(12) United States Patent
`Camp
`
`I 1111111111111111 11111 111111111111111 1111111111 lllll 111111111111111 11111111
`US006252543Bl
`US 6,252,543 Bl
`Jun.26,2001
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) LOCATION SYSTEM COMBINING
`RANGING MEASUREMENTS FROM GPS
`AND CELLULAR NETWORKS
`
`(75)
`
`Inventor: William 0. Camp, Chapel Hill, NC
`(US)
`
`(73)
`
`Assignee: Ericsson Inc., Research Triangle Park,
`NC (US)
`
`( *)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by O days.
`
`(21) Appl. No.: 09/315,002
`
`(22) Filed:
`
`May 19, 1999
`
`Related U.S. Application Data
`(60) Provisional application No. 60/087,207, filed on May 28,
`1998.
`Int. Cl.7 ............................... G0lS 5/02; H04B 7/185
`(51)
`(52) U.S. Cl. ................................ 342/357.06; 342/357.01;
`342/450; 342/463; 701/213; 455/422; 455/426;
`455/427; 455/456; 455/457; 327/291
`(58) Field of Search .......................... 342/357.01-357.17,
`342/450-465; 455/403, 422, 426, 427, 432,
`433, 456, 457; 380/247-250, 255, 270-273,
`31-34, 274; 701/200, 207, 213-216; 331/46-56;
`327 /291, 293, 298; 377 /106
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,982,324 * 11/1999 Watters et al. .................. 342/357.06
`6,081,229 * 6/2000 Soliman et al. ................ 342/357.05
`
`* cited by examiner
`
`Primary Examiner-Bernarr E. Gregory
`(74) Attorney, Agent, or Firm-Jenkens & Gilchrist, P.C.
`
`(57)
`
`ABSTRACT
`
`Methods and arrangements are provided for locating a
`mobile terminal within a mobile telecommunications sys(cid:173)
`tem. In certain embodiments, GPS ranging signals and
`cellular base station transmitted downlink signals are
`received by a mobile terminal, which is configured to
`determine its current location using a combination of these
`two types of ranging signals. In certain other embodiments,
`GPS ranging signals are received by the mobile terminal,
`which is also configured to transmit uplink signals to cellular
`base stations. The current location of the mobile station is
`determined by fusing measured data from each of these
`different ranging signal transmissions. By combining the
`available resources of satellite and terrestrial locating
`processes, the potential for locating a mobile terminal is
`significantly increased.
`
`26 Claims, 6 Drawing Sheets
`
`Satellite 2
`
`14
`
`X1. Y1. Z1. C1
`Satellite 1
`
`14
`
`38
`
`Terminal
`
`Satellite 3
`
`14
`
`20
`
`Basestation 4
`
`Basestation 4
`
`Xs. Ys. Zs
`
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`U.S. Patent
`
`Jun.26,2001
`
`Sheet 1 of 6
`
`US 6,252,543 Bl
`
`X2, Y 2, Z2. C2
`Satellite 2
`
`14
`
`X1. Y1, Z1, C1
`
`Satellite 1
`
`14
`
`Satellite 3
`
`14
`
`14
`
`Satellite 4
`
`• • •
`FIG. 1
`
`34
`
`LSC
`
`HLR ,~__, MSC/VLR
`
`26
`
`22
`
`GMSC
`
`BSC . . . . . - - - - - - - -~
`
`Basestation 2
`
`20
`
`Basestatian 3
`
`20
`
`X1,Y1,Z1
`
`20
`
`T1
`
`Terminal
`
`FIG. 2
`
`16
`
`20
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`U.S. Patent
`
`Jun.26,2001
`
`Sheet 2 of 6
`
`US 6,252,543 Bl
`
`Satellite 2
`
`14
`
`Satellite 3
