Interrogator and interrogation system employing the same
A control and processing system for use with an interrogator and an interrogation system employing the same. In one embodiment, the control and processing system includes a correlation subsystem having a correlator that correlates a reference code with a reply code from a radio frequency identification (RFID) tag and provides a correlation signal therefrom. The control and processing system also includes a decision subsystem that verifies a presence of the RFID tag as a function of the correlation signal.
1. A control and processing system, comprising:
a correlation subsystem operable with a processor configured to:
preload amplitude, phase, and delay information corresponding to a logical “0” and a logical “1” associated with a radio frequency identification (“RFID”) tag,
preload a reply code of said RFID tag,
produce a synthetic reference code from said reply code and said amplitude, phase, and delay information, and
correlate a reply including at least a portion of said reply code from said RFID tag with said synthetic reference code to produce a decision signal; and
a decision subsystem operable with said processor and configured to compare said decision signal against a threshold to verify a presence of said RFID tag.
2. The control and processing system as recited in claim 1 wherein said preloaded reply code comprises preamble bits and said reply comprises said preamble bits of said reply code.
3. The control and processing system as recited in claim 1 wherein said decision subsystem is further configured to employ said decision signal to uniquely identify said RFID tag.
4. The control and processing system as recited in claim 1 wherein preloaded said reply code comprises an entire reply code of said RFID tag.
5. The control and processing system as recited in claim 1 wherein said reply code is preloaded into said correlation subsystem by scanning said RFID tag during an initialization stage.
6. The control and processing system as recited in claim 1 wherein said correlation subsystem comprises multiple correlators configured to correlate at least one of multiple phases and delay information of said reply with at least one of multiple phases and delay information of said synthetic reference code to produce said decision signal.
7. The control and processing system as recited in claim 1 wherein said correlation subsystem comprises:
a correlator configured to correlate said reply including at least two bits of said reply code with at least two bits of said synthetic reference code to derive a correlation triangle;
a correlation threshold sensor configured to compare said correlation triangle to a threshold level to derive a pulse to ascertain a peak of said correlation triangle; and
a summer configured to average a plurality of pulses from said correlation threshold sensor to produce said decision signal.
8. The control and processing system as recited in claim 1 wherein correlation of said reply with said synthetic reference code is configured to increase a sensitivity of said correlation subsystem.
9. The control and processing system as recited in claim 1 wherein a plurality of antennas are employed to obtain additional gain from diversity for said reply.
10. The control and processing system as recited in claim 1 wherein said synthetic reference code is a spreading code.
11. A method, comprising:
preloading amplitude, phase, and delay information corresponding to a logical “0” and a logical “1” associated with a radio frequency identification (“RFID”) tag;
preloading a reply code of said RFID tag;
producing a synthetic reference code from said reply code and said amplitude, phase, and delay information;
correlating a reply including at least a portion of said reply code from said RFID tag with said synthetic reference code to produce a decision signal; and
comparing said decision signal against a threshold to verify a presence of said RFID tag.
12. The method as recited in claim 11 wherein said preloaded reply code comprises preamble bits and said reply comprises said preamble bits of said reply code.
13. The method as recited in claim 11 wherein said comparing comprises employing said decision signal to uniquely identify said RFID tag.
14. The method as recited in claim 11 wherein said preloaded reply code comprises an entire reply code of said RFID tag.
15. The method as recited in claim 11 wherein said preloading said reply code comprises scanning said RFID tag during an initialization stage.
16. The method as recited in claim 11 wherein said correlating comprises correlating at least one of multiple phases and delay information of said reply with at least one of multiple phases and delay information of said synthetic reference code to produce said decision signal.
17. The method as recited in claim 11 wherein said correlating comprises:
correlating said reply including at least two bits of said reply code with at least two bits of said synthetic reference code to derive a correlation triangle;
comparing said correlation triangle to a threshold level to derive a pulse to ascertain a peak of said correlation triangle; and
averaging a plurality of pulses from said comparing to produce said decision signal.
18. The method as recited in claim 11 wherein said correlating said reply with said synthetic reference code increases a sensitivity thereof.
19. The method as recited in claim 11 further comprising obtaining additional gain from diversity for said reply.
20. The method as recited in claim 11 wherein said synthetic reference code is a spreading code.