US007511604B2
`
`a2) United States Patent
`US 7,511,604 B2
`(10) Patent No.:
`Raphaeli et al.
`(45) Date of Patent:
`Mar. 31, 2009
`
`
`(54) METHOD AND SYSTEM FOR DISTANCE
`DETERMINATIONOF RF TAGS
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5/1989 Anders et al. sss... 340/10.1
`4,827,395 A *
`9/1995 Hooketal. occ. 340/10.2
`5,450,492 A *
`2/1996 Orthmann etal.
`........ 340/10.31
`5,489,908 A *
`5/1996 Kandluretal. ..... 342/44
`5,521,601 A *
`7/1998 Chieu
`5,777,561 A
`5,838,472 A * 11/1998 Welchetal. .......... 340/10.4
`Subject to any disclaimer, the term of this
`5,886,634 A *
`3/1999 Muhme.......... 340/572.1
`patent is extended or adjusted under 35
`Porors A . 1i009 Sober rieteensenseteeeesenss 340/10.4
`’
`’
`11s
`U.S.C. 154(b)by 404 days.
`5,986,570 A * 11/1999 Black etal. cscs 340/10.2
`.
`6,150,921 A * 11/2000 Werbetal. we. 340/10.1
`
`10/514,118
`(21) Appl. No.:
`6,157,321 A * 12/2000 Ricci oes 340/10.1
`:
`6,265,962 Bl
`7/2001 Blacket al.
`
`(22) PCT Filed:—May 4, 2003 6,335,685 BL 1/2002 Schrott et al.
`
`6,362,738 Bl
`3/2002 Vega
`6,377,203 B1*
`4/2002 Doany veces 342/44
`
`.
`6,563,417 BI1*
`5/2003 Shaw
`
`
`6,832,251 Bl* 12/2004 Gelvinetal. ccc. 709/224
`
`(75)
`
`Inventors: Ruth Raphaeli, Kfar Saba (IL); Dan
`Raphaeli, Kfar Saba (IL)
`
`(73) Assignee: Sandlinks Systems Ltd., Petach Tikva
`(IL)
`
`( ae ) Notice:
`
`(86) PCT No.:
`
`PCT/IL03/00358
`
`§ 371 (¢)(),
`(2), (4) Date:
`
`Nov. 12, 2004
`
`(87) PCT Pub. No.: WO03/098528
`PCT Pub. Date: Nov. 27, 2003
`
`OTHER PUBLICATIONS
`http://en.wikipedia.org/wiki/ultra-wideband.*
`* cited by examiner
`
`Primary Examiner—Brian A Zimmerman
`Assistant Examiner—Vemal U Brown
`(74) Attorney, Agent, or Firm—Mark M.Friedman
`(57)
`ABSTRACT
`
`(65)
`
`Prior Publication Data
`US2007/0109099 Al
`May 17, 2007
`Related U.S. Application Data
`(60) Provisional application No. 60/378,078, filed on May
`16, 2002.
`
`51)
`
`The presentinvention relates to a method and system (10) for
`distance determination of RF tags (4) and its applications
`g
`p
`Y:
`g
`based on measuring the roundtrip delay, avoiding determin-
`Int. Cl.
`istic collisions between a plurality of wide band response
`(2006.01)
`H04Q 5/22
`signals transmitted by the tags (4) by adding a pseudo-ran-
`(52) US. Ch ccc 340/10.2; 340/10.1; 340/10.3;
`dom time delay to the wide band response signal, and itera-
`340/10.5; 340/825.69; 340/825.72
`(58) Field of Classification Search................ 340/10.1,__tively reducing the collision probability between plurality of
`wide band response signals.
`340/10.2, 10.34, 10.4, 572.1, 10.5, 10.3,
`340/825.69, 825.72; 342/44; 370/342
`See application file for complete search history.