`
`X1.Y1,Z1,C1
`Satellite 1
`
`14
`
`38
`
`20
`
`Basestation 4
`
`Basestation 4
`
`Xs. Ys, Zs
`
`Link
`
`Clock
`
`40
`
`GPS Correlator
`
`FIG. 3
`, - - - - - - - - - - - - - ,
`I To Communication
`I
`47
`I
`I CONTROLLER
`I
`I
`I
`I
`I
`To Communication I
`I
`I
`Link
`L _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~
`~
`42
`FIG. 4
`
`38/20
`
`- /
`
`GPS CLOCK
`
`48
`
`50
`
`54
`
`Comparator
`
`56
`Message
`Generator
`
`T3
`
`52
`Frame Synch
`Generator
`
`44
`
`I
`I
`I
`I
`I
`I
`I
`I
`
`Ex.1011
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`U.S. Patent
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`Jun.26,2001
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`Sheet 3 of 6
`
`US 6,252,543 Bl
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`Basestation 2
`
`20
`
`Basestation 3
`
`X1. Y1, Z1, C1
`
`Basestation 1
`
`20
`
`T,
`
`60
`
`Terminal
`
`20
`
`Basestation 4
`
`• • •
`FIG. 5
`BASESTATI0N TIMING
`
`BS 3 -
`C3 ---(cid:173)
`BS 2 I - - - - - c2 __ _
`
`I
`
`I
`
`synch word
`
`,___ C1 _ _ _
`
`BS 1
`
`I
`
`I
`
`I
`
`I
`
`Reference time 0
`
`FIG. 6
`
`TERMINAL MEASUREMENTS
`
`UTC Time
`
`From BS 3
`
`1 - - - - - - T3 ------.-----,
`I
`'~ - - -
`
`From BS 2 -
`
`T2
`
`I
`
`I
`
`From BS 1
`
`,____ T1 --_,__-~
`I
`I
`
`1----------------------1•-Terminol Time
`Reference time 0
`
`FIG. 7
`
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`U.S. Patent
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`Jun.26,2001
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`Sheet 4 of 6
`
`US 6,252,543 Bl
`
`X2. Y 2. Z2. C2
`Satellite 2
`
`14
`
`Xi. Y,. Z,. C,
`Satellite 1
`
`;62
`
`14
`
`T1
`64
`
`Basestation 3
`
`20
`
`Xu. Yu. Zu, Tu
`
`20
`
`Basestation 4
`
`FIG. 8
`
`64
`
`10
`
`)
`
`, - - - - - - - - - - - - - -L 7
`I
`I
`n
`I
`I
`I
`I
`CORRELA TED
`I
`I
`GSM/GPS OUTPUTS
`L _______________ ~
`
`14
`
`FIG. 9
`
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`U.S. Patent
`
`Jun.26,2001
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`Sheet 5 of 6
`
`US 6,252,543 Bl
`
`12.4 MHz
`
`112
`
`102
`
`104
`
`J.J..Q
`
`ill
`
`120
`
`LO
`
`AGC
`
`10.1 MHz
`
`1 - - - - - - - 150 correlator outputs
`
`ill
`
`' - - - -~ - - - '
`
`1 - - - - - - - Peak detector output
`
`13.0 MHz clock
`
`FIG. 10
`
`Normal GSM Rx
`
`102
`
`I - - - -~ - - - - - 130
`I channel
`
`118
`
`120
`
`AGC
`
`10.1 MHz
`
`,___ ___ 150 correlator outputs
`
`ill
`
`' - - - -~ - - - '
`
`1 - - - - - - - Peak detector output
`
`13.0 MHz clock
`
`FIG. 11
`
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`U.S. Patent
`
`Jun. 26, 2001
`
`Sheet 6 of 6
`
`US 6,252,543 Bl
`
`;140
`
`10.1 MHz
`
`148
`
`' - - - - - - - - 1 146 ~
`
`144
`
`142
`
`13.0 MHz
`
`FIG. 12
`
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`US 6,252,543 Bl
`
`1
`LOCATION SYSTEM COMBINING
`RANGING MEASUREMENTS FROM GPS
`AND CELLULAR NETWORKS
`
`RELATED APPLICATION
`Under Title 35 United States Code §119(e), this appli(cid:173)
`cation claims the benefit of the filing data of U.S. Provisional
`Application No. 60/087,207, filed May 28, 1998.
