RFID readers system and methods for early hopping out of a frequency channel in the presence of RF interference

• US 7,592,897 B2
• Filed: 09/04/2007
• Issued: 09/22/2009
• Est. Priority Date: 04/25/2006
• Status: Active Grant

• Current Assignee: Mark Nair
• Original Assignee: Impinj, Inc.
• Inventors: Cooper, Scott A., Anderl, Thomas G., Diorio, Christopher J., Esterberg, Aanand
• Primary Examiner(s): Zimmerman; Brian A
• Assistant Examiner(s): Nguyen; Nam V
• Application Number:
  US11/849,737
• Publication Number:
  US 20070296603A1
• Time in Patent Office: 749 Days
• Field of Search: 340/10.2, 340/572.2, 455/509, 455/63.1, 375/133, 375/132, 370/468, 370/329
• 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 7/10069 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
• CPC Class Codes: G06K 7/10198 setting parameters for the interrogator, e.g. programming parameters and operating modes

Abstract

RFID readers, systems, and methods are provided for overcoming the effects of RF interference. While a system is communicating in a channel, RF interference is monitored. If it is low, then hopping to another channel is performed according to an ordinary decision. But if interference is high, then hopping out to another channel can be earlier than would be dictated by the ordinary decision under the same circumstances. The earlier hopping out can result in diminishing communication in channels with a lot of RF interference.

Claims

1. A Radio Frequency Identification (RFID) reader system for communicating with RFID tags using a plurality of communication channels, comprising:

an antenna; and

an operational processing block coupled to the antenna and operable to;

cause a first wireless signal to be transmitted via the antenna to the RFID tags, the first wireless signal having a frequency carrier in a first one of the channels;

determine whether or not objectionable interference has been detected based on a reply from at least one RFID tag communicating in the first channel and RF energy received in at least one of the channels available for communicating with the RFID tags; and

cause a second signal to be transmitted to the RFID tags, the second signal having a frequency carrier in a second channel, and

in which the second signal staffs to be transmitted at a first hopping time if no objectionable interference has been detected, and at a second hopping time earlier than the first hopping time if objectionable interference has been detected.

2. The system of claim 1, in which the operational processing block is further operable to:

receive tag signals from the RFID tags in response to the first signal; and

in which the first hopping time is upon determining from the tag signals that an inventory round of the RFID tags is complete.

3. The system of claim 1, in which

the first signal has been transmitted for a first dwell time, and

the first hopping time is upon determining that the first dwell time approaches a preset limit dwell time for dwelling in a single channel continuously.

4. The system of claim 1, in which

the second hopping time is upon determining that objectionable interference has been detected.

5. The system of claim 1, in which

the second hopping time is deferred for a time interval before starting transmitting the second signal, after determining that objectionable interference has been detected.

6. The system of claim 1, in which the operational processing block is further operable to:

determine whether or not subsequent objectionable interference has been detected for communicating in the second channel; and

cause a third signal to be transmitted to the RFID tags, the third signal having a frequency carrier in a third channel, and

in which the third signal staffs to be transmitted at a third hopping time if no subsequent objectionable interference has been detected, and at a fourth hopping time earlier than the third hopping time if subsequent objectionable interference has been detected.

7. The system of claim 1, in which the operational processing block is further operable to:

receive tag signals from the RFID tags in response to the first signal; and

in which it is determined whether or not objectionable interference has been detected at least from the tag signals.

8. The system of claim 7, in which

the first signal includes a command that mandates a specific tag reply, and

it is determined whether or not objectionable interference has been detected at least from whether the tag signals include or not the specific tag reply.

9. The system of claim 7, in which

a quality metric is computed in association with one of the received tag signals, and

it is determined whether or not objectionable interference has been detected at least from the quality metric.

10. The system of claim 9, in which

the quality metric is a signal-to-noise ratio.

11. The system of claim 9, in which

the quality metric is a distance of a measured signal from a decision threshold.

12. The system of claim 7, in which

a tag preamble matching metric is computed in association with one of the received tag signals, and

it is determined whether or not objectionable interference has been detected at least from the tag preamble matching metric.

