W0 96/156136
`
`PC!‘/US95Il4862
`
`30
`
`5.
`
`The system of claim 1, wherein the correction
`
`data comprises a position correction representing a
`comparison between a position fix based on the first
`
`position signals and the known position coordinates of
`
`5
`
`the reference positioning receiver.
`
`6.
`
`The system of Claim 1, wherein:
`
`the first position signals comprise time—of-arrival
`
`data received by the reference positioning receiver from
`
`10
`
`a plurality of satellites; and
`
`the correction data comprises pseudorange
`corrections for each satellite.
`
`15
`
`20
`
`25
`
`7.
`
`The system of Claim 1, further comprising:
`
`a memory coupled to the mobile unit,
`operable to store map data; and
`
`the memory
`
`the display
`a display coupled to the mobile unit,
`operable to display the location of the mobile unit and
`
`the map data.
`
`8.
`
`The system of Claim 1, further comprising a
`
`central controller coupled to the mobile unit,
`
`the
`
`central controller operable to receive the location of
`the mobile unit.
`
`The system of claim 1, wherein the mobile unit
`9.
`is mounted on a vehicle.
`
`10.
`
`The system of Claim 1, wherein the mobile unit
`
`30
`
`is housed in a portable, hand-held housing.
`
`Page 001353
`
`

`
`VN096fl&B6
`
`PCIflE9flLfl2
`
`31
`
`11.
`
`The system of Claim 1, wherein the mobile unit
`
`further comprises:
`a mobile communications device in communication with
`
`the cellular telephone network,
`
`the mobile communications
`
`device operable to receive correction data transmitted by
`
`the transmitter site;
`
`a mobile positioning receiver coupled to the mobile
`
`communications device,
`
`the mobile positioning receiver
`
`operable to receive second position signals from the
`
`positioning system; and
`
`a processor coupled to the mobile communications
`
`device and the mobile positioning receiver,
`
`the processor
`
`operable to determine the location of the mobile unit in
`
`response to the second position signals received from the
`
`mobile positioning receiver and the correction data
`received from the mobile communications device.
`
`10
`
`15
`
`Page 001354
`
`

`
`W0 96/151536
`
`PC!‘/lJS95ll4862
`
`32
`
`12.
`
`A locating system using a mobile communications
`
`network and a positioning system, comprising:
`
`a reference positioning receiver having known
`
`position coordinates and operable to receive first
`
`5
`
`position signals from the positioning system,
`
`the
`
`reference positioning receiver further operable to
`
`generate correction data in response to the first
`
`position signals and the known position coordinates;
`a first transmitter site of the mobile
`
`10
`
`communications network coupled to the reference
`
`positioning receiver;
`a second transmitter site of the mobile
`
`communications network coupled to the first transmitter
`
`15
`
`the second transmitter site operable to transmit
`site,
`correction data received from the first transmitter site;
`and
`
`a mobile unit in communication with the second
`
`transmitter site and the positioning system,
`
`the mobile
`
`unit operable to receive correction data transmitted by
`
`20
`
`the second transmitter site, the mobile unit further
`
`operable to receive second position signals from the
`
`positioning system and to determine the location of the
`
`mobile unit in response to the second position signals
`and the correction data.
`
`25
`
`13.
`
`The system of Claim 12, further comprising a
`
`communications link coupled to the first and second
`
`transmitter sites,
`
`the communications link operable to
`
`receive correction data from the first transmitter site
`
`30
`
`and to transmit the correction data to the second
`
`transmitter site.
`
`14.
`
`The system of Claim 12, wherein the second
`
`transmitter site transmits the correction data in a
`
`35
`
`control channel.
`
`Page 001355
`
`

