Ulllted States Patent [19]
`Green, Jr.
`
`US005926133A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,926,133
`Jul. 20, 1999
`
`[54] DIFFERENTIALLY CORRECTED POSITION
`LOCATION SYSTEM AND METHOD FOR
`MOBILE COMMUNICATION NETWORKS
`
`[75] Inventor; Donald R, Green, Jr,’ San Marcos,
`Calif.
`
`[73] Assignee: Denso Corporation, Kariya, Japan
`
`[21] App1_ No; 08/897,315
`
`[22]
`
`Filed:
`
`Jul. 21, 1997
`
`[51] Int. Cl.6 ................................................... .. H01Q 21/06
`[52] US. Cl. ........................ .. 342/363; 342/450; 342/457;
`342/463; 379/59; 455 /33_1; 455 /422
`[58] Field of Search ................................... .. 342/363, 450,
`342/457, 463_465; 379/59, 60, 185; 455/331,
`422, 575
`
`[56]
`
`References Cited
`
`U-S~ PATENT DOCUMENTS
`7/1972 Anderson et a1. .............. .. 343/112 TC
`3,680,121
`3/1988 Maloney et a1_ _
`4,728,959
`6/1992 Heller .................................... .. 342/450
`5,119,104
`6/1993 Mansell et a1. .
`5,223,844
`7/1993 Brown et a1- -
`5,225,842
`5/1994 Brown-
`573117194
`5,365,516 11/1994 Jandrell ................................... .. 370/18
`5,379,224
`1/1995 Brown et a1. .
`5,422,813
`6/1995 Schuchman et a1. .
`5,512,908
`4/1996 Herrick.
`5,548,583
`8/1996 Bustamante .
`
`OTHER PUBLICATIONS
`
`IEEE Communication Magazine, Oct. 1996 Position Loca
`tion Using Wireless Communications on Highways of the
`Future, T.S. Rappaport et al, pp. 33—41 (Also see Appln. p.
`6)
`
`Primary Examiner—Thomas H. TarcZa
`Assistant Examiner—Dao L. Phan
`Attorney, Agent, or Firm—Fish & Richardson PC.
`
`[57]
`
`ABSTRACT
`
`A system for determining the location of portable commu
`nieatien devices such as cellular telephones and the like has
`multiple small, dedicated multipath calibration transponders
`at known Positions- When a Portable Communication device
`initiates a call, base stations in the coverage area direct the
`transponders to generate response signals Which are received
`by the base stations. The characteristics of the signals from
`the portable device and the transponders are provided to a
`base station controller linked to the base stations. The base
`station controller derives a coarse position using the raW
`device Position information and uses the raw transponder
`position information and the transponder’s knoWn positions
`to derive a Correction vector representative of multipath
`distortion of transponder signals in the area of the portable
`device. Since the portable device Will generally experience
`the same distortion as the transponders in its area, the
`correction vector can be applied to the coarse device posi
`tion to obtain its true position.
