WO2008082089A1 - Radio frequency identification tag and reader, method of identifying tag, anti-collision method for tag - Google Patents

Radio frequency identification tag and reader, method of identifying tag, anti-collision method for tag Download PDF

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Publication number
WO2008082089A1
WO2008082089A1 PCT/KR2007/006265 KR2007006265W WO2008082089A1 WO 2008082089 A1 WO2008082089 A1 WO 2008082089A1 KR 2007006265 W KR2007006265 W KR 2007006265W WO 2008082089 A1 WO2008082089 A1 WO 2008082089A1
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WO
WIPO (PCT)
Prior art keywords
prefix
tag
frame
request signal
identifier
Prior art date
Application number
PCT/KR2007/006265
Other languages
French (fr)
Inventor
Sung Kwon Kim
Jae-Dong Shin
Sang-Soo Yeo
Original Assignee
Chung-Ang University Industry-Academy Cooperation Foundation
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Publication date
Application filed by Chung-Ang University Industry-Academy Cooperation Foundation filed Critical Chung-Ang University Industry-Academy Cooperation Foundation
Publication of WO2008082089A1 publication Critical patent/WO2008082089A1/en

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/0008—General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
    • G06K7/10019—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers.
    • G06K7/10029—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the time domain, e.g. using binary tree search or RFID responses allocated to a random time slot
    • G06K7/10039—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the time domain, e.g. using binary tree search or RFID responses allocated to a random time slot interrogator driven, i.e. synchronous
    • G06K7/10049—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the time domain, e.g. using binary tree search or RFID responses allocated to a random time slot interrogator driven, i.e. synchronous binary tree
    • H04B5/77—

Definitions

  • the present invention relates to a radio frequency identification tag and a reader, a method of identifying a radio frequency identification tag, and an anti-collision method of a radio frequency identification tag, and more particularly, to a radio frequency identification tag and a reader, a method of identifying a radio frequency identification tag, and an anti-collision method of a radio frequency identification tag that enable a radio frequency identification tag reader to accurately identify a radio frequency identification tag by preventing a collision among radio frequency identification tags.
  • a Radio Frequency Identification (RFID) tag is a kind of Automatic Identification and Data Capture (AIDC) technology and enables a tag reader to read data stored in an RFID tag in which a microchip is mounted in a non-contact manner using a radio frequency.
  • RFID Radio Frequency Identification
  • An RFID system generally includes an RFID tag attached to an object and an RFID tag reader.
  • the RFID tag includes a microchip for storing an identification code of an object and information about the object and an antenna for transmitting and receiving information to and from the RFID tag reader using a radio frequency.
  • the RFID tag reader includes an internal or external antenna and a controller for controlling transmission and reception of information.
  • a principle of transmitting and receiving information between the RFID tag reader and the RFID tag is as follows.
  • An antenna provided in the RFID tag reader forms an RF field, which is an electromagnetic field by emitting an active signal.
  • the RFID tag receives an active signal emitted from the antenna of the RFID tag reader and transmits information stored within the RFID tag to the RFID tag reader using the received active signal.
  • the RFID tag reader receives and analyzes information transmitted from the RFID tag and acquires intrinsic information stored in the RFID tag.
  • all RFID tags within an RF field simultaneously respond to a signal of the RFID tag reader. In this case, there is a problem that response signals of the RFID tags may collide.
  • various anti-collision technologies exist.
  • a conventional anti-collision technology is largely divided into an ALOHA-based algorithm and a tree-based algorithm.
  • the ALOHA-based algorithm is a slotted ALOHA algorithm and prevents a collision among RFID tags by dividing a time into slots and responding the RFID tag to only a slot allocated to itself.
  • the tree-based algorithm performs a process of identifying an RFID tag using an intrinsic identifier of the RFID tag having a tree structure.
  • the conventional ALOHA-based algorithm is based on uncertainty of a probability, the conventional ALOHA-based algorithm may not identify all RFID tags within an RF field of the RFID tag reader.
  • the conventional tree-based algorithm because RFID tags having similar identifiers increase when the RFID tags increase, a collision among the RFID tags may increase.
  • the conventional tree-based algorithm uses a method of increasing the depth of trees, however when the depth of the trees increases, much time is required for identifying the RFID tags. [Disclosure] [Technical Problem]
  • the present invention has been made in an effort to solve the above problems, and the present invention provides an RFID tag and a reader, a method of identifying an RFID tag, and an anti-collision method of an RFID tag that can efficiently prevent a collision in identifying a plurality of RFID tags.
  • an RFID tag reader including: an epoch size determination unit for determining the size of an epoch signal including at least one frame; an identifier request signal generator for generating an identifier request signal including a prefix and a number of a frame; a communication unit for transmitting the epoch signal and the identifier request signal and receiving a tag identifier from an RFID tag, having received the identifier request signal; an anti-collision unit for generating, when a plurality of tag identifiers selects any one of the frames, a sub-prefix by increasing a bit of the prefix of the frame and enabling the identifier request signal generator to generate an identifier request signal including the sub-prefix; and a tag identification unit for identifying, if a prefix or a sub-prefix of the tag identifier is identical to the prefix or the sub-prefix included in the identifier request signal, an RFID tag, having transmitted the tag identifier.
  • the anti-collision unit for generating, when
  • the epoch size determination unit may change, if the quantity of the tag identifiers for selecting any one of the frames included in the epoch signal is a reference value or more, the size of the epoch signal by increasing the quantity of the frames included in the epoch signal, and the communication unit may retransmit the changed epoch signal.
  • the any one frame may be a first frame among the frames included in the epoch signal.
  • a method of identifying an RFID tag including: determining the size of an epoch signal including at least one frame; generating an identifier request signal including a prefix and a number of a frame; transmitting the epoch signal and the identifier request signal; receiving a tag identifier including a prefix from an RFID tag, having received the identifier request signal; generating, when a plurality of tag identifiers selects any one of the frames, a sub-prefix by increasing a bit of the prefix of the frame and enabling an identifier request signal generator to generate an identifier request signal including the sub-prefix; and identifying, if a prefix or a sub-prefix of the tag identifier is identical to the prefix or the sub-prefix included in the identifier request signal, an RFID tag, having transmitted the tag identifier.
  • an identifier request signal including the coordinate prefix may be generated.
  • the size of the epoch signal may be changed by increasing the quantity of the frames included in the epoch signal.
  • an RFID tag including: a receiver for receiving an identifier request signal including the quantity of frames of a preset size from an RFID tag reader and including a prefix and a number of a frame; a frame selector for randomly selecting any one of the frames; a response signal generator for generating, if the frame included in the received identifier request signal is identical to the frame selected by the frame selector and if the prefix included in the identifier request signal is identical to a bit value of a specific bit of the tag identifier, a response signal including the tag identifier; and a transmitter for transmitting the response signal to the RF 1 ID tag reader.
