(12) United States Patent
`Chen et al.
`
`USOO6748224B1
`(10) Patent No.:
`US 6,748,224 B1
`(45) Date of Patent:
`Jun. 8, 2004
`
`(54) LOCAL POSITIONING SYSTEM
`(75) Inventors: Byron H. Chen, Whippany, NJ (US);
`Maria E. Palamara, Denville, NJ
`(US); Charles Varvaro, Glendale
`Heights, IL (US)
`(73) Assignee: Lucent Technologies Inc., Murray Hill,
`NJ (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`WO
`WO
`WO
`
`10/1998
`WO 98/47019
`10/1998
`WO 98/48294
`10/1998
`WO 98/48578
`OTHER PUBLICATIONS
`J.J. Caffery Jr. et al., “Overview of Radiolocation in CDMA
`Cellular Systems”, IEEE Communications Magazine, IEEE
`Service Center, Piscataway, NJ, US, vol. 36, No. 4, Apr. 1,
`1998pp 38-45.
`EPO Search Report dated Feb. 1, 2002.
`sk -
`cited by examiner
`Primary Examiner-Charles Appiah
`ASSistant Examiner J Moore
`
`Dec. 16, 1998
`(22) Filed:
`(51) Int. Cl." .................................................. H04Q 7/20
`(52) U.S. Cl. ..................... 455/456.1, 342/451; 342/458
`(58) Field of Search ................................. 455/456, 457,
`455/456.1-456.6; 342/450, 451, 457, 387,
`458
`
`(56)
`
`JP
`JP
`JP
`JP
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,058,200 A 10/1991 Huang et al. ................. 455/33
`5,646,632 A 7/1997 Khan et al. .......
`... 342/375
`6,208.297 B1 * 3/2001 Fattouche et al. .......... 342/450
`FOREIGN PATENT DOCUMENTS
`7-181242
`7/1995
`9-15314
`1/1997
`10-48322
`2/1998
`1O-322752
`12/1998
`
`A local positioning System (LPS) uses the radio propagation
`parameters in a CDMA forward link or TDMA reverse link
`to establish a mobile station's position. The mobile station
`receives pilot channel Signals from at least three distinct
`base stations and records the PN chip offset of the pilot
`channel signals. The LPS time difference of arrival triangu
`lation approach requires no additional Signal detection capa
`bilities. Base Stations Send out pilot channel Signals that
`arrive at a mobile Station with a particular phase and at least
`a predetermined minimum Strength. The mobile Station
`reports back the “visible' pilot channel Signals, their phases
`and Signal Strength to the LPS which uses a location non
`linear System, expressed as a set of cost functions, to
`estimate the mobile location. The LPS can also solve the
`9-1-1 mobile location problem for wireless CDMA systems
`by determining the position of a perSon in distreSS that has
`a digital cellular phone.
`
`25 Claims, 3 Drawing Sheets
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`EAD MOBILE SATION
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`ATA SA PLE
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`
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`BASE STATION
`ION
`NFORMA
`
`SAMPLE
`MATCH DATA
`WITH BASE STATION
`ON
`INFORMA
`
`MAE STANCES
`ES
`BETWEEN MOBILESTAON
`
`AND 8ASES ATIONS
`
`ETE
`MINE GEOGRAPHIC
`CORONATES OF
`
`MOBILES ATION
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`MORE DATA
`SAMPLES OF THE
`MOBILE STATION
`AVAILABLE
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`Petitioner Uber Ex-1032, 0001
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`

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`U.S. Patent
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`Jun. 8, 2004
`
`Sheet 1 of 3
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`US 6,748,224 B1
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`FIG. 1
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`b
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`bb2
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`bb3
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`b2
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`b2b3
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`b3
`
`FIG. 2
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`
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`b
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`Petitioner Uber Ex-1032, 0002
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`

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`U.S. Patent
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`Jun. 8, 2004
`
`Sheet 2 of 3
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`US 6,748,224 B1
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`FIG. 3A
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`'N
`
`O
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`ARTICLE OF
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`20
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`FIG. 3B
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`O
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`30
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`COMPUTER
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`FIG. 5
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`1000
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`900 H 700
`1.
