WO2008017889A1

WO2008017889A1 - Improvements relating to rfid readers

Info

Publication number: WO2008017889A1
Application number: PCT/GB2007/050482
Authority: WO
Inventors: Chien Yaw Wong; Da Xing; Duncan Mcfarlane
Original assignee: Redbite Solutions Limited
Priority date: 2006-08-10
Filing date: 2007-08-10
Publication date: 2008-02-14
Also published as: GB2440790A; GB2440790B; GB0615892D0

Abstract

The present invention relates to a controller 200, 210 for controlling RFID readers 100, 110. According to the invention, a controller 200, 210 is provided, suitable for controlling the communication of a plurality of RFID readers 100, 110 with at least one RFID tag 300, 310, 320, the controller 200, 210 comprising means for determining which of said plurality of RFID readers 100, 110 may be set to an active condition wherein an RFID reader 100, 110 may transmit a modulated RF signal for reception by an RFID tag 300, 310, 320, and which of said plurality of RFID readers 100, 110 may be set to an alternate condition wherein an RFID reader 10,110 may not transmit a modulated RF signal for reception by an RFID tag 300, 310, 320, the controller 200, 210 further comprising means for communicating a control signal to each RFID reader 100, 110 whereby each RFID reader 100, 110 may be set to a condition selected from amongst said active condition and said alternate condition, the controller 200, 210 being adapted to set each RFID reader 100, 110 to an active condition according to a sequence such that not more than one RFID reader 100, 110 of an overlap area is in an active condition. The invention has the advantage that collisions between readers 100, 110 in an overlap area can be avoided, and one-to-many communication between RFID readers 100, 110 and RFID tags 300, 310, 320 may be maintained.

Description

IMPROVEMENTS RELATING TO RFID READERS

The present invention relates to Radio Frequency Identification (RFID) systems. In particular, the invention relates to an anti-collision protocol for RFID reader transmissions when a reader is within the range of the interrogating field of another reader.

RFID systems rely on radio frequency-based communication between a reader and a transponder or tag of various types for identifying objects and have a variety of applications. In a typical arrangement of a passive RFID tag system according to the prior art, a tag reader transmits an interrogating radio frequency signal that energises a tag within range of the signal. The reader communicates a command to the tag by modulating the transmitted RF field. After transmitting the command, the reader continues transmitting a continuous wave (CW) to provide power for the tag to respond to the command. Upon receiving the command, the tag may reply to the reader via a predefined protocol.

Problems can arise in situations where more than one reader is in the vicinity of a tag, or more than one tag is in the vicinity of a reader since transmitted information can become corrupted when more than one device is attempting to communicate at the same time.

If a plurality of tags comes into the interrogating field of a reader, a one-to-many relationship between the reader and the tags is established, resulting in collisions between the tags. A 'tag collision' refers to the situation where more than one tag attempts to respond to a reader. This may occur when a reader transmits a modulated signal, and a plurality of tags respond with a modulated signal resulting in many-to-one communication in the communication channel of the same state. If there is more than one reader, 'many-to-many' communication results.

In response to this problem, a number of anti-collision protocols have been devised which are now well established. Generally, the aim of these protocols is to ensure there is only a one-to-one communication between a reader and a tag at any given time.

If a tag is positioned in an overlap area of the interrogating field of a plurality of readers, reader collision may result. Reader collision refers to the situation where more than two readers attempt to communicate with a single or multiple tags. The reader collision may occur even when two colliding readers are working at different frequencies by, for example, frequency hopping. There are two main reasons for the collision. One is due to a limited spectral band width which limits the number of frequency hopping channels, which means that there is a chance that two readers accidentally communicate with tags at the same frequency. The other reason is due to the design features of the tags, particularly for those low budget tags whose state machine status makes it impossible for them to accept commands from readers on two different frequencies simultaneously. This would result in tags being read successfully by one reader while failing to be read by other readers in unpredictable ways, or failing to be read by any of the readers randomly. In a heavy duty RFID environment where there may be a number of neighbouring readers constantly communicating with tags, the problem can be particularly acute.