`
`124 Claims, 5 Drawing Sheets
`
`REFERENCE
`CONTROLLER
`41
`
`
`
`MATCHING
`CONVERTER
`50
`54
`
`
`PACKET
`
`
`GENERATOR
`RF OSCILLATOR
`
`
`42
`
` 56
`
`
`PPM DELAY
`PULSE
`POWER
`
`
`
`
`GENERATOR
`GENERATOR
`AMPLIFIER
`
`
`
`
`46
`44
`48
`
`
`
`
`
`
`1
`
`APPLE 1006
`
`APPLE 1006
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`1
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`

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`U.S. Patent
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`U.S. Patent
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`FIG.5
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`TAG
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`READER
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`US 7,511,604 B2
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`1
`METHOD AND SYSTEM FOR DISTANCE
`DETERMINATION OF RF TAGS
`
`This application claimsthe benefit of priority of U.S. Pro-
`visional Patent Application No. 60/378,078, filed 16 May
`2002
`
`FIELD AND BACKGROUNDOF THE
`INVENTION
`
`Thepresent invention relates to distance determination of
`RFtags, used in RF identification systems, and more particu-
`larly, to a method and system for distance determination of
`RFtags andits applications, based on measuring the round
`trip delay.
`RF identification (RFID) systemsare used to track objects,
`animals and/or people in a large range of applications. RFID
`systemsare radio communication systems that communicate
`betweena radio transceiver, called a reader, and a numberof
`inexpensive devices called Tags. An RFID system generally
`includes a plurality oftags which are attached to objects being
`monitored and one or more readers which are used to com-
`municate with the tags. An encoder is optionally used to
`program the tags with unique identification information.
`Oneof the tasks commonly performed in RFID systemsis
`determining whichtagsare located in the vicinity ofa reader.
`For example, the reader may be located near a gate andit is
`desired to know whichtags pass through the gate. Generally,
`the readeris transmitting broadcast signals in its vicinity and
`the tags receiving the broadcast signal are responding to the
`broadcast signal. Moreover, it is required to prevent occur-
`rence of collisions between the response signals of different
`tags. Various methods have been suggested for preventing
`collisions. Exemplary collision overcoming methods are
`described in U.S. Pat. Nos. 5,777,561, 6,265,962 and 6,377,
`203.
`In U.S. Pat. No. 5,777,561, issued to Chieuetal, there is
`disclosed a method for selecting groups of radio frequency
`RF tags for communication between a base station and the
`tags. The tags are selected into groups according to a physical
`attribute of the signal transmitted by the tags to the base
`station, or according to the physical responseofthe tags to a
`physical attribute of the signal transmitted from the base
`station to the tags.
`In U.S. Pat. No. 6,265,962, issued to Black el al, there is
`disclosed a method for reading one or more RFID transpon-
`ders that are active and capable of communicating, compris-
`ing: providing a carrier signal; detecting the presence ofat
`least one transponder,
`the detecting including using a
`demodulator and modifying the carrier signal by suppressing
`the carrier signal for a predetermined numberof clock cycles;
`receiving data from all active transponders, the receiving
`including receiving the data in groups of one or morebits and
`checking the validity of each group of data as the group is
`received; determining whether a valid data transmission has
`been received by detecting inability to compute a proper
`synchronization word, a proper CRC, or a proper word
`length; in response to determining an invalid data transmis-
`sion, modifying the carrier signal to inform all active tran-
`sponders that there was an incomplete read; and transmitting
`the complete data for each transponder to a computer system
`for processing.
`In USS. Pat. No. 6,377,203, issued to Doany, there is dis-
`closed a method for simultaneously reading a serial number
`from multiple colliding RF signals from RF identification
`tags by employing a primary communication channel and
`multiple secondary channels. A locator or reader unit inter-
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`2
`rogates the tags, which respond with an RF signal. Upon
`receiving multiple signals, the locator or reader unit com-
`mands the RFID tags and requires them to transmit another
`response, whichis transmitted in one of the secondary chan-
`nels based on a portion of their unique serial identification
`number, thereby forcing the tags to sort in the secondary
`channels. These secondary channels are assigned using a
`portion of the unique serial identification numbers for the
`tags. The reader then detects an acknowledgmentin the occu-
`pied secondary channels and commandsa tag in a particular
`channel to move to the primary channel. Once the signal is
`transmitted in the primary channel, the reader reads the iden-
`tification number.Ifthere is further collision, the collided tags
`are returned to the secondary channelandsorted again using
`a differentportion of their ID number. This process continues
`until all the tags are sorted andidentified. Oncethetagsareall
`sorted, the tags are assigned yet another channel distinct from
`the secondary channels that are used for sorting.
