United States Patent [19J
`Trompower
`
`I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US005924040A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,924,040
`Jul. 13, 1999
`
`[54] WIRELESS COMMUNICATION SYSTEM
`HAVING BASE STATION WITH
`ADJUSTABLE POWER TRANSCEIVER FOR
`LOCATING MOBILE DEVICES
`
`[75]
`
`Inventor: Michael L. Trompower, Navarre, Ohio
`
`5,603,089
`5,615,409
`5,657,487
`
`2/1997 Searle et al. ............................ 455/562
`3/1997 Forssen ................................... 455/562
`8/1997 Doner ...................................... 455/456
`
`Primary Examiner-Edward F. Urban
`Attorney, Agent, or Firm-Renner, Otto, Boisselle &
`Sklar,P.L.L.
`
`[73] Assignee: Telxon Corporation, Akron, Ohio
`
`[57]
`
`ABSTRACT
`
`[21] Appl. No.: 08/752,906
`
`[22] Filed:
`
`Nov. 20, 1996
`
`Int. Cl.6
`................................ H04Q 7/20; H04Q 7/30
`[51]
`[52] U.S. Cl. ............................................. 455/456; 455/562
`[58] Field of Search ..................................... 455/422, 456,
`455/458, 561, 562; 342/357, 457
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,241,690
`5,293,642
`5,488,737
`5,508,707
`5,519,760
`5,602,555
`
`8/1993 Larsson et al. ........................... 455/70
`3/1994 Lo .
`1/1996 Harbin et al. ........................... 455/562
`4/1996 LeBlanc et al. ........................ 455/456
`5/1996 Borkowski et al. .
`2/1997 Searle et al. ............................ 455/562
`
`A network cellular communication system with power based
`locator system in which the location of a mobile commu(cid:173)
`nication unit within the network can be determined approxi(cid:173)
`mately. In particular, the power based locator system
`includes a pre-stored map of locations of a plurality of base
`stations within the network and the respective network cell
`coverage areas for those base stations. Each of the plurality
`of base stations is able to change the size of its respective
`cell by varying transmitter and receiver power levels. By
`incrementally changing its respective cell coverage area, the
`base station can effectively narrow down the region in which
`a mobile communication unit is located. The region infor(cid:173)
`mation is correlated with the pre-stored map of locations to
`determine approximately where in the cellular communica(cid:173)
`tion network the mobile communication unit is located.
`
`12 Claims, 8 Drawing Sheets
`
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`TERMINAL
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`60
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`I
`
`Twitter Exhibit 1044
`Twitter, Inc. v. BlackBerry Ltd.
`Page 00001
`
`

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`
`Page 00002
`
`

`

`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 2 of 8
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`Page 00003
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`

`

`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 3 of 8
`
`5,924,040
`
`110
`
`62
`
`98 '---~~~---,
`
`PROCESSOR
`
`100
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`MEMORY
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`XCEIVER
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`52
`
`Fig. 3A
`
`PROCESSOR
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`MEMORY
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`Fig. 38
`
`Page 00004
`
`

`

`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 4 of 8
`
`5,924,040
`
`60~
`
`103
`
`104
`
`PROCESSOR
`
`MEMORY
`
`XCEIVER
`
`102
`
`101
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`52
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`
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`132
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`USER INPUT
`DEVICE
`
`BAR CODE
`READER
`
`----134
`
`Fig. 4
`
`Page 00005
`
`

`

`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 5 of 8
`
`5,924,040
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`Page 00006
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`

`

`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 6 of 8
`
`5,924,040
`
`300
`
`START
`
`NO
`
`SELECT ANTENNA
`
`310
`
`320
`
`SELECT POWER LEVEL OF RECEIVER
`AND TRANSMITTER
`
`340
`
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`INFORM
`HOST
`COMPUTER
`
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`
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`
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`
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`
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`POWER LEVEL
`AVAILABLE
`
`380
`
`NO
`
`Fig. 6
`
`Page 00007
`
`

