RFID reader Q-parameter aided by RF power measurement

• US 8,077,013 B2
• Filed: 01/12/2007
• Issued: 12/13/2011
• Est. Priority Date: 01/12/2006
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Cooper, Scott A.
• Primary Examiner(s): BROWN, VERNAL U
• Application Number:
  US11/622,686
• Publication Number:
  US 20070164851A1
• Time in Patent Office: 1,796 Days
• Field of Search: 340/10.2, 340/572.1, 340/572.4, 340/10.3, 340/10.5
• US Class Current: 340/10.2
• CPC Class Codes: H04W 74/0875 with assigned priorities based access
• CPC Class Codes: H04W 99/00 Subject matter not provided for in other groups of this subclass

Abstract

RFID tag responses are detected by an RFID reader system. The tag response may be detected based on a reference measurement during a tag silent period and another one during the tag response. This helps determine whether a slot is empty or occupied, in a slotted aloha algorithm. The result is reported to the Q-algorithm for a better decision.

Claims

1. A Radio Frequency Identification (RFID) reader system for communicating with a plurality of RFID tags, the system operable to:

cause to be transmitted to the RFID tags a first reader command that communicates a first value for a Q parameter, the first reader command thus causing each of the RFID tags to occupy one of a plurality of first slots that are defined by the first value;

then cause a plurality of QueryRep commands to be transmitted sequentially to the RFID tags, each QueryRep command for examining a respective one of the first slots for its occupancy by causing any of the RFID tags occupying the respective first slot to backscatter a response within a tag response time window of the first slot and be silent at a tag silent period of the first slot that is outside the tag response time window of the first slot;

receive an initial reference signal during one of the tag silent periods of one of the first slots;

measure an aspect of the initial reference signal;

set a detection threshold from the measured aspect;

detect second signals during at least some of the tag response time windows of the examined first slots;

determine from the second signals whether the occupancy of the examined first slots is none of at least one of the RFID tags, in which the determination for at least a certain one of the first slots is performed by comparing the detection threshold to a power of a second signal corresponding to the certain slot;

decide according to the determined first slot occupancies and according to a Q-algorithm a second value for the Q parameter; and

then cause to be transmitted to the RFID tags a second reader command that communicates the second value for the Q parameter, the reader second command thus causing each of the RFID tags to occupy one of a plurality of second slots that are defined by the second value.

2. The system of claim 1, in which

one of the first reader command and the second reader command is one of a Query command and a QueryAdj command.

3. The system of claim 1, in which the tag silent period occurs before its corresponding tag response time window.

4. The system of claim 1, in which

the tag silent period occurs a delay time after its corresponding tag response time window.

5. The system of claim 4, in which

the delay time is increased if another reader command is caused to be transmitted between two of the QueryRep commands.

6. The system of claim 1, in which the aspect is one of power, voltage and current.

7. The system of claim 1, in which the aspect is measured from a plurality of measurements.

8. The system of claim 1, in which the detection threshold is determined as a quantity expressed in one of:

dB, Watts, Volts, Amps, and a number.

9. The system of claim 1, in which

the detection threshold is set by adjusting a filter in a receive circuit of the RFID reader system.

10. The system of claim 1, further operable to:

receive an updated reference signal during one of the tag silent periods of one of the first slots;

measure an aspect of the updated reference signal; and

update the detection threshold from the measured aspect of the updated reference signal.

11. The system of claim 1, in which the occupancy determination is performed similarly for all the slots.

12. The system of claim 1, in which the occupancy of the certain slot is determined to be none if the second signal power is less than the detection threshold.

13. The system of claim 1, in which the occupancy of the certain slot is determined to be at least one if the second signal power is greater than the detection threshold.

