(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY(PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`(43) International Publication Date
`27 November 2003 (27.11.2003)
`
`
`
`PCT
`
`QO AMTA
`
`(10) International Publication Number
`WO 03/098528 A2
`
`LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW,
`Mx, MZ, NI, NO, NZ, OM, PH, PL, PT, RO, RU, SC, SD,
`SE, SG, SK, SL, TJ, TM, TN, TR, TT, TZ, UA, UG, US,
`(21)
`International Application Number:=PCT/IL03/00358
`UZ, VC, VN, YU, ZA, ZM, ZW.
`
`(51)
`
`International Patent Classification’:
`
`G06K
`
`(22)
`
`International Filing Date:
`
`4 May 2003 (04.05.2003)
`
`(25)
`
`Filing Language:
`
`(26)
`
`Publication Language:
`
`(30)
`
`Priority Data:
`60/378,078
`
`English
`
`English
`
`16 May 2002 (16.05.2002)
`
`US
`
`(71)
`(72)
`
`Applicants and
`Inventors: RAPHAELI, Ruth [IL/IL]; 19 Halamed Hei
`St., 44394 Kfar Saba (IL). RAPHAELLDan [IL/IL]; 19
`Halamed Hei St., 44394 Kfar Saba (IL).
`
`(74)
`
`Common Representative: RAPHAELI, Ruth; 19 Ha-
`lamed Hei St., 44394 Kfar Saba (IL).
`
`(81)
`
`Designated States (national); AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CO, CR, CU,
`CZ, DE, DK, DM, DZ, EC, EE, ES, FI, GB, GD, GE, GH,
`GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC,
`
`(84)
`
`Designated States (regional): ARIPO patent (GH, GM,
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZM, ZW),
`Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European patent (AT, BE, BG, CH, CY, CZ, DE, DK, EE,
`ES, FI, FR, GB, GR, HU, IE, IT, LU, MC, NL, PT, RO,
`SE, SL SK, TR), OAPI patent (BF, BJ, CF, CG, CI, CM,
`GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG).
`
`Declarations under Rule 4.17:
`as to applicant's entitlement to applyfor and be granted a
`patent (Rule 4.17(ii)) for all designations
`as to the applicant's entitlement to claim the priority ofthe
`earlier application (Rule 4.1 7(iii)) for all designations
`of inventorship (Rule 4.17(iv)) for US only
`
`Published:
`
`without international search report and to be republished
`upon receipt of that report
`
`For two-letter codes and other abbreviations, refer to the “Guid-
`ance Notes on Codes and Abbreviations" appearingat the begin-
`ning ofeach regular issue of the PCT Gazette.
`
`(54) Title! METHOD AND SYSTEM FOR DISTANCE DETERMINATION OFRF TAGS
`
`:
`
`a10
`
`QAVOAA
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`03/098528A2
`
`TAG
`
`a
`
`TAG
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`4
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`TAG
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`TAG
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`4
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`(57) Abstract: The present invention relates to a method and system (10) for distance determination of RF tags (4) and its applica-
`cS tions, based on measuring the roundtrip delay, avoiding deterministic collisions between a plurality of wide band response signals
`transmitted by the tags (4) by adding a pseudo-random time delay to the wide band response signal, and iteratively reducing the
`S
`collision probability between plurality of wide band responsesignals.
`
`APPLE 1008
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`APPLE 1008
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`1
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`PCT/IL03/00358
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`METHOD AND SYSTEM FOR DISTANCE
`
`DETERMINATION OF RF TAGS
`
`FIELD AND BACKGROUND OF THE INVENTION
`
`invention relates to distance determination of RF tags, used in RF
`The present
`identification systems, and more particularly,
`to a method and system for distance
`
`10
`
`determination of RF tags andits applications, based on measuring the round trip delay.
`RF identification (RFID) systems are used to track objects, animals and/or people in a
`large range of applications.
