(12) United States Patent
`US 6,222,483 B1
`(10) Patent N0.:
`Twitchell et al.
`
`(45) Date of Patent: Apr. 24, 2001
`
`USOO6222483B1
`
`(54)
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`(75)
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`(73)
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`(21)
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`(22)
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`(51)
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`GPS LOCATION FOR MOBILE PHONES
`USING THE INTERNET
`
`Inventors: Robert W. Twitchell; Andrew Taylor,
`both of San Diego, CA (US)
`
`Assignee: Nokia Mobile Phones Limited, Espoo
`(F1)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Appl. No.: 09/163,221
`
`Filed:
`
`Sep. 29, 1998
`
`US. Cl.
`
`Int. Cl.7 ............................. G01S 5/02; H04B 7/185;
`H04Q 7/20
`.................................. 342/357.09; 342/357.1;
`455/456
`Field of Search ......................... 342/357.06, 357.09,
`342/357.1, 357.13, 450, 457; 455/456, 457,
`426; 701/214
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,043,736
`8/1991 Darnell et a1.
`....................... 342/357
`5,101,500 *
`3/1992 Marui .........
`455/32.1
`
`5,159,592
`10/1992 Perkins .......
`370/857
`
`5,225,842
`..
`7/1993 Brown et al.
`342/357
`
`5,289,527 *
`2/1994 Tiedemann, Jr.
`342/457
`5,365,450
`11/1994 Schuchman et a1.
`.
`364/449
`
`5,617,100
`4/1997 Akiyoski et a1.
`.................... 342/357
`5,663,734
`9/1997 Krasner ................................ 342/357
`5,752,218
`5/1998 Harrison et a1.
`701/207
`
`5,786,789
`7/1998 Janky .............
`342/357
`
`5,841,396 * 11/1998 Krasner ..........
`342/357.02
`..................... 455/426
`5,901,352 *
`5/1999 St—Pierre et al.
`5,917,444 *
`6/1999 Loomis et al.
`.................. 342/357.12
`FOREIGN PATENT DOCUMENTS
`
`WO 98/25157
`WO 99/19743
`WO 99/44073
`
`6/1998 (wo).
`4/1999 (wo).
`9/1999 (wo).
`
`OTHER PUBLICATIONS
`
`Valejo, A. et al., “Short—range DGPS for mobile robots with
`wireless Ethernet links”, AMC ’98—Coimbra, 1998 IEEE,
`pp. 334—339, XP—002127554.
`
`* cited by examiner
`
`Primary Examiner—Thomas H. Tarcza
`Assistant Examiner—Fred H. Mull
`
`(74) Attorney, Agent, or Firm—Perman & Green, LLP
`
`(57)
`
`ABSTRACT
`
`A position locating system and method are provided for
`determining a geographic location of a portable remote unit.
`The locating system includes a communications system
`having at least one base station and a system controller. The
`base station bi-directionally couples the remote unit to the
`system controller through wireless links. The locating sys-
`tem also includes a server coupled to the system controller
`by a communication infrastructure external to the commu-
`nications system. The server includes a data store which
`contains satellite positioning information. In response to a
`message from the remote unit, the server provides satellite
`information to the system controller over the communication
`infrastructure such that the provided satellite information is
`passed to the remote unit by the base station. The provided
`satellite information includes information to aid in acquiring
`a predetermined number of satellites within a satellite posi-
`tioning system. The acquired satellites provide coded signals
`for determining the geographic location of the remote unit.
`In one embodiment, the data communication system is a
`cellular telephone network and the communication infra-
`structure is the Internet. The Internet
`is coupled to the
`cellular telephone network through a public switched tele-
`phone network (PSTN).
`
`W0
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`97/14054
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`4/1997 (W0) .
`
`29 Claims, 7 Drawing Sheets
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`T-O—FT r0
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` .0.
