Method and system for contention resolution in radio frequency identification systems

• US 20040142655A1
• Filed: 01/05/2004
• Published: 07/22/2004
• Est. Priority Date: 08/17/2000
• Status: Abandoned Application

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Voegele, Kevin D.
• Application Number:
  US10/752,458
• Publication Number:
  US 20040142655A1
• Time in Patent Office: Days
• US Class Current: 455/1
• 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 7/10019 resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08

Abstract

A method and system for resolving contentions among passive identification tags. A reader may divide a possible range of tag values into a number of smaller ranges. For each smaller range, the reader may then poll the tags to determine which tags have tag values that fall within the smaller range. If more than one tag responds simultaneously, then the reader may further divide the smaller range into even smaller ranges and poll the tags with respect to those even smaller ranges. Once the range partition gets small enough, the reader may then opt to poll the tags for a match of each possible value in the range, rather than partitioning further. This arrangement enables the reader to efficiently identify tags, by quickly eliminating from analysis any range of tag values to which no tags match or only one tag matches.

Claims

1. A method for identifying a plurality of passive identification tags in a field of view, each tag having a respective identification value, and each tag having a register value within a predetermined range, the method comprising the following steps:

(a) splitting the predetermined range into a plurality of first sub-ranges;

(b) for each first sub-range, requesting each tag whose register value falls within the first sub-range to communicate the tag'"'"'s identification value; and

(c) in response to a determination that more than one tag has a register value within a given first sub-range, (i) splitting the given first sub-range into a plurality of second sub-ranges and (ii) for each second sub-range, requesting each tag whose register value falls within the second sub-range to communicate the tag'"'"'s identification value.

2. The method of claim 1, wherein each tag has a plurality of respective register values, and each tag'"'"'s identification value is defined as a combination of the tag'"'"'s respective register values.

3. The method of claim 1, wherein each passive identification tag is a radio frequency identification tag.

4. The method of claim 1, further comprising:

(d) in response to a determination that more than one tag has a register value within a given second sub-range, applying a partial read method to identify all tags whose register values fall within the given second sub-range.

5. The method of claim 1, wherein the predetermined range has a predetermined size, and wherein each of the plurality of first sub-ranges has a first size that is half the predetermined size.

6. The method of claim 5, wherein the predetermined size is 4096 values.

7. The method of claim 5, wherein each of the plurality of second sub-ranges has a second size that is half the first size.

8. The method of claim 1, further comprising:

(d) in response to a determination that more than one tag has a register value within a given second sub-range, (i) splitting the given second sub-range into a plurality of third sub-ranges and (ii) for each third sub-range, requesting each tag whose register value falls within the third sub-range to communicate the tag'"'"'s identification value.

9. The method of claim 8, wherein the predetermined range has a predetermined size, and wherein each of the plurality of third sub-ranges has a third size that is one eighth the predetermined size.

10. A reader programmed to perform the method steps of claim 1.

11. A method for identifying a plurality of passive identification tags in a field of view, each tag having a respective identification value, and each tag having a register value within a predetermined range, the method comprising:

splitting the predetermined range into a plurality of first sub-ranges;

a reader sending a first signal to the plurality of tags, the first signal containing a first preset value defining a given first sub-range of the plurality of first sub-ranges;

each tag of the plurality of tags receiving the first signal, responsively applying logic to determine whether the tag'"'"'s register value falls within the given first sub-range, and sending a response signal if the tag'"'"'s register value falls within the given first sub-range;

the receiver detecting a contention among responses from multiple tags, and the receiver thereafter responsively (i) splitting the given first sub-range into a plurality of second sub-ranges and (ii) sending a second signal to the plurality of tags, the second signal containing a second preset value defining a given second sub-range of the plurality of second sub-ranges; and

each tag of the plurality of tags receiving the second signal, responsively applying logic to determine whether the tag'"'"'s register value falls within the given second sub-range, and sending a response signal if the tag'"'"'s register value falls within the given second sub-range.

12. The method of claim 11, wherein the first preset value indicates an upper bound of the given first sub-range and a lower bound of the given first sub-range.

13. The method of claim 12, wherein the preset value indicates four most significant bits defining an upper bound of the first given sub-range and four most significant bits defining a lower bound of the first given sub-range.

14. The method of claim 11, wherein the response signal of the tag whose register value falls within the given first sub-range comprises an identification value of the tag.

15. The method of claim 14, wherein the response signal further comprises a checksum of the identification value.

16. The method of claim 11, wherein the response signal of the tag whose register value falls within the given second sub-range comprises an identification value of the tag.

17. The method of claim 16, wherein the response signal further comprises a checksum of the identification value.

18. A passive identification system comprising, in combination:

a reader;

a plurality of passive identification tags, each tag having a respective identification value, and each tag having a register value within a predetermined range;

the reader being arranged to send a first range-instruction to the tags, the first range-instruction defining a preset value indicative of a first range of register values;

each tag being arranged to receive the first range-instruction, to determine whether the tag'"'"'s register value falls within the first range, and, in response to a determination that the tag'"'"'s register value falls within the first range, to emit a signal defining the tag'"'"'s respective identification value;

the reader being further arranged to detect a contention and to responsively split the first range into a plurality of second ranges and to send a plurality of second range-instructions to the tags, each second range-instruction defining a preset value indicative of a respective second range of the plurality of second ranges; and

each tag being Further arranged to receive each second range-instruction, to determine whether the tag'"'"'s register value falls within the second range defined by the preset value of the second range-instruction, and, in response to a determination that the tag'"'"'s register value falls within the second range defined by the preset value of the second range-instruction, to emit a signal defining the tag'"'"'s respective identification value.

19. The system of claim 18, wherein each tag has a plurality of respective register values, and each tag'"'"'s identification value is defined as a combination of the tag'"'"'s respective register values.

20. The method of claim 18, wherein each passive identification tag is a radio frequency identification tag.

21. The method of claim 18, wherein the reader is further arranged to detect a contention with respect to the second range and to responsively apply a partial read method to resolve the contention.

22. The method of claim 18, wherein the signal defining the tag'"'"'s respective identification value further defines a checksum associated with the respective identification value.