`

`U.S. Patent
`
`Jul. 13, 1999
`
`Sheet 7 of 8
`
`5,924,040
`
`START
`
`400
`
`402
`
`INITIATE MOBILE TERMINAL
`LOCATION REQUEST
`
`WAIT FOR RESPONSES FROM
`BASE STATIONS
`
`410
`
`420
`
`NO
`
`HAVE ALL BASE
`STATIONS
`RESPONDED?
`
`YES
`
`PROCESS DAT A RECEIVED
`FROM BASE STATIONS IN
`CONJUNCTION WITH MAP
`INFORMATION
`
`DETERMINE LOCATION OF
`MOBILE TERMINALS
`
`430
`
`440
`
`UPDATE MOBILE TERMINAL
`LOCATION INFORMATION
`
`450
`
`Fig. 7
`
`Page 00008
`
`

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`
`MOBILE TERMINAL LOCATION
`
`DEVICE ID
`
`MOBILE TERMINAL
`
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`Page 00009
`
`

`

`5,924,040
`
`1
`WIRELESS COMMUNICATION SYSTEM
`HAVING BASE STATION WITH
`ADJUSTABLE POWER TRANSCEIVER FOR
`LOCATING MOBILE DEVICES
`
`TECHNICAL FIELD
`
`The present invention relates generally to wireless com(cid:173)
`munication systems, and more particularly to a cellular
`communication system which can determine approximately
`the location of mobile communication units within a cellular
`communication network.
`
`BACKGROUND OF THE INVENTION
`
`25
`
`2
`Generally, when a mobile communication unit is powered
`up, it "registers" with a base station through which the
`mobile communication unit can maintain wireless commu(cid:173)
`nication with the network. In order to register, the mobile
`5 communication unit must be within the cell range of the base
`station and the base station must likewise be situated within
`the effective cell range of the mobile communication unit. It
`is generally not possible to have one base station service a
`large area by itself. This is due to transmission power
`10 restrictions governed by the FCC and the fact that such a
`large cell range would add significantly to the size and
`weight of the mobile communication unit thereby making it
`less desirable to use. Thus, cellular communication systems
`generally have several base stations spaced apart such that
`15 the collective cell area coverage of the base stations is
`sufficient to cover the entire area in which the mobile
`communication unit may roam. As the location of the mobile
`communication unit changes, the base station with which the
`mobile communication unit was originally registered may
`20 fall outside of the geographic cell range of the mobile
`communication unit. Therefore, the mobile communication
`uni! may "deregister" with the base station it was originally
`registered to and register with another base station which is
`within its current communication range.
`The mobility of the mobile communication unit in the
`aforementioned systems creates the need to determine the
`respective location of the mobile communication units
`within the network. Systems for locating mobile communi(cid:173)
`cation units are known, however, most of these systems
`30 employ global position system (GPS) technology. The Glo(cid:173)
`bal Positioning System (GPS) is a network of approximately
`24 satellites and a dozen ground stations. The GPS network
`currently provides navigation information worldwide. A
`r~ceiver deri~es its three-dimensional position from ranging
`35 signals received from three or more satellites. However,
`GPS technology requires the use of expensive equipment
`and is generally not practicable for use in most local area
`network (LAN) based systems.
`U.S. Pat. No. 5,519,760 ('760) to Borkowski et al. dis-
`closes a cellular position locating system which does not
`requires the use of GPS technology. However, the '760
`patent only teaches a method for locating mobile devices in
`a cellular telephone network having a mobile switching
`center which provides necessary processing and switching to
`allow cellular phones to communicate with each other. This,
`of course, would have no benefit for locating mobile devices
`in a LAN, WAN or other cellular based system which does
`not have such a mobile switching center. Furthermore, the
`location information obtained in the system of the '760
`50 patent only pertains to which of several cell sites a mobile
