US007 116987B2
`
`(12) United States Patent
`Spain, Jr. et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,116,987 B2
`Oct. 3, 2006
`
`(54) LOCATION ESTIMATION OF WIRELESS
`TERMINALS THROUGH PATTERN
`MATCHING OF DEDUCED AND EMPIRICAL
`SIGNAL-STRENGTH MEASUREMENTS
`
`(75) Inventors: David Stevenson Spain, Jr., Portola
`Valley, CA (US); Robert Lewis
`Martin, Antioch, CA (US); Tarun
`Kumar Bhattacharya, San Jose, CA
`(US)
`(73) Assignee: Polaris Wireless, Inc., Santa Clara, CA
`(US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 200 days.
`(21) Appl. No.: 10/798.988
`
`(*) Notice:
`
`(22) Filed:
`
`Mar. 12, 2004
`
`(65)
`
`Prior Publication Data
`US 2005/OO14518 A1
`Jan. 20, 2005
`
`Related U.S. Application Data
`(60) Provisional application No. 60/488,866, filed on Jul.
`19, 2003.
`
`(51) Int. Cl.
`(2006.01)
`H04O 7/20
`(52) U.S. Cl. ............................... 455/456.1; 455/456.5;
`455/513
`(58) Field of Classification Search ............. 455/4.56.1,
`455/456.2, 456.3, 456.5, 513, 457, 134, 115.3,
`455/161.3, 402, 226.1, 226.2
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`4,818,998 A
`4/1989 Apsell et al.
`
`1, 1990 Sheffer
`4,891,650 A
`3/1990 Apsell et al.
`4,908,629 A
`3, 1994 LO
`5,293,642 A
`3, 1994 Vendetti et al.
`5,295,180 A
`2f1995 Bruckert et al.
`5,390,339 A
`5, 2001 LeBlanc et al.
`6,236,365 B1
`6.249.252 B1* 6/2001 Dupray ....................... 342/450
`6,266,534 B1* 7/2001 Raith et al. .
`... 455,456.3
`6,466.938 B1 * 10/2002 Goldberg .................... 7O7/1OO
`6,658.258 B1* 12/2003 Chen et al. ....
`... 455,456.1
`6,799,047 B1 * 9/2004 Bahl et al. ............... 455,456.1
`6,839,560 B1
`1/2005 Bahl et al.
`2003/02201 16 A1* 11/2003 Sagefalk et al. ......... 455,456.1
`2004/0152470 A1* 8/2004 Spain ...................... 455,456.1
`2004/0180671 A1* 9/2004 Spain ...................... 455,456.1
`FOREIGN PATENT DOCUMENTS
`WO 98,10538
`12/1998
`WO
`* cited by examiner
`Primary Examiner CongVan Tran
`(74) Attorney, Agent, or Firm—DeMont & Breyer, LLC
`
`ABSTRACT
`(57)
`A method of estimating the location of a wireless terminal is
`disclosed. The illustrative embodiment of the present inven
`tion is based on the observation that the signal strength of a
`signal from a transmitter is different at Some locations, and,
`therefore, the location of a wireless terminal can be esti
`mated by comparing the signal strength it currently observes
`against a map or database that correlates locations to signal
`strengths. Furthermore, the illustrative embodiment deduces
`the signal strength of one or more base stations control
`channels at the wireless terminal based on the principal of
`reciprocity, whether or not the wireless terminal can actually
`receive the base stations control channels but so long as the
`base station can receive and measure the uplink signal from
`the wireless terminal. The deduced signal-strength measure
`ments can then used—alone or in combination with the
`empirical signal-strength measurements—to estimate the
`location of the wireless terminal.
