CORRECTING FREQUENCY ERRORS IN FREQUENCY DIFFERENCE OF ARRIVAL GEOLOCATION SYSTEMS

• US 20140104108A1
• Filed: 10/15/2013
• Published: 04/17/2014
• Est. Priority Date: 10/15/2012
• Status: Active Grant

• Current Assignee: Zeta Associates, Inc. (Martin Marietta Corporation)
• Original Assignee: Zeta Associates, Inc. (Martin Marietta Corporation)
• Inventors: Holford, John M., Williams, James M., Glidewell, Michael E.
• Granted Patent: US 9,797,987 B2
• Time in Patent Office: Days
• US Class Current: 342/385
• CPC Class Codes: G01S 1/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 19/38 Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/02213 Receivers arranged in a network for determining the position of a transmitter
• CPC Class Codes: G01S 5/0246 involving frequency difference of arrival or Doppler measurements G01S5/02685 takes precedence
• CPC Class Codes: G01S 5/0249 Determining position using measurements made by a non-stationary device other than the device whose position is being determined
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence

Abstract

A frequency correction for frequency difference of arrival geolocation of transmitted target signals may be provided. A frequency of a target signal may be determined at a first collector based upon a first reference timebase source. A frequency of the target signal may be determined at a second collector based upon a second reference timebase source. An observed frequency of a reference carrier signal based upon the first reference timebase source may be determined at the second collector based upon the second reference timebase source. A relative timebase error between the first collector and the second collector may be calculated based upon a difference between the intended frequency of the reference carrier signal and the observed frequency of the reference carrier signal. A corrected frequency difference for the target signal may be calculated based upon the relative timebase error and a proportional scaling factor.

Claims

1. A computer-implemented method comprising:

determining a frequency of a target signal at a first collector based upon, at least in part, a first reference timebase source associated with the first collector;

determining an intended frequency of a reference carrier signal at the first collector based upon, at least in part, the first reference timebase source associated with the first collector;

determining a frequency of the target signal at a second collector based upon, at least in part, a second reference timebase source associated with the second collector;

determining an observed frequency of the reference carrier signal at the second collector based upon, at least in part, the second reference timebase source associated with the second collector;

calculating a relative timebase error between the first collector and the second collector based upon, at least in part, a difference between the intended frequency of the reference carrier signal and the observed frequency of the reference carrier signal; and

calculating a corrected frequency difference for the target signal based upon, at least in part, the relative timebase error and a proportional scaling factor.

2. The computer-implemented method of claim 1, wherein determining the intended frequency of the reference carrier signal includes transmitting the reference carrier signal having the intended frequency based upon, at least in part, the first reference timebase source.

3. The computer-implemented method of claim 1, wherein determining the frequency of the target signal at the first collector includes receiving data based upon, at least in part, a digitized representation of the target signal from the first collector.

4. The computer-implemented method of claim 3, wherein receiving the data based upon, at least in part, the digitized representation of target signal includes receiving the digitized representation modulated onto the reference carrier signal.

5. The computer-implemented method of claim 1, wherein determining the intended frequency of the reference carrier signal is based upon, at least in part, determining a predetermined intended frequency of the reference carrier signal.

6. The computer-implemented method of claim 1, wherein determining the intended frequency of the reference carrier signal includes:

receiving the reference carrier signal; and

determining the frequency of the received reference carrier signal based upon, at least in part, the first reference timebase source.

7. The computer-implemented method of claim 6, wherein receiving the reference carrier signal includes receiving the reference carrier signal at the first collector.

8. The computer-implemented method of claim 1, wherein the first collector is moving relative to a source of the target signal, the method further including:

determining a first state vector associated with the first collector, the first state vector including position and velocity information associated with the first collector;

determining a relative movement between the first collector and the second collector based upon, at least in part, the first state vector; and

wherein calculating the relative timebase error includes compensating for a frequency shift based upon, at least in part, the relative movement between the first collector and the second collector.

9. The computer-implemented method of claim 8, wherein the second collector is moving relative to the source of the target signal, the method further including:

determining a second state vector associated with the second collector, the second state vector including position and velocity information associated with the second collector;

wherein determining the relative movement between the first collector and the second collector is based upon, at least in part the first state vector and the second state vector; and

wherein calculating the relative timebase error includes compensating for the frequency shift based upon, at least in part, the relative movement between the first collector and the second collector.

10. The computer-implemented method of claim 1, further comprising geolocating a source of the target signal based upon, at least in part, calculated time difference of arrival and frequency difference of arrival of the target signal at the first collector and at the second collector and based upon, at least in part, the calculated corrected frequency difference for the target signal.

