RFID systems using distributed exciter network

• US 8,395,482 B2
• Filed: 03/24/2008
• Issued: 03/12/2013
• Est. Priority Date: 03/23/2007
• Status: Active Grant

• Current Assignee: Mojix Inc
• Original Assignee: Mojix Inc
• Inventors: Sadr, Ramin, Gevargiz, John, Lee, Robert, Manteghi, Majid, Oliver, Gordon, Collender, Mike, Jones, Christopher, Syed, Hasan
• Primary Examiner(s): BROWN, VERNAL U
• Application Number:
  US12/054,331
• Publication Number:
  US 20090146792A1
• Time in Patent Office: 1,814 Days
• Field of Search: 340/10.3, 340/10.4, 340/10.5, 340/572.2
• US Class Current: 340/10.3
• CPC Class Codes: G06K 7/01 Details
• CPC Class Codes: G06K 7/10158 methods and means used by the interrogation device for reliably powering the wireless record carriers using an electromagnetic interrogation field
• CPC Class Codes: G06K 7/10188 the repeating consisting of intelligently propagating data from record carriers via intermediate stations to the interrogation device, e.g. a distant RFID or RFID falling in a "shadow" region sending its identification data to an interrogation device using at least the help of one further RFID that is positioned in a region "visible" to the interrogation device, the further RFID therefore functioning as a relay station
• 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: G06Q 10/087 Inventory or stock management, e.g. order filling, procurement or balancing against orders

Abstract

RFID systems are disclosed that include at least one RFID receiver system and a distributed exciter architecture. The exciters can be connected via wired and/or wireless connections to the RFID receiver system and the RFID receiver system can control the activation of the exciters to detect the presence of RFID tags within interrogation spaces defined by the exciter topology. In several embodiments, the RFID receiver system performs location estimation to determine the interrogation space in which a specific RFID tag or collection of RFID tags is located. One embodiment of the invention includes an RFID receiver system configured to detect information from RFID tags within a receive coverage area, and a plurality of exciters defining a plurality of interrogation spaces within the receive coverage area of the RFID receiver system. In addition, the RFID receiver system is configured to transmit a control signal that identifies one of the plurality of exciters and includes information indicative of an RFID tag interrogation signal, the plurality of exciters are configured to receive the control signal, and the exciter identified in the control signal is configured to illuminate an interrogation space with the RFID tag interrogation signal.

Claims

1. An RFID system configured to manipulate RFID tags, comprising:

an RFID receiver system configured to detect information from RFID tags within a receive coverage area; and

a plurality of exciters defining a plurality of interrogation spaces within the receive coverage area of the RFID receiver system;

wherein the RFID receiver system is configured to transmit a control signal that identifies one of the plurality of exciters and includes information indicative of an RFID tag interrogation signal;

wherein the plurality of exciters are configured to receive the control signal;

wherein the exciter identified in the control signal is configured to illuminate an interrogation space with the RFID tag interrogation signal;

the RFID receiver system is configured to transmit a status signal at a first RF frequency that identifies one of the plurality of exciters;

the exciter is configured to extract at least the identity of the exciter identified by the status signal; and

the exciter is configured to generate a response signal and transmits the response signal at a second RF frequency.

2. The RFID system of claim 1, wherein the RFID receiver system communicates to at least one of the plurality of exciters via a wired connection.

3. The RFID system of claim 2, wherein:

the wired connection is a twisted pair cable; and

the control signal is a baseband signal.

4. The RFID system of claim 2, wherein the wired connection directly connects the exciter to the RFID receiver system.

5. The RFID system of claim 2, wherein the wired connection connects the exciter to another of the plurality of exciters, which is configured to relay control signals from the RFID receiver system via the wired connection.

6. The RFID system of claim 2, wherein:

the wired connection is a coaxial cable; and

the control signal is modulated at a first frequency.

