WO2004029652A1 - Method for avoiding collisions between rfid tags - Google Patents

Method for avoiding collisions between rfid tags Download PDF

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Publication number
WO2004029652A1
WO2004029652A1 PCT/AU2003/001190 AU0301190W WO2004029652A1 WO 2004029652 A1 WO2004029652 A1 WO 2004029652A1 AU 0301190 W AU0301190 W AU 0301190W WO 2004029652 A1 WO2004029652 A1 WO 2004029652A1
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WO
WIPO (PCT)
Prior art keywords
tags
replies
read
unread
time
Prior art date
Application number
PCT/AU2003/001190
Other languages
French (fr)
Inventor
David Malcolm Hall
David Bruce Murfett
Alfio Roberto Grasso
Original Assignee
Tagsys Australia Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tagsys Australia Pty Ltd filed Critical Tagsys Australia Pty Ltd
Priority to AU2003258380A priority Critical patent/AU2003258380A1/en
Publication of WO2004029652A1 publication Critical patent/WO2004029652A1/en

Links

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
    • G06K7/10—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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
    • G01S13/76—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted
    • G01S13/78—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe
    • G01S13/781—Secondary Surveillance Radar [SSR] in general
    • G01S13/784—Coders or decoders therefor; Degarbling systems; Defruiting systems
    • 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

Definitions

  • the present invention relates to an object management system wherein information bearing electronically coded radio frequency identification (RFID) tags are attached to objects which are to be identified, sorted, controlled and/or audited.
  • RFID radio frequency identification
  • the present invention relates to a method for avoiding continued destructive collisions between RFID tags especially in tagging systems which make use of a slotted aloha communication scheme.
  • the object management system of the present invention includes information passing between an interrogator which creates an electromagnetic interrogation field, and the electronically coded tags, which respond by issuing a reply signal that is detected by the interrogator, decoded and consequently supplied to other apparatus in the sorting, controlling or auditing process.
  • the objects to which the tags are attached may be animate or inanimate.
  • the interrogation medium may be other than electromagnetic, such as optical and/or acoustic.
  • the tags may be passive, i.e. they may have no internal energy source and may obtain energy for their reply from the interrogation field, or they may be active and may contain an internal energy source, for example a battery. Such tags respond only when they are within or have recently passed through the interrogation field.
  • the interrogation field may include functions such as signalling to an active tag when to commence a reply or series of replies or in the case of passive tags may provide energy, a portion of which may be used in constructing the reply.
  • FIG. 1 An interrogator 10, containing a transmitter and receiver, both operating under a controller, communicate via electromagnetic means with a code responding electronic tag 11.
  • a slotted aloha scheme refers to a communications scheme that is adapted to minimize collisions between tags. This is done by employing signals that are sent at precise time intervals or slots. Specifically, interrogator 10 can signal to each tag when a time slot is clear to send a reply.
  • an anti-collision scheme which reduces the population of replying tags is beneficial for expedient reading of all tags present in the field. To this end, it is desirable after a tag has sent its reply, to minimize interference with tags which have not been read.
  • One prior art approach is to turn off tags after they have been read.
  • An object of the present invention is to provide an alternative scheme for minimizing collisions.
  • An alternative to turning off tags after they have been read is to relegate their continuing replies to an invalid time interval or slot where they may not or cannot interfere with tags, which have not been read.
  • one or more special time slots may be allocated for such replies.
