(12) United States Patent
`Krasner et al.
`
`USOO6185427B1
`(10) Patent No.:
`US 6,185,427 B1
`(45) Date of Patent:
`Feb. 6, 2001
`
`(54) DISTRIBUTED SATELLITE POSITION
`SYSTEM PROCESSING AND APPLICATION
`NETWORK
`
`(75) Inventors: Norman F. Krasner, San Carlos; Mark
`Moeglein, Fremont; David Coleman,
`San Jose, all of CA (US)
`
`(73) Assignee: SnapTrack, Inc., San Jose, CA (US)
`(*) Notice:
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`(21) Appl. No.: 09/067,406
`
`5,379,047
`5,379,224
`5,379,320
`5,396,540
`
`1/1995 Yokev et al. ........................ 342/457
`1/1995 Brown et al. ........................ 364/449
`1/1995 Fernandes et al. ...................... 375/1
`3/1995 Gooch .................................... 379/59
`(List continued on next page.)
`page.
`FOREIGN PATENT DOCUMENTS
`242 099 A2 10/1987 (EP) ................................. G01S/5/14
`379 198A2
`7/1990 (EP) ................................. G01S/5/02
`512 789 A2 11/1992 (EP) ................................. G01S/5/14
`601 293 A3 6/1994 (EP) ................................. G01S/5/14
`2 264837
`9/1993 (GB).
`WO 94/28434
`12/1994 (WO) ............................... G01S/5/02
`WO 97 14054
`4/1997 (WO).
`WO 98.53573
`11/1998 (WO).
`
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 08/842.559, filed on
`Apr. 15, 1997, which is a continuation-in-part of application
`No. 08/708,176, filed on Sep. 6, 1996.
`(51) Int. Cl." ....................................................... H04Q 7/20
`(52) U.S. Cl. ..................... 455/456; 455/12.1; 342/357.1;
`342/357.09
`(58) Field of Search ............................ 342/357.1, 357.05,
`342/357.09; 455/456, 457, 12.1
`References Cited
`
`(56)
`
`4,445,118
`4,601,005
`4,701,934
`4,785,463
`4,797,677
`4,959,656
`4,998,111
`5,043,736
`5,119,102
`5202,829
`5,223,844
`5,225.842
`5,317,323
`5,323,163
`5,365,450
`
`U.S. PATENT DOCUMENTS
`4/1984 Taylor et al. ........................ 343.357
`7/1986 Kilvington .....
`... 364/6O2
`10/1987 Jasper .........
`... 375/1
`11/1988 Jane et al. ......
`... 375/1
`1/1989 MacDoran et a
`... 342/352
`9/1990 Kumar ...........
`... 342/418
`3/1991 Ma et al. .......
`... 342/352
`8/1991 Darnell et al. ....................... 342/357
`6/1992 Barnard ................................ 342/357
`4/1993 Geier ..........
`... 364/449
`6/1993 Mansell et al.
`... 342/357
`7/1993 Brown et al. ......
`... 342/357
`5/1994 Kennedy et al. .................... 342/457
`6/1994 Maki .................................... 342/357
`11/1994 Schuchman et al. ................ 364/449
`
`International Search Report for International Application
`No. PCT/US 99/07975 mailed on Sep. 1, 1999.
`International Search Report; dated Jun. 2, 1997; 7 pages.
`(List continued on next page.)
`Primary Examiner Nguyen Vo
`Assistant Examiner-Charles N. Appiah
`(74) Attorney, Agent, or Firm-Blakely, Sokoloff, Taylor &
`Zafman
`ABSTRACT
`(57)
`A System and method for processing in a distributed manner
`satellite position system (SPS) information. In one example
`of the invention, a first mobile SPS receiver receives SPS
`signals from a plurality of SPS satellites and transmits a
`position information to a wireleSS cell based Station which is
`coupled to a first communication network. The wireleSS cell
`based Station is coupled to a first digital processing System
`which receives the position information from the wireless
`cell based Station and calculates a location of the first mobile
`SPS receiver based upon the position information. The first
`digital
`ing t
`its this locati
`11
`ithout
`igital processing transmits Inis location, usually Wilnou
`any presentation of this location on the first digital process
`ing System, to a remotely located application digital pro
`cessing System which presents the location to a user of the
`application digital processing System.