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` Oi
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`GPS Satellites,
`16
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`Coded
`Signals, 14
`
`/40
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`Telecomm. /
`Circuitry /
`GPS Circuitry
`Remote
`Unit, 42
`
`Wireless Comm. System, 48
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`PSTN
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`Satellite
`I
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`Information ,2
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`Database, 54
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`'“temet
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`Internet
`Sewer. 56
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`Umfied Patents
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`Apr. 24, 2001
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`US. Patent
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`Apr. 24, 2001
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`US 6,222,483 B1
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`1
`GPS LOCATION FOR MOBILE PHONES
`USING THE INTERNET
`
`FIELD OF THE INVENTION
`
`This invention relates to a system for determining a
`latitude and longitude of an individual or object, and
`specifically, to a system which includes a hand-held locating
`unit and a telecommunications network which includes a
`
`5
`
`radiotelephone network, a satellite positioning system and
`the Internet.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`2
`tion of the signal, provides the range or distance value,
`referred to as a “pseudorange”, between the transmitting
`satellite and the remote unit. The distance is referred to as a
`
`“pseudorange” because, while the actual calculation may be
`accurate, errors may be introduced in the data by the fact,
`e.g., that a local clock, which is generated in the remote unit,
`may not be precisely synchronized with GPS time, and also
`by the fact that signal propagation through the atmosphere
`may encounter delays.
`Once the pseudorange computations are completed, the
`position of the remote unit
`is determined by using the
`pseudoranges and the satellite timing and ephemeris data.
`Typically, GPS signals from at least two or three line-of-
`sight positioning satellites are needed to supply sufficient
`information to derive accurate position determinations at an
`Earth-based station, such as the remote unit. Conventionally
`four such satellites are used to determine a terrestrial posi-
`tion estimate, three for triangulation and one for correcting
`for clock bias.
`
`the position of the
`In another type of a GPS system,
`remote unit is determined by utilizing the positioning signals
`received from in-view satellites (as described above) and
`also satellite information received over a telecommunica-
`tions link from a base station. The telecommunications link
`
`may be, for example, a two-way page system or a cellular
`communication system. Accordingly, the remote unit uti-
`lizes the information received from the GPS satellites and
`
`from the telecommunications link to compute pseudoranges
`and,
`in turn,
`to compute its latitudinal and longitudinal
`position. An exemplary embodiment of a position locating
`systems which utilizes positioning signals received from
`in-view satellites and satellite information received over a
`data communication link can be found in US. Pat. No.
`
`5,663,734, issued Sep. 2, 1997, entitled “GPS Receiver and
`Method For Processing GPS Signals”, by Norman F. Kras-
`ner. Similar systems are also disclosed in US. Pat. No.
`5,225,842, issued Jul. 6, 1993, entitled “Vehicle Tracking
`System Employing Global Positioning System (GPS)
`Satellites”, by Brown et al. and in US. Pat. No. 5,365,450,
`issued Nov. 15, 1994, entitled “Hybrid GPS/Data Line Unit
`For Rapid, Precise, and Robust Position Determination”, by
`Schuchman et al.
`
`In Schuchman et al., for example, there is disclosed a
`specialized server which resides on a cellular phone system.
`The specialized server includes a satellite almanac database
`which contains ephemeris and time models of a GPS satel-
`lite constellation. In one embodiment, the ephemerides and
`time model information is provided to the GPS receiver for
`use in a search and acquisition mode.
`In FIG. 1, a conventional GPS locating system 10 is
`shown. A remote unit 12 of the GPS locating system 10
`searches a predetermined band of frequencies to acquire
`coded signals 14 transmitted by orbiting GPS satellites 16.
`The remote unit 12 also establishes communication, via data
`link 18, with a service center 20 which services a region of
`a cellular phone system 22. The cellular phone system 22
`includes a satellite information database 24 which contains
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`Presently, position locating systems may include a por-
`table remote unit which comprises a receiver for receiving
`signals from a satellite positioning system (e.g., a global
`positioning system (GPS)),
`telecommunications circuitry,
`clock circuitry and a microprocessor for analyzing coded
`signals received from the satellite positioning system and
`from a telecommunications link, for example, a wireless
`communication network. The microprocessor of this inte-
`grated positioning and telecommunications system may ana-
`lyze the coded signals to determine the latitude and longi-
`tude of the portable remote unit. An exemplary integrated
`positioning and telecommunications system can be found in,
`for example, US. Pat. No. 5,043,736, issued Aug. 27, 1991,
`entitled “Cellular Position Locating System”, by Darnell et
`al., which discloses a portable locating unit useful both as a
`cellular telephone and a portable global positioning system.
`The determination of the position of the remote unit may
`be calculated with, or without, information provided to the
`remote unit over the telecommunications link, e.g., over the
`wireless communication network.
