I IIIII II Ill Ill Ill Ill II 111111111111111
`
`
`
`5,717,406
`
`[111 Patent Number:
`[19J
`
`United States Patent
`Sanderford et al.
`(45] Date of Patent:
`Feb. 10, 1998
`
`US005717406A
`
`(54] ENHANCED POSITION CALCULATION
`
`ABSTRACT
`
`(57]
`The invention discloses several computation and control
`
`
`
`(75] Inventors: H. Britton Sanderford, New Orleans,
`
`
`techniques which use historic information as well as other
`
`La.; Martin C. Poppe, Burlington, Vt.
`
`
`cues in order to enhance the accuracy of a radio position fix.
`
`These computational techniques include neural networks,
`[73] Assignee:
`Sanconix Inc., New Orleans, La.
`
`
`mapped grid coefficients as input to a set of simultaneous or
`differential equations, and table lookup of correction coef­
`
`
`
`ficients for known low accuracy positions. The invention
`Jun. 7, 1995
`[22]Filed:
`
`
`further discloses techniques for receiver array synchroniza­
`
`
`
`tion so that all system elements in a particular coverage area
`[51]fut. Cl.6 ........................................................
`GOlS 3/02
`
`
`obtain a time reference appropriate for time of flight radio
`(52] U.S. Cl .............................................. 342/457; 342/363
`
`
`
`
`
`location measurements. The invention further teaches tech­
`342/363. 457;
`(58] Field of Search .....................................
`
`
`
`niques to enhance the accuracy of a position fix by use of
`364/443, 449, 449.1
`
`
`
`both fixed references, which are located in a coverage area.
`as well as a mobile reference carried by a search team. The
`
`
`invention also discloses techniques to provide information
`appropriate to guide a search team to an unknown positioned
`
`
`
`
`transmitter that is located within a building or structure. The
`
`
`invention discloses techniques to train a central computing
`
`
`unit. by using actuarial data. so that multi-path errors
`
`
`
`resulting from fixed or mobile obstacles may be reduced.
`M. Blum
`Primary Examiner-Theodore
`Finn-Oblon. Spivak. McClelland.
`Attorney, Agent, or
`
`Maier & Neustadt. P.C.
`
`[21]Appl. No.: 487,522
`
`[56]
`
`
`
`References Cited
`
`FOREIGN PATENf DOCUMENTS
`
`470 151 11/1993 Sweden .
`
`
`0631453 A2 12/1994 Sweden .
`
`
`
`47 Claims, 11 Drawing Sheets
`
`100 LATITUDE
`
`!106 �'I 1
`!
`CENTRAL
`PROCESSING
`LONGITUDE
`DEVICE
`ALTITUDE
`� HISTORIC
`RECEWER
`'{ MOBILE
`UNKNOWN
`I ACCURACY OF
`
`I INFORMATION
`(XMIT
`REFERENCE
`POSITION
`CONVERGENCE
`: (COEFFICIENTS :
`REFERENCE
`XMITTER
`XMITTER
`1 OF I
`(MRX)105 GRID SYNC
`OPTIONAL)
`(UPX) 103
`I WEIGHTINGS}
`XMITTER
`(FRX) 104
`107
`'\l,.__flXED
`� ANTENNA
`OTHER
`REFERENCE
`QUADRANTS
`INFORMATION
`XMITTER
`AND CUES � [',..._101
`(OPTIONAL)
`
`7
`
`L-----!.....I
`
`I
`
`TOA/RTOA, SNR, ANT, (A,B,C,D)
`108
`
`Cisco v. TracBeam / CSCO-1007
`Page 1 of 26
`
`

`

`FIC. 1
`
`(A,B,C,D)
`
`108
`SNR. ANT,
`
`TOA/RTOA,
`
`101
`AND CUES
`INFORMATION
`OTHER
`I WEIGHTINGS)
`I OF I
`: (COEFFICIENTS
`CONVERGENCE
`� HISTORIC I I INFORMATION
`ACCURACY
`OF
`ALTITUDE
`DEVICE
`LONGITUDE
`PROCESSING
`CENTRAL
`LATITUDE
`
`l--0
`l--0
`
`�
`
`l--0
`
`�
`
`\Cl
`l--0
`9
`l--0
`?'
`�
`
`I
`:
`
`I
`
`100
`
`(OPTIONAL)
`QUADRANTS
`
`107
`
`(FRX) 104
`XMITTER
`REFERENCE
`� FIXED
`
`L-----�
`
`(MRX)105
`XMITTER
`REFERENCE
`\{ MOBILE
`
`�ANTENNA
`XMITTER
`GRID SYNC (UPX) 103
`OPTIONAL)
`XMITTER
`REFERENCE
`POSITION
`UNKNOWN {XMIT
`106 \{ RECEIVER
`
`Cisco v. TracBeam / CSCO-1007
`Page 2 of 26
`
`