`SOO
`1.
`pists, so
`DEIAIN ft). 1||||II
`IIHF
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`300
`200
`100
`O
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`1
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`4
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`7
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`16 19 22 25 28 31 34 37 40 43 46 49
`10 13
`TIME DEVIATION FROM SYNC (MicroSec x 0.02)
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`Petitioner Uber Ex-1032, 0003
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`

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`U.S. Patent
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`Jun. 8, 2004
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`Sheet 3 of 3
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`US 6,748,224 B1
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`FIG. 4
`
`
`
`READ MOBILE STATION
`DATA SAMPLE
`
`READ BASE STATION
`INFORMATION
`
`MATCH DATA SAMPLE
`WITH BASE STATION
`INFORMATION
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`ESTIMATE DISTANCES
`BETWEEN MOBILE STATION
`AND BASE STATIONS
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`DETERMINE GEOGRAPHIC
`COORDINATES OF
`MOBILE STATION
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`MORE DATA
`SAMPLES OF THE
`MOBILE STATION
`AVAILABLE
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`Petitioner Uber Ex-1032, 0004
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`

`

`1
`LOCAL POSITONING SYSTEM
`
`US 6,748.224 B1
`
`BACKGROUND OF THE INVENTION
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`15
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`25
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`I. Field of the Invention
`The present invention relates to determining the position
`of a mobile Station; more Specifically, to locating a mobile
`station using time difference of arrival (TDOA).
`II. Description of the Related Art
`A global positioning System (GPS) is commonly used to
`provide a receiver with accurate measurements of its loca
`tion. The GPS receiver receives a signal from satellites and
`determines its positions by performing TDOA calculations
`based on the known position of the satellites. The receiver is
`generally attached to a vehicle or boat and is provided for
`this single purpose. The expense of the GPS receivers has
`generally limited its purchasers to luxury vehicle, aircraft,
`and boat owners.
`Digital cellular/PCS phones have become a very conve
`nient and inexpensive way for a person to communicate with
`other perSons or communication Systems from wherever the
`perSon is located. The person can also call 9-1-1 in the event
`of an emergency. However, to date, wireleSS communication
`Systems can not accurately determine the location of the
`caller without the use of Satellites and GPS.
`Current wireleSS communication Systems use multiple
`access techniques to combine Signals from different Sources
`to permit many users to share a common medium without
`mutual interference. One of the basic types of multiple
`access techniques is code division multiple access (CDMA).
`In CDMA, each base Station transmits a pilot channel Signal,
`which is essentially an unmodulated pseudo-random noise
`(PN) sequence. The PN sequence comprises a sequence of
`PN chips, and each PN chip corresponds to a distance of
`about 800.4 feet. Each base station transmits the pilot
`channel Signal using a different timing offset Such that
`mobile Stations can distinguish from which base Station a
`pilot channel Signal was transmitted.
`The mobile Station is time Synchronized with a Serving
`base Station, i.e., the base Station in which the mobile Station
`is in communication. The mobile Searches time intervals
`referred to as Search windows for the pilot channel Signals.
`Each base Station is configured to transmit its pilot channel
`Signal Such that mobile Stations can expect to begin receiv
`ing no more than one pilot channel Signal within each Search
`window. When the mobile station detects a pilot channel
`Signal, it measures the pilot channel Signal Strength and
`records the phase of the pilot channel signal, in terms of PN
`50
`chips, as the pilot channel Signal arrives at the mobile
`Station. If the pilot channel Signal Strength exceeds a pre
`determined threshold, then the base station that transmitted
`the pilot channel signal is “visible” to the mobile station. The
`measurements and recordings are transmitted from the
`mobile Station to the Serving base Station or Some other
`predetermined location over a reverse link.