`unit is currently located. As cell site coverage areas are often
`very large, such information would not be sufficient for
`quickly and efficiently locating a mobile device.
`In view of the aforementioned shortcomings associated
`~ith con~entio~al communication systems involving locat(cid:173)
`mg mobile devices, there is a strong need in the art for a
`system and method for locating a mobile device in a cellular
`communication system wherein existing network compo-
`60 nents can be used to accurately narrow down and/or pinpoint
`the location of a mobile communication unit within the
`system.
`
`In recent years, the use of cellular communication sys(cid:173)
`tems having mobile communication units which communi(cid:173)
`cate with a hardwired network, such as a local area network
`(LAN) and a wide area network (WAN), has become wide(cid:173)
`spread. Retail stores and warehouse, for example, may use
`cellular communications systems to track inventory and
`replenish stock. The transportation industry may use such
`systems at large outdoor storage facilities to keep an accu(cid:173)
`rate account of incoming and outgoing shipments. In manu(cid:173)
`facturing facilities, such systems are useful for tracking
`parts, completed products and defects.
`A typical cellular communication system includes a num-
`ber of fixed base stations or access points interconnected by
`a s~stem backbone. Such cellular communication systems
`which have a system backbone may also be hereinafter
`referred to as a network communication system. Also
`included in many cellular communication systems are inter(cid:173)
`mediate base stations which are not directly connected to the
`system backbone. Intermediate base stations, often referred
`to as wireless base stations or repeaters, increase the area
`within which base stations connected to the system back(cid:173)
`bone can communicate with mobile communication units.
`A cellular communication system includes several base
`stations, each of which transmits and receives RF signals
`throughout a predetermined coverage area referred to as a
`cell. A cell is a geographic area in which a base station has
`sufficient signal strength to transmit and receive data from a
`mobile communication unit or other device with an accept(cid:173)
`able error rate. Thus, the outer boundary of a cell is
`determined not only by the radiated power of the base station
`transceiver (which determines the maximum range at which
`a mobile communication unit is able to receive a signal), but
`also by the effective radiated power of the mobile commu(cid:173)
`nic~tion units (which determines the maximum range at
`which the base station is able to receive a signal). Typically,
`base stations will be positioned along the backbone such that
`the combined cell area coverage from each base station
`provides full coverage of a building or site. Further, it is also
`typical to have the cell area of coverage from two or more
`base stations to overlap or be colocated.
`The shape of each cell is primarily determined by the type
`of antenna associated with a given base station. For instance,
`base stations which communicate with mobile communica(cid:173)
`tion units often have omnidirectional type antennas which
`provide for generally circular shaped cells and allow for a
`wide area of coverage. In many instances, however, the cell
`of a base station is not completely symmetrical because
`physical stf1;1-ctures within the cell may partially block sig(cid:173)
`nals emanatmg from the base station or create "dead spots"
`where no signal can pass. Further, the cell size may be
`decreased by machinery located in the vicinity of the base 65
`station which generates excessive noise levels that degrade
`a signal transmitted by the base station.
`
`40
`
`45
`
`55
`
`SUMMARY OF THE INVENTION
`
`The present invention provides a power based locator
`system. In accordance with the invention, an approximate
`location of a mobile communication unit within a cellular
`
`Page 00010
`
`

