Method of simultaneously reading multiple radio frequency tags, RF tags, and RF reader

• US 20040198222A1
• Filed: 10/02/2002
• Published: 10/07/2004
• Est. Priority Date: 10/02/2002
• Status: Active Grant

• Current Assignee: Battelle Memorial Institute
• Original Assignee: Battelle Memorial Institute
• Inventors: L. Priddy, Kevin, Pratt, Richard M., Lechelt, Wayne M., Hughes, Michael A., Ertin, Emre
• Granted Patent: US 6,995,655 B2
• Time in Patent Office: Days
• US Class Current: 455/41.1
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10059 transponder driven
• CPC Class Codes: G06K 7/10069 the collision being resolved in the frequency domain, e.g. by hopping from one frequency to the other frequency hopping or spread spectrum techniques H04B7/00

Abstract

An RF tag system, comprising an RF reader configured to issue a plurality of different RF commands and to provide a continuous RF illumination field, and a plurality of RF tags respectively including a permanent identification; wherein the plurality of RF tags are configured to respond to a certain RF command from the RF reader by transmitting their respective identifications by way of backscatter modulation of the RF illumination field, and wherein the RF tags are further configured to perform the responding by way of respective independently selected random radio frequencies and timeslots from respective pre-defined ranges of radio frequencies and timeslots.

Claims

1. A method of identifying RF tags, the method comprising:

issuing a wireless command using a reader, requesting that RF tags identify themselves;

illuminating a plurality of RF tags with a radio frequency field using the reader;

respective RF tags randomly selecting a radio frequency and a timeslot from a plurality of pre-defined radio frequencies and timeslots;

respective RF tags issuing a wireless response to the command, including information identifying the tag, using the selected radio frequency and timeslot;

receiving the wireless responses with the reader; and

issuing wireless acknowledgements from the reader to RF tags that have been successfully identified responsive to the receiving.

2. A method in accordance with claim 1 and further comprising the respective RF tags repeatedly randomly selecting radio frequencies and timeslots and issuing wireless responses until acknowledged by the reader.

3. A method of identifying RF tags using a reader, the method comprising:

issuing a wireless command, using the reader, requesting that RF tags identify themselves;

providing a radio frequency illumination field using the reader;

monitoring a plurality of radio frequencies simultaneously during each of a plurality of consecutive timeslots using the reader; and

receiving a plurality of wireless responses responsive to the command, at different ones of the radio frequencies and timeslots, using the reader.

4. A method in accordance with claim 3 wherein the receiving comprises simultaneously receiving at least two wireless responses at different radio frequencies.

5. A method in accordance with claim 3 and further comprising determining, using the reader, whether a collision occurred between responses and, if so, issuing another wireless command, using the reader, requesting that RF tags identify themselves.

6. A method in accordance with claim 3 and further comprising defining, using the reader, a first timeframe, wherein a timeframe is the number of timeslots during which the reader will accept responses, and wherein issuing the wireless command further comprises transmitting the timeframe definition to the RF tags.

7. A method in accordance with claim 6 wherein the monitoring is further defined as monitoring a plurality of radio frequencies simultaneously during each of a plurality of consecutive timeslots within the timeframe, using the reader.

8. A method in accordance with claim 7 and further comprising, using the reader, detecting whether a collision of responses occurred during the monitoring and, if so, issuing another wireless command including a second timeframe definition different from the first timeframe definition.

9. A radio frequency identification system, comprising:

an RF reader configured to issue an RF command requesting that RF tags identify themselves, to provide. a continuous RF illumination field, and to receive responses in any of a plurality of predefined timeslots and frequencies; and

a plurality of RF tags respectively including an identification number;

wherein the plurality of RF tags are configured to respond to the RF command from the RF reader by transmitting their respective identification numbers by way of backscatter modulation of the RF illumination field, and wherein the RF tags are further respectively configured to select a frequency from the plurality of predefined frequencies, to select a timeslot from the plurality of predefined timeslots, and to respond using the selected frequency and timeslot.

10. A radio frequency identification system in accordance with claim 9 wherein the reader is further configured to accept responses during a timeframe, wherein a timeframe is defined as a predetermined number of timeslots, wherein the reader is further configured to pre-select the number of the timeslots to be included within the timeframe, and to issue the number of the timeslots within the timeframe to the RF tags after issuing the RF command.

11. A radio frequency identification system in accordance with claim 10 wherein the RF tags are respectively further configured to respond at least once during the timeframe using the randomly selected frequency and timeslot.

12. A radio frequency identification system in accordance with claim 9 wherein the reader is further configured to simultaneously monitor all of the predefined frequencies during the timeslots.

13. A radio frequency identification system in accordance with claim 12 wherein the reader is further configured to record the identification numbers of tags from which responses were successfully received, and to determine how many responses were successfully received and how many collisions occurred.

14. A radio frequency identification system in accordance with claim 13, wherein the reader is further configured to issue a new command and a different number of the timeslots within a new timeframe, the number of timeslots being selected in response to at least one of the number of responses that were successfully received and the number of collisions that occurred.

15. A radio frequency identification system in accordance with claim 12 wherein the reader is further configured to issue respective RF acknowledgements to RF tags for which responses were successfully received by the reader.

16. A radio frequency identification system in accordance with claim 15 wherein the RF tags are further respectively configured to transmit a response to the new command if not yet acknowledged by the reader.

17. An RF tag for use with a reader, the RF tag comprising:

circuitry configured to selectively transmit an RF backscatter modulation communication, including data identifying the RF tag, responsive to an RF discovery command from the reader, wherein the circuitry is further configured to randomly select an IF frequency and a timeslot from a plurality of predetermined possible IF frequencies and timeslots prior to transmitting the RF backscatter modulation communication to the reader.

18. An RF tag in accordance with claim 17 wherein the circuitry is further configured to transmit the data identifying the RF tag responsive to each of successive discovery commands from the reader, using different randomly selected pairs of IF frequencies and timeslots.

19. An RF tag in accordance with claim 18 wherein the circuitry is further configured to cease transmitting the data identifying the RF tag, even though a discovery command has been received by the RF tag from the reader, responsive to receiving an RF acknowledgement from the reader indicating that the RF tag has been successfully identified by the reader.

20. A reader for use with an RF tag in an RFID system, the reader comprising:

circuitry configured to selectively transmit a plurality of different types of RF messages including a discovery command having timeframe information, indicating the timeframe during which a response will be processed, and configured to provide an RF illumination field after transmitting a discovery command, wherein the circuitry is further configured to selectively provide a time synchronization signal within the RF illumination field, wherein the circuitry is further configured to simultaneously monitor a plurality of IF frequencies, and wherein the circuitry is further configured to selectively issue an RF acknowledgement message, acknowledging successful identification of an RF tag, responsive to successfully receiving identification data from an RF tag on one of the plurality of IF frequencies by way of backscatter modulation of the RF illumination field.

21. A reader in accordance with claim 20, wherein the circuitry is further configured to detect whether a collision occurred between transmissions from different RF tags on at least one of the plurality of IF frequencies, and to selectively transmit another discovery command having timeframe information responsive to detecting the collision.