`Conventional methods of determining a mobile Station's
`geolocation generally require an indication of distances
`between at least three “visible” base stations and the mobile
`Station. The distance between a base Station and a mobile
`Station is equal to the time At for a signal to travel from the
`base Station to the mobile Station, multiplied by a wave
`Speed u of the Signal. If Atu is a distance from the mobile
`Station (having geographic coordinates (Xoyo)) to a first base
`Station (having known geographic coordinates (x,y)), Atul
`is a distance from the mobile Station to a Second base Station
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`2
`(having known geographic coordinates (X2y2)), and Atsu is
`a distance from the mobile Station to a third base Station
`(having known geographic coordinates (x,y)), then based
`on the Pythagorean theorem, the following equations can be
`derived for a time of arrival (TOA) approach:
`
`(1)
`
`(2)
`
`(3)
`
`to determine the mobile position (x,y). However, in
`CDMA, the time. At is unknown because mobile stations
`have no absolute time reference to measure At.
`ATDOA approach reduces the number of equations from
`three to two (equation (3) minus equation (1) and equation
`(2) minus equation (1)). The TDOA approach provides
`accurate location determinations if no System measurement
`errors or multi-path effects, described below, are present.
`Unfortunately, System measurement errors and multi-path
`effects generally exist and cause deviations from true loca
`tion determinations. Therefore the above equations cannot
`be used directly to accurately determine the mobile Station
`M’s geolocation.
`SUMMARY OF THE INVENTION
`The present invention addresses these problems by pro
`viding a local positioning System (LPS) designed to use
`radio propagation parameters in code-division multiple
`access (CDMA) forward links or time-division multiple
`access (TDMA) reverse links to estimate a mobile station's
`position.
`The LPS determines the position of the mobile using
`triangulation methods by minimizing two set of equations,
`called cost functions. The first Set of cost functions represent
`distance errors from the “visible” base stations to the mobile
`Station, and the Second Set of cost functions represents
`position errors in the location estimation of the mobile
`Station. Both Sets of cost functions include variables com
`mon to more than one of the cost functions within the Set.
`The cost functions are minimized by estimating values for
`the unknown variables within each equation So that the
`distance or position errors in the Set are as close to Zero as
`possible.
`To determine the geographical coordinates of a mobile
`Station when the distances between the mobile Station and
`the base stations are not known, the LPS first estimates the
`distance from the mobile Station to the base Stations to
`mitigate the System measurement errors and multi-path
`effect. After the distances are estimated, the LPS estimates
`the geographic coordinates of the mobile station (Xoyo),
`based on the estimated distances.
`In a preferred embodiment, the LPS is a software imple
`mentation on a computer to determine the geographic loca
`tion (geolocation) of a mobile station. The LPS receives a
`data Sample including information indicating arrival times of
`pilot channel Signals at a mobile Station and accesses base
`Station information indicating the location of at least three
`cellular or PCS base stations to which the arrival time
`information is associated. The LPS then estimates the dis
`tances from the mobile Station to the base Stations by
`minimizing a first Set of equations or cost functions and
`estimates the geolocation of the mobile Station by minimiz
`ing a Second Set of equations or cost functions based on the
`estimated distances.
`
`Petitioner Uber Ex-1032, 0005
`
`

`

`US 6,748.224 B1
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`15
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`The LPS of the present invention provides the benefit of
`using existing equipment to provide GPS-like positioning
`capabilities. The LPS requires no additional Signal detection
`capabilities, and only requires a minor modification to the
`existing wireleSS telephone Systems. No additional hardware
`is needed other than the standard CDMA/TDMA system,
`making the LPS cost effective. The LPS can also solve the
`9-1-1 mobile location problem for wireless CDMA/TDMA
`systems. Therefore, the LPS can determine the position of a
`perSon in distress from their digital phone.
