Transmit diversity for passive backscatter RFID

• US 8,922,350 B2
• Filed: 12/08/2011
• Issued: 12/30/2014
• Est. Priority Date: 12/08/2011
• Status: Active Grant

• Current Assignee: Disney Enterprises Incorporated (The Walt Disney Company)
• Original Assignee: Disney Enterprises Incorporated (The Walt Disney Company)
• Inventors: Griffin, Joshua D., Hasan, Azhar, Zhou, Chenming
• Primary Examiner(s): Zimmerman, Brian
• Assistant Examiner(s): MCCORMACK, THOMAS S
• Application Number:
  US13/314,905
• Publication Number:
  US 20130147609A1
• Time in Patent Office: 1,118 Days
• US Class Current: 340/10.5
• 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 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H04B 5/0056 for use in interrogation, identification or read/write systems record carriers G06K7/00, G06K19/00; for railways B61L3/12
• CPC Class Codes: H04B 5/77 for interrogation
• CPC Class Codes: H04B 7/06 at the transmitting station

Abstract

Techniques are presented for adaptively increasing power delivered to an RF tag. In one embodiment, a tag reader uses multiple transmit antennas to increase the power delivered to an RF tag without increasing the transmission power. The tag reader may perform transmit diversity (or a related antenna diversity schema) to ensure that transmitted signals from the multiple transmit antennas constructively interfere at the location of the RF tag. The tag reader may transmit a pilot signal and measure a phase associated with a received signal from the RF tag. The tag reader may then use the phase to determine a phase shift for each of the plurality of antennas. The phase shift may then be applied to any subsequent signals transmitted by the antennas to ensure that the signals interfere at the RF tag'"'"'s location.

Claims

1. A method of delivering power to an RF tag, comprising:

transmitting a pilot signal from a first antenna, the first antenna selected from a plurality of antennas coupled to an RF tag reader;

measuring a first phase of a modulated signal received from the RF tag, wherein the modulated signal is emitted by the RF tag in response to the pilot signal;

determining a phase shift by identifying, based on the first phase of the modulated signal, a phase delay of a forward link in a backscatter channel corresponding to the first antenna of the plurality of antennas; and

phase shifting a first signal transmitted by at least one of the plurality of antennas based on the phase shift, wherein the phase shift is selected to cause interference between the first signal and at least a second signal transmitted from a different antenna of the plurality of the antennas at a location of the RF tag.

2. The method of claim 1, wherein the RF tag is a passive or semi-passive RF tag and backscatters the modulated signal using only power delivered by the first signal or the second signal, and wherein the first and second signals constructively interfere at the location of the RF tag.

3. The method of claim 1, wherein determining the phase shift by identifying the phase delay of the forward link further comprises dividing the first phase by two to generate the phase delay of the forward link,

wherein the first antenna and the at least one of the plurality of antennas are the same antenna,

wherein the first signal is phase shifted by the phase delay of the forward link, and

wherein the RF tag reader operates in a monostatic mode.

4. The method of claim 3, further comprising:

transmitting the pilot signal from a second antenna selected from the plurality of antennas, wherein the first antenna is not transmitting the pilot signal;

measuring a second phase of a modulated signal received from the RF tag in response to the pilot signal transmitted by the second antenna;

determining a different phase shift from the second phase of the modulated signal;

dividing the different phase shift by two to generate a half phase shift; and

phase shifting a third signal transmitted by the second antenna based on the half phase shift.

5. A tag reader configured to communicate with an RF tag, comprising:

an interface configured to couple to a plurality of antennas,

wherein a first antenna selected from the plurality of antennas is configured to transmit a pilot signal,

wherein the tag reader is configured to measure a first phase from a modulated signal received from the RF tag, the modulated signal is emitted in response to the pilot signal, and

wherein the tag reader is configured to determine a phase shift by one of (i) identifying, based on the first phase, a phase delay of a forward link in a backscatter channel corresponding to the first antenna of the plurality of antennas and (ii) identifying, based on the first phase, a phase delay difference between forward links corresponding to the first antenna and to a second antenna of the plurality of antennas, respectively; and

a phase shifting component configured to phase shift at least a first signal transmitted by at least one of the plurality of antennas based on the phase shift, wherein the phase shift is selected to cause interference between the first signal and at least a second signal transmitted from a different antenna of the plurality of the antennas at a location of the RF tag.