7. The RFID system of claim 6, wherein:

the exciter is configured to down convert the control signal to extract at least the identity of the exciter identified by the control signal; and

the exciter is configured to up convert and transmit the RFID tag interrogation signal at a second RF frequency, when the exciter is the exciter identified by the control signal.

8. The RFID system of claim 7, wherein the control signal specifies the frequency of the second RF frequency.

9. The RFID system of claim 8, wherein the second RF frequency is the same as the first RF frequency.

10. The RFID system of claim 3, wherein:

the exciter is configured to extract at least the identity of the exciter identified by the control signal; and

the exciter is configured to up convert and transmit the RFID tag interrogation signal at a transmit RF frequency, when the exciter is the exciter identified by the control signal.

11. The RFID system of claim 10, wherein the control signal specifies the transmit RF frequency.

12. The RFID system of claim 1, wherein the RFID receiver system communicates with at least one of the plurality of exciters via a wireless connection.

13. The RFID system of claim 12, wherein the wireless connection is a direct connection between the RFID receiver system and the exciter.

14. The RFID system of claim 12, wherein the wireless connection is between the exciter and a second of the plurality of exciters.

15. The RFID system of claim 14, wherein the second of the plurality of exciters is configured to relay control signals from the RFID receiver system via the wireless connection.

16. The RFID system of claim 12, wherein:

the control signal is modulated at a first RF frequency; and

the exciter is configured to down convert the control signal to extract at least the identity of the exciter identified by the control signal.

17. The RFID system of claim 16, wherein the exciter is configured to up convert and transmit the RFID tag interrogation signal at a second RF frequency when the exciter is the exciter identified by the control signal.

18. The RFID system of claim 17, wherein the control signal specifies the frequency of the second RF frequency.

19. The RFID system of claim 16, wherein the exciter is configured to generate an RFID tag interrogation signal and modulate the RFID tag interrogation signal onto a second RF frequency.

20. The RFID system of claim 19, wherein the control signal specifies the frequency of the second RF frequency.

21. The RFID system of claim 1, wherein the waveform of the response signal is similar to the waveform generated by an illuminated RFID tag.

22. The RFID system of claim 1, wherein the status signal specifies the frequency of the second RF frequency.

23. The RFID system of claim 1, wherein the RFID receiver system is configured to transmit control signals that activate a plurality of the exciters to transmit RFID tag interrogation signals at different frequencies.

24. The RFID system of claim 23, wherein the control signals transmitted by the RFID receiver system cause the plurality of activated exciters to transmit in accordance with a frequency hopping protocol.

25. The RFID system of claim 23, wherein the RFID receiver system is configured to allocate frequencies to exciters randomly.

26. The RFID system of claim 23, wherein:

the RFID receiver system possesses information concerning the exciter distribution topology; and

the RFID receiver system uses the topology information when allocating frequencies to activated exciters.

27. The RFID system of claim 1, wherein the control signal includes an n-bit address.

28. The RFID system of claim 1, wherein the control signal includes all the necessary signal characteristics and parameters to generate the desired waveform output from the exciter.

29. The RFID system of claim 28, wherein the control signal includes information that can be used by an exciter to perform transmit power calibration.

30. The RFID system of claim 28, wherein the control signal includes information indicative of a transmission frequency selection.

31. The RFID system of claim 1, further comprising:

a second RFID receiver system configured to detect information from RFID tags within a second receive coverage area; and

a plurality of exciters defining a plurality of interrogation spaces within the receive coverage area of the second RFID receiver system;

wherein the second RFID receiver system is configured to transmit a control signal that identifies one of the plurality of exciters and includes information indicative of an RFID tag interrogation signal;

wherein the plurality of exciters within the coverage area of the second RFID receiver system are configured to receive the control signal from the second RFID receiver system; and

wherein the exciter identified in the control signal is configured to illuminate an interrogation space within the coverage area of the second RFID receiver system with the RFID tag interrogation signal.

