Ulllted States Patent [19]
`Sheffer et al.
`
`US005 8445 22A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,844,522
`Dec. 1, 1998
`
`[54] MOBILE TELEPHONE LOCATION SYSTEM
`AND METHOD
`
`[75] Inventors: Eliezer A_ She?'er, San Diego; Paul J_
`Bouchard, Valley Center, both of Calif.
`
`[73] Assignee: Trackmobile, Inc., San Diego, Calif.
`
`[21] Appl. No.: 543,031
`[22] Filed:
`Oct. 13, 1995
`
`6
`[51] Int. Cl. ...................................................... .. G01S 3/02
`[52] US. Cl. ....................... .. 342/457; 455/321; 455/331
`[58] Field of Search ......................... .. 342/457; 455/321,
`455/331, 541, 561
`
`[56]
`
`References Cited
`
`US‘ PATENT DOCUMENTS
`4,177,466 12/1979 Reagan ............................ .. 343/112 TC
`4,704,734 11 /1987 Menich et a1, _
`4,726,050
`2/1988 Menich et al. .
`4,728,959
`3/1988 Maloney et al. ...................... ..
`477307187
`3/1988 Menich ct a1~ -
`4,742,357
`5/1988 Rackley ................................ .. 342/457
`4’891’65O
`1/1990 She?er
`342/457
`5,055,851 10/1991 Sheffer ....... ..
`342/457
`572037009
`4/1993 Bogusz et a1‘
`“ 455/331
`572187367
`6/1993 She?er et a1_
`342/457
`5,293,642
`3 /1994 L0 ______________ __
`455 /33_1
`5,293,645
`3/1994 Sood .............. ..
`455/541
`5,317,323
`5/1994 Kennedy et al.
`342/457
`5,327,144
`7/1994 Stilp et al. ............................ .. 342/387
`
`2/1995 Chia ...................................... .. 342/457
`5,394,158
`7/1995 TsuZuki et al
`379/58
`5,434,904
`5/1996 Sheffer ......... ..
`379/58
`5,515,419
`2/1997 LeBlanc et al. ........................ .. 379/60
`5,602,903
`FOREIGN PATENT DOCUMENTS
`
`0417944 3/1991 European Pat- Om -
`Primary Examiner—Theodore M. Blum
`Attorney, Agent, or Firm—Brown, Martin, Haller &
`Mcclam’ LLP
`[57]
`
`ABSTRACT
`
`Awireless network based location system and method uses
`an existing Wireless Communication network to locate the
`position of any active phone or transceiver unit in the
`network. The system includes a plurality of agile vector
`sensor units, one each installed at each antenna site in the
`network, and a remote central monitoring station to which
`wireless network users can call for assistance in the event of
`an emergency The System is designed to locate a Portable
`phone transceiver unit using the reverse voice channel signal
`transmitted by the transceiver unit. Each agile vector sensor
`unit locks onto the reverse Voice Channel to determine
`azimuth and signal strength in the reverse voice channel, and
`also tracks any Changes in Voice Channel by monitoring the
`forward voice channel. In the event of a voice channel
`.
`.
`change, the sensor unit tunes to the new voice channel. The
`azimuth, signal strength, and reverse vo1ce channel infor
`mation collected is used to track the location of a transceiver
`unit in real time.
`
`25 Claims, 13 Drawing Sheets
`
`14
`TELEPHONE
`\\COMPANY co
`
`Apple, Inc. Exhibit 1039 Page 1
`
`

`
`Apple, Inc. Exhibit 1039 Page 2
`
`

`
`Apple, Inc. Exhibit 1039 Page 3
`
`

`
`Apple, Inc. Exhibit 1039 Page 4
`
`

`
`Apple, Inc. Exhibit 1039 Page 5
`
`

`
`Apple, Inc. Exhibit 1039 Page 6
`
`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 6 0f 13
`
`5,844,522
`
`IDLE STATE
`h
`
`82
`/(
`v
`SCAN FCC FOR:
`MINT, MINZ, INIT. VC
`SCAN FVC FOR:
`REASSIGNED \/C
`
`n
`
`.