6. The tag reader of claim 5, wherein the RF tag is a passive or semi-passive RF tag and backscatters the modulated signal using only power delivered by the first signal or the second signal, and wherein the first and second signal constructively interfere at the location of the RF tag.

7. The tag reader of claim 5, wherein determining the phase shift based on the first phase of the modulated signal further comprises dividing the first phase by two to generate the phase delay of the forward link,

wherein the first antenna and the at least one of the plurality of antennas are the same antenna,

wherein the first signal is phase shifted by the phase delay of the forward link, and

wherein the RF tag reader operates in a monostatic mode.

8. The tag reader of claim 7, wherein the pilot signal is transmitted from the second antenna selected from the plurality of antennas, wherein the first antenna is not transmitting the pilot signal,

wherein a second phase of a modulated signal received from the RF tag in response to the pilot signal transmitted by the second antenna is measured,

wherein a different phase shift, based on the second phase of the modulated signal, is determined,

wherein the different phase shift is divided by two to generate a half phase shift, and

wherein a third signal transmitted by the second antenna is phase shifted based on the half phase shift.

9. The tag reader of claim 5, wherein the pilot signal is transmitted from each of the plurality of antennas simultaneously and wherein the RF tag reader operates in a monostatic mode.

10. The tag reader of claim 9, wherein determining the phase shift based on the first phase of the modulated signal further comprises:

receiving on the first antenna the modulated signal received from the RF tag in response to the pilot signals transmitted from the plurality of antennas, the modulated signal including the first phase;

receiving on the second antenna of the plurality of antennas a different modulated signal received from the RF tag in response to the pilot signals transmitted from the plurality of antennas, the different modulated signal including a second phase; and

determining the phase delay difference based on the first and second phases, wherein the phase shift shifts a third signal transmitted by one of the first antenna and the second antenna based on the phase delay difference.

11. The tag reader of claim 5, wherein the RF tag reader operates in a bistatic mode, and wherein the first antenna is a transmit antenna.

12. The tag reader of claim 11, wherein determining the phase shift from the first phase of the modulated signal further comprises:

receiving on the second antenna of the plurality of antennas the modulated signal received from the RF tag in response to the pilot signal transmitted from the first antenna, the modulated signal including the first phase;

transmitting the pilot signal from a third antenna selected from the plurality of antennas, wherein the first antenna is not transmitting the pilot signal;

receiving on the second antenna a different modulated signal received from the RF tag in response to the pilot signal transmitted from the third antenna, the different modulated signal including a second phase; and

determining the phase delay difference based on the first and second phases, wherein the phase shift shifts a third signal transmitted by one of the one of the first antenna and the third antenna based on the phase delay difference.

13. A system, comprising:

a passive or semi-passive RF tag; and

a tag reader configured to communicate with the RF tag, comprising;

an interface configured to couple to a plurality of antennas, wherein a first antenna selected from the plurality of antennas is configured to transmit a pilot signal, wherein the tag reader is configured to measure a first phase from a modulated signal received from the RF tag, the modulated signal is emitted in response to the pilot signal, and wherein the tag reader is configured to determine a phase shift by one of (i) identifying, based on the first phase, a phase delay of a forward link in a backscatter channel corresponding to a first antenna of the plurality of antennas and (ii) identifying, based on the first phase, a phase delay difference between forward links corresponding to the first antenna and to a second antenna of the plurality of antennas, respectively; and

a phase shifting component that phase shifts a first signal transmitted by at least one of the plurality of antennas based on the phase shift, wherein the phase shift is selected to cause interference between the first signal and at least a second signal transmitted from a different antenna of the plurality of the antennas at a location of the RF tag.

14. The system of claim 13, wherein determining the phase shift based on the phase of the modulated signal further comprises dividing the first phase by two to generate the phase delay of the forward link,

wherein the first antenna and the at least one of the plurality of antennas are the same antenna,

wherein the first signal is phase shifted by the phase delay of the forward link, and

wherein the RF tag reader operates in a monostatic mode.

