Object location system and method using RFID

An object location system for locating an object having an RFID tag, the object location system comprising:

• an RFID reader, the RFID reader transmitting at least three transmitted signals to the RFID tag and receiving at least three backscatter modulated signals from the RFID tag, wherein at least two of the at least three transmitted signals have a different fundamental frequency;
• and
• a distance calculator, the distance calculator determining a phase for each of the at least three backscatter modulated signals from the RFID tag, the distance calculator determining a distance to the RFID tag 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.

An object location system for locating objects having RFID tags, the object location system comprising:

• an array of RFID readers distributed around an area, each of the array of RFID readers transmitting at least three transmitted signals to an RFID tag and receiving at least three backscatter modulated signals from the RFID tag, wherein the at least three transmitted signals from each RFID reader have a fundamental frequency with a randomly selected 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.