`
`TECHNICAL FIELD OF THE INVENTION
`
`The present invention relates to mobile telecommunica(cid:173)
`tion systems, and more particularly to methods and arrange(cid:173)
`ments for locating mobile terminals.
`
`2
`receiver(s). For example, in an urban environment, the LOS
`is often blocked by building and/or other structures, while in
`certain other environments the naturally occurring terrain
`and/or other features (e.g., mountains, canyons, forests,
`5 weather, etc.) can reduce the LOS, attenuate the transmitted
`signals, or produce multipath signals at the receiver. For
`many higher frequency signals or weaker signals, the loss of
`LOS or the introduction of such obstacles, can render the
`location technique significantly inaccurate, or completely
`10 unavailable.
`Consequently, there is a need for methods and arrange(cid:173)
`ments that provide location techniques having improved
`accuracy, reliability, and/or accessibility.
`
`BACKGROUND
`
`15
`
`SUMMARY
`
`It is desirable, and in certain places mandated by law, that
`mobile telecommunication network providers be able to
`determine an approximate geographical location of a mobile
`terminal (MT), such as, for example, an actively communi(cid:173)
`cating cellular telephone.
`There are a variety of MT location techniques currently
`being tested or used. These location techniques can be
`grouped into three basic categories.
`The first basic category includes "uplink signal" location
`techniques, wherein the mobile telecommunications net(cid:173)
`work is configured to determine where the MT is located
`based on ranging measurements associated with one or more
`uplink signals, which are transmitted by the MT and
`received by a requisite number of receivers having known 30
`locations, such as, for example, cellular telephone base
`stations (BSs ).
`The second basic category includes "downlink signal"
`location techniques, wherein the mobile telecommunica(cid:173)
`tions network is configured to determine where the MT is
`located based on ranging measurements associated with the
`reception, by the MT, of downlink signals from a requisite
`number of transmitters having known locations.
`The third basic category includes using location services
`not associated with either the uplink or downlink signals
`used in the mobile telecommunications network. One
`example, of such a location service is the Global Positioning
`System (GPS) in which GPS receivers collect and analyze
`ranging measurements from signals transmitted by GPS
`satellites having known locations. Currently, there are
`twenty-four (24)GPS satellites in orbit.
`The location techniques in each of these three basic
`categories include collecting ranging measurements such as,
`for example, a time of arrival (TOA), a time difference of
`arrival (TDOA), an observed time difference (OTD), or the
`like. These ranging measurements are gathered by detecting
`one or more measurement features within the transmitted/
`received signal(s). Each of the various location techniques
`has certain limitations or drawbacks that can significantly
`reduce their accuracy.
`By way of example, currently available or proposed TOA,
`TDOA, and OTD location techniques that utilize existing
`BSs typically require that at least three (3) or more BSs
`receive the transmitted uplink signal from the MT, or
`conversely that the MT receive transmitted downlink signals
`from at least three BSs to perform the locating process.
`Similarly, with respect to the GPS, a GPS receiver needs to
`receive transmitted signals from at least four ( 4) GPS
`satellites to perform the locating process.
`Unfortunately, at certain times there is not always a clear
`line-of-sight (LOS) between the requisite transmitter(s) and
`
`In accordance with certain aspects of the present
`invention, methods and arrangements are provided for locat(cid:173)
`ing a mobile terminal. The methods and arrangements
`combine terrestrial-based location techniques with satellite-
`20 based location techniques, resulting in improved accuracy,
`reliability, and accessibility. For example, considering the
`three basic categories identified in the Background section,
`above, the present invention provides various methods and
`arrangements for combining at least portions of the location
`25 techniques in the first and/or second categories with the
`location techniques in the third category.
`Thus, for example, the above stated needs and others are
`met by a mobile terminal locating method, in accordance
`with certain embodiments of the present invention. The
`method includes receiving a signal from at least one satellite,
`and a signal from at least one terrestrial transmitter, using the
`mobile terminal. The method further includes measuring a
`"time of flight" for each of the received signals and con-
`35 verting each of the resulting time of flight measurements to
`corresponding range values. The range values are then used
`by the mobile station to determine its approximate position.