15. The system of claim 14, wherein the pilot signal is transmitted from the second antenna selected from the plurality of antennas, wherein the first antenna is not transmitting the pilot signal,

wherein a second phase of a modulated signal received from the RF tag in response to the pilot signal transmitted by the second antenna is measured,

wherein a different phase shift from the second phase of the modulated signal is determined,

wherein the different phase shift is divided by two to generate a half phase shift, and

wherein a third signal transmitted by the second antenna is phase shifted based on the half phase shift.

16. The system of claim 13, wherein the pilot signal is transmitted from each of the plurality of antennas simultaneously and wherein the RF tag reader operates in a monostatic mode.

17. The system of claim 16, wherein determining the phase shift based on the first phase of the modulated signal further comprises:

receiving on the first antenna the modulated signal received from the RF tag in response to the pilot signals transmitted from the plurality of antennas, the modulated signal including the first phase;

receiving on the second antenna of the plurality of antennas a different modulated signal received from the RF tag in response to the pilot signals transmitted from the plurality of antennas, the different modulated signal including a second phase; and

determining the phase delay difference based on the first and second phases, wherein the phase shift shifts a third signal transmitted by one of the first antenna and the second antenna based on the phase delay difference.

18. The system of claim 13, wherein the RF tag reader operates in a bistatic mode, and wherein the first antenna is a transmit antenna.

19. The system of claim 18, wherein determining the phase shift from the first phase of the modulated signal further comprises:

receiving on the second antenna of the plurality of antennas the modulated signal received from the RF tag in response to the pilot signal transmitted from the first antenna, the modulated signal including the first phase;

transmitting the pilot signal from a third antenna selected from the plurality of antennas, wherein the first antenna is not transmitting the pilot signal;

receiving on the second antenna a different modulated signal received from the RF tag in response to the pilot signal transmitted from the third antenna, the different modulated signal including a second phase; and

determining the phase delay difference based on the first and second phases, wherein the phase shift shifts a third signal transmitted by one of the one of the first antenna and the third antenna based on the phase delay difference.

20. The system of claim 13, wherein the first and second signal constructively interfere at the location of the RF tag.

21. A method of delivering power to an RF tag, comprising:

transmitting a pilot signal from a first antenna, the first antenna selected from a plurality of antennas coupled to an RF tag reader;

measuring a first phase of a modulated signal received from the RF tag, wherein the modulated signal is emitted by the RF tag in response to the pilot signal;

determining a phase shift by identifying, based on the first phase, a phase delay difference between forward links corresponding to the first antenna and to a second antenna of the plurality of antennas, respectively; and

phase shifting a first signal transmitted by at least one of the plurality of antennas based on the phase shift, wherein the phase shift is selected to cause interference between the first signal and at least a second signal transmitted from a different antenna of the plurality of the antennas at a location of the RF tag.

22. The method of claim 21, wherein the pilot signal is transmitted from each of the plurality of antennas simultaneously and wherein the RF tag reader operates in a monostatic mode.

23. The method of claim 22, wherein determining the phase shift from the first phase of the modulated signal further comprises:

receiving on the first antenna the modulated signal received from the RF tag in response to the pilot signals transmitted from the plurality of antennas, the modulated signal including the first phase;

receiving on the second antenna of the plurality of antennas a different modulated signal received from the RF tag in response to the pilot signals transmitted from the plurality of antennas, the different modulated signal including a second phase;

determining the phase delay difference based on the first and second phases, wherein the phase shift shifts a third signal transmitted by one of the first antenna and the second antenna based on the phase delay difference.

24. The method of claim 21, wherein the RF tag reader operates in a bistatic mode, and wherein the first antenna is a transmit antenna.

25. The method of claim 24, wherein determining the phase shift from the first phase of the modulated signal further comprises:

receiving on the second antenna of the plurality of antennas the modulated signal received from the RF tag in response to the pilot signal transmitted from the first antenna, the modulated signal including the first phase;

transmitting the pilot signal from a third antenna selected from the plurality of antennas, wherein the first antenna is not transmitting the pilot signal;

receiving on the second antenna a different modulated signal received from the RF tag in response to the pilot signal transmitted from the third antenna, the different modulated signal including a second phase;

determining the phase delay difference based on the first and second phases, wherein the phase shift shifts a third signal transmitted by one of the one of the first antenna and the third antenna based on the phase delay difference.