RFID readers and systems with antenna switching upon detecting too few tags and methods

• US 8,120,494 B1
• Filed: 05/16/2007
• Issued: 02/21/2012
• Est. Priority Date: 07/21/2006
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Aiouaz, Ali, Dietrich, Paul, Ord, David, Khwaja, Omar
• Primary Examiner(s): La, Anh V
• Application Number:
  US11/749,281
• Time in Patent Office: 1,742 Days
• Field of Search: 3405721-5728, 340/10.1, 340/10.2, 340 361- 363, 340/7.25, 340/7.27, 340/571, 340/505, 705/1, 705/28, 705/29, 235/375, 235/385, 343/853, 343/876
• US Class Current: 340/572.7
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device
• CPC Class Codes: G06K 7/10475 arrangements to facilitate interaction with further interrogation devices, e.g. such that at least two interrogation devices may function and cooperate in a network of such devices
• CPC Class Codes: G08B 13/14 by lifting or attempted removal of hand-portable articles

Abstract

RFID readers, reader systems, and methods are provided that utilize smart antenna switching. A first signal is transmitted from a first antenna estimating presence of tags within the antennas field of view. If fewer than a predefined number of tags are estimated, the system switches to a second antenna. Otherwise, the tags found in the field of view of the first antenna are inventoried before switching to the second antenna.

Claims

1. A method for an RFID reader system coupled to at least a first antenna and a second antenna, comprising:

causing the first antenna to radiate a first signal for estimating how many tags are likely present in the first antenna'"'"'s field of view; and

if fewer than a preset number of tags are estimated in the first antenna'"'"'s field of view, causing the second antenna to radiate a second signal for estimating how many tags are likely present in the second antenna'"'"'s field of view,

else inventorying tags estimated in the first antenna'"'"'s field of view.

2. The method of claim 1, in which

the preset number is learned by the reader based on tag responses.

3. The method of claim 1, in which

the second signal is radiated regardless of whether any tags are estimated as present in the first antenna'"'"'s field of view.

4. The method of claim 1, in which

the second signal is radiated responsive to estimating that no tags are present in the first antenna'"'"'s field of view.

5. The method of claim 1, in which

first tags are estimated as present in the first antenna'"'"'s field of view, and

the second signal is radiated without addressing individually the first tags.

6. The method of claim 1, further comprising:

determining a power level of received tag responses;

comparing the determined power level to an expected power level of a single tag response; and

estimating how many tags are likely present based on the comparison.

7. The method of claim 1, further comprising:

if fewer than the preset number of tags are estimated in the second antenna'"'"'s field of view, then causing a third antenna coupled to the RFID reader system to radiate a third signal for estimating how many tags are likely present in the third antenna'"'"'s field of view,

else inventorying tags estimated in the second antenna'"'"'s field of view.

8. The method of claim 1, further comprising:

selecting the second antenna before completing causing the first antenna to radiate such that no signal is radiated from the first antenna beyond the first signal.

9. The method of claim 8, in which

selecting the second antenna is delayed until an operation for a specific tag is complete.

10. The method of claim 9, in which

the tag operation is completed when a predefined criterion is satisfied.

11. The method of claim 10, in which

the predefined criterion includes at least one of:

a decision based on completion of an inventory operation; and

a decision based on an expiration of a time out period.

12. The method of claim 10, in which

the predefined criterion further includes:

a decision based on a predefined Q parameter value.

13. The method of claim 12, in which

the Q parameter value is one of:

learned by the RFID reader system based on tag responses and dictated by the first signal.

14. The method of claim 12, in which

the Q parameter has a value of at least 2.

15. The method of claim 1, in which

the first signal is for performing a partial query operation to estimate the presence of the tags such that if one of a valid preamble and a collision is detected, a tag is estimated, else no tag is estimated.

16. The method of claim 1, in which

first tags, fewer than the preset number, are estimated as present in the first antenna'"'"'s field of view, and

the second signal is radiated without addressing individually the first tags.

17. The method of claim 1, further comprising:

selecting the second antenna among a plurality of antennas associated with the RFID reader system based on one of;

a first predefined algorithm, an order of available antennas, and by random selection, in which the selection is different depending on whether any tags are sensed through the first antenna.

18. The method of claim 17, in which

if no tags are sensed, selecting a third antenna according to one of the first algorithm and a second algorithm.