`The mostsignificantlimitation ofeachofthe just described
`collision overcoming methods of U.S. Pat. Nos. 5,777,561,
`6,265,962 and 6,377,203, is that all of these collision over-
`coming methodsare time consuming. Moreover, the required
`time greatly increases with the numberoftags participating in
`the collision.
`
`In one collision avoiding method used with the ALOHA
`protocol (described below), transmitters re-transmitting after
`a collision, wait a pseudo-random period before re-transmit-
`ting the signal, so that the chance ofa collision occurring
`between the retransmitted signals is small. The random peri-
`ods are longerthan the transmitted signals, such that response
`signals of transmitters selecting different random delays do
`not collide. ALOHA protocol is implemented according to
`the following twoprinciples: (a) Ifa station has data to trans-
`mit, transmit it. (b) If transmissionscollision from different
`stations occurs, wait a random time and transmit the data
`again. Additional information regarding the ALOHAproto-
`col can be found in “Computer Communications”, Principles
`and Business Applications, by Andy Sloane, Mcgraw Hill
`ISBN 0 07 709443 3.
`
`In someapplications, it is important to know that the iden-
`tified tag is located within a certain distance from the reader.
`For example, the identification of the tag may be required in
`order to open a doorto an access-limited area If a tag remote
`from the readeris identified by the reader, the door may be
`opened to an unauthorized individual.
`Onesolution to that distance measurement problem is to
`limit the transmission rangeofthe reader. This, however, may
`cause sometags not to be identified due to their orientation
`and/or interference.
`In USS. Pat. No. 6,335,685, issued to Schrottel al, there is
`disclosed an apparatus and method for locating containers
`and contents of containers using radio frequency tags. A base
`station system for communicating with radio frequency tags
`attached to one or more objects. The base station has com-
`puters having CPUs and memories. A separate position detec-
`tor determinesthe position ofthe tags within a time increment
`and within a field of the base station. A communication pro-
`cess, executed by the CPUs, reads information from the tags
`within the time increment andassociates the position deter-
`mined with the informationofthe respective tag in the memo-
`ries. The method features a movable base station antenna
`
`providing a narrow tag interrogation beam is used as the
`position detector. The antenna of the reader is designed to
`have rotational motion to allow for scanning in a vertical
`plane. Scanning accomplishedas a function of position with
`the antenna scanning vertically while the object moveshori-
`zontally. In that mode of scanning, each tag is scanned indi-
`
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`

`US 7,511,604 B2
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`4
`of the response signals, a distance between the reader and the
`terminalstation from whichthe responsesignal wasreceived.
`To one of ordinary skill in the art, there is thus a needfor,
`and it would be highly useful to have a method anda corre-
`sponding system, for determination of RF tags, based on
`measuring the roundtrip delay. Moreover, to one of ordinary
`skill in the art, there is also a need for a method and a corre-
`sponding system, for determination of RF tags, based on
`measuring the round trip delay by using a single channel.
`Operation by a single channel simplifies the RFID system
`design and reduces the cost of implementation.
`It is also desirable to have a collision overcoming method
`consuming minimal time that is almost not increasing with
`the numberof tags participating in the collision.
`Furthermore,it is desirable to have a collision overcoming
`methodthat is relatively simple, inexpensive to implement
`and does not require a plurality of readers in different loca-
`tions.
`
`SUMMARY OF THE INVENTION
`
`3
`vidually as it passes the base station antenna so that the
`combination of horizontal object motion with vertical scan-
`ning results in a xy coordinate associated with each tag read-
`out. The horizontal motion can be determined by knowing the
`velocity of the object.
`However, the just described method suggesting using a
`separate position detector to detect the position of the tag
`identified by the reader is notably limited because it adds to
`the cost and complexity of the RFID system. In addition, the
`position detection is performedafterthe tags are identified in
`a separate stage, which adds to the time required for the
`system operation.
