RFID BEAM FORMING SYSTEM

• US 20080012710A1
• Filed: 06/28/2007
• Published: 01/17/2008
• Est. Priority Date: 07/11/2006
• Status: Active Grant

• Current Assignee: Mojix Inc
• Original Assignee: Mojix Inc
• Inventors: Sadr, Ramin
• Granted Patent: US 7,873,326 B2
• Time in Patent Office: Days
• US Class Current: 340/572.1
• 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 an 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 from the RFID tag to alter relative phase between them; and

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

2. The method of claim 1 wherein processing the signals further comprises:

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

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

combining the adjusted relative phase signals with the reference signal to form an amplitude weighted combination of phase aligned signals having a higher gain than the signals from any one of the antenna elements.

3. The method of claim 2 wherein combining further comprises:

autocorrelating the reference signal;

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

separately accumulating the correlation results;

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

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

4. The method of claim 3 wherein correlating the signals further comprises:

conjugating the signals.

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

6. The invention of claim 3 wherein deriving the RFID tag information further comprises:

combining the beam steered signals; and

detecting the RFID tag information from the combined beam steered signals.

7. The method of claim 6 wherein the interrogation signals from each of the 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

then

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

8. The method of claim 2 wherein selecting the reference signal further comprises:

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

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

9. 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.

10. The method of claim 1 further comprising:

iterating the transmitting, processing and deriving to further alter the relative phases.

11. The method of claim 1 wherein processing the signals further comprises:

estimating the relative phase difference between the signals from each of the other antenna elements and the reference signal; and

deriving the relative range from each of the antenna elements to the RFID tag in accordance with the relative phase difference for each such antenna element.

12. The method of claim 11 further comprising:

deriving the location of the RFID tag from the relative ranges for each such antenna element.

13. The method of claim 1 wherein processing the signals further comprises:

deriving the relative phase differences between the signals from each of the other antenna elements and the reference signal; and

deriving relative direction of arrival of the received signals from the RFID tag at each of the antenna elements.

14. The method of claim 13 further comprising:

deriving relative direction of arrival information of signals from the RFID tag at each antenna element of a second array of antenna elements in response to second interrogation signals transmitted by the second array; and

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

15. The method of claim 14 further comprising:

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

16. The method of claim 10 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 in the direction of arrival information for each antenna element.

17. The method of claim 16 wherein the algorithm is the MUSIC algorithm.

18. The method of claim 14 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 at each frequency to derive range information; and

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

19. The method of claim 1 further comprising:

calibrating each antenna element 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 to compensate for such determined errors.

20. The method of claim 1 further comprising:

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

correcting the processing of the received signals to compensate for such interference signals.

21. The method of claim 20 wherein calibrating the array further comprises:

detecting the interference signals during a quite time period when signals from the RFID tag resulting from the transmitted interrogation signals are not received by the antenna elements.

22. The method of claim 21 wherein detecting the interference signals further comprises:

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

determining, for each of the 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.

23. The method of claim 1 further comprising:

selecting signals for a selected RFID tag from which information is to be derived, from signals from a plurality of RFID tags, based on a spatial location of the selected RFID tag relative to the spatial location of other ones of the plurality of RFID tags.

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

steering first transmitted RFID tag interrogation signals from an array of antenna elements to a first RFID tag;

steering second transmitted RFID tag interrogation signals to a second RFID tag;

processing signals received by each of the antenna elements from the RFID tag in response to the first and second RFID tag interrogation signals; and

deriving information from the first and second RFID tag from the processed received signals.

25. The method of claim 24 wherein processing signals received by each of the antenna elements 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.

26. The method of claim 24 wherein processing signals received by each of the antenna elements further comprises:

beamforming the signals received in response to the transmitted RFID tag interrogation signals to maximize a ratio of the signals received from the RFID tags compared to interference and noise.