`
`47 Claims, 9 Drawing Sheets
`
`Apple, Inc. Exhibit 1035 Page 1
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`
`Sheet 1 019
`
`5,926,133
`
`FIG. I
`PRIOR ART
`
`‘
`
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`FIG. 2A
`PRIOR ART
`
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`1111111F‘11J J
`H JFJ I J1 ll HJF HJI
`_111111 IFlLJLlLlL/ <
`11111111119111/ Q 1
`
`__11__1 DUUQQ
`?r? 11111317 QQ
`IFUIFHlF/AAA
`
`Apple, Inc. Exhibit 1035 Page 2
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`
`Sheet 2 of9
`
`5,926,133
`
`FIG. 2B
`PRIOR ART
`
`FIG. 2C
`PRIOR ART
`
`JLJLJlglLrill-Hl-Hzull‘zk
`IEZHZTLILJLJLJLJLHI]
`1E7T[][1L_Jl IYHHJI/ /
`_ILJL_J [_|LJL_H_JLLL%/<
`DISTORIEDTT%IJIM Hill-77$
`ACTUAL :
`11mm‘? Q
`7£1E1U4>§©<
`
`93:1 QQQV/Q \
`
`Apple, Inc. Exhibit 1035 Page 3
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`
`Sheet 3 of9
`
`5,926,133
`
`FIG. 3
`
`FIG. 4
`
`Apple, Inc. Exhibit 1035 Page 4
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`
`Sheet 4 of9
`
`5,926,133
`
`F I G . 5
`
`ROVERIB
`
`BASE
`STATION I 4
`
`TRANSPONDER
`I 2
`
`BASE STATION
`CONTROLLER I 8
`
`IOO~
`
`E-QII
`—> REQUEST —)
`
`IO2~
`
`~
`104
`
`IO6~
`
`IO8~
`
`IIO~
`
`II2~
`
`II4~
`
`SELECT
`TRANSPONDERS
`
`WAKE UP
`—’ CALL _—’
`
`POWER UP
`
`-<—RESPONSE <——
`
`SLEEP
`
`RAW
`POSITION
`
`POSITION
`DATA
`
`4;
`
`Apple, Inc. Exhibit 1035 Page 5
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`Sheet 5 of9
`FIG. 6
`
`5,926,133
`
`L_.__.________.____.
`
`~20
`
`22
`
`FIG. 7
`
`Q
`
`ANTENNA
`CONNECTION
`NETWORK
`A
`‘L
`
`24
`\
`TRANSMITTER RECEIVER <—-—
`
`T26 J
`
`CONTROLLER
`
`3O“\J|TIMERE POWER SUPPLY
`
`2a /
`
`Apple, Inc. Exhibit 1035 Page 6
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`
`Sheet 6 of9
`
`5,926,133
`
`FIG.8
`
`ROVER I 6
`
`BASE
`STATION I 4
`
`II6~
`
`1I8~
`
`HIGH POWER
`COMMAND
`
`HIGH POWER
`RESPONSE
`
`FIG.9
`
`ROVER I6
`
`BASE
`STATION I4
`
`BASE STATION
`CONTROLLER I8
`
`__> E-9II _,
`REQUEST
`
`___> E-9II ____,
`REPORT
`
`‘_INSUFFICIENT<_
`RECEPTION
`
`<_HICH POWER<__
`COMMAND
`
`IOO~
`
`I20~
`
`122~
`
`I24~
`
`Apple, Inc. Exhibit 1035 Page 7
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`
`Sheet 7 of9
`
`5,926,133
`
`F l G. IO
`
`BASE
`STATION 14
`
`TRANSPONDER
`T2
`
`T04~
`
`T2s~
`
`128~
`
`—>WAKE UP
`
`_>H|GH POWER
`COMMAND
`
`HIGH POWER
`*- RESPONSE
`
`FIG. l2
`
`ROVER Ts
`
`BASE
`STATION 14
`
`BASE STATION
`CONTROLLER 18
`
`T00~
`
`_, E-911
`REQUEST
`
`Apple, Inc. Exhibit 1035 Page 8
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`Sheet 8 of9
`FIG. ll
`
`5,926,133
`
`@ GET BASE STATION
`
`‘30” RAW POSITION DATA
`l
`132“ GET coAnsE
`ROVER POSITION PRC
`&
`GET COARSE TRANSPONDER
`134'\ POSITIONS Pm
`J,
`GET TRANSPONDER
`136x DISTORTION VECTORS an
`J,
`GET TRANSPONDER
`138'\ DISTORTION VECTOR
`MACNITUDES | bTil
`&
`GET RELATIVE DISTORTION
`140'\ VECTOR WEIGHTS vm
`&
`_
`GET MULTIPATH
`142\ DISTORTION VECTOR 5R
`9
`144’\ GET ACTUAL POSITION Pra
`
`Apple, Inc. Exhibit 1035 Page 9
`
`

`
`U.S. Patent
`
`Jul. 20, 1999
`
`Sheet 9 0f 9
`
`5,926,133
`
`FIG. I3
`
`@ GET BASE STATION
`
`138A
`
`RAW POSITION DATA
`I
`150m GET COARSE
`ROVER POSITION PRc
`I
`152“ GET TRANSPONOER
`DISTORTION VECTORS OTi
`I
`GET TRANSPONOER
`DISTORTION VECTOR
`MAGNITUDES IéTiI
`I
`140% GET RELATIVE DISTORTION
`VECTOR WEIGHTS W“
`I
`_
`142x GET MULTIPATH
`DISTORTION VECTOR 6R
`I
`GET ACTUAL POSITION Pra
`
`(jg
`
`Apple, Inc. Exhibit 1035 Page 10
`
`

`
`1
`DIFFERENTIALLY CORRECTED POSITION
`LOCATION SYSTEM AND METHOD FOR
`MOBILE COMMUNICATION NETWORKS
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention is directed to a system for locating
`the position of a unit in a communication network and to a
`method for performing such position location. More
`speci?cally, it is directed to a system and method for
`performing position location in a mobile communication
`netWork such as a cellular telephone or personal communi
`cation system (PCS) netWork.