`RFID systems are radio communication systems
`that
`communicate between a radio transceiver, called a reader, and a number of inexpensive
`
`devices called Tags. An RFID system generally includesa plurality of tags which are attached
`
`15
`
`to objects being monitored and one or more readers which are used to communicate with the
`
`tags. An encoder is optionally used to program the tags with unique identification
`
`information.
`
`Oneofthe tasks commonly performed in RFID systems is determining which tags are
`
`located in the vicinity of a reader. For example, the reader may belocated near a gate andit is
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`20
`
`desired to know which tags pass through the gate. Generally, the reader is 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 occurrenceof collisions between the
`
`response signals of different tags. Various methods have been suggested for preventing
`collisions. Exemplary collision overcoming methodsare described in U.S. patents 5,777,561,
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`25
`
`6,265,962 and 6,377,203.
`
`In U.S. Patent No. 5,777,561, issued to Chieu et al, there is disclosed a method for
`
`selecting groupsofradio frequency RF tags for communication betweena basestation 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 physicalattribute of the signal transmitted from the base stationto the tags.
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`30
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`2
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`In U.S. Patent No. 6,265,962, issued to Black el al, there is disclosed a method for
`reading one or more RFID transponders that are active and capable of communicating,
`comprising: 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 number of clock cycles; receiving data from all active
`transponders, the receiving including receiving the data in groups of one or more bits 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 transmission, modifying the carrier signal to inform all active transponders that
`
`there was an incomplete read; and transmitting the complete data for each transponder to a
`
`computer system for processing.
`In U.S. Patent No.
`6,377,203,
`
`issued to Doany,
`
`there is disclosed a method for
`
`10
`
`15
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`20
`
`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 interrogates the tags, which respond with an RF signal.
`Upon receiving multiple signals, the locator or reader unit commands the RFID tags and
`requires them to transmit another response, which is transmitted in one of the secondary
`channels based ona portion oftheir uniqueserial 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
`acknowledgment in the occupied secondary channels and commands a tag inaparticular
`channel to move to the primary channel. Once the signal is transmitted in the primary
`channel, the reader reads the identification number. If there is further collision, the collided
`tags are returned to the secondary channel and sorted again using a different portion of their
`ID number. This process continues until all the tags are sorted and identified. Once the tags
`
`25
`
`are all sorted, the tags are assigned yet another channel distinct from the secondary channels
`
`that are used for sorting.
`The most significant limitation of each of the just described collision overcoming
`methods of U.S. patents 5,777,561, 6,265,962 and 6,377,203, is that all of these collision
`overcoming methods are time consuming. Moreover, the required time greatly increases with
`
`30
`
`the numberoftags participatingin the collision.
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`3
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`In one collision avoiding method used with the ALOHAprotocol (described below),
`
`transmitters re-transmitting after a collision, wait a pseudo-random period before re-
`
`transmitting the signal, so that the chance ofa collision occurring between the retransmitted
`signals is small. The random periods are longer than the transmitted signals, such that
`response signals of transmitters selecting different random delays do not collide. ALOHA
`protocol is implemented accordingto the following twoprinciples: (a) If a station has data to
`transmit, transmit it.
`(b) If transmissions collision from different stations occurs, wait a
`
`random time and transmit the data again. Additional information regarding the ALOHA
`
`protocol can be found in “Computer Communications”, Principles and Business Applications,
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`10
`
`by Andy Sloane, Mcgraw Hill ISBN 0 07 709443 3.
`
`In some applications, it is important to know that the identified 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 reader is identified by
`
`the reader, the door may be opened to an unauthorized individual.
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`15
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`_ Onesolution to that distance measurement problem is to limit the transmission range of
`
`the reader. This, however, may cause sometags notto be identified due-to their orientation
`
`and/or interference.
`
`In U.S. Patent No. 6,335,685, issued to Schrott el al, there is disclosed an apparatus and
`
`method for locating containers and contents of containers using radio frequency tags. A base
`
`20
`
`station system for communicating with radio frequency tags attached to one or more objects.