A method currently used to avoid the reader collision problem is to allow a reader to listen before transmitting (known as 'listen before talk', or LBT). During the listening stage, if a first reader detects a transmission from another reader, the first reader will wait for a random length of time before listening again. If, following the waiting period, the first reader does not detect transmission from another reader, it commences transmission of its signal. This technique reduces the possibility of a reader collision but has the disadvantage that reader collision can still occur, such as when two previously silent readers simultaneously commence transmission.

It is known from JP 2003150916 to provide a system for preventing interference between mutual radio tag readers by using a sleep/release algorithm. Initially, each reader starts in a sleep state and asks for a release. There is no network management, but rather a one-to-one reader control algorithm.

It is known from JP 200268140 to provide a non-contact ID tag system in which the power consumption of a reader is reduced by switching off a power amplifier of the reader in accordance with a predetermined time pattern. It is possible to avoid interference between neighbouring readers by ensuring that both are not on at the same time. However, this system is inflexible, relying on a fixed algorithm, and does not work well in a network environment. It is known from JP 2004266550 to provide a method for managing time allocation for RFID readers so as to avoid overlap between neighbouring readers by using predetermined time slots. There is no communication between controllers, and no consideration of high level network configuration.

It is known from GB 2 341 046 to provide a transponder ID system in which neighbouring readers communicate the identities of detected transponders to each other so as to avoid multiple detections and collisions. A non-exclusive (non- synchronised) mode is used to read tags in an overlapping region to ensure that all tags are read by the available readers. There is no consideration of reader collision problems.

According to a first aspect of the present invention there is provided a controller suitable for controlling the communication of a plurality of RFID readers with at least one RFID tag, the controller comprising means for determining which of said plurality of RFID readers may be set to an active condition wherein an RFID reader may transmit a modulated RF signal for reception by an RFID tag, and which of said plurality of RFID readers may be set to an alternate condition wherein an RFID reader may not transmit a modulated RF signal for reception by an RFID tag, the controller further comprising means for communicating a control signal to each RFID reader whereby each RFID reader may be set to a condition selected from amongst said active condition and said alternate condition, the controller being adapted to set each RFID reader to an active condition according to a sequence such that not more than one RFID reader of an overlap area is in an active condition.

The invention has the advantage that collisions between readers in an overlap area can be avoided, and one-to-many communication between RFID readers and RFID tags may be maintained.

Preferably, the alternate condition is a condition selected from amongst a condition in which the RFID reader may listen to authorised communication between an RFID reader and a tag, and a condition in which the RFID reader is in a hibernate condition whereby the RFID reader may not listen to authorised communication between an RFID reader and a tag. The means for communication of the control signal to an RFID reader may be at least one selected from amongst a wired communication channel and a wireless communication channel. This has the advantage that maximum flexibility in locating RFID readers can be achieved, for example in locations to which it is difficult or undesirable to route a wired communication channel, at the same time permitting the cost savings typical of wired systems in locations where routing of a wired communication channel is acceptable.

Preferably, the wired communication channel may comprise cable selected from amongst com (serial) cable, parallel cable, Fieldbus™ and Ethernet™ cable, and said wireless communication channel may comprise a wireless Fieldbus™, Bluetooth™, GPRS, GSM or 802.1 1 channel.

The controller may be integrated with at least one of said plurality of RFID readers. This has the advantage of making the overall system more compact, and reduces the number of components required thereby reducing the cost. In some embodiments, the controller physically resides within at least one of said plurality of RFID readers.

In other embodiments, the controller is separate from said plurality of RFID readers, for example not being physically integrated or resident within any of said plurality of RFID readers.

In some embodiments, the controller may be retrofitted to an existing RFID reader, either internally or as an external plug-in or wireless component. This allows existing RFID reader systems to be upgraded without the expense of replacing all or any of the RFID readers.