`
`61 Claims, 9 Drawing Sheets
`
`
`
`
`
`
`
`Location
`Server
`
`PSTN andlor other 21a
`Communication Infrastructure(s)
`
`
`
`20
`--
`
`24a
`
`42a
`
`GPSRef
`RCwr
`41a
`
`23 h
`
`
`
`
`
`
`
`30a
`Application Server
`
`24b
`
`te
`
`GPS Ref
`Rcy
`4b 420
`
`20C 5
`
`29
`
`3.
`31a
`Application Server
`
`itles
`
`Instacart, Ex. 1036
`
`1
`
`

`

`US 6,185,427 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`5/1995 Gilhousen et al. .................. 375/705
`5,416,797
`5/1995 Johnson .....
`... 342/357
`5,420,592
`7/1995 Yokev et al. ..
`... 375/202
`5,430,759
`1/1996 Weinberg et al. .
`... 375/200
`5,483,549
`1/1996 Singer et al. ..
`... 342/457
`5,485,163
`9/1997 Krasner ................................ 342/357
`5,663,734
`5/1998 Huston et al. ....................... 342/357
`5,751,244
`6/1998 Cisneros et al. ...
`... 701/213
`5,774,829
`9/1999 Hagerman et al.
`... 342/457
`5,952,969
`5,960,341 * 9/1999 LeBlanc et al. ...
`... 455/426
`5,973,643 * 10/1999 Hawkes et al. ...................... 342/457
`5,982,324 * 11/1999 Watters et al................... 342/357.06
`5.999,124 * 12/1999 Sheynblat........................ 342/357.09
`OTHER PUBLICATIONS
`Amateur Radio Catalog, Summer 1996; pp. 52-55.
`Navigation; Journal of the Institute of Navigation; Summer
`1978; vol. 25; No. 2.
`
`
`
`Navstar GPS User Equipment Introduction; Feb. 1991;
`Public Release Version.
`Cortland, Laurence J., Loran-C Vehicle Tracking in
`Detroit's Public Safety Dispatch System; Journal of Institute
`of Navigation; vol. 36; No. 3; Fall 1989; pp. 223-233.
`Rodgers, Arthur, R. and Anson, Peter; Animal-borne GPS:
`Tracking the Habitat; GPS World; Jul. 1994; pp. 21-22.
`Peterson, Benjamin, et al.; GPS Receiver Structures for the
`Urban Canyon; ION-GPS-95, Session C4, Land Vehicular
`Applications; Palm Springs, CA.; Sep. 1995.
`RTCM Recommended Standards For Differential Navstar
`GPS Service; Version 2.0; RTCM Paper 134–89; SC
`104–68; Jan. 1, 1990.
`Raab, F.H., et al.; An Application of the Gobal Positioning
`System to Search and Rescue and Remote Tracking; Navi
`gation Journal of The Institute of Navigation; vol. 24, No. 3;
`Fall 1977; pp. 216–228.