`
`WO 96115636
`
`PCTIUS95ll-1862
`
`33
`
`15.
`
`The system of claim 12, wherein the reference
`
`positioning receiver is mounted on the first transmitter
`site.
`
`5
`
`16.
`
`The system of claim 12, wherein the known
`
`position coordinates of the reference positioning
`receiver are based on data received by the reference
`
`positioning receiver over a statistically significant
`
`period of time.
`
`10
`
`17.
`
`The system of Claim 12, wherein the correction
`
`data comprises a position correction representing a
`
`comparison between a position fix based on the first
`
`position signals and the known position coordinates of
`
`15
`
`the reference positioning receiver.
`
`18.
`
`The system of Claim 12, wherein:
`
`the first position signals comprise time-of-arrival
`
`data received by the reference positioning receiver from
`
`20
`
`a plurality of GPS satellites; and
`the correction data comprises pseudorange
`
`corrections for each GPS satellite.
`
`19.
`
`The system of Claim 12, further comprising:
`
`25
`
`a memory coupled to the mobile unit,
`
`the memory
`
`operable to store map data; and
`the display
`a display coupled to the mobile unit,
`operable to display the location of the mobile unit and
`the map data.
`
`30
`
`35
`
`The system of Claim 12, further comprising a
`20.
`central controller coupled to the mobile unit,
`the
`
`central controller operable to receive the location of
`
`the mobile unit.
`
`Page 001356
`
`

`
`WO 96115636
`
`PCI'IUS95Il4862
`
`34
`
`The system of Claim 12, wherein the mobile unit
`21.
`is mounted on a vehicle.
`
`22.
`
`The system of Claim 12, wherein the mobile
`
`5
`
`unit is housed in a portable, hand-held housing.
`
`23.
`
`The system of Claim 12, wherein the mobile unit
`
`further comprises:
`a mobile communications device in communication with
`
`10
`
`the cellular telephone network,
`
`the mobile communications
`
`device operable to receive correction data transmitted by
`
`the second transmitter site;
`
`a mobile positioning receiver coupled to the mobile
`
`communications device,
`
`the mobile positioning receiver
`
`15
`
`operable to receive second position signals from the
`
`positioning system; and
`
`a processor coupled to the mobile communications
`
`device and the mobile positioning receiver,
`
`the processor
`
`operable to determine the location of the mobile unit in
`
`20
`
`response to the second position signals received from the
`
`mobile positioning receiver and the correction data
`received from the mobile communications device.
`
`Page 001357
`
`

`
`WO 96115636
`
`PCIVUS95/14862
`
`35
`
`An apparatus for locating a vehicle within the
`24.
`service area of a cellular telephone network and a
`
`positioning system, comprising:
`
`a positioning receiver on the vehicle and operable
`
`to receive first position signals from the positioning
`
`system;
`
`a mobile communications device on the vehicle and
`
`coupled to a transmitter site of the cellular telephone
`
`network,
`
`the mobile communications device operable to
`
`receive correction data transmitted by the transmitter
`
`site; and
`
`a processor on the vehicle and coupled to the
`
`positioning receiver and the mobile communications
`
`the controller operable to determine the location
`device,
`of the vehicle in response to the first position signals
`and the correction data.
`
`25.
`
`The apparatus of Claim 24, wherein the mobile
`
`communications device receives the correction data in a
`
`control channel transmitted by the transmitter site of
`
`the cellular telephone network.
`
`26.
`
`The apparatus of Claim 24, further comprising:
`
`a memory coupled to the processor.
`
`the memory
`
`operable to store map data; and
`
`a display coupled to the processor,
`
`the display
`
`operable to display the location of the vehicle and the
`map data.
`
`27.
`
`The apparatus of Claim 24, further comprising a
`
`central controller coupled to the mobile communications
`
`the central controller operable to receive the
`device,
`location of the vehicle.
`
`28.
`
`The apparatus of Claim 24, wherein the
`
`correction data comprises a position correction.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Page 001358
`
`

`
`W0 96/156216
`
`PCI‘/US95/14862
`
`36
`
`29.
`
`The apparatus of Claim 24, wherein the
`
`correction data comprises pseudorange corrections from a
`
`plurality of satellites in the positioning system.
`
`Page 001359
`
`

