Method and system of using active RFID tags to provide a reliable and secure RFID system

• US 20050093679A1
• Filed: 10/29/2004
• Published: 05/05/2005
• Est. Priority Date: 10/31/2003
• Status: Active Grant

• Current Assignee: Li-Cheng R. Zai, Xinyu Zang
• Original Assignee: Li-Cheng R. Zai, Xinyu Zang
• Inventors: Zai, Li-Cheng Richard, Zang, Xinyu
• Granted Patent: US 7,176,797 B2
• Time in Patent Office: Days
• 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

The system of the present invention includes a large-zone RFID reader, a plurality of small-zone RFID readers, and a plurality of RFID tags. The large-zone RFID reader covers areas which are not covered by the small-zone RFID readers. The output power of the small-zone RFID readers is controlled by the large-zone RFID reader based on RFID tag operation patterns of the small-zone RFID readers. The system reliability is improved by a method that uses reliable RFID tags, RFID reader beacon signals, and RFID tag'"'"'s repetitive transmitting signals to detect tag failures. The system security is provided by a method that uses integrated crypto engines in both the RFID tags and RFID readers.

Claims

1. A RFID system comprising:

at least one small-zone RFID reader to cover an area;

a large-zone RFID reader to cover gaps among the at least one small-zone RFID reader within the area, and

at least one active RFID tag,

wherein the at least one active RFID tag first try to become associated with the at least one small-zone RFID reader and if the at least one active RFID tag cannot become associated with one of the at least one small-zone RFID reader, the at least one active RFID tag that cannot become associated with the small-zone RFID reader is associated with the large-zone RFID reader.

2. The RFID system of claim 1 wherein said at least one small-zone RFID reader and said large-zone RFID reader simultaneously operate using multiple frequencies.

3. The RFID system of claim 2 wherein each of said small-zone RFID readers and said large-zone RFID reader has a frame structure comprising a beacon period, a contention access period, and a scan period.

4. The RFID system of claim 3 wherein each of said at least one active RFID tag repetitively broadcasts request-association signals to any of said at least one small-zone RFID reader and said large-zone RFID reader,

if said at least one active RFID tag is associated with said at least one small-zone RFID reader, said at least one active RFID tag communicates with the associated at least one small-zone RFID reader during the contention access period and said at least one active RFID tag stops sending said request-association signals;

or

if said at least one active RFID tag is associated with said large-zone RFID reader, said at least one active RFID tag communicates with the associated large-zone RFID reader during the contention access period and said at least one active RFID tag sends repetitive said request-association signals in said scan period.

5. The RFID system of claim 4 wherein said at least one small-zone RFID reader or said large-zone RFID reader uses the scan period to detect said request-association signals,

if the request-association signals are received at said at least one small-zone RFID reader or said large-zone RFID reader, said at least one small-zone RFID reader or said large-zone RFID reader directs said at least one active RFID tag to a beacon channel of said at least one small-zone RFID reader or said large-zone RFID reader, which received the request-association signals to complete the association process between said at least one active RFID tag and said at least one small-zone RFID reader or said large-zone RFID reader and uses the beacon period and the contention access period to communicate with said at least one active RFID tag that has become associated with said at least one small-zone RFID reader or said large-zone RFID reader.

6. The RFID system of claim 4 wherein after said at least one small-zone RFID reader detects said request-association signals, said at least one small-zone RFID reader listens to a scan channel for a monitoring window, said monitoring window being based on a received signal strength indicator (RSSI) of a signal transmitted by said at least one active RFID tag.

7. The RFID system of claim 6 wherein a length of said monitoring window of said small-zone RFID reader is inversely proportional to said RSSI of the signal transmitted by said at least one active RFID tag.

8. The RFID system of claim 4 wherein after said large-zone RFID reader detects said request-association signals, said large-zone RFID reader listens to a scan channel for a monitoring window, said monitoring window being greater than any said monitoring window of said small-zone RFID readers.

9. The RFID system of claim 1 wherein said at least one small-zone RFID reader and said large-zone RFID reader simultaneously operate using a single frequency.