19. An RFID reader system coupled to at least a first antenna and a second antenna, comprising:

a control circuit configured to;

cause the first antenna to radiate a first signal for estimating whether any tags are present in the first antenna'"'"'s field of view; and

if fewer than a preset number of tags are estimated in the first antenna'"'"'s field of view, cause the second antenna to radiate a second signal for estimating whether any tags are present in the second antenna'"'"'s field of view,

else inventory tags estimated in the first antenna'"'"'s field of view.

20. The RFID reader system of claim 19, in which

the preset number is learned by the reader based on tag responses.

21. The RFID reader system of claim 19, in which the control circuit is further configured to:

if fewer than the preset number of tags are estimated in the second antenna'"'"'s field of view, then cause a third antenna coupled to the RFID reader system to radiate a third signal for estimating whether any tags are present in the third antenna'"'"'s field of view,

else inventory tags estimated in the second antenna'"'"'s field of view.

22. The RFID reader system of claim 19, in which the control circuit is further configured to:

select the second antenna before completing causing the first antenna to radiate such that no signal is radiated from the first antenna beyond the first signal.

23. The RFID reader system of claim 22, in which

selecting the second antenna is delayed until an operation for a specific tag is completed.

24. The RFID reader system of claim 23, in which

the tag operation is completed when a predefined criterion is satisfied.

25. The RFID reader system of claim 24, in which

the predefined criterion includes at least one of:

a decision based on completion of an inventory operation; and

a decision based on an expiration of a time out period.

26. The RFID reader system of claim 24, in which

the predefined criterion further includes:

a decision based on a predefined Q parameter value.

27. The RFID reader system of claim 26, in which

the Q parameter value is one of:

learned by the RFID reader system based on tag responses and dictated by the first signal.

28. The RFID reader system of claim 27, in which

the Q parameter has a value of at least 2.

29. The RFID reader system of claim 19, in which

the first signal is for performing a partial query operation to estimate the presence of the tags such that if one of a valid preamble and a collision is detected, a tag is estimated, else no tag is estimated.

30. The RFID reader system of claim 19, in which

the second signal is radiated regardless of whether any tags are estimated as present in the first antenna'"'"'s field of view.

31. The RFID reader system of claim 19, in which

the second signal is radiated responsive to estimating that no tags are present in the first antenna'"'"'s field of view.

32. The RFID reader system of claim 19, in which

first tags, fewer than the preset number, are estimated as present in the first antenna'"'"'s field of view, and

the second signal is radiated without addressing individually the first tags.

33. The RFID reader system of claim 19, in which the control circuit is further configured to:

select the second antenna among a plurality of antennas associated with the RFID reader system based on one of;

a first predefined algorithm, an order of available antennas, and by random selection, in which the selection is different depending on whether any tags are sensed through the first antenna.

34. The RFID reader system of claim 33, in which

if no tags are estimated, selecting a third antenna according to one of the first algorithm and a second algorithm.

35. The RFID reader system of claim 19, in which the control circuit is further configured to:

determine a power level of received tag responses;

compare the determined power level to an expected power level of a single tag response; and

estimate how many tags are likely present based on the comparison.

36. A Digital Signal Processing (DSP) chip for an RFID reader coupled to at least a first antenna and a second antenna, the DSP chip comprising:

circuitry configured to;

cause the first antenna to radiate a first signal for estimating whether any tags are present in the first antenna'"'"'s field of view; and

if fewer than a preset number of tags are estimated in the first antenna'"'"'s field of view, cause the second antenna to radiate a second signal for estimating whether any tags are present in the second antenna'"'"'s field of view,

else inventory tags estimated in the first antenna'"'"'s field of view.

37. The DSP chip of claim 36, in which

the preset number is learned by the reader based on tag responses.

38. The DSP chip of claim 36, in which the circuitry is further configured to:

if fewer than the preset number of tags are estimated in the second antenna'"'"'s field of view, then cause a third antenna coupled to the RFID reader system to radiate a third signal for estimating whether any tags are present in the third antenna'"'"'s field of view,

else inventory tags estimated in the second antenna'"'"'s field of view.

39. The DSP chip of claim 36, in which the circuitry is further configured to:

select the second antenna before completing causing the first antenna to radiate such that no signal is radiated from the first antenna beyond the first signal.

40. The DSP chip of claim 39, in which

selecting the second antenna is delayed until a tag operation is completed.

41. The DSP chip of claim 40, in which

the tag operation is completed when a predefined criterion is satisfied.

42. The DSP chip of claim 41, in which

the predefined criterion includes at least one of:

a decision based on completion of an inventory operation; and

a decision based on an expiration of a time out period.

43. The DSP chip of claim 41, in which

the predefined criterion further includes:

a decision based on a predefined Q parameter value.