`2. Description of Related Art
`The ever-increasing popularity of mobile communication
`devices such as cellular telephones and the like brings With
`it a need for increased reliability and functionality of those
`devices. As users come to rely on Wireless telephone net
`Works more and more and those telephones become ubiq
`uitous in everyday life, the netWorks must be capable of
`accommodating an ever-Widening range of demands.
`One such demand, promulgated in June, 1996 by the US.
`Federal Communications Commission (FCC) as FCC
`Docket Number 94-102, requires that future Wireless ser
`vices provide a site location feature for its mobile units. This
`feature is primarily for use in providing emergency call
`service capability, complementary to the emergency 911
`(E-911) service familiar to most Wireline telephone users. To
`provide emergency services to a caller, it is advantageous for
`any communication system used to make an emergency call
`to be able to automatically identify the location of the caller.
`This is because in emergency situations time is of the
`essence and further, the caller may not knoW his or her
`location, may give an incorrect or otherWise inaccurate
`location, or may become incapacitated during the course of
`the call.
`In the case of Wireline netWorks, such position identi?
`cation is a relatively simple matter of correlating the caller’s
`telephone number With a list of numbers and corresponding
`addresses. In the case of Wireless E-911 service, hoWever,
`the very mobility Which makes the portable telephones so
`useful precludes a simple lookup technique for position
`location. Thus, a method of “dynamic” position location
`must be used in mobile netWorks.
`A number of position location systems are based on the
`Global Positioning System (GPS) implemented by the US.
`Department of Defense (DoD). GPS is a constellation of
`tWenty-four active satellites circling the earth in precisely
`timed and controlled orbits so that betWeen ?ve and eight
`satellites are theoretically in line-of-sight radio contact With
`any point on earth at a given time. Each satellite broadcasts
`a uniquely-coded signal Which can be picked up by an
`appropriately equipped GPS receiver, or “rover”. The rover
`timing is synchroniZed With that of the satellites and is
`equipped With ephemeral data that alloWs it to precisely
`calculate the position of each of the satellites at any given
`time. It receives signals from three or more of the satellites
`and calculates its distance from each based on the travel time
`of its respective signal. Each of the distances de?nes a
`sphere centered on its respective satellite, and the intersec
`tion of all spheres is the actual location of the rover.
`GPS position location is not perfect, hoWever. Various
`sources of errors can cause the rover’s detected position to
`differ from its actual position signi?cantly, and their com
`bined effect may even be to prevent the system from meeting
`
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`5,926,133
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`2
`the minimum 125 meter accuracy requirement set by the
`FCC. In civilian applications, the largest error source by far
`is called “selective availability” and is the result of the DoD
`deliberately decreasing the integrity of the civilian portion of
`the GPS satellite signals to deny hostile parties high
`accuracy positioning capability. Other errors are due to
`natural conditions, such as ionospheric and tropospheric
`conditions, and some, such as satellite clock and orbit errors,
`receiver noise and multipath propagation effects, stem from
`arti?cial sources.