`BRIEF DESCRIPTION OF THE DRAWINGS
`The invention will be described in detail with reference to
`the following drawings, wherein like numerals represent like
`elements and:
`FIG. 1 illustrates a mobile station located inside of a
`triangle formed by three distinct base Stations,
`FIG. 2 illustrates a mobile station located outside of a
`triangle formed by three distinct base Stations,
`FIG. 3a is a schematic perspective view of the LPS
`implementation according to a preferred embodiment of the
`invention;
`FIG. 3b is a schematic perspective view of the LPS
`implementation according to another preferred embodiment
`of the invention; and
`FIG. 4 illustrates a flowchart of a preferred embodiment
`of the LPS;
`FIG. 5 is a chart illustrating an example performance
`analysis of the LPS.
`DETAILED DESCRIPTION OF THE
`INVENTION
`The embodiments described herein are used in a CDMA
`35
`forward link triangulation (FLT) system. It is understood
`that the embodiments are also applicable to a TDMA reverse
`link triangulation (RLT) system upon Synchronization of the
`base Stations.
`The LPS determines the geographic coordinates of the
`mobile Station by receiving a data Sample representing
`information regarding the mobile Station, accessing base
`Station information regarding at least three base Stations, and
`estimating the location of the mobile station. The LPS
`determines the location of the mobile Station by minimizing
`a first Set of equations or cost functions to estimate the
`distances between the mobile Station and base Stations based
`on the data Sample and the base Station information, and then
`minimizing a Second Set of equations or cost functions to
`estimate the geographic coordinates of the mobile Station.
`The LPS is based on TDOA which uses measured phase
`shift or chip offset information of the pilot channel Signals
`transmitted from particular base stations that are “visible” to
`the mobile Station. ATDOA triangulation approach requires
`time or propagation delay measurements from at least three
`“visible” base stations. If less than three base stations are
`“visible' to the mobile station, then the LPS will wait for a
`mobile station report of three “visible” base stations or
`adjust Signal Strength threshold levels to allow the mobile to
`recognize more pilot channel Signals from other base Sta
`tions. The mobile Station frequently measures the pilot
`channel Signal phases So that the location estimation can be
`accrued and made more precise over time.
`FIG. 1 shows a point representing mobile station M
`located inside a triangle of points representing “visible' base
`65
`Stations b1, b and b at respective distances d, d2 and d.
`from the mobile station M. The distances between the base
`
`4
`Stations are measured as: length bib between base Stations
`b and b, length bb between base stations b, and b, and
`length baba between base Stations b2 and b. Angles C.12, C.
`and C
`are formed by arcs bMb, b. Mbs and bMb,
`respectively. In FIG. 1, angle C
`is equal to 360 degrees
`minus angles C., and C. FIG. 2 is similar to FIG. 1 except
`mobile Station M is located outside triangle bibb and angle
`C.2s is equal to angles C.12 plus C-13.
`FIG. 3a illustrates a diagram of an LPS implementation.
`The LPS includes a computer 10 and an article of manu
`facture 20 and may be located at one of the base stations.
`The article of manufacture 20 includes a computer-readable
`medium and an executable program for locating the mobile
`station M.
`FIG. 3b illustrates an alternative LPS implementation.
`The LPS 1 includes the computer 10 for receiving a signal
`30 carrying the executable program for locating the mobile
`station M. The signal 30 is transmitted in a digital format
`either with or without a carrier wave.
`FIG. 4 illustrates a flowchart of LPS for locating the
`mobile station M in a preferred embodiment. At step S10,
`the LPS 1 reads in data samples (for example, Sector number,
`pilot phase and strength of the pilot channel signal) from the
`mobile station M. At step S20, the LPS 1 reads in a cell site
`table which includes information Such as the base station ID,
`Sector numbers of the base Stations, and the base Stations
`geographic location measured in, for example, latitude and
`longitude. At step S30, the sector numbers of the data
`Samples are matched with those in the cell Site table to
`determine from where the pilot channel Signals originated. If
`the pilot channel Signals are from at least three base Stations,
`then the triangle bb2b is formed, as shown in FIG. 1 or 2,
`and the distances between the mobile station M and the base
`Stations b, b and b and the geolocation of the mobile
`station M can be determined.