`

`5,924,040
`
`4
`system for receiving wireless communications and a trans(cid:173)
`mitting system for transmitting wireless communications,
`the at least one base station including a first antenna; at least
`one mobile communication unit for communicating with the
`5 system backbone via the at least one base station, the at least
`one mobile communication unit having a mobile commu(cid:173)
`nication unit transmitter for transmitting wireless commu(cid:173)
`nications to the at least one base station and a mobile
`communication unit receiver system for receiving wireless
`communications from the at least one base station; wherein,
`the at least one base station can vary its cell coverage area
`so that the system can determine approximately where the at
`least one mobile communication unit is located with respect
`to the base station; and a host computer for receiving from
`the at least one base station the location information of the
`mobile communication unit with respect to the base station,
`wherein the host computer upon receiving the location
`information of the mobile communication unit with respect
`to the base station processes the information in conjunction
`with pre-stored map information to determine the location of
`the mobile communication unit within the network, the
`prestored map information including information relating to
`the location of the at least one base station within the
`network.
`To the accomplishment of the foregoing and related ends,
`the invention then comprises the features hereinafter fully
`described and particularly pointed out in the claims. The
`following description and the annexed drawings set forth in
`detail certain illustrative embodiments of the invention.
`These embodiments are indicative, however, of but a few of
`the various ways in which the principles of the invention
`may be employed. Other objects, advantages and novel
`features of the invention will become apparent from the
`following detailed description of the invention when con-
`35 sidered in conjunction with the drawings.
`
`3
`communication network is determined. In particular, the
`present invention includes a pre-stored map of locations of
`a plurality of base stations within the network and the
`respective network cell coverage areas for those base sta(cid:173)
`tions. Each of the plurality of base stations is able to change
`the size and/or shape of its respective cell by varying
`transmitter and receiver power levels and/or antennas. By
`incrementally changing its respective cell coverage area, the
`base station can effectively narrow down the region in which
`a mobile communication unit is located. The region infor- 10
`mation is correlated with the pre-stored map of locations to
`determine approximately where in the cellular communica(cid:173)
`tion network the mobile communication unit is located.
`In accordance with a preferred embodiment of the present
`invention, a cellular communication system is provided, 15
`including: at least one base station having a communication
`cell coverage area, the at least one base station being
`coupled to a system backbone, the at least one base station
`including a receiving system for receiving wireless commu(cid:173)
`nications and a transmitting system for transmitting wireless 20
`communications, the at least one base station including a
`first antenna; and at least one mobile communication unit for
`communicating with the system backbone via the at least
`one base station, the at least one mobile communication unit
`having a mobile communication unit transmitter for trans- 25
`mitting wireless communications to the at least one base
`station and a mobile communication unit receiver system for
`receiving wireless communications from the at least one
`base station; wherein, the at least one base station can vary
`its cell coverage area so that the system can determine 30
`approximately where the at least one mobile communication
`unit is located.
`In accordance with another embodiment of the invention,
`a base station to be used in determining the location of a
`mobile communication unit in a cellular communication
`system is provided, the base station including: a transmitter
`for transmitting a signal; a receiver for receiving a signal;
`at least one amplifier for changing the gain of at least one
`of the transmitter and receiver; and a processor for control- 40
`ling the transmitter and receiver, wherein the processor
`employs the at least one amplifier to change the gain of at
`least one of the transmitter and receiver in order to change
`a cell coverage area of the base station such that an approxi(cid:173)
`mate location of the mobile terminal can be determined.
`According to still yet another embodiment of the
`invention, a method of locating a mobile communication
`unit within a network cellular communication system is
`provided, the method including the steps of: using a host
`computer to initiate a mobile communication unit location 50
`request to at least one base station; using the at least one base
`station to monitor for the mobile communication unit,
`wherein the base station upon locating the mobile commu(cid:173)
`nication unit varies its cell coverage area in order to deter(cid:173)
`mine approximately the location of the mobile communica- 55
`tion unit with respect to the at least one base station; using
`the at least one base station to send the mobile communi(cid:173)
`cation unit location information to the host computer; and
`using the host computer to process the mobile communica(cid:173)
`tion unit location information received from the at least one 60
`base station in order to determine the location of the mobile
`communication unit with respect to the network.
`According to a further embodiment of the invention, a
`cellular communication system is provided, including: at
`least one base station having a communication cell coverage 65
`area, the at least one base station being coupled to a system
`backbone, the at least one base station including a receiving
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings:
`FIG. 1 is a system diagram of a network communication
