Method and apparatus for determining changing signal frequency

• US 7,222,035 B1
• Filed: 11/17/2004
• Issued: 05/22/2007
• Est. Priority Date: 11/17/2004
• Status: Active Grant

• Current Assignee: Topcon GPS, LLC
• Original Assignee: Topcon GPS, LLC
• Inventors: Zhodzishsky, Mark I., Veitsel, Victor A., Yudanov, Sergey, Prasolov, Victor A.
• Primary Examiner(s): Hoff; Marc S.
• Assistant Examiner(s): Desta; Elias
• Application Number:
  US10/990,605
• Time in Patent Office: 916 Days
• Field of Search: 702/75, 702/125, 702/176, 702/177, 702/149, 702/69, 324/76.44, 324/76.39, 324/76.52, 324/76.29, 324/76.53, 324/76.17, 386/50
• US Class Current: 702/75
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/254 relating to Doppler shift of satellite signals
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain

Abstract

A method and apparatus for estimating the changing frequency of a signal received by a satellite receiver from, illustratively, positioning system satellites is disclosed that enables a more accurate measurement of the change in frequency of that signal due to movement of the satellite receiver relative to those satellites. The system includes a PLL having a numerically controlled oscillator (NCO) and a filter of frequency estimates (FFE). In operation, an analog signal is received at the satellite receiver and the PLL tracks the changing signal frequency and outputs non-smoothed frequency estimates into the FFE. The FFE then smoothes noise in the signal to produce a more accurate smoothed frequency estimate of the input signal. Comparing multiple estimates over time allows Doppler shift of the signal frequency received by the satellite receiver to be calculated more precisely, thus resulting in more accurate satellite receiver velocity vector determinations and, hence, position measurements.

Claims

1. A method of estimating the frequency of a signal, said method comprising:

receiving an analog signal characterized in part by a frequency;

generating in a phase locked loop a non-smoothed estimate of said frequency;

providing said non-smoothed estimate of said frequency to a filter of frequency estimates comprising a plurality of reactive elements; and

generating from said filter of frequency of estimates a smoothed estimate of said frequency.

2. The method of claim 1 wherein the step of generating in a phase locked loop comprises:

converting an analog signal into a digital signal;

providing said digital signal to a phase discriminator;

generating a phase difference signal which is a function of a phase difference between the phase of said digital signal and the phase of a reference signal generated by an oscillator;

providing said phase difference signal to an first instantaneous element having a first constant transfer coefficient; and

providing said phase difference signal to a first integrating block.

3. The method of claim 2 wherein said first integrating block comprises a second instantaneous element having a second constant transfer coefficient, said method further comprising:

providing said phase difference signal to said second instantaneous element; and

providing an output of said second instantaneous element to said accumulator,

wherein the output of said accumulator comprises the output of said first integrating block.

4. The method of claim 2 wherein said integrating block comprises a second instantaneous element having a second constant transfer coefficient, a third instantaneous element having a third constant transfer coefficient, a first accumulator, a second accumulator and an adder, both of said instantaneous elements comprising constant transfer coefficients, said method further comprising:

providing said phase difference signal into said second instantaneous element;

providing said phase difference signal into said third instantaneous element;

providing the output of said third instantaneous element into said second accumulator;

providing the output of said second accumulator into said adder;

providing the output of said second instantaneous element into said adder;

adding the output of said second instantaneous element and the output of said second accumulator; and

providing the output of said adder into said first accumulator,

wherein the output of said first accumulator comprises the output of said integrating block.

5. The method of claim 2 further comprising:

adding the output of said first instantaneous element to the output of said

first integrating block to generate an added signal; and

providing said added signal into said oscillator.

6. The method of claim 2 further comprising:

providing into said oscillator a frequency signal generated by said integrating block; and

providing into said oscillator a phase signal generated by said first instantaneous element.

7. The method of claim 5 wherein the said added signal comprises an unsmoothed input signal frequency estimate.

8. The method of claim 5 wherein the output of said first integrating block comprises an unsmoothed input signal frequency estimate.

9. The method of claim 6 wherein said frequency signal comprises an unsmoothed input signal frequency estimate.

10. The method of claim 6 further comprising:

multiplying said phase signal φ

_NCO by a coefficient h, φ

_NCO is an estimated phase obtained from the phase difference generated by said phase discriminator;

said coefficient h defined by the equation;

$h=\frac{{\mathrm{\Delta <br><br>\Phi <br><br>}}_{\mathrm{NCO}}}{2<br><br>\mathrm{\pi <br><br>}*T_r*{\mathrm{\Delta <br><br>F}}_{\mathrm{NCO}}}$

wherein Δ

Φ

_NCO is the change over discrete time T_r of a phase of said oscillator;

φ

_NCO is an estimated phase obtained from the phase difference generated by said phase discriminator; and

Δ

F_NCO is the change over discrete time T_r of the frequency of said oscillator; and

adding said frequency signal to said phase signal to generate an unsmoothed input signal frequency estimate.

11. The method of claim 1, further comprises:

providing a non-smoothed estimate of said frequency into a difference element of said filter of frequency estimates.

12. The method of claim 11 further comprising:

providing the output of said difference element into an instantaneous element;

providing the output of said difference element into an integrating block;

providing the output of said instantaneous element and the output of said integrating block into an adder;

providing the output of said adder into an accumulator; and

providing the output of said accumulator into said difference element.

13. The method of claim 12 wherein the output of said accumulator comprises a first output of said filter of frequency estimates.

14. The method of claim 12 wherein the output of said integrating block comprises a second output of said filter of frequency estimates.

15. The method of claim 11 further comprising:

providing the output of said difference element into an accumulator;

providing the output of said accumulator into an integrating block;

providing the output of said accumulator into an instantaneous element;

providing the output of said instantaneous element and the output of said integrating block into an adder; and

providing the output of said adder into said difference element.

16. The method of claim 15 wherein the output of said adder comprises a first output of said filter of frequency estimates.

17. The method of claim 15 wherein the output of said integrating block comprises a second output of said filter of frequency estimates.

18. Apparatus for use in producing a smoothed estimate of the frequency of an input signal, said apparatus comprising:

a phase locked loop adapted to generate a nonsmoothed frequency estimate of a received radio signal; and

a filter of frequency estimates comprising a plurality of reactive elements adapted to receive said nonsmoothed estimate and to generate a smoothed frequency estimate of said received radio signal.

19. The apparatus of claim 18 wherein said phase locked loop further comprises:

an oscillator for generating a reference signal;

a phase discriminator adapted to generate an estimate of the difference between a phase of said reference signal and a phase of a received radio frequency signal;

a first instantaneous element connected to at least a first output of said phase discriminator;

a first integrating block connected to said at least a first output of said phase discriminator;

a first adder for adding the output of said first instantaneous element to the output of said first integrating block; and

a second adder for adding the output of said first adder to the output of said first instantaneous element.

20. The apparatus of claim 19 wherein said filter of frequency estimates is adapted to selectively receive at least one of the output of said first integrating block or the output of said second adder.

21. The apparatus of claim 20 wherein said filter of frequency estimates comprises:

a difference element;

a second instantaneous element;

a second integrating block;

a third adder; and

an accumulator.

22. The apparatus of claim 21 wherein said filter of frequency estimates further comprises:

a first output comprising at least a first output of said accumulator; and

a second output comprising at least a first output of said second integrating block.

23. The circuit of claim 21 wherein said filter of frequency estimates further comprises:

a first output comprising at least a first output of said difference element; and

a second output comprising at least a first output of said second integrating block.