(12) United States Patent
`Daudelin et al.
`
`USOO691.5123B1
`(10) Patent No.:
`US 6,915,123 B1
`(45) Date of Patent:
`Jul. 5, 2005
`
`(54) METHOD AND SYSTEM FOR MONITORING
`AN OPERATIONAL AREA OFA
`SUBSCRIBER STATION
`
`(75) Inventors: Douglas Streeter Daudelin,
`Independence, NJ (US); Zoran Siveski,
`New York City, NY (US)
`
`(73) Assignee: Lucent Technologies Inc., Murray Hill,
`NJ (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/517,059
`(22) Filed:
`Mar 2, 2000
`9
`(51) Int. Cl. ............................ H04Q 7/20; H04M 1/66
`(52) U.S. Cl. ....................... 455/410; 455/411; 455/423;
`455/67.11; 455/4.56.1
`(58) Field of Search ................................. 455,410,411,
`455/423,456.1, 432.1, 67.11, 67.16, 421,
`435.1; 340/5.2, 5.8
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,711,000 A * 1/1998 Ploeg et al. ................ 455/423
`
`5,715,518 A * 2/1998 Barrere et al. ............... 340/5.8
`5.835,857 A 11/1998 Otten ......................... 455/410
`5,870,672 A * 2/1999 Stoddard et al. ............ 455/410
`5,905.950 A * 5/1999 Anell ......................... 455/421
`5.940,751 A * 8/1999 Kaplan et al. .............. 455/411
`6,026,304 A
`2/2000 Hilsenrath et al. .......... 455/456
`6,269,246 B1
`7/2001 Rao et al. ................... 455/456
`
`* cited by examiner
`
`Primary Examiner Erika A. Gray
`(57)
`ABSTRACT
`A System and method for monitoring the operational area of
`one or more Subscriber Stations in a wireleSS System facili
`tates determining whether Subscriber Stations are operating
`in their authorized coverage areas or not. The System and
`method first defines a characteristic composite fingerprint
`for a Subscriber station associated with the operation of a
`Subscriber Station in an authorized coverage area. An opera
`tional area monitor monitors an operational composite fin
`gerprint for the Subscriber Station. The monitor or another
`network element compares the operational composite fin
`gerprint to the characteristic composite fingerprint to deter
`mine if the Subscriber Station is operating within the autho
`rized coverage area or the restricted coverage area.
`
`25 Claims, 7 Drawing Sheets
`
`DEFINE A CHARACTERISTIC COMPOSITE FINGERPRINT FOR
`A MOBILE STATION OPERATING IN AN AUTHORIZED REGION
`
`MONITOR AN OPERATIONAL COMPOSITE
`FINGERPRINT FOR THE MOBILE STATION
`
`COMPARE THE OPERATIONAL COMPOSITE FINGERPRINT TO THE
`CHARACTERISTIC COMPOSITE FINGERPRINT TO DETERMINE IF THE
`MOBILE STATION IS OPERATING WITHIN THE AUTHORIZED
`REGION OR A RESTRICTED REGION
`
`SOO
`
`S102
`
`S104
`
`Page 1 of 17
`
`SAMSUNG EX-1067
`
`

`

`U.S. Patent
`
`Jul. 5, 2005
`
`Sheet 1 of 7
`
`US 6,915,123 B1
`
`?2:1 NOIIYOIINGHIÊN
`
`
`BEINHO
`
`HOIINGH
`WNNELNW
`
`02
`
`??
`
`\– – – – – – – – – – – –-’
`
`92
`
`
`
`
`
`
`
`
`
`
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`
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`Page 2 of 17
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`

`

`U.S. Patent
`U.S. Patent
`
`Jul. 5, 2005
`Jul. 5, 2005
`
`Sheet 2 of 7
`Sheet 2 of 7
`
`US 6,915,123 B1
`US 6,915,123 B1
`
`FIG.
`
`1B
`
`
`
`
`
`10
`
`BTS
`
`108
`
`Page 3 of 17
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`Page 3 of 17
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`

