a2, United States Patent
`US 6,181,944 B1
`(10) Patent No.:
`Uebayashiet al.
`(45) Date of Patent:
`Jan. 30, 2001
`
`
`US006181944B1
`
`(54) MOBILE STATION POSITION ESTIMATION
`SCHEME FOR CELLULAR MOBILE
`COMMUNICATION SYSTEM
`
`(75)
`
`Inventors: Shinji Uebayashi; Kouji Ohno; Seizo
`Onoe,all of Yokohama (JP)
`
`(73) Assignee: NTT Mobile Communications
`Network Inc., Tokyo (JP)
`
`(*) Notice:
`
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`3/1999 Parl et al. oecceesecsseeneeeees 342/457
`5,883,598 *
`8/1999 Yun ow.
`wee 342/457
`5,945,949 *
`5,973,643 * 10/1999 Hawkesetal. ...
`we 342/457
`6,011,974 *
`1/2000 Cedervallet al.
`w. 455/456
`6,026,305 *
`1/2000 Salinger Ct al. eceeeseeeee 455/456
`* cited by examiner
`
`
`
`Primary Examiner—Daniel S. Hunter
`Assistant Examiner—Yemane Woldetatios
`(74) Attorney, Agent, or Firm—Oblon, Spivak, McClelland,
`Maier & Neustadt, P.C.
`
`(57)
`
`ABSTRACT
`
`(21) Appl. No.: 09/041,764
`(22)
`Filed:
`Mar. 13. 1998
`,
`,
`(30)
`Foreign Application Priority Data
`
`A mobile station position estimation scheme for a cellular
`mobile communication system whichis capable of estimat-
`ing a position of a mobile station in a simple manner even
`in the general cellular mobile communication systems in
`which basestations are not synchronized. According to this
`Mar. 14, 1997
`(IP) eceeeceessssesssseesssssesssessssesssesenees 9-061170
`:
`:
`sae
`:
`:
`:
`mobile station position estimation scheme, a first signal
`
`(SL) Ente C1 iccecsccsscsssseeemessssasssesesesesenenensasan H04Q 7/20=sequence andasecond signal sequence which are uniquely
`(52) U.S. Che ceeceecssssesesseeeee 455/456; 455/422; 455/432;
`predetermined for the mobile station are exchanged between
`455/456; 455/457
`the mobile station and the base station, and then a position
`(58) Field of Search 0... 455/422, 456,
`of the mobile station is estimated at one station amongthe
`455/457; 701/207; 342/442, 457
`base station and the mobile station, by obtaining a phase
`difference betweenthe first signal sequence and the second
`signal sequence and calculating an estimated distance
`between the base station and the mobile station according to
`the phase difference.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3,646,580 *
`2/1972 Fuller et al. wc 455/524
`5,508,708
`4/1996 Ghoshetal. .
`
`40 Claims, 9 Drawing Sheets
`
`PERIOD g OF PNI1
`POSITION ESTIMATION REFERENCE
`PNI
`PNI |
`SIGNAL TRANSMITTED BY MOBILE
`PN1
`STATION DEVICE 100
`| UPLINK TRANSMISSION DELAY
` POSITION ESTIMATION REFERENCE
`SIGNAL RECEIVED BY
`PN1
`PN1
`PN1
`BASE STATION DEVICE 200
`
`
`
`
`
`DOWNLINK TRANSMISSION DELAY
`
`
`PN2
`
`PN2
`
`PN2
`
`POSITION ESTIMATION RESPONSE
`SIGNAL TRANSMITTED BY
`BASE STATION DEVICE 200
`
`POSITION ESTIMATION RESPONSE
`SIGNAL RECEIVED BY MOBILE
`STATION DEVICE 100
`
`PHASE DIFFERENCE A MEASURED
`BY PHASE COMPARISON UNIT 108
`
`APPLE 1019
`
`APPLE 1019
`
`1
`
`