`
`
`
`W0 96/156136
`
`PCUUfi$flMM2
`
`37
`
`A method for locating a mobile unit within the
`30.
`service area of a cellular telephone network and a
`positioning system, comprising:
`receiving first position signals from the
`positioning system at a reference positioning receiver
`having known position coordinates;
`generating correction data in response to the first
`position signals and the known position coordinates;
`receiving correction data at a cellular transceiver
`
`in the mobile unit;
`receiving second position signals from a positioning
`system at a mobile positioning receiver in the mobile
`unit; and
`determining the location of the mobile unit in
`response to the second position signals and the
`correction data.
`
`The method of Claim 30, wherein the correction
`31.
`data is received at the cellular transceiver in a control
`channel.
`
`The method of Claim 30, wherein the correction
`32.
`data comprises a position correction representing a
`comparison between a position fix based on the first
`position signals and the known position coordinates of
`the reference positioning receiver.
`
`The method of Claim 30, wherein:
`33.
`the positioning system comprises a plurality of
`satellites; and
`the correction data comprises pseudorange
`corrections for each satellite.
`
`34.
`
`The method of Claim 30, further comprising the
`ation of the mobile unit on a
`
`step of displaying the loc
`map.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Page 001360
`
`

`
`W0 96/15636
`
`PCT/US95ll4862
`
`38
`
`The method of Claim 30, further comprising the
`35.
`step of receiving the location of the mobile unit at a
`remote location.
`
`5
`
`The method of Claim 30, wherein the positioning
`36.
`system is GPS.
`
`Page 001361
`
`

`
`‘WO9flflflK
`
`PCWU$%flflM2
`
`39
`
`5
`
`10
`
`A system for locating a mobile unit within the
`37.
`service area of a mobile communications network,
`
`comprising:
`a plurality of transmitter sites within the mobile
`communications network, each transmitter site operable to
`
`transmit time-of-arrival data, each transmitter site
`
`having known position coordinates;
`a mobile communications device on the mobile unit
`
`the mobile
`and coupled to the transmitter sites,
`communications device operable to receive time—of-arrival
`
`data transmitted by at least three transmitter sites;
`
`a memory on the mobile unit and operable to store
`
`known position coordinates of the transmitter sites; and
`
`a processor on the mobile unit and coupled to the
`
`15
`
`mobile communications device and the memory,
`
`the
`
`processor operable to receive time-of-arrival data from
`the mobile communications device,
`the processor further
`
`operable to determine the position of the mobile unit in
`response to the time-of-arrival data received from the
`transmitter sites and the known position coordinates of
`
`the transmitter sites stored in the memory.
`
`38.
`
`The system of Claim 37, wherein the transmitter
`
`sites are associated with a cellular telephone system.
`
`39.
`
`The system of Claim 37, wherein the transmitter
`
`sites simultaneously transmit time—of-arrival data.
`
`The system of Claim 37, wherein the controller
`40.
`is operable to determine the position of the mobile unit
`using triangulation techniques.
`
`20
`
`25
`
`30
`
`The system of Claim 37, wherein the transmitter
`41.
`sites furnish time—of-arrival data in response to a
`
`35
`
`request by the mobile unit.
`
`Page 001362
`
`

`
`W0 96/15636
`
`PCTIUS9511-1862
`
`40
`
`42.
`
`The system of claim 37, wherein time-of-arrival
`
`data contains information relating to the time of
`transmission of the time-of-arrival data from the
`
`transmitter sites.
`
`43.
`
`The system of claim 37, further comprising a
`
`clock coupled to the transmitter sites,
`
`the clock
`
`operable to synchronize the transmission of time-of-
`arrival data from the transmitter sites.
`
`10
`
`Page 001363
`
`

`
`WO 96115636
`
`PCI'IUS95Il4862
`
`41
`
`44.
`
`A system for locating a mobile unit within the
`
`service area of a mobile communications network,
`
`comprising:
`
`a plurality of transmitter sites within the mobile
`
`communications network, each transmitter site operable to
`
`transmit time-of-arrival data and known position
`
`coordinates associated with each transmitter site;
`
`a mobile communications device on the mobile unit
`
`and coupled to the transmitter sites,
`
`the mobile
`
`communications device operable to receive time-of-arrival
`
`data and known position coordinates transmitted by at
`
`least three transmitter sites; and
`
`a processor on the mobile unit and coupled to the
`
`mobile communications device,
`
`the processor operable to
`
`receive time-of—arrival data and known position
`
`coordinates from the mobile communications device,
`
`the
`
`processor further operable to determine the position of
`the mobile unit in response to the time-of—arrival data
`
`and the known position coordinates.
`
`The system of Claim 44, wherein the transmitter
`45.
`sites are associated with a cellular telephone system.
`
`46.
`
`The system of Claim 44, wherein the transmitter
`
`sites simultaneously transmit time-of—arrival data and
`
`known position coordinates.
`
`47.
`
`The system of Claim 44, wherein the controller
`
`is operable to determine the position of the mobile unit
`
`using triangulation techniques.
`
`48.
`
`The system of Claim 44, wherein the transmitter
`
`sites furnish time-of—arrival data and known position
`
`coordinates in response to a request by the mobile unit.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Page 001364
`
`