`Fag. 7
`
`CDC)‘ D|A|_S#
`Avg;
`‘
`
`84
`)
`1!
`SCAN RVC FOR: K
`RSSI, AZIMUTH. TEMP.
`SCAN FCC FOR:
`MIN1, N||N2, lNlT. \/C
`SCAN FVC FOR:
`REASSIGNED \/C
`
`85
`
`f
`
`TRANSMIT
`SCANNED DATA :
`~.
`TO CDC].
`ALSO APPEND
`AVSi ID
`
`861
`
`YES
`
`,, \
`,
`NO SHUT-OFF’
`COMMAND
`FROM
`7 CDC 9
`J
`-
`
`Apple, Inc. Exhibit 1039 Page 7
`
`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 7 0f 13
`
`5,844,522
`
`88
`SUBSCRIBER
`CALL
`‘f
`
`v
`CELL NET
`ASSIGNS CELL S|TE_f 89
`TO SUBS. PHONE
`v
`90
`MTSO ROUTES
`CALL THROUGH _f
`PSTN TO COC
`U
`CDC OPERATOR J51
`QUERIES CALLER
`AS TO HIS/HER
`NAME
`
`I
`CDC OPERATOR _f 92
`QUERIES SUBS.
`DATA BASE
`FOR ESN / NAME
`v
`CDC OPERATOR _f 93
`REQUESTS A CALL
`TRACE FROM MTSO
`BASED ON SUBS.
`NAME
`V
`CALL TRACE RECORD _f94
`INCLUDES ACTIVE CELL
`SECTOR ID
`vO|CE CHANNEL
`
`[95
`
`V
`NEIGHBOR CELLS
`TO ACTIVE CELL
`ARE SELECTED
`FROM CELL
`SITE DATABASE
`
`Fig. 5 A
`
`Apple, Inc. Exhibit 1039 Page 8
`
`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 8 0f 13
`
`5,844,522
`
`‘
`
`F19. 85’
`
`REQUEST SENT FOR
`96
`SELECTED CELL SITES
`TO ACTIVATE THERE -f
`Avg
`II
`f97
`AVS MONITORS
`CHANGES IN FCC, T
`FvC AND RvC
`II
`ALL AVS’S SEND _/98
`DATA COLLECTED
`BACK TO REQUESTING
`CDS, INCLUDING NAME,
`FCC, RSSi AZIMUTH,
`vOICE CHANNEL, PREv.
`vOICE CHANNEL
`II
`CDC RECEIVES /99
`DATA PACKETS‘
`I
`DETERMINE
`CURRENT vOICE
`CHANNEL ASSIGNED
`TO CALLING PHONE
`
`_/1O0
`
`131
`COMPUTE ~f
`POSITION
`NO
`USING RSSI
`AND AZIMUTH
`
`>3 UNITS
`RESPONDED
`?