`

`U.S. Patent
`
`Jan. 30, 2001
`
`Sheet 1 of 9
`
`US 6,181,944 B1
`
`TRANSMISSION
`SIGNAL
`GENERATION
`UNIT
`
`PN1
`GENERATION
`UNIT
`
`TRANSMISSION
`101} SIGNAL
`PROCESSING
`UNIT
`
`102
`
`107
`
`PN2
`
`GENERATION
`
`UNIT
`
`PHASE
`
`DETECTION
`
`UNIT
`
`111
`
`MOBILE STATION
`DEVICE
`
`105
`
`TRANS-
`MISSION
`vA
`
`tareON
`
`FIG.1
`
`
`DEVICE
`
`
`110
`
`109
`
`DISTANCE
`PHASE
`POSITION CALCULATION‘|COMPARISON
`
`
`ESTIMATION||trvrp UNIT
`UNIT
`
`211
`
`RECEPTION
`UNIT
`
`207
`
`206
`PHASE
`DETECTION
`UNIT
`
`201
`GENERATION
`UNIT
`
`200
`
`202
`
`PN2
`GENERATION
`UNIT
`
`TRANS-
`
` MISSION
`
`SIGNAL
`PROCESSING
`UNIT
`
`
`
`SYNCHRONIZED
`TRANSMISSION
`UNIT
`
`BASE STATION
`
`208
`
`
`
`BASE STATION
`POSITION
`INFORMATION
`GENERATION
`UNIT
`
`203
`
`TRANSMISSION
`SIGNAL
`GENERATION
`UNIT
`
`2
`
`

`

`Jan. 30, 2001
`
`Sheet 2 of 9
`
`US 6,181,944 B1
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`
`
`80.LINDNOSIYVdNODASVHdAd
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`

`U.S. Patent
`
`Jan. 30, 2001
`
`Sheet 3 of 9
`
`US 6,181,944 B1
`
`FIG.3
`
`100
`
`MOBILE
`STATION
`
`4
`
`

`

`U.S. Patent
`
`Jan. 30, 2001
`
`Sheet 4 of 9
`
`US 6,181,944 B1
`
`
`
`AQAA
`
`5
`
`
`

`

`U.S. Patent
`
`Jan. 30, 2001
`
`Sheet 5 of 9
`
`US 6,181,944 B1
`
`FIG.5
`
`BASE STATION
`
`Dim)
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`

`

`U.S. Patent
`
`Jan. 30, 2001
`
`Sheet 6 of 9
`
`US 6,181,944 B1
`
`FIG,7
`
`100
`
`TRANSMISSION
`SIGNAL
`GENERATION
`UNIT
`
`PN}
`GENERATION
`
`UNIT
`
`PN2
`
`GENERATION
`
`UNIT
`
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`101 SIGNAL
`PROCESSING
`UNIT
`
`
`
`102
`
`107
`
`PHASE
`
`DETECTION
`
`UNIT
`
`MOBILE STATION
`
`DEVICE
`
`105
`
`111
`
`ere,ON
`
`200
`
`110
`
`109
`
`PHASE
`DISTANCE
`POSITION CALCULATION#4COMPARISON
`
`ESTIMATION
`UNIT
`UNIT
`UNIT
`
`
`
`PHASE
`
`PN1
`
`UNIT
`
`202
`
`
`201
`207
`206
`211
`
`DrapeION[+]DETECTION GENERATION
`
`
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`UNIT
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`PHASE
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`
`GENERATION
`COMPARISON
`
`UNIT UNIT
`208
`
`
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`TRANS-
`BASE STATION
`
`MISSION
`POSITION
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`TRANSMISSIONbe}SIGNAL INFORMATION
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`BASE STATION
`
`UNIT
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`
`
`
`7
`
`

`

`U.S. Patent
`
`8OH
`
`Jan. 30, 2001
`
`Sheet 7 of 9
`
`US 6,181,944 B1
`
`
`
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`

`

`U.S. Patent
`
`Jan. 30, 2001
`
`Sheet 8 of 9
`
`US 6,181,944 B1
`
`FIG.9
`
`(1) BROADCAST
`INFORMATION (PN3)
`
`(2) POSITION ESTIMATION
`
`
`
`BASE
`STATION
`
`K™ REFERENCE SIGNAL(PN1,A)REINDININALCENTA)
`
`(3) POSITION ESTIMATION
`RESPONCE SIGNAL(PN2,E,d1)
`
`
`MOBILE
`STATION
`
`9
`
`