10. The RFID system of claim 9 wherein each of said small-zone RFID readers and said large-zone RFID readers has a frame structure comprising a beacon period, a contention access period, and a scan period.

11. The RFID system of claim 10 wherein each of said at least one active RFID tag repetitively broadcasts request-association signals to any of said at least one small-zone RFID reader and said large-zone RFID reader,

if said at least one active RFID tag is associated with said at least one small-zone RFID reader, said at least one active RFID tag communicates with the associated at least one small-zone RFID reader during the contention access period and said at least one active RFID tag stops sending said request-association signals;

or

if said at least one active RFID tag is associated with said large-zone RFID reader, said at least one active RFID tag communicates with the associated said large-zone RFID reader during the contention access period and said at least one active RFID tag repetitively sends said request-association signals in said scan period.

12. An RFID system of claim 11 wherein each of said at least one small-zone RFID reader adjusts its beacon period to follow an end of the contention access period of said large-zone RFID reader plus a small random time period.

13. The RFID system of claim 11 wherein said at least one small-zone RFID reader or said large-zone RFID reader uses the scan period to detect said request-association signals,

if the request-association signals are received at said at least one small-zone RFID reader or said large-zone RFID reader, said at least one small-zone RFID reader or said large-zone RFID reader directs said at least one active RFID tag to a beacon channel of said at least one small-zone RFID reader or said large-zone RFID reader which received the request-association signals to complete the association process between said at least one active RFID tag and said at least one small-zone RFID reader or said large-zone RFID reader and uses the beacon period and the contention access period to communicate with the at least one active RFID tag that has become associated with said at least one small-zone RFID reader or said large-zone RFID reader.

14. The RFID system of claim 11 wherein after said at least one small-zone RFID reader detects said request-association signals, said at least one small-zone RFID reader listens to a scan channel for a monitoring window, said monitoring window being based on a received signal strength indicator (RSSI) of a signal transmitted by said at least one active RFID tag.

15. The RFID system of claim 14 wherein a length of said monitoring window is inversely proportional to said RSSI of the signal transmitted by said at least one active RFID tag.

16. The RFID system of claim 11 wherein after said large-zone RFID reader detects said request-association signals, said large-zone RFID reader listens to a scan channel for a monitoring window, said monitoring window being greater than any said monitoring window of said small-zone RFID readers.

17. The RFID system of claim 1 wherein said large-zone RFID reader checks the number of active RFID tags that are associated with the large-zone RFID reader;

and

said large-zone RFID reader sends a request to said at least one small-zone RFID reader to increase their output power if the number of active RFID tags that are associated with the large-zone RFID reader is greater than a first threshold;

or

said large-zone RFID reader sends a request to said at least one small-zone RFID reader to reduce their output power if the number of active RFID tags that are associated with the large-zone RFID reader is lower than a second threshold.

18. The RFID system of claim 1 wherein the at least one RFID active tag comprises:

a transmitter section operable to transmit packets to said at least one small-zone RFID reader and/or said large-zone RFID reader using a transmitter antenna;

a receiver section operable to receive packets from said at least one small-zone RFID reader and/or said large-zone RFID reader using a receiver antenna; and

a transmitting fault indicator generating audible or visible alarms depending on a condition of said transmission section or said receiver section.

19. The RFID system of claim 18 wherein said at least one active RFID tag broadcasts repetitive, request-association signals to associate said at least one active RFID tag with said at least one small-zone RFID reader or said large-zone RFID reader, randomly wakes up to listen to beacons of said small-zone RFID reader or said large-zone RFID reader when said at least one active RFID tag is not associated with any said small-zone RFID reader or said large-zone RFID reader, starts to measure time after detecting a first beacon of said at least one small-zone RFID reader or said large-zone RFID reader, and counts a number of transmitted packets from said at least one active RFID tag that are not acknowledged by said small-zone RFID reader or said large-zone RFID reader when it is associated with the said small-zone RFID reader or said large-zone RFID reader.

20. The RFID system of claim 19 wherein the at least one active RFID tag triggers said fault indicator when elapsed time after detecting the first beacon is greater than a time threshold or when a number of packets that are not acknowledged by the associated said small-zone RFID reader or said large-zone RFID reader exceeds a threshold.

