RFID tag location using synthesized-beam RFID readers

1. A method to estimate a location of a Radio Frequency Identification (RFID) integrated circuit (IC) coupled to an antenna, the method comprising:

generating multiple radio-frequency beams, each directed to a different target location;

transmitting multiple interrogating signals on each beam;

receiving, on each beam, at least one response from the IC to the interrogating signals;

determining, for each beam, a response rate;

selecting a first beam having a first response rate and a second beam having a second response rate, wherein the first beam partially overlaps the second beam to form an overlap region; and

using a target location of the first beam, a target location of the second beam, and the first and second response rates to estimate the IC location within the overlap region.

2. The method of claim 1 , wherein a ratio of a first distance between the first beam target location and the estimated IC location to a second distance between the second beam target location and the estimated IC location corresponds to a ratio of the first and second response rates.

3. The method of claim 1 , further comprising:

transmitting the multiple interrogating signals at multiple radio frequencies; and

determining the first and second response rates at a first one of the multiple radio frequencies.

4. The method of claim 3 , wherein a ratio of a first distance between the rust beam target location and the estimated IC location and to a second distance between the second beam target location and the estimated IC location corresponds to both:

a ratio of the first response rate to the second response rate; and

a ratio of a third response rate to a fourth response rate, wherein the third response rate is associated with the first beam, the fourth response rate is associated with the second beam, and the third and fourth response rates are determined at a second radio frequency different from the first radio frequency.

5. The method of claim 3 , further comprising selecting the first radio frequency based on at least one of an environmental condition, a previously received IC response, a performance characteristic of the IC, and a tag population size.

6. The method of claim 1 , further comprising refining the estimated IC location by comparing a sensitivity contour of at least one of the first and second beams to a frequency-dependent operating profile of at least one of the IC and a tag including the IC.

7. The method of claim 1 , further comprising:

selecting a third beam having a third target location and a third response rate, wherein the third beam partially overlaps the first and second beams to form the overlap region, and

using the first, second, and third beam target locations and the first, second, and third response rates to estimate the IC location, wherein:

a ratio of a first distance between the first beam target location and the estimated IC location to a second distance between the second beam target location and the estimated IC location corresponds to a ratio of the first and second response rates; and

a ratio of the first distance to a third distance between the third beam target location and the estimated IC location corresponds to a ratio of the first and third response rates.

8. The method of claim 1 , further comprising generating the multiple beams from at least one of a synthesized-beam RFID reader and multiple RFID readers.

9. The method of claim 1 , wherein each beam response rate is a count of responses received on the respective beam divided by the number of interrogating signals transmitted on the respective beam.

10. The method of claim 1 , further comprising:

determining, based on map information, excluded locations for the RFID IC; and

removing the excluded locations from the region.

11. A method to estimate a location of a Radio Frequency Identification (RFID) integrated circuit (IC) coupled to an antenna, the method comprising:

generating multiple pairs of radio-frequency (RF) beams, wherein each beam pair is directed to a different target location and the beams within each beam pair cooperatively provide RF power to the target location;

transmitting multiple interrogating signals on at least one beam of each beam pair;

receiving, on at least one beam of each beam pair, at least one response from the IC to the interrogating signals;

determining, for each beam pair, a response rate;

selecting a first beam pair having a first response rate and a second beam pair having a second response rate, wherein the first beam pair partially overlaps the second beam pair to form an overlap region; and

using a target location of the first beam pair, a target location of the second beam pair, and the first and second response rates to estimate the IC location within the overlap region.

12. The method of claim 11 , wherein at least one of:

one beam of at least one pair transmits the interrogating signal and the other beam transmits a substantially unmodulated continuous-wave signal; and

both beams of at least one pair transmit synchronized interrogating signals.

13. The method of claim 11 , wherein a ratio of a first distance between the first beam pair target location and the estimated IC location to a second distance between the second beam pair target location and the estimated IC location corresponds to a ratio of the first and second response rates.

14. The method of claim 13 , further comprising:

transmitting the multiple interrogating signals at multiple radio frequencies, and

determining the first and second response rates at a first one of the multiple radio frequencies.

15. The method of claim 14 , wherein estimating the IC location within the overlap region includes estimating the IC location such that a ratio of a first distance between the IC location and the first beam target location to a second distance between the IC location and the second beam target location corresponds to both:

a ratio of the first response rate to the second response rate; and

a ratio of a third response rate to a fourth response rate, wherein the third response rate is associated with the first beam pair, the fourth response rate is associated with the second beam pair, and the third and fourth response rates are determined at a second radio frequency different from the first radio frequency.

16. The method of claim 14 , further comprising selecting the first frequency based on at least one of an environmental condition, previously received IC replies, a performance characteristic of the RFID IC, and a tag population size.

17. The method of claim 14 , further comprising selecting transmitting radio frequencies for each beam in a pair to avoid generating beat notes.

18. The method of claim 11 , further comprising:

selecting a third beam pair having a third target location and a third response rate, wherein the third beam pair partially overlaps the first and second beam pairs to form the overlap region, and

using the first, second, and third beam target locations and the first, second, and third response rates to estimate the IC location, wherein:

a ratio of a first distance between the first beam pair target location and the estimated IC location to a second distance between the second beam pair target location and the estimated IC location corresponds to a ratio of the first and second response rates; and

a ratio of the first distance to a third distance between the third target location and the estimated IC location corresponds to a ratio of the first and third response rates.

19. A method for a Radio Frequency Identification (RFID) synthesized-beam reader (SBR) to estimate a location of an RFID integrated circuit (IC) coupled to an antenna, the method comprising:

serially synthesizing each of multiple beams according to a scan pattern, each beam directed to a respective target location;

transmitting a series of interrogating signals on each beam;

receiving, on each beam, at least one response from the RFID IC to the series of interrogating signals;

determining, for each beam, a response rate;

selecting a first beam having a first response rate and a second beam having a second response rate, wherein the first beam partially overlaps the second beam to form an overlap region; and

using a target location of the first beam, a target location of the second beam, and the first and second response rates to estimate the IC location within the overlap region.

20. The method of claim 19 , further comprising, for each beam:

discriminating, based on the beam's response rate, whether the IC is in a sidelobe of the beam; and

if the IC is in the sidelobe, then excluding the beam's response rate when estimating the location of the IC.