  • an anti-collision method of an RFID tag including: transmitting an epoch signal to RFID tags; receiving, by the RFID tags, a signal for randomly selecting a frame included within the epoch signal; performing a query tree algorithm in any one of the frames; and increasing, if the quantity of collisions generating in the any one frame is a reference value or more, the size of the epoch signal.
  • a query tree algorithm may be performed in frames after the any one frame.
  • the any one frame may be a first frame among the frames included in the epoch signal.
  • a computer readable recording medium on which a program for executing the anti-collison method of an RFID tag in the computer is recorded.
  • a method of identifying an RFID tag, and an anti-collision method of the RFID tag of the present invention a plurality of RFID tags positioned within an RF field of the RFID tag reader can be accurately identified and a time required for identifying the RFID tag can be reduced.
  • FIG. 1 is a block diagram illustrating a configuration of an RFID tag reader according to an exemplary embodiment of the present invention
  • FIG. 2 is a flowchart illustrating a process of determining an epoch size included in an epoch signal
  • FIG. 3 is a diagram illustrating a frame number and a prefix included in an identifier request signal
  • FIG. 4 is a tree diagram illustrating a process in which an RFID tag reader performs a query tree algorithm in one frame number according to an exemplary embodiment of the present invention
  • FIG. 5 is a flowchart illustrating a process of an anti-collision method of an RPID tag reader according to an exemplary embodiment of the present invention
  • FIG. 6 is a block diagram illustrating a configuration of an RFID tag according to an exemplary embodiment of the present invention
  • FIG. 7 is a graph comparing the quantity of queries based on the quantity of RPID tags in a conventional anti-collision method and a Framed Query Tree (FQT) anti-collision method according to an exemplary embodiment of the present invention
  • FIG. 8 is a graph comparing the quantity of transmissions of an identifier request signal and the quantity of receptions of a response signal required for identifying one RFID tag in a conventional anti-collision method and a FQT anti-collision method according to an exemplary embodiment of the present invention.
  • FQT Framed Query Tree
  • FIG. 1 is a block diagram illustrating a configuration of an RFID tag reader according to an exemplary embodiment of the present invention.
  • the RFID tag reader includes an epoch size determination unit 110, an identifier request signal generator 120, an anti-collision unit 130, a communication unit 140, a tag identification unit 150, and a queue 160.
  • the epoch size determination unit 110 determines the size of an epoch signal having a preset size.
  • the size of the epoch signal is the size that can include a frame number and may be previously set according to a communication method between an RFID tag reader and an RFID tag.
  • the size of the epoch signal may be set with an experimentally measured value so that the depth of a tree formed by performing a query tree algorithm within one frame is not so deep. Further, the size of the epoch signal may be differently set according to the quantity of RFID tags positioned within an RF range in which the reader can identify the RFID tags. In this case, the size of the epoch signal may be set to correspond to a half of the quantity of the RFID tags positioned within an RF range in which the reader can identify the RFID tags.
  • the epoch size determination unit 110 sequentially allocates intrinsic frame numbers to each of frames of the determined quantity and determines an epoch size by multiplying the quantity of the frames to the frame size.
  • the epoch size determination unit 110 allocates each intrinsic frame number of '1' up to the determined quantity to each of the frames.
  • the frame number is a reference value for determining whether the RFID tag itself is a response target of an identifier request signal, having transmitted by the reader.
  • the determined epoch size is a value for providing information about the quantity of frames, having transmitted by the reader to the RFID tag.
  • the reader cannot know the quantity of RFID tags positioned within an RF field that can be identified by the reader until the RFID tags are identified. Therefore, in order to determine the proper quantity of frames, the epoch size determination unit 110 performs an estimation process of a first frame test. For this, if the quantity of collisions of the tag identifiers is a preset reference value or more through a frame to perform identification, the epoch size determination unit 110 changes the epoch size by increasing the quantity of frames. In this case, if the reference value is set to be small, the quantity of transmissions of an identifier request signal including an unnecessary frame number that is not selected by the RFID tag increases. If the reference value is set to be large, an estimating process is lengthened. Therefore, the reference value may be experimentally set to '3'.
  • the epoch size determination unit 110 changes an epoch size by increasing the quantity of frames.
  • a first frame test is performed as follows. An epoch size is set to be small at a first stage, and if the quantity of collisions is a collision threshold or more in a first frame, an identification process is stopped and after an epoch size is increased, and an anti-collision method is again started.
  • tag identifiers which are response signals of an identification request signal are frequently collided at the identifier request signal including the first frame number
  • tag identifiers, which are response signals may be frequently collided at an identifier request signal including the remaining frame numbers.
  • FIG. 2 is a flowchart illustrating a process of determining an epoch size included in an epoch signal.
  • the epoch size determination unit 110 determines the size of an epoch signal having a preset size (S200).
  • the communication unit 140 transmits an epoch signal including information about the determined size of the epoch signal to at least one RFID tag existing within an RF range (S210).
  • the communication unit 140 transmits a corresponding identifier request signal satisfying a prefix and a number of a frame to perform identification generated by the identifier request signal generator 120 (S220).
  • the epoch size determination unit 110 receives a tag identifier including a prefix from an RFID tag, having received the identifier request signal (S230).
  • the epoch size determination unit 110 determines whether the quantity of receptions of tag identifiers from a plurality of RFID tags through a frame to perform identification is a reference value or more (S240).
  • the epoch size determination unit 110 increases the epoch size by multiplying the epoch size (S250). Thereafter, the epoch size determination unit 110 repeatedly performs a process of steps S210 to S250.
  • the epoch size determination unit 110 terminates a process of determining the epoch size.
  • the identifier request signal generator 120 generates an identifier request signal including a prefix and a number of a frame to perform selected identification.
  • the frame number is one of frame numbers intrinsically allocated to frames of the determined quantity within the epoch size.
  • the identifier request signal generator 120 generates an identifier request signal sequentially including the frame number starting from the smallest one. Further, the identifier request signal generator 120 generates two identifier request signals having the same frame number, however including a prefix of a 'low' value and a prefix of a 'high' value.
  • a prefix that has the same bit number and in which only a value of a final bit is different is referred to as a coordinate prefix.
  • a prefix that has the bit number greater by one bit than that of the other prefixes and that has all bit values of the other prefixes is referred to as a sub-prefix of the other prefixes. That is, the sub-prefix is a prefix in which a bit having a 'low' or 'high' value is added to an existing prefix.
  • FIG. 3 is a diagram illustrating a frame number and a prefix included in an identifier request signal.
  • the identifier request signal generator 120 generates identifier request signals of four frames. Further, the identifier request signal generator 120 generates four identifier request signals including a frame number 1 I', each having a prefix 1 O', a prefix 1 I', a prefix 1 OO', and a prefix '01'.