`
`In one type of a GPS system, which operates without
`information provided over the telecommunications link, the
`precise position of each of a plurality of satellites at any
`given time are transmitted to the Earth in the form of coded
`signals. The coded signals contain information as to the
`position of each of the satellites in space with respect to GPS
`time, and also, an indication of the precise time at which
`each one of the signals was transmitted from each one of the
`satellites. This information may be referred to as ephemeris
`data. The coded signals also include high rate repetitive
`signals referred to as pseudorandom (PN) sequences. Each
`GPS satellite broadcasts a signal with a unique offset to a PN
`sequence.
`
`The coded signals are transmitted by the GPS satellites
`within a predetermined band of frequencies. The remote
`units search the predetermined band of frequencies in an
`effort to acquire the coded signals from in-view GPS satel-
`lites.
`In the acquisition process, a remote unit receives
`signals from the GPS satellites and performs a correlation
`operation. The correlation operation evaluates the received
`signals and searches for known PN sequences. The detection
`of a known PN sequence within a received signal is an
`indication that the received signal is a GPS coded signal.
`Once the PN sequence search is complete and a coded signal
`is acquired, the range or distance between the GPS satellite
`transmitting the signal and a receiver, e.g. the remote unit,
`may be determined. The distance is determined by using the
`time of transmission of the coded signal and by noting the
`time that the signal is received at the remote unit from one
`of the satellites. The remote unit calculates a propagation
`time delay from the time difference, i.e. from the difference
`between the time the coded signal was transmitted and the
`time the signal was received at the remote unit. The calcu-
`lated time delay, when multiplied by the speed of propaga-
`
`ephemerides and timing data for the GPS satellites 16 within
`a GPS satellite constellation.
`
`60
`
`The remote unit 12 of this conventional GPS locating
`system 10 uses the coded signals 14 and ephemeris and
`timing data to determine the latitudinal and longitudinal
`position of the remote unit 12. The remote unit 12 also uses
`the data from the satellite information database 24 to aid its
`search for in-view GPS satellites 16 of the GPS constella-
`
`65
`
`tion. Aprior knowledge of the location of the GPS satellites
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`US 6,222,483 B1
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`3
`16 can decrease the time required to acquire the coded
`signals 14 from the GPS satellites 16.
`The satellite information database 24 is stored in a spe-
`cialized server 26 of the cellular phone system 22. Thus, the
`ephemerides and timing data of the GPS satellites 16 can be
`requested by the remote unit 12, retrieved from the satellite
`information database 24, and passed by the cellular phone
`system 22 through the service center 20 over data link 18 to
`the requesting remote unit 12. The received ephemerides and
`timing data can then be used, with the received coded signals
`14, to determine the latitude and longitude of the remote unit
`12.
`
`As can be appreciated, delays may be experienced in this
`process of requesting and receiving data from the satellite
`information data base 24 of the cellular phone system 22.
`For example, delays in the transmission of a request for data
`by the remote unit 12, the reception and processing of the
`request in the cellular phone system 22, and the retrieval and
`transmission of data from the satellite information data base
`
`24 back to the remote unit 12, may compromise the validity
`of the information provided. That is, the delays may result
`in the remote unit 12 receiving information that a GPS
`satellite is at a first position when, in fact, the GPS satellite
`has passed the first position and is in a second position.
`Under these circumstances the attempt to aid the search for
`in-view satellites has failed and may have increased the
`actual acquisition time.
`As demonstrated above, the ability of a remote station to
`rapidly locate, track and acquire position information from
`in-view, earth orbiting GPS satellites is desirable. Satellite
`ephemerides and timing information can be provided to aid
`the acquisition process. While it is also desirable to achieve
`the goal of rapid acquisition and tracking, it is undesirable
`to provide a specialized server in a radiotelephone system to
`accomplish the goal.
`OBJECTS AND ADVANTAGES OF THE
`INVENTION
`
`It is therefore a first object and advantage of this invention
`to provide a method and a system to enhance the ability of
`a remote unit
`to locate,
`track and acquire the position
`information from GPS satellites while avoiding the necessity
`to provide a specialized GPS server in a radiotelephone
`system.
`It is a further object and advantage of this invention to
`provide satellite ephemerides data, prior to acquisition, to
`aid a remote unit in rapidly locating and acquiring in-view,
`GPS satellites,
`the ephemerides being provided from a
`server that is coupled to the radiotelephone system through
`a communication network external to the radiotelephone
`system such as the Internet.
`It is another object and advantage of this invention to
`provide satellite ephemerides data from a single server that
`is coupled to one or more radiotelephone systems through a
`communication network external to the one or more radio-
`
`telephone systems, the one or more radiotelephone systems
`being coupled directly or indirectly to the external commu-
`nication network.