21. The RFID system of claim 19 wherein said at least one small-zone RFID reader or said large-zone RFID reader counts a number of unacknowledged packets sent to said at least one active RFID tag when said at least one active RFID tag is associated with said at least one small-zone RFID reader or said large-zone RFID reader;

and

sends an event indicating a tag receiving fault to an external device linked to the said small-zone RFID reader or said large-zone RFID reader when the number of unacknowledged packets exceeds a threshold for triggering said fault indicator.

22. The RFID system of claim 1 wherein said at least one small-zone RFID reader and/or said large-zone RFID reader sends a read/write request to said at least one active RFID tag;

said at least one active RFID tag responds with a challenge packet to tag authority;

said at least one small-zone RFID reader and/or large-zone RFID reader sends a response including a session key;

said at least one active RFID tag decodes the session key; and

both said at least one small-zone RFID and/or large-zone RFID reader and said at least one active RFID tag use the session key to encrypt and decrypt data sent between them.

23. A RFID system comprising:

at least one small-zone RFID reader using multiple-frequencies to cover an area;

a large-zone RFID reader to cover gaps among the at least one small-zone RFID reader within the area, and

at least one active RFID tag,

wherein the at least one active RFID tag first try to become associated with the at least one small-zone RFID reader and if the at least one active RFID tag cannot become associated with one of the at least one small-zone RFID reader, the at least one active RFID tag that cannot become associated with the small-zone RFID reader is associated with the large-zone RFID reader.

24. A RFID system comprising:

at least one small-zone RFID reader using a single frequency to cover an area;

a large-zone RFID reader to cover gaps among the at least one small-zone RFID reader within the area, and

at least one active RFID tag,

wherein the at least one active RFID tag first try to become associated with the at least one small-zone RFID reader and if the at least one active RFID tag cannot become associated with one of the at least one small-zone RFID reader, the at least one active RFID tag that cannot become associated with the small-zone RFID reader is associated with the large-zone RFID reader.

25. A RFID system comprising:

at least one RFID reader, and

at least one active RFID tag, said active RFID tag comprising;

a transmitter section operable to transmit packets to a RFID reader using a transmitter antenna;

a receiver section operable to receive packets from said RFID reader using a receiver antenna; and

a transmitting fault indicator generating audible or visible alarms depending on a condition of said transmission section or said receiver section.

26. The RFID system of claim 25 wherein said active RFID tag broadcasts repetitive, request-association signals to associate said active RFID tag with the RFID reader, randomly wakes up to listen to beacons of the RFID reader when the active RFID tag is not associated with any said RFID reader, starts to measure time after detecting a first beacon of said RFID reader, and counts a number of transmitted packets from said active RFID tag that are not acknowledged by said RFID reader when it is associated with the said RFID reader.

27. The RFID system of claim 26 wherein said active RFID tag triggers said fault indicator when elapsed time after detecting the first beacon is greater than a time threshold or when a number of packets that are not acknowledged by the associated RFID reader exceeds a threshold.

28. The RFID system of claim 26 wherein said RFID reader counts the number of unacknowledged packets sent to said RFID tag for responding to the request-association packets;

and

sends an event indicating a tag receiving fault to an external device linked to said RFID reader when the number of unacknowledged packets exceeds a threshold for triggering said fault indicator.

29. A method of operating a RFID system comprising the steps of:

operating at least one small-zone RFID reader to cover an area;

operating a large-zone RFID reader to cover gaps among the at least one small-zone RFID reader within the area, and

operating at least one active RFID tag,

wherein the at least one active RFID tag first try to become associated with the at least one small-zone RFID reader and if the at least one active RFID tag cannot become associated with one of the at least one small-zone RFID reader, the at least one active RFID tag that cannot become associated with the small-zone RFID reader is associated with the large-zone RFID reader.

30. The method of claim 29 wherein said at least one small-zone RFID reader and said large-zone RFID reader simultaneously operate using multiple frequencies.

31. The method of claim 29 wherein each of said small-zone RFID readers and said large-zone RFID reader has a frame structure comprising a beacon period, a contention access period, and a scan period.