`In U.S. Pat. No. 5,977,913, issued to Christ, there is dis-
`closed a methodfor locating an object within a predetermined
`area comprising thesteps of: (a) sensing a signal output by the
`object using a plurality of sensors disposed within the prede-
`termined area; (b) forwarding a plurality of received signal
`levels from the plurality of sensors to a central processor; (c)
`comparing the plurality of received signal levels with a plu-
`rality of reference values to determinea location of the alarm
`signal, wherein step (c) comprises performing a bestfit analy-
`The present invention relates to distance determination of
`sis of the plurality of received signal levels with the plurality
`RFtags, used in RF identification systems, and more particu-
`of reference values; (d) transmitting one at a timeaplurality
`larly, to a method and system for distance determination of
`of reference transmission signals; (e) measuring a received
`RFtags andits applications, based on measuring the round
`signal level output from each ofthe plurality of sensors after
`each transmission.
`trip delay by using a single channel.
`Thus, according to the present invention, there is provided
`a method and a corresponding system for communicating
`between a reader and a plurality of RF tags, including the
`steps of: (a) a reader is transmitting a wide band broadcast
`interrogation signal, (b) at least one tag is waiting to receive
`the wide band broadcastinterrogation signal, (c) at least one
`of the at least one tag is waiting to receive the wide band
`broadcast interrogation signal is receiving the wide band
`broadcast interrogation signal and transmitting at least one
`wide band response signal, (d) the reader receiving at least
`one wide bandresponsesignal, wherein the at least one wide
`band response signal received by the reader may include
`overlapping wide band response signals wheneverit is com-
`prising of a plurality of wide band responsesignals transmit-
`ted by a plurality of the tags, and (i) the reader detecting the
`distinguishable wide band response signals, transmitted by
`the tags, includedin the at least one wide bandresponsesignal
`received by the reader,(ii) the reader is estimating the number
`of wide band response signals to the wide band broadcast
`interrogation signal, (111) the reader analyzing the distinguish-
`able wide band response signals in order to determine their
`roundtrip delay, (e) the reader is estimating whethera colli-
`sion between a plurality of the wide band response signals
`occurred and when the readeris estimating that the collision
`occurred, the reader is transmitting at least one additional
`wide band broadcast interrogation signal. Whereby the at
`least one additional wide band broadcastinterrogation signal
`is initiating anew communicating session between the reader
`and the plurality of RF tags in order to reduce the collision
`probability between the plurality of wide band responsesig-
`nals transmitted by the tags.
`According to another aspect of the present invention, there
`is provided a method and a corresponding system for defining
`a programmable reader cell in RFID system, including the
`steps of: (a) a reader is transmitting a wide band broadcast
`interrogation signal, (b) at least one tag is waiting to receive
`the wide band broadcastinterrogation signal, (c) at least one
`of these at least one tag is waiting to receive said wide band
`broadcast interrogation signal is receiving the wide band
`broadcast interrogation signal and transmitting at least one
`wide band responsesignal, (d) the reader is receiving at least
`
`However, position detection systems, such as described in
`USS. Pat. No. 5,977,913, are complex and generally require a
`plurality of readers in different locations.
`In U.S. Pat. No. 6,362,738, issued to Vega, there is dis-
`closed a RFID reader containing a detector circuit for detect-
`ing the presence of a signal carrier frequency transmitted by
`the transponder in response to a signal from the reader. The
`detector circuit has a resonator circuit which is connected to
`a receiver electrode. The resonator comprises a piezoelectric
`element with a high quality factor ‘Q’ at the resonant fre-
`quency to enhance sensitivity. The alarm carrier signal is
`rectified and fed to either a peak detector or an envelope
`detector circuit. A voltage source generates a voltage thresh-
`old to allow for operating range adjustment. A comparator
`compares both voltages and generates an alarm signal if the
`voltage signal reaches the threshold voltage. The RFID fur-
`ther having the capability to read the RFID contents.
`The system disclosed in U.S. Pat. No. 6,362,738 limits the
`range ofthetags it identifies by relating only to signals whose
`voltage level is above a predetermined threshold. The thresh-
`old may be user-adjustedin order to allow fordifferent ranges
`of operation. The use ofpowerthresholdsis inaccurate, as the
`power may dependon the orientation of the tag and/or on
`obstructions between the tag and the reader. In addition, the
`system ofU.S. Pat. No. 6,362,738 doesnotdisclose a solution
`for resolving collisions when a plurality of tags respond
`together.