`

`REFLECTOR
`
`FIXED
`
`;;,
`
`FIC.3
`
`PATH -----__
`
`RADIO PROPAGATION
`1
`307
`
`/-----
`
`--
`
`\
`
`\
`
`\
`
`208
`
`�204
`
`\
`
`\
`
`r----�-l---­
`
`\
`\
`
`209 205 --TOA ERR 206
`
`102
`RECEIVER
`
`POINT
`PATH 203
`TO
`POINT
`
`UPX 103
`� FIC.2
`
`\
`
`OBSTACLE
`
`FIXED
`
`Cisco v. TracBeam / CSCO-1007
`Page 3 of 26
`
`

`

`L ____________ /_J
`: ODOMETER,
`1 GPS, DEAD RECKONING, CALIBRATE
`: DETERMINED BY:MAP
`1 ABSOLUTE
`: RADIO
`:
`I XMITTER DATA I
`: 406 407 :
`
`-IN, ETC. 1
`MATCHING, :
`POSITION
`
`USER CALL
`
`I
`
`D 1
`
`FIC.4
`
`><-><--
`
`402
`
`>( --
`
`>( --
`
`TRAINING TRANSMITTER 401
`
`MULTI STORY BUILDING 10.3
`
`408
`
`+
`
`REFERENCE
`
`I
`I
`
`I ,--__ __..___..__------.
`
`BEACON i TRANSMITTER
`
`,---------------7
`
`103 UPX \
`:v \\
`USER CALL -IN
`
`----------""""\
`
`Cisco v. TracBeam / CSCO-1007
`Page 4 of 26
`
`

`

`�11:s,� _ TYPICAL
`51�
`�EURAL_NOD�
`: 511 512 OUTPUT
`509 I
`1 INPUT
`i -- WEIGHTING
`FACTOR
`( + /-) 507
`� ---------:7
`OUTPUT
`LAYER ESTIMATE
`RMS ACCURACY
`► ALTITUDE
`505
`517
`►LONG ITUDE
`\-----<>-++t--� LATITUDE
`MEASUREMENTS]
`TD, TOA, OR
`RTOA
`BASE DRIFT
`CORRECTED
`RECEI VER TIME
`YIELD
`MAY BE PROVIDED
`TO
`[ ALTERNATIVE
`OUTPUTS
`510
`
`14 SOB I
`
`1513
`
`1 5
`
`l
`
`I
`I
`
`1
`
`I
`I
`
`EA
`
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`2=
`
`RO
`
`ON
`
`HIDDEN LAYER
`
`IC. S
`
` F
`502
`
`"------o---�
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`504
`
`,...._ __ -o-t-
`
`,...._ __ -6-H-
`
`-=----
`
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`
`516 \,_ 500
`POSIT ION (I. E,JEAR) , INPUT
`LAYER
`�
`DATA' CLOCK & TIME OF SEASON
`TIME / // _
`PHASE SUCH AS REAL
`{
` df;-,
`R SYSTEM CU
` OTHE
`MODULATI
`515
`PHASE,
`RTOA F
`'Y' -
`M RECEIVER
`CARRIER
`RECEIVER,ANO/iOR
`514
`RAKE TYPE RTOA 1 ,-RTOA
`TD-
`FROM
`RTOA/TOAs 513
`TOA RELATIVE TO GPS REF
`MULTIPLE
`ANO/OR 512
`(ABCD) 2XTOA FROM SPHERICAL
`ANT INPUT
`OPTIONS
`FROM EACH RECEIVER
`SNR.
`EDGE SLOPE,
`FUNCT ION LEADING
`CORRELATION
`RTOA,
`TOA/
`(OPTIONAL)
`FROM THAT UPX
`LAST "N" R
`DINGS
`
`-ct
`-ct
`
`Cisco v. TracBeam / CSCO-1007
`Page 5 of 26
`
`

`

`U.S. Patent
`Sheet 5 of 11 5,717,406
`Feb. 10, 1998
`
`CORRECTION MATRIX
`LONGITUDE 602
`
`1
`
`2 3
`
`LATITUDE
`601
`
`MAY CONTAIN GROSS
`lAT, LON, ALT
`
`CORRECTION FACTOR
`604 605
`603
`OR
`606 607
`TOA/RTOA
`�UPX 103
`
`CORRECTION FACTORS
`F OR 1 OR MORE RECEIVERS
`
`/
`
`609
`608
`
`_,.....6
`00
`
`FIC.6
`
`CORRECTION
`LAT, LON, ALT 1
`
`---- FACTOR(S) 702
`701
`
`LAT, LON, ALT 2
`
`701
`
`LAT, LON, ALT 3
`701
`
`N
`
`700
`
`FIG.7
`
`Cisco v. TracBeam / CSCO-1007
`Page 6 of 26
`
`

