 104, 107, the TxPower (dBm) and the Antenna Gain
`(dBi) are ?xed constants and thus the EIRP for each of the
`antennas is a known value. See. C. A. Balanis. “Antenna
`Theory: Analysis and Design”, John Wley & Sons, New
`York, 1982.
`The second term of equation (1). propagation loss. is
`modeled based upon the Hata model, which is illustrated in
`FIG. 4. The model is of the form:
`
`55
`
`60
`
`65
`
`Propagation Loss(dB)=A+B log d
`where A is the 1 Km intercept point which depends on the
`height of the antenna and the frequency being transmitted.
`and includes a component which is due to the antenna height
`above the ground. B is the propagation path slope, and d is
`the distance of the mobile telephone from the antenna (in
`kilometers). As shown in FIG. 4. EIRP(dBm)-A is the RSSI
`value of the line 402 at d=l km, and B is the slope of the line
`402. For further information on the Hata model see. M. Hata.
`“Empirical Formula for Propagation Loss in Land Mobile
`Radio Services”. IEEE Transactions on Vehicular
`Technology, Vol. VT-29, No. 3, Aug. 1980.
`
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`8
`telephone 120 from each of the antennas 102. 104 and 107
`Such a case is illustrated in FIG. 6. in which the location
`estimate is within area 602. The area 602 is delimited by
`drawing the three lines 606, 607. and 608, which are tangent
`to the circles 616, 617. and 618 respectively. These three
`lines 606. 607, and 608 are adjusted such that they de?ne a
`triangle of reduced area. The area de?ned by such a triangle
`is the location estimate area shown in FIG. 6 as area 602.
`If the resulting distances d2. d4 and d, are accurate
`estimates of the distance of the mobile telephone 120 from
`each of the antennas 102. 104 and 107. then the drawn
`circles would intersect at a point. Such a case is ‘illustrated
`in FIG. 7 , in which the location estimate is shown as point
`702.
`Since the only variable in the distance equation is the
`propagation path slope B, it is possible to improve the
`accuracy of the location estimate by varying the estimates or
`B2. B4 and B7 to reduce the error component of the calcu
`lated distances d2. d4 and d,.
`The basis for this technique is illustrated in FIG. 8. Lines 7
`which represent the distance between antennas 102. 104. and
`107 are drawn. Line L2_7 represents the distance between
`antennas 102 and 107. Line LM represents the distance
`between antennas 102 and 104. Line L4_7 represents the
`distance between antennas 104 and 107. The lengths of lines
`L24. L24, and L4_7 are known because the locations (in
`latitude and longitude coordinates) of the cell site antennas
`are known. As before, the lines d2, d4 and (17 represent the
`calculated distances of the mobile telephone 120 from each
`of the antennas 102, 104 and 107. respectively. From the law
`of cosines:
`
`7
`Thus, equation (1) becomes:
`
`Solving for distance d:
`
`d: 10% [EIRP-RSSl-A]
`
`(3)
`
`In equation (3). EIRP is a known constant for each of the cell
`site antennas; the RSSI value is lmown based on measure
`ments made by the mobile telephone 120; and the 1 lqn
`intercept point. A. is a known constant depending on the
`height of the antenna and the frequency being transmitted.
`Thus. the only unknown in equation (3) is the propagation
`path slope B. It is known that B is environment dependent
`and is generally bound as:
`
`20 dB/dcc (line of sight)§B§45 dB/dec [heavy urban).
`Typically. propagation path slope is given in terms of terrain
`and building density. Typically categories are:
`Suburban: B=3O
`Urban: B=35
`Downtown: 13:40
`Thus. by estimating the value of B for each antenna, the
`distances d2. d4. and d7 of the mobile telephone 120 from
`antennas 102. 104. 107 respectively, can be calculated as
`follows:
`
`20
`
`25
`
`i IEIRPrRSSIrAZI
`
`d 10% [mm-mum]
`
`4 =
`
`i [Elm-mom]
`[17:10!"