`

`U.S. Patent
`
`Jan. 30, 2001
`
`Sheet 9 of 9
`
`US 6,181,944 B1
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`
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`

`US 6,181,944 B1
`
`1
`MOBILE STATION POSITION ESTIMATION
`SCHEME FOR CELLULAR MOBILE
`COMMUNICATION SYSTEM
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a mobile station position
`estimation scheme for estimating a position of a mobile
`station in a cellular mobile communication system for
`carrying out communications between a mobile station and
`base stations, and a base station device and a mobile station
`device for realizing this mobile station position estimation
`scheme.
`
`2. Description of the Background Art
`In the conventional cellular mobile communication
`system, it has been impossible to estimate a position of a
`mobile station in communication state, and for this reason it
`has been pointed out that there is a problem that a position
`of a source of an emergency call (such as dial “110” and
`“119” in Japan, dial “911” in U.S.A.) cannot be identified.
`There are well knownradio based techniques for estimat-
`ing a position such as the radio navigation schemes for
`airplanes and ships (beacon,
`loran, microwave landing
`system, etc.). However, these techniques are not suitable for
`the cellular mobile communications.
`
`Namely, the beacon requires a radar on a mobile station
`device so thatit is not suitable for compact implementation
`of a mobile station device. The hyperbolic line of position
`scheme such as loran requires synchronization among base
`stations. In general, base stations of the cellular mobile
`communications are not synchronized with each other so
`that this scheme is not applicable to the cellular mobile
`communications, except for the IS-95 scheme of the Ameri-
`can ELA/TIA standard which has synchronization among
`base stations. The microwave landing system can measure a
`position of an airplane within a particular area at high
`precision by using a special directional antenna, but it is
`difficult to measure an arbitrary position of a mobilestation
`by using a simple radio equipment.
`Recently, the position measurement scheme called GPS
`(Global Positioning System)
`that utilizes satellite has
`becomepopular, but this is also a system that requires high
`precision synchronization among satellite stations, and
`thereforeit is applicable only to the IS-95 scheme mentioned
`above, and not applicable to the general cellular mobile
`communication systems which are asynchronous systems.
`Thus there has been a problem that the conventionally
`known radio based position estimation techniques are not
`suitable for the general cellular mobile communications
`because the compact implementation of a mobile station
`device or a radio device of a base station becomesdifficult
`
`and the synchronization among base stations is required.
`SUMMARYOF THE INVENTION
`
`It is therefore an object of the present invention to provide
`a mobile station position estimation scheme for a cellular
`mobile communication system whichis capable of estimat-
`ing a position of a mobile station in a simple manner even
`in the general cellular mobile communication systems in
`which base stations are not synchronized.
`According to one aspect of the present invention there is
`provided a mobile station position estimation method in a
`cellular mobile communication for carrying out communi-
`cations between mobile stations and base stations, compris-
`ing the steps of: (a) exchanging between a basestation and
`
`2
`a mobile station a first signal sequence and a second signal
`sequence which are uniquely predetermined for the mobile
`station; and (b) estimating a position of the mobile station at
`one station amongthe base station and the mobilestation, by
`obtaining a phase difference between the first signal
`sequence and the second signal sequence and calculating an
`estimated distance between the base station and the mobile
`station according to the phase difference.
`According to another aspect of the present invention there
`is provided a base station device at a base station in a cellular
`mobile communication system for carrying out communi-
`cations between mobile stations and base stations, compris-
`ing: a reception unit for receiving a first signal sequence
`transmitted by a mobile station, which is uniquely predeter-
`mined for the mobile station; and a transmission unit for
`transmitting a second signal sequence which is uniquely
`predetermined for the mobilestation, to the mobile station in
`synchronization with the first signal sequence received by
`the reception unit, so as to enable the mobile station to
`estimate a position of the mobile station by calculating an
`estimated distance between the base station and the mobile
`station according to a phase difference between the first
`signal sequence and the second signal sequence.
`According to another aspect of the present invention there
`is provided a mobile station device at a mobile station in a
`cellular mobile communication system for carrying out
`communications between base stations and mobile stations,
`comprising: a reception unit for receiving a first signal
`sequence transmitted by a base station, which is uniquely
`predetermined for the mobile station; and a transmission unit
`for transmitting a second signal sequence which is uniquely
`predetermined for the mobile station, to the base station in
`synchronization with the first signal sequence received by
`the reception unit, so as to enable the base station to estimate
`a position of the mobile station by calculating an estimated
`distance between the base station and the mobile station
`according to a phase difference between the first signal
`sequence and the second signal sequence.
`According to another aspect of the present invention there
`is provided a base station device at a base station in a cellular
`mobile communication system for carrying out communi-
`cations between mobile stations and base stations, compris-
`ing: a transmission unit for transmitting to a mobile station
`a first signal sequence which is uniquely predetermined for
`the mobile station; a reception umit for receiving a second
`signal sequence transmitted by the mobile station, which is
`uniquely predetermined for the mobile station; and a posi-
`tion estimation unit for estimating a position of the mobile
`station by obtaining a phase difference by comparing phases
`of the first signal sequence transmitted by the transmission
`unit and the second signal sequence received by the recep-
`tion unit, and calculating an estimated distance between the
`base station and the mobile station according to the phase
`difference.
`
`According to another aspect of the present invention there
`is provided a mobile station device at a mobile station in a
`cellular mobile communication system for carrying out
`communications between mobile stations and basestations,
`comprising: a transmission unit for transmitting to a base
`station a first signal sequence which is uniquely predeter-
`mined for the mobile station; a reception unit for receiving
`a second signal sequence transmitted by the base station,
`which is uniquely predetermined for the mobile station; and
`a position estimation unit for estimating a position of the
`mobile station by obtaining a phase difference by comparing
`phasesofthe first signal sequence transmitted by the trans-
`mission unit and the second signal sequence received by the
`
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`