`

`U.S. Patent
`Sheet 6 of 11 5,717,406
`Feb. 10, 1998
`
`COMPUTE A
`POSITION FIX
`800
`
`�Y ______ DONE
`
`REDUCE THE TOA OR
`802
`RTOA OF RECEIVER "N"
`
`y
`
`"N"
`OF RECEIVER
`THE LAST TOA/TD
`RESTORE
`804
`
`LET N=N+ 1 805
`
`FIC.B
`
`CONVERGENCE ERROR NOT ACCEPTABLE
`MAY HAVE BEEN GAINED
`IMPROVEMENT
`BUT SOME
`
`Cisco v. TracBeam / CSCO-1007
`Page 7 of 26
`
`

`

`U.S. Patent Feb. 10, 1998 Sheet 7 of 11
`
`5,717,406
`
`\
`\
`\
`\
`\
`\
`102
`\
`\
`\
`\
`
`-.....
`
`\ I
`\ I
`' 7'- 903
`
`I
`I
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`
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`
`904
`I
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`'voPx 103 :
`I
`903
`...... .,.,,� ......
`I .._
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`1
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`
`/
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`/
`
`// RECEIVER
`102
`//
`
`/
`/
`
`14TH FLOOR
`
`\ I
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`I
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`
`ELEVATORS
`
`____
`
`...
`
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`
`.....
`
`/ � 903
`I \
`I \ FIG.9B
`
`Cisco v. TracBeam / CSCO-1007
`Page 8 of 26
`
`

`

`CHARACTERISTICS
`
`DELAY SPREAD PROFILE FROM UPX 103
`
`1001
`TIME
`
`a,
`
`00
`
`�
`
`�
`
`a
`
`= .....
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`
`1002
`
`tLEADING EDGE
`
`FIC.10
`
`....;J
`�
`....;J
`....
`Ol
`
`( 100-500ns)
`
`SIGNAL INDOOR LOCATIONS
`
`ARRIVING
`
`TIME = 0 MARKER 1004
`
`USEFUL
`
`FOR
`
`= FIRST
`RECEIVE
`
`Cisco v. TracBeam / CSCO-1007
`Page 9 of 26
`
`

`

`UPX 103
`REFERENCE
`1207
`SYNCHRONIZATION
`PERIODIC
`
`BETWEEN REF & UPX)
`
`+ DRIFT(TIME
`
`COUNTER=RTOA
`
`COUNTE R 1200 FIC. 12
`CLOCK RESET
`
`.01 TO 2ppm
`TIME BASE
`
`DETECTION
`
`__ STO_P..... l 206SIGNAL
`Q START
`
`1202 UPX SIGNAL
`
`1201
`
`---1-20-5 __._____--' FIRST ARRIVING
`
`1103
`
`SIGNAL
`
`REFERENCE
`
`1105 1203
`
`1100
`
`RESET
`COUNTER
`
`'---------.-----'
`
`CLOCK
`
`UPDATE)
`BOUNDARY.OR
`LAST GPS
`----CLOCK RTOA+DRIFT
`(TIME SINCE 1
`
`FIC.11
`
`RTOA
`
`1102
`
`SIGNAL DETECTION
`FIRST ARRIVING
`
`UPX 103
`
`1103
`\
`
`1101
`
`SYSTEM
`OR
`REFERENCE
`GPS
`
`.._R_EF_ER_EN_CE_____, l l 04
`SYNCHRONIZATION
`
`SATELLITE
`SECOND
`LATCH=
`
`Cisco v. TracBeam / CSCO-1007
`Page 10 of 26
`
`

`

`COUNTER
`(SINCE
`LATCH = RTOA + RANDOM# + DRIFT TIME
`
`START)
`MOD (AT MOD COUNT FROM I.AST FRX
`(OPTIONAL)
`
`START-UP)
`
`RECEPTION
`
`OFFSET
`1305
`
`LATCH <t--------'
`
`\
`1302
`
`1301
`
`\I
`
`
`
`OTHER RECEIVER)
`{CAN BE FROM
`UPX 103
`
`/ FRX 1308
`
`I
`
`SIGNAL
`FIRST ARRIVING
`
`DETECTION
`\
`1303
`
`FIC.13
`
`XMIT ONCE PER
`
`XMITTER
`BEACON
`
`\
`1300
`
`"\xxx COUNTS
`
`COUNTER
`
`MODULO
`
`CLOCK t>
`ppm
`1304
`.01 TO 2
`TIME BASE
`
`Cisco v. TracBeam / CSCO-1007
`Page 11 of 26
`
`