`Multipath propagation results When a radio Wave travels
`from a source (e.g., a GPS satellite) to a destination (e.g., a
`rover) through a space populated With objects that re?ect
`radio Waves. As shoWn in FIG. 1, if a line-of-sight path
`exists betWeen the satellite and rover, direct reception occurs
`via a true signal TS. HoWever, the signal may be re?ected off
`of objects in the region to produce re?ected Waves Which
`travel a longer distance and therefore are delayed relative to
`the original signal and appear as separate signals to the
`rover. Multipath re?ection signals may include components
`from tWo sources: static components Which result from
`re?ections off of stationary objects such as mountains,
`buildings and the like, such as signal SR; and dynamic
`components Which result from re?ections off of moving
`objects such as vehicles, such as signal DR.
`FIGS. 2A—2C shoW the effects of multipath propagation
`on the position location process. FIG. 2A shoWs an idealiZed
`typical topography, e.g., a city area of several blocks. FIG.
`2B shoWs the same area as it might appear to rovers in the
`area based on GPS position information distorted by mul
`tipath propagation. FIG. 2C shoWs hoW the position of a
`rover in the area might be mistakenly detected based on such
`corrupted information.
`Although the deleterious effects of multipath propagation
`have been illustrated in the context of GPS position location,
`such problems Will of course be encountered in many types
`of communication With a rover, e.g., communication from a
`base station or the like.
`With the exception of multipath propagation, all of these
`errors are experienced by receivers in the same general area
`to an equal degree, and a technique called “differential GPS”
`(DGPS) makes use of this fact to increase position location
`accuracy. DGPS uses a reference receiver Whose actual
`position is precisely knoWn in proximity to the mobile
`receiver. The reference receiver calculates its predicted
`position based on signals from the GPS satellites and
`compares it to its actual, precisely knoWn position to derive
`a differential correction. This information is passed along to
`the rover via a separate information channel, e.g., radio, and
`is used by the rover to correct its position. Multipath
`propagation effects cannot be corrected in this Way, since
`they change signi?cantly With a small change in position and
`a particular set of corrections are generally valid only for a
`given rover at a given location at a given moment in time.
`It is possible to incorporate a rover into a mobile tele
`phone unit and to provide the GPS positional information
`during an E-911 session; hoWever, this approach has some
`draWbacks. For example, GPS receivers are relatively
`expensive, and including such a unit in a cellular telephone
`or the like Would substantially increase its cost (particularly
`one With DPGS capability). Further, GPS receivers are
`complicated electronic devices Which consume signi?cant
`amounts of poWer. Inclusion of one in a portable telephone
`Would either shorten the telephone’s battery life or require
`the use of larger capacity (and consequentially larger siZe)
`batteries. Thus, the telephone’s siZe must be increased to
`accommodate the batteries and the additional GPS circuitry.
`
`Apple, Inc. Exhibit 1035 Page 11
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`

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`5,926,133
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`3
`Moreover, GPS satellites provide a relatively Weak, high
`frequency (carriers in the range of 1.2—1.6 GHZ) signal
`Which does not penetrate buildings and other dense struc
`tures Well and Which requires the use of specialized direc
`tional antennas. Additionally, DPGS operation requires the
`use of reference receivers Which are not universally avail
`able. Further, the ?rst position determination by a GPS
`receiver after it is turned on (called a “cold reading”, as
`opposed to a “hot reading” made by a unit that has been
`operating for a period of time) can take up to ?fteen
`minutes—clearly unacceptable in the E-911 environment.
`Finally, the need for a GPS receiver in each handset Would
`mean that eXisting handsets lacking such functionality could
`not be used for Wireless E-911 position determination.