14. A method for a Radio Frequency Identification (RFID) reader system to inventory a population of RFID tags, comprising:

causing to be transmitted to the RFID tags a first reader command that communicates a first value for a Q parameter, the first reader command thus causing each of the RFID tags to occupy one of a plurality of first slots that are defined by the first value;

then causing a plurality of QueryRep commands to be transmitted sequentially to the RFID tags, each QueryRep command for examining a respective one of the first slots for its occupancy by causing any of the RFID tags occupying the respective first slot to backscatter a response within a tag response time window of the first slot and be silent at a tag silent period of the first slot that is outside the tag response time window of the first slot;

receiving an initial reference signal during one of the tag silent periods of one of the first slots;

measuring an aspect of the initial reference signal;

setting a detection threshold from the measured aspect;

detecting second signals during at least some of the tag response time windows of the examined first slots;

determining from the second signals whether the occupancy of the examined first slots is none or at least one of the RFID tags, in which the determination for at least a certain one of the first slots is performed by comparing the detection threshold to a power of a second signal corresponding to the certain slot;

deciding according to the determined first slot occupancies and according to a Q algorithm a second value for the Q parameter; and

then causing to be transmitted to the RFID tags a second reader command that communicates the second value for the Q parameter, the reader second command thus causing each of the RFID tags to occupy one of a plurality of second slots that are defined by the second value.

15. The method of claim 14, in which one of the first reader command and the second reader command is one of a Query command and a Query Adj command.

16. The method of claim 14, in which the tag silent period occurs before its corresponding tag response time window.

17. The method of claim 14, in which the tag silent period occurs a delay time after its corresponding tag response time window.

18. The method of claim 17, in which the delay time is increased if another reader command is caused to be transmitted between two of the QueryRep commands.

19. The method of claim 14, in which the aspect is one of power, voltage and current.

20. The method of claim 14, in which the aspect is measured from a plurality of measurements.

21. The method of claim 14, in which the detection threshold is determined as a quantity expressed in one of:

dB, Watts, Volts, Amps, and a number.

22. The method of claim 14, in which the detection threshold is set by adjusting a filter in a receive circuit of the RFID reader system.

23. The method of claim 14, further comprising:

receiving an updated reference signal during one of the tag silent periods of one of the first slots;

measuring an aspect of the updated reference signal; and

updating the detection threshold from the measured aspect of the updated reference signal.

24. The method of claim 14, in which the occupancy determination is performed similarly for all the slots.

25. The method of claim 14, in which the occupancy of the certain slot is determined to be none if the second signal power is less than the detection threshold.

26. The method of claim 14, in which the occupancy of the certain slot is determined to be at least one if the second signal power is greater than the detection threshold.

27. A component for a Radio Frequency Identification (RFID) reader system operable to communicate with a plurality of RFID tags, the component operable to:

receive a first inventory instruction that includes a first value for a Q parameter;

cause to be transmitted to the RFID tags a first reader command that communicates the first value for the Q parameter, the first reader command thus causing each of the RFID tags to occupy one of a plurality of first slots that are defined by the first value;

then cause a plurality of QueryRep commands to be transmitted sequentially to the RFID tags, each QueryRep command for examining a respective one of the first slots for its occupancy by causing any of the RFID tags occupying the respective first slot to backscatter a response within a tag response time window of the first slot and be silent at a tag silent period of the first slot that is outside the tag response time window of the first slot;

receive an initial reference signal during one of the tag silent periods of one of the first slots;

measure an aspect of the initial reference signal;

set a detection threshold from the measured aspect;

detect second signals during at least some of the tag response time windows of the examined first slots;

determine from the second signals whether the occupancy of the examined first slots is none or at least one of the RFID tags, in which the determination for at least a certain one of the first slots is performed by comparing the detection threshold to a power of a second signal corresponding to the certain slot;

transmit a report informing of the determined occupancy;

receive a second inventory instruction that includes a second value for the Q parameter that has been determined responsive to the report; and

then cause to be transmitted to the RFID tags a second reader command that communicates the second value for the Q parameter, the reader second command thus causing each of the RFID tags to occupy one of a plurality of second slots that are defined by the second value.

28. The component of claim 27, in which

one of the first reader command and the second reader command is one of a Query command and a QueryAdj command.