`
`YES
`r132
`II
`ASSIGN"
`COMPUTE COMPUTE POSITIONS/‘102
`LOWEST
`POSITION
`USING AZIMUTH FOR
`CONFIDENCE
`A FROM
`DIFFERENT TRIPLETS
`LEvEL TO
`AZIMUTH
`POSITION
`DATA
`
`103
`
`r124
`DO
`A MAJORITY NO CALCULATE
`OF THE TRIPLETS
`POS|T|ON B
`POSITIONS
`FROM R551
`AGREE
`
`Apple, Inc. Exhibit 1039 Page 9
`
`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 9 0f 13
`
`5,844,522
`
`AVERAGE /IO4 POSITION C
`@ POSITIONS TO
`FROM CELL
`POSITION A
`SITE AND SECTOR
`
`/125
`/
`
`I
`CALCULATE /IO5
`@ POSITION B
`FROM RSSI
`*
`CALCULATE
`POSITION C
`FROM CELL
`SITE AND SECTOR
`
`,
`/ HO
`
`126
`
`'
`F 2g. 8G
`
`1/128
`USE B AS
`pOSmON
`AND ASSIGN
`CONFIDENCE
`LEVEL 6
`I
`
`CONFIDENCE
`LEvEL 5 TO
`POSITION
`I
`
`122
`USE RESULT
`A AND
`ASSIGN
`CONFIDENCE
`LEvEL 4
`
`I
`ASSIG‘N
`CONFIDENCE CONFIDENCE ASSIGN HIGHEST
`POSSIBLE
`LEVEL
`LEVEL 2
`CONFIDENCE
`3 T0
`T0 POSITION
`LEVEL 1 To
`POSITION
`POSITION
`133
`I
`I
`I
`//
`DISPLAY POSITION ON MAP
`COMPUTER WITH SIZE OF SPOT —
`CORRESPONDING TO CONFIDENCE =
`LEvEL
`
`I
`,I34
`SEND POSITION
`/
`CONFIDENCE
`LEvEL AND vOICE
`CHANNEL TO FRY
`
`,/136
`157 SEND MESSAGES
`@_ AvS UNITS TO
`DISCONTINUE
`TRANSMISSION
`
`GO To
`99
`
`Apple, Inc. Exhibit 1039 Page 10
`
`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 10 0f 13
`
`5,844,522
`
`Fig. 9
`
`PROBABLE PHONE
`LOCATION
`
`H4
`AZlMUTl-l TOLERANCE
`
`AVS #1
`
`AVS #2
`
`SECTOR #1
`
`Fig. 70
`
`W
`AZlMUTH TOLERANCE
`
`AVS #1
`
`AVS #2
`
`Apple, Inc. Exhibit 1039 Page 11
`
`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 11 0f 13
`
`5,844,522
`
`‘~ 1/ 131/
`
`/
`
`ACTIVE
`
`PROBABLE
`AREA
`
`Apple, Inc. Exhibit 1039 Page 12
`
`

`
`U.S. Patent
`
`Dec. 1, 1998
`
`Sheet 12 0f 13
`
`5,844,522
`
`F29’. 73 CHANNEL NUMBER
`CONTROL CH.
`VOICE CH. #1 VOICE CH. #2.. 513_554,_
`
`VOICE CH
`#1023
`
`Z Z
`RSSI AZIMUTH RSSI AZIMUTI-I RSSI AZIMUTH RSSI AZIMUTH
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`
`'7
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`
`Apple, Inc. Exhibit 1039 Page 13
`
`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 13 0f 13
`
`5,844,522
`
`F/L'QQ 75 CHANNEL NUMBER
`CONTROL CH.
`voICE CH. #1 VOICE CH. #2.. 313—354..
`Z Z
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`Fig, 7 6 CHANNEL NUMBER
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`
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`
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`
`Apple, Inc. Exhibit 1039 Page 14
`
`

`
`1
`MOBILE TELEPHONE LOCATION SYSTEM
`AND METHOD
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates generally to a location
`system and method for locating the position of a mobile
`telephone, and is particularly concerned With a system using
`an eXisting Wireless telephone or communications network,
`such as cellular, PCS, or other types of Wireless communi
`cation netWorks, in locating a target telephone Within the
`netWork in the event of an emergency situation, or for other
`reasons.
`Numerous location systems have been proposed in the
`past for locating the position of a target emitting a radio or
`cellular signal. All previous systems have been subject to
`various disadvantages. Some proposed methods are satellite
`based, for eXample using the Global Positioning System, or
`GPS, With receivers receiving signals from orbiting satellites
`in order to determine approXimate location. HoWever, such
`a system has limited operation in heavily built urban areas
`and cannot readily provide voice or data communications.