`
`19 Claims, 14 Drawing Sheets
`
`Populate Signat-Strength Database
`
`Query Wireless Switching Center(s) to Provide Uplink and Downlink Signal
`Strength Measurements
`
`
`
`Deduce Signal Strengths of Downlink Signals From Uplink Signal-Strength
`Measurements
`
`Estimate Location of Wireless Terminal Based On Downlink Signal-Strength
`Measurements, Downlink Deduced Signal Strengths, and Signal-Strength
`Database
`
`
`
`
`
`Use Location of Wireless Terminal
`
`401
`
`402
`
`403
`
`404
`
`405
`
`Page 1 of 25
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`SAMSUNG EX-1008
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`US 7,116,987 B2
`
`1.
`LOCATION ESTMLATION OF WIRELESS
`TERMINALS THROUGH PATTERN
`MATCHING OF DEDUCED AND EMPIRCAL
`SIGNAL-STRENGTH MEASUREMENTS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application claims the benefit of:
`i. U.S. Provisional Patent Application No. 60/488,866, filed
`19 Jul. 2003, and entitled “Location Estimation of Wire
`less Terminals Through Pattern Matching of Deduced
`Signal Strengths, which application is also incorporated
`by reference.
`The underlying concepts, but not necessarily the nomen
`clature, of the following are incorporated by reference:
`i. U.S. Pat. No. 6,269,246, issued 31 Jul. 2001;
`ii. U.S. patent application Ser. No. 09/532,418, filed 22 Mar.
`2000;
`iii. U.S. patent application Ser. No. 10/128,128, filed 22 Apr.
`2002:
`iv. U.S. patent application Ser. No. 10/299,398, filed 18 Nov.
`2002:
`v. U.S. patent application Ser. No. 10/357,645, filed 4 Feb.
`2003;
`vi. U.S. patent application Ser. No. 60/449,569, filed 24 Feb.
`2003; and
`vii. U.S. patent application Ser. No. 60/461,219, filed 8 Apr.
`2003.
`
`FIELD OF THE INVENTION
`
`10
`
`15
`
`25
`
`30
`
`The present invention relates to telecommunications in
`general, and, more particularly, to a technique for estimating
`the location of a wireless terminal.
`
`35
`
`BACKGROUND
`
`2
`Such interested parties might include both the user of the
`wireless terminal and remote parties. There are a variety of
`reasons why the user of a wireless terminal might be
`interested in knowing his or her own location. For example,
`the user might be interested in telling a remote party where
`he or she is.
`There are a variety of reasons why a remote party might
`be interested in knowing the location of the user. For
`example, the recipient of a 911 emergency call from a
`wireless terminal might be interested in knowing the loca
`tion of the wireless terminal so that emergency services
`vehicles can be dispatched to that location.
`There are many techniques in the prior art for estimating
`the location of a wireless terminal.
`In accordance with one technique, the location of a
`wireless terminal is estimated to be at the centroid of the cell
`in which the wireless terminal is located. This technique is
`advantageous in that it does not require that additional
`hardware be added to the wireless terminal or to the wireless
`telecommunications system, and this means that the first
`technique can be inexpensively implemented in legacy sys
`tems. The first technique is only accurate, however, to a few
`kilometers, and, therefore, it is generally not acceptable for
`applications (e.g., emergency services dispatch, etc.) that
`require higher accuracy.
`In accordance with a second technique, the location of a
`wireless terminal is estimated by triangulating the angle of
`arrival or the time of arrival of the signals transmitted by the
`wireless terminal to be located at various receivers. This
`technique is accurate to within a few hundreds of meters and
`is advantageous in that it can be used with legacy wireless
`terminals. It is disadvantageous, however, in that it generally
`requires that hardware be added to the telecommunication
`system's base stations, and this is very expensive.
`In accordance with a third technique, the location of a
`wireless terminal is estimated by a radio navigation unit,
`such as a Global Positioning System (GPS) receiver, that is
`incorporated into the wireless terminal. This technique is
`accurate to within tens of meters and is advantageous in that
`it does not require that additional hardware be added to the
`telecommunication systems infrastructure. The third tech
`nique is disadvantageous, however, in that it cannot be used
`with legacy wireless terminals that do not comprise a radio
`navigation unit.
`Therefore, the need exists for a technique for estimating
`the location of a wireless terminal with higher resolution
`than the first technique and that can be inexpensively
`implemented in legacy systems.
