Systems and methods for RFID tag locating using constructive interference
A system and method for locating radio-frequency identification tags within a predetermined area. The method can incorporate sub-threshold superposition response mapping techniques, alone, or in combination with other methods for locating radio-frequency identification tags such as but not limited to time differential on arrival (TDOA), frequency domain phase difference on arrival (FD-PDOA), and radio signal strength indication (RSSI). The system can include a plurality of antennas dispersed in a predefined area; one or more radio-frequency identification tags; a radio-frequency transceiver in communication with said antennas; a phase modulator coupled to the ra-dio-frequency transceiver; and a system controller in communication with said transceiver and said phase modulator. Calibration techniques can be employed to map con-structive interference zones for improved accuracy.
1. A method for locating a radio-frequency identification tag, comprising:
estimating coordinates at which a transmitted signal power of a plurality of antennas rises above an activation threshold of the radio-frequency identification tag;
modulating a transmission power of the plurality of antennas based on the estimating;
transmitting an initial activation signal at the modulated transmission power from the plurality of antennas;
receiving a first response signal from the radio-frequency identification tag by the plurality of antennas;
analyzing the first response signal received by the plurality of antennas from the radio-frequency identification tag; and
estimating a position of the radio-frequency identification tag based upon said analyzing.
2. The method of claim 1 , wherein transmitting the initial activation signal comprises transmitting by a selected antenna selected from among the plurality of antennas.
3. The method of claim 1 , wherein analyzing the first response signal comprises:
altering a transmission signal property of the initial activation signal;
transmitting a secondary activation signal with the altered signal property; and
receiving a second response signal from the radio-frequency identification tag via the plurality of the antennas.
4. The method of claim 3 , wherein altering the transmission signal property of the initial activation signal comprises adjusting a power level of the secondary activation signal such that only the radio-frequency identification tag transmits the secondary response signal.
5. The method of claim 1 , wherein the coordinates are determined based on historical data.
6. The method of claim 1 , wherein said estimating comprises modeling a permittivity of a volume of interest at said coordinates.
7. The method of claim 1 , wherein the coordinates are generated as a function of a calibration reference disposed on a movable object.
8. The method of claim 1 , wherein the coordinates are determined based on a stored map of one or more areas where the transmission power is above the activation threshold.
9. A system for locating a radio-frequency identification tag, the system comprising:
a plurality of antennas configured to transmit a signal; and
a controller operably coupled to the plurality of antennas and configured to:
estimate coordinates at which a transmitted signal power of the plurality of antennas rises above an activation threshold of radio-frequency identification tag;
modulate a transmission power of the plurality of antennas based on the coordinates; and
estimate a position of the radio-frequency identification tag by analyzing a first response signal received by the plurality of antennas in response to the signal.
10. The system of claim 9 , wherein the controller is further configured to:
estimate the coordinates based on historical data.
11. A method for locating a radio-frequency identification tag, the method comprising:
transmitting a first activation signal from at least one antenna of a plurality of antennas;
receiving a first response to the first activation signal from the radio-frequency identification tag by the plurality of antennas;
determining a position of the radio-frequency identification tag at a first accuracy based on the first response;
transmitting second and third activation signals, each of the second and third activation signals having a signal strength different than a signal strength of the first activation signal; and
determining the position of the radio-frequency identification tag at a second accuracy higher than the first accuracy based upon the second and third activation signals.
12. The method of claim 11 , wherein the second and third activation signals are transmitted simultaneously.
13. The method of claim 11 , wherein the second and third signals are transmitted at a power determined based on historical location data.
14. The method of claim 11 , wherein the second and third signals are transmitted at a signal strength determined based on a stored map of one or more areas where the signal strength is above an activation threshold.
15. The method of claim 14 , wherein the stored map comprises an angle of orientation of an antenna in the plurality of antennas.
16. The method of claim 14 , wherein the stored map comprises a radiation pattern of the plurality of antennas.
17. The method of claim 11 , wherein each of the second and third activation signals has a signal strength below a signal strength of the first activation signal.
18. A system for locating a radio-frequency identification tag, the system comprising:
a plurality of antennas; and
a controller operably coupled to the plurality of antennas and configured to:
determine a position of the radio-frequency identification tag at a first accuracy based on a first signal transmitted a first power higher than a power threshold; and
determine a position of the radio-frequency identification tag at a second accuracy higher than the first accuracy based on second and third signals transmitted at transmission powers lower than the power threshold.
19. The system of claim 18 , wherein the controller is further configured to select the power threshold based on historical data.
20. The system of claim 18 , wherein the controller is further configured to select the power threshold based on a stored map of one or more areas where the first power is above the power threshold.