`US 6,181,944 B1
`
`3
`4
`sequence transmitted by a base station, which is uniquely
`reception unit, and calculating an estimated distance
`predetermined for the mobile station; and a transmission unit
`between the base station and the mobile station according to
`
`the phase difference. for obtainingafirst phase difference by comparing phases of
`the first signal sequence received by the reception unit and
`According to another aspect of the present invention there
`a second signal sequence which is uniquely predetermined
`is provided a basestation device at a base station in a cellular
`for the mobile station, and transmitting the second signal
`mobile communication system for carrying out communi-
`sequence and information onthefirst phase difference to the
`cations between mobile stations and base stations, compris-
`base station, so as to enable the base station to obtain a
`ing: a transmission unit for transmitting to a mobile station
`second phase difference by comparing phases of the first
`a first signal sequence which is uniquely predetermined for
`signal sequence and the second signal sequence and estimate
`the mobile station; a reception umt for receiving a second
`a position of the mobile station by calculating an estimated
`signal sequence which is uniquely predetermined for the
`distance between the base station and the mobile station
`mobile station and information on a first phase difference
`accordingto the first phase difference and the second phase
`indicating a phase difference between the first signal
`difference.
`sequence and the second signal sequence as obtained by the
`mobile station, which are transmitted by the mobile station;
`and a position estimation unit for estimating a position of the
`mobile station by obtaining a second phase difference by
`comparing phasesofthe first signal sequence transmitted by
`the transmission unit and the second signal sequence
`received by the reception unit, and calculating an estimated
`distance between the base station and the mobile station
`according to the first phase difference received by the
`reception unit and the second phase difference.
`According to another aspect of the present invention there
`is provided a mobile station device at a mobile station in a
`cellular mobile communication system for carrying out
`communications between mobile stations and basestations,
`comprising: a transmission unit for transmitting to a base
`station a first signal sequence which is uniquely predeter-
`mined for the mobile station; a reception unit for receiving
`a second signal sequence which is uniquely predetermined
`for the mobile station and information on a first phase
`difference indicating a phase difference between the first
`signal sequence and the second signal sequence as obtained
`by the base station, which are transmitted by the base
`station; and a position estimation unit for estimating a
`position of the mobile station by obtaining a second phase
`difference by comparing phasesof the first signal sequence
`transmitted by the transmission unit and the second signal
`sequence received by the reception unit, and calculating an
`estimated distance between the base station and the mobile
`
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`25
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`Other features and advantages of the present invention
`will become apparent from the following description taken
`in conjunction with the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a mobile station device and
`a base station device for realizing a mobile station position
`estimation scheme according to the first embodiment of the
`present invention.
`FIG. 2 is a timing chart for explaining a manner of
`calculating a distance between a mobile station and a base
`station in a mobile station position estimation scheme
`according to the first embodimentof the present invention.
`FIG. 3 is a diagram showing an exemplary estimated
`position of the mobile station obtained by a mobile station
`position estimation scheme according to the first embodi-
`ment of the present invention, for a case of using one base
`station.
`
`FIG. 4 is a diagram showing an exemplary estimated
`position of the mobile station obtained by a mobile station
`position estimation scheme according to the first embodi-
`ment of the present invention, for a case of using two base
`stations.
`
`FIG. 5 is a diagram showing an exemplary estimated
`position of the mobile station obtained by a mobile station
`position estimation scheme according to the first embodi-
`mentof the present invention, for a case of using one sector
`of one base station.
`
`FIG. 6 is a diagram showing an exemplary estimated
`position of the mobile station obtained by a mobile station