`Such systems also require specialiZed end-user equipment.
`Additionally, these systems can locate a target to an approXi
`mate area of 100 yards. In practice, this may not be suf?cient
`to pinpoint a phone Which may be Within a building, for
`eXample.
`Other systems involve use specialiZed radio positioning
`methods. HoWever, this also requires installation of heavy
`infrastructure, and requires specialiZed end-user telephone
`equipment. A number of location systems have also been
`proposed Which use eXisting cellular telephone netWork
`infrastructure. For example, US. Pat. Nos. 5,218,367, 5,055,
`851 and 4,891,650 of Sheffer all describe locating systems
`Which utiliZe cellular technology. In US. Pat. No. 5,218,
`367, the cellular telephone itself is modi?ed to receive signal
`strength and cell identifying information from all adjacent
`cell sites, and to transmit this information to a monitoring
`station Which includes a computer programmed to calculate
`an approXimate vehicle location. One disadvantage of this
`system is that it can only be used to locate specialiZed, or
`modi?ed, cellular telephones and cannot locate
`conventional, unmodi?ed phones.
`In US. Pat. No. 4,728,959 of Maloney et al. a location
`system is described in Which detector units are used to detect
`reverse control channel signals emitted from mobile phones,
`and determine aZimuth angles for the phone to determine the
`direction from Which the signals are emitted. Phase angle
`measurements of the direction of the phone from a plurality
`of land stations are processed to produce a probability
`density function, producing an X-y coordinate area repre
`senting the most likely location of the phone.
`This system is subject to a number of disadvantages,
`along With the other knoWn system Which locate only a
`rough, X-y coordinate position. An X-y coordinate position is
`unlikely to be suf?cient to pinpoint the location of the
`mobile phone With suf?cient accuracy, particularly in a
`heavily built-up, urban area including multi-story buildings
`and underground parking lots. Even if the correct building
`can be located, Which is not certain given the accuracy of
`these systems, the location of the individual calling for help
`Within the building Will be completely unknoWn, and a
`signi?cant amount of eXtra time Will be necessary in search
`ing the building from ?oor to ?oor. In an emergency
`situation, the caller must be found as quickly as possible, and
`this is not feasible With systems of the type described by
`Maloney.
`
`15
`
`35
`
`45
`
`55
`
`65
`
`5,844,522
`
`2
`Another disadvantage of Maloney is the use of a reverse
`control channel signal to locate a mobile phone. Each cell
`site in a cellular system has a ?Xed control channel fre
`quency over Which forWard control channel signals are
`transmitted to mobile phones in the vicinity. All mobile
`phones assigned to that cell site Will use the same frequency
`to transmit reverse control channel, or RCC, signals back to
`the cell site. The identi?cation code or NAM for each phone
`Will be embedded in the emitted RCC signal packet. RCC
`signals are not emitted continuously, but only in an irregular
`fashion depending on reorder conditions, such as hand-off.
`For each mobile phone, the RCC signal is emitted in short
`bursts at irregular time intervals. Thus, there may be rela
`tively long periods of time When no RCC signal is emitted.
`Another problem is that up to 60 phones may be assigned to
`the same cell site at any time, and the only Way they can be
`distinguished from one another using the RCC signal is by
`deciphering each RCC received to determine the NAM of
`the desired target, Which may or may not be emitting an
`RCC signal at the time. Thus, this location system is
`relatively unreliable and does not alloW a target phone
`location to be pinpointed With suf?cient accuracy to enable
`emergency assistance to be deployed quickly to the target.
`
`SUMMARY OF THE INVENTION
`It is an object of this invention to provide a neW and
`improved location system and method using cellular or other
`Wireless telephone technology.