`To date, the inventor is unaware ofprior art teaching of a
`method of communicating between a reader and one or more
`terminalstations features receiving from a plurality of termi-
`nal stations a plurality of RF response signals, determining
`for the plurality of the received response signals a round trip
`delay, and thereby determining, for each of the response
`signals, a distance betweenthe reader andthe terminalstation
`from which the response signal wasreceived.
`Moreover, the inventor is unawareofprior art teaching of a
`method of communicating between a reader and one or more
`terminalstations features receiving from a plurality of termi-
`nal stations, on a single channel, a plurality of RF response
`signals, determining for the plurality of the received response
`signals a roundtrip delay, and thereby determining, for each
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`US 7,511,604 B2
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`5
`one wide bandresponsesignal, wherein the at least one wide
`band response signal received by the reader may include
`overlapping wide band response signals wheneverit is com-
`prising of a plurality of wide band responsesignals transmit-
`ted by a plurality of tags, (e) reader detecting at least one
`response sequence included in the at least one wide band
`response signal received by reader, and deciding whether one
`or more tags answeredto the wide band broadcast interroga-
`tion signal, (f) reader analyzing the at least one detected
`response sequence,in order to determine the roundtrip delay
`of at least one of the at least one wide band responsesignal
`received by the reader, (g) the reader comparing a predefined
`threshold to the roundtrip delay of at least one of at least one
`wide band response signal received by the reader, and per-
`forming a task with tags having roundtrip delay that is pass-
`ing the predefined thresholdtest.
`According to another aspect of the present invention, there
`is provided a method and a corresponding system for locating
`the position of at least one RF tag in relation to the position of
`at least two readers, including the steps of: (a) Each ofthe at
`least two readers is independently transmitting a wide band
`broadcast interrogation signal, (b) at least one tag is waiting to
`receive the wide band broadcastinterrogation signals, (c) the
`at least one tag is transmitting a wide band responsesignal to
`each one of the wide band broadcast interrogation signals it
`received, wherein each wide band response signal includes
`identification information about the interrogating reader and
`aboutthe transmitting tag, (d) each one of at least two readers
`are receiving at least one of the wide band responsesignals,
`wherein the at least one wide band responsesignal received
`by the readers may include overlapping wide band response
`signals whenever it is comprising of a plurality of wide band
`response signals transmitted by a plurality of tags, (e) each
`oneofthe at least two readersis detecting the at least one wide
`band response signal, deciding whether one or more tags
`answeredto its wide band broadcastinterrogation signal, and
`analyzing the at least one wide band responsesignal, trans-
`mitted by a tag, in order to determinethe roundtrip delay and
`identification information,(f) each of the at least two readers
`is transferring distance and identity information of the tags
`and the readeritself to a central processing unit, by using the
`information transferred from each one of the at least two
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`readers, the central processing unit is locating the position of
`the at least one tag in relation to the positionofthe at least two
`readers.
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`The present invention for distance determination of RF
`tags successfully address limitations of presently known
`methods by providing a simpler, more rapid, and therefore,
`morecost effective system, than currently used techniques for
`distance determination and discrimination of RF tags accord-
`ing to their distance from the reader. The method of the
`present invention is readily implemented using one channel
`or a plurality of channels, and at least one reader.
`Implementation of the method and corresponding system
`ofthe present invention for distance determination of RF tags
`involves performing or completing selected tasks or steps
`manually, semi-automatically, fully automatically, and/or, a
`combination thereof. Moreover, according to actual instru-
`mentation and/or equipmentused for implementing a particu-
`lar preferred embodiment of the disclosed method and sys-
`tem, several selected steps of the present invention could be
`performed by hardware, by software on any operating system
`of any firmware, or a combination thereof. In particular, as
`hardware, selected steps of the invention could be performed
`by a computerized network, a computer, a computer chip, an
`electronic circuit, hard-wired circuitry, or a combination
`thereof, involving a plurality of digital and/or analog, electri-
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`cal and/or electronic, components, operations, and protocols.