`

`U.S. Patent Feb. 10, 1998 Sheet 11 of 11 5,717,406
`
`(ENHANCED
`POSITION
`CALCUlATION)
`
`RCV 2 1403
`
`CORRECTED
`LINE - OF - POSITION
`1404
`(ERROR
`FROM A
`RECEIVER
`PAIR/TD)
`
`RCV1 1402
`
`CORRECTED
`- - __.,.
`LINE - OF - POSITION
`
`1401
`
`(ERROR
`CO�PUTATIONALY
`REDUCTED TO
`A SINGLE
`RECEIVER)
`
`FREE SPACE
`
`LINE -Of -POSITION
`
`FROM A TD 1400
`
`RTOA RCVl -RTOA
`RCV2= TO (HYPERBOLIC
`LINE-OF-POSITION)
`TOA = SPHERICAL
`LINE-OF-POSITION
`FIC.14
`
`Cisco v. TracBeam / CSCO-1007
`Page 12 of 26
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`

`

`5,717,406
`
`1
`
`FIELD OF INVENTION
`
`BACKGROUND OF THE INVENTION
`
`DISCUSSION OF THE BACKGROUND
`
`SUMMARY OF THE INVENTION
`
`2
`tion is mandatory, even in a heavily radio frequency shielded
`
`
`
`ENHANCED POSITION CALCULATION
`
`
`
`environment such as a multi-story high-rise building. In
`
`
`
`order to increase the Signal-to-Noise Ratio available to a
`
`
`system receiver from a system transmitter whose operation
`
`
`
`5 is constrained to the preceding conditions, it is desirable to
`This invention relates to life safety systems where a radio
`
`
`
`
`
`
`locate the receiver on a ground-based platform as opposed to
`
`
`
`transmitter broadcasts from an unknown location; the
`
`
`an orbital one. The ground-based receiver platform does
`
`
`unknown location can be estimated using a set of receivers
`
`
`
`have a disadvantage due to a fairly complex radio wave
`
`and a signal processing network designed using a neural
`
`
`travel path from the system transmitter (multi-path signal
`
`
`network or an associative memory.
`
`
`
`10 distortion). Urban and suburban multi-path distortion may
`
`
`
`be quite severe, as it's cause increases dramatically with
`
`each new object inserted into the path from system trans­
`
`
`mitter to system receiver (i.e. buildings, vehicles.
`
`
`
`structures). These objects cause destructive "copies"
`The need exists for a highly reliable and accurate system
`
`
`
`
`
`
`15 (echoes) of the radio signal to be generated each time the
`
`
`
`which can locate a radio transmitter in an unknown position
`
`
`
`
`signal "reflects" (bounces) off of one. The echoes arrive at
`
`
`
`in a citywide or local area of coverage. Applications include
`
`
`the system receiver later in time than the desired ( direct
`
`
`
`personal safety from assault or medical causes, roadside
`
`
`
`
`path) signal, causing loss of signal. or producing erroneous
`
`
`
`
`assistance, child monitoring for kidnapping recovery, moni­
`
`
`measurements. The analysis of how a particular environ-
`
`toring of the elderly to reduce walk aways, drug
`
`
`20 ment will induce multi-path distortion is called a "Delay
`
`
`
`enforcement. early release or parolee monitoring. as well as
`
`
`
`
`Spread Profile". Delay spread profile analysis shows multi­
`
`
`
`
`
`stolen vehicle or stolen equipment recovery. The unknown
`
`
`path echoes on the order of one to five microseconds are not
`
`
`
`
`position radio transmitter broadcasts a signal that reflects oft'
`
`
`uncommon in urban and suburban environments. Delay
`
`
`
`of objects, such as buildings or buses, before arriving at a
`
`
`
`spreads of this magnitude cause one thousand feet to one
`
`
`
`series of receivers. These reflections cause several versions
`
`
`25 mile potential error to a transmitter's calculated position if
`
`
`
`of the same signal, delayed by different amounts depending
`
`
`error removal tactics are not employed.
`
`
`on the number of reflections incurred. to be superimposed
`
`
`
`with one another. This distorts the transmitted signal and. if
`
`
`
`
`uncorrected, prevents reception and processing of the signal.
`
`
`
`
`
`
`
`Present systems include inherent drawbacks. such as 30
`
`of the prior art discussed above.
`
`
`continual monitoring, which require full time surveillance
`The second object is to achieve a position fix accuracy and
`
`
`
`
`
`
`operation or GPS services which require physically larger
`
`
`
`
`reliability appropriate for life safety applications.
`units with short battery lives and which must operate out­
`
`
`
`doors in reasonably good view of several satellites. Stanford
`
`
`A third object of the invention is to locate a low Signal­
`
`Telecom, in "RF Design" October 1992, teaches
`the use of 35
`
`
`to-Noise Ratio transmission with increased accuracy.
`
`
`
`signal averaging to reduce multi-path errors. 'The tracking
`
`A further object of the invention is to be able to locate a
`error is not always the same sign since the multi-path will
`
`
`
`transmitter which is located inside of a multi-story building.
`
`
`
`either subtract or add to the signal depending on its carrier
`
`This process may be further aided by the employment of a
`
`phase with respect to that of the direct signal. In the moving
`search team equipped with a mobile reference unit.
`
`
`
`
`vehicles. multi-path tends to change sign rather rapidly and 40
`
`
`A further object of the invention is to remove position fix
`
`is noiselike, averaging out in the long term."
`
`errors which result from fixed obstacles.
`
`
`In Spread Spectrum Systems, Third Edition, Dixon
`
`
`Another object of the invention is to remove errors from
`
`
`teaches the use of spread spectrum in time of flight to yield
`
`
`
`mobile obstacles. This requires either additional receivers or
`
`position fix information. Sanderford, et al .• in U.S. Pat. No.
`
`the ability to employ time diversity.
`4.799,062
`sites so 45
`
`disclose the use of additional receiving
`
`
`A further object of the invention is to correct drift errors
`
`
`that signals from one or more receiving sites that suffer from
`
`
`
`which result from imperfect time references contained
`
`
`
`
`delays, due to multi-path errors, can be removed as inputs to
`
`within the various system elements as well as to provide a
`
`
`
`a least squares fit algorithm. Sanderford further teaches the
`
`
`point or points of common synchronization for the compu­
`
`
`use of a mobile reference transmitter carried by a search
`
`
`
`tation of Relative Time-of-Arrival readings.
`
`
`
`team which is guided by a central dispatch station. The 50
`
`A further object of the invention is to learn the signature
`
`
`
`guidance is provided through a differential term derived
`
`
`of an area or areas frequented by a user to increase the
`from a poll reply of the unknown positioned transmitter.
`
`
`accuracy of a position fix made at a future time in that same
`
`
`However, this technique requires that the unknown posi­
`location.
`
`
`tioned transmitter have two-way communication capabili­
`A further object of the invention is to provide intelligent
`
`ties.
`ss
`
`
`
`averaging or weighting of previous position fixes in order to
`
`
`Global positioning systems also provide radio location
`
`
`
`
`further enhance the accuracy of the most recent position fix.
`
`
`
`capability if connected in a manner to re-transmit latitude,
`
`
`Another object of the invention is to provide cues appro­
`
`
`longitude, altitude information to a remote central monitor­
`
`priate to guide a search team equipped with a mobile
`
`
`ing station. GPS has several shortcomings as compared to
`
`reference unit to find a transmitter of unknown position.
`
`
`
`
`
`the instant invention for the applications contemplated 60
`
`
`