`* cited by examiner
`
`2
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 1 of 9
`
`US 6,185,427 B1
`
`10a
`
`12a
`
`Mobile GPS
`
`To telephone
`network Or Other
`COmmunications
`links, for dispathing,
`Or Other Services
`
`10b
`
`12b
`
`Mobile GPS
`
`
`
`BaseStation
`
`130
`
`11d
`
`10C
`
`12C
`
`11C
`
`Mobile GPS
`
`Mobile GPS
`
`FIG. 1
`
`3
`
`

`

`U.S. Patent
`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 2 of 9
`
`US 6,185,427 B1
`US 6,185,427 B1
`
`92
`
`VeOld ve
`
`}8YSd9
`
`IAOY
`
`
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`AY
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`JO8AleS
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`oe
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`
`
`
`(s)osnjonysesjulUoeO|UNWWO
`
`4
`
`
`
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 3 of 9
`
`US 6,185,427 B1
`
`101 M
`
`as a -- -
`
`---------
`
`103
`-1
`
`103a
`
`----
`
`is
`Regional
`SMSC
`
`107
`
`Mobile
`Switching
`Center
`
`105a
`
`
`
`
`
`
`
`Communication NetWOrk
`(e.g., SS7)
`
`107a
`
`109a
`
`104
`
`'
`
`106
`
`- - - - - - - - -
`104b
`
`9"
`CellBase
`Cell Base
`
`V
`
`104a
`
`L - - - - - - - m
`
`MSC
`S
`
`106a
`108a
`
`Mobile
`Switching
`Center
`
`GPS
`LOCation
`Server
`
`GPS
`Reference
`Network
`
`111
`
`112
`
`110a
`
`GPS
`LOCation
`Server
`
`109
`
`
`
`Communication Network(s)
`(e.g., PSTN)
`
`110
`
`114
`
`116
`
`Application
`Server
`
`Application
`Server
`
`FIG.2B
`
`5
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 4 of 9
`
`US 6,185,427 B1
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`To/from Cellular
`Switching Centers
`Or Land-based
`Phone System Switch(es)
`or Cell Site(s)
`
`
`
`
`
`
`
`MODEM. Or
`Other Interface
`
`GPS Signal Source
`(e.g., Network of
`GPS Receivers Providing
`Differential GPS
`Information and
`Providing GPS Signal
`Data)
`
`MODEM Or
`Other Interface
`
`54
`
`Data Processing Unit
`(e.g., Computer System)
`
`aa rare are re-
`
`Optional
`
`GPS Receiver
`
`
`
`Mass Storage
`(e.g., for Software)
`and Storage for Cell-based
`Information Source
`
`MODEM. Or
`Other Interface
`
`52
`
`64
`
`TO/from Other
`PrOCeSSOrS
`(e.g., ComputerS On
`NetWOrk Or
`Through Phone System)
`
`FIG. 3
`
`6
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 5 of 9
`
`US 6,185,427 B1
`
`
`
`GPS
`Receiver
`
`Communication
`System
`TranSCeiver
`
`FIG. 4
`
`7
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 6 of 9
`
`US 6,185,427 B1
`
`91
`
`GPS
`Reference
`Receiver
`
`
`
`-90
`
`PrOCeSSOr and
`NetWOrk
`Interface
`
`
`
`
`
`
`
`TO
`Communication
`NetWOrk
`
`FIG. 5
`
`8
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 7 of 9
`
`US 6,185,427 B1
`
`
`
`(IdV OSWS) GZX
`
`8/ || /||
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`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`9
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 8 of 9
`
`US 6,185,427 B1
`
`
`
`uoneog]JOAIa08Y
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`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 9 of 9
`
`US 6,185,427 B1
`
`Mobile GPS Unit Transmits Short Message
`(e.g., Address of Current Base Station and E911)
`
`Base Station Receives Message and Sends to MSC
`Which ForWards it to SMSC
`
`SMSC Sends Message to a Local Server (e.g., Routing it
`to an Available Location Server Through Packet Switched Net)
`
`LOCation Server Determines Satellite information and
`Sends This in Short Message Addressed to Mobile
`Through SMSC
`
`SMSC Receives Short Message and Determines MSC
`Currently Communicating With Mobile and Sends the
`Short Message to This MSC Which Forwards to
`Base Station Currently Communication With Mobile
`
`Mobile GPS Unit Receives Satellite Information
`and Computes and Sends Pseudoranges (As a
`Short Message(s)) to Base Station
`
`Base Station Sends Pseudoranges to Location Server
`Through MSC and SMSC
`
`Location Server Computes Latitude and Longitude
`(But DoesNot Display Position) and Sends This
`Information to a LOCation Database Server and
`to PSAP Which Displays Position on a Map
`
`
`
`
`
`
`
`
`
`FIG. 8
`
`301
`
`303
`
`305
`
`307
`
`309
`
`311
`
`313
`
`315
`
`11
`
`

`

`1
`DISTRIBUTED SATELLITE POSITION
`SYSTEM PROCESSING AND APPLICATION
`NETWORK
`RELATED APPLICATIONS
`This application is a continuation-in-part of U.S. patent
`applications Ser. No. 08/842,559, filed Apr. 15, 1997 by
`Norman F. Krasner and Ser. No. 08/708,176 filed Sep. 6,
`1996 by Norman F. Krasner and Richard Girerd.