  • the identifier request signal generator 120 generates six identifier request signals including a frame number '4', each having a prefix 1 O', a prefix '1', a prefix 1 OO', a prefix 1 Ol', a prefix 1 OlO 1 , and a prefix 'Oi l'.
  • the prefix T is a coordinate prefix of the prefix 1 O'
  • the prefix 1 OO' is a sub-prefix of the prefix 1 O'.
  • the anti-collision unit 130 When tag identifiers are received from a plurality of RFID tags through a frame to perform identification, the anti-collision unit 130 generates a sub-prefix by increasing a bit of a prefix included in the identifier request signal. When tag identifiers are received from a plurality of RFID tags through a frame to perform identification, the received RFID tags cannot be identified due to a collision. In order to prevent the collision, the anti-collision unit 130 increases a bit of a prefix included in the transmitted identifier request signal to generate two sub-prefixes in which a bit value of the increased bit is 'low' and 'high'.
  • the anti-collision unit 130 When a number of a frame to perform identification is T and the prefix number is 1 O', if tag identifiers are received from two RFID tags, the anti-collision unit 130 generates sub-prefixes OO' and 1 Ol', as shown in
  • the anti-collision unit 130 enables the identifier request signal generator 120 to generate an identifier request signal including a number of a frame to perform identification and a sub-prefix generated by the anti-collision unit 130.
  • the anti-collision unit 130 generates an identifier request signal including the frame number '1' and the generated sub-prefix '00' and an identifier request signal including the frame number '1' and the generated sub-prefix 1 Ol'.
  • the communication unit 140 transmits an epoch signal including an epoch size and an identifier request signal including a prefix and a number of a frame to perform identification.
  • the identifier request signal generator 120 When the identifier request signal generator 120 generates an identifier request signal, the communication unit 140 transmits the generated identifier request signal to a plurality of RFID tags positioned within an RF field of the RFID tag reader according to an exemplary embodiment of the present invention. Further, when the identifier request signal generator 120 generates an identifier request signal by the anti-collision unit 130, the communication unit 140 trsnsmits the generated identifier request signal to RFID tags positioned within an RF field of an RFID tag reader according to an exemplary embodiment of the present invention.
  • the communication unit 140 When the communication unit 140 intends to transmit the identifier request signal, a plurality of different identifier request signals each having a different prefix exists, hi order to select an identifier request signal to transmit among the generated plurality of identifier request signals, the communication unit 140 detects an identifier request signal stored in the queue 160 and transmits the detected identifier request signal to the RFID tag.
  • the communication unit 140 receives a tag identifier including a prefix from an RFID tag, having received the identifier request signal.
  • the tag identifier is a value intrinsically allocated to the RFID tag and is stored in the RFID tag to distinguish from other RFID tags.
  • the anti-collision unit 130 When the communication unit 140 simultaneously receives tag identifiers from a plurality of RFID tags, the anti-collision unit 130 generates a sub-prefix by increasing a bit of a prefix included in the identifier request signal.
  • the identifier request signal generator 120 generates an identifier request signal including a number of a frame to perform identification and a sub-prefix generated by the anti-collision unit 130. The generated identifier request signal is stored in the queue 160.
  • the tag identification unit 150 identifies an RFID tag, having transmitted the tag identifier.
  • the communication unit 140 receives a tag identifier from a single RFID tag through a frame to perform identification
  • the tag identification unit 150 identifies the RFID tag, having transmitted the tag identifier.
  • the tag identifier received by the communication unit 140 is an entire tag identifier of the RFID tag or a bit of a portion in which a bit of a prefix included in the transmitted identifier request signal is removed from the tag identifier.
  • the tag identification unit 150 identifies an RFID tag, having transmitted the tag identifier through the received tag identifier.
  • the tag identification unit 150 generates a tag identifier by adding a prefix included in a transmitted identifier request signal to the received tag identifier and identifies an RFID tag to which the portion of the tag identifier is transmitted through the generated tag identifier.
  • the identifier request signals generated by the identifier request signal generator 120 are stored in the queue 160.
  • the anti-collision unit 130 sequentially reads from a firstly stored identifier request signal among the stored identifier request signals from the queue 160, and the read identifier request signals are transmitted through the communication unit 140.
  • the transmitted identifier request signals are deleted from the queue 160.
  • the queue 160 may be replaced with a stack.
  • FIG. 4 is a tree diagram illustrating a process in which an RFID tag reader performs a query tree algorithm in one frame number according to an exemplary embodiment of the present invention.
  • Binary numerical values in each terminal node indicate identifiers of RFID tags positioned within an RF field of an RFID tag reader. That is, the RFID tags positioned within an RF field of the RFID tag reader have five 4-bit tag identifiers of OOlO 1 , '0011', Ol I l', 1 IOlO 1 , and 1 IOI l'. Binary numerical values in circles of non-terminal nodes indicate prefixes. A value 'e' is a special prefix value that can be matched to all tags within an area.
  • Dotted line nodes indicate non-terminal nodes in which the received identifiers of identifier request signals including prefixes collide with each other
  • solid line nodes indicate non-terminal nodes in which the received identifiers of identifier request signals including prefixes do not collide with each other
  • double line nodes indicate non-terminal nodes in which the received identifier does not exist.
  • 'S' indicates the transmitted order of a prefix included in an identifier request signal
  • 'Q' indicates the bit number of the prefix included in the identifier request signal
  • 'R' indicates the length of a tag identifier, having received from the RFID tag.
  • FIG. 5 is a flowchart illustrating a process of an anti-collision method of an RFID tag reader according to an exemplary embodiment of the present invention.
  • the epoch size determination unit 110 determines the size of an epoch siganl (S500).
  • a process of determining the size of an epoch signal is the same as that shown in FIG. 2.
  • the communication unit 140 transmits an epoch signal generated by the epoch size determination unit 110 to at least one RFID tag (S505).
  • the identifier request signal generator 120 generates each identifier request signal including each coordinate prefix and a number of a frame to perform selected identification among frame numbers intrinsically allocated to frames of the determined quantity within the epoch size and stores the identifier request signals in the queue 160 (S510).
  • the communication unit 140 transmits the identifier request signal read from the queue 160 and deletes the transmitted identifier request signal from the queue 160 (S515).
  • the communication unit 140 receives a tag identifier including a prefix from the RFID tag, having received the tag identifier request signal (S520).
  • the anti-collision unit 130 determines whether a tag identifier is received from one RFID tag through a frame to perform identification (S525). If a tag identifier is received from one RFID tag through a frame to perform identification, the tag identification unit 150 determines whether a prefix of the tag identifier received through a frame to perform identification is identical to the prefix included in the identifier request signal (S530). If a prefix of the tag identifier received through a frame to perform identification is identical to the prefix included in the identifier request signal, the tag identification unit 150 identifies an RFID tag, having transmitted the tag identifier (S535) and determines whether the queue 160 is empty (S545). If the queue 160 is not empty, a process of steps S515 to S545 is repeatedly performed until the queue 160 is empty.