`

`U.S. Patent
`
`Jul. 5, 2005
`
`Sheet 3 of 7
`
`US 6,915,123 B1
`
`FIG. 2
`
`DEFINE A CHARACTERISTIC COMPOSITE FINGERPRINT FOR
`A MOBILE STATION OPERATING IN AN AUTHORIZED REGION
`
`MONITOR AN OPERATIONAL COMPOSITE
`FINGERPRINT FOR THE MOBILE STATION
`
`COMPARE THE OPERATIONAL COMPOSITE FINGERPRINT TO THE
`CHARACTERISTIC COMPOSITE FINGERPRINT TO DETERMINE IF THE
`MOBILE STATION IS OPERATING WITHIN THE AUTHORIZED
`REGION OR A RESTRICTED REGION
`
`SOO
`
`S102
`
`S104
`
`FIG. 3
`
`NUMBER OF
`OBSERVATIONS
`
`SMALLER COMPONENT
`COUNTER
`LOEST
`
`LARGER COMPONENT COUNTER
`
`PROPAGATIONAL DELAY
`REFERENCE RANGE
`
`Page 4 of 17
`
`

`

`U.S. Patent
`
`Jul. 5, 2005
`
`Sheet 4 of 7
`
`US 6,915,123 B1
`
`FIG. 4
`
`1.0
`
`
`
`EMPIRICAL
`PROBABILITY DENSITY
`FUNCTION OF
`PROPAGATIONAL DELAY
`OBSERVATIONS
`
`PROBABILITY
`
`PROPAGATIONAL DELAY
`
`-- as
`
`FIG. 5
`
`NUMBER OF
`OBSERVATIONS
`
`O
`
`FIRST SECTOR
`ANTENNA SET
`
`— T
`
`SECOND SECTOR
`ANTENNA SET
`
`THIRD SECTOR
`ANTENNA SET
`
`OBSERVATION OF RECEIVE SIGNALS
`
`Page 5 of 17
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`

`

`U.S. Patent
`
`Jul. 5, 2005
`
`Sheet 5 of 7
`
`US 6,915,123 B1
`
`FIG EA
`
`ATEACHSAMPLING PERIOD)
`
`S50
`
`SELECT A FIRST FINGER ASSIGNMENT OF A
`RAKE RECEIVER, WHERE THE FIRST FINGER ASSIGN
`MENT IS ASSOCIATED WITH A RECEIVE SIGNAL
`
`S52
`
`S54
`IS THE SELECTED FINGER
`ASSIGNMENT MATURE? / NO
`YES
`
`S56
`
`INCREMENT A COUNTER FOR A
`TOTAL NUMBER OF OBSERVATIONS OF
`MATURE FINGER ASSIGNMENTS
`
`YES
`
`IS THE SELECTED
`FINGER ASSIGNMENT THE
`LAST FINGER ASSIGNMENT2
`NO
`
`S58
`
`S60-
`
`WAIT FOR THE NEXT SAMPLING
`INTERVAL UNTIL DONE
`
`SELECT THE NEXT
`FINGER ASSIGNMENT
`
`S62
`SG4
`
`GET THE RECEIVE SIGNAL CHARACTERISTICS OF THE SELECTED FINGER ASSIGNMENT
`FOR AN OBSERVATION THE RECEIVE SIGNAL CHARACTERISTICS MAYBE DESIGNATED
`A FINGERPRINT AND MAY INCLUDE A PROPAGATIONAL DELAY AND AN ANTENNA IDENTIFIER
`
`s
`OR
`S72
`
`REFER TO A FIRST HISTOGRAM OF OBSERVATIONS OF PROPAGATIONAL DELAYS AND /S66
`A SECOND HISTOGRAM OF OBSERVATIONS OF ANTENNA IDENTIFIERS THE FIRST
`HISTOGRAM INCLUDES COUNTER BINS ASSOCIATED WITH DIFFERENT RANGES OF
`PROPAGATIONAL DELAYS. THE SECOND HISTOGRAM INCLUDES ANTENNA SET
`COUNTERS ASSOCIATED WITH DIFFERENT ANTENNA IDENTIFIERS
`
`UPDATE THE SECOND HISTOGRAM BY INCREMENTING ONE OF
`THE ANTENNA SET COUNTERS, WHICH CORRESPONDS TO THE ANTENNA
`IDENTIFIER OF THE SELECTED FINGER ASSIGNMENT
`
`SS8
`
`
`
`IS AND OBSERVED PROPAGATIONAL DELAY OF THE SELECTED
`FINGER ASSIGNMENT WITHIN A REFERENCE RANGE2
`YES
`
`UPDATE THE FIRST HISTOGRAM OF PROPAGATIONAL
`DELAY OBSERVATIONS BY INCREMENTING THE COUNTER
`BIN ASSOCIATED WITH THE OBSERVED PROPAGATIONAL
`DELAY ON THE SELECTED FINGER ASSIGNMENT
`
`
`
`Page 6 of 17
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`