`Some of these problems are solved by a technique called
`“cellular geolocation”, in Which cellular base stations moni
`tor transmissions from a mobile unit (typically, reverse voice
`channel or reverse control channel transmissions) and apply
`an angle of arrival (AOA) or time difference of arrival
`(TDOA) technique to the transmissions to determine the
`position of the unit. As described in Rappaport et al.,
`“Position Location Using Wireless Communications on
`HighWays of the Future”, IEEE Communications Magazine
`pp. 33—41 (Oct. 1996), the AOA technique uses highly
`directional antennas to determine the precise angle at Which
`each base station receives the mobile unit transmission, and
`the mobile unit’s position is resolved by triangulation With
`the knoWn positions of the base stations. Much like GPS, the
`complementary TDOA technique measures the relative
`delay in reception of the mobile transmissions at each base
`station, determines the distance traveled by the transmis
`sions to each base station based on its respective delay, and
`resolves the mobile unit’s position by resection.
`These approaches, hoWever, are still susceptible to posi
`tion determination errors resulting from multipath propaga
`tion and other effects. The need to take such error sources
`into account cannot be overlooked in E-911 applications,
`and is particularly critical in congested urban areas Where
`users are in close quarters and concentrated multipath envi
`ronments eXist.
`
`SUMMARY OF THE INVENTION
`
`In vieW of the above problems of the prior art, it is an
`object of the present invention to provide a position location
`system for mobile communication netWorks Which is
`capable of making highly accurate position determinations.
`It is another object of the present invention to provide a
`position location system for mobile communication net
`Works that is largely unaffected by multipath propagation
`effects.
`It is still another object of the present invention to provide
`a position location system for mobile communication net
`Works that provides accurate position determinations inde
`pendently of satellite and atmospheric-related errors and the
`like.
`It is yet another object of the present invention to provide
`a position location system for mobile communication net
`Works that provides accurate position determinations and
`does not require the use of handsets having special func
`tionality.
`The above objects are achieved by providing multiple
`small, dedicated multipath calibration transponders in the
`coverage area of the base stations at knoWn positions. When
`a rover initiates an E-911 session, the base stations direct the
`transponders to generate response signals. These response
`signals are received by the base stations, and the character
`
`4
`istics of the signals from the rover and the transponders are
`provided to a base station controller linked to the base
`stations. The base station controller derives a coarse position
`using the raW rover position information and uses the raW
`transponder position information and their knoWn positions
`to derive a correction vector representative of multipath
`distortion of transponder signals in the area of the rover.
`Since the rover Will generally experience the same distortion
`as the transponders in its area, the correction vector can be
`applied to the coarse rover position to obtain its true posi
`tion.
`Alternatively, rather than deploying an array of
`transponders, multipath distortion effects at multiple sites
`may be logged in advance using a single transmitter and
`stored by the base station controller. Then, in place of the
`base stations directing the transponders to issue response
`signals, the base station controller can derive a correction
`vector for the rover’s position based on the logged site data
`and use that vector to correct the coarse rover position.
`Other objects and features of the present invention Will
`appear in the course of the description thereof, Which
`folloWs.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`Additional objects and advantages of the present inven
`tion Will be more readily apparent from the folloWing
`detailed description of preferred embodiments thereof When
`taken together With the accompanying draWings in Which:
`FIG. 1 shoWs typical avenues of multipath propagation
`betWeen a GPS satellite and a rover;
`FIGS. 2A—2C shoW the distortion of a rover’s position
`due to multipath effects in an urban topography;
`FIG. 3 shoWs a ?rst preferred embodiment of the present
`invention in such a topography;
`FIG. 4 shoWs transponders according to the ?rst embodi
`ment providing response signals to base stations for differ
`ential correction of a rover position;
`FIG. 5 shoWs transactions betWeen the rover, base stations
`and transponders in the ?rst embodiment When determining
`position of the rover during the course of an E-911 call;
`FIG. 6 shoWs the operation of base stations, transponders
`and a base station controller to determine the position of a
`rover under multipath distortion conditions in the ?rst
`embodiment;
`FIG. 7 is a block diagram of a multipath calibration
`transponder according to the ?rst embodiment;
`FIG. 8 shoWs a variation on the ?rst embodiment in Which
`the rover selectively provides a high poWer transmission;
`FIG. 9 shoWs a variation on the ?rst embodiment Where
`the rover’s initial E-911 request is not received by enough
`base stations and it retransmits at a high poWer level;
`FIG. 10 shoWs a variation on the ?rst embodiment When
`a transponder’s response is not received by the base station
`and the transponder retransmits at a high poWer level;
`FIG. 11 shoWs the processing of the base station controller
`in the ?rst embodiment When correcting the rover’s position
`for multipath distortion;
`FIG. 12 shoWs transactions When determining the rover’s
`position according to a second preferred embodiment of the
`present invention; and
`FIG. 13 shoWs base station controller correction process
`ing in the second embodiment.