`
`The base station has computers having CPUs and memories. A separate position detector
`
`determines the position of the tags within a time increment and within a field of the base
`
`station. A communication process, executed by the CPUs, reads information from the tags
`
`within the time increment and associates the position determined with the information of the
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`25
`
`respective tag in the memories.
`
`The method features a movable base station antenna
`
`providing a narrow tag interrogation beam is used as the position detector. The antenna ofthe
`
`reader is designed to have rotational motion to allow for scanning in a vertical plane.
`
`Scanning accomplished as a function of position with the antenna scanning vertically while
`
`the object moves horizontally. In that mode of scanning, each tag is scanned individually as it
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`30
`
`passes the base station antenna so that the combination of horizontal object motion with
`
`vertical scanning results in a xy coordinate associated with each tag readout. The horizontal
`
`motion can be determined by knowing thevelocity of the object.
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`However, the just described method suggesting using a separate position detector to
`
`detect the position ofthe tag identified by the readeris notably limited because it adds to the
`
`cost and complexity of the RFID system. In addition, the position detection is performed after
`
`the tags are identified in a separate stage, which adds to the time required for the system
`
`operation.
`
`In U.S. Patent No. 5,977,913, issued to Christ, there is disclosed a method for locating
`
`an object within a predetermined area comprising the stepsof: (a) sensing a signal output by
`
`the object using a plurality of sensors disposed within the predetermined area; (b) forwarding
`
`a plurality of received signal levels from the plurality of sensors to a central processor; (c)
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`10
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`comparing the plurality of received signal
`
`levels with a plurality of reference values to
`
`determine a location of the alarm signal, wherein step (c) comprises performing a best fit
`
`analysis of the plurality of received signal levels with the plurality of reference values; (d)
`
`transmitting one at a time a plurality of reference transmission signals; (e) measuring a
`
`received signal level output from each of the plurality of sensors after each transmission.
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`15
`
`However, position detection systems, such as described in U.S. patent 5,977,913, are
`complex and generally require a plurality ofreaders in different locations.
`In U.S. Patent No. 6,362,738,
`issued to Vega,
`there is disclosed a RFID reader
`
`containing a detector circuit
`
`for detecting the presence of a signal carrier frequency
`
`transmitted by the transponderin responseto a signal from the reader. The detector circuit has
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`20
`
`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 frequency 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 threshold to allow for
`
`operating range adjustment. A comparator compares both voltages and generates an alarm
`
`25
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`signal if the voltage signal reaches the threshold voltage. The RFID further having the
`
`capability to read the RFID contents.
`
`The system disclosed in U.S. patent 6,362,738 limits the range of the tags it identifies by
`
`relating only to signals whose voltage level is above a predetermined threshold. The threshold
`
`may be user-adjusted in order to allow for different ranges of operation. The use of power
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`30
`
`thresholds is inaccurate, as the power may depend on the orientation of the tag and/or on
`
`obstructions between the tag and the reader. In addition, the system of U.S. patent 6,362,738
`
`doesnot disclose a solution for resolving collisions whenaplurality of tags respond together.
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`5
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`To date, the inventor is unaware of prior art teaching of a method of communicating
`
`between a reader and one or more terminal stations features receiving from a plurality of
`
`terminal stations a plurality of RF response signals, determining for the plurality of the
`
`received response signals a roundtrip delay, and thereby determining, for each of the response
`
`signals, a distance between the reader and the terminal station from which the response signal
`
`was received.
`
`Moreover, the inventor is unaware ofprior art teaching of a method of communicating
`
`between a reader and one or more terminal stations features receiving from a plurality of
`
`terminal stations, on a single channel, a plurality of RF response signals, determining for the
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`10
`
`plurality of the received response signals a round trip delay, and thereby determining, for each
`
`of the response signals, a distance between the reader and the terminal station from which the
`
`response signal was received.