44. The DSP chip of claim 43, in which

the Q parameter value is one of:

learned by the RFID reader system based on tag responses and dictated by the first signal.

45. The DSP chip of claim 43, in which

the Q parameter has a value of at least 2.

46. The DSP chip of claim 36, in which

the first signal is for performing a partial query operation to estimate the presence of the tags such that if one of a valid preamble and a collision is detected, a tag is estimated, else no tag is estimated.

47. The DSP chip of claim 36, in which

the second signal is radiated one of:

regardless of whether any tags are estimated as present in the first antenna'"'"'s field of view and responsive to estimating that no tags are present in the first antenna'"'"'s field of view.

48. The DSP chip of claim 36, in which

first tags, fewer than the preset number, are estimated as present in the first antenna'"'"'s field of view, and

the second signal is radiated without addressing individually the first tags.

49. The DSP chip of claim 36, in which the circuitry is further configured to:

select the second antenna among a plurality of antennas associated with the RFID reader system based on one of;

a first predefined algorithm, an order of available antennas, and by random selection, in which the selection is different depending on whether any tags are sensed through the first antenna.

50. The DSP chip of claim 49, in which

if no tags are estimated, selecting a third antenna according to one of the first algorithm and a second algorithm.

51. The DSP chip of claim 36, in which the circuitry is further configured to:

determine a power level of received tag responses;

compare the determined power level to an expected power level of a single tag response; and

estimate how many tags are likely present based on the comparison.

52. A computer-readable medium with computer-executable instructions encoded thereon for controlling operations of an RFID reader system coupled to at least a first antenna and a second antenna, the instructions comprising:

causing the first antenna to radiate a first signal for estimating whether any tags are present in the first antenna'"'"'s field of view; and

if fewer than a preset number of tags are estimated in the first antenna'"'"'s field of view, causing the second antenna to radiate a second signal for estimating whether any tags are present in the second antenna'"'"'s field of view,

else inventorying tags estimated in the first antenna'"'"'s field of view.

53. The computer-readable medium of claim 52, in which

the preset number is learned by the reader based on tag responses.

54. The computer-readable medium of claim 52, in which the instructions further comprise:

if fewer than the preset number of tags are estimated in the second antenna'"'"'s field of view, then causing a third antenna coupled to the RFID reader system to radiate a third signal for estimating whether any tags are present in the third antenna'"'"'s field of view,

else inventorying tags estimated in the second antenna'"'"'s field of view.

55. The computer-readable medium of claim 52, in which

the second antenna is selected before completing causing the first antenna to radiate such that no signal is radiated from the first antenna beyond the first signal.

56. The computer-readable medium of claim 55, in which

selecting the second antenna is delayed until an operation for a specific tag is completed.

57. The computer-readable medium of claim 56, in which

the tag operation is completed when a predefined criterion is satisfied.

58. The computer-readable medium of claim 57, in which

the predefined criterion includes at least one of:

a decision based on completion of an inventory operation; and

a decision based on an expiration of a time out period.

59. The computer-readable medium of claim 57, in which

the predefined criterion further includes:

a decision based on a predefined Q parameter value.

60. The computer-readable medium of claim 59, in which

the Q parameter value is one of:

learned by the RFID reader system based on tag responses and dictated by the first signal.

61. The computer-readable medium of claim 59, in which

the Q parameter has a value of at least 2.

62. The computer-readable medium of claim 52, in which

the first signal is for performing a partial query operation to estimate the presence of the tags such that if one of a valid preamble and a collision is detected, a tag is estimated, else no tag is estimated.

63. The computer-readable medium of claim 52, in which

the second signal is radiated one of:

regardless of whether any tags are estimated as present in the first antenna'"'"'s field of view and responsive to estimating that no tags are present in the first antenna'"'"'s field of view.

64. The computer-readable medium of claim 52, in which

first tags, fewer than the preset number, are estimated as present in the first antenna'"'"'s field of view, and

the second signal is radiated without addressing individually the first tags.

65. The computer-readable medium of claim 52, in which the instructions further comprise:

selecting the second antenna among a plurality of antennas associated with the RFID reader system based on one of;

a first predefined algorithm, an order of available antennas, and by random selection, in which the selection is different depending on whether any tags are sensed through the first antenna.

66. The computer-readable medium of claim 65, in which

if no tags are estimated, selecting a third antenna according to one of the first algorithm and a second algorithm.

67. The computer-readable medium of claim 52, in which the instructions further comprise:

determining a power level of received tag responses;

comparing the determined power level to an expected power level of a single tag response; and

estimating how many tags are likely present based on the comparison.