`BACKGROUND OF THE INVENTION
`The present invention relates to processing data in a
`Satellite positioning System, Such as a Global Positioning
`System (GPS), and more particularly relates to methods and
`apparatuses which distribute the information processing and
`15
`usage of GPS data.
`GPS receivers normally determine their position by com
`puting relative times of arrival of Signals transmitted Simul
`taneously from a multiplicity of GPS (or NAVSTAR) sat
`ellites. These Satellites transmit, as part of their message,
`both Satellite positioning data as well as data on clock
`timing, so-called “ephemeris' data. The term “ephemeris” or
`“Satellite ephemeris is used to mean a representation, Such
`as an equation, which specifies the positions of Satellites (or
`a satellite) over a period of time or time of day. The process
`of Searching for and acquiring GPS Signals, reading the
`ephemeris data for a multiplicity of Satellites and computing
`the location of the receiver from this data is time consuming,
`and results in Significant power drain, especially for hand
`held type units.
`There are two principal functions of GPS receiving sys
`tems: (1) computation of the pseudoranges to the various
`GPS satellites, and (2) computation of the position of the
`receiving platform using these pseudoranges and Satellite
`timing and ephemeris data. The pseudoranges are simply the
`time delays measured between the received signal from each
`Satellite and a local clock. The Satellite ephemeris and timing
`data is extracted from the GPS Signal once it is acquired and
`tracked. AS Stated above, collecting this information nor
`mally takes a relatively long time (18 Seconds to several
`minutes) and must be accomplished with a good received
`Signal level in order to achieve low error rates.
`Most GPS receivers utilize correlation methods to com
`pute pseudoranges. These correlation methods are per
`formed in real time, often with hardware correlators. GPS
`Signals contain high rate repetitive signals called pseudo
`random (PN) sequences. The codes available for civilian
`applications are called C/A codes, and have a binary phase
`reversal rate, or “chipping rate, of 1.023 MHz and a
`repetition period of 1023 chips for a code period of 1 mSec.
`The code Sequences belong to a family known as Gold
`codes. Each GPS Satellite broadcasts a signal with a unique
`Gold code. Alternative methods, as exemplified in U.S. Pat.
`No. 5,663,734, operate on Snapshots of data and utilize fast
`convolution methods to compute the pseudoranges.
`All of the above Systems may benefit by communicating
`with the resources of a remote site, or "server utilizing a
`wireleSS communications System, Such as a cellular tele
`phone System. Such a Server may provide assistance data to
`the mobile GPS receivers to enhance their performance, it
`may receive data from the GPS receivers and perform
`further processing on Such data to complete or refine a
`position calculation, or it may do both. In addition, the
`remote site may include various display and application
`resources, for example, dispatching means to Send emer
`gency or repair resources to the user of the GPS mobile, or
`to provide route guidance or other concierge Services.
`
`65
`
`45
`
`50
`
`55
`
`60
`
`US 6,185,427 B1
`
`25
`
`35
`
`40
`
`2
`Thus, the above server provides two functions: (1) Loca
`tion Server functions, which provide assistance to the
`mobile GPS receivers to enhance their performance, and (2)
`Application Server functions, which display the location of
`the mobile GPS receiver and provide auxiliary services,
`Such as roadside assistance.