`
`It is still another object and advantage of this invention to
`time stamp messages requesting satellite ephemerides data
`and messages providing the requested ephemerides data to
`indicate a quality of the received ephemerides data, and also
`to aid a remote unit in locating and acquiring in-view, GPS
`satellites.
`
`Further objects and advantages of this invention will
`become more apparent from a consideration of the drawings
`and ensuing description.
`
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`4
`SUMMARY OF THE INVENTION
`
`The foregoing and other problems are overcome and the
`objects and advantages are realized by methods and appa-
`ratus in accordance with embodiments of this invention,
`wherein a system and methods for locating and acquiring
`GPS satellites used to determine a precise latitude and
`longitude of a remote unit are disclosed.
`A position locating system for determining a geographic
`location of a portable remote unit includes a telecommuni-
`cations system having at least one base station and a system
`controller. The base station bi-directionally couples the
`remote unit to the system controller through wireless links.
`The locating system also includes a server coupled to the
`system controller by a communication network infrastruc-
`ture external to the telecommunications system. The server
`includes a data store which contains satellite positioning
`information.
`In response to a request
`for satellite
`information, the server provides satellite information to the
`system controller over the communication network infra-
`structure such that
`the provided satellite information is
`passed to the remote unit by the base station. The provided
`satellite information includes information to aid in acquiring
`a predetermined number of satellites within a satellite coded
`system. The acquired satellites provide coded signals that
`are utilized to determine the geographic location of the
`remote unit. The selected satellites represent GPS satellites
`in-view of the base station as determined from the requested
`satellite information.
`
`In one embodiment, the telecommunications system is a
`cellular telephone network and the communication network
`infrastructure is the Internet which is coupled to the cellular
`telephone network through a public switched telephone
`network (PSTN). In another embodiment, the communica-
`tion network infrastructure is directly coupled to the cellular
`telephone network.
`Also disclosed is a method for determining a geographic
`location of a portable remote unit. The method includes the
`steps of: (a) providing a telecommunication system com-
`prising at least one base station and a system controller, the
`at least one base station bi-directionally coupling the remote
`unit to the system controller through wireless links; (b)
`requesting satellite information from a server coupled to the
`system controller by a communications network infrastruc-
`ture external to the telecommunications system; (c) in reply
`to the request, retrieving the requested satellite information
`from the server; (d) providing the retrieved satellite infor-
`mation to the remote unit; and (e) acquiring a predetermined
`number of satellites of a satellite positioning system in
`accordance with the provided satellite information, wherein
`the acquired satellites provide coded signals for determining
`the geographic location of the remote unit.
`In one embodiment, the satellite information provided to
`the remote unit may include, for example, satellite almanac,
`ephemeris, and timing information, as well as information
`that specifies which satellites are expected to be in-view and
`their expected signal strengths (pseudorange corrections).
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The above set forth and other features of the invention are
`
`made more apparent in the ensuing Detailed Description of
`the Invention when read in conjunction with the attached
`Drawings, wherein:
`FIG. 1 is schematic diagram of a conventional GPS
`locating system which utilizes satellite ephemeris data in an
`acquisition mode;
`
`Unified Patents
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`US 6,222,483 B1
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`FIG. 2 is schematic diagram of an integrated GPS locating
`and telecommunications system in accordance with the
`present invention;
`FIG. 3 is schematic diagram of a remote unit of the
`integrated GPS locating and telecommunications system of
`FIG. 2;
`FIGS. 4A and 4B are flowcharts illustrating the integrated
`GPS locating and telecommunications system’s use of sat-
`ellite information;
`FIG. 5 is a flowchart illustrating a remote unit’s use of
`satellite information to facilitate the acquisition of in-view
`GPS satellites to determine its position; and
`FIG. 6 is a schematic diagram of a reverse communication
`channel request for a satellite information message and a
`forward communication channel message for providing the
`requested satellite information.
`Identically labelled elements appearing in different ones
`of the above described figures refer to the same elements but
`may not be referenced in the description for all figures.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Referring to FIGS. 2 and 3, and accordance with the
`present invention, an integrated GPS locating and telecom-
`munications system 40 is shown. A remote unit 42 of the
`integrated system 40 includes GPS circuitry (60, 62) for
`receiving signals from a QPS satellite positioning system,
`telecommunications circuitry (64, 66 and 68) for supporting
`the transmission and the reception of RF signals over a
`telecommunications link, e.g. a RF link 44 between the
`remote unit 42 and a base station 46 of a wireless commu-
`
`nications network 48. The GPS (60, 62) and telecommuni-
`cations circuitry (64, 66 and 68) enables the remote unit 42
`to function as a combined portable GPS receiver and a
`mobile radiotelephone.