`
`W0 96/156156
`
`PCl'IUS95Il-3862
`
`4 2
`
`49.
`
`The system of Claim 44, wherein time-of-arrival
`
`data contains information relating to the time of
`
`transmission of the time-of—arriva1 data from the
`
`transmitter sites.
`
`5
`
`50.
`
`The system of Claim 44, further comprising a
`
`clock coupled to the transmitter sites,
`
`the clock
`
`operable to synchronize the transmission of time-of-
`arrival data and known position coordinates from the
`
`10
`
`transmitter sites.
`
`Page 001365
`
`

`
`W0 96/156256
`
`PCl"IlJS95Il4862
`
`Page 001366
`
`

`
`
`
`W0 96,1536
`
`PCITUS95/14862
`
`I I I I I I I I I I I I I I I I I I I I I
`
`J
`
`4s 0'Z"""I
`
`l.____.__—_____
`
`
`
`
`
`
`
`
`———-—-—————----———*—'—1 E’!
`
`
`
`Page 001367
`
`

`
`W0 96Il5636
`
`PCT/US95!14862
`
`5.052
`
`‘'''''--_-"'''|
`
`m
`
`,zwI3N.‘8
`
`r"|lI'.I|':'I"I"
`
`582$.n
`
`&>Emzs:
`
`w6?‘
`
`Page 001368
`
`
`

`
`INTERNATIONAL SEARCH REPORT
`
`International application No.
`PCT/US9S/14862
`
`
`
`
`
` A.
`CLASSIFICATION OF SUBJECT MATTER
`IPC(6)
`:H04Q 7/00
`US CL :455/33.1
`According to Interrtational Patent Classification (IPC) or to both national classification and IPC
`B.
`FIELDS SEARCHED
`
`
`
`
`Minimum documentation searched (classification system followed by classification symbols)
`
`U.S.
`2
`455I33.l,89.54.I,56.l.33.4,53.l; 342/357, 379/61
`
`
`
` Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched
`
`
`
`
`
`Electronic data base consulted during the international search (name of data base and, where practicable, search terms used)
`APS
`search terms: gps,global positioning system,ceI|ular
`
`C.
`
`
`
`DOCUMENTS CONSIDERED TO BE RELEVANT
`Citation of document, with indication, where appropriate. of the relevant passages
`US, A, 5,389,934 lKASS) 14 February 1995, figs 1,2,col 1,
`line 20 - col 2, line 54)
`
`
`
`
`
`US. A. 5,225,842 (BROWN ET AL) 06 July 1993, fig 1, col
`4, line 48 - col 6, line 43
`
`
`
`
`
`Relevant to claim No.
`1-50
`
`1-50
`
`
`
`24-29
`
`
`US, A, 5,119,102 (BARNARD) 02 June 1992, figs 1,3, col
`1, line 57 — col 2, line 52.
`
`
`
` 4,6,16-18,
`3
`9
`, 4 1
`-
`43,46,48-50
`
`US, A, 5,323,322 (MUELLER ET AL) 21 June 1994, fig 1,
`col 12, line 21-68.
`
`1-50
`
`
`
`Sec patent family annex.
`later document puhlillted after the international filing date or priority
`date and not in conflict with the Ipplitalion but cited to undenund the
`principle or theory underlying the invention
`nnnot
`'
`d
`f parucu‘
`; the hinted ‘
`c:::::_:d°n°vcl or ::m';h|::'c:;u":i ‘O hvorliugmuveuz;
`what the document it taken alone
`
`E]
`
`‘X’
`
`‘Y’
`
`'A'
`‘E’
`‘L’
`
`
`
`
`
`‘T’
` Special categonu of cited documentt:
`
`_
`‘
`,
`docuntentdefututg the general state of the on which is not conltderd
`to be part of particular relevance
`
`,
`,
`,
`.
`.
`earlier document published on or after the tnternnuonal filing date
`douiment which may throw doubu on priority cIaim(a)> or which is
`
`
`cited to utabliah the publication date of another cttauon or other
`document of particular relevance: the claimed invention mnnot be
`-
`-
`
`conaflered to involve an inventive step when the document
`in
`Ipocm re‘-on (I. weclfied)
`
`eotnhinni with one or more otheraudtdocttmenta. Iuclt combination
`document referring to an oral disclosure. uae. exhibition or other
`'0'
`
`
`being ohviouatoapetionkilledintheart
`mum
`
`
`
`documenl mum," of um mm "W “any
`-33
`document published prior to the international Filing date but Later than
`the priority date claimed
`
`
`Date of mailing of the international search report
`
`Date of the actual completion of the international search
`
`1 3 FEB 1996'
`07 JANUARY 1996
`
`uthorizcd officer
`Name and mailing address of the ISA/US
`ti/ISHILIP 1. SOBUTKA
`Commissioner of Patents and Trademarks
`Box PCT
`
`
`Washington. D.C. 20231
`T lehone N04
`
`
`
`Facsimile No.
`(703 305-3230
`Fortn PCT/ISA/210 (second shect)(luly l992)i
`
`
`
`“LQQ
`
`Page 001369
`
`(703) 305-4825
`
`
`
`
`‘P’
`
`
`
`
`
`US, A, 5,155,490 (SPRADLEY, JR. ET AL) 13 October
`1992,
`figs 1,2, col 1, line 44 - col 4, line 19.
`
`
`
`