`
`SUMMARY OF THE INVENTION
`
`The present invention enables the estimation of the loca
`tion of a wireless terminal without the addition of hardware
`to either the wireless terminal or to the telecommunication
`system's base stations. Some embodiments of the present
`invention are, therefore, ideally suited for use with legacy
`telecommunications systems.
`The illustrative embodiment of the present invention is
`based on the observation that the signal strength of a signal
`from a transmitter is different at Some locations, and, there
`fore, the location of a wireless terminal can be estimated by
`comparing the signal strength it currently observes against a
`map or database that correlates locations to signal strengths.
`For example, if a particular radio station is known to
`transmit a strong signal to a first location and a weak signal
`to a second location, and a given wireless terminal at an
`unknown location is receiving the radio station with a weak
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`FIG. 1 depicts a map of a geographic region that is
`serviced by a wireless telecommunications system, which
`system provides wireless telecommunications service to
`wireless terminals (e.g., wireless terminal 101) within the
`region. The heart of the telecommunications system is
`wireless switching center 110, which might also be known
`as a mobile switching center (“MSC) or a mobile telephone
`45
`switching office (“MTSO).
`Typically, wireless Switching center 111 is connected
`through a plurality of intermediate network elements (e.g.,
`base station controllers, etc.) to a plurality of base stations
`(e.g., base stations 102-1, 102-2, and 102-3), which are
`dispersed throughout the geographic area serviced by the
`system. As depicted in FIG. 1, base station 102-2 serves
`wireless terminal 101.
`As is well known to those skilled in the art, wireless
`Switching center 111 is responsible for, among other things,
`establishing and maintaining calls between wireless termi
`nals and between a wireless terminal and a wireline terminal
`(which is connected to the system via the local and/or
`long-distance telephone networks and which are not shown
`in FIG. 1).
`The salient advantage of wireless telecommunications
`over wireline telecommunications is the mobility that is
`afforded to the users of the wireless telecommunications
`system. On the other hand, the salient disadvantage of
`wireless telecommunications lies in that fact that because the
`user is mobile, an interested party might not be able to
`readily ascertain the location of the user.
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`signal, it is more likely that the wireless terminal is at the
`second location than it is at the first location.
`The accuracy of the estimate of the location of a wireless
`terminal can be enhanced when the principle uses multiple
`transmitters and multiple signals. A simplified example
`illustrates this point. A first radio station, Radio Station A,
`transmits a strong signal to Location 1 and Location 2, but
`a weak signal to Location 3 and Location 4, and a second
`radio station, Radio Station B, transmits a strong signal to
`Location 1 and Location 3, but a weak signal to Location 2
`and Location 4. This information is Summarized in the table
`below and forms the basis for a map or database that
`correlates locations to signal strength.
`
`TABLE 1.
`
`Illustrative Signal Strength Database (Absolute Signal Strength
`
`Radio Station A
`
`Radio Station B
`
`Location 1
`Location 2
`Location 3
`Location 4
`
`Strong Signal
`Strong Signal
`Weak Signal
`Weak Signal
`
`Strong Signal
`Weak Signal
`Strong Signal
`Weak Signal
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`receive the base stations control channels but so long as the
`base station can receive and measure an uplink traffic
`channel signal from the wireless terminal. This is accom
`plished in accordance with the principal of reciprocity. The
`principal of reciprocity states that the attenuation of a signal
`transmitted from Point A to Point B is the same as that for
`a signal that is transmitted from Point B to Point A.
`In other words, the signal strength of the base stations
`control channel signal at the wireless terminal, R can be
`deduced from the strength at which the control channel
`signal is transmitted by the base station, T, and the attenu
`ation of that signal between the base station and the wireless
`terminal. A by the function:
`(Eq. 1)
`R-To-Aid
`The principal of reciprocity indicates that the attenuation
`of the signal between the base station and the wireless
`terminal, A, equals the attenuation of that signal between
`the wireless terminal and the base station, A., as represented
`by Equation 2:
`
`The attenuation of the signal between the wireless termi
`nal and the base station, A, is equal to the strength at which
`the signal is transmitted by the wireless terminal, T, minus
`the signal strength of the signal as measured by the base
`station, R., as represented by Equation 3:
`(Eq. 3)
`A-T-R.