`Additionally, or alternatively, as software, selected steps of
`the invention could be performed by a data processor, such as
`a computing platform, executing a plurality of computer pro-
`gram types of software instructions or protocols using any
`suitable computer operating system.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`invention is herein described, by way of
`The present
`example only, with reference to the accompanying drawings.
`With specific reference now to the drawings in detail, it is
`stressedthatthe particulars shown are by way of example and
`for purposes of illustrative discussion of the preferred
`embodimentsofthe present invention only, and are presented
`in the cause of providing what is believed to be the most
`useful and readily understood description of the principles
`and conceptual aspects ofthe presentinvention.In this regard,
`no attempt is made to show structural details of the present
`invention in more detail than is necessary for a fundamental
`understanding ofthe invention, the description taken with the
`drawings making apparentto those skilled in the art how the
`several forms of the invention may be embodied in practice.
`Identical structures, elements or parts which appear in more
`than onefigure are preferably labeled with a sameor similar
`numberin all the figures in which they appear. In the draw-
`ings:
`FIG. 1 is a schematic block diagram illustrating an exem-
`plary preferred embodimentof a radio frequency identifica-
`tion (RFID) system,
`in accordance with an exemplary
`embodimentof the present invention;
`FIG.2 is a schematic time chart illustrating an exemplary
`preferred embodiment of a broadcast signal, in accordance
`with an exemplary embodimentofthe present invention;
`FIG.3 is a schematic block diagram illustrating an exem-
`plary preferred embodimentof a reader, in accordance with
`an exemplary embodimentofthe present invention; and
`FIG.4 is a schematic block diagram illustrating an exem-
`plary preferred embodimentof a tag, in accordance with an
`exemplary embodimentofthe present invention;
`FIG. 5 is a schematic block diagram illustrating an exem-
`plary preferred embodiment of a system for defining a pro-
`grammable reader cellin RFID system,in accordance with an
`exemplary embodimentofthe present invention;
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The present invention relates to distance determination of
`RFtags, used in RF identification systems, and more particu-
`larly, to a method and system for distance determination of
`RFtags andits applications, based on measuring the round
`trip delay by using one or more channels.
`Hereinafter, the term ‘channel’ refers to an allocation of
`resources providing a link between a transmitter and a
`receiver. Exemplary channels are frequency band, timeslot,
`space direction and spreading code.
`Hereinafter, the term ‘wide bandsignals’ or the equivalent
`term ‘spread spectrum signals’ refers to any spread spectrum
`signals types such as: direct sequence (DS), frequency-hop-
`ping (FH), multi-carrier CDMA,chirp signals, short or long
`pulses of any shape with or without time hopping.
`Hereinafter, the term “reader cell” refers to a predeter-
`mined bounded volume,such as the volume bounded within
`a specified radius or between two radii. The accuracy of the
`bounds of the bounded volumeis dictated from the imple-
`
`9
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`

`US 7,511,604 B2
`
`7
`mentation and the physical limitations. Tags located in the
`readercell are valid tags for the current session.
`The present invention features a unique method, and a
`corresponding RFID system featuring a reduced numberof
`transmitted massagesin relationto prior art systems, whereby
`the distance between a tag and a reader is measured without a
`preliminary synchronization and without requesting only one
`tag to answerto each reader transmission.
`Another unique featureis the ability ofdefining a program-
`mable readercell in the RFID system ofthe present invention,
`enabling performing a task with authorized tags having round
`trip delay that is passing a predefined thresholdtest, based on
`the novel and unique steps ofa reader transmitting a broadcast
`interrogation signal, at least one tag respondingto the broad-
`cast
`interrogation signal,
`reader receiving at
`least one
`response signal, wherein that at least one responsesignalis
`possibly overlapping, detecting the at least one response
`sequence, deciding whether one or more tags answeredto the
`broadcast interrogation signal, and analyzing at least one
`responsesignal, transmitted by an authorizedtag 4, in order to
`determine the roundtrip delay (RTD), and performing a task
`with authorized tags having a predetermined roundtrip delay
`(RTD).
`Moreover, the present invention is enabling the user to
`locate the position of at least one RF tag in relation to the
`position of at least two readers more cost-effectively than
`prior art systems.