13. The system of claim 12, in which

the tag preamble matching metric is determined from how well a preamble of one of the received tag signals matches an expected preamble.

14. The system of claim 7, in which

it is determined whether an error has been detected in one of the received tag signals,

an error detection count is updated if it is determined that the error has been so detected, and

it is determined whether or not objectionable interference has been detected at least from the error detection count.

15. The system of claim 14, in which

it is determined that objectionable interference has been detected if the error detection count exceeds a threshold, and that objectionable interference has not been detected otherwise.

16. The system of claim 14, in which

the error detection count is rendered as a ratio with a total number of the tag signals.

17. The system of claim 14, in which

the first signal has been transmitted for a current dwell time, and

it is determined whether or not objectionable interference has been detected from the current dwell time in addition to the error detection count.

18. The system of claim 17, in which

for a given error correction count, it is determined that objectionable interference has been detected if the current dwell time is smaller than a low limit or larger than a high limit, and that objectionable interference has not been detected otherwise.

19. The system of claim 1, in which the operational processing block is further operable to:

receive RF energy associated with transmitting in the first channel; and

in which it is determined whether or not objectionable interference has been detected at least from the received RF energy.

20. The system of claim 19, in which

the RF energy is received from all channels available for communicating with the RFID tags.

21. The system of claim 19, in which

the RF energy is received only from the first channel.

22. The system of claim 19, in which

the RF energy is received from a neighborhood of detected channels, and

it is determined that objectionable interference has been detected if the received RF energy is larger than a first threshold, and that objectionable interference has not been detected otherwise.

23. The system of claim 1, in which the operational processing block is further operable to:

choose the second channel in a manner that disfavors all of the channels in a neighborhood of the first channel.

24. The system of claim 23, in which

the neighborhood includes all channels within a number N1 of the first channel.

25. The system of claim 23, in which the operational processing block is further operable to:

receive RF energy associated with transmitting in the first channel; and

in which it is determined whether or not objectionable interference has been detected at least from the received RF energy, and

a size of the neighborhood is determined by one of a manner of receiving the RF energy and the amount of received RF energy.

26. The system of claim 23, in which

the channels in the neighborhood have much less chance of being chosen than the remaining ones of the available channels.

27. The system of claim 23, in which

the channels in the neighborhood have no chance of being chosen, and

each of the remaining ones of the available channels has an approximately equal chance of being chosen.

28. The system of claim 23, in which

some of the available channels outside the neighborhood have been used with lesser preference than others of the channels, and

the second channel is chosen so as to further compensate for the lesser preference.

29. The system of claim 1, in which the operational processing block is further operable to:

detect one of the channels as an interferer'"'"'s channel, and

choose the second channel in such a way that a resulting tag backscatter avoids a center frequency of the interferer'"'"'s channel.

30. The system of claim 29, in which

a certain channel is detected as the interferer'"'"'s channel if the certain channel has RF energy above a preset high threshold, while the RF energy in at least one of its neighboring channels are below a preset low threshold.

31. The system of claim 29, in which

the second channel is chosen in a manner that disfavors all of the channels in a neighborhood of the interferer'"'"'s channel.

32. The system of claim 29, in which

the interferer'"'"'s channel is chosen as the second channel.

33. A method for communicating with Radio Frequency Identification (RFID) tags and using a plurality of communication channels, comprising:

causing a first wireless signal to be transmitted to the RFID tags, the first wireless signal having a frequency carrier in a first one of the channels;

determining whether or not objectionable interference has been detected based on a reply from at least one RFID tag communicating in the first channel and RF energy received in at least one of the channels available for communicating with the RFID tags; and

causing a second signal to be transmitted to the RFID tags, the second signal having a frequency carrier in a second channel, and

in which the second signal staffs to be transmitted at a first hopping time if no objectionable interference has been detected, and at a second hopping time earlier than the first hopping time if objectionable interference has been detected.

34. The method of claim 33, further comprising:

determining whether or not subsequent objectionable interference has been detected for communicating in the second channel; and

causing a third signal to be transmitted to the RFID tags, the third signal having a frequency carrier in a third channel, and

in which the third signal staffs to be transmitted at a third hopping time if no subsequent objectionable interference has been detected, and at a fourth hopping time earlier than the third hopping time if subsequent objectionable interference has been detected.