`herein. These include direct signal propagation through the
`
`All radio location systems must provide at least two major
`
`
`
`interior of multi-story buildings, the increased size and
`
`
`functions: (1) to accurately determine a first arriving radio
`
`
`weight due to the requirement of the inclusion of a receiver
`
`
`signal or to determine some appropriate attribute of a radio
`
`
`
`as well as a transmitter, and reduced battery life due to the
`
`signal which can be used to determine a transmitter's
`
`
`
`current drain of the element of the GPS receiver. The 65
`
`
`
`position, (2) computational techniques which are appropri­
`
`
`
`
`applications require physically small devices. long battery
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`ate to convert the information gained into useful position fix
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`
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`life. and imply transmit-only operation. Successful opera-
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`information which typically includes latitude, longitude and
`
`A first object of the invention is to overcome the problems
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`Cisco v. TracBeam / CSCO-1007
`Page 13 of 26
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`5,717,406
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`3
`4
`employed to enhance the position location accuracy of
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`
`
`altitude. The invention and the embodiments disclosed
`
`
`
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`cellular type radio systems by the use of the amplitude,
`
`
`herein are concerned with this second area of functionality
`
`
`
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`phase, and antenna quadrant information available. Further,
`
`required in a radio location system.
`
`
`any combination of the above techniques may be used to
`The disclosed invention uses historic information, train­
`
`
`
`
`
`5 further enrich the information available to the computational
`
`
`ing sessions, special system reference cues, as well as
`
`
`elements disclosed herein.
`
`
`ongoing learning in order to enhance a radio location
`
`
`All of the techniques disclosed herein can benefit from an
`
`
`
`system's position calculation accuracy. The invention fur­
`
`
`
`
`
`initial training session, although the training session may
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`ther seeks to reduce overall system drift errors caused by the
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`
`
`actually be accomplished during the system's nonnal opera-
`
`imperfection of the time bases used in the various system
`tion. One such training
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`
`session consists of driving a vehicle
`10
`elements.
`
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`around a city or suburban area or area of coverage interest.
`Tests were perf onned in both urban and suburban areas
`
`
`Such vehicle would be equipped with a reference transmit­
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`with a direct sequence spread spectrum, time of flight
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`ter. In addition, the vehicle would be equipped with a
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`measuring system. The said system was a transponding
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`
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`technique, or techniques, capable of independently estab-
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`return time of flight measurement measuring device. It used
`
`
`
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`lishing the accurate location of the vehicle. In this manner,
`15
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`approximately 1.2 megachip per second, 127 chips and a
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`the so equipped vehicle would communicate both indepen­
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`
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`sliding correlator to acquire the signal. In downtown areas
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`dent position information as well as beacon transmissions
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`large distance measurement jumps of 600 to 1200 feet were
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`capable of being measured by the radio location system's
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`
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`logged. These jumps were repeatable if the receiving unit
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`distributed receivers. This training information could be
`
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`was brought into the same range of proximity of the previ­
`
`20 used to create table or matrix lookup correction factors or to
`
`
`ously noted jump. When observing the immediate surround­
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`
`
`
`establish the appropriate weighting coefficients in a neural
`
`ings of areas in which these jumps occurred. it was consis­
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`network. This information could be collected and used in
`
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`tently noted that large buildings or structures obscured the
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`real time or appropriately post processed by any one of the
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`direct path of the signal. The sliding correlator was still able
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`neural network training techniques as known in the art Such
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`
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`to acquire a first arriving signal, however, said signal was
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`
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`25 neural network training techniques include, but are not
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`delayed by the added propagation path forced by the large
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`
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`limited to, back propagation, recurrent back propagation,
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`building or structure. Therefore. even a perfectly accurate
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`probabilistic neural network. learning vector quantization
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`time of flight receiving device would yield errors due to the
`
`and k-means clustering.
`
`geometry of the environment in which the system was
`In addition to the either initial or ongoing training, other
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`operated. In order to increase the accuracy and reliability of
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`A user of the radio 30 specific training may be employed.
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`the positioning information therefore requires additional
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`location service who carries a UPX on their person may
