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

• US 6,995,655 B2
• Filed: 10/02/2002
• Issued: 02/07/2006
• Est. Priority Date: 10/02/2002
• Status: Expired due to Fees

• Current Assignee: Battelle Memorial Institute
• Original Assignee: Battelle Memorial Institute
• Inventors: Pratt, Richard M., Lechelt, Wayne M., Hughes, Michael A., Priddy, Kevin L., Ertin, Emre
• Primary Examiner(s): Zimmerman, Brian
• Assistant Examiner(s): YANG, CLARA I
• Application Number:
  US10/263,809
• Publication Number:
  US 20040198222A1
• Time in Patent Office: 1,224 Days
• Field of Search: 340/10.2, 370/442, 370/458, 455/417
• US Class Current: 340/10.2
• 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, the reader accepting responses during a predetermined timeframe which includes a plurality of timeslots;

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;

issuing wireless acknowledgements from the reader to RF tags that have been successfully identified responsive to the receiving and at the end of the timeframe; and

if any collision was detected, the reader issuing a command to cause unacknowledged RF tags to randomly select a radio frequency and timeslot for another response.

2. 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, the reader accepting responses during a predetermined timeframe;

defining a plurality of consecutive timeslots, within the timeframe, using the reader, by interruption of a carrier;

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

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

issuing wireless acknowledgements from the reader to RF tags that have been successfully identified responsive to the receiving and at the end of the timeframe; and

if any collision was detected, the reader issuing a command to cause unacknowledged RF tags to randomly select a radio frequency and timeslot in which to provide another response, after issuing the wireless acknowledgements.

3. A method in accordance with claim 2 wherein the receiving comprises simultaneously receiving at least two wireless responses at different radio frequencies.

4. A method in accordance with claim 2 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.

5. A method in accordance with claim 2 wherein issuing the wireless command further comprises transmitting the timeframe definition to the RF tags.

6. A method in accordance with claim 5 wherein, if a collision was detected, the reader issues a second timeframe definition different from the first timeframe definition.

7. 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 during a timeframe, and to receive responses in any of a plurality of predefined timeslots, within the timeframe, 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, and the reader being further configured to issue wireless acknowledgements from the reader to RF tags that were successfully identified responsive to the receiving and at the end of the timeframe and, if any collision was detected, to, after the acknowledgements, issue a command to cause unacknowledged RF tags to randomly select a radio frequency and timeslot for another response.

8. A radio frequency identification system in accordance with claim 7 wherein the RF tags are respectively further configured to respond at least once during the timeframe using the randomly selected frequency and timeslot.

9. A radio frequency identification system in accordance with claim 7 wherein the reader is further configured to simultaneously monitor all of the predefined frequencies during the timeslots.

10. A radio frequency identification system in accordance with claim 9 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.

11. A radio frequency identification system in accordance with claim 10 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.

12. 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, 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 by interruption of a carrier, 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, 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; 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, to repeatedly randomly select radio frequencies and timeslots and issue wireless responses in the selected radio frequencies and timeslots until acknowledged by the reader, and wherein the reader is further configured to issue respective RF acknowledgements to RF tags for which responses were successfully received by the reader at the end of the timeframe.

13. A radio frequency identification system in accordance with claim 12 wherein the RF tags are further respectively configured to transmit a response to the new command if not yet acknowledged by the reader.

14. 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 channels, 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 channels by way of backscatter modulation of the RF illumination field, at the end of the timeframe.

15. A reader in accordance with claim 14, 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 channels, and to selectively transmit another discovery command having timeframe information responsive to detecting the collision.