`position estimation scheme according to the first embodi-
`mentof the present invention, for a case of using two sectors
`of two basestations.
`
`station accordingto the first phase difference received by the
`reception unit and the second phase difference.
`According to another aspect of the present invention there
`is provided a basestation device at a base station in a cellular
`mobile communication system for carrying out communi-
`FIG. 7 is a block diagram of a mobile station device and
`cations between mobile stations and base stations, compris-
`a base station device for realizing a mobile station position
`ing: a reception unit for receiving a first signal sequence
`estimation scheme according to the second embodiment of
`transmitted by a mobile station, which is uniquely predeter-
`the present invention.
`mined for the mobile station; and a transmission unit for
`FIG. 8 is a timing chart for explaining a manner of
`obtainingafirst phase difference by comparing phasesof the
`calculating a distance between a mobile station and a base
`first signal sequence received by the reception unit and a
`station in a mobile station position estimation scheme
`second signal sequence which is uniquely predetermined for
`according to the second embodiment of the present inven-
`tion.
`the mobile station, and transmitting the second signal
`sequence and information onthefirst phase difference to the
`mobile station, so as to enable the mobile station to obtain
`a second phase difference by comparing phasesofthe first
`signal sequence and the second signal sequence and estimate
`a position of the mobile station by calculating an estimated
`distance between the base station and the mobile station
`accordingto the first phase difference and the second phase
`difference.
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`According to another aspect of the present invention there
`is provided a mobile station device at a mobile station in a
`cellular mobile communication system for carrying out
`communications between mobile stations and basestations,
`comprising: a reception unit for receiving a first signal
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`FIG. 9 is a schematic diagram of signals exchanged
`between a mobile station device and a base station device for
`realizing a mobile station position estimation scheme
`according to the third embodimentof the present invention.
`FIG. 10 is a timing chart for explaining a manner of
`calculating a distance between a mobile station and a base
`station in a mobile station position estimation scheme
`according to the third embodimentof the present invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Referring now to FIG. 1 to FIG. 6, the first embodiment
`of a mobile station position estimation schemefor a cellular
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`US 6,181,944 B1
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`5
`mobile communication system according to the present
`invention will be described in detail.
`
`FIG. 1 show configurations of a mobile station device 100
`and a basestation device 200 for realizing the mobile station
`position estimation schemeofthe first embodiment, for an
`exemplary case in which the mobile station device 100
`measures a distance from the base station device 200 and
`estimates its own position.
`The mobile station device 100 comprises a PN1 genera-
`tion unit 101 for generating a first unique signal sequence
`PN1, a PN2 generation unit 102 for generating a second
`unique signal sequence PN2, a transmission signal genera-
`tion unit 103 for generating transmission signals, a trans-
`mission signal processing unit 104 for obtaining mobile
`station transmission signals of a prescribed format using the
`transmission signals from the transmission signal generation
`unit 103 and the first unique signal sequence PN1 from the
`PN1 generation unit 101, a transmission unit 105 for trans-
`mitting the mobile station transmission signals from the
`transmission signal processing unit 104 through an antenna
`111, a reception unit 106 for receiving base station trans-
`mission signals from a base station through the antenna 111,
`a phase detection unit 107 for detecting a phase of received
`signals received by the reception unit 106, a phase compari-
`son unit 108 for comparing phases of the received signals
`and the mobile station transmission signals to obtain a phase
`difference, a distance calculation umt 109 for calculating a
`distance between the mobile station device 100 and the base
`
`station device 200 according to the phase difference
`obtained by the phase comparison unit 108, and a position
`estimation unit 110 for estimating a position of the mobile
