Methods and systems for determining a range rate for a backscatter transponder

Patent metadata

Field	Value
Publication number	US-9599703-B2
Application number	US-201414456589-A
Country	US
Kind code	B2
Filing date	Aug 11, 2014
Priority date	Aug 26, 2013
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

Methods for determining a range rate of a backscatter transponder and readers implementing the methods are described. The reader transmits a continuous wave signal and receives a modulated reflected response signal from the transponder, mixes the modulated reflected response signal with the carrier frequency to produce a downconverted signal, bandpass filters the downconverted signal to pass a bandpass filtered signal containing at least the modulation frequency, applies a non-linear amplitude transfer function to produce a modulation-suppressed signal, and measures the frequency of the modulation-suppressed signal and determines the range rate from the measured frequency.

First claim

What is claimed is:

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.

2. The method claimed in claim 1 , wherein the modulation comprises either bipolar phase modulation or bipolar amplitude modulation.

3. The method claimed in claim 2 , wherein the modulation comprises on-off keying.

4. The method claimed in claim 1 , wherein the bandpass filter has a low cut-off that passes the modulation frequency and attenuates the downconverted carrier frequency, and a high cut-off that is below the carrier frequency.

5. The method claimed in claim 1 , wherein the non-linear amplitude transfer function comprises a square function, and applying the non-linear amplitude transfer function comprises squaring the bandpass filtered signal.

6. The method claimed in claim 1 , wherein the non-linear amplitude transfer function comprises an absolute magnitude function, and applying the non-linear amplitude transfer function comprises discarding the polarity of the bandpass filtered signal.

7. The method claimed in claim 1 , wherein measuring the frequency includes detecting zero-crossings of the modulation-suppressed signal.

8. The method claimed in claim 1 , wherein measuring the frequency includes detecting amplitude minima of the modulation-suppressed signal.

9. A reader for determining a range rate of a vehicle-mounted backscatter transponder in a roadway, the reader comprising:
a transmitter to generate a continuous wave signal having a carrier frequency;
an antenna to transmit the continuous wave signal and to receive a modulated reflected response signal from the transponder, wherein the modulation is at a modulation frequency, and wherein the range rate is a rate of change of a distance between the transponder and the antenna;
a mixer to mix the modulated reflected response signal with the carrier frequency to produce a downconverted signal;
a bandpass filter to filter the downconverted signal to pass a bandpass filtered signal containing at least the modulation frequency;
a non-linear amplitude transfer function to produce a modulation-suppressed signal when the function is applied to the bandpass filtered signal to remove modulation; and
a frequency measurer to measure the frequency of the modulation-suppressed signal and to determine the range rate from the measured frequency.

10. The reader claimed in claim 9 , wherein the modulation comprises either bipolar phase modulation or bipolar amplitude modulation.

11. The reader claimed in claim 10 , wherein the modulation comprises on-off keying.

12. The reader claimed in claim 9 , wherein the bandpass filter has a low cut-off that passes the modulation frequency and attenuates the downconverted carrier frequency, and a high cut-off that is below the carrier frequency.

13. The reader claimed in claim 9 , wherein the non-linear amplitude transfer function comprises a square function to square the bandpass filtered signal.

14. The reader claimed in claim 9 , wherein the non-linear amplitude transfer function comprises an absolute magnitude function that discards the polarity of the bandpass filtered signal.

15. The reader claimed in claim 9 , wherein the frequency measurer is configured to detect zero-crossings of the modulation-suppressed signal.

16. The reader claimed in claim 9 , wherein the frequency measurer is configured to detect amplitude minima of the modulation-suppressed signal.

17. A non-transitory computer-readable medium storing processor-executable instructions which, when executed, cause a processor to carry out the method claimed in claim 1 .

Assignees

• Kapsch Trafficcom Ag

Inventors

• Vinski Lila
• Kohli Japjeev
• Malarky Alastair

Classifications

• G06K7/10207 Primary

  parameter settings related to power consumption of the interrogator · CPC title

• G01S13/82

  wherein continuous-type signals are transmitted · CPC title

• G08G1/052

  with provision for determining speed or overspeed {(speed measuring in general G01P)} · CPC title

• G01S13/92

  for velocity measurement · CPC title

• G01S13/583 Primary

  using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets · CPC title