`A paper was provided by Raab in 1977 on splitting the
`functionality of GPS processing between mobile GPS
`receivers and a remote basestation. See Raab, et al., “An
`Application of the Global Positioning System to Search and
`Rescue and Remote Tracking,” Navigation, Vol. 24, No. 3,
`Fall 1977, pp. 216-227. In one method of Raab’s paper the
`remote GPS receiver computes the times of arrival of the
`satellite signals at the remote GPS receiver (so-called
`“pseudoranges”) and transmits these times-of-arrival to a
`central Site via a data relay where the final position calcu
`lation of the mobile is computed. Raab also talks about
`providing assistance information including approximate
`time and position to the remote unit. Raab also discusses
`So-called “retransmission methods” in which the raw GPS
`Signal is relayed directly to the remote basestation.
`Other patents, such as U.S. Pat. Nos. 4,622,557, 5,119,
`102, 5,379,224, and 5,420,592 discuss variations of the
`retransmission method. U.S. Pat. No. 4,622,557 utilizes an
`analog retransmission method whereas U.S. Pat. Nos. 5,119,
`102, 5,379,224, and 5,420,592 utilize digital means to store
`and then forward a digitized record of the sampled GPS
`Signal. These patents describe communications between one
`or more mobile units and a single basestation which may
`incorporate functions of GPS calculation as well as ancillary
`functions described above.
`The U.S. Pat. No. 4,445,118 by Taylor discusses trans
`mission of aiding data, such as GPS satellites in view from
`a basestation to remote units via a communication link. In
`addition, in one variation, a tracking application for trucks,
`Taylor describes a System in which pseudorange data is sent
`from the trucks to the remote basestation which computes
`the final position. Variations on this pseudorange transfer
`method include U.S. Pat. Nos. 5,202,829 and 5,225,842.
`Again, this prior art envisioned a single basestation contain
`ing GPS aiding functions as well as display and other
`ancillary functions.
`FIG. 1 shows a block diagram of the prior art which
`utilizes a basestation to Supplement GPS Signal processing.
`Mobile units 12a, 12b, 12c, and 12d in this example contain
`a combination of a GPS receiver and a wireless modem.
`Attached to the GPS unit are GPS antennas 10a, 10b, 10c,
`and 10d for receiver GPS signals from GPS satellites (not
`shown for simplicity) and antennas 11a, 11b, 11c, and 11d
`for communication to and from a basestation 20 which
`includes a basestation antenna 17. In Some implementations,
`this communication may be in one direction only.
`BaseStation 9 contains a signal processing unit 15 which
`may provide aid to the mobile GPS units to help them obtain
`positioning information and/or it may complete or refine the
`position calculations of these units based upon data trans
`mitted to it from these units, together with auxiliary data
`which it may gather with its own GPS antenna 18. The signal
`processing unit 15 may contain its own GPS receiver and
`GPS antenna in order to determine its own position and
`provide differential corrections to the data transmitted to it
`from the mobile GPS units. Basestation 9 also includes a
`display 14 and computer equipment which is coupled to the
`Signal processing unit 15 by a connection 16 and which
`allows an operator to visually track the position of the
`mobiles and provide manual and Semiautomatic commands
`
`12
`
`

`

`US 6,185,427 B1
`
`3
`to these units via the aforementioned communications linkS.
`In Some cases, unit 14 together with Signal processing unit
`15 is termed a “workstation.”
`Although FIG. 1 shows a wireless link from each mobile
`GPS unit to the basestation, this link may actually be a
`wireleSS link to a modem, Such as one at a cell Site followed
`by a wired or other link to the basestation as shown in FIG.
`1. The important thing to note is that the configuration of
`FIG. 1 consists of a single basestation site and this bases
`tation includes both the functions of GPS assistance and
`applications Support (e.g. position monitoring, dispatching,
`etc.).
`There are many limitations in the implementation of FIG.
`1. For example, utilizing a single WorkStation in this “star'
`configuration means that there may be long path delays from
`each of the GPS mobile units to and from the basestation.