`The distances between mobile station M and the visible
`base Stations b, b and b are estimated at Step S40. The
`computer 10 calculates for distance di Such that a set of cost
`functions for distance errors are minimized and determines
`distances d and d based on the estimated distance d. The
`estimation of distance d and the determination of distances
`d and d based on distance d will be described below.
`The LPS determines the geographic coordinates of mobile
`station M at S50 using TDOA. The LPS 1 calculates the
`local coordinates of the mobile Station M, i.e., (Xo, yo) in
`relation to the Serving base station b, and converts the local
`coordinates (Xo, yo) to global latitude and longitude based on
`the known latitudes and longitudes of the base Stations b, b.
`and b. When Succeeding pilot channel Signal phase mea
`Surements and recordings exist, the geolocation of the
`mobile Station M can be re-estimated and averaged to
`provide an even more accurate analysis.
`Step S40-Estimating Distances Between the Mobile Sta
`tion and the Base Stations
`The two most critical System measurement errors in a
`TDOA approach are rounding errors in the pilot channel
`Signal phase measurement and Synchronization errors
`among base Stations. For the pilot channel Signal phase
`measurement, if one chip corresponds to 800.4 feet, then the
`rounding error (worst case half a chip) contributes to 400.2
`feet in deviation of location. The rounding error can be
`represented by random variable T when satisfying a uni
`form distribution.
`Ideally, each base Station is time Synchronized with the
`other base Stations. Each base Station could also be time
`Synchronized using a GPS clock. However, the actual clockS
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`Petitioner Uber Ex-1032, 0006
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`US 6,748.224 B1
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`S
`in the base stations tend to drift around a nominal value. The
`drifting error can be represented as a random variable T.,
`satisfying another uniform distribution. The influence of the
`error Sources can be added to equal System measurement
`error T, which is the sum of random variables T. plus T.
`Accordingly, a measured pilot channel Signal phase p is
`equal to a true pilot channel Signal phase plus a System
`measurement error T.
`TDOA works best if the measurements being used are
`those belonging to line-of-Sight (LOS) signals because a
`Straight line is the shortest line between two points.
`Unfortunately, it is not always possible for the mobile station
`M to receive LOS signals from the base stations b, b. and
`b. A single signal transmitted from any of the base stations
`bi, b and b may reflect off different objects Such as
`buildings, trees and vehicles before it reaches the mobile
`Station M, and therefore take a longer path than if the Signal
`were a LOS Signal. This multi-path effect causes a delay in
`the arrival of the signal and detrimentally affects the TDOA
`estimate.
`Since there is no guarantee that a mobile station M will
`acquire line-of-Sight (LOS) signals from the visible base
`Stations b, b. and b, the delay in arrival time caused by a
`multi-path Signal must be accounted for when using TDOA
`to determine the distance between the mobile station M and
`25
`the base Stations b, b and b. However, the amount of delay
`differS depending on the distance and the objects located
`between the mobile station M and the base stations b, b.
`and b and is therefore very difficult to model. Accordingly,
`a single multi-path parameter u represents the proportional
`time delay caused by the multi-path effect and is modeled as
`a non-random parameter instead of a random number
`because the Single multi-path parameter it must be estimated
`for all pilot channel Signals. Multi-path parameter it is
`generally less than 1, and would equal its maximum of 1 if
`the mobile station M only acquired LOS signals from the
`Visible base Stations b, b and b.
`It should be noted that one Single multi-path parameter ut
`is assumed which implies a homogenous multi-path effect.