`

`U.S. Patent
`
`Jul. 5, 2005
`
`Sheet 6 of 7
`
`US 6,915,123 B1
`
`FIG. GB
`
`IF THE OBSERVED PROPAGATIONAL DELAY IS LOWER THAN THE REFERENCE RANGE,
`INCREMENT A SMALLER COMPONENT COUNTER. IF THE OBSERVED PROPAGATIONAL DELAY
`IS GREATER THAN THE REFERENCE RANGE, INCREMENT A LARGER COMPONENT COUNTER
`
`
`
`S74
`
`FIG. 7
`PREPARE AN OPERATIONAL COMPOSITE FINGERPRINT FOR COMPARISON WITH A
`CHARACTERISTIC COMPOSITE FINGERPRINT, RETRIEVE OR ESTABLISH AN ANTENNA
`MASK AND PROPAGATAIONAL DELAY MASK ASSOCIATED WITH THE CHARACTERISTIC
`COMPOSITE FINGERPRINT THE OPERATIONAL COMPOSITE FINGERPRINT INCLUDES A
`FIRST HISTOGRAM OF PROPAGATIONAL DELAY OBSERVATIONS AND A SECOND
`HISTOGRAM OF ANTENNA OBSERVATIONS
`
`S3
`
`
`
`
`
`
`
`DOES THE SECOND HISTOGRAM FALL WITHIN
`THE ANTENNA MASK ASSOCIATED WITH THE
`CHARACTERISTIC COMPOSITE FINGERPRINT
`
`O
`
`DOES THE FIRST HISTOGRAM FALL WITHIN THE
`PROPAGATIONAL DELAY MASK ASSOCIATED
`WITH THE CHARACTERISIC COMPOSITE
`FINGERPRINT
`YES
`
`THE SUBSCRIBER STATION IS MOST LIKELY OPERATING/S6
`IN AN AREA WITHIN THE AUTHORIZED COVERAGE AREA
`
`THE SUBSCRIBER STATION IS OPERATING IN AN AREA OUTSIDE THE
`AUTHORIZED COVERAGE AREA OR WITHIN A RESTRICTED COVERAGE AREA
`
`S38
`
`Page 7 of 17
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`

`

`U.S. Patent
`
`Jul. 5, 2005
`
`Sheet 7 of 7
`
`US 6,915,123 B1
`
`FIG. 9
`
`PREPARE AN OPERATIONAL COMPOSITE FINGERPRINT FOR COMPARISON WITH A
`CHARACTERISTIC COMPOSITE FINGERPRINT
`RETRIEVE OR ESTABLISH AN ANTENNA
`MASK AND AN ALLOWED PROMINENT CHARACTERISTIC RANGE OF PROPAGATAIONAL
`DELAYS ASSOCIATED WITH THE CHARACTERISTIC COMPOSITE FINGERPRINT
`THE
`OPERATIONAL COMPOSITE FINGERPRINT INCLUDES A FIRST HISTOGRAM OF
`PROPAGATIONAL DELAY OBSERVATIONS AND A SECOND HISTOGRAM OF ANTENNA
`OBSERVATIONS.
`
`
`
`
`
`S44
`
`DOES THE SECOND HISTOGRAM FALL WITHIN
`THE ANTENNA MASK ASSOCIATED WITH THE
`CHARACTERISTIC COMPOSITE FINGERPRINT
`YES
`
`
`
`DOES THE FIRST HISTOGRAM COMPLY WITH THE
`ALLOWED PROMINENT CHARACTERISTIC RANGE
`OF PROPAGATIONAL DELAYS ASSOCIATED WITH
`THE CHARACTERISTIC COMPOSITE FINGERPRINT2
`YES
`
`
`
`THE SUBSCRIBER STATION IS MOST LIKELY OPERATING-S36
`IN AN AREA WITHIN THE AUTHORIZED COVERAGE AREA
`
`
`
`
`
`
`
`THE SUBSCRIBER STATION IS OPERATING IN AN AREA OUTSIDE THE
`AUTHORIZED COVERAGE AREA OR WITHIN A RESTRICTED COVERAGE AREA
`
`S38
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`Page 8 of 17
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`