`station device 100 according to the distance calculated by
`the distance calculation unit 109.
`
`Onthe other hand, the base station device 200 comprises
`a reception unit 206 for receiving the mobile station trans-
`mission signals from a mobile station through an antenna
`211, a phase detection unit 207 for detecting a phase of
`received signals received by the reception unit 206, a PN1
`generation unit 201 for generating the first unique signal
`sequence PN1, a PN2 generation unit 202 for generating the
`second unique signal sequence PN2, a transmission signal
`generation unit 203 for generating transmission signals, a
`base station position information generation unit 208 for
`generating a base station position information, a transmis-
`sion signal processing unit 204 for obtaining base station
`transmission signals of a prescribed format using the trans-
`mission signals from the transmission signal generation unit
`203, the second unique signal sequence PN2 from the PN2
`generation unit 202 and the basestation position information
`from the base station position information generation unit
`208, and a synchronized transmission unit 205 for transmit-
`ting the base station transmission signals from the transmis-
`sion signal processing unit 204 in synchronization with the
`received signals received from the mobilestation.
`Note here that the first unique signal sequence PN1 and
`the second unique signal sequence PN2 are signal sequences
`that are uniquely predetermined for each mobile station.
`In the mobile station device 100 and the base station
`
`the mobile station
`device 200 with these configuration,
`position estimation is carried out, for example, when this
`mobile station originates an emergency call, when a user of
`this mobile station wishes to check his/her own position,
`when a user of a fixed network or another mobile station
`
`wishes to check a position of this mobile station, etc. When
`this mobile station originates an emergencycall, the position
`estimation can be realized by carrying out the following
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`operation in a course of a call origination procedure. When
`a user of this mobile station wishes to check his/her own
`position, the user issues a position check request signal to
`the mobile station device 100 such that the mobile station
`device 100 carries out the following operation upon receiv-
`ing this position check request signal. When a userofa fixed
`network or another mobile station wishes to check a position
`of this mobile station, a position check request signal is
`transmitted to the mobile station device 100 from a base
`station whichis currently in communication with this mobile
`station such that the mobile station device 100 carries out the
`
`following operation upon receiving this position check
`request signal.
`Namely, upon receiving the position check request signal,
`the mobile station device 100 generates the first unique
`signal sequence PN1 to be used for the position estimation
`at the PN1 generation unit 101. Then,the transmission signal
`processing unit 104 converts this first unique signal
`sequence PN1 along with any other necessary transmission
`signals from the transmission signal generation unit 103 into
`a prescribed format, so as to obtain a position estimation
`reference signal, and the transmission unit 105 transmitsthis
`position estimation reference signal
`to the base station
`device 200 through the antenna 111.
`Whenthis position estimation reference signal from the
`mobile station is received through the antenna 211 at the
`reception unit 206 of the base station device 200, the first
`unique signal sequence PN1 is generated at the PN1 gen-
`eration unit 201, and a phase of PN1in the received position
`estimation reference signal is detected by using the gener-
`ated PN1 at the phase detection unit 207. Then, the second
`unique signal sequence PN2 is generated at the PN2 gen-
`eration unit 202, and the transmission signal processing unit
`204 converts this second unique signal sequence PN2 along
`with the base station position information from the base
`station position information generation unit 208 and any
`other necessary transmission signals from the transmission
`signal generation unit 203 into a prescribed format, so as to
`obtain a position estimation response signal. The synchro-
`nized transmission unit 205 then transmits this position
`estimation response signal to the mobile station device 100
`through the antenna 211 in synchronization with the phase of
`the received PN1. Here, the base station position informa-
`tion is an information indicating latitude,
`longitude and
`altitude of the base station, for example.
`Whenthis position estimation response signal from the