32. The method of claim 31 further comprising the steps of:

each of said at least one active RFID tag repetitively broadcasting request-association signals to any of said at least one small-zone RFID reader and said large-zone RFID reader,

if said at least one active RFID tag is associated with said at least one small-zone RFID reader, said at least one active RFID tag communicating with the associated at least one small-zone RFID reader during the contention access period and said at least one active RFID tag stops sending said request-association signals;

or

if said at least one active RFID tag is associated with said large-zone RFID reader, said at least one active RFID tag communicating with the associated large-zone RFID reader during the contention access period and said at least one active RFID tag repetitively sends said request-association signals in said scan period.

33. The method of claim 32 further comprising the steps of:

detecting said request-association signals at said at least one small-zone RFID reader or said large-zone RFID reader during the scan period;

if the request-association signals are detected at said at least one small-zone RFID reader or said large-zone RFID reader, directing said at least one active RFID tag to a beacon channel of said at least one small-zone RFID reader or said large-zone RFID reader which received the request-association signals to complete the association process between said at least one active RFID tag and said at least one small-zone RFID reader or said large-zone RFID reader and communicating during the beacon period and the contention access period with said at least one active RFID tag that has become associated with said at least one small-zone RFID reader or said large-zone RFID reader.

34. The method of claim 32 wherein after said at least one small-zone RFID reader detects said request-association signals further comprising the steps of:

said at least one small-zone RFID reader listening to a scan channel for a monitoring window, said monitoring window being based on a received signal strength indicator (RSSI) of a signal transmitted by said at least one active RFID tag.

35. The method of claim 34 wherein a length of said monitoring window is inversely proportional to said RSSI of the signal transmitted by at least one active RFID tag.

36. The method of claim 32 wherein after said at large-zone RFID reader detects said request-association signals further comprising the steps of:

said large-zone RFID reader listening to a scan channel for a monitoring window, said monitoring window being greater than any monitoring window of said small-zone RFID readers.

37. The method of claim 29 wherein said at least one small-zone RFID reader and said large-zone RFID reader simultaneously operate using a single frequency.

38. The method of claim 37 wherein each of said small-zone RFID readers and said large-zone RFID reader has a frame structure comprising a beacon period, a contention access period, and a scan period.

39. The method of claim 38 further comprising the steps of:

each of said at least one active RFID tag repetitively broadcasting request-association signals to any of said at least one small-zone RFID reader and said large-zone RFID reader,

if said at least one active RFID tag is associated with said at least one small-zone RFID reader, said at least one active RFID tag communicating with the associated at least one small-zone RFID reader during the contention access period and said at least one active RFID tag stops sending said request-association signals;

or

if said at least one active RFID tag is associated with said large-zone RFID reader, said at least one active RFID tag communicating with the associated large-zone RFID reader during the contention access period and said at least one active RFID tag repetitively sends said request-association signals in said scan period.

40. An method of claim 39 wherein each of said at least one small-zone RFID reader adjusts its beacon period to follow an end of the contention access period of said large-zone RFID reader plus a small random time period.

41. The method of claim 39 further comprising the step of:

detecting said request-association signals at said at least one small-zone RFID reader or said large-zone RFID reader during the scan period;

if the request-association signals are detected at said at least one small-zone RFID reader or said large-zone RFID reader, directing said at least one active RFID tag to a beacon channel of said at least one small-zone RFID reader or said large-zone RFID reader which received the request-association signals to complete the association process between said at least one active RFID tag and said at least one small-zone RFID reader or said large-zone RFID reader and communicating during the beacon period and the contention access period with the at least one active RFID tag that has become associated with said at least one small-zone RFID reader or said large-zone RFID reader.

42. The method of claim 39 wherein after said at least one small-zone RFID reader detects said request-association signals further comprising the steps of:

said at least one small-zone RFID reader listening to a scan channel for a monitoring window, said monitoring window being based on a received signal strength indicator (RSSI) of a signal transmitted by at least one active RFID tag.

43. The method of claim 42 wherein a length of said monitoring window is inversely proportional to said RSSI of the signal transmitted by said at least one active RFID tag.