`
`
`
`woaw INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(51) International Patent Classification 6 :
` (11) International Publication Number:
`W0 97/33382
`
`
`(43) International Publication Date:
`12 September l997 (l2.09.97)
`
`I-104B 7/185, G01S 5/02
`
`
`
`
`
`
`
`(21) International Application Number:
`PCT/US97/03512
` (81) Designated States: AL, AM, AT, AT (Utility model), AU, AZ,
`
`BA, BB, BG, BR, BY. CA, CH, CN, CU, CZ, CZ (Utility
`
`7 March 1997 (07.03.97)
`(22) International Filing Date:
`model), DE, DE (Utility model), DK, DK (Utility model),
`EE, EE (Utility model), ES, F1, F1 (Utility model). GB, GE,
`GH, HU, IL, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR.
`LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ,
`PL, PT, RO, RU, SD, SE, SG, SI, SK, SK (Utility model),
`TJ, TM, TR, ’I'l", UA, UG, US, UZ, VN, YU, ARIPO patent
`(GH, KE, LS, MW, SD, SZ, UG), Eurasian patent (AM, AZ,
`BY, KG, KZ, MD, RU, TJ, TM), European patent (AT, BE,
`CH, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL,
`PT, SE), OAPI patent (BF, BJ, CF, CG. CI, CM, GA, GN,
`
`ML, MR, NE, SN, TD, TG).
`
`
`
`(30) Priority Data:
`08/612,582
`08/759,523
`
`8 March 1996 (08.03.96)
`4 December 1996 (04.12.96)
`
`US
`US
`
`(71) Applicant (for all designated States except US): SNAPTRACK,
`INC. [US/US]; Suite 250, 4040 Moorpark Avenue, San Jose,
`CA 95117 (US).
`
`
`
`
`
`
`
`
`
`
`
`
`
`(72) Inventor; and
`(75) [nventorlApplicant (for US only): KRASNER, Nonnan, F.
`[US/US]; 117 Coventry Court, San Carlos, CA 94070 (US).
`
`('74) Agents: SCHELLER, James, C., Jr. et al.; Blakely, Sokoloff,
`Taylor & Zafman L.L.P,, 7th floor, l2400 Wilshire Boule-
`vard, Los Angeles, CA 90025 (US).
`
`Published
`
`With international search report.
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
` (54) Title: AN IIVIPROVED GPS RECEIVER UTILIZING A COMMUNICATION LINK
`
` (57) Abstract
`
` A precision carrier frequency signal for calibrating a local oscillator (56) of a GPS receiver which is used to acquire GPS signals.
`
`
`
`
`‘The precision carrier frequency signal is used to calibrate the local oscillator such that the output of the local oscillator, which is used to
`acquire GPS signals, is modified by a reference signal generated from the precision carrier frequency signal. The GPS receiver locks (53)
`to this precision carrier frequency signal and generates the reference signal.
`In another aspect of the invention, satellite almanac data is
`transmitted to a remote GPS receiver unit (20) from a base station (12) via a communication link. The remote GPS receiver unit uses this
`satellite almanac data to detem-tine approximate Doppler data for satellites in view of the remote GPS receiver unit.
`
`
`
`Page 001370
`
`