`
`SUMMARY OF THE INVENTION
`A System and method for processing in a distributed
`manner satellite position system (SPS) information. In one
`example of the invention, a first mobile SPS receiver
`receives SPS signals from a plurality of SPS satellites and
`transmits a position information to a wireleSS cell based
`Station which is coupled to a first communication network.
`The wireleSS cell based Station is coupled to a first digital
`processing System which receives the position information
`from the wireleSS cell based Station and calculates a location
`of the first mobile SPS receiver based upon the position
`information. The first digital processing transmits this
`location, usually without any presentation of this location on
`the first digital processing System, to a remotely located
`application digital processing system which presents the
`location to a user of the application digital processing
`System.
`In one particular example of the invention, a network of
`Servers is described for processing, or assisting in the
`processing, of GPS Signals received by a set of geographi
`cally dispersed users. The network has the property that it
`aids the processing of Such signals and is geographically
`Separated from display and dispatching centers. Advantages
`of this topology of this example include low latency in the
`GPS assistance operation, high redundancy and fault
`tolerance, and flexibility in communications protocols. One
`feature of the invention is the use of distributed message
`passing methods and protocols to allow the use of process
`ing Systems to communicate with one another reliably and
`Seamlessly. For example, one processing System will typi
`cally packetize data and Send data packets from itself to
`another processing System in the overall System.
`Other exemplary Systems and methods are described
`below as embodiments of the present invention.
`BRIEF DESCRIPTION OF THE DRAWINGS
`The present invention is illustrated by way of example
`and not limitation in the figures of the accompanying
`drawings in which like references indicate Similar elements.
`FIG. 1 shows a prior art GPS tracking system.
`FIG. 2A illustrates an example of a distributed processing
`System using GPS information according to the present
`invention.
`FIG. 2B shows another example of a distributed process
`ing System using GPS information according to the present
`invention.
`FIG. 3 illustrates an implementation of a location server
`System according to one embodiment of the invention.
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`FIG. 4 depicts an example of a combined GPS receiver
`and communication System according to one embodiment of
`the present invention.
`FIG. 5 illustrates an example of a GPS reference station
`according to one embodiment of the invention.
`FIG. 6 shows an example of a distributed system for
`processing GPS information in a "911" situation.
`FIG. 7 shows an example of a distributed system for
`processing GPS information for a location based Service.
`FIG. 8 is a flowchart which describes a method for using
`a distributed processing System to proceSS GPS information
`in a "911" situation.
`
`DETAILED DESCRIPTION
`The present invention relates to a distributed processing
`system for processing GPS information. The following
`description and drawings are illustrative of the invention and
`are not to be construed as limiting the invention. Numerous
`Specific details are described to provide a thorough under
`Standing of the present invention. However, in certain
`instances, well known or conventional details are not
`described in order to not unnecessarily obscure the present
`invention.
`FIG. 2A is a block diagram which shows an exemplary
`architecture for a distributed processing System of the inven
`tion. This architecture includes cells 20a, 20b, and 20c, each
`of which includes its respective wireleSS cell based Station
`(“cell basestation”). Thus, cell basestation 37a performs
`wireless communications to and from mobile GPS receivers
`1a, 1b, 1c, and 1d, each of which includes a wireless
`communication System, in the cell 20a. Similarly, cell bas
`estation 37b in cell 20b provides 2-way wireless communi
`cations with mobile GPS receivers 2a, 2b, 2c, and 2d, each
`of which includes a wireleSS communication System Such as
`a cell telephone. The cell 20c includes mobile GPS receivers
`3a, 3b, 3c, and 3d which are capable of performing 2-way
`wireless communications with the cell basestation 37c. It
`will be understood that in certain embodiments of the
`invention, some mobile GPS receivers may be capable of
`only 1-way communications (transmissions to the
`basestation) wherein the mobile GPS unit determines its
`position (by determining pseudoranges and reading trans
`missions of Satellite ephemeris data) and transmits the
`position to an application Server. Each cell basestation
`includes a respective connection (e.g. connections 21a, 21b,
`or 21c) from the basestation to a communication infrastruc
`ture 40.