`That is, the delay caused by the multi-path effect is assumed
`to be the same for each pilot channel Signal even though the
`multi-path effect on the pilot channel Signal from each of the
`base Stations b, b and b is different. A multi-path param
`eter u that represent a uniform extra delay can Substantially
`alleviate the multi-path effect. The multi-path parameter ut
`may be varied in a certain range defined by a model
`asSociated with typical environments Such as rural, urban,
`Suburban, highway, etc.
`Mobile station M does not know the exact time (as
`synchronized with GPS) that the base station b, transmits a
`pilot channel Signal nor the exact time that the mobile Station
`M receives the pilot channel Signal in order to determine the
`time that it takes for the pilot channel Signal to travel from
`the base station b, to the mobile station M. Therefore the
`distances d, d and d between the base Stations b, and the
`mobile station M are unknown.
`However, the base Stations are Synchronized with each
`other, and the mobile station M is synchronized with the
`serving base station b. Thus the mobile station M can record
`chip offsets of pilot channel Signal phases emitted from
`remote base Stations band b in relation to the pilot channel
`Signal of the Serving base Station b. Therefore, the mobile
`M can determine the additional time-after receipt of the
`pilot channel Signal from the Serving base Station
`b-required for the pilot channel Signals to travel from the
`65
`remote base Stations b and b to the mobile Station M
`because the phase of the remote base Stations b and b are
`
`6
`measurable in relation to the phase of the Serving base
`Station b, which is set to Zero due to the Synchronization of
`the mobile station M with the base station b. The mobile
`Station M identifies a pilot channel Signal phase p as a phase
`difference between the pilot channel Signal phase recordings
`of base Stations b and b, and identifies a pilot channel
`Signal phase p as a phase difference between the pilot
`channel Signal phase recordings of base Stations b1 and b.
`Accordingly, distance dequals distance d plus 800.4 feet
`times the pilot channel Signal phase p, or
`d=d+800.4(p)ft
`(4)
`Similarly, distance d equals distance d plus 800.4 feet
`times the pilot channel signal phase ps, or
`d=d+800.4(p)ft
`
`(5)
`
`However, distance d must be estimated before distances da
`and d can be determined.
`Consequently, the LPS 1 estimates distance d. To Search
`for an estimate for distance d, the following equations
`(6)–(8) are cost functions that are minimized for distance
`errors F12, Fs, and F23:
`
`for distance d, multi-path parameter u and angles C., and
`Substituting for distances d and d based on equations (4)
`and (5). The cost functions for distance errors F2, F and
`F must be minimized to arrive at the best estimate for
`distance d.
`The minimization of cost functions F, F, and F can
`be accomplished using well known minimization
`approaches, Such as by Steepest decent or incremental Search
`with respect to d. For example, using an incremental Search
`approach, the above cost functions can be minimized by
`estimating a range for the distance d and the multi-path
`parameter u, Solving the equations (6)–(8) for each prede
`termined increment in the ranges, and Selecting the distance
`d, multi-path parameter u and angles C2, C. and C2a that
`provide the distance errorS F, F, and F closest to Zero.
`After distance d is estimated, distances d and d can be
`determined using equations (4) and (5).
`Equations (6)–(8) have four unknown values, namely
`distance d, the multi-path parameter it, and angles C.2 and
`C. AS discussed above, angle C
`is equal to 360 degrees
`minus angles C.
`and C. when the mobile Station M is
`located inside triangle bb2bs. Angle C2 is equal to angles
`C.
`plus C. when mobile Station M is located outside
`triangle bibaba. However, the angles C.12 and C. are deter
`mined based on the estimated distance d, in other words the
`Values of the angles C.12 and C.
`are determined according
`the value of distance d.
`A skilled practitioner would readily understand that the
`CDMA (and TDMA) systems can measure a round trip delay
`of a pilot channel Signal emitted from the Serving base
`station b to the mobile station M and back to the serving
`base station b. This round trip delay provides the benefit of
`allowing the LPS 1 to use a more narrow Scope for estimat
`ing the range of distance d.
