Patent ID: 9599703
Date: 2017-03-21
CPC Classifications: G01S,G06K,G08G

Claim:
1. A method of determining a range rate of a vehicle-mounted backscatter transponder in a roadway using an automatic vehicle identification system, the system including an antenna defining a coverage area for communicating with the backscatter transponder, the range rate being a rate of change of a distance between the transponder and the antenna, the method comprising: transmitting, via the antenna, a continuous wave signal having a carrier frequency; receiving a modulated reflected response signal from the transponder, wherein the modulation is at a modulation frequency; converting the modulated reflected response signal to a downconverted signal by mixing the modulated reflected response signal with the carrier frequency; bandpass filtering the downconverted signal to pass a bandpass filtered signal containing at least the modulation frequency; applying a non-linear amplitude transfer function to the bandpass filtered signal to remove modulation and produce a modulation-suppressed signal; measuring the frequency of the modulation-suppressed signal; and determining the range rate based upon a Doppler shift corresponding to the measured frequency of the modulation-suppressed signal.