  • the anti-collision unit 130 if tag identifiers are received from a plurality of RFID tags through a frame to perform identification, the anti-collision unit 130 generates identifier request signals each including the generated sub-prefix by increasing a bit of a prefix included in the identifier request signal and a number of a frame to perform identification and stores the identifier request signals in the queue 160 (S540), and determines whether the queue 160 is empty (S545).
  • two sub-prefixes of the same level are generated by increasing one by one the bit number of a previous prefix and the generated identifier request signal includes each sub-prefix.
  • a process of steps S515 to S545 is repeatedly performed until the queue 160 is empty.
  • FIG. 6 is a block diagram illustrating a configuration of an RFID tag according to an exemplary embodiment of the present invention.
  • the RFID tag includes a receiver 610, a frame number selector 620, and a response signal generator 630.
  • the receiver 610 receives an epoch signal including an epoch size corresponding to the quantity of the frames of a preset size from the RFID tag reader.
  • the epoch size is determined by the epoch size determination unit 110 provided in an RFID tag reader according to an exemplary embodiment of the present invention, and the epoch signal is generated by the epoch signal dermination unit 110.
  • the receiver 610 receives an identifier request signal including a prefix and a number of a frame to perform selected identification among frame numbers intrinsically allocated to frames of the determined quantity within the epoch size.
  • the identifier request signal is a signal generated by the identifier request signal generator 120 of the RFID tag reader.
  • the frame number selector 620 randomly selects one of frame numbers sequentially intrinsically allocated to each of frames of the quantity corresponding to an epoch size included in the received epoch signal.
  • the frame number selector 620 calculates the quantity of the frames by dividing the epoch size into frame sizes.
  • the frame number selector 620 randomly selects a frame number within the calculated quantity of the frames.
  • the response signal generator 630 If the frame number included in the received identifier request signal is identical to the frame number selected by the frame number selector 620 and if the prefix included in the identifier request signal is identical to a bit value of a specific bit of a tag identifier, the response signal generator 630 generates a response signal including a tag identifier intrinsically allocated to itself. The response signal generator 630 determines whether the frame number included in the received identifier request signal is identical to the frame number selected by the frame number selector 620 in order to determine whether the RFID tag itself is an RFID tag to generate a response signal.
  • the response signal generator 630 determines whether the prefix included in the identifier request signal is identical to a bit value of a specific bit of the tag identifier. In this case, the response signal generator 630 determines whether the prefix included in the identifier request signal is identical to a bit value of a first bit of the tag identifier. If the prefix included in the identifier request signal is identical to a bit value of a specific bit of the tag identifier, the response signal generator 630 generates a response signal to transmit a tag identifier intrinsically allocated to the RFID tag to the RFID tag reader according to an exemplary embodiment of the present invention.
  • the transmitter 640 transmits a response signal generated by the response signal generator 630 to the RFID tag reader.
  • FIG. 7 is a graph comparing the quantity of queries based on the quantity of RFID tags in a conventional anti-collision method and a FQT anti-collision method according to an exemplary embodiment of the present invention.
  • the query quantity 710 of the FQT anti-collision method decreases, compared with the query quantities (720, 730, 740, and 750) of conventional different anti-collision methods.
  • FIG. 8 is a graph comparing the quantity of transmissions of an identifier request signal and the quantity of receptions of a response signal required for identifying one RFID tag in conventional anti-collision methods and a FQT anti-collision method according to an exemplary embodiment of the present invention.
  • the query quantity 810 per RFID tag is constant regardless of the increase of the quantity of the RFID tags. Further, it can be seen that the query quantity 810 per RFID tag of the anti-collision method according to an exemplary embodiment of the present invention is smaller than the query quantities (820, 830, 840, and 850) per RFID tag of existing anti-collision methods.
  • an exemplary embodiment of the present invention can be embodied with a computer readable code in a computer readable recording medium.
  • the computer readable recording medium may include all kinds of recording devices in which data that can be read by a computer system are stored.
  • the computer readable recording medium may include, for example, a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device.
  • the computer readable redocridng medium may also include implementations that can be embodied in a form of carrier waves (e.g. transmission through Internet).
  • the computer readable recording medium is distributed to a computer system connected to a network, and the computer readable code is stored and executed with a distribution manner.

Abstract

An RPID tag and a reader, a method of identifying an RFID tag, and an anti-collision method of an RFID tag are provided. An epoch size determination unit determines the size of an epoch signal having a preset size. An identifier request signal generator generates an identifier request signal including a prefix and a number of a frame to perform selected identification among frame numbers intrinsically allocated to frames of the determined quantity within the size of an epoch signal. If tag identifiers are received from a plurality of RFID tags through a frame to perform identification, an anti-collision unit generates a sub-prefix by increasing a bit of a prefix included in an identifier request signal and then enables the identifier request signal generator to generate an identifier request signal including a sub-prefix and a number of a frame to perform identification. A communication unit transmits an epoch signal and an identifier request signal including a prefix and a number of a frame to perform identification, and receives a tag identifier including a prefix from an RFID tag, having received the identifier request signal. If a prefix of a tag identifier received through a frame to perform identification is identical to the prefix included in the identifier request signal, a tag identification unit identifies an RFID tag, having transmitted the tag identifier.

Description

[DESCRIPTION] [Invention Title]
RADIO FREQUENCY IDENTIFICATION TAG AND READER, METHOD OF IDENTIFYING TAG, ANTI-COLLISION METHOD FOR TAG [Technical Field]
The present invention relates to a radio frequency identification tag and a reader, a method of identifying a radio frequency identification tag, and an anti-collision method of a radio frequency identification tag, and more particularly, to a radio frequency identification tag and a reader, a method of identifying a radio frequency identification tag, and an anti-collision method of a radio frequency identification tag that enable a radio frequency identification tag reader to accurately identify a radio frequency identification tag by preventing a collision among radio frequency identification tags. [Background Art]
A Radio Frequency Identification (RFID) tag is a kind of Automatic Identification and Data Capture (AIDC) technology and enables a tag reader to read data stored in an RFID tag in which a microchip is mounted in a non-contact manner using a radio frequency.
An RFID system generally includes an RFID tag attached to an object and an RFID tag reader. The RFID tag includes a microchip for storing an identification code of an object and information about the object and an antenna for transmitting and receiving information to and from the RFID tag reader using a radio frequency. The RFID tag reader includes an internal or external antenna and a controller for controlling transmission and reception of information.
In the RFID system, a principle of transmitting and receiving information between the RFID tag reader and the RFID tag is as follows. An antenna provided in the RFID tag reader forms an RF field, which is an electromagnetic field by emitting an active signal. When the RFID tag enters the RF field, the RFID tag receives an active signal emitted from the antenna of the RFID tag reader and transmits information stored within the RFID tag to the RFID tag reader using the received active signal. The RFID tag reader receives and analyzes information transmitted from the RFID tag and acquires intrinsic information stored in the RFID tag. When a plurality of RFID tags exists within an RF field in which the RFID tag reader can identify the RFID tag, all RFID tags within an RF field simultaneously respond to a signal of the RFID tag reader. In this case, there is a problem that response signals of the RFID tags may collide. In order to solve the problem, various anti-collision technologies exist.
