Traffic sensor and method for providing a stabilized signal

• US 7,474,259 B2
• Filed: 09/13/2005
• Issued: 01/06/2009
• Est. Priority Date: 09/13/2005
• Status: Active Grant

• Current Assignee: Sensys Networks Inc. (Tagmaster AB)
• Original Assignee: EIS Electronic Integrated Systems
• Inventors: Manor, Dan
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Brainard; Timothy A
• Application Number:
  US11/223,982
• Publication Number:
  US 20070236365A1
• Time in Patent Office: 1,211 Days
• Field of Search: 342/174
• US Class Current: 342/174
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 13/91 for traffic control G01S13/93 takes precedence
• CPC Class Codes: G01S 7/35 Details of non-pulse systems
• CPC Class Codes: G01S 7/4004 of parts of a radar system
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors
• CPC Class Codes: H03L 7/06 using a reference signal applied to a frequency- or phase-locked loop

Abstract

A traffic sensor is mounted at a fixed location to monitor multiple lanes of traffic. The traffic sensor (a) generates a programmable time-varying modulating signal; (b) generates a modulated microwave signal based on the programmable time-varying modulating signal; (c) radiates the modulated microwave signal in a radiation beam at an object; (d) provides a proportional calibration signal based on the modulated microwave signal; (e) measures parameters of the calibration signal, and (f) corrects the programmable time-varying modulating signal based on the parameters of the calibration signal.

Claims

1. A vehicular traffic sensor for mounting at a fixed location to monitor multiple lanes of traffic, the vehicular traffic sensor comprising:

a processor unit for generating a programmable time-varying frequency modulating signal;

a transceiver unit for receiving the programmable time-varying frequency modulating signal from the processor unit and for generating a linear frequency modulated microwave signal based on the programmable time-varying frequency modulating signal;

at least one antenna for (i) receiving the linear frequency modulated microwave signal from the transceiver unit, (ii) forming a radiation beam, (iii) radiating the linear frequency modulated microwave signal in the radiation beam at an object; and

, (iv) receiving the modulated microwave signal reflected back from the object; and

a signal stabilizing unit for receiving a portion of the linear frequency modulated microwave signal from the transceiver unit and for providing a proportional calibration signal back to the processor;

wherein the processor unit is further operable to (i) receive the calibration signal from the signal stabilizing unit, (ii) measure frequency parameters of the calibration signal, and (iii) correct the programmable time-varying frequency modulating signal based on the frequency parameters of the calibration signal to increase the linearity of the modulated microwave signal; and

the processor comprises a curve-fitting module for determining an inverse non-linear function from the frequency parameters of the calibration signal, the processor unit being operable to generate the programmable time-varying frequency modulating signal based on the inverse non-linear function to compensate for distortion introduced by the transceiver unit.

2. The traffic sensor as defined in claim 1 wherein

the processor further comprises a memory for storing an ordered sequence of numbers calculated using the inverse non-linear function, and a DAC for generating the time-varying modulating signal as a time-ordered sequence of voltages determined based on the ordered sequence of numbers, and

the transceiver comprises a voltage controlled oscillator for generating the modulated microwave signal based on the programmable time-varying frequency modulating signal generated by the DAC.

3. The traffic sensor as defined in claim 2 wherein the voltage controlled oscillator is a voltage tunable dielectric resonator oscillator.

4. The traffic sensor as defined in claim 2 wherein the curve-fitting module comprises (i) a frequency-measurement counter circuit for measuring the calibration signal frequency at three frequency levels resulting from setting the programmable time-varying modulating signal at three different signal levels, (ii) calculating from the three frequency levels the inverse non-linear function required and (iii) generating the sequence of numbers based on the inverse non-linear function.

5. The traffic sensor as defined in claim 2 wherein the memory comprises a dual port memory having a pair of independent memory components wherein one memory component is operable to provide the ordered sequence of numbers to the DAC while a new ordered sequence of numbers for a new inverse non-linear function is being stored on the other memory component.