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`DETAILED DESCRIPTION OF THE
`PRESENTLY PREFERRED EXEMPLARY
`EMBODIMENTS
`A coverage area 10 of a mobile communication system
`has a constellation of multipath calibration transponders 12
`
`Apple, Inc. Exhibit 1035 Page 12
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`5,926,133
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`5
`disposed at predetermined, precisely known locations
`therein as shoWn in FIG. 3. In addition to the transponders
`12, the system also includes several base stations 14 Which
`are Within the communication range of the transponders 12,
`located at precisely knoWn positions and separated from one
`another by relatively large distances, and a base station
`controller 18 (shoWn in FIG. 6) Which controls transactions
`betWeen base stations 14.
`When, for eXample, a rover 16 places an E-911 call and
`it is necessary to determine its position, the base stations 14
`each receive a signal from the rover 16 as shoWn by the solid
`arroWs in FIG. 4. Normally, position determination using an
`AOA, TOA or TDOA technique based on the signals from
`the rover 16 received by the base stations 14 might be
`corrupted by multipath effects as described above; hoWever,
`the base stations 14 also receive signals from the transpon
`ders 12, and those signals are used for position correction to
`counter such multipath effects, as Will be described in
`greater detail beloW.
`As is knoWn in the art, the rover 16 is associated With a
`given base station 14 With Which it places outgoing calls and
`from Which it receives incoming calls, and as the rover 16
`moves, the base station 14 With Which it is associated is
`changed through a process called “handing off”. When a
`user of the rover 16 places an E-911 call, the rover 16 sends
`an E-911 request to the base station 14 With Which it is
`currently associated as shoWn in Step 100 of FIG. 5. That
`base station 14 receives the request and initiates the process
`to locate the position of the rover 16. Speci?cally, it selects
`transponders 12 to be used to determine the position of the
`rover 16 in Step 102 and sends a “Wake up” call to those
`transponders 12 in Step 104.
`Preferably, the transponders selected are those in the
`general vicinity of the rover 16. Determination of the general
`vicinity requires a preliminary position determination Which
`may be done by, e.g., performing a coarse position deter
`mination using one or more of the aforementioned AOA,
`TOA or TDOA techniques Without the bene?t of the signals
`from the transponders 12, using a different relatively loW
`resolution location technique, or simply de?ning the general
`vicinity as a predetermined area around the base station 14.
`Alternatively, the base station 14 may send the Wake-up call
`to all transponders Within its communication area. Further,
`the base station 14 need not send the Wake-up call to all
`targeted transponders 12 itself, and it may instead send
`requests to other base stations 14 close to it to issue some of
`the Wake-up calls.
`Each transponder 12 includes an antenna connection
`netWork 20 connected to a receiver 22 Which receives the
`Wake-up signal from the base station 14, a transmitter 24
`Which transmits a response signal to the base station 14 as
`described beloW, and a controller 26 Which controls the
`operation of the receiver 22 and transmitter 24 and Which
`controls the application of poWer thereto from a poWer
`supply 28 as shoWn in FIG. 7. Preferably, the poWer supply
`is driven by rechargeable batteries, e.g., Ni-MeH or Li-ion
`units) Which may be trickle charged by AC utility mains, or
`by solar cells, Wind poWer or the like for self-suf?cient
`operation.