A conventional anti-collision technology is largely divided into an ALOHA-based algorithm and a tree-based algorithm. The ALOHA-based algorithm is a slotted ALOHA algorithm and prevents a collision among RFID tags by dividing a time into slots and responding the RFID tag to only a slot allocated to itself. The tree-based algorithm performs a process of identifying an RFID tag using an intrinsic identifier of the RFID tag having a tree structure.
Because the conventional ALOHA-based algorithm is based on uncertainty of a probability, the conventional ALOHA-based algorithm may not identify all RFID tags within an RF field of the RFID tag reader. In the conventional tree-based algorithm, because RFID tags having similar identifiers increase when the RFID tags increase, a collision among the RFID tags may increase. In order to solve the problems, the conventional tree-based algorithm uses a method of increasing the depth of trees, however when the depth of the trees increases, much time is required for identifying the RFID tags. [Disclosure] [Technical Problem]
The present invention has been made in an effort to solve the above problems, and the present invention provides an RFID tag and a reader, a method of identifying an RFID tag, and an anti-collision method of an RFID tag that can efficiently prevent a collision in identifying a plurality of RFID tags. [Technical Solution]
According to an aspect of the present invention, there is provided an RFID tag reader including: an epoch size determination unit for determining the size of an epoch signal including at least one frame; an identifier request signal generator for generating an identifier request signal including a prefix and a number of a frame; a communication unit for transmitting the epoch signal and the identifier request signal and receiving a tag identifier from an RFID tag, having received the identifier request signal; an anti-collision unit for generating, when a plurality of tag identifiers selects any one of the frames, a sub-prefix by increasing a bit of the prefix of the frame and enabling the identifier request signal generator to generate an identifier request signal including the sub-prefix; and a tag identification unit for identifying, if a prefix or a sub-prefix of the tag identifier is identical to the prefix or the sub-prefix included in the identifier request signal, an RFID tag, having transmitted the tag identifier. The anti-collision unit may enable, when a coordinate prefix of the prefix exists, the identifier request signal generator to generate an identifier request signal including the coordinate prefix by providing the coordinate prefix to the identifier request signal generator.
The epoch size determination unit may change, if the quantity of the tag identifiers for selecting any one of the frames included in the epoch signal is a reference value or more, the size of the epoch signal by increasing the quantity of the frames included in the epoch signal, and the communication unit may retransmit the changed epoch signal.
The any one frame may be a first frame among the frames included in the epoch signal. According to another aspect of the present invention, there is provided a method of identifying an RFID tag, including: determining the size of an epoch signal including at least one frame; generating an identifier request signal including a prefix and a number of a frame; transmitting the epoch signal and the identifier request signal; receiving a tag identifier including a prefix from an RFID tag, having received the identifier request signal; generating, when a plurality of tag identifiers selects any one of the frames, a sub-prefix by increasing a bit of the prefix of the frame and enabling an identifier request signal generator to generate an identifier request signal including the sub-prefix; and identifying, if a prefix or a sub-prefix of the tag identifier is identical to the prefix or the sub-prefix included in the identifier request signal, an RFID tag, having transmitted the tag identifier.
When a coordinate prefix of the prefix exists, an identifier request signal including the coordinate prefix may be generated.
If the quantity of the tag identifiers for selecting any one of the frames included in the epoch signal is a reference value or more, the size of the epoch signal may be changed by increasing the quantity of the frames included in the epoch signal.
The any one frame may be a first frame among the frames included in the epoch signal. According to another aspect of the present invention, there is provided an RFID tag including: a receiver for receiving an identifier request signal including the quantity of frames of a preset size from an RFID tag reader and including a prefix and a number of a frame; a frame selector for randomly selecting any one of the frames; a response signal generator for generating, if the frame included in the received identifier request signal is identical to the frame selected by the frame selector and if the prefix included in the identifier request signal is identical to a bit value of a specific bit of the tag identifier, a response signal including the tag identifier; and a transmitter for transmitting the response signal to the RF1ID tag reader.
According to another aspect of the present invention, there is provided an anti-collision method of an RFID tag, including: transmitting an epoch signal to RFID tags; receiving, by the RFID tags, a signal for randomly selecting a frame included within the epoch signal; performing a query tree algorithm in any one of the frames; and increasing, if the quantity of collisions generating in the any one frame is a reference value or more, the size of the epoch signal.
If the quantity of collisions generating in the any one frame is smaller than the reference value, a query tree algorithm may be performed in frames after the any one frame.
The any one frame may be a first frame among the frames included in the epoch signal.
According to another aspect of the present invention, there is provided a computer readable recording medium on which a program for executing the anti-collison method of an RFID tag in the computer is recorded. [Advantageous Effects]
According to an RFID tag and a reader, a method of identifying an RFID tag, and an anti-collision method of the RFID tag of the present invention, a plurality of RFID tags positioned within an RF field of the RFID tag reader can be accurately identified and a time required for identifying the RFID tag can be reduced. [Description of Drawings]
The embodiment of the invention will be described in detail with reference to the following drawings in which like numerals refer to like elements.
FIG. 1 is a block diagram illustrating a configuration of an RFID tag reader according to an exemplary embodiment of the present invention; FIG. 2 is a flowchart illustrating a process of determining an epoch size included in an epoch signal;
FIG. 3 is a diagram illustrating a frame number and a prefix included in an identifier request signal;
FIG. 4 is a tree diagram illustrating a process in which an RFID tag reader performs a query tree algorithm in one frame number according to an exemplary embodiment of the present invention;
FIG. 5 is a flowchart illustrating a process of an anti-collision method of an RPID tag reader according to an exemplary embodiment of the present invention; FIG. 6 is a block diagram illustrating a configuration of an RFID tag according to an exemplary embodiment of the present invention;
FIG. 7 is a graph comparing the quantity of queries based on the quantity of RPID tags in a conventional anti-collision method and a Framed Query Tree (FQT) anti-collision method according to an exemplary embodiment of the present invention; and FIG. 8 is a graph comparing the quantity of transmissions of an identifier request signal and the quantity of receptions of a response signal required for identifying one RFID tag in a conventional anti-collision method and a FQT anti-collision method according to an exemplary embodiment of the present invention.
[Best Mode] Hereinafter, exemplary embodiments of an RPID tag and a reader, a method of identifying an RFID tag, and an anti-collision method of an RFID tag will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating a configuration of an RFID tag reader according to an exemplary embodiment of the present invention. Referring to FIG. 1, the RFID tag reader includes an epoch size determination unit 110, an identifier request signal generator 120, an anti-collision unit 130, a communication unit 140, a tag identification unit 150, and a queue 160.