  • Replies may also be relegated to an invalid time interval or slot when the interrogator does not expect a reply. This may include the blind time or interval associated with the turn around time between an interrogator signalling and the reply time of an unread tag.
  • Another invalid time interval or slot exists during the pre-cursor or preamble portion of a valid time interval or slot. The pre-cursor or preamble portion is transmitted before the tag information is transmitted. Because such a time slot is much shorter than the length of a normal reply, the relegated reply will need to be much shorter (ie. truncated) relative to a normal reply.
  • relegation may be achieved by time shifting or translating replies of read tags to an invalid time slot as described above.
  • a method for avoiding destructive collisions between read and unread RFID tags said method including modifying replies of said read tags such that the modified replies do not occupy substantially the same time slots as replies of unread tags.
  • the step of modifying may include time shifting the replies of read tags such that the modified replies do not overlap time slots associated with replies of unread tags.
  • Replies of read tags may be time shifted to time slots associated with turn around times of an interrogator adapted to read the tags.
  • replies of read tags may be time shifted to at least one reserved time slot.
  • Unread tags may be instructed not to reply during the or each reserved time slot.
  • the step of modifying may include truncating the replies of read tags such that the modified replies do not overlap time slots associated with data portions in the replies of unread tags.
  • FIG. 1 shows an electronic tag ready system to which the method for avoiding collisions of the present invention may be applied
  • FIG. 2 shows examples of relegated replies according to the present invention.
  • FIG. 2 shows a timing diagram illustrating examples of time slots into which replies of tags which have been read may be relegated to minimize interference with tags which have not been read.
  • FIG. 2(a) shows time slots that are occupied by commands transmitted by interrogator 10.
  • FIG. 2(b) shows time slots associated with the turn around time of interrogator 10. The turn around time is the dead time after a command has been sent by interrogator 10 and before its receive circuits can settle down after a transmission activity. A reply received during this dead time slot is most unlikely to be decoded by interrogator 10.
  • Fig. 2(b) also shows an example of a reserved time slot being a time slot that is reserved for tags, that have already been read. Unread tags may be instructed not to reply during the reserved time slot.
  • FIG. 2(c) and 2(d) show valid time slots being time slots that are occupied by transmissions from unread tags 1 and 2 respectively. Collisions during valid time slots may be minimized by reducing the population of tags replying during these time slots.
  • the population of replying tags may be reduced by turning off tags after they have transmitted their data, ie. after the tags have been read. However, the population of replying tags may also be reduced by time shifting the replies of read tags to time intervals which occupy time slots other than the valid time slots shown in Figs. 2(c) and 2(d).
  • Fig. 2(e) shows a time shifted reply that has been time shifted or relegated to a time slot that substantially overlaps the dead time or turn around time slots shown in Fig. 2(b).
  • FIG. 2(f) shows an example wherein a read reply has been time shifted or relegated to a time slot which represents the pre-cursor or pre-amble of a valid reply time slot as shown in Fig. 2(c). Providing that the read reply does not extend into the information or data portion of the valid reply time slot it is unlikely to interfere with data from an unread tag 1. However, the read reply will have to be time shortened or truncated so that it does not extend into the data slot of unread tag 1.
  • FIG. 2(g) shows an example wherein a read reply is time shifted or relegated to a time slot which is specifically reserved for read tags. As described above unread tags may be instructed not to reply during the reserved time slot.