`Normally, the transponders 12 are in an energy-saving
`sleep mode in Which only those circuits necessary to rec
`ogniZe a Wake-up call and activate the remainder of the
`transponder 12 are active. The sleep mode may be one in
`Which only the receiver 22 and controller 26 are active (the
`antenna connection netWork 20 is generally a passive
`network) so that the receiver 22 can receive the Wake-up
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`6
`signal and the controller 26 can direct the poWer supply 28
`to poWer up the transmitter 24 responsive to receipt of the
`Wake-up signal and drive the transmitter 24 to transmit the
`response signal, or it may be a slotted sleep mode,. Whereby
`the receiver 22 is normally off and only the controller 26 (or,
`alternatively, only a poWer-up timer 30) is active. In this
`case, the controller 26 directs the poWer supply 28 to poWer
`up the receiver 22 and transmitter 24 periodically to check
`for a Wake-up signal, or the poWer-up timer 30 similarly
`controls the other transponder components.
`In any case, When a transponder 12 receives a Wake-up
`call, it comes up to full poWer in Step 106 of FIG. 5,
`transmits the response signal to all base stations 14 Within
`range in Step 108, and returns to its sleep mode in Step 110.
`To distinguish the transponder response signals from one
`another and correlate them With their respective units, each
`transponder 12 should incorporate a unique identi?cation
`code in its response signal.
`The response signal may be at a predetermined frequency
`and poWer level, or it may be at a frequency and poWer level
`coded in the Wake-up signal. The poWer level may be a
`poWer level used by mobile units such as the rover 16 in
`normal communications. Alternatively, to ensure that the
`transponder signal is received by several base stations 14 so
`that a reliable position determination can be made, the poWer
`may be at a level higher than the generally alloWed range,
`i.e., one that is used only for such emergency communica
`tions.
`Along these lines, the base station 14 associated With the
`rover 16 may also send a command to the rover 16 instruct
`ing it to transmit at a higher than normal poWer level, as
`shoWn at Step 116 in FIG. 8. The ensuing high poWer
`transmission from the rover 16 in Step 118 ensures that its
`signal, too, Will be received by several base stations 14. This
`is a special concern in loW-poWer CDMA cellular and PCS
`communication systems Which are designed to provide a
`single base station communication path to a particular rover
`and Which therefore cannot guarantee connectivity to mul
`tiple base stations.
`The high poWer transmission command from the base
`station 14 to the rover 16 in Step 116 and reception of the
`rover’s response in Step 118 may be performed at any point
`betWeen reception of the rover’s E-911 request in Step 100
`and calculation of the rover’s raW position in Step 112
`(described in greater detail beloW).
`Further, to minimiZe disruption of other communications
`sessions, the base station 14 might request a high-poWer
`response from the rover 16 only When it is advised by the
`base station controller 18 that the number of other base
`stations 14 receiving the rover’s E-911 request Was too small
`to make an accurate position determination. This function
`may be implemented if each base station 14 sends an E-911
`call report to the base station controller 18 as shoWn in Step
`120 of FIG. 9 responsive to an E-911 call request directed to
`it or any other base station 14. Then, if the base station
`controller 18 determines that the number of base stations 14
`Within range of the rover’s normal poWer level transmissions
`is too small, it can notify the base station 14 associated With
`the rover 16 in Step 122 so that the base station 14 can direct
`the rover 16 to make a high poWer response in Step 124.
`As an alternative to the above techniques, the rover 16
`may be designed to alWays transmit E-911 requests at a high
`poWer level. This Will simplify system operation; hoWever,
`it does so at the cost of disrupting communications of other
`rovers 16 in the area. In any case, high poWer transmission
`on the rover end of course requires the use of a modi?ed
`rover.