`In certain embodiments, the satellite is part of the Global
`Positioning System ( GPS) and the terrestrial transmitter is a
`40 base station within a mobile telecommunications system. In
`still other embodiments the method also includes using a
`single time measuring unit, located within the mobile
`terminal, to measure the respective time of flights for both
`the first type of signals and the second type of signals.
`In accordance with further embodiments of the present
`invention, an arrangement for use in a mobile terminal and
`a mobile telecommunications system is also provided. Each
`of these embodiments, includes at least one time measuring
`unit that is configured to receive a signal associated with at
`50 least one satellite and a signal associated with at least one
`terrestrial transmitter. The time measuring unit is further
`configured to measure a time of flight for each of the
`received signals, convert each of the resulting time of flight
`measurements to corresponding range values, and determine
`55 and output an approximate position of the mobile terminal
`using the range values.
`In accordance with still further embodiments of the
`present invention, another method for locating a mobile
`terminal is provided. This method also meets the above
`60 stated needs and others and includes receiving a plurality of
`first type signals from a plurality of satellites, and transmit(cid:173)
`ting at least one second type of signal to a plurality of base
`stations, using the mobile terminal. The method further
`includes measuring a time of flight for each of the first type
`65 of signals received at the mobile terminal and measuring a
`time of flight for each of the second type of signals received
`at the plurality of base stations. Additionally, the method
`
`45
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`3
`includes converting each of the resulting time of flight
`measurements to range values, and determining an approxi(cid:173)
`mate position of the mobile terminal using the range values.
`In certain further embodiments, the satellite is part of a
`Global Positioning System (GPS). This method can be used 5
`with only two satellite signals and two base stations by
`synchronizing clocks within at least each of the two satel(cid:173)
`lites and at least each of the two base stations. This method
`can also be used if there are signals from at least two
`satellites and at least three base stations receive the second 10
`type of signal from the mobile station, or conversely, if there
`are signals from at least three satellites and at least two base
`stations receive the second type of signal from the mobile
`station.
`An arrangement for use with a mobile telecommunica- 15
`tions system in locating a mobile terminal is also provided,
`in accordance with certain further embodiments of the
`present invention. The arrangement includes a satellite loca(cid:173)
`tion system, such as, for example, GPS, having a plurality
`satellites configured to output a plurality of first type signals.
`A plurality of base stations and at least one location deter(cid:173)
`mining node are provided within the mobile telecommuni(cid:173)
`cations system. The arrangement further includes a mobile
`station that is in radio communication with at least one of the
`plurality of base stations and configured to transmit at least 25
`one second type of signal to at least one of the plurality of
`base stations, and receive the plurality of first type signals
`from the plurality of satellites. Here, the mobile station
`measures a time of flight for each of the first type of signals
`and provides a range value for each of the first type of 30
`signals received to the location determining node. The
`plurality of base stations are configured to receive the
`second type of signal from the mobile terminal, measure a
`time of flight for each of the second type of signals and
`communicate a range value for each of the second type of 35
`signals received to the location determining node. The
`location determining node is then able to determine an
`approximate position of the mobile terminal various range
`values.
`In accordance with still further embodiments of the 40
`present invention, a shared clock arrangement is provided.
`In certain embodiments this shared clock arrangement is
`advantageously used to relate two (2) different clock signals,
`such as, for example, a local mobile terminal or base station
`clock signal and a GPS clock signal. The shared clock
`arrangement includes a correlator, which correlates a first
`clock signal with a second clock signal and outputs a
`correlated clock signal. The arrangement also includes a
`frame generator that receives the first clock signal and
`outputs a corresponding generated frame signal. The corre(cid:173)
`lated clock signal and the generated frame signal are then
`provided to a comparator, which measures the algebraic sum
`of the two signals and outputs a corresponding summed
`output clock signal.