`The network of FIG. 2A contains the following constitu
`ent elements:
`A. Mobile GPS units (e.g. unit 1a) communicating infor
`mation to and from cellular basestations using a cellular
`type communications System.
`B. Location servers (e.g. servers 32 or 33) that can
`communicate with the mobile GPS units via the public
`Switched communication network (PSTN) or other
`communications infrastructure (e.g. leased lines,
`Satellites, etc.) which in turn can communicate with the
`cellular basestations (e.g. station 37a).
`C. Separate application servers (e.g. Servers 22 or 23) that
`can display the results of location information Supplied
`by the location Servers and permit auxiliary Services,
`Such as dispatching, to be performed.
`D. A communication infrastructure 40 which may include
`a public Switched telephone network and/or a dedicated
`network, Such as a packet Switched data network.
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`E. Separate GPS reference receivers (e.g. GPS reference
`Stations 24a or 24b), which can measure ranging infor
`mation from the GPS satellites over a wide geographi
`cal area and receive and process their navigation mes
`Sage data.
`In general, all of these network elements can communi
`cate with one another as seen in FIG. 2A. However, in
`preferred embodiments, the GPS reference receivers com
`municate with the location Servers and the location Servers
`communicate mainly with the application Servers and with
`the mobile GPS receivers.
`Although each mobile is shown in FIG. 2A to be com
`municating with one cell basestation, it should be appreci
`ated that in many mobile telephone situations, for example,
`a mobile may in fact communicate with a multiplicity of cell
`basestations, although it is normally the case that only one
`Such baseStation at a given instance in time will process most
`of the information to and from the mobile. Simultaneous
`communications with multiple basestations allows for rapid
`handoff from one cell site to the next as the mobile moves
`from one location to the next. Hence, a given mobile in cell
`20a, for example, might be monitoring the emissions of the
`basestation within its cell as well as a basestation within a
`neighboring cell such as cell 20b. It would perform the bulk
`of its communications with cell 20a until a handover
`occurred, in which case it would perform the bulk of its
`communications with cell 20b.
`An aspect of the current invention is the Separation of the
`location servers, as exemplified by 32 and 33, from the
`application ServerS 22 and 23. It should be appreciated that
`the location Servers themselves may only consist of Software
`components that are resident on other processing Systems
`attached to the cellular network. Such processing Systems
`may perform other functions Such as voice and data mes
`Saging Services. The location Server Software then may
`utilize existing computational components associated with
`these Services and not utilize a processor Solely for its own
`use. In other configurations, the location Server may consist
`of an embedded circuit board in a multiprocessor computer.
`This configuration may ensure a desired throughput capa
`bility of the server. In preferred embodiments, the location
`Server is autonomous and has no display or operator inter
`action functions, other than those required for occasional
`fault testing.
`In FIG. 2A, location server 33 is physically located within
`the same cell site as the mobile units in cell 20b. Server 32,
`however, is not located within any of the cells shown, but
`can service the data from cells 20a and 20c. In fact, even
`server 33 could process data from cells 20a and 20c,
`although server 32 may be preferred for this task due to its
`proximity. Utilizing a network of servers as shown in FIG.
`2A provides reliability and redundancy which is important in
`emergency response applications. Furthermore, in emer
`gency response applications there may be a flood of calls for
`Service, which could overload a Star-based System Such as in
`FIG. 1. The network approach of FIG. 2A overcomes these
`bottlenecks.