`
`To one of ordinary skill in theart, there is thus a need for, and it would be highly useful
`
`to have a method and a corresponding system, for determination of RF tags, based on
`
`15
`
`measuring the round trip delay. Moreover, to one of ordinary skill in the art, there is also a
`
`need for a method and a corresponding 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
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`20
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`is almost not increasing with the numberoftags participating in thecollision.
`
`Furthermore, it is desirable to have a collision overcoming method that is relatively
`
`simple,
`
`inexpensive to implement and does not require a plurality of readers in different
`
`locations.
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`25
`
`SUMMARY OF THE INVENTION
`
`The present
`
`invention relates to distance determination of RF tags, used in RF
`
`identification systems, and more particularly,
`
`to a method and system for distance
`
`determination of RF tags and its applications, based on measuring the roundtrip delay by
`
`using a single channel.
`
`30
`
`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 broadcastinterrogation signal,
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`(b) at least one tag is waiting to receive the wide band broadcast interrogation 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 band responsesignal,
`wherein the at least one wide band response signal received by the reader may include
`overlapping wide band response signals wheneverit is comprising of a plurality of wide band
`
`response signals transmitted by a plurality of the tags, and (i) the reader detecting the
`
`distinguishable wide band response signals, transmitted by the tags, included in the at least
`
`one wide band response signal received bythe reader, (ii) the reader is estimating the number
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`10
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`of wide band response signals to the wide band broadcast interrogation signal, (iii) the reader
`
`analyzing the distinguishable wide band response signals in order to determinetheir roundtrip
`
`delay, (e) the reader is estimating whether a collision between a plurality of the wide band
`
`response signals occurred and when the reader is estimating that the collision occurred, the
`
`reader is transmitting at
`
`least one additional wide band broadcast interrogation signal.
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`15
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`Whereby the at least one additional wide band broadcast interrogation signal is initiating a
`
`new communicating session between the reader and the plurality of RF tags in order to reduce
`
`the collision probability between the plurality of wide band response signals transmitted by
`
`the tags.
`
`According to another aspect of the present invention, there is provided a method and a
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`20
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`corresponding system for defining a programmable reader cell in RFID system, including the
`
`steps of: (a) a reader is transmitting a wide band broadcastinterrogation 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 broadcastinterrogation signal and transmitting at least one wide band response
`signal, (d)
`the reader is receiving at least one wide band response signal, wherein the at
`least one wide band response signal received by the reader may include overlapping wide
`band response signals wheneverit is comprising of a plurality of wide band response signals
`transmitted by a plurality oftags, (e) reader detecting at least one response sequence included
`in the at least one wide bandresponsesignal received by reader, and deciding whether one or
`
`more tags answered to the wide band broadcastinterrogation signal, (f) reader analyzingtheat
`least one detected response sequence, in order to determine the round trip delay ofat least one
`of the at least one wide band response signal received by the reader, (g) the reader comparing
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`30
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`a predefined thresholdto the roundtrip delay of at least one of at least one wide band response
`
`signal received by the reader, and performing a task with tags having roundtrip delay that is
`
`passing 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 of the at
`
`least two readers is
`
`independently transmitting a wide band broadcast interrogation signal, (b) at least onetagis
`
`waiting to receive the wide band broadcast interrogation signals, (c) the at least one tag is
`
`transmitting a wide band response signal to each one of the wide band broadcastinterrogation
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`10
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`signals
`
`it
`
`received, wherein each wide band response signal
`
`includes
`
`identification
`
`information about the interrogating reader and about the transmitting tag, (d) each one of at
`
`least two readers are receiving at least one of the wide band response signals, wherein the at
`
`least one wide band response signal received by the readers may include overlapping wide
`
`band response signals whenever it is comprising ofa plurality of wide band response signals
`
`a =
`
`transmitted by a plurality of tags, (e) each one of the at least two readers is detecting the at
`
`least one wide band response signal, deciding whether one or more tags answered to its wide
`band broadcast interrogation signal, and analyzing the at least one wide band response signal,
`transmitted by a tag, in order to determine the roundtrip delay andidentification information,
`
`(f) each ofthe at least two readersis transferring distance and identity information ofthe tags
`
`20
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`and the reader itself to a central processing unit, by using the information transferred from
`
`each one of the at least two readers, the central processing unit is locating the position of the
`at least one tag in relation to the position ofthe at least two readers.