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`tactics which use both past history and other system cues in
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`either initially or periodically call in to a central station
`
`order to overcome both fixed and moving radio obstacles.
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`operator or to a voice command type system. At that time.
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`The prior art does not teach overcoming these problems
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`the user may verbally or numerically indicate his or her
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`using the techniques of the present invention. Stanford
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`a 35 physical location at that time. The user would then initiate
`
`Telecom does not teach the use of historic information to
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`sequence of transmissions on their UPX. The user may stand
`create a data base or weightings in order to correct future
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`in one position or may walk in a slow circle in order to
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`readings. Dixon does not teach the use of training. or
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`enrich the variety of resulting position fixes received by the
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`historical data base information, or pointing functions
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`central monitoring processor. An alternative to calling in to
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`derived from past information or other system cues in order
`40 a system,
`the UPX may be equipped with a small radio
`
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`to enhance the calculation of the position fix. Sanderford
`receiver or a local H-field receiver. Upon the UPX receiving
`
`does not disclose the use of historic information in order to
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`a properly coded message, the UPX may automatically
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`
`
`enhance the accuracy of the position calculation.
`
`invoke a training burst of transmissions. The initiating
`
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`Furthermore. although GPS systems can provide some posi­
`devices may be located in the user's office or if the UPX
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`tion information, GPS systems do not use historic informa­
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`45 used is affixed to an inanimate object, the initiating device
`
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`tion or of error weightings in order to enhance the accuracy
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`may be located in a known or suspected path of the UPX
`
`of the position fix calculation.
`
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`travel. The initiating device may be encoded with informa­
`
`
`tion relating to latitude, longitude and altitude so that the
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`The instant invention uses one-way communication and
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`central procession can associate this "known" information
`
`can further input the mobile reference Time-of-Arrival/
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`50 with the position fixes directly resulting from the initiating
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`Relative-Time-of Arrival unit into a neural network. thereby
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`device's forced training burst sequence. Either of these
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`enhancing information available to compute a position fix.
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`techniques may be used to establish an electronic "finger­
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`The instant invention is intended to increase the accuracy
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`
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`print" of likely UPX locations which require a high degree
`of a radio location system through computational means
`
`
`of accuracy in subsequent position fix calculations.
`
`which is located at some central receiving site. The inputs to
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`In addition to potential initial training sessions, fixed
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`these enhanced calculation devices/methods can be any one 55
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`references may be installed in part or all of a coverage area.
`
`of a number of position determination measuring tech­
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`These fixed references would either transmit their known
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`niques. For example, Time-of-Arrival information or Rela­
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`latitude, longitude, altitude position or transmit their ID
`
`tive Tune-of-Arrival information can be derived from chirp
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`which would later be associated with known latitude,
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`spread spectrum, pulsed radio, a combination of wave
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`60 longitude, altitude information in some central data base.
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`shaped pulse with phase information, phase information
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`Further, these fixed references may be made a portion of the
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`from a sin wave with no wave shaping, or by the correlation
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`receiving unit's which are distributed across a city or
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`either serial or parallel of a direct sequence spread spectrum
`
`coverage area. These fixed references may be at similar
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`transmission. In addition to the Time-of-Arrival techniques.
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`altitudes but would benefit from being held at various
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`multiple antennas can be used to establish the X, Y, Z phase
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`Z-axis position detennination. 65 altitudes in order to enhance
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`of a received H field or E field signal. Electrically rotated
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`Since these fixed references are at known. stationary
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`phase antennas such as VOR may also be employed. The
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`locations. their resulting Time-of-Arrival/Relative Time-of-
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`invention and techniques described herein may also be
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`Cisco v. TracBeam / CSCO-1007
`Page 14 of 26
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`