`In many GPS configurations utilizing basestation assis
`tance it is necessary to coordinate time between the mobile
`units and the basestations. For example, coordination of time
`between the mobile and basestation to 10 millisecond accu
`racy can allow the basestation to perform final position
`calculations based upon pseudoranges Supplied to it with a
`Small error on the order of Several meters (see, for example,
`the cited paper by Raab, Section 7, page 226). Without such
`time coordination the basestation will estimate the position
`of the GPS satellites (e.g. from its own GPS receiver) at an
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`incorrect time relative to the time at which the mobile is
`making its measurements. Since the Satellites are moving
`rapidly, this erroneous position of the GPS satellites trans
`lates to an error in the position calculation of the mobile,
`when this calculation is done at the basestation. One Solution
`to this problem is to locate the location Server in proximity
`to the mobiles, e.g. at a Switching center (termed a Mobile
`Switching Center, MSC). Thus, the path delay from the
`mobile to the location Server may be short, as compared to
`a Single basestation which may be located thousands of
`miles away.
`Another example of the utility of the architecture of FIG.
`2A is in applications for emergency response, Such as
`wireleSS 911 capability. In Such applications the application
`servers of FIG. 2A are termed Public Safety Answering
`Points (PSAP's) and may be numerous in number when
`Servicing a metropolitan area. A location Server, Such as
`server 32, would in this case service a number of cell sites
`and route location data to such PSAP's. Additional Appli
`cation Servers may be utilized in Such a Situation to act as
`an intermediary between the location server and the PSAP's.
`For example, Such application Servers may perform the
`latitude/longitude to Street address transformation. Hence, in
`this application there may be two classes of application
`servers. The redundancy and distribution of the location and
`application Servers in this case provide much greater reli
`ability than would be possible with the star topology of the
`prior art of FIG. 1.
`FIG. 2B shows another example of a distributed GPS
`processing system 101 of the invention which is used with
`a cell based communication System which includes a plu
`rality of cell Sites, each of which is designed to Service a
`particular geographical region or location. Examples of Such
`cellular based or cell based communication Systems are well
`known in the art, Such as the cell based telephone Systems.
`The cell based communication system 101 includes three
`cells 102,103, and 104. It will be appreciated that a plurality
`of other cells with corresponding cell Sites and/or cellular
`service areas may also be included in the system 101 and
`coupled to one or more cell based Switching centers, Such as
`the mobile Switching center 105 and the mobile Switching
`center 106, each of which are coupled to a public Switched
`telephone network (PSTN) 112.
`Within each cell, Such as the cell 102, there is a wireless
`cell basestation Such as cell basestation 102a which is
`designed to communicate through a wireleSS communication
`medium with a communication receiver which may be
`combined with a mobile GPS receiver to provide a com
`bined system such as the receiver 102b shown in FIG. 2B.
`An example of Such a combined System having a GPS
`receiver and a communication System is shown in FIG. 4 and
`may include both a GPS antenna 77 and a communication
`system antenna 79.
`Each cell site is coupled to a mobile Switching center. In
`FIG. 2B, cell bases 102a and 103a are coupled to Switching
`center 105 through connections 102c and 103c respectively,
`and cell base 104a is coupled to a different mobile Switching
`center 106 through connection 104c. These connections are
`typically wire line connections between the respective cell
`base and the mobile Switching centers 105 and 106. Each
`cell base includes an antenna for communicating with com
`munication Systems Serviced by the cell site. In one
`example, the cell Site may be a cellular telephone cell Site
`which communicates with mobile cellular telephones in the
`area Serviced by the cell Site.
`In a typical embodiment of the present invention, the
`mobile GPS receiver, Such as receiver 102b, includes a cell
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`based communication System which is integrated with the
`GPS receiver Such that both the GPS receiver and the
`communication System are enclosed in the same housing.
`One example of this is a cellular telephone having an
`integrated GPS receiver which shares common circuitry
`with the cellular telephone transceiver. When this combined
`System is used for cellular telephone communications, trans
`missions occur between the receiver 102b and the cell base
`102a. Transmissions from the receiver 102b to the cell base
`102a are then propagated over the connection 102c to the
`mobile Switching center 105 and then to either another
`cellular telephone in a cell Serviced by the cellular Switching
`center 24 or through a connection (typically wired) to
`another telephone through the land-based telephone System/
`network 112. It will be appreciated that the term wired
`includes fiber optic