RFID beam forming system

• US 8,768,248 B2
• Filed: 12/30/2010
• Issued: 07/01/2014
• Est. Priority Date: 07/11/2006
• Status: Active Grant

• Current Assignee: Mojix Inc
• Original Assignee: Mojix Inc
• Inventors: Sadr, Ramin
• Primary Examiner(s): Pham, Tuan
• Application Number:
  US12/982,557
• Publication Number:
  US 20110090059A1
• Time in Patent Office: 1,279 Days
• Field of Search: 455/41.1, 455/41.2, 455/13.3, 455/67.11, 455/67.16, 455/562.1, 455/575.7, 455/269, 455/272, 370/335, 370/339, 370/338, 340/10.1, 340/10.3, 340/572.1, 340/539.22, 342/450, 343/757, 343/700, 343/846, 343/848, 343/860
• US Class Current: 455/41.1
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal
• CPC Class Codes: G01S 13/762 with special measures concerning the radiation pattern, e.g. S.L.S. aerials or aerial systems providing at least two radiation patterns, e.g. providing sum and difference patterns, H01Q25/00
• CPC Class Codes: G01S 13/765 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 7/023 Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36
• CPC Class Codes: G01S 7/0236 Avoidance by space multiplex
• CPC Class Codes: G01S 7/282 Transmitters
• CPC Class Codes: G01S 7/288 Coherent receivers
• CPC Class Codes: G01S 7/2883 using FFT processing
• 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 7/10009 sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
• CPC Class Codes: G06K 7/10316 using at least one antenna particularly designed for interrogating the wireless record carriers antennas in general H01Q1/22
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence
• CPC Class Codes: H01Q 25/00 Antennas or antenna systems providing at least two radiating patterns arrangements for changing or varying the orientation or the shape of the directional pattern H01Q3/00
• CPC Class Codes: H01Q 3/30 varying the relative phase between the radiating elements of an array H01Q3/2605, H01Q3/2658, H01Q3/2682, H01Q3/44 take precedence
• CPC Class Codes: H04B 7/0617 for beam forming

Abstract

A multi-protocol, multi-band array antenna system may be used in Radio Frequency Identification (RFID) system reader and sensory networks. The antenna array may include array elements with an integrated low noise amplifier. The system may employ digital beam forming techniques for transmission and steering of a beam to a specific sensor tag or group of tags in a cell. The receive beam forming network is optimized for detecting signals from each sensor tag. Narrow and wideband interferences may be excised by an interference nulling algorithm. Space division multiplexing may be used by the antenna system to enhance system processing capacity.

Claims

1. A method for deriving information from an RFID tag, comprising:

transmitting RFID tag interrogation signals from an array of antenna elements to an RFID tag;

processing signals received by each of the antenna elements in the array of antenna elements from the RFID tag to alter relative phase between them, where processing received signals comprises;

selecting received signals from one of the antenna elements in the array of antenna elements as a reference signal;

adjusting the relative phase of the received signals from each of the other antenna elements in the array of antenna elements relative to the reference signal; and

combining the adjusted relative phase received signals with the reference signal to form an amplitude weighted combination of phase aligned signals having a higher gain than the signals received from the RFID tag from any one of the antenna elements, where combining the adjusted relative phase received signals with the reference signal comprises;

autocorrelating the reference signal;

correlating each of the received signals from the other antenna elements in the array of antenna elements with the reference signal;

separately accumulating the correlation results;

delaying the signals received from each of the antenna elements in the array of antenna elements to compensate for accumulation delay; and

applying the accumulated correlations from each of the antenna elements in the array of antenna elements as a beam forming coefficient to the delayed signals received by that antenna element to produce beam steered signals from each of the said antenna elements; and

deriving information from the RFID tag from a combination of the processed received signals.

2. The method of claim 1, wherein correlating each of the received signals further comprises conjugating the signals.

3. The method of claim 1 wherein autocorrelation of the reference signal provides a measure of an absolute magnitude of the reference signal.

4. The method of claim 1 wherein deriving information from the RFID tag further comprises:

combining the beam steered signals; and

detecting RFID tag information from the combined beam steered signals.

5. The method of claim 4 wherein the RFID tag interrogation signals transmitted from the array of antenna elements includes a predetermined pattern and detecting the RFID tag information further comprises:

detecting the predetermined pattern from the combined beam steered signals; and

detecting the RFID tag information from a portion of the beam steered signals having a predetermined relationship to the detected predetermined pattern.

6. The method of claim 1 wherein selecting received signals from one of the antenna elements in the array of antenna elements as the reference signal further comprises:

processing the received signals from each of the antenna elements to determine the relative magnitudes of the received signals; and

selecting the received signal from the antenna element with the highest relative magnitude as the reference signal.

7. The method of claim 1 further comprising:

transmitting second RFID tag interrogation signals at a second frequency to derive RFID tag information from a second RFID tag.

