Multi-reader coordination in RFID system

• US 7,898,391 B2
• Filed: 07/01/2005
• Issued: 03/01/2011
• Est. Priority Date: 07/01/2005
• Status: Active Grant

• Current Assignee: Novanta Corporation (Novanta Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Pappu, Ravikanth Srinivasa, Maguire, Yael Gregory, Reynolds, Matthew Stephen
• Primary Examiner(s): Zimmerman; Brian A
• Assistant Examiner(s): Syed; Nabil H
• Application Number:
  US11/171,443
• Publication Number:
  US 20070001813A1
• Time in Patent Office: 2,069 Days
• Field of Search: 340/10.2, 340/572.1, 340/572.4, 340/10.1, 340/10.3, 340/10.31, 342/44, 370/328
• US Class Current: 340/10.2
• 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 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas

Abstract

A method of operating a plurality of Radio Frequency Identification (RFID) readers includes operating the readers according to a spatial-division and time-division synchronization schedule. Each reader may be associated with a reader group, and the schedule may specify a duration of time that all of the readers in a group may be active. Readers in different reader groups may be scheduled independent of readers in other reader groups.

Claims

1. A method of operating a plurality of Radio Frequency Identification (RFID) readers in a group, the method comprising:

determining, by each of the plurality of readers, transmission characteristics of each of the other readers during a calibration phase;

generating, based on the determination, a spatial-division and time-division synchronization schedule for the plurality of readers in the group, the synchronization schedule specifying one or more scheduled turns for each reader to operate at a specific transmission power level, communication protocol and operating frequency, such that the plurality of readers do not unduly interfere with each other; and

operating the plurality of readers according to the synchronization schedule, wherein a reader in a group may further operate out of its one or more scheduled turns if it determines that operation of a scheduled reader will not unduly interfere with its out-of-turn operation and the reader in the group changing a respective communication protocol when another reader not in the group is detected.

2. A method as in claim 1 wherein each reader may be associated with at least one reader group, and wherein the schedule specifies a duration of time that all of the readers in a group may be active, and wherein readers in different reader groups may be scheduled independent of readers in other reader groups.

3. A method as in claim 2 wherein the readers within a group operate according to a time division multiple access (TDMA) schedule.

4. A method as in claim 1 wherein the readers operate according to one of the following scheduling schemes:

(a) central network coordination with no radio frequency (RF) synchronization;

or

(b) central network coordination with synchronization controlled at least in part by radio transmission;

or

(c) central network coordination with RF carrier, reader modulation and tag synchronization for reception;

or

(d) central network coordination with RF carrier, reader modulation and tag synchronization for transmission and reception.

5. A method as in claim 1 wherein scheduling information is transported via a network.

6. A method as in claim 1 wherein scheduling information is transported wirelessly.

7. A method as in claim 1 each reader may be associated with a reader group, and wherein the schedule specifies one or more communication protocols to be employed for communication with tags.

8. In a system in which a plurality of Radio Frequency Identification (RFID) readers in a group are operating, a method comprising:

determining, by each of the plurality of readers, transmission characteristics of each of the other readers during a calibration phase;

generating, based on the determination, a spatial-division and time-division synchronization schedule for the plurality of readers in the group, the synchronization schedule specifying one or more scheduled turns for each reader to operate at a specific transmission power level, communication protocol and operating frequency, such that the plurality of readers do not unduly interfere with each other;

by the first reader of the plurality of RFID readers in the group, obtaining the schedule, the schedule specifying a time at which the first reader may operate; and

the first reader operating out of turn if it determines that operation of a scheduled reader will not unduly interfere with its out-of-turn operation and the first reader changing a respective communication protocol when another reader not in the group is detected.

9. A method as in claim 8 further comprising:

monitoring the scheduled reader; and

determining whether an energy level of a signal from the scheduled reader drops below a certain threshold; and

based at least in part on said determining, operating the first reader out of turn if it determines that operation of a scheduled reader will not unduly interfere with its out-of-turn operation if the energy level of the signal from the scheduled reader drops below the threshold.

10. A method as in claim 8 further comprising:

receiving a message from the scheduled reader; and

determining, based at least in part on the message, a likelihood of noninterference with the scheduled reader, and

operating the first reader if it determines that operation of a scheduled reader will not unduly interfere with the first reader'"'"'s operation.

11. A method of operating a plurality of Radio Frequency Identification (RFID) readers, the method comprising:

identifying at least some of the readers for grouping into a group;

assigning at least one rule to the group; and

operating the readers in the group according to the at least one rule,

wherein the at least one rule specifies that at least some readers in the group should reduce transmission power, change operating frequency or change communication protocol if a reader not in the group is detected such that operation of the reader not in the group and the readers in the group should not unduly interfere with each other, the method further comprising;

changing a respective communication protocol of at least some readers in the group when a reader not in the group is detected.

12. A method as in claim 11 wherein the at least one rule specifies that at least some readers in the group should turn off if a reader not in the group is detected, the method further comprising:

turning off all readers in the group when a reader not in the group is detected.

13. A method as in claim 11 wherein the grouping further comprises:

determining a degree to which each of the plurality of readers interferes with each of the other of the plurality of readers;

grouping readers based at least in part on said determining.

14. A method as in claim 13 wherein the grouping comprises:

grouping readers that do not interfere with each other into the same group.

15. A method as in claim 11 wherein the group comprises readers associated with a certain material handling process or operation.

16. A method as in claim 11 wherein the group comprises spatially proximate readers.

17. A method as in claim 11 further comprising:

scheduling readers in each group independent of readers in each other group.

18. A method as in claim 11 wherein readers within a group communicate with each other wirelessly.

19. A method as in claim 18 wherein scheduling information is interleaved with RFID tag communication.

20. A method as in claim 18 wherein readers within a group communicate with each other using the same radio hardware that is normally used to communicate with RFID tags.

21. A method as in claim 11, further comprising changing the operating frequency of at least some readers in the group when a reader not in the group is detected.

22. A method as in claim 11, further comprising changing the transmission power of at least some readers in the groups when a reader not in the groups is detected.