The epoch size determination unit 110 determines the size of an epoch signal having a preset size. The size of the epoch signal is the size that can include a frame number and may be previously set according to a communication method between an RFID tag reader and an RFID tag. The size of the epoch signal may be set with an experimentally measured value so that the depth of a tree formed by performing a query tree algorithm within one frame is not so deep. Further, the size of the epoch signal may be differently set according to the quantity of RFID tags positioned within an RF range in which the reader can identify the RFID tags. In this case, the size of the epoch signal may be set to correspond to a half of the quantity of the RFID tags positioned within an RF range in which the reader can identify the RFID tags.
The epoch size determination unit 110 sequentially allocates intrinsic frame numbers to each of frames of the determined quantity and determines an epoch size by multiplying the quantity of the frames to the frame size. The epoch size determination unit 110 allocates each intrinsic frame number of '1' up to the determined quantity to each of the frames. The frame number is a reference value for determining whether the RFID tag itself is a response target of an identifier request signal, having transmitted by the reader. Further, the determined epoch size is a value for providing information about the quantity of frames, having transmitted by the reader to the RFID tag.
The reader according to an exemplary embodiment of the present invention cannot know the quantity of RFID tags positioned within an RF field that can be identified by the reader until the RFID tags are identified. Therefore, in order to determine the proper quantity of frames, the epoch size determination unit 110 performs an estimation process of a first frame test. For this, if the quantity of collisions of the tag identifiers is a preset reference value or more through a frame to perform identification, the epoch size determination unit 110 changes the epoch size by increasing the quantity of frames. In this case, if the reference value is set to be small, the quantity of transmissions of an identifier request signal including an unnecessary frame number that is not selected by the RFID tag increases. If the reference value is set to be large, an estimating process is lengthened. Therefore, the reference value may be experimentally set to '3'.
If the quantity of receptions of the tag identifier from a plurality of RFID tags through a frame to perform identification is three times or more, the epoch size determination unit 110 changes an epoch size by increasing the quantity of frames. Such a first frame test is performed as follows. An epoch size is set to be small at a first stage, and if the quantity of collisions is a collision threshold or more in a first frame, an identification process is stopped and after an epoch size is increased, and an anti-collision method is again started. The reason why changing an epoch size at the first frame test is that if tag identifiers, which are response signals of an identification request signal are frequently collided at the identifier request signal including the first frame number, tag identifiers, which are response signals may be frequently collided at an identifier request signal including the remaining frame numbers.
FIG. 2 is a flowchart illustrating a process of determining an epoch size included in an epoch signal. Referring to FIG. 2, the epoch size determination unit 110 determines the size of an epoch signal having a preset size (S200).
The communication unit 140 transmits an epoch signal including information about the determined size of the epoch signal to at least one RFID tag existing within an RF range (S210).
The communication unit 140 transmits a corresponding identifier request signal satisfying a prefix and a number of a frame to perform identification generated by the identifier request signal generator 120 (S220).
The epoch size determination unit 110 receives a tag identifier including a prefix from an RFID tag, having received the identifier request signal (S230).
The epoch size determination unit 110 determines whether the quantity of receptions of tag identifiers from a plurality of RFID tags through a frame to perform identification is a reference value or more (S240).
If the quantity of receptions of tag identifiers from a plurality of RFID tags through a frame to perform identification is a reference value or more, the epoch size determination unit 110 increases the epoch size by multiplying the epoch size (S250). Thereafter, the epoch size determination unit 110 repeatedly performs a process of steps S210 to S250.
If the frame is not a first frame and if the quantity of receptions of tag identifiers from a plurality of RFID tags through a frame to perform identification is smaller than a reference value, the epoch size determination unit 110 terminates a process of determining the epoch size. The identifier request signal generator 120 generates an identifier request signal including a prefix and a number of a frame to perform selected identification. The frame number is one of frame numbers intrinsically allocated to frames of the determined quantity within the epoch size.
The identifier request signal generator 120 generates an identifier request signal sequentially including the frame number starting from the smallest one. Further, the identifier request signal generator 120 generates two identifier request signals having the same frame number, however including a prefix of a 'low' value and a prefix of a 'high' value.
Here, a prefix that has the same bit number and in which only a value of a final bit is different is referred to as a coordinate prefix. Further, a prefix that has the bit number greater by one bit than that of the other prefixes and that has all bit values of the other prefixes is referred to as a sub-prefix of the other prefixes. That is, the sub-prefix is a prefix in which a bit having a 'low' or 'high' value is added to an existing prefix.
FIG. 3 is a diagram illustrating a frame number and a prefix included in an identifier request signal. Referring to FIG. 3, the identifier request signal generator 120 generates identifier request signals of four frames. Further, the identifier request signal generator 120 generates four identifier request signals including a frame number 1I', each having a prefix 1O', a prefix 1I', a prefix 1OO', and a prefix '01'. The identifier request signal generator 120 generates six identifier request signals including a frame number '4', each having a prefix 1O', a prefix '1', a prefix 1OO', a prefix 1Ol', a prefix 1OlO1, and a prefix 'Oi l'. Here, the prefix T is a coordinate prefix of the prefix 1O', and the prefix 1OO' is a sub-prefix of the prefix 1O'.
When tag identifiers are received from a plurality of RFID tags through a frame to perform identification, the anti-collision unit 130 generates a sub-prefix by increasing a bit of a prefix included in the identifier request signal. When tag identifiers are received from a plurality of RFID tags through a frame to perform identification, the received RFID tags cannot be identified due to a collision. In order to prevent the collision, the anti-collision unit 130 increases a bit of a prefix included in the transmitted identifier request signal to generate two sub-prefixes in which a bit value of the increased bit is 'low' and 'high'. When a number of a frame to perform identification is T and the prefix number is 1O', if tag identifiers are received from two RFID tags, the anti-collision unit 130 generates sub-prefixes OO' and 1Ol', as shown in
FIG. 3.
Thereafter, the anti-collision unit 130 enables the identifier request signal generator 120 to generate an identifier request signal including a number of a frame to perform identification and a sub-prefix generated by the anti-collision unit 130. hi more detail, the anti-collision unit 130 generates an identifier request signal including the frame number '1' and the generated sub-prefix '00' and an identifier request signal including the frame number '1' and the generated sub-prefix 1Ol'.
The communication unit 140 transmits an epoch signal including an epoch size and an identifier request signal including a prefix and a number of a frame to perform identification. When the identifier request signal generator 120 generates an identifier request signal, the communication unit 140 transmits the generated identifier request signal to a plurality of RFID tags positioned within an RF field of the RFID tag reader according to an exemplary embodiment of the present invention. Further, when the identifier request signal generator 120 generates an identifier request signal by the anti-collision unit 130, the communication unit 140 trsnsmits the generated identifier request signal to RFID tags positioned within an RF field of an RFID tag reader according to an exemplary embodiment of the present invention. When the communication unit 140 intends to transmit the identifier request signal, a plurality of different identifier request signals each having a different prefix exists, hi order to select an identifier request signal to transmit among the generated plurality of identifier request signals, the communication unit 140 detects an identifier request signal stored in the queue 160 and transmits the detected identifier request signal to the RFID tag.