`
`45
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`A more complete understanding of the various methods
`and arrangements of the present invention may be had by
`reference to the following detailed description when taken in
`conjunction with the accompanying drawings wherein:
`FIG. 1 is a block diagram depicting a satellite-based
`mobile receiver location system, such as, for example, the
`Global Positioning System (GPS) provided by the U.S.
`Department of Defense;
`FIG. 2 is a block diagram depicting an exemplary portion 65
`of a mobile telecommunications system having an uplink
`time-of arrival (TOA) mobile terminal (MT)location system;
`
`60
`
`FIG. 11 is a block diagram depicting portions of yet
`another exemplary embodiment of a GPS configured
`receiver that is modified for use in a MT, in accordance with
`certain other embodiments of the present invention, and
`50 configured to process both GPS signals and base station
`ranging signals associated with a combined GPS and down(cid:173)
`link TOA, TDOA, or OTD MT location system, for
`example, as in FIG. 8; and
`FIG. 12 is a block diagram depicting an exemplary phase
`55 locked loop arrangement that can be used in the exemplary
`GPS configured receivers of FIGS. 10 and 11, in accordance
`with certain embodiments of the present invention.
`
`US 6,252,543 Bl
`
`20
`
`4
`FIG. 3 is a block diagram depicting an exemplary com(cid:173)
`bined GPS and uplink TOA MT location system for use in
`a mobile telecommunications system, for example, as in
`FIG. 2, in accordance with certain embodiments of the
`present invention;
`FIG. 4 is a block diagram depicting an exemplary shared
`clock arrangement for use in either a MT or a base station
`(BS) within a mobile telecommunications system, in accor(cid:173)
`dance with certain embodiments of the present invention;
`FIG. 5 is a block diagram depicting an exemplary portion
`of a mobile telecommunications system having a downlink
`TOA, time difference of arrival (TDOA), or observed time
`difference (OTD) MT location system for use, in place of the
`uplink TOA MT location system, within a mobile telecom(cid:173)
`munications system, for example, as in FIG. 2;
`FIG. 6 is a graph depicting a time line and certain unique
`signal features associated with downlink transmitted signals
`from three different base stations, which are, for example,
`part of a MT location system, as in FIG. 5;
`FIG. 7 is a graph depicting a time line and certain unique
`signal features associated with downlink transmitted signals
`received by a MT from three different base stations, which
`are, for example, part of a MT location system, as in FIG. 5;
`FIG. 8 is a block diagram depicting an exemplary com(cid:173)
`bined GPS and downlink TOA, TDOA, or OTD MT location
`system for use in a mobile telecommunications system, for
`example, as in FIGS. 2 and 5, in accordance with certain
`further embodiments of the present invention;
`FIG. 9 is a block diagram depicting portions of an
`exemplary GPS configured receiver that is modified for use
`within a MT, in accordance with certain embodiments of the
`present invention, and configured to process both GPS
`signals and base station ranging signals associated with a
`combined GPS and downlink TOA, TDOA, or OTD MT
`location system, for example, as in FIG. 8;
`FIG. 10 is a block diagram depicting portions of an
`exemplary embodiment of a GPS configured receiver that is
`modified for use in a MT, in accordance with certain further
`embodiments of the present invention, and configured to
`process both GPS signals and base station ranging signals
`associated with a combined GPS and downlink TOA,
`TDOA, or OTD MT location system, for example, as in FIG.
`8;
`
`DETAILED DESCRIPTION
`
`A Introduction
`
`In accordance with certain aspects of the present
`invention, a mobile terminal (M1), such as, for example, an
`actively communicating cellular telephone, is located by
`combining conventional location technologies associated
`with mobile telecommunication network systems and the
`Global Positioning System (GPS).
`
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`US 6,252,543 Bl
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`6
`i~vention can, therefore, be adapted for use with a variety of
`different types of mobile terminals, other system's
`transmitters, and/or special purpose transmitters. For
`convenience, however, the exemplary embodiments
`described herein are directed towards combining certain
`aspects of a conventional mobile telecommunications net(cid:173)
`work (e.g., a cellular network) and the existing GPS.