`
`The present invention for distance determination of RF tags successfully address
`
`25
`
`limitations of presently known methods by providing a simpler, more rapid, and therefore,
`
`more cost effective system, than currently used techniques for distance determination and
`
`discrimination of RF tags according to their distance from the reader. The method ofthe
`
`present invention is readily implemented using one channel ora plurality of channels, and at
`
`least one reader.
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`30
`
`Implementation of the method and corresponding system of the 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,
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`according to actual instrumentation and/or equipment used for implementing a particular
`preferred embodiment of the disclosed method and system, 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, electrical 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 program
`types of software instructionsor protocols using any suitable computer operating system.
`
`10
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The present invention is herein described, by way of example only, with reference to the
`
`accompanying drawings. With specific reference now to the drawings in detail, it is stressed
`that the particulars shown are by way of example and for purposesofillustrative discussion of
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`15
`
`20
`
`the preferred embodiments of the 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 of the present invention. 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 of the invention, the description taken with the drawings making
`apparentto those skilled in the art how the several formsof the invention may be embodied in
`practice.
`Identical structures, elements or parts which appear in more than one figure are
`preferably labeled with a same orsimilar numberin all the figures in which they appear.
`In
`the drawings:
`
`FIG. 1 is a schematic block diagram illustrating an exemplary preferred embodiment of
`a radio frequency identification (RFID) system, in accordance with an exemplary embodiment
`of the present invention;
`
`FIG. 2 is a schematic time chart illustrating an exemplary preferred embodiment of a
`broadcastsignal, in accordance with an exemplary embodimentofthe present invention;
`FIG. 3 is a schematic block diagram illustrating an exemplary preferred embodiment of
`a reader, in accordance with an exemplary embodimentofthe present invention; and
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`FIG. 4 is a schematic block diagram illustrating an exemplary preferred embodiment of
`
`a tag, in accordance with an exemplary embodimentof the present invention;
`
`FIG. 5 is a schematic block diagram illustrating an exemplary preferred embodiment of
`
`a system for defining a programmable reader cell in RFID system, in accordance with an
`
`exemplary embodimentof the present invention;
`
`DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`The present
`
`invention relates to distance determination of RF tags, used in RF
`
`identification systems, and more particularly,
`
`to a method and system for distance
`
`10
`
`determination of RF tags and its 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.
`
`15
`
`Hereinafter, the term 'wide band signals’ or the equivalent term 'spread spectrum signals'
`
`refers to any spread spectrum signals types such as: direct sequence (DS), frequency-hopping
`(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 predetermined bounded volume, such as
`
`20
`
`25
`
`the volume bounded within a specified radius or between two radii. The accuracy of the
`bounds of the bounded volume is dictated from the implementation and the physical
`limitations. Tags located in the reader cell are valid tags for the current session.
`
`The present invention features a unique method, and a corresponding RFID system
`featuring a reduced number oftransmitted massagesin relation to 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 answer to each reader transmission.
`
`Another unique feature is the ability of defining a programmable readercell in the RFID
`
`system of the present invention, enabling performing a task with authorized tags having round
`
`trip delay that is passing a predefined threshold test, based on the novel and unique steps of a
`reader transmitting a broadcast
`interrogation signal, at
`least one tag responding to the
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`30
`
`broadcast interrogation signal, reader receiving at least one response signal, wherein that at
`
`least one response signal is possibly overlapping, detecting the at least one response sequence,
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`deciding whether one or more tags answered to the broadcast
`
`interrogation signal, and
`
`analyzing at
`
`least one response signal,
`
`transmitted by an authorized tag 4,
`
`in order to
`
`determine the round trip delay (RTD), and performing a task with authorized tags having a
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`predetermined roundtrip delay (RTD).
