WO2003085843A2

WO2003085843A2 - Transponder-based communication systems

Info

Publication number: WO2003085843A2
Application number: PCT/IB2003/001235
Authority: WO
Inventors: Hendrik Lodewyk Van Eeden
Original assignee: Ip And Innovation Company Holdings (Proprietary) Limited
Priority date: 2002-04-05
Filing date: 2003-04-04
Publication date: 2003-10-16
Also published as: WO2003085843A3; AU2003216574A1; AU2003216574A8

Abstract

A method of communicating between a transponder (12..18) and an interrogator (20) includes transmitting an announcement signal (34) from the transponder (12..18) to the interrogator (20), the announcement signal (34) including an identification code associated with the transponder (12..18), the communication signal including at least a portion of the identification code of the transponder (12..18) or a derivative thereof, thereby enabling the transponder (12..18) to identify the communication signal from the interrogator (20) as being directed at the transponder (12..18).

Description

TRANSPONDER-BASED COMMUNICATION SYSTEMS

THIS INVENTION relates to transponder-based communication systems. In particular, it relates to a method of communicating between a transponder and an interrogator, to a transponder, and to a transponder-based communications system.

Radio frequency (RF) electronic identification or communication systems including an interrogator or reader and a plurality of transponders, typically passive transponders, are well known in the art. In use, the interrogator or reader energises the passive transponders by transmitting an interrogation signal. Each energised transponder either automatically responds with a response signal, often including an identification code associated with the transponder (TTF or Tag Talks First protocol) or is commanded to respond (RTF or Reader Talks First protocol). The response signals are received by the reader and further action may then be taken, e.g. reading data from the transponder, writing data to the transponder, deactivating the transponder, or the like. Data read from the transponder may be used to identify transponders and goods associated with the transponders and/or to count the transponders and/or goods, or for telemetry purposes, or the like. However, when a plurality of transponders are energised simultaneously, it may well happen that the response signals overlap in time, that the transmissions clash and that the data in the response signals is lost. Systems of the aforementioned kind thus typically provide for anti-clash or anti-collision measures or protocols.

When a number of transponders are present, and the interrogator wishes to communicate with a particular transponder, problems occur in obtaining singular communication between the reader and the transponder.

In most of the read/write protocols applied to RFID systems, of which the applicant is aware, it is a requirement that only one transponder must be present, or that the reader or interrogator must initiate the communications between the transponder and the interrogator (RTF). In this last case, the reader must in some way be made aware that there is a transponder present to be communicated with, or it must poll for tags. When the reader must be made aware that there is a transponder present, this can be achieved by many means, e.g. a light beam, trip switches, optical detection, manual intervention by an operator, or the like. However, in all these cases additional equipment is required for automatic operation.

If the reader has to poll for transponders, the rate of polling will determine the rate at which transponders can move through the energy field of the interrogator, meaning that slow polling might miss fast-moving transponders. Any polling, however, results in a lot of RF noise being generated by the reader, thereby possibly interfering with other electronic equipment or with other RFID systems nearby.

TTF protocols are also known in which singular communication between the reader and the transponder is achieved by timing the reader commands relative to the transponder's transmissions. These types of protocols are fraught with problems. One example of a typical problem is the case where two transponders transmit at nearly identical times. A reader command that follows is accepted by both transponders.

It is an object of the invention to provide an alternative to RTF read/write RFID protocols or timed TTF protocols, which overcomes to at least some extent the known weaknesses of these protocols.

According to one aspect of the invention, there is provided a method of communicating between a transponder and an interrogator, the method including transmitting an announcement signal from the transponder to the interrogator, the announcement signal including an identification code associated with the transponder; and transmitting at least one communication signal from the interrogator to the transponder, the communication signal including at least a portion of the identification code of the transponder or a derivative thereof, thereby to enable the transponder to identify the communication signal from the interrogator as being directed at the transponder. The method may include activating the transponder to enable the transponder to transmit its announcement signal. Activating the transponder may include transmitting an activation signal from the interrogator. In one embodiment of the invention, the transmitting of the announcement signal from the transponder to the interrogator is in response to the transponder entering an energy field transmitted by the interrogator. Thus, the method of the invention establishes a so-called Tag Talks First Read/Write protocol for communication between a transponder and an interrogator.