`With this in mind, certain features associated with the
`various methods and arrangements in accordance with the
`present invention will now be described with particular
`references to existing systems and certain exemplary math(cid:173)
`ematical equations.
`
`10
`
`30
`
`5
`Each of these discrete systems employs location tech(cid:173)
`niques having certain characteristics in common. For
`example, each of these systems require the collection of a
`requisite number of ranging measurements from signals
`p~ssed between _transmitter(s) and receiver(s), wherein 5
`either the transmitter(s) or the receiver(s) have known or
`determinable locations (i.e., positions).
`Further, each of the collected ranging measurements can
`be converted from a time interval measurement to a corre(cid:173)
`~ponding distance measurement, for example, by multiply(cid:173)
`mg by the speed of light or an expected speed of transmis-
`sion associated with the signal. Once the conversion from
`time to distance has been accomplished then traditional
`triangulation, or other like mathematical techniques can be
`used to determine the positional coordinates of the MT
`' 15
`based on the known locations and calculated distances.
`In the case of a time of arrival (TOA) location technique,
`for example, the positions of the base stations (BSs) are
`known and do not change over time. The ranging measure(cid:173)
`ments can occur in a variety of ways, including: 1) having
`each BS measure the TOA of a synchronized word (synch 20
`word), as broadcast repeatedly in an uplink signal from the
`MT; 2) having each BS measure the timing advance required
`for communication with the terminal; and/or 3) having the
`MT separately measure a TOA based on a synch word in the
`transmitted downlink signal from each of the BSs. Assuming 25
`that the MT is positioned within a relatively planar
`envi~onment, distance information from three (3) BSs is
`reqmred to solve for x and y positional coordinates on the
`ground and the unknown time of broadcast of the synch
`word (either uplinked or downlinked).
`In the case of the GPS location technique, the positions of
`the GPS satellites vary with regard to time. Thus, a GPS
`receiver needs to receive an accurate measurement of time
`from the GPS satellites (or an accurate GPS-related source
`on the ground) in order to know the positions of the GPS
`satellites at the time of the ranging measurements. The
`ranging measurements between the GPS receiver and each
`of at least four ( 4) GPS satellites occurs by: 1) finding the
`starting point on the 1023 chip long Gold code sequence
`wit~in the signal transmitted by each GPS satellite; 2)
`~ndmg the start time of a bit edge; and 3) finding the start
`time of the data message. The resulting "time of flight" for
`the signal received from each GPS satellite is then converted
`to distance. The resulting four ( 4) range measurements allow
`for a ~olution to the GPS receiver's position in x, y and z
`coordmates and for determination of the unknown time
`difference between the GPS time and the GPS receiver's
`independent clock.
`Thus, in the examples above, the underlying location 50
`process for both the mobile telecommunication network and
`the GPS essentially rely upon receiving signals from certain
`known positions, and gathering ranging measurements from
`a sufficient number of signals to solve for the MT's location.
`These common characteristics and others will be 55
`?escri~ed in more detail below to show how the present
`mvent10n advantageously combines location techniques
`and/or locating processes by providing mathematical solu(cid:173)
`tions that can be processed to solve for the positional
`coordinates of the MT.
`In accordance with certain aspects of the present
`invention, the signal sources can include any viable combi(cid:173)
`nation of terrestrial-based transmitters, and space-based
`transmitters having static and/or dynamic positions with
`respect to time.
`Those skilled in the art will further recognize that the
`methods and arrangements in accordance with the present
`
`35
`
`GPS Location System Examples
`FIG. 1 is a block diagram depicting a conventional
`satellite-based location system 10, such as, for example, the
`GPS, which includes a receiver 12 and a constellation of at
`least four ( 4) satellites 14, from which distances to receiver
`12 are determined by receiver 12 upon acquiring and inter(cid:173)
`preting the signals from each. These determined distances
`are often referred to as "pseudoranges" because they repre~
`sent ranges to the satellites with an inherent error caused by
`the use of a local clock within receiver 12 that is not
`"synchronized" to GPS time. Nevertheless, based on the
`positions of the satellites at the time of the measurements
`one can produce a solution for the x, y and z coordinates of
`receiver 12, as well as the time shift or difference between
`the local clock within receiver 12 and GPS time.