In other words, embodiments of the present invention envisage configurations in which a controller may physically reside either inside or outside one or more of the RFID readers, or may be a stand-alone controller, and wherein both RFID readers with an integral controller and RFID readers without an integral controller can be controlled by another controller, either integral with or associated with a particular RFID reader, or a stand-alone controller.

In some embodiments, the controller may be located remotely from said plurality of RFID readers. In a second aspect of the invention there is provided an RFID system comprising a plurality of RFID readers, each of said plurality of RFID readers having a controller, said controller having means for controlling the RFID reader, one of said controllers being a master controller, the master controller comprising means for determining which of said plurality of RFID readers may be set to an active condition wherein said RFID reader may transmit a modulated RF signal for reception by an RFID tag, and which of said plurality of RFID readers may be set to an alternate condition wherein said RFID reader may not transmit a modulated RF signal for reception by an RFID tag, the master controller further comprising means for communicating a control signal to each RFID reader whereby each RFID reader may be set to a condition selected from amongst said active condition and said alternate condition, the controller being adapted to set each RFID reader to an active condition according to a sequence such that not more than one RFID reader of an overlap area is in an active condition.

Preferably, the alternate condition is a condition selected from amongst a condition in which the RFID reader may listen to authorised communication between an RFID reader and a tag, and a condition in which the RFID reader is in a hibernate condition whereby the RFID reader may not listen to authorised communication between an RFID reader and a tag.

Preferably, each controller is adapted to be selectable as a master controller by means selected from among a manual determination by an operator and an automatic determination by the RFID system. This has the advantage of enhancing the flexibility of the RFID system to adapt to events such as expansion or contraction of the system according to demand, or failure of one or more RFID readers. Thus, if the controller acting as master controller fails, the system can automatically reassign another controller to be the master controller.

Each controller which is not a master controller may have means for registering a reader with which it is associated with the master controller.

The master controller may further comprise means for determining whether a reader wishing to join the RFID system has permission to be added to the RFID system. The master controller may be adapted to raise an alert if a reader not having permission to be added to the RFID system wishes to be added to the RFID system. The master controller further comprises means for detecting if a reader tries to communicate with RFID tags without authorization, and means for providing an alert if a reader tries to communicate with RFID tags without authorization.

The means for communication between controllers may be a wired communication channel or may be a wireless communication channel. The wired communication channel may comprise cable selected from amongst com (serial) cable, parallel cable, Fieldbus™ and Ethernet™ cable, and said wireless communication channel may comprise a wireless Fieldbus™ Bluetooth™, GPRS, GSM or 802.1 1 channel.

In addition to or instead of the controller of the present invention being adapted to avoid reader collision by way of a master/slave configuration, the controller may be adapted selectively to enable and disable its communication antenna. Where the controller has more than one antenna, it may be adapted to enable its antennae in a predetermined sequence. Furthermore, a "master" controller may be adapted to enable/disable and/or sequence the antennae of one or more predetermined "slave" controllers as well as its own antenna or antennae.

Moreover, a "federation" model may be employed, in which a slave controller may itself be a master controller for another group of slave controllers. In other words, a federation of controllers comprises at least one master controller with a subset of slave controllers, at least one of which subset of slave controllers is a master controller for a further subset of slave controllers, and so forth.

Advantageously, the controller is provided with a control algorithm to enable it to make control decisions. The controller and/or the control algorithm may be adapted or configured to monitor or take into account at least one of: power levels of RFID readers, backscattered power of RFID tags, priority settings of RFID readers, RF noise levels in the ambient environment, channel allocations and corresponding noise levels, RFID reader locations, RFID tag locations, RF spectrum regulations for the country of operation, and reader-to-tag and/or tag-to-reader response time latency. Other factors may be taken into consideration as appropriate. For a better understanding of the present invention and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings, in which:

FIGURE 1 illustrates schematically the problem of interference between tag readers according to the prior art; and

FIGURE 2 is a schematic diagram of an apparatus according to the present invention.