`According to one aspect of the present invention, a
`portable phone tracking system is provided, Which utiliZes
`parts of an eXisting Wireless telephone communication sys
`tem such as a cellular phone netWork. Each cellular phone
`netWork includes a plurality of cell or antenna sites for
`receiving and transmitting Wireless voice and control chan
`nel signals When linked With a Wireless or cellular phone in
`the vicinity of the antenna site, and for linking the cellular
`phone to another phone via a mobile telephone sWitching
`of?ce, or MTSO, and the public telephone netWork. Each
`antenna or cell site covers a predetermined area and Will be
`the active cell site for any portable phones making or
`receiving calls Within that area. Special hand-off procedures
`are used for transferring calls from an active cell site to a
`neighboring cell site When the phone moves from one cell
`area to another. The cellular phone system Will operate in a
`certain frequency range divided into separate channels,
`some of Which Will be assigned as voice or communication
`channels for forWard and reverse communication and others
`of Which are assigned as control and/or signaling channels
`for sending forWard and reverse control signals. Each caller
`in the netWork Will be assigned an initial communication
`channel, for voice or other types of communications, via the
`forWard control channel (FCC) of the active cell site. The
`initially assigned reverse voice channel may be changed
`quite rapidly and several times during a call. The tracking
`system of this invention is designed to track the initial
`reverse voice channel and all reassigned reverse voice
`channels for a particular call on a real-time basis during the
`entire call duration, and to use the determined voice chan
`nels as a beacon to direction ?nding equipment in order to
`locate the eXact position of the cellular phone.
`According to the present invention, a Wireless phone
`location system is provided, Which includes a plurality of
`agile vector sensor units, each agile vector sensor unit being
`mounted at a respective cell site in a cellular telephone
`netWork such that an agile vector sensor unit is located at
`every cell site in the netWork, and each agile vector sensor
`unit comprising a scanning assembly for scanning over the
`
`Apple, Inc. Exhibit 1039 Page 15
`
`

`
`3
`frequency range of the telephone network and detecting any
`calls Within the range of the scanning assembly, a direction
`?nder assembly for determining azimuth and signal strength
`of the particular voice channel, a receiver assembly for
`receiving control and voice channel signals of the cell site
`and the target phone and determining the identi?cation code
`of all phones in the area connected to that cell site, and the
`initially assigned voice channel for each connected phone,
`an information storage system for storing the identi?cation
`code and initial voice channel of connected calls, and the
`aZimuth and signal strength for each detected voice channel
`signal, and a receiver assembly for detecting and storing neW
`voice channel assignments, and tuning the direction ?nder
`assembly automatically and rapidly to the neW voice chan
`nels to determine aZimuth and signal strength in each neW
`voice channel on a real-time basis. The system also includes
`a monitoring system at a remote facility for determining the
`currently active cell site for a selected phone in the netWork
`and the initially assigned voice channel for that phone,
`determining neighboring cell sites to the currently active
`cell, and sending control signals to the sensor units at the
`active and neighboring cell sites to begin transmitting col
`lected information for at least a selected phone to the
`monitoring station, and an analyZer for determining a prob
`able location area for the selected phone from the informa
`tion received from the sensor units.
`The monitoring system may command the sensor units to
`transmit all stored information for all calls in the vicinity,
`and may be programmed to ?lter or extract information for
`the selected phone from the incoming data. Preferably, all
`sensor units continuously scan and collect information on at
`least the voice channel assignments, and Write over the
`previously collected information unless activated by a con
`trol signal from the monitoring system. When activated,
`sensor units periodically transmit collected information to
`the monitoring system.