`
`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCI‘ on the front pages of pamphlets publishing inremational
`applications under the PCT.
`AM
`Armenia
`Austria
`AT
`Australia
`AU
`BB
`Barbados
`BE
`Belgium
`Burkina Fasu
`BF
`BG
`Bulgaria
`Benin
`BJ
`BR
`Brazil
`BY
`Belarus
`CA
`Canada
`CF
`Central African Republic
`CG
`Congo
`Switzerland
`CH
`CI
`Cote d'Ivoire
`Camervon
`CM
`China
`CN
`Czechoslovakia
`CS
`CZ
`Czech Republic
`DE
`Germany
`DK
`Denmark
`EE
`Estonia
`ES
`Spain
`FI
`Finland
`France
`FR
`Gabon
`GA
`
`United Kingdom
`Georgia
`Guinea
`Greece
`Hungary
`Ireland
`Iraly
`Japan
`Kenya
`Kyrgyatan
`Democratic People’ 5 Republic
`of Korea
`Republic of Korea
`Kazakhstan
`Liechtenstein
`Sri Lanka
`Liberia
`Lirlruania
`Luxemborrx
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`Mali
`Mongolia
`Mauritania
`
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`R0
`RU
`SD
`SE
`SG
`SI
`SK
`SN
`SZ
`TD
`TG
`T1
`1'!‘
`UA
`UG
`US
`UZ
`VN
`
`Malawi
`Mexico
`Niger
`Nerlnrlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Trinidad and Tobago
`Ukraine
`Uganda
`United Sales of America
`Uzbekistan
`Vie: Nam
`
`Page 001371
`
`

`
`WO 97/33382
`
`PCT/US97/03512
`
`AN IMPROVED GPS RECEIVER UTILIZING A COMMUNICATION
`LINK
`
`BAQKGRQUND OF THE INVENTION
`
`RELATED APPLICATIONS
`
`This application is a continuation-in—part of U.S. Patent Application Serial
`No. 08/612,582, filed on March 8, 1996 by Norman F. Krasner.
`This application is also related to and hereby claims the benefit of the filing
`date of a provisional patent application by the same inventor, Norman F. Krasner,
`which application is entitled Low Power, Sensitive Pseudorange Measurement
`Apparatus and Method for Global Positioning Satellites Systems, Serial No.
`60/005,318, filed October 9, 1995.
`
`l .
`
`FIELD OF THE INVENTIQN
`
`The present invention relates to receivers capable of determining
`position information of satellites and, in particular, relates to such receivers
`which find application in global positioning satellite (GPS) systems.
`
`2.
`
`BAQKQRQUND ART
`
`GPS receivers normally determine their position by computing
`relative times of arrival of signals transmitted simultaneously from a
`multiplicity of GPS (or NAVSTAR) satellites. These satellites transmit, as
`part of their message, both satellite positioning data as well as data on clock
`timing, so-called "ephemeris" data. 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, often requiring several minutes. In many cases, this lengthy
`processing time is unacceptable and. furthemiore, greatly limits battery life
`in micro—miniaturized portable applications.
`
`Another limitation of current GPS receivers is that their operation is
`limited to situations in which multiple satellites are clearly in view, without
`obstructions, and where a good quality antenna is properly positioned to
`receive such signals. As such, they normally are unusable in portable, body
`
`Page 001372
`
`