`system in accordance with the present invention;
`FIG. 2 is a system diagram of a network communication
`system which includes a base station having a directional
`antenna which can change the direction of a signal in
`45 accordance with the present invention;
`FIG. 3A is a block diagram of a hard wired base station
`in accordance with the present invention;
`FIG. 3B is a block diagram of a wireless base station in
`accordance with the present invention;
`FIG. 3C is a block diagram of a host computer in
`accordance with the present invention;
`FIG. 4 is a block diagram of an exemplary mobile
`communication unit in accordance with the present inven(cid:173)
`tion;
`FIG. 5 is a schematic diagram representing an exemplary
`format for information packets which are communicated
`between devices in a network communication system in
`accordance with the present invention;
`FIG. 6 is a flowchart suitable for programming the opera(cid:173)
`tion of a base station in order to determine approximately the
`location of a mobile communication unit in accordance with
`the present invention;
`FIG. 7 is a flowchart suitable for programming the opera(cid:173)
`tion of a host computer to determine approximately the
`location of a mobile communication unit in accordance with
`the present invention; and
`
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`5,924,040
`
`5
`FIG. 8 is an illustration of a table of identification codes
`of respective base stations, the respective cell coverage area
`of the base stations, the identification codes of mobile
`communication units and the respective locations of the
`mobile communication units which is maintained by a 5
`processor according to the invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`The present invention will now be described with refer(cid:173)
`ence to the drawings wherein like reference numerals are
`used to refer to like elements throughout. As mentioned
`above, the present invention relates to cellular communica(cid:173)
`tion systems which include mobile communication units that
`can roam from cell to cell. Such mobile communication
`units can be data terminals, telephones, pagers, automobiles,
`etc. In the exemplary embodiment described hereinafter, the
`mobile communication unit is a mobile data terminal used to
`communicate data such as inventory or the like.
`Accordingly, the terms "mobile communication unit" and
`"mobile terminal" are used interchangeably throughout the
`specification and claims. However, it is recognized that the
`invention contemplates other types of mobile devices and is
`not intended to be limited to systems using mobile data
`terminals.
`Referring now to FIG. 1, a cellular communication system 25
`50 is shown in accordance with the exemplary embodiment
`of the present invention. The cellular communication system
`50 includes a network backbone 52. The network backbone
`52 may be a hardwired data communication path made of
`twisted pair cable, shielded coaxial cable or fiber optic cable,
`for example, or may be wireless or partially wireless in
`nature. Coupled to the network backbone 52 are several base
`stations 54. Only two base stations 54a are shown hardwired
`to the network backbone 52, however, it is understood that
`more than two hardwired base stations 54a may be physi- 35
`cally connected to the network backbone 52. The base
`stations 54 may be hardwired to the network backbone 52
`such as base stations 54a or may wirelessly couple to the
`backbone 52 such as base station 54b. Each base station 54
`serves as an entrance point through which wireless commu(cid:173)
`nications may occur with the network backbone 52. The
`wireless base station 54b may be employed to expand the
`effective communication range of the cellular communica(cid:173)
`tion system 50 and/or be used to provide more accurate
`location information in accordance with the present inven(cid:173)
`tion. As is conventional, each wireless base station 54b
`associates itself, typically by registration, with another base
`station or a host computer 60 coupled to the network
`backbone 52, whether hardwired or wireless, such that a link
`is formed between itself and other devices situated on the
`network backbone 52.
`Each base station 54 is capable of wirelessly communi(cid:173)
`cating with other devices in the communication system 50
`via respective antennas commonly denoted by reference
`numeral 62. The antenna 62 for any particular device may be
`of any type suitable for use in a network cellular commu(cid:173)
`nication system, such as an omni-directional antenna (62a),
`a yagi-type antenna (62b), etc. A geographic cell with each
`base station 54 defines a region of coverage in which
`successful wireless communications may occur. Depending
`on the type of antenna 62 selected and output power of the
`respective base station 54, the geographic cell may take one
`of several different forms and sizes. For example, the
`antenna 62 could be an omni-directional antenna if a gen(cid:173)
`erally spherical cell area of coverage is desired. A directed
`yagi-type antenna could be used as the antenna 62 for a more
`directed elliptical cell area of coverage.
`
`6
`The cellular communication system 50 also includes one
`or more mobile communication units 66. The mobile com(cid:173)
`munication units 66 each include an antenna 67 for wire(cid:173)
`lessly communicating with other devices. Each mobile com(cid:173)
`munication unit 66 communicates with devices on the
`network backbone 52 via a selected base station 54 and/or
`with other mobile communication units. Further, in the event
`the host computer 60 is capable of directly transmitting and
`receiving wireless communication, the mobile communica-
`10 tion unit 66 may communicate directly with the host com(cid:173)
`puter 60. Upon roaming from one cell to another, the mobile
`communication unit 66 is configured to associate itself with
`a new base station 54 if within range.
`In searching for a mobile communication unit 66 accord-
`15 ing to the present invention, the host computer 60 initially
`broadcasts a request for a particular mobile communication