`To determine the location of receiver 12 in three
`dimensions, receiver 12 needs to make ranging measure(cid:173)
`ments to at least four ( 4) satellites 14. For a GPS receiver
`this is typically not a problem, since the current GPS
`constellation of twenty-four (24) satellites provides cover(cid:173)
`age for about 99% of the Earth's surface. Of course, receiver
`12, preferably needs to have a significantly clear line-of(cid:173)
`sight (LOS) to the sky to provide optimal performance.
`As depicted in FIG. 1, the listed coordinates for receiver
`12 and each satellite 14 are expressed in an Earth Centered
`Earth Fixed reference system. Thus, X;, Y;, and Z; represent,
`respe~tively, the known positional coordinates of each (i'h
`)
`satellite 14. C; represents the time correction for each (i'h
`)
`satellite 14 relative to GPS time. Xu, Yu, and Zu represent
`the unknown coordinates of receiver 12. T
`represents the
`time difference between GPS time and i~ernal terminal
`clock time of receiver 12. Finally, P; represents the measured
`code phase of the signal from each (i'h
`) satellite 14.
`In accordance with certain embodiments of the present
`invention, GPS location techniques can be simplified some(cid:173)
`what when applied to a cellular phone system. For example,
`a_n advantage can be gained through the reasonable assump(cid:173)
`tion that the unknown position of receiver 12 ( e.g., a cellular
`phone having a GPS receiver) to be operating (i.e., commu(cid:173)
`nicating with a BS) will be within about 300 km or less of
`a k~own location (i.e., the location of the BS). Therefore, by
`takmg the measured code phase of each GPS signal and
`adding an appropriate number of milliseconds for example
`to each measurement representing the nea~est, rounded
`down integer millisecond (NI) signal propagation time from
`each (i'h
`) satellite 14 to the approximate location of receiver
`60 12, the pseudoranges PR; for each (i'h
`) satellite 14 can be
`obtained by:
`
`40
`
`45
`
`(1)
`PR;-(P;+N;+C;)/c
`Wherein, c represents the speed of light, preferably cor-
`65 rected for propagation effects
`By measuring the code phase of each signal receiver 12 is
`essentially finding the start of the Gold Code sequence (1023
`
`Ex.1011
`APPLE INC. / Page 10 of 17
`
`

`

`US 6,252,543 Bl
`
`7
`bits long) for that satellite 14 relative to an internal clock
`within receiver 12. This measurement, preferably, needs to
`be done to an accuracy of about a few nanoseconds to
`maintain an overall accuracy of feet in the location method.
`It does not matter that the internal clock is not synchronized 5
`to the GPS clock because that error is solved for by using
`four ( 4) rather than three (3) satellite ranging measurements.
`Thus, there are four ( 4) equations and four ( 4) unknowns:
`
`8
`VLR 24 is further connected to a Home Location Register
`(HLR) 26 and a Gateway Mobile Switching Center (GMSC)
`28. GMSC 28 provides connectivity to at least one further
`communications network 30 through which calls can be
`connected between MT 18 and at least one telecommunica(cid:173)
`tions terminal (TT) 32. A location service controller (LSC)
`34 is provided to request and/or otherwise control/configure
`MT 18 and BSs 20 to conduct a MT locating process. Such
`arrangements, and similar arrangements for system 16 are
`well known.
`A typical cellular phone signal, for example, provides
`many opportunities for conducting ranging measurements.
`The ranging measurements are usually based on one or more
`identifiable or unique features in the signal(s) that are uplink
`15 transmitted by MT 18 to BSs 20. Examples of unique
`features include a frame synch word, or the bit synch pattern
`used to train a receiver equalizer. Regardless of the type of
`unique feature employed, it is determined ahead of time or
`otherwise established, for example, by LSC 34, that a
`20 particular unique feature is the common point to measure
`TOA at the various BSs, 20.