8. The method of claim 1 further comprising:

iterating the transmitting, processing and deriving to further alter the relative phases between the signals received by each of the antenna elements in the array of antenna elements from the RFID tag.

17. The method of claim 1 further comprising:

calibrating each antenna element in the array of antenna elements to determine errors in relative phase for each such antenna element for one or more test signals; and

correcting the processing of the signals received by each such antenna element from the RFID tag to compensate for such determined errors.

18. The method of claim 1 further comprising:

calibrating the array of antenna elements for interference signals received by the antenna elements in the array of antenna elements from sources other than the RFID tag; and

correcting the processing of the signals received by the antenna elements in the array of antenna elements from the RFID tag to compensate for such interference signals.

19. The method of claim 18 wherein calibrating the array of antenna elements further comprises:

detecting an interference signal during a quiet time period when the interrogation signals are not being transmitted.

20. The method of claim 19 wherein detecting the interference signal further comprises:

filtering signals received by each antenna element in the array of antenna elements with a plurality of banks of filters at different frequencies;

determining, for each of the antenna elements in the array of antenna elements, if one or more of the plurality of banks of filters contain substantial, interference signals during the quiet time period so that signals from such one or more of the plurality of filter banks can be modified to correct the processing of signals from that antenna element.

22. The method of claim 1, further comprising steering the transmitted RFID tag interrogation signals from an array of antenna elements to the RFID tag.

23. The method of claim 22 wherein processing signals received by each of the antenna elements from the RFID tag further comprises beamforming the signals received in response to at least one of the transmitted RFID tag interrogation signals to reduce effects of interference in the signals.

24. The method of claim 1, wherein the amplitude weighted combination of phase aligned signals has a higher gain than the signals from any one of the antenna elements in the array of antenna elements.

25. The method of claim 1, further comprising estimating direction of arrival information for signals received by the array of antenna elements from the RFID tag, from the determined relative phase differences.

26. The method of claim 25 wherein using the estimated direction of arrival information further comprises:

estimating a range from the array of antenna elements to the RFID tag; and

determining location data related to the RFID tag from the estimated direction of arrival information and the estimated range from the array of antenna elements to the RFID tag.

27. The method of claim 25 further comprising processing signals received by each of the antenna elements in the array of antenna elements from the RFID tag through a series of CIC filters having different frequency responses to reduce interfering signals before estimating direction of arrival information.

28. The method of claim 27 wherein processing signals received by each of the antenna elements in the array of antenna elements from the RFID tag through the series of CIC filters further comprises down-converting the signals received from the RFID tag from an RF band to an IF band in accordance with different frequency responses of the series of CIC filters.

29. The method of claim 27 wherein processing signals received by each of the antenna elements in the array of antenna elements from the RFID tag through the series of CIC filters further comprises:

determining characteristics of a communication channel between the array of antenna elements and the RFID tag in accordance with information derived from signals received from the RFID tag over a period of time long enough to indicate channel characteristics; and

compensating the signals received from the RFID tag in response to the RFID interrogation signals for the determined channel characteristics.

30. The method of claim 29 wherein compensating the signals received from the RFID tag further comprises adjusting a different frequency response of the series of CIC filters in accordance with the determined channel characteristics.

31. The method of claim 27 wherein processing signals received by each of the antenna elements in the array of antenna elements from the RFID tag through the series of CIC filters further comprises processing the signals with a FIR filter, providing a first level of FIR filtering, before applying the FIR filter processed signals to a CIC filter in the series of CIC filters so that the combination of the FIR filter followed by the CIC filter provides a second, higher level of FIR filtering with substantially less complexity than a FIR filter providing the second, higher level of FIR filtering directly.

32. The method of claim 22, wherein the same array of antenna elements is used to transmit RFID tag interrogation signals and receive signals from the RFID tag.

33. The method of claim 22, wherein the array of antenna elements used to transmit RFID tag interrogation signals and the array of antenna elements used to receive signals from the RFID tag are distributed.

34. The method of claim 22, wherein beamforming is used to focus a transmitted beam to a desired location in space.

35. The method of claim 23, wherein the beamforming is performed using a filter including a paraunitary lattice filter bank.

36. The method of claim 23, wherein the beamforming is performed using a filter including a CIC filter.

37. The method of claim 23, wherein the beamforming is optimized using adaptive beamforming.

38. The method of claim 23, wherein the beamforming is achieved by applying appropriate phase corrections to the signals.

39. The method of claim 38, wherein the beamforming further comprises applying complex weights to each signal.

40. The method of claim 39, wherein the complex weights include amplitude components.

41. The method of claim 22, wherein the complex weights include phase components.

42. The method of claim 1 wherein transmitting RFID tag interrogation signals from the array of antenna elements to the RFID tag comprises modulating an RF waveform and applying the RF waveform to the array of antenna elements.