6. The traffic sensor as defined in claim 1 wherein the processor further comprises a re-calibration timing module for determining when to re-calibrate the inverse non-linear function.

7. The traffic sensor as defined in claim 1 wherein the signal stabilizing unit comprises (i) an oscillator for generating a reference-locked signal, the oscillator being phase-locked to a clock signal, and (ii) a down converter unit for generating the calibration signal at a difference frequency between the reference-locked signal and the microwave transceiver signal.

8. The traffic sensor as defined in claim 1 wherein the signal stabilizing unit comprises a frequency divider circuit for generating the calibration signal at a frequency proportional to the frequency of the microwave transceiver signal.

9. The traffic sensor as defined in claim 1 wherein the signal stabilizing unit comprises a frequency reduction module for reducing a calibration signal frequency prior to measuring the parameters of the calibration signal.

10. The traffic sensor as defined in claim 9 wherein the frequency reduction module comprises at least one of (i) a frequency divider circuit for generating a frequency proportional to the frequency of the microwave transceiver signal, and (ii) a down-converter to lower the calibration signal frequency.

11. The traffic sensor as defined in claim 1 wherein the curve-fitting module comprises (i) a frequency-measurement counter circuit for measuring the calibration signal frequency at three frequency levels resulting from setting the programmable time-varying modulating signal at three different signal levels, and (ii) calculating from the three frequency levels the inverse non-linear function required.

12. A method of operating a traffic sensor for mounting at a fixed location to monitor multiple lanes of traffic, the method comprising:

(a) generating a programmable time-varying frequency modulating signal;

(b) generating a linear frequency modulated microwave signal based on the programmable time-varying frequency modulating signal;

(c) radiating the linear frequency modulated microwave signal in a radiation beam at an object;

(d) providing a proportional calibration signal based on the linear frequency modulated microwave signal;

(e) measuring frequency parameters of the calibration signal, and

(f) correcting the programmable time-varying frequency modulating signal based on the frequency parameters of the calibration signal to increase the linearity of the linear frequency modulated microwave signal;

wherein

step (f) further comprises determining and periodically updating an inverse non-linear function from the frequency parameters of the calibration signal, and

step (a) comprises generating the programmable time-varying frequency modulating signal based on the inverse non-linear function to compensate for distortion introduced in step (b).

13. The method as defined in claim 12 wherein step (a) comprises storing an ordered sequence of numbers calculated using the inverse non-linear function, and generating the time-varying modulating signal as a time-ordered sequence of voltages determined based on the ordered sequence of numbers.

14. The method as defined in claim 13 wherein the traffic sensor comprises a dual port memory for storing the ordered sequence of numbers calculated using the inverse non-linear function, the dual port memory having a pair of memory components, the method further comprising

providing the ordered sequence of numbers from one memory component to generate the time-varying modulating signal;

and concurrently, storing a new ordered sequence of numbers for a new inverse non-linear function on the other memory component.

15. The method as defined in claim 12 wherein step (e) comprises reducing a calibration signal frequency prior to measuring the frequency parameters of the calibration signal.

16. The method as defined in claim 12 further comprising switching between a normal operation mode and a calibration mode, wherein step (f) occurs during the calibration mode.

17. The method as defined in claim 16 wherein, during the calibration mode,

step (a) comprises setting the programmable time-varying frequency modulating signal at three different signal levels;

step (e) comprises measuring the calibration signal frequency at three frequency levels resulting from setting the programmable time-varying modulating signal at the three different signal levels;

step (f) comprises calculating the inverse non-linear function from the three frequency levels.

18. The method as defined in claim 12 wherein, during the calibration mode,

step (a) comprises setting the programmable time-varying frequency modulating signal at three different signal levels;

step (e) comprises measuring the calibration signal frequency at three frequency levels resulting from setting the programmable time-varying modulating signal at the three different signal levels;

step (f) comprises calculating the inverse non-linear function from the three frequency levels.