Abstract

A method is disclosed for avoiding destructive collisions between read and unread RFID tags. The method includes modifying replies of the read tags such that the modified replies do not occupy substantially the same time slots as replies of unread tags. The step of modifying may include time shifting or truncating the replies of the read tags such that the modified replies do not overlap time slots associated with the replies of unread tags or with data portions in the replies of the unread tags.

Description

METHOD FOR AVOIDING COLLISIONS BETWEEN
RFID TAGS
FIELD OF THE INVENTION
The present invention relates to an object management system wherein information bearing electronically coded radio frequency identification (RFID) tags are attached to objects which are to be identified, sorted, controlled and/or audited. In particular the present invention relates to a method for avoiding continued destructive collisions between RFID tags especially in tagging systems which make use of a slotted aloha communication scheme.
BACKGROUND OF THE INVENTION
The object management system of the present invention includes information passing between an interrogator which creates an electromagnetic interrogation field, and the electronically coded tags, which respond by issuing a reply signal that is detected by the interrogator, decoded and consequently supplied to other apparatus in the sorting, controlling or auditing process. The objects to which the tags are attached may be animate or inanimate. In some variants of the system the interrogation medium may be other than electromagnetic, such as optical and/or acoustic.
Under normal operation the tags may be passive, i.e. they may have no internal energy source and may obtain energy for their reply from the interrogation field, or they may be active and may contain an internal energy source, for example a battery. Such tags respond only when they are within or have recently passed through the interrogation field. The interrogation field may include functions such as signalling to an active tag when to commence a reply or series of replies or in the case of passive tags may provide energy, a portion of which may be used in constructing the reply.
One example of an electronic tag reading system is illustrated in Figure 1. In Figure 1 an interrogator 10, containing a transmitter and receiver, both operating under a controller, communicate via electromagnetic means with a code responding electronic tag 11.
A slotted aloha scheme refers to a communications scheme that is adapted to minimize collisions between tags. This is done by employing signals that are sent at precise time intervals or slots. Specifically, interrogator 10 can signal to each tag when a time slot is clear to send a reply.
When a plurality of tags co-exists in an interrogating electromagnetic field, an anti-collision scheme which reduces the population of replying tags is beneficial for expedient reading of all tags present in the field. To this end, it is desirable after a tag has sent its reply, to minimize interference with tags which have not been read. One prior art approach is to turn off tags after they have been read. An object of the present invention is to provide an alternative scheme for minimizing collisions.
SUMMARY OF THE INVENTION
An alternative to turning off tags after they have been read is to relegate their continuing replies to an invalid time interval or slot where they may not or cannot interfere with tags, which have not been read. In a slotted system one or more special time slots may be allocated for such replies. Replies may also be relegated to an invalid time interval or slot when the interrogator does not expect a reply. This may include the blind time or interval associated with the turn around time between an interrogator signalling and the reply time of an unread tag. Another invalid time interval or slot exists during the pre-cursor or preamble portion of a valid time interval or slot. The pre-cursor or preamble portion is transmitted before the tag information is transmitted. Because such a time slot is much shorter than the length of a normal reply, the relegated reply will need to be much shorter (ie. truncated) relative to a normal reply.
In general relegation may be achieved by time shifting or translating replies of read tags to an invalid time slot as described above. According to one aspect of the present invention there is provided a method for avoiding destructive collisions between read and unread RFID tags, said method including modifying replies of said read tags such that the modified replies do not occupy substantially the same time slots as replies of unread tags.
The step of modifying may include time shifting the replies of read tags such that the modified replies do not overlap time slots associated with replies of unread tags. Replies of read tags may be time shifted to time slots associated with turn around times of an interrogator adapted to read the tags. Alternatively, replies of read tags may be time shifted to at least one reserved time slot. Unread tags may be instructed not to reply during the or each reserved time slot. The step of modifying may include truncating the replies of read tags such that the modified replies do not overlap time slots associated with data portions in the replies of unread tags.
DESCRIPTION OF A PREFERRED EMBODIMENT
A preferred embodiment of the present invention will now be described with reference to the accompanying drawings wherein:
FIG. 1 shows an electronic tag ready system to which the method for avoiding collisions of the present invention may be applied; and
FIG. 2 shows examples of relegated replies according to the present invention.
FIG. 2 shows a timing diagram illustrating examples of time slots into which replies of tags which have been read may be relegated to minimize interference with tags which have not been read.
In particular, FIG. 2(a) shows time slots that are occupied by commands transmitted by interrogator 10. FIG. 2(b) shows time slots associated with the turn around time of interrogator 10. The turn around time is the dead time after a command has been sent by interrogator 10 and before its receive circuits can settle down after a transmission activity. A reply received during this dead time slot is most unlikely to be decoded by interrogator 10. Fig. 2(b) also shows an example of a reserved time slot being a time slot that is reserved for tags, that have already been read. Unread tags may be instructed not to reply during the reserved time slot.
FIG. 2(c) and 2(d) show valid time slots being time slots that are occupied by transmissions from unread tags 1 and 2 respectively. Collisions during valid time slots may be minimized by reducing the population of tags replying during these time slots. The population of replying tags may be reduced by turning off tags after they have transmitted their data, ie. after the tags have been read. However, the population of replying tags may also be reduced by time shifting the replies of read tags to time intervals which occupy time slots other than the valid time slots shown in Figs. 2(c) and 2(d). One example of a time shifted reply of a read tag is shown in Fig. 2(e). The example of Fig. 2(e) shows a read reply that has been time shifted or relegated to a time slot that substantially overlaps the dead time or turn around time slots shown in Fig. 2(b).
FIG. 2(f) shows an example wherein a read reply has been time shifted or relegated to a time slot which represents the pre-cursor or pre-amble of a valid reply time slot as shown in Fig. 2(c). Providing that the read reply does not extend into the information or data portion of the valid reply time slot it is unlikely to interfere with data from an unread tag 1. However, the read reply will have to be time shortened or truncated so that it does not extend into the data slot of unread tag 1.
FIG. 2(g) shows an example wherein a read reply is time shifted or relegated to a time slot which is specifically reserved for read tags. As described above unread tags may be instructed not to reply during the reserved time slot. Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