`As is further known, such MT locating processes can be
`enhanced in several ways to reduce errors, such as averaging
`multiple measurements or measuring the first peak in the
`25 signal such as would be done to minimize multipath errors.
`Because the BS towers, etc., will be on the Earth's surface,
`there is little opportunity to determine the altitude of MT 18.
`This means that system 16 can use a minimum of three (3)
`BSs 20 to determine the positional coordinates of MT 18,
`30 and the timing difference between MT 18 and BSs 20
`(assuming that the clocks in BSs 20 are synchronized).
`However, for the purpose of the mathematical problems
`that follow in this description, it will be assumed that four
`(4) BSs 20 are used, as shown in FIG. 2. Here, X;, Y;, and
`Z; represent the known positional coordinates of each (i'h
`)
`BS 20. Xu Yu and Zu represent the unknown positional
`coordinates' of MT 18. TBu represents the time difference
`between BS ( cellular) time and MT clock time. T; represents
`the measured time of the unique feature of the signal(s) from
`MT18.
`One way to use GPS with a cellular phone system is to
`presume that the individual BSs 20 include a GPS receiver,
`and/or are otherwise capable of obtaining GPS time with
`45 which to measure the TOA, Th of the unique feature in the
`signal(s) from MT 18. In such a situation, therefore, TBucan
`become Tu with proper synchronization between the two
`sets of measurements. As such the (i'h
`) pseudorange can be
`determined as the observed time divided by the speed of
`light, as we do not know TBu when the signal feature was
`sent. Thus,
`
`(2) 10
`
`Those skilled in the art will recognize that this set of
`problems can be solved in several different ways. One way
`is to presume that receiver 12 is at the approximate known
`location, (as is done herein for certain exemplary embodi(cid:173)
`ments of the combined GPS/cellular phone network locating
`process), and then to calculate the differences between the
`measured pseudoranges, PRI, and the calculated
`pseudoranges, PR;', to that location. Thus, multiplying the
`vector of such pseudorange "differences" by the inversion of
`the coefficients of the 4 by 4 matrix formed by the direction
`vectors to the satellites 14, yields a delta X, Y, Z and T,
`which are added to the initial assumed location and time
`error (0) to obtain the correct values for those variables. In
`this case, Xu', Yu', Zu' are the values for the approximate
`known location of receiver 12. R;' is the distance to each (i'h
`)
`satellite 14 from the approximate known location of receiver
`12. We leave PR;' as a pseudorange in the following and not
`as R;', because one often leaves out the N; in PR;' in this
`calculation without a substantial impact. This is shown in the
`following equations:
`
`PR1 -PR;
`
`PR2 -PR;
`
`PR, -PR;
`
`PR4 -PR4
`
`(3)
`
`(X1-X[;)/R; (Y1-Y[;)/R;
`
`(Z1-Z[;)/R;
`
`(X2 -X[;)/ R;
`(Z2 -Z[;)/ R;
`(Y2 -Y[;)/ R;
`(X,-X[;)/R3 (Y,-Y[;)/R3 (Z,-Z[;)/R3
`(X4 -X[;)/ R4
`(Y4 -Y[;)/ R4
`(Z4 -Z[;)/ R4
`
`X
`
`Xu-X[;
`
`Yu -Y[;
`
`Zu-Z~
`
`cTu
`
`Which can be defined as:
`
`dPR-HxdX
`
`(4)
`
`With an inverted H matrix providing:
`
`35
`
`40
`
`(5) 50
`
`This equation ( 5) is iteratively or recursively calculated
`until the solution converges for Xu, Yu, and Zu and the time
`ambiguity.
`
`C. Uplink TOA Location System Examples
`
`As before with system 10 in FIG. 1, this pseudorange is
`55 equal to the real range corrected for the unknown time:
`
`(6)
`
`Reference is now made, to FIG. 2, which is a block
`diagram of an exemplary mobile telecommunications sys(cid:173)
`tem 16 that is configured to perform a conventional uplink
`TOA location technique based on ranging measurements 60
`associated with at least one uplink signal from a MT 18 and
`received by at least four ( 4) or more BSs 20.
`BSs 20 ar