The communication signal from the interrogator to the transponder may include commands to the transponder. These commands may be commands to write data to the transponder, to read data stored in EEPROM memory from the transponder, to switch the transponder off, to change baud rates, to change anti-collision parameters, or the like.

The transmitting of the announcement signal from the transponder to the interrogator may be effected in an anti-collision manner. The applicant is aware of many anti-collision protocols which may be used when a plurality of transponders are present or potentially present. However, in a preferred embodiment of the invention, the anti-collision method as disclosed in US 6,154,136, the disclosure of which is incorporated herein by way of reference, is used. Thus, the method may include delaying the transmission of the announcement signal for a random period after activation of the transponder, and the method may include, if no signal is received by the transponder from the interrogator, repeatedly transmitting the announcement signal, with a random interval between transmissions, until the signal from the transponder is correctly received by the interrogator and acknowledged by the interrogator.

The transponder may be a passive RFID transponder, and in particular a UHF transponder.

The method may include, when the communication signal from the interrogator to the transponder includes a write command, transmitting the received data from the transponder to the interrogator as a confirmation of receipt of the write command. The identification code associated with the transponder may comprise an identification code portion and a cyclic redundancy check (CRC) portion, e.g. a 48-bit identification code portion and a 16-bit CRC portion.

According to another aspect of the invention, there is provided a transponder which includes receiver means for receiving a signal; transmitter means for transmitting a signal; memory means storing an identification code or configured to store an identification code; and logic means configured to compare a received signal with the identification code stored in the memory means and if the received signal includes a code which corresponds to a preselected degree with the stored code in the memory means, or a derivative thereof, to act on any instructions contained in said received signal.

The transponder may be a passive RFID transponder, and in particular may be a UHF transponder.

The logic means may be configured to control the transmitting means in order to transmit the identification code in the memory means. In a preferred embodiment of the invention, the logic means is configured to employ an anti-collision protocol when controlling the transmitting means. The anti-collision protocol may be as hereinbefore described.

The memory means may be a solid state memory. The memory means may be configured to, in addition to the identification code, store other data in digital format.

The identification code stored in the memory means may be as hereinbefore described.

The logic means may be configured to transmit received data by means of the transmitter means when a received signal includes a write command to write data to the memory means. According to a further aspect of the invention, there is provided a transponder-based communication system which includes a plurality of transponders at least one of which is configured intermittently to transmit a signal which includes an identification code associated with the transmitting transponder; and an interrogator configured to receive the signals and capable of transmitting a signal which includes at least a portion of the identification code of one of the transponders or a derivative thereof, thereby to enable said one of the transponders to identify the signal as being directed to said one transponder.

The at least one transponder may be a transponder as hereinbefore described.

Further features of the invention will become apparent from the following description and diagrammatic drawings.

In the drawings: Figure 1 shows a schematic drawing of a transponder-based communication system comprising four transponders and an interrogator; Figure 2 shows a functional flow diagram of commands executed by a logic device in each of the transponders of the system of Figure 1 ; and

Figure 3 shows a typical command sequence of two of the transponders and the interrogator of the system of Figure 1.

In Figure 1 reference numeral 10 generally indicates a transponder-based communication system.