27. The method of claim 24 further comprising:

transmitting third RFID tag interrogation signals to a third RFID tag at a different time than the first RFID tag interrogation signals were transmitted; and

discriminating signals received from the third RFID tag from signals received from the first RFID tag in accordance with the time difference.

28. The method of claim 24 further comprising:

transmitting a third RFID tag interrogation signals to a third RFID tag at a different frequency than a frequency at which the first RFID tag interrogation signals were transmitted; and

discriminating signals received from the third RFID tag from signals received from the first RFID tag in accordance with the frequency difference.

29. The method of claim 24 wherein processing signals received by each of the antenna elements further comprises:

determining a calibration factor for each antenna element in accordance with signals received by that antenna element from a calibration signal transmitter at a known location during a calibration test; and

applying the calibration factor for each antenna element while processing signals received in response to the first and second RFID tag interrogation signals.

30. A method of deriving information from an RFID tag, comprising:

determining a calibration factor for an array of antenna elements in accordance with signals received by that antenna element from a calibration signal transmitter during a calibration test;

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

applying the calibration factor while processing signals received from an RFID tag in response to the RFID tag interrogation signals, and deriving information from the RFID tag from the processed signals.

31. A method of deriving information from an RFID tag, comprising:

transmitting RFID interrogation signals using an array of antenna elements;

processing signals received from RFID tags in response to the RFID interrogation signals with a series of CIC filters having different frequency responses; and

reconstructing information from the RFID tags from signals stored in the CIC filters after the signals have been received from the RFID tags.

32. The method of claim 31 wherein reconstructing information from the RFID tags further comprises:

removing interference from processed signals in accordance with the different frequency responses of the series of CIC filters.

33. The method of claim 31 wherein processing signals received from RFID tags in response to the RFID interrogation signals further comprises:

down-converting the received signals from an RF band to an IF band in accordance with the different frequency responses of the series of CIC filters.

34. The method of claim 31 wherein processing signals received from RFID tags in response to the RFID interrogation signals further comprises:

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

compensating the signals received from the RFID tags in response to the RFID interrogation signals for the channel characteristics in accordance with the different frequency responses of the series of CIC filters.

35. An RFID system comprising:

an antenna array having a plurality of antenna elements;

a digital receive processing block responsive to signals received by each antenna element to derive RFID tag information from the signals; and

a CIC filter in the digital receive processing block for selectively processing portions of the received signals so that the selected portions are maintained after receipt long enough to derive the RFID tag information by post processing.

36. The invention of claim 35 wherein the digital receive processing block further comprises:

a FIR filter providing a first level of FIR filtering for processing the received signals and applying the FIR filter processed signals to the CIC filter wherein 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.

37. The invention of the claim 36 wherein the CIC filter removes multiple images of a desired received signal portion present in an output of the FIR filter having the first level of FIR filtering.

38. The invention of claim 35 further comprising:

a receive beamformer responsive to signals received by each antenna element to combine such received signals to produce and apply a beam steered combined signal to the digital receive processing block to derive RFID tag information from signals received from a first selected direction.

39. The invention of claim 38 wherein the receive beamformer combines such received signals to apply a second beam steered combined signal to the digital receive processing block to derive RFID tag information from signals received from a second selected direction.

40. The invention of claim 35 further comprising:

a receive beamformer responsive to signals from the antenna to provide spatial domain multiplexing to selectively derive RFID tag information from signals received from a plurality of selected directions.

41. The invention of claim 40 wherein the digital receive processing block combines frequency domain multiplexing with the spatial domain multiplexing to selectively derive RFID tag information from a plurality of closely located RFID tags.

42. The invention of claim 40 wherein the digital receive processing block combines time domain multiplexing with the spatial domain multiplexing to selectively derive RFID tag information from a plurality of closely located RFID tags.

43. The invention of claim 40 wherein the digital receive processing block combines time and frequency domain multiplexing with the spatial domain multiplexing to selectively derive RFID tag information from a plurality of closely located RFID tags.