`
`Apple, Inc. Exhibit 1035 Page 13
`
`

`
`5,926,133
`
`8
`In other Words, assume the base station controller 18 has
`received raW position data from several base stations 14 as
`shoWn in Step 130 of FIG. 11. Then, it then calculates a
`coarse rover position PRC=(XRC, yRC) in Step 132 and in Step
`134 calculates n coarse transponder positions PT1C=(XT1C,
`yT1c)> PT2c=(XT2c> yTZc) '
`'
`' PTnc=(XTnc> yTnc) based on the
`data from the base stations 14. Then, the actual, knoWn
`positions of the transponders being denoted by PT1a=(XT1a,
`yT1a)> PT2a=(XT2a> yTZa) '
`'
`' PTna=(XTna> yTna) the Vector 611'
`representing the displacement of each transponder i due to
`multipath distortion is determined according to the equation
`
`(1)
`6T1‘: (xi-m _xTic)I+(yTia_y 7%)]7
`in Step 136. Should more base stations 14 than are necessary
`to make coarse position determinations for the rover 16 and
`the transponders 12 respond, an appropriate averaging,
`Weighting or other correction technique may be used to
`obtain the coarse positions, or the additional base station
`data may be used to correct for geometric dilution of
`precision, thereby increasing the accuracy of the process.
`The magnitude |6Ti| of each distortion vector ST,- repre
`senting the distance the coarse transponder position PTZ-C of
`transponder i is displaced from the actual transponder posi
`tion PTl-a is calculated using the equation
`
`10
`
`15
`
`25
`
`7
`Similarly, the base station 14 can initially request a
`normal power level response from the transponders 12 in
`Step 104 of FIG. 5 and issue a second, high poWer response
`request only to transponders 12 Whose responses Were not
`received the ?rst time in Step 126 of FIG. 10 so that those
`transponders 12 provide a response Which can be received in
`Step 128. If the base station 14 still does not receive a
`response from a particular transponder 12, it may send a
`message to the base station controller 18 indicating that the
`transponder 12 may be malfunctioning (the operation of the
`transponders 12 can also be checked by periodic status
`polling by the base stations 14). Alternatively, high poWer
`transmissions may be authoriZed by the emergency operator
`or other authorities. In any case, the transponders 12 may
`stay aWake for a predetermined time period, or until they
`receive a sleep command from a base station 14, so that they
`Will be able to receive the high poWer transmission com
`mand in Step 126 and make the appropriate response in Step
`128.
`Each base station 14 receives the response signals from
`transponders 12 Within its communication range in Step 108
`of FIG. 5 or Step 128 of FIG. 10 as Well as the original E-911
`request from the rover 16 in Step 100 of FIG. 5 or its
`subsequent high-poWer response in Step 118 of FIG. 8, and
`the reception conditions of these signals are used to derive
`coarse position information for each of the transponders 12
`and the rover 16 in Step 112 of FIG. 5. For eXample, each
`of the base stations 14 may determine the angle of reception
`of each response signal (for AOA systems), the absolute time
`of reception of each response signal (for TOA systems) or
`the relative time of reception of each response signal (for
`TDOA systems) using a technique knoWn in the art, and in
`Step 114 provide that information to the base station con
`troller 18.
`Since each of the base stations 14 can obtain precisely
`synchroniZed timing information via the GPS system, a
`TDOA technique is used in the preferred embodiment and is
`supplemented With AOA for added accuracy; hoWever,
`another technique or combination of techniques may be used
`instead. Additionally, cellular system information such as
`Which sector the rover 16 is currently located in, handoff
`information and the like can be used in the position deter
`mination process. Further, in areas in Which users’ traf?c
`patterns are constrained, a geographic database can be used
`to provide inferred AOA information for use in the process.
`Finally, Whatever geolocation technique or techniques are
`used can be augmented With a GPS receiver in the rover 16.
`The receiver can derive positional GPS information in the
`normal manner and relay it to its base station 14; hoWever,
`to minimiZe the siZe of the rover and loWer its poWer
`consumption and cost, the receiver may simply take a
`“snapshot” of the GPS data it receives and relay it to the base
`station 14 or another centraliZed facility for processing. Of
`course, this approach has the draWback of requiring the use
`of a modi?ed rover 16.
`The base station controller 18 uses the signal information
`corresponding to the rover 16 to calculate a coarse positio