Patent ID: 8742975

Claim:
A method for measuring distance between a modulated backscatter target and a reader, the target having at least two backscatter reflection states; the method mitigating detrimental effects of noise clutter and multi-path signals, comprising the steps of: transmitting a first radar signal during a first backscatter reflection state of the target; transmitting a second radar signal during a second backscatter reflection state of the target; receiving a first reflected radar signal from the target during said first backscatter reflection state of the target; receiving a second reflected radar signal from the target during said second backscatter reflection state of the target; compressing said first and second reflected radar signals using a signal compression process; subtracting said compressed first reflected radar signal from said compressed second reflected radar signal to produce a difference signal having a peak; determining round trip time delay to the modulated backscatter target from the time of said peak; and calculating the distance based on said round trip time delay.