`

`5,717,406
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`6
`5
`building. A typical home may represent approximately 10
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`Arrival information may be used to calibrate the system or
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`dB of signal attenuation at 900 MHz. A multi-story building
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`to provide further training to a neural network. Further, these
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`can easily cause 30 dB of signal attenuation. This attenua-
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`fixed references can be used to remove or compensate drift
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`tion must be either overcome by transmitted power, closer
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`caused by imperfect time references used by the various
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`receiver sites, reduced information bandwidth, longer
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`system elements. In either a Relative Time-of-Arrival or 5
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`transmissions, making the position fix processor tolerant of
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`Time-of-Arrival radio location system, an accurate time base
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`poor and noisy signals, or any combination of these tech­
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`is used as a reference to provide time of flight information.
`niques.
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`Any drift or inaccuracy in these time references will cause
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`system errors.
`Multi-path/obstacle removal may be accomplished by the
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`The present invention provides additional accuracy by 10
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`
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`processor methods disclosed herein and fall into two cat­
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`egories: 1) fixed obstacle and 2) mobile obstacles. A fixed
`
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`providing an estimate of a position from which a transmitter
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`obstacle is a large building or structure that will cause a
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`is transmitting even when not all of the receivers receiver the
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`multi-path reflection which is repeatable over some long
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`transmitted signal. Furthermore, not all receivers have to
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`period of time. The initial training sessions isolate these
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`receive all training signals either.
`
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`Some position/location errors in the location system can 15
`
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`anomalous added paths and adapt them to the neural net­
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`work or error correction matrix or table. Once the anomalies
`
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`be on a periodic or seasonal basis or the result of local
`
`are learned, the added path and error term actually becomes
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`weather systems. Time-of-day as well as time or season may
`
`
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`useful information to enhance the accuracy of the position
`
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`be further input to the neural network/processor. The posi­
`fix calculation.
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`tion computing means may then use previous daily or yearly
`20
`Mobile obstacles are compensated for by direct tactics.
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`historic information to enhance the accuracy of the position.
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`One of three tactics may be employed to reduce the errors
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`A search team may also be employed to locate a UPX for
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`from such obstacles. Additional receivers may be used such
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`life safety applications. The search team can force a trans­
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`that a receiver suspected of a multi-path error may be
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`mission from their MRX within certain known locations,
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`eliminated from a position fix calculation such as a least
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`they also can receive those UPX transmissions from the
`25
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`squares fit. In the alternative, when using a neural network
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`MRX unit which they carry. That information may be
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`for the position fix calculation, the network may automati-
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`combined with the search team's absolute reference posi­
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`
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`cally discount or proportionally reduce the weighting of the
`tion. Such absolute position may be entered by the search
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`input from a suspect receiver. If a mobile obstacle moves in
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`team and transmitted by the MRX or via any method that
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`a relatively short period of time, then time diversity may be
