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

• US 9,599,703 B2
• Filed: 08/11/2014
• Issued: 03/21/2017
• Est. Priority Date: 08/26/2013
• Status: Active Grant

• Current Assignee: Kapsch TrafficCom AG (Datax Handelsgmbh)
• Original Assignee: Kapsch TrafficCom AG (Datax Handelsgmbh)
• Inventors: Vinski, Lila, Kohli, Japjeev, Malarky, Alastair
• Primary Examiner(s): BYTHROW, PETER M
• Application Number:
  US14/456,589
• Publication Number:
  US 20150054675A1
• Time in Patent Office: 953 Days
• Field of Search: 342/42, 342/51, 342 70- 72, 342/104, 342/115, 342/175
• US Class Current: 1/1
• CPC Class Codes: G01S 13/583 using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets
• CPC Class Codes: G01S 13/74 Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
• CPC Class Codes: G01S 13/75 using transponders powered from received waves, e.g. using passive transponders , or using passive reflectors
• CPC Class Codes: G01S 13/82 wherein continuous-type signals are transmitted
• CPC Class Codes: G01S 13/92 for velocity measurement
• CPC Class Codes: G06K 7/10207 parameter settings related to power consumption of the interrogator
• CPC Class Codes: G06K 7/10366 the interrogation device being adapted for miscellaneous applications
• CPC Class Codes: G06K 7/10425 the interrogation device being arranged for interrogation of record carriers passing by the interrogation device
• CPC Class Codes: G08G 1/052 with provision for determining speed or overspeed speed measuring in general G01P

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.

Claims

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.

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.

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.