`

`US 6,915,123 B1
`
`1
`METHOD AND SYSTEM FOR MONITORING
`AN OPERATIONAL AREA OFA
`SUBSCRIBER STATION
`
`FIELD OF THE INVENTION
`The present invention relates generally to a wireleSS
`communications System, and more particularly, to a method
`and System for monitoring an operational area of a Sub
`Scriber Station.
`
`25
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`35
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`40
`
`15
`
`BACKGROUND
`Wireless service providers sometimes provide different
`coverage areas for communication Services and assign dif
`ferent billing rates to the coverage areas. For example, a
`Service provider may provide communications Service
`within a limited coverage area and an extended coverage
`area. By definition, the extended coverage area affords
`communication Service Over a greater geographic region
`than the limited coverage area. Because of the greater
`coverage area associated with the extended coverage area,
`the Service provider may charge a premium billing rate for
`the Subscribers communications within the extended cover
`age area, as opposed to the limited coverage area.
`If a Subscriber Station is capable of operating anywhere in
`the extended coverage area or in the limited coverage area,
`the opportunity for Subscriber fraud arises. For instance, a
`Subscriber that only pays the Service provider for operation
`in the limited coverage area may attempt to improperly use
`the Subscriber Station in the extended coverage area. That is,
`a Subscriber may simply move the Subscriber station from its
`authorized limited coverage area without paying requisite
`charges to the Service provider for operation in the extended
`coverage area. Thus, a need exists for a method and System
`for monitoring in what area a Subscriber Station is operating
`(i.e., the operational area of the Subscriber station) on a
`wireleSS communications System.
`SUMMARY OF THE INVENTION
`In accordance with one aspect of the invention, a System
`and method for monitoring the operational area of one or
`more Subscriber Stations in a wireleSS System facilitates
`determining whether Subscriber Stations are operating in
`their authorized coverage areas or not. The System and
`method first defines a characteristic composite fingerprint
`for a Subscriber Station associated with the operation of a
`Subscriber Station in its authorized coverage area. A com
`posite fingerprint refers to a Statistical compilation of
`detected Signal characteristics of a receive Signal received
`from the Subscriber Station. A characteristic composite fin
`gerprint refers to a composite fingerprint associated with the
`Subscriber Station transmitting within an authorized cover
`age area or another known area. An authorized coverage area
`is a coverage area where communications Service is inten
`tionally provided to a particular Subscriber Station. In
`contrast, a restricted coverage area is a coverage area where
`communication Service to a particular Subscriber Station is
`prohibited or limited. An operational area monitor monitors
`an operational composite fingerprint for the Subscriber Sta
`60
`tion. The operational composite fingerprint refers to a com
`posite fingerprint that is determined while a Subscriber
`Station is active (i.e., communicating with the base station),
`regardless of whether the Subscriber Station is located in the
`authorized coverage area or the restricted coverage area. The
`monitor or another network element compares the opera
`tional composite fingerprint to the characteristic composite
`
`45
`
`50
`
`55
`
`65
`
`2
`fingerprint to determine if the Subscriber Station is operating
`within the authorized coverage area or the restricted cover
`age area. Thus, the method and System of the invention is
`well-Suited for fraud detection in wireleSS communications
`and for restricting communications Service for one or more
`Subscriber Stations to an authorized coverage area.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1A shows a block diagram of a wireless communi
`cations System in accordance with the invention.
`FIG. 1B illustrates multi-path Signal propagation between
`a base Station and a Subscriber Station in the wireleSS
`communication system of FIG. 1A.
`FIG. 2 is a flow diagram of a method for monitoring the
`operational area of a Subscriber Station in a wireleSS System
`in accordance with FIG. 1A.
`FIG. 3 is a histogram showing the number of times each
`propagational delay factor has been observed on at least one
`uplink antenna Set of a base Station in accordance with the
`invention.
`FIG. 4 is a graph of a probability density function of
`various propagational delays observed on an uplink antenna
`Set in accordance with the invention.
`FIG. 5 is a histogram of a number of times received
`Signals were observed on each antenna Set of a Sectorized
`base Station in accordance with the invention.
`FIGS. 6A and 6B are a flow chart illustrating a method for
`forming a composite fingerprint in accordance with the
`invention.
`FIG. 7 is a flow chart illustrating one procedure for
`comparing an operational composite fingerprint to a char
`acteristic composite fingerprint in accordance with the
`invention.
`FIG. 8 is a flow chart of an alternate procedure for
`comparing the operational composite fingerprint to the char
`acteristic composite fingerprint in accordance with the
`invention.
`
`DETAILED DESCRIPTION
`Wireless Communication System
`In accordance with the invention, FIG. 1A shows a block
`diagram of a wireleSS communication System 11 for deter
`mining whether one or more Subscriber Stations 26 are
`operating within an authorized coverage area 36. Base
`stations 10 provide coverage defined in terms of cells or
`Sectors thereof. A restricted coverage area 38 and an autho
`rized coverage area 36 may be defined for each correspond
`ing Subscriber Station 26.
`An authorized coverage area 36 includes a region within
`a cell or a sector which the Subscriber station 26 is autho
`rized to use. For example, an authorized coverage area 36
`may include a coverage area that Serves a Subscriber's
`busineSS or residence as a fixed wireleSS Service. Although
`the authorized coverage area 36 in FIG. 1A is a round area,
`the authorized coverage area may have another shape. The
`authorized coverage area 36 may be associated with the
`Signal coverage provided by one or more base Stations.
`Although the authorized coverage area 36 may be fully
`contained within a cell or Sector as shown, the authorized
`coverage area 36 may be formed by the union of or over
`lapping of coverage areas within adjacent cells or Sectors.
`A restricted coverage area 38 includes one or more cells
`or Sectors, or geographic portions thereof, which represent a
`Service area that the Subscriber Station 26 is not authorized
`
`Page 9 of 17
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`