`It should be appreciated that the wireless communications
`system 48 can be, for example, a cellular telephone network,
`a personal communication services (PCS) system, a paging
`network and a trunked dispatch communications system
`such as a fleet dispatched service (e.g., a police or other
`safety agency communications service that requires com-
`munications within a group of mobile users).
`The remote unit 42 further includes timing circuitry 70
`and a microprocessor 72 for analyzing coded signals
`received from the GPS satellite system and from the wireless
`communications network 48. The remote unit 42 also
`
`includes a memory 74 for storing system parameters such as,
`for example, previously received GPS signals and a plurality
`of constants and variables that are used by the micropro-
`cessor 72 during the operation of the integrated GPS
`receiver and mobile wireless communications device such as
`
`the memory 74
`the mobile radiotelephone. For example,
`stores the values of various radiotelephone system param-
`eters (e.g., cellular system parameters and a number assign-
`ment module (NAM)). An operating program for controlling
`the operation of microprocessor 72 is also stored in a portion
`of the memory 74 (typically in a ROM device).
`The telecommunications circuit 68 includes a modulator,
`a demodulator, a user interface such as a conventional
`earphone or speaker, a conventional microphone, a display,
`and a user input device, typically a keypad, all of which are
`coupled to the microprocessor 72. The remote unit 42 may
`also include a battery 76 for powering the various circuits
`that are required to operate the remote unit 42, or
`alternatively, include circuitry to enable the remote unit 42
`to be vehicle mounted.
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`It should therefore be understood that the remote unit 42
`can be a vehicle mounted or a handheld device. It should
`
`further be appreciated that when operating as a mobile
`radiotelephone the remote unit 42 may be capable of oper-
`ating with one or more air interface standards, modulation
`types, and access types. By example, the remote unit 42 may
`be capable of operating with any of a number air interface
`standards such as IS-136, GSM and 18-95 (CDMA). It
`should thus be clear that the teaching of this invention is not
`to be construed to be limited to any one particular type of
`mobile radiotelephone or air interface standard.
`In accordance with the present invention, the micropro-
`cessor 72 of this integrated positioning and telecommuni-
`cations system 40 analyzes the received, coded signals to
`determine the latitude and longitude of the remote unit 42.
`As shown in FIG. 2, the base station 46 is a part of the
`wireless communications network 48 which comprises a
`mobile switching center (MSC) 50 and an Interworking
`function (IWF) 52. The MSC 50 and the IWF 52 provide a
`connection to landline trunks when the remote unit 42 is
`
`involved in a call. The MSC 50 and the IWF 52 also provide
`a connection between the remote unit 42 and a communi-
`cation network infrastructure external to the wireless com-
`
`munications system 48. In a preferred embodiment of the
`present invention, the communication network infrastruc-
`ture is the Internet. As such, the MSC 50 and the IWF 52
`provide a connection between the remote unit 42 and the
`Internet via the PSTN or some other network.
`In one
`embodiment, the IWF 52 includes an Internet communica-
`tion interface. In another embodiment, the IWF 52 is directly
`connected to the Internet and, thus, does not interface with
`the PSTN.
`
`As used herein, the expression the “Internet” refers to an
`infrastructure whose protocols and operating rules effec-
`tively permits the creation of a world-wide “network of
`networks.” By connecting a computing device to the
`Internet, graphic and textual data may be requested and
`received by the computing device from any source also
`connected to the Internet. Thus, a matrix of interconnected
`communication devices, which have the ability to exchange
`information between one another, is formed.
`In general, devices connected to the Internet will adhere
`to TCP/IP protocols. Traditionally,
`fiber optics, wires,
`cables, switches, routers and other communications tech-
`nologies connect
`individual computing devices over the
`public switched telephone network (PSTN), or directly, to
`the Internet. Once connected,
`the individual computing
`device becomes “linked” to the other communicating
`devices on the Internet such that there is a perception that
`there is no physical distance between any of the devices.
`That is, whether a device is physically located next the
`commuting device or on another continent
`the devices
`function as if they are physically connected.