44. The method of claim 39 wherein after said large-zone RFID reader detects said request-association signals further comprising the steps of:

said large-zone RFID reader listening to a scan channel for a monitoring window, said monitoring window being greater than any monitoring window of said small-zone RFID readers.

45. The method of claim 29 further comprising the step of said large-zone RFID reader checking the number of active RFID tags that are associated with said large-zone RFID reader;

and

said large-zone RFID reader sending a request to said at least one small-zone RFID reader to increase their output power if the number of active RFID tags that are associated with the large-zone RFID reader is greater than a first threshold;

or

said large-zone RFID reader sending a request to said at least one small-zone RFID reader to reduce their output power if the number of active RFID tags that are associated with the large-zone RFID reader is lower than a second threshold.

46. The method of claim 29 wherein the at least one RFID active tag comprises:

a transmitter section operable to transmit packets to said at least one small-zone RFID reader and/or said large-zone RFID reader using a transmitter antenna;

a receiver section operable to receive packets from said at least one small-zone RFID reader and/or said large-zone RFID reader using a receiver antenna; and

a transmitting fault indicator generating audible or visible alarms depending on a condition of said transmission section or said receiver section.

47. The method of claim 46 further comprising the step of:

said at least one active RFID tag sending repetitive, request-association signals to associate said at least one active RFID tag with said at least one small-zone RFID reader or said large-zone RFD reader;

randomly waking up to listen to beacons of said small-zone RFID reader or said large-zone RFID reader when said at least one active RFID tag is not associated with any said small-zone RFID reader or said large-zone RFID reader;

starting to measure time after detecting a first beacon of said at least one small-zone RFID reader or said large-zone RFID reader; and

counting a number of transmitted packets from said at least one active RFID tag that are not acknowledged by said small-zone RFID reader or said large-zone RFID reader when it is associated with the associated small-zone RFID reader or said large-zone RFID reader.

48. The method of claim 47 further comprising the step of:

triggering said fault indicator when elapsed time after detecting the first beacon is greater than a time threshold or when a number of packets that are not acknowledged by the associated small-zone RFID reader or said large-zone RFID reader exceeds a threshold.

49. The method of claim 46 further comprising the steps of:

said at least one small-zone RFID reader or said large-zone RFID reader counting a number of unacknowledged packets sent to said at least one active RFID tag when said at least one active RFID tag is associated with at least one small-zone RFID reader or said large-zone RFID reader; and

sending an event indicating a tag receiving fault to an external device linked to the said small-zone RFID reader or said large-zone RFID reader when the number of unacknowledged packets exceeds a threshold for triggering said fault indicator.

50. The method of claim 29 further comprising the steps of:

said at least one small-zone RFID reader and/or said large-zone RFID reader sending a read/write request to said at least one active RFID tag;

said at least one active RFID tag responding with a challenge packet to tag authority;

said at least one small-zone RFID reader and/or large-zone RFID reader sending a response including a session key;

said at least one active RFID tag decoding the session key; and

both said at least one small-zone RFID and/or large-zone RFID reader and said at least one active RFID tag using the session key to encrypt and decrypt data sent between them.

51. The method of claim 29 further comprising the following steps:

the at least one active RFID tag setting a TRANSIT flag if it detects changes in receiving a new RFID reader identification ID number from said at least one small-zone RFID reader or said large-zone RFID reader which is different from the previously stored RFID reader identification ID number;

the active RFID tag clearing said TRANSIT flag if it does not detect changes in said previously stored RFID reader identification ID number for a period of time exceeding a threshold;

the active RFID tag sending transit event to said at least one small-zone RFID reader or said large-zone RFID reader that is associated with said at least one active RFID tag; and

said at least one small-zone RFID reader or said large-zone RFID reader using the transit event to select all the active RFID tags with their TRANSIT flag set.

52. A method for improving RFID tag security in a RFID system comprising the following steps:

sending a read/write request from a RFID reader to a RFID tag;

sending a response from said RFID tag including a challenge packet to tag authority;

sending a response from said RFID reader including session key;

decoding the session key at said RFID tag; and

using the session key at the RFID reader and RFID tag to encrypt and decrypt data sent between them.