`Preferably, a plurality of ?eld response units or vehicles
`are provided, each having an extra, stand alone ?eld direc
`tion ?nder unit including a receiver for linking the unit to the
`monitoring system at the remote site, and an automatic tuner
`for automatically tuning the unit to a selected voice channel
`received from the monitoring system. When the monitoring
`system determines an approximate location for a selected
`phone, one or more ?eld response units are dispatched to the
`area, With the direction ?nder unit in each vehicle linked to
`the monitoring system. The monitoring system Will transmit
`all voice channel changes in real time for that caller to the
`?eld direction ?nder units to tune them automatically to the
`current voice channel for the selected call, so that they can
`hone in on the selected call and locate the precise position
`of the portable phone. Thus, unlike previous phone location
`systems Which locate call position to an accuracy of 100
`yards or so only, and provide only a tWo-dimensional or x-y
`position for the target, this system enables a direction ?nder
`to lock on to the uniquely assigned reverse voice channel of
`a calling phone, and to track and lock onto changed voice
`channels on a real-time basis, so that the caller can be
`located With pinpoint accuracy in X, y and Z coordinates.
`This is extremely important in an emergency medical or
`crime situation, for example, Where an accuracy of 100
`yards Will not necessarily enable the caller to be found
`quickly. Also, if the caller is in an underground or above
`ground parking lot or in a multi-story building, the radio
`direction ?nder unit Will still be able to pinpoint Z coordinate
`position Within the building.
`Previous location systems, such as Maloney, compute x-y
`coordinate location only, and use signals Which are not on at
`
`10
`
`15
`
`25
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`all times. Since these signals are not on at all times, they
`cannot be used as a beacon for direction ?nding equipment.
`The system of this invention, in contrast, uses the reverse
`voice channel signal, Which is alWays on, as a tracking
`beacon for a ?eld direction ?nder unit to track the x, y and
`Z coordinate position quickly and accurately.
`The remote monitoring station Will be able to determine
`the currently assigned voice channel for a selected call, and
`Will control sensor units at neighboring cell site to scan this
`voice channel and collect aZimuth and signal strength infor
`mation for the current voice channel, and to transmit that
`information to the monitoring station. This information can
`then be used in the location determination. The system
`preferably includes at least one local computer Which is
`connected to each MTSO in the netWork, and Which is
`programmed to trap all calls to the monitoring center,
`including the active cell identi?cation, sector number and
`initial voice channel assignment from the cellular carrier
`MTSO (mobile telephone sWitching of?ce) Which is cur
`rently handling the selected phone, and to transmit that
`information to the central monitoring station. The local
`computer may be physically located at one of the MTSO
`sites in the system and include a modem for communicating
`With all the other MTSO sites, or it may be located at the
`central monitoring station and linked to all MTSO sites via
`modem. The system includes a cell site data base of the
`geographical location of each cell site, and a neighboring
`cell site data base of the nearest neighbors of each cell site.
`These data bases may be located at the local computer or at
`the central monitoring station.
`Preferably, the central monitoring station includes a plu
`rality of Work stations each including a ?rst, phone location
`computer for determining an approximate phone location
`and a second, map computer for displaying a map including
`the calculated position. Portable phones in the cellular
`netWork may make emergency calls to the central monitor
`ing station, and all such calls are assigned to a particular
`Workstation based on current Work load. Receipt of an
`emergency call Will initiate a phone location procedure, in
`Which the identi?cation code for that phone is determined,
`the netWork is searched for that identi?cation code and the
`currently active cell site for that phone, and the sensor units
`at the active cell site and neighboring sites are activated to
`begin transmitting data on at least that call to the monitoring
`station.
`According to another aspect of the present invention, a
`method of locating a portable phone is provided, Which
`comprises the steps of:
`providing an agile vector sensor unit at each cell site in a
`cellular netWork;
`determining the active cell site and neighboring cell sites
`for a selected phone Which is currently in use;
`activating the sensor unit at the active cell site to scan the
`forWard voice channel of the active cell site to detect
`any voice channel assignment changes for connected
`calls;
`determining the neW voice channel of any connected call;
`tuning the sensor unit to all currently assigned reverse
`voice channels in turn and determining the aZimuth and
`signal strength for each reverse voice channel signal;
`transmitting neW voice channel assignments, aZimuth and
`signal strength information to a central monitoring
`station;
`at the central monitoring station, determining the cur
`rently assigned voice channel for a selected phone and
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`controlling sensor units at neighboring cell sites to scan
`that voice channel and collect and transmit azimuth and
`signal strength information to the central monitoring
`station; and
`determining an approximate phone location from the
`aZimuth and signal strength information received from
`the active and neighboring cell sensor units.