Claims

1. A method for avoiding destructive collisions between read and unread RFID tags, said method including modifying replies of said read tags such that the modified replies do not occupy substantially the same time slots as replies of unread tags.
2. A method according to claim 1 wherein said step of modifying includes time shifting the replies of said read tags such that the modified replies do not overlap time slots associated with said replies of unread tags.
3. A method according to claim 1 wherein said step of modifying includes truncating the replies of said read tags such that the modified replies do not overlap time slots associated with data portions in the replies of said unread tags.
4. A method according to claim 2 including time shifting said replies of said read tags to at least one reserved time slot.
5. A method according to claim 4 wherein said unread tags are instructed not to reply during the or each said reserved time slot.
6. A method according to claim 2 including time shifting said replies of said read tags to time slots associated with turn around times of an interrogator adapted to read said tags.
7. A method according to any one of the preceding claims wherein said tags are included in a system which makes use of a slotted aloha communication scheme.
8. A method for avoiding destructive collisions between read and unread RFID tags substantially as herein described with reference to the accompanying drawings.
PCT/AU2003/001190 2002-09-27 2003-09-10 Method for avoiding collisions between rfid tags WO2004029652A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003258380A AU2003258380A1 (en) 2002-09-27 2003-09-10 Method for avoiding collisions between rfid tags

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU2002951699 2002-09-27
AU2002951699A AU2002951699A0 (en) 2002-09-27 2002-09-27 Method of avoiding continued destructive tag collisions in an slotted aloha anti-collision scheme

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004020956A1 (en) * 2004-04-28 2005-11-17 Atmel Germany Gmbh Communication methods in RFID or remote sensor systems
US7538676B2 (en) 2006-06-06 2009-05-26 International Business Machines Corporation System and method for swapping tag reads based on statistical analysis of known environment
US9785804B2 (en) 2004-07-09 2017-10-10 Amtech Systems, LLC Multi-protocol RFID system
CN115665715A (en) * 2022-12-26 2023-01-31 北京通成网联科技有限公司 Group reading response method and device for RFID (radio frequency identification) tags

Citations (3)

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Publication number Priority date Publication date Assignee Title
US5124699A (en) * 1989-06-30 1992-06-23 N.V. Netherlandsche Apparatenfabriek Nedap Electromagnetic identification system for identifying a plurality of coded responders simultaneously present in an interrogation field
US5537105A (en) * 1991-01-04 1996-07-16 British Technology Group Limited Electronic identification system
US5557280A (en) * 1992-08-26 1996-09-17 British Technology Group Limited Synchronized electronic identification system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5124699A (en) * 1989-06-30 1992-06-23 N.V. Netherlandsche Apparatenfabriek Nedap Electromagnetic identification system for identifying a plurality of coded responders simultaneously present in an interrogation field
US5537105A (en) * 1991-01-04 1996-07-16 British Technology Group Limited Electronic identification system
US5557280A (en) * 1992-08-26 1996-09-17 British Technology Group Limited Synchronized electronic identification system

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004020956A1 (en) * 2004-04-28 2005-11-17 Atmel Germany Gmbh Communication methods in RFID or remote sensor systems
DE102004020956B4 (en) * 2004-04-28 2009-03-26 Atmel Germany Gmbh Communication methods in RFID or remote sensor systems
US8054162B2 (en) 2004-04-28 2011-11-08 Atmel Corporation Communication method in RFID or remote sensor systems
US8477017B2 (en) 2004-04-28 2013-07-02 Atmel Corporation Method, system, and integrated circuit for communication in RFID or remote sensor systems
US9785804B2 (en) 2004-07-09 2017-10-10 Amtech Systems, LLC Multi-protocol RFID system
US7538676B2 (en) 2006-06-06 2009-05-26 International Business Machines Corporation System and method for swapping tag reads based on statistical analysis of known environment
CN115665715A (en) * 2022-12-26 2023-01-31 北京通成网联科技有限公司 Group reading response method and device for RFID (radio frequency identification) tags
CN115665715B (en) * 2022-12-26 2023-04-07 北京通成网联科技有限公司 Group reading response method and device for RFID (radio frequency identification) tags

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