Four transponders 12, 14, 16 and 18 are shown moving past an interrogator

20, in a direction indicated by arrow 22. Radio frequency transmissions in the Ultra High Frequency (UHF) band, emitted by the interrogator 20 produce an energy field 24 through which the transponders 12, 14, 16 and 18 pass. The power of the transmissions is used to power the transponders 12, 14, 16 and 18. The transponder 12 has already passed through the energy field 24, the transponders 14 and 16 are still in the energy field 24 and the transponder 18 still has to enter the energy field 24. The transponders 12, 14, 16 and 18 communicate with the interrogator 20 by using a Tag Talks First (TTF) protocol in accordance with the invention. It is to be appreciated that the reading distance between the interrogator 20 and the transponders 12, 14, 16 and 18 can be increased, by increasing the power of the RF transmissions.

Each transponder 12, 14, 16 and 18 includes an integrated circuit (not shown), an antenna (not shown), EEPROM memory (not shown) storing a unique ID code for the transponder, as well as possibly additional memory, and associated circuitry. The integrated circuit includes a logic device.

As a transponder 12, 14, 16 or 18 enters the energy field 24 the transponder is activated by the energy field 24 to transmit a digital announcement signal to the interrogator 20. The transponders 12, 14, 16, 18 use an anti-collision protocol as previously described in US patent 6,154,136, which includes cyclic redundancy checks (CRC's) to detect erroneous signals. Had the transponders 12, 14, 16 and 18 not used the anti-collision protocol and there were two transponders 14 and 16 in the energy field 24 simultaneously, it would have been highly probable that both would have transmitted their announcement signals to the interrogator 20 simultaneously. This would then have resulted in the interrogator 20 not being able to receive any of the announcement signals correctly, and the transponders 14 and 16 may have moved past the interrogator 20 without being detected.

The logic device (not shown) in the transponders executes the logic steps shown in Figure 2. The logic device starts execution at 30 and then waits for a random time delay 32 before transmitting an announcement signal (indicated by reference numeral 34), containing a unique factory programmed identification (ID) code. The logic device then awaits a response from the interrogator 20, as indicated by reference numeral 36. In the event of no response 38 from the interrogator 20, or if the response from the interrogator 20 does not include the correct identification code, the logic device again waits for a random time delay 32. In the event of a response 40 containing the correct identification code from the interrogator 20, the logic device reads and executes the command from the interrogator 20, as indicated by reference numeral 42. The logic device can receive a command to suspend the random time delay 32 or to change the maximum initial random time delay 32.

Due to the different random time delays 32 of the two transponders 14 and 16, the probability of simultaneous transmission of their announcement signals is very low. In the improbable event that the announcement signals overlap, the interrogator will not respond to either signal (shown by reference numeral 38), thereby triggering another random time delay 32.

A typical command sequence between the interrogator 20 and the transponder 20 is shown in Figure 3. On a first line 100 the transmissions of the transponder 14 are shown over time, a second line 102 shows the transmissions of the transponder 16, and a third line 104 shows the transmissions of the interrogator 20.

When the two transponders 14 and 16 enter the energy field 24 two signals 106 and 108 including the unique ID codes of the transponders 14 and 16 partially overlap in time. The effect thereof is that the interrogator 20 can not detect either of the signals 106 or 108 of the transponders 14 or 16. The transponder 14 then retransmits a signal 110 after waiting for another random time delay 32, but the interrogator 20 does not respond thereto as can be seen on line 104. After waiting for a random time delay 32, the transponder 16 transmits a signal 112 which includes the unique ID code of the transponder 16. The signal 112 does not overlap with a signal from the transponder 14. The interrogator 20 correctly receives the signal and uses the unique ID code received from the transponder 16 in a write command 116 followed by data 118 to be written to the memory of the transponder 16.

The invention is illustrated by the transmission of the signal 116, containing the unique ID code of the transponder 16. The transponder 16, being only responsive to its own ID code, can now communicate with the interrogator 20 in the presence of transmissions from other transponders, without interference from such transmissions.