`unit (e.g., mobile communication unit 66a). The host com(cid:173)
`puter 60 includes a pre-stored map of the geographical
`layout of the cellular communication network. The map
`20 includes the locations of the base stations 54 and the cell
`coverage areas of each respective base station 54. Since each
`base station 54 can change its effective cell coverage area,
`the map also includes the cell coverage area of each different
`sized cell associated with a particular base station 54. For
`instance, still referring to FIG. 1, base station 54a 1 has
`respective cell coverage areas 70A, 70s and 70c. Base station
`54a 2 has respective cell coverage areas 72A, 72s and 72c.
`The map, has stored therein the location of base station 54a 1
`and the cell coverage area of its respective cells 70A, 70s and
`30 70c- Although only three different cell sizes are illustrated
`for a particular base station 54, it is understood that the base
`stations 54 can vary their respective cells any suitable
`number of times and sizes and the map can store the
`respective coverage areas of each of those cell sizes.
`Once the host computer 60 initiates a search for a par-
`ticular mobile communication unit (e.g., mobile communi(cid:173)
`cation unit 66a), all of the base stations 54 within the
`network begin monitoring for that particular mobile com(cid:173)
`munication unit 66a. Once one or more base stations 54
`40 locate the mobile communication unit 66a being searched
`for, the base stations 54 change their cell sizes to further
`narrow the location of the mobile communication unit 66a.
`For example, if the mobile communication unit 66a is within
`the respective cells 70c, 72c of base stations 54a 1 54a2 ,
`45 these base stations 54a 1 54a2 then will decrease th~ir cell
`coverage areas to respectively 70s and 72s. Since the mobile
`communication unit 66a is still in communication with each
`base station 54a 1 54a 2 , each base station 54a 1 54a2 changes
`its cell coverage' area to 70A and 72A, respe~tively. At this
`50 point, the mobile communication unit 66a is not able to
`communicate with either base station 54a 1 54a 2 . Thus, each
`base station 54a 1 54a 2 knows that the m~bile communica(cid:173)
`tion unit is at lea'st within the cell area defined by 70s and
`72s, respectively, but not closer than the cell areas defined
`55 by 70A and 72A, respectively. Each base station 54a 1 54a 2
`acts autonomously of the other, and sends its resp~ctive
`information to the host computer 60. Thus, base station 54a 1
`will inform the host computer 60 that mobile communica(cid:173)
`tion unit 66a is within cell coverage area 70s but not 70A.
`60 Likewise, base station 54a 2 will inform the host computer 60
`that mobile communication unit 66a is within cell coverage
`area 72s but not 72A" After the host computer 60 receives all
`information from the base stations 54 relating to the location
`of mobile communication unit 66m the host computer makes
`65 a determination via the map where the mobile communica(cid:173)
`tion unit 66a is located. In this instance, since it is known that
`the mobile communication unit 66a is located within cell
`
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`5,924,040
`
`7
`areas 70s and 72s the mobile communication unit 66a must
`be located in the region where these two cells overlap-this
`region is shown by crosshatching in FIG. 1.
`In another example, the host computer is now searching
`for mobile communication unit 66s. The host computer 5
`initiates a location request to all base stations 54 within the
`network for the location of mobile communication unit 66s.
`In response, the base stations 54 begin to monitor for mobile
`communication unit 66s. Base stations 54a1 54a 2 both have
`found mobile communication unit 66s within their respec- 10
`tive cells 70c and 72c. Next, both base stations decrease the
`size of their respective cell area coverage to 70s and 72s.
`In this example, base station 54a1 cannot communicate
`with mobile communication unit 66s within the cell range
`defined by 70s, however, base station 54a 2 is still able to 15
`communicate with mobile communication unit 66s. Base
`station 54a 1 informs the host computer 60 that mobile
`communication unit 66s is within the range defined by cell
`70c, but not within the range defined by cell 70s· Base
`station 54a 2 continues to decrease its cell coverage area to 20
`cell 72A. Base station 54a2 is not able to communicate with
`mobile communication unit 66s within this cell range.
`Accordingly, base station 54a2 knows that mobile commu(cid:173)
`nication unit 66s is within the range defined by cell 72s, but
`not within the range defined by cell 72A-this information is 25
`passed on to the host computer 60. Once all of the base
`stations 54 have sent the host computer 60 their respective
`location information relating to mobile communication unit
`66s. The host computer processes the information and
`correlates the information with the pre-stored map to deter- 30
`mine that the mobile communication unit 66s is located
`within a region defined as an area bounded by the outer
`perimeter of cells 70c and 70s, which overlaps with the area
`bounded by the outer perimeter of cells 72s and 72A.
`In yet another example, the host computer initiates a 35
`search for mobile communication unit 66c- In response, the
`base stations 54 begin to monitor for mobile communication
`unit 66c. Only base station 54b has found mobile commu(cid:173)
`nication unit 66c- The base station 54b knows that mobile
`communication unit 66c is within the range of its respective 40
`cell 74c. Next, base station 54b decreases the size of its
`respective cell area coverage to 74s . However, the base
`station 54b cannot communicate with the mobile communi(cid:173)
`cation unit 66c within this cell area. Thus, base station 54b
`knows that mobile communication unit 66c is within the 45
`range between cells 74c and 74s, and this information is
`communicated to the host computer 60. Once all of the base
`stations 54 have sent the host computer 60 their respective
`location information relating to mobile communication unit
`66c. The host computer processes