`During the location process, the central monitoring station
`Will receive information on neW voice channel assignments
`on an ongoing basis, so that the voice channel for the
`selected phone can be updated as necessary, and the correct
`voice channel information can be used to re-tune the sensor
`units as necessary. Field response units can then be
`dispatched, With their oWn direction ?nder units being
`automatically tuned and re-tuned With each change in voice
`channel.
`This system and method uses the reverse voice channel of
`a portable phone as a signal to lock onto. The reverse voice
`channel is the only uniquely identi?able signal emitted by a
`portable phone Which is emitted, or “on,” continuously over
`the entire duration of a call. Thus, it is the best signal to use
`for locking onto, and tracking, a portable phone. HoWever,
`the reverse voice channel assignment may be changed
`several times during a call, and this system enables such
`changes to be detected quickly, so that the system can tune
`to a neWly assigned voice channel on an ongoing basis, and
`receive and analyZe aZimuth and signal strength information
`for the current voice channel at all times and in real time.
`The system of this invention does not require any modi
`?cation Whatsoever to the hardWare or softWare of any
`portable phone, cell site, or MTSO of an eXisting cellular
`system. It simply adds on to an eXisting system or netWork,
`in the form of an agile vector sensor unit mounted at each
`cell site but not connected, in any Way, to the cell site
`electronics/netWork, a separate central monitoring station
`for controlling the sensor units and receiving data from the
`sensor units, and one or more local computers for connection
`to each MTSO either locally or remotely, as Well as auto
`matically tunable direction ?nder units in each of a plurality
`of ?eld response units for pinpointing a call location once an
`approXimate location has been determined. Only one central
`monitoring station is needed for locating any mobile phone,
`nationWide or even WorldWide.
`This system is intended to be used primarily for locating
`a portable phone in the event of an emergency. HoWever, it
`may also be used to detect cellular phone clones, since it can
`locate any currently active phone by identi?cation number
`or NAM, and can detect if more than one phone having the
`same NAM is in use simultaneously, or if a NAM is being
`used in the Wrong city for a particular subscriber. The central
`monitoring station may broadcast to all agile vector sensor
`units, nationWide, to determine the location of any phone
`having a selected NAM, for anti-fraud purposes. The system
`may also be used for netWork management purposes.
`The system of this invention enables a portable phone
`making a call to be located much more accurately and
`eXactly than Was previously possible, so that ?eld response
`units can hone in on the originating voice channel signals
`With great precision. This can enable a caller in an emer
`gency situation to be located much faster than Was previ
`ously possible, Which can be critical.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`The present invention Will be better understood from the
`folloWing detailed description of a preferred embodiment of
`the invention, taken in conjunction With the accompanying
`draWings, in Which like reference numerals refer to like
`parts, and in which:
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`FIG. 1 is a schematic block diagram of a cellular phone
`system incorporating a location system according to a pre
`ferred embodiment of the present invention;
`FIG. 2 is more detailed block diagram of the location
`system;
`FIG. 3 is a schematic block diagram of Workstation at the
`central monitoring station or communication and dispatch
`center of the location system;
`FIG. 4 is a block diagram of the location processing or
`algorithm computer at a Workstation;
`FIG. 5 a block diagram of one of the agile vector sensor
`units of the location system;
`FIG. 6 is a graphical illustration of information collected
`at an agile vector sensor unit;
`FIG. 7 is a schematic ?oW diagram of operation of an
`agile vector sensor unit;
`FIG. 8 is a schematic ?oW diagram of the location system;
`FIG. 9 is a graphical illustration of a triangulation process
`for determining an approXimate phone position;
`FIG. 10 is a graphical illustration of a procedure using
`sector information for checking a calculated phone position
`for accuracy;
`FIG. 11 is a graphical illustration of a procedure using
`signal strength information as an eXtra data reference to
`determine location;
`FIG. 12 is a graphical illustration of another location
`algorithm; and
`FIGS. 13—16 are graphical illustrations of successive
`steps in one speci?c eXample of a location procedure.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`FIG. 1 of the draWings illustrates a Wireless or cellular
`communication system incorporating the location system
`according to a preferred embodiment of the present
`invention, and FIGS. 2—16 illustrate various components of
`the location system and steps in the location method of the
`preferred embodiment.