`
`wo 97/33382
`
`PCT/US97/03512
`
`mounted applications; in areas where there is significant foliage or building
`
`blockage; and in in-building applications.
`
`There are two principal functions of GPS receiving systems: (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 normally takes a relatively long time (30
`seconds to several minutes) and must be accomplished with a good received
`
`signal level in order to achieve low error rates.
`
`Virtually all known GPS receivers utilize correlation methods to
`compute pseudoranges. These correlation methods are perfomted in real
`time, often with hardware correlators. GPS signals contain high rate
`
`repetitive signals called pseudorandom (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.
`
`For a signal received from a given GPS satellite. following a
`
`downconversion process to baseband, 21 correlation receiver multiplies the
`received signal by a stored replica of the appropriate Gold code contained
`within its local memory, and then integrates, or lowpass filters, the product
`
`in order to obtain an indication of the presence of the signal. This process is
`
`termed a "correlation" operation. By sequentially adjusting the relative
`timing of this stored replica relative to the received signal, and observing the
`correlation output, the receiver can determine the time delay between the
`
`received signal and a local clock. The initial determination of the presence
`of such an output is termed "acquisition." Once acquisition occurs, the
`process enters the "tracking" phase in which the timing of the local reference
`is adjusted in small amounts in order to maintain a high correlation output.
`The correlation output during the tracking phase may be viewed as the GPS
`
`Page 001373
`
`

`
`WO 97/33382
`
`PCT/US97/03512
`
`signal with the pseudorandom code removed, or, in common terminology,
`"despread." This signal is narrow band. with bandwidth commensurate
`
`with a 50 bit per second binary phase shift keyed data signal which is
`superimposed on the GPS waveform.
`
`The correlation acquisition process is very time consuming,
`especially if received signals are weak. To improve acquisition time, many
`GPS receivers utilize a multiplicity of correlators (up to 12 typically) which
`allows a parallel search for correlation peaks.
`
`Another approach to improve acquisition time is described in U.S.
`Patent No. 4,445,118. This approach uses the transmission of Doppler
`information from a control basestation to a remote GPS receiver unit in
`
`order to aid in GPS signal acquisition. While this approach does improve
`acquisition time, the Doppler information is accurate for only a short
`period of time as the GPS satellites orbit the earth at relatively high speeds.
`Thus, a further transmission of Doppler information will be necessary in
`order for a remote unit to use accurate Doppler information.
`
`An approach for improving the accuracy of the position
`determination by a remote GPS receiver unit is also described in U.S.
`Patent No. 4,445,118, referred to as the Taylor patent.
`In the Taylor
`patent, a stable frequency reference is transmitted to a remote GPS receiver
`unit from a basestation in order to eliminate a source of error due to a poor
`quality local oscillator at the remote GPS receiver unit. This method uses a
`
`special frequency shift keyed (FSK) signal that must be situated in
`frequency very close to the GPS signal frequency. As shown in Figure 4
`of the Taylor patent, the special FSK signal is about 20 MHz below the
`1575 MHz GPS signal. Moreover, the approach described in the Taylor
`patent uses a common mode rejection mechanism in which any error in the
`local oscillator (shown as L.O. 52) of the receiver will appear in both the
`GPS channel and the reference channel and hence be canceled out. There
`is no attempt to detect or measure this error. This approach is sometimes
`referred to as a homodyne operation. While this approach provides some
`advantages, it requires that the two channels be closely matched, including
`closely matched in frequency. Moreover, this approach requires that both
`
`Page 001374
`
`