29. The component of claim 27, in which the tag silent period occurs before its corresponding tag response time window.

30. The component of claim 27, in which

the tag silent period occurs a delay time after its corresponding tag response time window.

31. The component of claim 30, in which

the delay time is increased if another reader command is caused to be transmitted between two of the QueryRep commands.

32. The component of claim 27, in which the aspect is one of power, voltage and current.

33. The component of claim 27, in which the aspect is measured from a plurality of measurements.

34. The component of claim 27, in which the detection threshold is determined as a quantity expressed in one of:

dB, Watts, Volts, Amps, and a number.

35. The component of claim 27, in which the detection threshold is set by adjusting a filter in a receive circuit of the RFID reader system.

36. The component of claim 27, further operable to:

receive an updated reference signal during one of the tag silent periods of one of the first slots;

measure an aspect of the updated reference signal; and

update the detection threshold from the measured aspect of the updated reference signal.

37. The component of claim 27, in which the occupancy determination is performed similarly for all the slots.

38. The component of claim 27, in which the occupancy of the certain slot is determined to be none if the second signal power is less than the detection threshold.

39. The component of claim 27, in which the occupancy of the certain slot is determined to be at least one if the second signal power is greater than the detection threshold.

40. A method for a component of a Radio Frequency Identification (RFID) reader system, comprising:

receiving a first inventory instruction that includes a first value for a Q parameter;

causing to be transmitted to the RFID tags a first reader command that communicates the first value for the Q parameter, the first reader command thus causing each of the RFID tags to occupy one of a plurality of first slots that are defined by the first value;

then causing a plurality of QueryRep commands to be transmitted sequentially to the RFID tags, each QueryRep command for examining a respective one of the first slots for its occupancy by causing any of the RFID tags occupying the respective first slot to backscatter a response within a tag response time window of the first slot and be silent at a tag silent period of the first slot that is outside the tag response time window of the first slot;

receiving an initial reference signal during one of the tag silent periods of one of the first slots;

measuring an aspect of the initial reference signal;

setting a detection threshold from the measured aspect;

detecting second signals during at least some of the tag response time windows of the examined first slots;

determining from the second signals whether the occupancy of the examined first slots is none or at least one of the RFID tags, in which the determination for at least a certain one of the first slots is performed by comparing the detection threshold to a power of a second signal corresponding to the certain slot;

transmitting a report informing of the determined occupancy;

receiving a second inventory instruction that includes a second value for the Q parameter that has been determined responsive to the report; and

then causing to be transmitted to the RFID tags a second reader command that communicates the second value for the Q parameter, the reader second command thus causing each of the RFID tags to occupy one of a plurality of second slots that are defined by the second value.

41. The method of claim 40, in which one of the first reader command and the second reader command is one of a Query command and a QueryAdj command.

42. The method of claim 40, in which the tag silent period occurs before its corresponding tag response time window.

43. The method of claim 40, in which the tag silent period occurs a delay time after its corresponding tag response time window.

44. The method of claim 43, in which the delay time is increased if another reader command is caused to be transmitted between two of the QueryRep commands.

45. The method of claim 40, in which the aspect is one of power, voltage and current.

46. The method of claim 40, in which the aspect is measured from a plurality of measurements.

47. The method of claim 40, in which the detection threshold is determined as a quantity expressed in one of:

dB, Watts, Volts, Amps, and a number.

48. The method of claim 40, in which the detection threshold is set by adjusting a filter in a receive circuit of the RFID reader system.

49. The method of claim 40, further comprising:

receiving an updated reference signal during one of the tag silent periods of one of the first slots;

measuring an aspect of the updated reference signal; and

updating the detection threshold from the measured aspect of the updated reference signal.

50. The method of claim 40, in which the occupancy determination is performed similarly for all the slots.

51. The method of claim 40, in which the occupancy of the certain slot is determined to be none if the second signal power is less than the detection threshold.

52. The method of claim 40, in which the occupancy of the certain slot is determined to be at least one if the second signal power is greater than the detection threshold.