`Step S50-Determining the Geolocation of the Mobile
`Station
`After distances d, d and d are estimated, then the
`mobile station M Cartesian coordinates (Xo, yo) can be
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`Petitioner Uber Ex-1032, 0007
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`

`

`7
`estimated by minimizing equations (9)-(11) for cost func
`tions G, G and G:
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`US 6,748.224 B1
`
`8
`is equal to angle C.12 plus
`In the above example, angle C
`angle C. Therefore the mobile Station M is not located
`within triangle bibbs, but instead is located outside of
`length bb.
`Distance Deviation of Estimates
`The lower line in FIG. 5 shows an example of distance
`deviation (ft) between the true location and LPS estimated
`location of mobile station M based on the time deviation (us)
`caused by System measurement errors, including rounding
`errors in the pilot channel Signal phase measurement and
`Synchronization errors. The upper line represents the maxi
`mum error for performance over a Snapshot of time. If a
`Snapshot is extended over time and the distance deviations
`are averaged, the distance deviation would become the lower
`mean error line. Accordingly, if the base Stations are
`Synchronized, the rounding error in pilot channel Signal
`phase measurement alone approaches 200 feet.
`Reverse Link Triangulation (RLT)
`In North American TDMA systems, the time arrival is
`obtained at the base stations rather than at the mobile
`Stations. The mobile Station transmits a coded digital veri
`fication color code (CDVCC) signal as the identity of the
`mobile station. Upon receiving the CDVCC signal, the
`receiving base Station time Stamps the time of receiving the
`CDVCC signal. If the base stations are synchronized, then
`the base Stations determine the relative time differences
`between arrival of the CDVCC signals by Subtracting the
`time of the receipt of the Signal at the first base Station from
`the time of the later received Signals at other base Stations.
`Accordingly, the LPS is applicable to both CDMA and
`TDMA systems.
`Therefore, equations (6)–(11) can also be applied to
`TDMARLT geolocation systems if the clock signals or base
`Stations involved in locating a particular mobile Station are
`Synchronized. The Synchronization could be done by instal
`lation of GPS. Reverse link signals are transmitted from
`mobile Stations to base Stations through the reverse link,
`which is generally a different frequency band than the
`forward link of CDMA systems, but in a same frequency
`band and different time slots for TDMA systems.
`ATDMA reverse link would provide the benefits of better
`location accuracy if the time arrival is measured at the base
`Stations because there would be no chip-rounding error as in
`a CDMA forward link. In addition, the power control in
`TDMA is not as stringent as in CDMA, therefore making it
`easier for Several base Station to “see' Signals from the
`mobile. Inputs needed by TDMA reverse link triangulation
`include the identity of the mobile requesting location
`Service, the relative time arrivals at the base Stations, loca
`tion (latitude/longitude) of all base stations, and the round
`trip delay (measured continuously in TDMA for time align
`ment purposes). The strength of signal from the mobile
`Station is also desired and can be measured at neighboring
`base Stations for assistance of handoff.
`While this invention has been described in conjunction
`with Specific embodiments thereof, it is evident that many
`alternatives, modifications, and variations will be apparent
`to those skilled in the art. Accordingly, the preferred embodi
`ments of the invention as set forth herein are intended to be
`illustrative, not limiting. Various changes may be made
`without departing from the Spirit and Scope of the invention
`as defined in the following claims.
`What is claimed is:
`1. A method for determining the position of a mobile
`Station, comprising the Steps of:
`(a) receiving pilot channel signal information indicating
`arrival times of pilot channel Signals at the mobile
`Station;
`
`where G, i=1, 2, and 3 represents the position error and is
`Zero in an ideal case. However, Since distances d, d and da
`are estimated, equations (7-9) will not be solved exactly, but
`the best estimate of (Xo, yo) can be found by minimizing G.