43. The method of claim 42 wherein transmitting RFID tag interrogation signals from the array of antenna elements to the RFID tag further comprises filtering the RF waveform with a paraunitary lattice filter bank and a cascaded integrator comb (CIC) filter.

44. The method of claim 1 wherein processing received signals further comprises filtering received signals with a cascaded integrator comb (CIC) filter and FIR filter bank.

45. The method of claim 1 further comprising:

measuring relative phases of two received signals at two different frequencies;

determining a path length d of the received signals using the equation

9. A method for deriving information from an RFID tag, comprising:

transmitting RFID tag interrogation signals from an array of antenna elements to an RFID tag;

processing signals received by each of the antenna elements in the array of antenna elements from the RFID tag to alter relative phase between them, where processing received signals comprises;

estimating a relative phase difference between the signals from the antenna elements in the array of antenna elements and a reference signal; and

deriving a relative range from the antenna elements in the array of antenna elements to the RFID tag in accordance with the relative phase difference between the signals from the antenna elements in the array of antenna elements and the reference signal; and

deriving information from the RFID tag from a combination of the processed received signals.

10. The method of claim 9 further comprising:

deriving a location for the RFID tag from the relative range from the antenna elements in the array of antenna elements to the RFID tag.

46. The method of claim 9 wherein transmitting RFID tag interrogation signals from the array of antenna elements to the RFID tag comprises modulating an RF waveform and applying the RF waveform to the array of antenna elements.

47. The method of claim 46 wherein transmitting RFID tag interrogation signals from the array of antenna elements to the RFID tag further comprises filtering the RF waveform with a paraunitary lattice filter bank and upsampling the RF waveform with a cascaded integrator comb (CIC) filter.

48. The method of claim 9 wherein processing received signals further comprises filtering received signals with a cascaded integrator comb (CIC) filter and FIR filter bank.

49. The method of claim 9 wherein deriving the relative range to the RFID tag in accordance with the relative phase difference between the signals from the antenna elements in the array of antenna elements and the reference signal comprises determining the relative range d using the equation

11. A method for deriving information from an RFID tag, comprising:

transmitting RFID tag interrogation signals from an array of antenna elements to an RFID tag;

processing signals received by each of the antenna elements in the array of antenna elements from the RFID tag to alter relative phase between them, where processing received signals comprises;

deriving a relative phase difference between the signals from the antenna elements in the array of antenna elements and a reference signal; and

deriving a relative direction of arrival of the received signals from the RFID tag in accordance with the relative phase difference between the signals from the antenna elements in the array of antenna elements and the reference signal; and

deriving information from the RFID tag from a combination of the processed received signals.

12. The method of claim 11 further comprising:

deriving a relative direction of arrival of signals received from the RFID tag with respect to a second array of antenna elements in response to second interrogation signals transmitted by the second array of antenna elements; and

determining a location of the RFID tag by combining the relative direction of arrival information derived from signals received at each array of antenna elements.

13. The method of claim 12 further comprising:

iterating the transmitting, processing and deriving to improve accuracy of relative direction of arrival information derived from the signals at each array of antenna elements after the RFID tag information has been derived.

14. The method of claim 13 wherein iterating further comprises:

combining the RFID tag information derived from each of a plurality of iterations to form a correlation matrix; and

applying an algorithm to the correlation matrix to reduce multipath effects based upon the direction of arrival information for each array of antenna elements.

15. The method of claim 14 wherein the algorithm is the MUSIC algorithm.

16. The method of claim 11 further comprising:

transmitting second RFID tag interrogation signals at a second frequency;

determining relative signal phase information for signals received by at least one antenna element of the array of antenna elements at each frequency to derive range information; and

determining a location for the RFID tag by combining the range information with direction of arrival information.

21. The method of claim 11 further comprising:

transmitting second RFID interrogation signals to a second RFID tag, the second RFID tag closely located in space to the RFID tag;

deriving a second relative direction of arrival information for signals received from the second RFID tag in response to the second RFID interrogation signals; and

using the relative direction of arrival for signals received from the RFID tag and the second relative direction of arrival information for signals received from the second RFID tag to distinguish data received from the RFID tag from data received from the second RFID tag.

50. The method of claim 11 wherein transmitting RFID tag interrogation signals from the array of antenna elements to the RFID tag comprises modulating an RF waveform and applying the RF waveform to the array of antenna elements.

51. The method of claim 50 wherein transmitting RFID tag interrogation signals from the array of antenna elements to the RFID tag further comprises filtering the RF waveform with a paraunitary lattice filter bank and upsampling the RF waveform with a cascaded integrator comb (CIC) filter.

52. The method of claim 11 wherein processing received signals further comprises filtering received signals with a cascaded integrator comb (CIC) filter and FIR filter bank.