`3
`to use. In FIG. 1A, the restricted coverage area 38 is
`indicated by the dashed lines. Here, the restricted coverage
`area 38 surrounds the authorized coverage area 36.
`One or more base Stations 10 communicate to a base
`station controller 34. For example, a base station 10 that
`ordinarily provides coverage to the Subscriber Station 26 in
`the authorized coverage area 36 communicates with the base
`station controller 34. The base station controller 34 is
`coupled to a wireleSS Switching center 32. The wireleSS
`Switching center 32 is coupled to an authentication center 28
`and a home location register 30. A subscriber station 26 may
`transmit to one or more base Stations 10 via a reverse
`channel. In a preferred embodiment, the base station 10
`comprises a CDMA capable base Station.
`Each base Station 10 may contain a plurality of directional
`antenna Sets (20, 22, and 24). For illustrative purposes, a
`base station 10 in FIG. 1A is associated with three sets of
`directional antennas designated a first antenna Sector Set 20,
`a Second antenna Sector Set 22 and a third antenna Sector Set
`24, although other numbers of antennas and configurations
`may be used to practice the invention, Such as a Single
`antenna per Set.
`In general, an operational area monitor 12 may be imple
`mented as Software instructions on an existing or commer
`cially available base station 10 or by the addition of both
`hardware and Software instructions to an existing base
`station. For illustrative purposes as shown in FIG. 1A, the
`operational area monitor 12 includes an antenna monitor 14
`and a propagational delay measurer 16 coupled to a proces
`Sor 18. In turn, the processor 18 is coupled to a Storage
`device 19.
`Reception of Subscriber Station Signals
`Referring to FIG. 1B, the Subscriber station 26 transmits
`a reverse channel Signal to the base Station 10. AS shown in
`FIG. 1B, the reverse channel may be transmitted as an
`omnidirectional Signal with Signal components 108 radiating
`into many different directions. The reverse channel Signal
`may be received at the base station 10 as a plurality of
`receive signals 107 offset in time from each other. The
`conversion of the Single transmitted Signal from the Sub
`scriber station 26 to multiple temporally offset receive
`signals 107 at the base station 10 is sometimes referred to as
`multi-path reception. Multi-path reception occurs where the
`receive signal 107 is reflected from an obstacle 105 and
`takes multiple propagational paths between the Subscriber
`station 26 and the base station 10. For example, the base
`station 10 may receive a direct or line-of-sight signal 109
`from the subscriber station 26 and a group of reflective
`signals 111 over various indirect paths from the subscriber
`Station 26. Thus, the base Station receiver may receive one
`receive signal or multiple temporally offset receive signals
`107 transmitted from the Subscriber station 26.
`In the context of a code-division multiple access System,
`the baseband Signal modulation includes spreading by a
`pseudo-random code Sequence. To demodulate the Signal, a
`demodulator of the base station 10 must despread the
`received modulated Signal by the same pseudo-random code
`Sequence used for encoding, but by a temporal offset that
`depends on the delay encountered by the reverse channel
`Signal during propagation between the Subscriber Station 26
`and the base station 10.
`A receiver of the base station 10 preferably comprises a
`rake receiver, which independently demodulates different
`temporally offset versions of the receive signal 107 from a
`Subscriber station 26 and then combines the different
`
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`US 6,915,123 B1
`
`4
`versions, to achieve diversity gain where possible. The rake