35. The method of claim 33, further comprising:

receiving tag signals from the RFID tags in response to the first signal; and

in which it is determined whether or not objectionable interference has been detected at least from the tag signals.

36. The method of claim 35, in which

a quality metric is computed in association with one of the received tag signals, and

it is determined whether or not objectionable interference has been detected at least from the quality metric.

37. The method of claim 35, in which

it is determined whether an error has been detected in one of the received tag signals,

an error detection count is updated if it is determined that the error has been so detected, and

it is determined whether or not objectionable interference has been detected at least from the error detection count.

38. The method of claim 37, in which

the first signal has been transmitted for a current dwell time, and

it is determined whether or not objectionable interference has been detected from the current dwell time in addition to the error detection count.

39. The method of claim 38, in which

for a given error correction count, it is determined that objectionable interference has been detected if the current dwell time is smaller than a low limit or larger than a high limit, and that objectionable interference has not been detected otherwise.

40. The method of claim 33, further comprising:

receiving RF energy associated with transmitting in the first channel; and

in which it is determined whether or not objectionable interference has been detected at least from the received RF energy.

41. The method of claim 33, further comprising:

choosing the second channel in a manner that disfavors all of the channels in a neighborhood of the first channel.

42. The method of claim 33, further comprising:

detecting one of the channels as an interferer'"'"'s channel, and

choosing the second channel in such a way that a resulting tag backscatter avoids a center frequency of the interferer'"'"'s channel.

43. A machine-readable storage medium with instructions encoded thereon for operating a Radio Frequency Identification (RFID) reader system to communicate with RFID tags using a plurality of communication channels, the RFID reader system including at least one antenna, the instructions such that, if read and executed by the RFID reader system, actions result comprising:

causing a first wireless signal to be transmitted via the antenna of the RFID to the RFID tags, the first wireless signal having a frequency carrier in a first one of the channels;

determining at a processor of the RFID reader system whether or not objectionable interference has been detected based on a reply from at least one RFID tag communicating in the first channel and RF energy received in at least one of the channels available for communicating with the RFID tags; and

causing a second signal to be transmitted via the antenna of the RFID to the RFID tags, the second signal having a frequency carrier in a second channel, and

in which the second signal starts to be transmitted at a first hopping time if no objectionable interference has been detected, and at a second hopping time earlier than the first hopping time if objectionable interference has been detected.

44. The medium of claim 43, in which the actions further comprise:

determining whether or not subsequent objectionable interference has been detected for communicating in the second channel; and

causing a third signal to be transmitted to the REID tags, the third signal having a frequency carrier in a third channel, and

in which the third signal starts to be transmitted at a third hopping time if no subsequent objectionable interference has been detected, and at a fourth hopping time earlier than the third hopping time if subsequent objectionable interference has been detected.

45. The medium of claim 43, in which the actions further comprise:

receiving tag signals from the RFID tags in response to the first signal; and

in which it is determined whether or not objectionable interference has been detected at least from the tag signals.

46. The medium of claim 45, in which

a quality metric is computed in association with one of the received tag signals, and

it is determined whether or not objectionable interference has been detected at least from the quality metric.

47. The medium of claim 45, in which

it is determined whether an error has been detected in one of the received tag signals,

an error detection count is updated if it is determined that the error has been so detected, and

it is determined whether or not objectionable interference has been detected at least from the error detection count.

48. The medium of claim 47, in which

the first signal has been transmitted for a current dwell time, and

it is determined whether or not objectionable interference has been detected from the current dwell time in addition to the error detection count.

49. The medium of claim 43, in which the actions further comprise:

receiving RF energy associated with transmitting in the first channel; and

in which it is determined whether or not objectionable interference has been detected at least from the received RF energy.

50. The medium of claim 43, in which the actions further comprise:

choosing the second channel in a manner that disfavors all of the channels in a neighborhood of the first channel.

51. The medium of claim 43, in which the actions further comprise:

detecting one of the channels as an interferer'"'"'s channel, and

choosing the second channel in such a way that a resulting tag backscatter avoids a center frequency of the interferer'"'"'s channel.