Further, the communication unit 140 receives a tag identifier including a prefix from an RFID tag, having received the identifier request signal. The tag identifier is a value intrinsically allocated to the RFID tag and is stored in the RFID tag to distinguish from other RFID tags. When the communication unit 140 simultaneously receives tag identifiers from a plurality of RFID tags, the anti-collision unit 130 generates a sub-prefix by increasing a bit of a prefix included in the identifier request signal. Next, the identifier request signal generator 120 generates an identifier request signal including a number of a frame to perform identification and a sub-prefix generated by the anti-collision unit 130. The generated identifier request signal is stored in the queue 160.
If a prefix of the tag identifier received through a frame to perform identification is identical to the prefix included in the identifier request signal, the tag identification unit 150 identifies an RFID tag, having transmitted the tag identifier. When the communication unit 140 receives a tag identifier from a single RFID tag through a frame to perform identification, the tag identification unit 150 identifies the RFID tag, having transmitted the tag identifier. The tag identifier received by the communication unit 140 is an entire tag identifier of the RFID tag or a bit of a portion in which a bit of a prefix included in the transmitted identifier request signal is removed from the tag identifier. When the communication unit 140 receives an entire tag identifier, the tag identification unit 150 identifies an RFID tag, having transmitted the tag identifier through the received tag identifier. Alternatively, when the communication unit 140 receives a portion of the tag identifier, the tag identification unit 150 generates a tag identifier by adding a prefix included in a transmitted identifier request signal to the received tag identifier and identifies an RFID tag to which the portion of the tag identifier is transmitted through the generated tag identifier.
The identifier request signals generated by the identifier request signal generator 120 are stored in the queue 160. The anti-collision unit 130 sequentially reads from a firstly stored identifier request signal among the stored identifier request signals from the queue 160, and the read identifier request signals are transmitted through the communication unit 140. The transmitted identifier request signals are deleted from the queue 160. The queue 160 may be replaced with a stack.
FIG. 4 is a tree diagram illustrating a process in which an RFID tag reader performs a query tree algorithm in one frame number according to an exemplary embodiment of the present invention.
Referring to FIG. 4, nodes indicated by oblique lines do not actually exist. Binary numerical values in each terminal node indicate identifiers of RFID tags positioned within an RF field of an RFID tag reader. That is, the RFID tags positioned within an RF field of the RFID tag reader have five 4-bit tag identifiers of OOlO1, '0011', Ol I l', 1IOlO1, and 1IOI l'. Binary numerical values in circles of non-terminal nodes indicate prefixes. A value 'e' is a special prefix value that can be matched to all tags within an area. Dotted line nodes indicate non-terminal nodes in which the received identifiers of identifier request signals including prefixes collide with each other, solid line nodes indicate non-terminal nodes in which the received identifiers of identifier request signals including prefixes do not collide with each other, and double line nodes indicate non-terminal nodes in which the received identifier does not exist. For numerical values denoted in a form of S (Q, R) at the right upper end of each non-terminal node, 'S' indicates the transmitted order of a prefix included in an identifier request signal, 'Q' indicates the bit number of the prefix included in the identifier request signal, and 'R' indicates the length of a tag identifier, having received from the RFID tag.
FIG. 5 is a flowchart illustrating a process of an anti-collision method of an RFID tag reader according to an exemplary embodiment of the present invention.
Referring to FIG. 5, the epoch size determination unit 110 determines the size of an epoch siganl (S500). A process of determining the size of an epoch signal is the same as that shown in FIG. 2.
The communication unit 140 transmits an epoch signal generated by the epoch size determination unit 110 to at least one RFID tag (S505).
The identifier request signal generator 120 generates each identifier request signal including each coordinate prefix and a number of a frame to perform selected identification among frame numbers intrinsically allocated to frames of the determined quantity within the epoch size and stores the identifier request signals in the queue 160 (S510).
The communication unit 140 transmits the identifier request signal read from the queue 160 and deletes the transmitted identifier request signal from the queue 160 (S515). The communication unit 140 receives a tag identifier including a prefix from the RFID tag, having received the tag identifier request signal (S520).
The anti-collision unit 130 determines whether a tag identifier is received from one RFID tag through a frame to perform identification (S525). If a tag identifier is received from one RFID tag through a frame to perform identification, the tag identification unit 150 determines whether a prefix of the tag identifier received through a frame to perform identification is identical to the prefix included in the identifier request signal (S530). If a prefix of the tag identifier received through a frame to perform identification is identical to the prefix included in the identifier request signal, the tag identification unit 150 identifies an RFID tag, having transmitted the tag identifier (S535) and determines whether the queue 160 is empty (S545). If the queue 160 is not empty, a process of steps S515 to S545 is repeatedly performed until the queue 160 is empty.
Alternatively, if tag identifiers are received from a plurality of RFID tags through a frame to perform identification, the anti-collision unit 130 generates identifier request signals each including the generated sub-prefix by increasing a bit of a prefix included in the identifier request signal and a number of a frame to perform identification and stores the identifier request signals in the queue 160 (S540), and determines whether the queue 160 is empty (S545). In this case, two sub-prefixes of the same level are generated by increasing one by one the bit number of a previous prefix and the generated identifier request signal includes each sub-prefix. Also, in this case, if the queue 160 is not empty, a process of steps S515 to S545 is repeatedly performed until the queue 160 is empty.
FIG. 6 is a block diagram illustrating a configuration of an RFID tag according to an exemplary embodiment of the present invention.
Referring to FIG. 6, the RFID tag includes a receiver 610, a frame number selector 620, and a response signal generator 630.
The receiver 610 receives an epoch signal including an epoch size corresponding to the quantity of the frames of a preset size from the RFID tag reader. The epoch size is determined by the epoch size determination unit 110 provided in an RFID tag reader according to an exemplary embodiment of the present invention, and the epoch signal is generated by the epoch signal dermination unit 110. The receiver 610 receives an identifier request signal including a prefix and a number of a frame to perform selected identification among frame numbers intrinsically allocated to frames of the determined quantity within the epoch size. The identifier request signal is a signal generated by the identifier request signal generator 120 of the RFID tag reader.
The frame number selector 620 randomly selects one of frame numbers sequentially intrinsically allocated to each of frames of the quantity corresponding to an epoch size included in the received epoch signal. The frame number selector 620 calculates the quantity of the frames by dividing the epoch size into frame sizes. The frame number selector 620 randomly selects a frame number within the calculated quantity of the frames.