`receiver includes multiple demodulators, which are Some
`times referred to as fingers. In the presence of multi-path
`propagation, a group of fingers of the rake receiver may be
`dynamically assigned to a number of temporally offset
`versions of a Signal for a reverse channel Signal of a
`Subscriber station 26. The receiver of base station 10
`includes a signal Searcher which repetitively Scans the
`receive signals 107 incident upon the antenna Sets of the
`base Station 10 to identify the highest quality, temporally
`offset versions of a receive signal 107 for assignment to the
`fingers of the rake receiver.
`Each finger of the rake receiver may be dynamically
`assigned a unique temporal offset, which may be referred to
`as the propagational delay factor. At a Sampling interval, a
`finger is preferably assigned to a specific propagational
`delay and a specific antenna. The propagational delay rep
`resents a temporal offset which when applied to a reference
`pseudo-random code allows demodulation of a receive Sig
`nal by the finger. That is, the rake receiver may time-shift the
`reference pseudo-random code Sequence to demodulate the
`receive signal. Regardless of whether multi-path propaga
`tion is present, during a Sampling interval, the antenna
`monitor 12 preferably measures the number of observations
`of a Subscriber Station's Signal received on each particular
`uplink antenna Set (20, 22, or 24) associated with the base
`station 10. An observation represents the detection of a valid
`reverse link Signal above a noise floor during a Sampling
`interval. An uplink antenna Set (20, 22, or 24) refers to one
`or more antennas that may receive a reverse link Signal from
`a subscriber station 26 to a base station 10. For example, an
`uplink antenna Set may include two antennas to realize
`Space-diversity reception.
`Propagational Delay Measurer
`The propagational delay measurer 16 measures the num
`ber of observations of various propagational delays for a
`given Subscriber Station 26 during a call or data transmis
`Sion. The propagational delays refer to the different propa
`gational delays that are present in the uplink receive signals
`that traverse different propagational paths from the Sub
`scriber station 26 to the base station 10. In a code-division,
`multiple-access (CDMA) system, the propagational delay
`measurer 16 may measure a propagational delay by com
`paring the reference pseudo-random code Sequence with the
`receive pseudo-random code Sequence. The time offset
`between the reference pseudo-random code Sequence and
`the received pseudo-random code Sequence represents the
`propagational delay factor. Here, the time offset measured is
`caused by the multi-path propagational delays and should
`not be confused with the pseudo-random code Sequence
`offsets that can exist between different base stations 10 and
`Sectors of a code-division, multiple-access System to pro
`duce orthogonal code relations that reduce or minimize
`interference between base Stations 10 Serving proximate
`geographic regions.
`Each of the observed propagational delays falls within a
`range of possible propagational delays between the Sub
`scriber station 26 and the base station 10 serving the
`Subscriber Station 26 when the Subscriber Station is operating
`in the authorized coverage area. The values of the propaga
`tional delays vary with the location of the subscriber station
`and are determined by characteristics of terrain (e.g.,
`topology), geometry of obstacles (e.g., morphology), reflec
`tive characteristics of obstacles, the distance between the
`Subscriber station 26 and the base station 10, or other
`relevant factors. A shorter propagational delay likely repre
`
`Page 10 of 17
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`