`By Substituting Equation 3 into Equation 2 and Equation
`2 into Equation 1, the signal strength of the base stations
`control channel signal at the wireless terminal, R can be
`deduced from the strength at which the control channel
`signal is transmitted by the base station, T, the strength at
`which the signal is transmitted by the wireless terminal, T.,
`and the signal strength of the uplink traffic channel signal
`from the wireless terminal as measured by the base station,
`R, as represented by Equation 4:
`
`The deduced signal-strength measurements can then
`used—alone or in combination with the empirical signal
`strength measurements—to estimate the location of the
`wireless terminal.
`The illustrative embodiment comprises: receiving a sig
`nal-strength measurement for a first downlink signal that is
`received by a wireless terminal and a signal-strength mea
`Surement for an uplink signal that is transmitted by the
`wireless terminal; and estimating the location of the wireless
`terminal based on the signal-strength measurement for the
`first downlink signal and on the signal-strength measure
`ment for the uplink signal.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 depicts a map of a portion of a wireless telecom
`munications system in the prior art.
`FIG. 2 depicts a map of the illustrative embodiment of the
`present invention.
`FIG. 3 depicts a block diagram of the salient components
`of location system 212.
`FIG. 4 depicts a broad overview of the salient operations
`performed by the illustrative embodiment in ascertaining the
`location of wireless terminal 201 in geographic region 200.
`FIG. 5 depicts a flowchart of the salient operations
`performed in operation 401.
`
`If a given wireless terminal at an unknown location receives
`Radio Station A with a weak signal and Radio Station B with
`a strong signal, it is more likely that the wireless terminal is
`at Location 3 than it is at either Location 1, 2, or 4.
`Furthermore, the accuracy of the estimate of the location
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`of a wireless terminal can be enhanced when the signal
`strength of each signal at each location is quantified. A
`simplified example illustrates this point. If a particular radio
`station is known to be received in one location with a
`strength of -50 dBm, at a second location with a strength of
`35
`-53 dBm, and at a third location with a strength of -55 dBm,
`then the reception of the signal with a strength of -56 dBm
`Suggests that the wireless terminal is more likely at the third
`location than at either the first or second location.
`In the prior art, a wireless terminal measures the signal
`strength of the control channels of the base stations that it
`can receive and that are not serving it and reports some or
`all of those signal-strength measurements back to the wire
`less Switching center. In the prior art this is performed so that
`the wireless Switching center can intelligently decide which
`base station the wireless terminal should be served by. In
`accordance with the illustrative embodiment of the present
`invention, these signal-strength measurements are also used,
`in conjunction with a map or database that correlates loca
`tions to signal strength, to estimate the location of the
`wireless terminal.
`In general, more signal-strength measurements provide a
`better estimate of the location of the wireless terminal than
`fewer signal-strength measurements, and, therefore, the
`acquisition of additional signal-strength measurements is
`55
`typically advantageous. One way of acquiring an additional
`signal-strength measurement is to actually physically mea
`Sure a signal at the wireless terminal, but most legacy
`terminals are not equipped to measure and report on an
`arbitrary number of signals.
`Another way of acquiring a 'signal-strength measure
`ment is by inference or deduction based on other informa
`tion, and this is what the illustrative embodiment does.
`In particular, the illustrative embodiment deduces the
`signal strength of one or more base stations control chan
`nels at the wireless terminal based on the principal of
`reciprocity, whether or not the wireless terminal can actually
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`FIG. 6 depicts a map of how geographic region 200 is
`partitioned into 500 locations in accordance with the illus
`trative embodiment of the present invention.
`FIG. 7a depicts a graph that shows that the signal strength
`of an electromagnetic signal decreases, in general, as a
`function of the distance from the transmitter and in an
`environment with no radio frequency obstacles.