`Therefore, and in accordance with the present invention,
`GPS satellite information, for example ephemerides and
`timing data, stored in a satellite information database 54 on
`an Internet server 56 is available to one or more telecom-
`
`munications systems having access, either directly or
`indirectly, to the Internet. Upon request, at a predetermined
`time or at an occurrence of a predefined event, the Internet
`server 56 provides the GPS satellite information, i.e. the
`ephemeris and timing data, to the wireless communications
`system 48, over the PSTN or directly thereto, for transmis-
`sion to the remote unit 42 over the RF link 44. It can be
`
`appreciated that many wireless telecommunications
`systems, i.e. systems operated by numerous wireless service
`
`Unified Patents
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`Exhibit 1014
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`Page 11 of 15
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`Unified Patents
`Exhibit 1014
`Page 11 of 15
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`US 6,222,483 B1
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`7
`providers, can access the satellite information database 54
`via the Internet interface. As such, the complexity of pro-
`viding the conventional specialized GPS server in each
`telecommunications system is avoided.
`Additionally, the storing of the GPS satellite ephemerides
`and the timing data in the satellite information database 54
`on the communication network infrastructure external to the
`wireless communications system 48, i.e. the Internet server
`56, provides a flexible method of transferring data between
`the remote units and the satellite information database 54.
`
`Accordingly, as a mobile radiotelephone user roams to
`networks operated by different wireless service providers the
`GPS data is accessible as long as a current service provider
`can access the external communication infrastructure. For
`
`example, it can be appreciated that wireless service provid-
`ers (e. g., cellular service providers) may employ one or more
`bearer services, such as Short Message Service (SMS),
`IS-707 circuit data, and 18-707 packet data, as a base station
`to remote unit communication protocol. As a mobile radio-
`telephone user moves from a “home” service provider which
`employs, for example, a SMS bearer service to another
`service provider which supports circuit switched data or
`packet data, the GPS positioning data which was accessed
`by the mobile radiotelephone user in the home service
`provider may be accessed in the circuit switched data
`provider as long as the circuit switched data provider
`permits the mobile radiotelephone user to access the Inter-
`net. By implementing GPS positioning using an Internet
`server, there is no need for each service provider (the SMS
`or the circuit switched data provider) to actively support
`GPS positioning, or for each service provider to maintain a
`specialized server which supports GPS positioning.
`Furthermore, a third party such as, for example, an Internet
`Service Provider, could establish and maintain a centralized
`GPS positioning server on the Internet and make the server
`available to mobile radiotelephone users using a number of
`mobile telephone networks.
`FIGS. 4A and 4B illustrate an algorithm for determining
`the latitude and longitude of a remote unit, e.g., the remote
`unit 42. In FIG. 4A,
`the algorithm for determining the
`latitude and longitude of the remote unit 42 begins at Block
`100. At Block 110, the remote unit 42 formats a message
`which includes a time stamp and an approximate location of
`the remote unit 42. Preferably, the time stamp is the GPS
`time while the approximate location of the remote unit is
`determined according to one of the following methods.
`Since a base station that services the remote units oper-
`ating within a predetermined region, or cell, of the wireless
`telecommunications network is at a fixed location, the base
`station’s latitude and longitude are known. In some cellular
`networks, for example a CDMA network, the base station’s
`latitude and longitude, and a GPS time are provided to the
`remote units operating within the cell. Therefore, in wireless
`networks which provide the base station’s latitude and
`longitude and the GPS time to the remote units the approxi-
`mate location field and the time stamp field of the message
`formatted by these remote units contains the base station’s
`known latitude and longitude, and the GPS time.
`However, in wireless networks which do not provide the
`base station’s latitude and longitude or the GPS time to the
`remote units, the approximate location field and the time
`stamp field of the message formatted by the remote units
`contain other information that provides a less precise initial
`location of and time stamp for the remote unit, for example,
`the network’s System ID (SID) and a value from a real time
`system clock of the remote unit. In some cellular networks
`all base stations within a specific geographic region, e.g. a
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`city, have an equivalent SID value. Since multiple base
`stations share equivalent SID values, a less precise initial
`location of a remote unit is included in the message format-
`ted by the remote unit. While providing a less precise remote
`unit location than is possible when transmitting the base
`station’s known latitude and longitude, the SID value pro-
`vides some bounds on the possible location of the remote
`unit.
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`At Block 120, the message is transmitted from the remote
`unit 42 to the base station 46 servicing the remote unit 42 on
`a reverse communication channel of the RF link 44.
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`Referring briefly to FIG. 6, one embodime