`Example Estimation and Coordinate Conversion
`The mobile station M is synchronized with the base
`Stations. Consequently, in the mobile Station M reply mes
`Sage that is sent back to base Station b, the phase shift of the
`reference pilot channel Signal transmitted by base Station b
`is Set to Zero. The pilot channel Signal phases from base
`Stations band b are recorded in chip off-sets from the Zero
`phase shift of base Station b. Accordingly, once distance d
`is estimated, distances d and d can be determined directly
`as discussed above.
`In accordance with steps S10 and S20 of FIG. 4, the LPS
`1 gathers input information including mobile Station M
`information and base station b, b. and b information. For
`example, the mobile Station M records pilot channel Signals
`emitted from base Station b with a base Station identifying
`pilot PN of 432 and a pilot channel signal strength of 17
`(-8.5 dB); from base station b with a base station identi
`fying pilot PN of 76, a pilot channel signal phase p equal
`to 4 PN chips, and a pilot channel Signal Strength of 21
`(-10.5 dB); and from base station b with a base station
`identifying pilot PN of 220, a pilot channel Signal phase p
`equal to 3 PN chips, and a pilot channel Signal Strength of
`19 (–9.5 dB). In accordance with step S30 of FIG. 4, the
`pilot PNs that are reported by the mobile station M are
`matched with pilot PNs in the sector information stored in a
`cell Site table to determine from which base Stations b, b.
`and b the pilot channel Signals were Sent. Here, base Station
`b is cell number 138, transmitting a pilot PN of 432 and is
`located at latitude 40.861389 and longitude -73.864167;
`base station b is cell number 140, transmitting a pilot PN of
`76 and is located at latitude 40.867500 and longitude
`-73.884722; and base station b is cell number 43, trans
`mitting a pilot PN of 220 and is located at latitude 40.878.889
`and longitude -73.871389.
`The base Station latitudes and longitudes are converted
`into a local coordinate System (x,y). Base Station b’s
`coordinates (0,0) are set as the origin, base station bas
`coordinates (x,0) are set to be on the X-axis, and base Station
`b's coordinates (X, y) are determined from the known
`distances among the base Stations.
`In accordance with step S40 of FIG. 4, cost function
`equations (6)–(8) are then minimized to estimate that dis
`tance d=0.801 miles, multi-path parameter u=0.98, angle
`C=1.784084 radians, angle O.-3.002281 radians and
`angle C=1.218859 radians. Based on estimated distance
`d, distances d and d are determined directly as described
`above to equal 0.983620 miles and 0.839603 miles, respec
`tively. In accordance with step S50 of FIG. 4, equations
`(9)-(11) are then minimized to determine that the local
`Cartesian coordinates (x, y) equal (0.237018, 0.357580).
`These coordinates can be converted back to latitude and
`longitude so that the mobile station M's location can be
`more easily marked on a map to show which Street it is
`located. In this example, the local Cartesian coordinates
`(0.237018, 0.357580) of the mobile station M's geographic
`location are converted to latitude 40.867465 and longitude
`-73-865885.
`
`15
`
`25
`
`35
`
`40
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`45
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`50
`
`55
`
`60
`
`65
`
`Petitioner Uber Ex-1032, 0008
`
`

`

`US 6,748.224 B1
`
`9
`bestimating a distance from the mobile station to one of
`a plurality of base Stations by minimizing a set of
`distance error cost functions including angles formed
`by the base Stations and the mobile Station; and
`c) estimating the location of the mobile Station by
`minimizing a Set of position error cost functions based
`on the pilot channel Signal information and on base
`Station information indicating the location of the plu
`rality of base stations to which the arrival time infor
`mation is associated.
`2. The method of claim 1, wherein the position error cost
`functions are derived from the equations:
`
`where u is a multi-path effect parameter, d is a distance
`from the mobile Station to a first base Station, d i