As can further be seen in Figure 3, the interrogator 20 then transmits a read command 122 which includes the unique ID code of the transponder 16. Random transmission 124 from the transponder 14 is ignored by the interrogator 20. The transponder 16 responds by transmitting data 128 corresponding to the data 118 received from the interrogator 20, thereby acknowledging correct receipt of the transmissions 116 and 118 from the interrogator 20. The overlapping transmission 124 could interfere with communication between the transponder 16 and the interrogator 20, in which case the reader will have to try again later.

The transponder 14 again transmits a signal 130 which includes the unique ID of the transponder 14 after another random time delay 32. In this instance the transmission does not overlap with any other transmissions from the transponder 16 or the interrogator 20. The interrogator 20 acknowledges by transmitting a read command 134 which includes the unique ID code of the transponder 14. The transponder 14 correctly receives the signal 134 and responds by sending the data 138 stored in its memory.

It is to be appreciated that the power of the RF transmissions, the number of tags in the energy field, and the total data packets transmitted and received, influence the rate at which data can be read from tags.

The inventor believes that the invention provides a new method of communicating between a transponder and an interrogator, a new transponder and a new transponder based communications system, which at least to some extent address the problems associated with conventional RTF read/write RFID protocols and timed TTF protocols.

Claims

CLAIMS:

1. A method of communicating between a transponder and an interrogator, the method including transmitting an announcement signal from the transponder to the interrogator, the announcement signal including an identification code associated with the transponder; and transmitting at least one communication signal from the interrogator to the transponder, the communication signal including at least a portion of the identification code of the transponder or a derivative thereof, thereby to enable the transponder to identify the communication signal from the interrogator as being directed at the transponder.

2. The method as claimed in claim 1 , which includes activating the transponder to enable the transponder to transmit its announcement signal.

3. The method as claimed in claim 2, in which activating the transponder includes transmitting an activation signal from the interrogator.

4. The method as claimed in any one of the preceding claims, in which transmitting of the announcement signal from the transponder to the interrogator is effected in an anti-collision manner.

5. The method as claimed in any one of the preceding claims, which includes, when the communication signal from the interrogator to the transponder includes a write command, transmitting the received data from the transponder to the interrogator as a confirmation of receipt of the write command.

6. The method as claimed in any one of the preceding claims, in which the identification code associated with the transponder comprises an identification code portion and a cyclic redundancy check (CRC) portion.

7. A transponder which includes receiver means for receiving a signal; transmitter means for transmitting a signal; memory means storing an identification code or configured to store an identification code; and logic means configured to compare a received signal with the identification code stored in the memory means and if the received signal includes a code which corresponds to a preselected degree with the stored code in the memory means, or a derivative thereof, to act on any instructions contained in said received signal.

8. The transponder as claimed in claim 7, which is a passive RFID transponder.

9. The transponder as claimed in claim 7 or claim 8, in which the logic means is configured to control the transmitting means in order to transmit the identification code in the memory means.

10. The transponder as claimed in claim 9, in which the logic means is configured to employ an anti-collision protocol when controlling the transmitting means.

11. The transponder as claimed in any one of claims 7 to 10 inclusive, in which the logic means is configured to transmit received data by means of the transmitter means when a received signal includes a write command to write data to the memory means.

12. A transponder-based communication system which includes a plurality of transponders at least one of which is configured intermittently to transmit a signal which includes an identification code associated with the transmitting transponder; and an interrogator configured to receive the signals and capable of transmitting a signal which includes at least a portion of the identification code of one of the transponders or a derivative thereof, thereby to enable said one of the transponders to identify the signal as being directed to said one transponder.

13. The transponder-based communication system as claimed in claim 12, in which the at least one transponder is a transponder as claimed in any one of claims 7 to 11 inclusive.

14. A method of communicating between a transponder and an interrogator as claimed in claim 1 , substantially as herein described and illustrated.

15. A transponder as claimed in claim 7, substantially as herein described and illustrated.

16. A transponder-based communication system as claimed in claim 12, substantially as herein described and illustrated.

17. A new communication method, a new transponder or a new transponder- based communication system, substantially as herein described.