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`would accurately determine and communicate the mobile
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`30 employed. In this case, if a particular reading is suspect of
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`reference team's position. This technique may be particu­
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`error due to a mobile obstacle, a method seeks to obtain
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`larly useful in a multi-story building whereby the search
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`further position fix readings which may be unaffected by the
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`team would initiate a reference transmission once they enter
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`mobile obstacle. As a final alternative, multi-path errors,
`
`the first floor of the target building.
`
`short or long. can only increase the apparent time of flight/
`
`
`
`If any of the computing elements, as disclosed herein, 35
`
`
`TOA/KI'OA readings since the multi-path error is caused
`
`
`
`predict that the UPX is in motion, then signal averaging may
`
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`from a reflection which causes the traveled path to be longer
`
`
`be invoked in order to reduce Gaussian type error terms in
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`than the geometric point-to-point path. Methods are dis­
`
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`the Time-of-ArrivaVRelative Time-of-Arrival readings.
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`
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`closed herein which intelligently reduce the Time-of-
`
`
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`Further. a simple calculation can be provided to monitor and
`
`
`
`ArrivaVRelative Time-of-Arrival until the triangulation or
`
`
`predict the direction and velocity of the UPX. If a neural 40
`
`
`
`least squares fit model yields the lowest error term or an
`
`
`
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`network is used to provide the position fix calculation, then
`
`error term of an acceptable level.
`
`
`the last M position fixes of a particular UPX may further be
`The position processor means may be implemented using
`
`
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`used as input to the neural network's matrix. In this manner,
`
`
`
`a neural network. a correction factor matrix, or a correction
`
`
`
`the neural network may take advantage of the past M
`
`
`
`factor lookup table. Neural networks provide inherent inter­
`
`
`
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`readings in order to enhance the position fix accuracy of the 45
`
`
`
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`polation between previously learned data points so that even
`
`most recent received transmission.
`
`
`
`if unexpected or error prone inputs are encountered, the
`
`
`The position fix processor will input either Relative
`
`neural network will automatically provide the best fit to its
`
`
`
`Time-of-Arrival or Time-of-Arrival or time difference infor­
`
`
`past training experience. When using the matrix lookup or
`
`
`
`mation from each of the receivers obtaining a message from
`
`
`table lookup techniques, additional methods must be pro­
`50
`
`
`
`a particular UPX. In addition, the receivers may also provide
`
`
`
`vided to correct multi-path errors if a UPX is located in
`
`
`signal-to-noise ratio information and antenna quadrant infor­
`
`
`
`between two or more matrix points, or in between the two
`
`mation. Receivers may be outfitted with four or eight
`
`most likely table lookup points. In these cases, additional
`
`
`
`directional antennas. If four or eight independent receivers
`
`
`interpolation can be used to enhance position calculation
`
`are utilized, then any one or several of the four or eight
`
`
`accuracy. Interpolation algorithms include linear
`
`
`
`
`receivers may provide valuable radio location information to 55
`
`
`
`interpolation, linear approximation, linear regression, simul-
`
`the position fix processor.
`
`
`
`
`
`taneous equations, a system of differential equations, or the
`
`
`The use of an error correction table, a matrix lookup
`like.
`
`
`
`technique, or the use of neural network processing tech­
`The neural network will directly yield outputs including
`
`
`
`
`
`
`
`niques will increase the accuracy of the position fixes
`
`
`
`
`latitude, longitude and altitude. The matrix lookup or table
`
`
`
`
`generated. This means that signals received or signal-to-60
`
`
`
`lookup must input to other position calculation algorithms as
`
`
`noise ratio may still be adequate to provide the services as
`
`are known in the art. These include triangulation,
`
`
`
`contemplated herein. The ability to work with low signal­
`
`
`
`
`multilateration, least squares fit algorithms and the like.
`
`
`
`to-noise ratio signals will facilitate the use of more distant
`
`
`If only one or two of a constellation of phase repeaters are
`
`
`
`
`receiver sites and enriched information gathered from
`
`
`
`
`able to successfully receive a weak signal. the remainder of
`
`
`
`receiver sites more distant than a first ring constellation of 65
`
`the nearby phase repeaters can be made more sensitive
`
`
`
`receivers. Using low signal-to-noise ratios also provides the
`
`
`
`
`through a windowing function, provided that the UPX
`
`
`
`ability to locate a transmitter deep within a multi-story
`
`Cisco v. TracBeam / CSCO-1007
`Page 15 of 26
`
`

`

`5,717,406
`
`10 Lo messrfi duration
`g b,t uration
`
`7
`8
`
`transmits on a sleep interval pattern which is known to the
`
`of the cesium atomic clocks used by the GPS satellite
`
`
`system. The output of such a receiver can produce one
`
`
`necessary system elements. In addition to this, the chip
`
`second time ticks such that every system receiver outfitted
`position would also be known within one or several chips
`
`with a GPS receiver would simultaneously receive a "begin­
`which c