The problem of interference between RFID readers 100, 1 10 and a plurality of tags 300, 310, 320 is well known and a typical situation is shown schematically in Figure 1. Where an overlap area exists between the RF fields 600, 610 of readers 100, 1 10, reader collision may occur. Similarly, tag collision may occur where a plurality of tags 300, 310, 320 attempt to communicate with one or more readers 100, 1 10 simultaneously.

In a preferred embodiment of the invention, a controller is associated with each RFID reader. Thus, as illustrated schematically in Figure 2, controller 200 is associated with reader 100 and controller 210 is associated with reader 1 10. The controllers 200, 210 communicate with one another via a dedicated communication channel 900, forming a controller communication network. The communication channel 900 may be a wired communication channel (for example using com (serial), parallel, Fieldbus™ or Ethernet cable), a wireless communication channel (for example using wireless Fieldbus™, Bluetooth, GPRS, GSM or 802.1 1 etc), or even via the RFID antenna of the readers.

In a preferred embodiment of the invention, the controller 200, 210 hardware is integrated with the RFID reader 100, 1 10, although in other embodiments they may be separate.

The controllers 200, 210 may be configured such that the master controller is automatically (or semi-automatically) selected by the reader controllers 200, 210 according to defined protocols, or the master controller may be selected manually by an operator.

In a preferred embodiment of the invention, the master controller is responsible for authenticating readers 100, 1 10 wishing to join the reader network according to defined criteria. The master controller may be configured to raise an alert if an un-authenticated reader 100, 1 10 wants to join the network, such as by displaying a message, or sounding an alarm, etc. Similarly, if a reader 100, 1 10 tries to communicate with RFID tags 300, 310, 320 without authorization, an alert may be generated.

The master controller is responsible for authorizing authenticated readers 100, 1 10 to communicate with tags 300, 310, 320 at the appropriate time. A reader 100, 1 10 may be authorized to perform a full reader-tag communication (reader TX-RX), listen to authorized communication between readers 100, 1 10 and tags 300, 310, 320, or be instructed to enter a 'hibernate' mode, where the reader 100, 1 10 neither transmits nor receives RFID signals, but waits for a message from the master controller.

In the present embodiment the algorithm by which the master controller authorizes the readers 100, 1 10 to communicate only allows one reader 100, 1 10 to perform a full- mode communication between tags 300, 310, 320 at any one time. In alternate embodiments, other types of communication may be allowed.

A controller 200, 210 which is in slave mode is responsible for authenticating itself, i.e. registering the reader 100, 1 10 with which it is associated with the master controller, and controlling the reader 100, 1 10 according to commands received from the master controller.

In a further embodiment of the invention, there is no master controller, but rather each controller 200, 210 associated with a reader 100, 1 10 is a slave that decides independently when to broadcast based on a set of rules. The rules might for example comprise a bidding/auction protocol.

In a still further embodiment, there are two master controllers, each having one or more slave controllers associated with them, each of the master and slave controllers being individually associated with a reader 100, 1 10. The master controllers are adapted to communicate with each other, and with their respective slave controllers, to coordinate communication with one or more tags 300, 310, 320. Such a system could be expanded into a hierarchical structure of master controllers and slave controllers.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS:

1. A controller suitable for controlling the communication of a plurality of RFID readers with at least one RFID tag, the controller comprising means for determining which of said plurality of RFID readers may be set to an active condition wherein an RFID reader may transmit a modulated RF signal for reception by an RFID tag, and which of said plurality of RFID readers may be set to an alternate condition wherein an RFID reader may not transmit a modulated RF signal for reception by an RFID tag, the controller further comprising means for communicating a control signal to each RFID reader whereby each RFID reader may be set to a condition selected from amongst said active condition and said alternate condition, the controller being adapted to set each RFID reader to an active condition according to a sequence such that not more than one RFID reader of an overlap area is in an active condition.

2. The controller of claim 1 wherein a controller in the alternate condition may listen to authorised communication between an RFID reader and a tag.