`Tt is to be understood that the present invention is not
`limited in its application to the details ofthe order or sequence
`of steps of operation or implementation of the method for
`distance determination of RF tags or to the details of con-
`struction, arrangement, and, composition of the correspond-
`ing system and its applications, set forth in the following
`description, drawings, or examples. The present invention is
`capable of other embodimentsor ofbeing practiced or carried
`out in various ways. Also, it is to be understood that the
`phraseology, terminology,and, notation, employed herein are
`for the purpose of description and should not be regarded as
`limiting. Moreover, the method and corresponding system of
`the present invention can be implemented in a variety of
`configurations, for example, using different frequency band.
`Throughout the following description and accompanying
`drawings there is first provided detailed description of the
`method and corresponding system for communicating
`between a reader and a plurality of RF tags of the present
`invention, followed thereafter by detailed descriptions of two
`different exemplary preferred applications ofthe method and
`corresponding system of the present invention.
`The method and corresponding system for communicating
`between a reader and a plurality of RF tags of the present
`invention are illustrated in FIGS. 1-4. The method andcorre-
`sponding system of the present invention are readily extend-
`able and applicable to the following description of two dif-
`ferent sets of exemplary preferred applications.
`The first set of exemplary preferred application of the
`method and corresponding system for communicating
`between a reader and a plurality of RF tags of the present
`invention, relates to a method and a corresponding system for
`defining a programmable reader cell in RFID system, as
`illustrated in FIG.5.
`
`The second set of exemplary preferred application of the
`method and corresponding system for communicating
`between a reader and a plurality of RF tags of the present
`invention, relates to a method and a corresponding system for
`locating the position of at least one RF tag in relation to the
`position ofat least two readers.
`
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`10
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`15
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`20
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`25
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`30
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`40
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`45
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`8
`In the following description of the method of the present
`invention, included are only main orprincipal steps needed
`for sufficiently understanding proper ‘enabling’ utilization
`and implementation of the disclosed method and system for
`distance determination of RF tags andits applications, based
`on measuring the round trip delay by using one or more
`channels. Accordingly, descriptions ofthe various required or
`optional minor, intermediate, and/or, sub steps, which are
`readily known by one of ordinary skill in the art, and/or,
`which are available in the prior art and technical literature
`relating to the field of sampling analog signals, are not
`includedherein.
`
`Steps, components, operation, and implementation of the
`method and corresponding system for distance determination
`of RF tags andits applications, based on measuring the round
`trip delay by using one or more channels, according to the
`present invention, are better understood with reference to the
`following description and accompanying drawings.
`Referring now to the drawings, FIG.1 is a schematic block
`diagram illustrating an exemplary preferred embodimentof
`radio frequency identification (RFID) system, in accordance
`with an exemplary embodiment of the present invention.
`RFID System 10 features the following primary components:
`(a) reader 2, (b) at least one RF tag 4. System 10 may include
`substantially any numberoftags 4 from one to thousandsor
`more. FIG. 1 showsonly a few tags 4 which happenedto be in
`the vicinity ofreader 2. Othertags 4 not shown mayalsoexist.
`In addition, although only one reader 2 is shown, system 10
`may include a plurality of readers 2. Generally, each tag 4 is
`identified with a unique identification (ID) that identifies the
`tag 4, and system 10 is used for detecting and/or identifying
`and/or performingtasks with tags 4 located at a specific range
`from reader 2.
`
`Each primary component, and additional components,
`needed for enabling the use of RFID system 10 are described
`in the following detailed description of the preferred embodi-
`ment of the method and corresponding system for communi-
`cating between a reader and a plurality of RF tags of the
`present invention.
`In step (a) of the preferred method for communicating
`between a reader and a plurality of RF tags of the present
`invention there is a reader 2 transmitting a wide band broad-
`cast interrogation signal 20.
`In order to determine whether one or more tags 4 are ina
`specific range from reader 2, and optionally the identity of
`one or moretags 4, reader 2 transmits a wide band broadcast
`interrogation signal, sometimesshortly referred to as “broad-
`cast interrogation signal’. A wide band broadcastinterroga-
`tion signalis a general signal, withouta tag identification, that
`may or may not contain