`FIG.7b depicts a graph that shows that the signal strength
`of an electromagnetic signal decreases, in general, as a
`function of the distance from the transmitter and in an
`environment with two radio frequency obstacles.
`FIG. 8 depicts a map of the signal-strength measurements
`of the signal radiated from base station 202-1 at each
`location in geographic region 200.
`FIG.9 depicts a map of the signal-strength measurements
`of the signal radiated from base station 202-2 at each
`location in geographic region 200.
`FIG. 10 depicts a map of the signal-strength measure
`ments of the signal radiated from base station 202-3 at each
`location in geographic region 200.
`FIG. 11 depicts a flowchart of the salient operations
`performed in operation 402
`FIG. 12 depicts a flowchart of the salient operations
`performed in operation 1102.
`FIG. 13 depicts a flowchart of the salient operations
`performed in operation 1103.
`FIG. 14 depicts a flowchart of the salient operations
`performed in operation 404.
`
`DETAILED DESCRIPTION
`
`6
`off MeasurementRequest and Handoff MeasurementRe
`quest2 to elicit signal-strength measurements from another.
`Base stations 202-1, 202-2, and 202-3 are well-known to
`those skilled in the art and communicate with wireless
`Switching center 211 through cables and other equipment
`(e.g., base station controllers, etc.) that are not shown in FIG.
`2. As depicted in FIG. 2, wireless terminal 201 is serviced
`by base station 202-2. Although the illustrative embodiment
`comprises three base stations, it will be clear to those skilled
`in the art how to make and use embodiments of the present
`invention that comprise any number of base stations.
`Each of base stations 202-1, 202-2, and 203-3 is capable,
`in well-known fashion, of:
`i. measuring the signal strength of an uplink traffic channel
`signal as transmitted by wireless terminal 201 and report
`ing that measurement to wireless Switching center 211;
`and
`ii. informing wireless Switching center 211 of the strength at
`which it transmits the control channel.
`The first of these capabilities is performed, for example, by
`the Digital Locate Radio in IS-136 TDMA systems. It will
`be clear to those skilled in the art how to make and use
`alternative embodiments of the present invention in which
`Some of the base stations measure another uplink signal,
`Such as an uplink signaling channel signal, etc.
`In accordance with the illustrative embodiment, base
`station 202-1 receives and measures the signal strength of
`the uplink signal S (depicted as a dashed Zig-Zag arrow in
`FIG. 2) from wireless terminal 201. Base station 202-1 is in
`the vicinity of wireless terminal 201, but base station 202-1
`is neither (1) the serving base station for wireless terminal
`201 nor (2) on wireless terminal 201’s list of neighboring
`base stations. Although the illustrative embodiment depicts
`only one base station in the vicinity of wireless terminal 201
`for receiving and measuring the strength of the uplink signal
`S and that is neither (1) the serving base station nor (2) on
`wireless terminal 201’s list of neighboring base stations, it
`will be clear to those skilled in the art how to make and use
`embodiments of the present invention that have any number
`of Such base stations.
`In accordance with the illustrative embodiment, base
`station 202-2 is the serving base station for wireless terminal
`201 and, therefore, base station 202-2 receives and measures
`the signal strength of the uplink signal S (depicted as a
`dashed zig-zag arrow in FIG. 2) from wireless terminal 201.
`In accordance with the illustrative embodiment, wireless
`terminal 201 does not measure the signal strength of the
`control channel from base station 202-2. In accordance with
`the illustrative embodiment, wireless terminal 201 receives
`a downlink traffic channel (depicted as a solid Zig-Zag arrow
`in FIG. 2) from base station 202-2. Although the illustrative
`embodiment depicts only one serving base station for wire
`less terminal 201, it will be clear to those skilled in the art
`how to make and use embodiments of the present invention
`that have one or more serving base stations (e.g., in IS-95
`Code-Division Multiple Access systems, etc.).
