Multi-resolution object location system and method

A method of locating an object having an RFID tag, the method comprising the steps of:

• determining a general location of the object using at least one transmission from the object;
• transmitting a plurality of transmitted signals from an RFID reader to the RFID tag, the plurality of transmitted signals having a fundamental frequency difference;
• receiving a plurality of backscatter-modulated signals from the RFID tag;
• determining a phase for each of the plurality of backscatter-modulated signals;
• and
• computing a distance to the RFID tag by determining a rate of change of the phase in the plurality of backscatter-modulated signals with respect to a rate of change in the fundamental frequency of the plurality of transmitted signals.

An object location system for locating an object, the object location system comprising:

• an object locator, the object locator receiving at least one transmission from a multi-mode RFID tag operating in an active mode on the object, the object locator determining a general location of the object from the at least one transmission from the multi-mode RFID tag;
• an array of RFID readers distributed around an area, a plurality of the array of RFID readers transmitting at least three transmitted signals to the multi-mode RFID tag, the plurality of the array of readers selected from the array of RFID readers based on the general location of the object, each of the plurality of the array of RFID readers receiving at least three backscatter-modulated signals from the multi-mode RFID tag, wherein the at least three transmitted signals from each RFID reader have a fundamental frequency with a fundamental frequency difference;
• and
• a distance calculator, the distance calculator determining a phase of the at least three backscatter-modulated signals received at each RFID reader, the distance calculator determining a distance from each RFID reader by performing a linear trend fit of the phase in the at least three backscatter-modulated signals and the fundamental frequency of the at least three transmitted signals to determine a rate of change of the phase with respect to a rate of change of the fundamental frequency.