`base station is received through the antenna 111 at
`the
`reception unit 106 of the mobile station device 100, the
`second unique signal sequence PN2 is generated at the PN2
`generation unit 102, and a phase of PN2 in the received
`position estimation response signal is detected by using the
`generated PN2 at the phase detection unit 107. Then, the
`phase comparison unit 108 compares the phase of PN1 in the
`position estimation reference signal transmitted by the trans-
`mission unit 105 and the phase of PN2 in the position
`estimation response signal received by the reception unit
`106, and detects their phase difference. Then, the distance
`calculation unit 109 calculates a distance between the
`mobile station device 100 and the base station device 200
`
`from this phase difference, and the position estimation unit
`110 estimates the position of this mobile station from the
`distance calculated by the distance calculation unit 109 and
`the base station position information of the base station
`device 200 contained in the position estimation response
`signal received by the reception unit 106.
`FIG. 2 is a timing chart for explaining the principle for
`calculating the distance between the base station and the
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`US 6,181,944 B1
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`7
`mobile station in this first embodiment. FIG. 2 shows an
`exemplary case where the first and second unique signal
`sequences PN1 and PN2 have the equal period. Here, PN1
`and PN2 are used as marker signals for measuring a trans-
`mission time, and there is no need to continuously transmit
`them throughout
`the position estimation period. For
`example, signals to be transmitted periodically such as
`frame synchronization signal can be used as PN1 and PN2.
`The position estimation reference signal transmitted from
`the mobile station device 100 is received at the base station
`
`device 200 after as much delay as a transmission time of an
`uplink transmission path. The base station device 200 trans-
`mits the position estimation response signal in synchroni-
`zation with the received position estimation reference signal.
`The mobile station device 100 receives this position esti-
`mation response signal after as much delay as a transmission
`time of a downlink transmission path, and compares the
`phase of the transmitted position estimation reference signal
`with the phase of the received position estimation response
`signal. Here,
`the measured phase difference can be con-
`verted into a time value A [sec.], where A represents a
`transmission delay time for going and returning.
`Consequently, the distance D between the mobile station
`device 100 and the base station device 200 can be given by:
`
`D=Ac/2 [m]
`
`where c is the speed oflight (which is approximately equal
`to 3x10* m/s).
`FIG. 3 illustrates a manner of estimating the mobile
`station position in this first embodiment. Namely,
`it
`is
`possible to estimate the mobile station device 100 as existing
`on a circle distanced from the base station device 200 by the
`distance D.
`In practice,
`the measured phase difference
`contains someerror. Taking this error into account, the phase
`difference as converted into a time value can be given by
`Aza [sec.], for example, and then the distance D can be
`expressed as:
`
`(Ata)c=Dta=D+6
`
`where d=cac. In this case, the estimated position is given by
`a shaded region shown in FIG. 3.
`It is possible to improve the precision of the estimated
`position if the mobile station measures distances with
`respect to a plurality of base stations. FIG. 4 shows an
`exemplary case where distances with respect to two base
`stations are measured. In this case, the mobile station device
`100 measures the distance with respect to the base station
`device 200 by the above described procedurefirst. When the
`distance between the mobile station device 100 and the base
`station device 200 is given by D1+61 [m] by accounting for
`error, the first estimated area (a single hatching circular area
`centered around the base station device 200) shown in FIG.
`4 can be obtained. Next,
`the mobile station device 100
`similarly measures the distance with respect to another base
`station device 300 by the above described procedure. When
`the distance between the mobile station device 100 and the
`base station device 300 is given by D2+62 [m] by account-
`ing for error, the second estimated area (a single hatching
`circular area centered around the base station device 300)
`shown in FIG. 4 can be obtained. Then,
`the estimated
`position of the mobile station device 100 is given by an
`overlapping portion (a double hatching area) of the first
`estimated area and the second estimated area.
`In addition