32. The RFID system of claim 1, wherein:

the RFID receiver system is configured to detect RFID tag information when an exciter illuminates an interrogation space with an RFID tag interrogation signal; and

the RFID receiver system is configured to determine whether the detected RFID tag information is from an RFID tag located within the interrogation space illuminated by the exciter.

33. The RFID system of claim 32, further comprising:

a sensor located within the illuminated interrogation space configured to detect changes within the interrogation space;

wherein the sensor is configured to communicate sensor output to the RFID receiver system; and

wherein the RFID receiver system is configured to determine whether the detected RFID tag information is from an RFID tag located within the interrogation space illuminated by the exciter using information including the sensor output.

34. The RFID system of claim 32, wherein:

the RFID receiver system is configured to detect RFID tag information when other exciters illuminate other interrogation spaces with RFID tag interrogation signals; and

the RFID receiver system is configured to determine whether the detected RFID tag information is from an RFID tag located within the interrogation space illuminated by the exciter using information including the RFID tag information detected when other exciters illuminated other interrogation spaces.

35. The RFID system of claim 32, wherein:

the RFID tag information is an RF signal;

the RFID receiver system is configured to collect information concerning features of the RFID tag information RF signal; and

the RFID receiver system is configured to determine whether the detected RFID tag information is from an RFID tag located within the interrogation space illuminated by the exciter using information including the features of the RFID tag information RF signal.

36. The RFID system of claim 35, wherein the collected features of the RFID tag information RF signal include signal strength, signal-to-noise ratio, and direction of arrival.

37. The RFID system of claim 32, wherein:

the RFID receiver system repeatedly causes a plurality of exciters to sequentially illuminate a plurality of interrogation spaces and records the detection of RFID tag information; and

the RFID receiver system is configured to determine whether detected information is from an RFID tag located within an interrogation space illuminated by one of the plurality of exciters using information including the rate at which the RFID tag information is detected when the interrogation space is illuminated.

38. The RFID system of claim 37, wherein:

the RFID receiver system possesses information concerning the exciter topography;

the RFID receiver system is configured to estimate expected detection rates for RFID tags in different interrogation spaces; and

the RFID receiver system is configured to determine whether detected information is from an RFID tag located within an interrogation space illuminated by one of the plurality of exciters using information including the rate at which the RFID tag information is detected when the interrogation space is illuminated and the expected detection rates for RFID tags in different interrogation spaces.

39. The RFID system of claim 38, wherein the RFID receiver system is configured to determine movement of an RFID tag from one interrogation space to another interrogation space using information including the rate at which the information is detected when interrogation spaces are illuminated and the expected detection rates for RFID tags in different interrogation spaces.

40. A method of estimating the location of an RFID tag within a plurality of interrogation spaces, comprising:

repeatedly illuminating each of the plurality of interrogation spaces;

recording the illuminated interrogation space when the RFID tag is detected;

determining the rate at which the RFID tag is detected when each interrogation space is illuminated;

recording the rate at which the RFID tag is detected for each interrogation space and for each exciter;

obtaining information concerning the topology of the plurality of interrogation spaces;

estimating expected detection rates for RFID tags in different interrogation spaces using information concerning the interrogation space topography; and

comparing the rate at which RFID tag information is detected when an interrogation space is illuminated with expected detection rates for the interrogation space when an RFID tag is located within different interrogation spaces.

41. The method of claim 40, wherein estimating expected detection rates for RFID tags in different interrogation spaces using information concerning the interrogation space topography further comprises determining the following:

42. The method of claim 41, wherein the quantity p(x_a|y_{{poll, sense}}^ej) is evaluated using the following:

43. The method of claim 42, wherein RR_e,xj is determined empirically by counting the number of times a tag is read in a fixed time interval and dividing this quantity by the number of total possible reads that were possible in the same time duration.

44. The method of claim 41, wherein estimating expected detection rates for RFID tags in different interrogation spaces using information concerning the interrogation space topography further comprises keeping read fraction statistics during key time intervals surrounding the read events.

45. The method of claim 44, wherein the read fraction statistics are approximated with a Gaussian distribution.