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`Moreover, the present invention is enabling the user to locate the position of at least one
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`RF tag in relation to the position of at least two readers more cost-effectively than prior art
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`systems.
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`It is to be understood that the present invention is not limited in its application to the
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`details of the order or sequence of steps of operation or implementation of the method for
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`10
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`distance determination of RF tags or to the details of construction, arrangement, and,
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`composition of the corresponding system and its applications, set forth in the following
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`description, drawings, or examples. The present invention is capable of other embodiments or
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`of being 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
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`15
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`the present invention can be implemented in a variety of configurations, for example, using
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`different frequency band,
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`Throughoutthe following description and accompanying drawingsthereis first provided
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`20
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`detailed description of the method and corresponding system for communicating between a
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`reader and a plurality of RF tags of the present invention, followed thereafter by detailed
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`descriptions of two different exemplary preferred applications of the method and
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`corresponding system of the present invention.
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`The method and corresponding system for communicating between a reader and a
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`25
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`plurality of RF tags of the present invention are illustrated in FIGS. 1-4. The method and
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`corresponding system of the present invention are readily extendable and applicable to the
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`following description of two different sets of exemplary preferred applications.
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`The first set of exemplary preferred application of the method and corresponding system
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`for communicating between a reader and a plurality of RF tags of the present invention,
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`30
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`relates to a method and a corresponding system for defining a programmable readercell in
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`RFID system,as illustrated in FIG.5.
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`WO 03/098528
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`PCT/IL03/00358
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`il
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`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 anda corresponding system for locating the position ofat least
`one RF tag in relation to the position of at least two readers.
`
`In the following description of the method of the present invention, included are only
`main or principal steps needed for sufficiently understanding proper'enabling'utilization and
`implementation of the disclosed method and system for distance determination of RF tags and
`its applications, based on measuring the round trip delay by using one or more channels.
`Accordingly, descriptions of the various required or optional minor, intermediate, and/or, sub
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`10
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`steps, which are readily known byone ofordinary skill in the art, and/or, which are available
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`in the prior art and technical literature relating to the field of sampling analogsignals, are not
`included herein.
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`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, accordingto the present invention, are better
`understoodwith reference to the following description and accompanying drawings.
`Referring now to the drawings, FIG.
`1 is a schematic block diagram illustrating an
`exemplary preferred embodiment of 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
`mayinclude substantially any numberof tags 4 from one to thousands or more. FIG. 1 shows
`only a few tags 4 which happenedto be in the vicinity of reader 2. Other tags 4 not shown
`may also exist.
`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 performing
`tasks with tags 4 located at a specific range from reader2.
`
`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
`embodiment of the method and corresponding system for communicating between a reader
`and a plurality ofRF tags ofthe present invention.
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`20
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`2D
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`30
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`12
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`12
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`WO 03/098528
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`PCT/IL03/00358
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`12
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`In step (a) of the preferred method for communicating between a reader anda plurality
`of RF tags of the present invention there is a reader 2 transmitting a wide band broadcast
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`interrogation signal 20.
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`In order to determine whether one or moretags 4 are in a specific range from reader 2,
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`and optionally the identity of one or more tags 4, reader 2 transmits a wide band broadcast
`interrogation signal, sometimes shortly referred to as ‘broadcast interrogation signal’. A wide
`band broadcast interrogation signal is a generalsignal, without a tag identification, that may or
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`may not contain data. The transmission of the wide band broadcast interrogation signal may
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`be performed at a high repetition rate, for example: every tenth of a second, so as to
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`10
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`substantially continuously monitorthe vicinity of reader 2. Alternatively, the transmission of
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`the wide band broadcast interrogation signal may be performed at a low repetition rate, for
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`example: according to a predetermined scheme and/or under human control. The wide band
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`broadcast interrogation s