`US 6,915,123 B1
`
`S
`Sents a direct or line-of-Site propagational path between the
`Subscriber station 26 and the base station 10, whereas a
`longer propagational delay may result from multi-path
`propagation between the Subscriber Station 26 and the base
`station 10. If the impact of the distance between the Sub
`scriber station 26 and the base station 10 predominates over
`other propagational factors, the values of propagational
`delays may be generally correlated to each other within a
`circumferential Zone about a base Station 10 Site. A charac
`teristic of a particular receive signal may include not only its
`propagational delay, but also the antenna identifier of the
`antenna Set over which the receive signal is received at a
`demodulating finger.
`
`15
`
`6
`tical compilation of the data from multiple fingerprints of the
`receive signals 107, which are sampled from a subscriber
`Station 26 during a call duration or data transmission dura
`tion. A composite fingerprint has a distribution of Signal
`characteristics (e.g., propagational delay and antenna
`identifiers) which are influenced by the location and physical
`features of the operational area from which the subscriber
`Station 26 transmits. ). Advantageously, Selecting only
`mature fingerprints of finger assignments for inclusion in the
`composite fingerprint prevents the composite fingerprint
`from being corrupted by Spurious Signals or interference. If
`the Subscriber Station 26 transmits from a Second operational
`area that is different from and Sufficiently geographically
`Separated from a first operational area, a first composite
`fingerprint associated with the first operational area is likely
`to differ from a Second composite fingerprint associated with
`the Second operational area in a Statistically significant
`C.
`The difference between an operational composite finger
`print and a characteristic composite fingerprint is that the
`operational composite fingerprint may be associated with
`any location of the Subscriber Station, whereas the charac
`teristic composite fingerprint is only associated with an
`authorized coverage area. The operational composite finger
`print may be compared with a previously computed char
`acteristic composite fingerprint to determine whether the
`Subscriber Station is operating outside of an authorized
`operational area. In an alternate configuration, the opera
`tional composite fingerprint may be used as an input to
`compute a characteristic composite fingerprint So long as the
`Subscriber Station is operating from a known operational
`area or geographic location.
`Processor of Operational Area Monitor
`The antenna monitor 14 provides the processor 18 with
`the number of observations of reverse signals on antenna
`Sets, with reference to corresponding antenna identifiers
`observed on a Sampling interval by Sampling interval basis.
`The propagational delay measurer 16 Similarly provides
`observations of measured propagational delays to the pro
`ceSSor 18 on a Sampling interval by Sampling interval basis.
`The processor 18 processes the foregoing measurements of
`antenna observations and propagational delays for a call of
`a particular Subscriber Station 26 operating in its authorized
`geographic area 36 to obtain the characteristic composite
`fingerprint. The processor 18 Stores the characteristic com
`posite fingerprint in an archival database in a Storage device
`19. The storage device 19 and the processor 18 may regu
`larly or periodically Send updates of characteristic composite
`fingerprints or fingerprint information to a home location
`register 30, an authentication center 28, or any other central
`network element to facilitate record-keeping of potentially
`fraudulent activity of a subscriber station 26. The processor
`18 may also send alert data to the authentication center 28
`if the operational area monitor 12 detects a Subscriber Station
`26 operating outside of its authorized coverage area 36.
`The home location register 30 stores subscriber informa
`tion on the Subscriberstations 26, Such as the extent to which
`certain Subscriber features are activated or not. The home
`location register 30 also provides an indication of where the
`Subscriber station 26 is active or what base station 10 the
`Subscriber Station 26 most recently used.
`Authentication Center
`The authentication center 28 is responsible for verifying
`the identity of subscriber stations 26 to distinguish autho
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`35
`
`Fingerprint
`A fingerprint refers to a Snapshot of the Signal character
`istics of a receive signal 107. The Signal characteristics may
`include one or more of the following: propagational delay,
`antenna identifier, and Signal quality indicator (e.g., Signal
`to-noise ratio or a short-term average of Signal Strength). The
`highest quality, if not all, receive signals may be assigned to
`and demodulated by fingers. Therefore, the operational area
`monitor 12 preferably forms a composite fingerprint by
`periodically collecting the fingerprints of mature fingers. A
`mature finger is defined as a finger which has been assigned
`25
`to a Seemingly valid receive Signal for a significant period of
`time (e.g., 200 milliseconds).
`In an alternate embodiment, the operational area monitor