`
`wo 97/33382
`
`PCT/US97l03512
`
`frequencies remain fixed, so frequency hopping techniques are not
`
`compatible with this approach.
`
`SQMMARY
`
`In one aspect of the present invention, a mobile GPS receiver
`
`receives a precision carrier frequency signal from a source providing the
`
`precision carrier frequency signal. The receiver locks to this frequency
`
`signal and provides a reference signal which is used to calibrate (e.g.,
`stabilize or correct) a local oscillator that is used to acquire GPS signals.
`
`An apparatus which practices this aspect includes. in one embodiment, a
`first antenna which receives GPS signals and a downconverter coupled to
`
`the first antenna. The downconverter is coupled to a local oscillator which
`
`provides a first reference signal to the downconverter. The apparatus also
`includes a second antenna for receiving a precision carrier frequency signal
`
`from a source providing the precision carrier frequency signal and an
`automatic frequency control (AFC) circuit coupled to the second antenna.
`The AFC circuit provides a second reference signal to the local oscillator to
`calibrate the first reference signal which is used to acquire GPS signals
`
`received through the first antenna. The frequency of the precision carrier
`
`frequency signal may vary from transmission to transmission.
`One embodiment of the present invention provides a method for
`
`determining the position of a remote GPS receiver by transmitting GPS satellite
`information, including satellite almanac data, to the remote unit or mobile GPS
`unit from a basestation via a data communication link. The satellite almanac data is
`
`then used to determine Doppler data for satellites in view of the remote unit. The
`remote unit uses this Doppler data and received GPS signals from in view
`satellites to subsequently compute pseudoranges to the satellites. The computed
`pseudoranges are then transmitted to the basestation where the position of the
`remote unit is calculated. Various embodiments of apparatuses which can perform
`this method are also described.
`
`BRIEF DESQRIEI IQN OF THE DRAWINGS
`The present invention is illustrated by way of example and not limitation in
`the figures of the accompanying drawings in which references indicate similar
`elements and in which:
`
`Page 001375
`
`

`
`WO 97/33382
`
`PCT/US97/03512
`
`Figure 1A is a block diagram of the major components of a remote
`
`or mobile GPS receiving system utilizing the methods of the present
`
`invention. and shows data links that may exist between a basestation and the
`remote.
`
`Figure 1B is a block diagram of an alternative GPS mobile unit.
`
`Figure 1C is a block diagram of another alternative GPS mobile unit.
`
`Figures 2A and 2B provide two alternatives for the RF and IF
`
`portions of a receiver which is an embodiment of the present invention.
`
`Figure 3 shows a flow chart of the major operations (e. g. software
`
`operations) performed by the programmable DSP processor in accordance
`
`with the methods of the present invention.
`
`Figures 4A-4E illustrates the signal processing waveforms at various
`
`stages of processing according to the methods of the present invention.
`
`Figure 5A illustrates a basestation system in one embodiment of the
`present invention.
`
`Figure 5B illustrates a basestation system in an alternative
`
`embodiment of the present invention.
`
`Figure 6A illustrates a GPS mobile unit having, according to one
`aspect of the present invention. local oscillator calibration.
`
`Figures 6B and 6C show other embodiments of GPS mobile units
`
`having local oscillator calibration.
`
`Figure 7 is a flow chan which shows a power management method
`
`for a mobile unit according to one embodiment of the present invention.
`
`Figure 8 shows a method for deriving Doppler information for
`
`satellites in view from satellite almanac data provided to a mobile unit.
`
`DETAILED DESCRIPTION OF Tl-IE INVENTIQN
`
`This invention concerns apparatuses and methods for computing the
`position of a mobile, or remote, object in a manner that results in the remote
`
`hardware having very low power dissipation and the ability to operate with
`very low received signal levels and yet provide accurate measurements of
`
`position information. That is, power consumption is reduced while receiver
`
`sensitivity and accuracy is increased. This is also made possible by the
`
`receipt and use at the remote unit of a stable frequency communication
`signal. This is made possible by the implementation of the remote receiving
`
`Page 001376
`
`

`
`W0 97/33382
`
`PCT/US97/03512
`
`functions, as shown in Figure 1A, as well as the transmission of satellite
`
`almanac information from a separately located basestation 10 to the remote
`or GPS mobile unit 20.
`
`It should be noted that pseudoranges may be used to compute the
`
`remote's geographical position in many different ways. Three examples
`are:
`
`1 .
`
`Method 1: By re-transmitting the satellite data messages to the
`
`remote 20 from the basestation 10, the remote 20 may combine this
`
`infonnation with the pseudorange measurements to compute its
`
`position. See, for example, U.S. patent No. 5,365,450. which