`As illustrated in FIG. 1, a cellular communication system
`includes a plurality of radio transmitters or cell sites 10 each
`covering a predetermined area. All cell sites 10 in a particu
`lar region Will be linked via an MTSO or mobile telephone
`sWitching office 12 to a telephone company central office 14.
`There Will be a number of MTSO’s each linked to cell sites
`in a different region, over the entire area covered by the
`communication system, according to standard cellular tech
`nology. Calls transmitted to the central of?ce 14 are relayed
`to the appropriate telephone numbers via telephone lines or
`microWave link 16, also in a conventional manner. A con
`ventional cellular or portable phone unit 18 may therefore be
`used to make calls Within the area covered by the cellular
`phone system.
`When the user Wishes to make a cellular or Wireless call,
`they simply punch in the appropriate phone number on the
`key pad 20 of the cellular phone. Such calls are transmitted
`via the closest adjacent cell site 10 to the MTSO for that cell
`site, and are conveyed from there via the central of?ce 14 to
`the selected phone subscriber. Calls are conveyed back to the
`cellular phone in a similar manner. The location system and
`method of this invention can locate the approximate position
`of any conventional, AMPS analog cellular phone, irrespec
`tive of brand name, Without requiring any modi?cation of
`the phone unit itself. Although the preferred embodiment of
`the invention is described in conjunction With an eXisting
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`cellular phone network, it Will be understood that the loca
`tion system and method may alternatively be used With other
`Wireless communication systems Which may be available in
`the future, such as the so-called PCS or personal commu
`nication system or satellite-based communication systems
`using communications technology other than cellular.
`In order to better understand the phone location system
`and method of this invention, operation of a conventional
`cellular phone system or netWork Will ?rst be brie?y
`described. Each cellular phone system operates over an
`assigned frequency range Which is divided into a number of
`separate channels, typically channels 1 to 1023, each chan
`nel corresponding to a certain frequency. A large number of
`these channels Will be voice or communication channels for
`subscribers communication signals, While certain channels
`Will be control channels for sending control signals to and
`from cellular phones. Each cell site Will have a speci?c
`forWard control channel or FCC assigned to it. When a
`phone call is activated at a cell site, the cellular netWork
`assigns an initial voice channel for that phone. The initial
`voice channel assignment is transmitted to the calling phone
`via the FCC or forWard control channel. Voice signals are
`then transmitted from the phone over the assigned reverse
`voice channel (RVC). During the call, the initial RVC may
`be changed by the cellular system for various reasons but
`particularly during hand-offs, and such changes may occur
`at a very rapid rate. If the portable phone is moving, change
`in voice channel assignment can occur as a result of move
`ment from the area of one cell site to another (inter-cell).
`Even if the portable phone remains in the same area, changes
`in voice channel assignment can also occur as a result of
`signal variation or proximity to cell boundaries, for eXample
`(intra-cell). After the initial voice channel assignment,
`changes in voice channel assignment are transmitted to the
`cellular phone via the forWard voice channel or FVC.
`In a preferred embodiment of the invention, as schemati
`cally illustrated in FIG. 1, a central monitoring station or
`communication and dispatch center (CDC) 2