`10 may use factors other than maturity to Select fingers from
`which to take fingerprints for observation and computation
`of a composite fingerprint or a characteristic composite
`fingerprint. For example, in an alternate embodiment the
`operational area monitor 12 may use a Signal quality
`indicator, as opposed to a minimum tracking time associated
`with maturity. In another alternative embodiment, the opera
`tional area monitor 12 may collect fingerprints from the
`Signal Search results from which finger assignments of the
`rake receiver are derived.
`In each of the above embodiments, the Signal character
`istics for the fingerprint are readily available in existing
`CDMA base stations. Therefore, the operational area moni
`tor 12 may comprise Software instructions for a commer
`cially available base Station, without any additions to the
`base Station hardware. Alternatively, the operational area
`monitor 12 may comprise a separate receiving and data
`processing System that Searches for receive signals 107 and
`measures their characteristics independently from mecha
`nisms of an existing base Station. Other variations may be
`apparent to those skilled in the art, without departing from
`the Scope of the invention.
`Composite Fingerprints
`Prior to monitoring the operational area of a Subscriber
`Station, the operational area monitor 12 takes a characteristic
`composite fingerprint of a Subscriber Station 26. A charac
`teristic composite fingerprint is a Statistical compilation of
`multiple fingerprints taken while a Subscriber Station 26 is
`operating within its authorized operational area. The char
`acteristic composite fingerprint is considered to be a repre
`Sentative SuperSet of any composite fingerprint taken from
`the authorized area. The characteristic composite fingerprint
`provides a reference for Subsequent comparison to an opera
`tional composite fingerprint.
`During a call, the operational area monitor 12 takes
`occasional fingerprints of the receive signals 107 and forms
`a composite fingerprint. A composite fingerprint is a Statis
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`US 6,915,123 B1
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`7
`rized Subscriber stations 26 from unauthorized Subscriber
`Stations 26. The operational area monitorS 12 within various
`base Stations 10 within the wireleSS communications System
`may report communications activity of particular Subscriber
`Stations 26 in their restricted coverage areas 38 as potentially
`fraudulent activity. The authentication center 28 may be
`programmed to provide reports of potentially fraudulent
`activity to a service provider where the subscriber station 26
`has been detected with an operational composite fingerprint
`that differs from a characteristic composite fingerprint. A
`history of potentially fraudulent activity may be addressed
`by the service provider as the service provider sees fit. For
`example, the Service provider may charge a Subscriber
`Station, which is assigned to a fixed wireleSS Service within
`an authorized coverage area, a premium Service charge upon
`detection of repeated communications activity within the
`restricted coverage area. Alternately, the Service provider
`may wish to establish a new characteristic composite fin
`gerprint upon repeated detection of communications activity
`in the restricted coverage area in the event that the charac
`teristic composite fingerprint is corrupt or inaccurate.
`Instead of waiting for the Service provider to analyze the
`reports of potentially fraudulent activity, in an alternate
`embodiment, the authentication center 28 may automatically
`deny access to, or immediately terminate in-progreSS com
`25
`munication with unauthorized Subscriber stations. The
`authentication center 28 may cooperate with the operational
`area monitor 12 and respond to its provision of alert data to
`terminate the access of a Subscriber Station 26 to the wireleSS
`communication System and archive possible fraudulent
`transgressions if the Subscriber Station 26 moves from an
`authorized coverage area 26 to a restricted coverage area 28.
`Method for Monitoring Operational Area of a
`Subscriber Station
`FIG. 2 is a flow diagram of a method for monitoring the
`geographic operational area of a Subscriber Station 26 in
`accordance with the wireless system of FIG. 1A. Starting in
`step S100, an operational area monitor 12 of a base station
`10 defines a characteristic composite fingerprint of a Sub
`Scriber Station 26 operating in the authorized coverage area
`36. A fingerprint comprises at least one observation of a
`propagational delay and may include one observation of an
`antenna identifier. The observations of propagational delay
`and antenna identifiers may be used to identify a specific
`receive signal 107 during a Sampling period. A composite
`fingerprint represents data collected from a group of finger
`prints.
`In Step S100, a characteristic composite fingerprint may
`be defined in accordance with various alternative tech
`niques. A characteristic composite fingerprint is associated
`with a geographic operational area, in the authorized cov
`erage area 36, of a subscriber station 26. Each subscriber
`station 26 serviced by the wireless system 11 may