3. The controller of claim 1 wherein a controller in the alternate condition is in a hibernate mode, wherein the controller may not listen to authorised communication between an RFID reader and a tag.

4. The controller of any preceding claim, wherein the means for communication of the control signal to said RFID reader is a wired communication channel.

5. The controller of any one of claims 1 to 3, wherein the means for communication of the control signal to said RFID reader is a wireless communication channel.

6. The controller of any preceding claim, wherein the controller is integrated with at least one of said plurality of RFID readers.

7. The controller of claim 6, wherein the controller physically resides within at least one of said plurality of RFID readers.

8. The controller of any one of claims 1 to 5, wherein the controller is separate from said plurality of RFID readers.

9. The controller of claim 8, wherein the controller is not physically integrated or resident within any of said plurality of RFID readers.

10. The controller of any one of claims 1 to 5, 8 or 9, wherein the controller is located remotely from said plurality of RFID readers.

1 1. The controller of any preceding claim, the controller being configured to monitor or take into account at least one of: power levels of RFID readers, backscattered power of RFID tags, priority settings of RFID readers, RF noise levels, channel allocations and corresponding noise levels, RFID reader locations, RFID tag locations, RF spectrum regulations, and reader-to-tag and/or tag-to-reader response time latency.

12. An RFID system comprising a plurality of RFID readers, each of said plurality of RFID readers having a controller, said controller having means for controlling the RFID reader, one of said controllers being a master controller, the master controller comprising means for determining which of said plurality of RFID readers may be set to an active condition wherein said RFID reader may transmit a modulated RF signal for reception by an RFID tag, and which of said plurality of RFID readers may be set to an alternate condition wherein said RFID reader may not transmit a modulated RF signal for reception by an RFID tag, the master controller further comprising means for communicating a control signal to each controller, whereby each RFID reader may be set to a condition selected from amongst said active condition and said alternate condition, the master controller being adapted to set each RFID reader to an active condition according to a sequence such that not more than one RFID reader of an overlap area is in an active condition.

13. The RFID system of claim 12, wherein a controller in the alternate condition may listen to authorised communication between an RFID reader and a tag.

14. The RFID system of claim 12, wherein a controller in the alternate condition is in a hibernate mode, wherein the controller may not listen to authorised communication between an RFID reader and a tag.

15. The RFID system of any one of claims 12 to 14, wherein each controller is adapted to be selectable as a master controller manually by an operator.

16. The RFID system of any one of claims 12 to 14, wherein each controller is adapted to be selectable as a master controller automatically by the RFID system.

17. The RFID system of any one of claims 12 to 16, wherein the means for communicating a control signal is a wired communication channel.

18 The RFID system of any one of claims 12 to 16, wherein the means for communicating a control signal is a wireless communication channel.

19. The RFID system of any one of claims 12 to 18, wherein a controller which is not a master controller has means for registering a reader with which it is associated with the master controller.

20. The RFID system of claim 19, wherein the master controller further comprises means for determining whether a reader wishing to join the RFID system has permission to be added to the RFID system.

21. The RFID system of claim 20, wherein the master controller is adapted to raise an alert if a reader not having permission to be added to the RFID system wishes to be added to the RFID system.

22. The RFID system of claim 21 , wherein the master controller further comprises means for detecting if a reader tries to communicate with RFID tags without authorization, and means for providing an alert if a reader tries to communicate with RFID tags without authorization.

23. The RFID system of any one of claims 12 to 22, wherein at least one of the RFID readers is provided with an integral controller.

24. The RFID system of claim 23, wherein the controller physically resides within the at least one RFID reader.

25. The RFID system of any one of claims 12 to 22, wherein at least one of the RFID readers is provided with an external controller.

26. The RFID system of any one of claims 12 to 25, further comprising at least slave controller that is controlled by the master controller.

27. The RFID system of claim 26, wherein at least one slave controller is configured as a master controller for a subset of further slave controllers.

28. A controller suitable for controlling the communication of a plurality of RFID readers with at least one RFID tag, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

29. An RFID system substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.