`In accordance with the illustrative embodiment, base
`station 202-3 is on wireless terminal 201’s list of neighbor
`ing base stations, and, therefore, wireless terminal 201
`receives and measures the signal strength of the control
`channel (depicted as a dotted Zig-Zag arrow in FIG. 2) from
`base station 202-3. Although the illustrative embodiment
`depicts only one base station on wireless terminal 201’s list
`of neighboring base stations, it will be clear to those skilled
`in the art how to make and use embodiments of the present
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`FIG. 2 depicts a map of the illustrative embodiment of the
`present invention, which comprises: wireless Switching cen
`ter 211, location system 212, base stations 202-1, 202-2, and
`202-3, and wireless terminal 201, which are interconnected
`as shown. The illustrative embodiment provides wireless
`telecommunications service to most of geographic region
`200, in well-known fashion, and is also capable of estimat
`ing the location of wireless terminal 201 within geographic
`region 200.
`The illustrative embodiment operates in accordance with
`the Global System for Mobile Communications (formerly
`known as the Groupe Speciale Mobile), which is ubiqui
`tously known as “GSM. After reading this disclosure,
`however, it will be clear to those skilled in the art how to
`make and use embodiments of the present invention that
`operate in accordance with other protocols, such as the
`Universal Mobile Telephone System (“UMTS”), CDMA
`2000, and IS-136 TDMA.
`Wireless switching center 211 is a switching center as is
`well-known to those skilled in the art in most respects but is
`different in that it is capable of communicating with location
`system 212 in the manner described below. After reading
`this disclosure, it will be clear to those skilled in the art how
`to make and use wireless switching center 211. It will also
`be clear to those skilled in the art that a wireless switching
`center is also known by other names. Such as a mobile
`Switching center, a mobile telephone Switching office, etc.
`The illustrative embodiment comprises one wireless
`Switching system, but after reading this specification it will
`be clear to those skilled in the art how to make and use
`embodiments of the present invention that use two or more
`systems to obtain signal-strength measurements. Typically,
`this is useful when a wireless terminal is near the boundary
`of one or more systems. When two or more systems are used
`to obtain signal-strength measurements, one wireless
`Switching center can use the IS-41 protocol messages Hand
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`invention in which a wireless terminal has any number of
`base stations in its list of neighboring base stations.
`Base station 202-3 is in the vicinity of wireless terminal
`201, and, therefore, base station 202-3 receives and mea
`Sures the signal strength of the uplink signal S (depicted as
`a dashed Zig-Zag arrow in FIG. 2) from wireless terminal
`201. This is not a necessary consequence of base station
`202-3 being on wireless terminal 201’s list of neighboring
`base stations, but is merely a result of the proximity of base
`station 202-3 and wireless terminal 201. In some embodi
`ments of the present invention a base station on a wireless
`terminals list of neighboring base stations will be able to
`receive and measure the signal strength of the uplink signal
`S from wireless terminal 201 and in some cases it will not.
`It will be clear to those skilled in the art how to make and
`use embodiments of the present invention in which some,
`none, or all of the base stations on a wireless terminals list
`of neighboring base stations are able to receive and measure
`the signal strength of the uplink signal S from wireless
`terminal 201.
`Wireless terminal 201 is a standard GSM wireless termi
`nal as it is currently manufactured and used throughout the
`world. Wireless terminal 201 is equipped, in well-known
`fashion, with the hardware and Software necessary to mea
`Sure and report to wireless Switching center 211 on the signal
`25
`strength of signals from the base stations that are on its list
`of neighboring base stations.
`A GSM wireless terminal, such as wireless terminal 201,
`is capable of reporting the signal strength of a signal as one
`of 64 levels between -47 dBm and -110 dBm. Any signal
`stronger than -47 dBm is reported as -47 dBm, and any
`signal weaker than -110 dBm is reported as -110 dBm.
`In accordance with the illustrative embodiment of the
`present invention all of the specific portions of the radio
`frequency spectrum fall within the same band that wireless
`terminal 201 uses to communicate with