`
`(4)
`
`(5)
`
`35
`
`(6)
`
`where EIRPn is the eifective isotropic radiated power of the
`antenna in cell n, An is the 1 km intercept point between the
`mobile telephone 120 and cell n. and B is the estimated
`propagation path slope of the environment in cell 11.
`After the distances d2. d4. and (17 are calculated, a location
`area is determined by plotting the following circles. as
`illustrated in FIG. 5:
`a circle 502 of radius (12 centered at antenna 102;
`a circle 504 of radius d4 centered at antenna 104; and
`a circle 507 of radius (17 centered at antenna 107.
`The intersection area 510 of circles 502. 504. 507 estimates
`the location of the mobile telephone 120 within the geo—
`graphic serving area 100. Since the values or B2. B4 and B7
`are estimates. the resulting distances d2. d4 and d7 will have
`a certain error component based upon the estimate of B. The
`calculated distances d2. d4 and d7 will have other error
`components as well, based upon cell characteristics other
`than propagation path slope. Examples of such cell charac
`teristics are the relative height of the mobile telephone to
`each cell site antenna and the gain reduction due to antenna
`pattern rolloif. The algorithm described herein does not take
`these other error components into account. However. one
`skilled in the art could readily modify the described algo
`rithm to account for these error components. In FIG. 5. d2.
`d, and d, are overestimates of the distance of the mobile
`telephone 120 from each of the antennas 102. 104 and 107.
`and thus the resulting location can only be determined to be
`within area 510.
`It is also possible that the resulting distances d2. (14 and d7
`would be underestimates of the distance of the mobile
`
`55
`
`65
`
`solving for the angles m. n. and 0:
`
`Referring again to FIG. 8, it is known that Am+£n+£o=360
`and thus 360—(Am+An+Lo)=0. Now. substituting for the
`angles m, n. and o:
`
`~The calculation of the distances d2. d4 and (17 will be most
`accurate when each of the terms of equation 7 re positive and
`when the left side of the equation equals 0. The only
`variables in the calculations of d2. d4 and d7 are the
`propagation path slopes B2, B4 and B7. respectively. which
`values are generally bound as: 20 dBldec§B§45 dB/dec.
`Thus. the values d2. d4 and d7 are calculated using equations
`4. 5. and 6 while varying the propagation path slopes B2. B4.
`and 137 between 20 dB/dec and 45 dB/dec. The resulting
`
`T-Mobile / TCS / Ericsson EXHIBIT 1007
`T-Mobile / TCS / Ericsson v. TracBeam
`Page 11
`
`

`
`9
`distances d2, d4 and d., are then used to evaluate equation 7.
`The values of d2. d4 and d7 for which the result of equation
`7 is closest to 0 with all its terms positive gives values for
`d2. d4 and d7 with reduced error components.
`When the distances d2, d4 and d, which have the reduced
`error components are found, the location area of the mobile
`telephone 120 is determined by plotting appropriate circles
`as described above. The geographic location (i.e. latitude
`and longitude) of antennas 102, 104. 107 in the geographic
`serving area 100 are known and. in one embodiment. are
`stored as cell site-information 236 in the memory 234 of the
`MLM 230. The MLM 230 uses these known cell site
`locations to determine the geographic location of the esti
`mated location area using techniques which are well known
`in the art. For example, the actual geographic location of the
`mobile telephone can then be determined by plotting the
`estimated location area on a geographic map. This calculated
`location area is the zone 2 location.
`As discussed above, a GPS (global positioning satellite)
`receiver/processor unit 125 is required as a component in the
`mobile telephone 120 which is to be located. As is well
`known in the art, a GPS receiver/processor receives signals
`from satellites orbiting the earth and translates these signals
`into latitude and longitude coordinates of the position of the
`GPS receiver/processor. A typical GPS receiver/proces sor is
`accurate to within approximately 50 feet. The MLM 230
`uses information provided by the GPS receiver in the mobile
`telephone 120 to increase the accuracy of the geographic
`location estimate.
`A known problem with GPS receivers is that location
`accuracy requ