If the frame number included in the received identifier request signal is identical to the frame number selected by the frame number selector 620 and if the prefix included in the identifier request signal is identical to a bit value of a specific bit of a tag identifier, the response signal generator 630 generates a response signal including a tag identifier intrinsically allocated to itself. The response signal generator 630 determines whether the frame number included in the received identifier request signal is identical to the frame number selected by the frame number selector 620 in order to determine whether the RFID tag itself is an RFID tag to generate a response signal. If the frame number included in the received identifier request signal is identical to the frame number selected by the frame number selector 620, the response signal generator 630 determines whether the prefix included in the identifier request signal is identical to a bit value of a specific bit of the tag identifier. In this case, the response signal generator 630 determines whether the prefix included in the identifier request signal is identical to a bit value of a first bit of the tag identifier. If the prefix included in the identifier request signal is identical to a bit value of a specific bit of the tag identifier, the response signal generator 630 generates a response signal to transmit a tag identifier intrinsically allocated to the RFID tag to the RFID tag reader according to an exemplary embodiment of the present invention.
The transmitter 640 transmits a response signal generated by the response signal generator 630 to the RFID tag reader.
FIG. 7 is a graph comparing the quantity of queries based on the quantity of RFID tags in a conventional anti-collision method and a FQT anti-collision method according to an exemplary embodiment of the present invention.
Referring to FIG. 7, it can be seen that as the quantity of RFID tags increases, the query quantity 710 of the FQT anti-collision method according to an exemplary embodiment of the present invention decreases, compared with the query quantities (720, 730, 740, and 750) of conventional different anti-collision methods.
FIG. 8 is a graph comparing the quantity of transmissions of an identifier request signal and the quantity of receptions of a response signal required for identifying one RFID tag in conventional anti-collision methods and a FQT anti-collision method according to an exemplary embodiment of the present invention.
Referring to FIG. 8, in the FQT anti-collision method according to an exemplary embodiment of the present invention, it can be seen that the query quantity 810 per RFID tag is constant regardless of the increase of the quantity of the RFID tags. Further, it can be seen that the query quantity 810 per RFID tag of the anti-collision method according to an exemplary embodiment of the present invention is smaller than the query quantities (820, 830, 840, and 850) per RFID tag of existing anti-collision methods.
Further, an exemplary embodiment of the present invention can be embodied with a computer readable code in a computer readable recording medium. The computer readable recording medium may include all kinds of recording devices in which data that can be read by a computer system are stored. The computer readable recording medium may include, for example, a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. The computer readable redocridng medium may also include implementations that can be embodied in a form of carrier waves (e.g. transmission through Internet). Further, the computer readable recording medium is distributed to a computer system connected to a network, and the computer readable code is stored and executed with a distribution manner.
The embodiment of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

[CLAIMS] [Claim 1 ]
An RFID tag reader comprising: an epoch size determination unit for determining the size of an epoch signal comprising at least one frame; an identifier request signal generator for generating an identifier request signal comprising a prefix and a number of a frame; a communication unit for transmitting the epoch signal and the identifier request signal and receiving a tag identifier from an RFID tag, having received the identifier request signal; an anti-collision unit for generating, when a plurality of tag identifiers selects any one of the frames, a sub-prefix by increasing a bit of the prefix of the frame and enabling the identifier request signal generator to generator an identifier request signal comprising the sub-prefix; and a tag identification unit for identifying, if a prefix or a sub-prefix of the tag identifier is identical to the prefix or the sub-prefix included in the identifier request signal, an RFID tag, having transmitted the tag identifier.
[Claim 2]
The RFID tag reader of claim 1, wherein the anti-collision unit enables, when a coordinate prefix of the prefix exists, the identifier request signal generator to generate an identifier request signal comprising the coordinate prefix by providing the coordinate prefix to the identifier request signal generator.
[Claim 3]
The RFID tag reader of claim 1, wherein the epoch size determination unit changes, if the quantity of the tag identifiers for selecting any one of the frames included in the epoch signal is a reference value or more, the size of the epoch signal by increasing the quantity of the frames included in the epoch signal, and the communication unit retransmits the changed epoch signal.
[Claim 4]
The RFID tag reader of claim 3, wherein the any one frame is a first frame of the frames included in the epoch signal.
[Claim 5]
A method of identifying an RPID tag, comprising: determining the size of an epoch signal comprising at least one frame; generating an identifier request signal comprising a prefix and a number of a frame; transmitting the epoch signal and the identifier request signal; receiving a tag identifier comprising a prefix from an RFID tag, having received the identifier request signal; generating, when a plurality of tag identifiers selects any one of the frams, a sub-prefix by increasing a bit of the prefix of the frame and generating, by an identifier request signal generator, an identifier request signal comprising the sub-prefix; and identifying, if a prefix or a sub-prefix of the tag identifier is identical to the prefix or the sub-prefix included in the identifier request signal, an RFID tag, having transmitted the tag identifier.
[Claim 6]
The method of claim 5, wherein when a coordinate prefix of the prefix exists, an identifier request signal comprising the coordinate prefix is generated.
[Claim 7]
The method of claim 5, wherein if the quantity of the tag identifiers for selecting any one of the frames included in the epoch signal is a reference value or more, the size of the epoch signal is changed by increasing the quantity of the frames included in the epoch signal.
[Claim 8]
The method of claim 7, wherein the any one frame is a first frame among the frames included in the epoch signal.
[Claim 9] An RFID tag comprising: a receiver for receiving an identifier request signal comprising the quantity of frames of a preset size from an RFID tag reader and comprising a prefix and a number of a frame; a frame selector for randomly selecting any one of the frames; a response signal generator for generating, if the frame included in the received identifier request signal is identical to the frame selected by the frame selector and if the prefix included in the identifier request signal is identical to a bit value of a specific bit of the tag identifier, a response signal comprising the tag identifier; and a transmitter for transmitting the response signal to the RFID tag reader. [Claim 10] An anti-collision method of an RFID tag, comprising: transmitting an epoch signal to RFID tags; receiving, by the RFID tags, a signal for randomly selecting a frame included in the epoch signal; performing a query tree algorithm in any one of the frames; and increasing, if the quantity of collisions generating in the any one frame is a reference value or more, the size of the epoch signal. [Claim 11 ]
The anti-collision method of claim 10, wherein if the quantity of collisions generating in the any one frame is smaller than the reference value, a query tree algorithm is performed in frames after the any one frame. [Claim 12]
The anti-collision method of claim 10, wherein the any one frame is a first frame among the frames included in the epoch signal. [Claim 13]
A computer readable recording medium on which a program for executing the anti-collision method of an RFID tag cited in claims 10 to 12 in the computer is recorded.
PCT/KR2007/006265 2006-12-29 2007-12-05 Radio frequency identification tag and reader, method of identifying tag, anti-collision method for tag WO2008082089A1 (en)

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