11. A computer program product comprising a computer readable medium having a plurality of instructions stored thereon, which, when executed by a processor, cause the processor to perform operations including:

determining a frequency of a target signal at a first collector based upon, at least in part, a first reference timebase source associated with the first collector;

determining an intended frequency of a reference carrier signal at the first collector based upon, at least in part, the first reference timebase source associated with the first collector;

determining a frequency of the target signal at a second collector based upon, at least in part, a second reference timebase source associated with the second collector;

determining an observed frequency of the reference carrier signal at the second collector based upon, at least in part, the second reference timebase source associated with the second collector;

calculating a relative timebase error between the first collector and the second collector based upon, at least in part, a difference between the intended frequency of the reference carrier signal and the observed frequency of the reference carrier signal; and

calculating a corrected frequency difference for the target signal based upon, at least in part, the relative timebase error and a proportional scaling factor.

12. The computer program product of claim 11, wherein the instructions for determining the intended frequency of the reference carrier signal include instructions for transmitting the reference carrier signal having the intended frequency based upon, at least in part, the first reference timebase source.

13. The computer program product of claim 11, wherein the instructions for determining the frequency of the target signal at the first collector include instructions for receiving data based upon, at least in part, a digitized representation of the target signal from the first collector.

14. The computer program product of claim 13, wherein the instructions for receiving the data based upon, at least in part, the digitized representation of target signal include instructions for receiving the digitized representation modulated onto the reference carrier signal.

15. The computer program product of claim 11, wherein determining the intended frequency of the reference carrier signal is based upon, at least in part, determining a predetermined intended frequency of the reference carrier signal.

16. The computer program product of claim 11, wherein the instructions for determining the intended frequency of the reference carrier signal include instructions for:

receiving the reference carrier signal; and

determining the frequency of the received reference carrier signal based upon, at least in part, the first reference timebase source.

17. The computer program product of claim 16, wherein the instructions for receiving the reference carrier signal include instructions for receiving the reference carrier signal at the first collector.

18. The computer program product of claim 11, wherein the first collector is moving relative to a source of the target signal, and further including instructions for:

determining a first state vector associated with the first collector, the first state vector including position and velocity information associated with the first collector;

determining a relative movement between the first collector and the second collector based upon, at least in part, the first state vector; and

wherein calculating the relative timebase error includes compensating for a frequency shift based upon, at least in part, the relative movement between the first collector and the second collector.

19. The computer program product of claim 18, wherein the second collector is moving relative to the source of the target signal, and further including instructions for:

determining a second state vector associated with the second collector, the second state vector including position and velocity information associated with the second collector;

wherein determining the relative movement between the first collector and the second collector is based upon, at least in part the first state vector and the second state vector; and

wherein calculating the relative timebase error includes compensating for the frequency shift based upon, at least in part, the relative movement between the first collector and the second collector.

20. The computer program product of claim 11, further comprising instructions for geolocating a source of the target signal based upon, at least in part, calculated time difference of arrival and frequency difference of arrival of the target signal at the first collector and at the second collector and based upon, at least in part, the calculated corrected frequency difference for the target signal.

21. A computing system comprising:

a processor and a memory module coupled with the processor, the processor being configured for;

determining a frequency of a target signal at a first collector based upon, at least in part, a first reference timebase source associated with the first collector;

determining an intended frequency of a reference carrier signal at the first collector based upon, at least in part, the first reference timebase source associated with the first collector;

determining a frequency of the target signal at a second collector based upon, at least in part, a second reference timebase source associated with the second collector;

determining an observed frequency of the reference carrier signal at the second collector based upon, at least in part, the second reference timebase source associated with the second collector;

calculating a relative timebase error between the first collector and the second collector based upon, at least in part, a difference between the intended frequency of the reference carrier signal and the observed frequency of the reference carrier signal; and

calculating a corrected frequency difference for the target signal based upon, at least in part, the relative timebase error and a proportional scaling factor.

22. The computing system of claim 21, wherein determining the intended frequency of the reference carrier signal includes transmitting the reference carrier signal having the intended frequency based upon, at least in part, the first reference timebase source.

23. The computing system of claim 21, wherein determining the frequency of the target signal at the first collector includes receiving data based upon, at least in part, a digitized representation of the target signal from the first collector.

24. The computing system of claim 23, wherein receiving the data based upon, at least in part, the digitized representation of target signal includes receiving the digitized representation modulated onto the reference carrier signal.

25. The computing system of claim 21, wherein determining the intended frequency of the reference carrier signal is based upon, at least in part, determining a predetermined intended frequency of the reference carrier signal.

26. The computing system of claim 21, wherein determining the intended frequency of the reference carrier signal includes:

receiving the reference carrier signal; and

determining the frequency of the received reference carrier signal based upon, at least in part, the first reference timebase source.

27. The computing system of claim 26, wherein receiving the reference carrier signal includes receiving the reference carrier signal at the first collector.

28. The computing system of claim 21, wherein the first collector is moving relative to a source of the target signal, the processor and memory module further configured for:

determining a first state vector associated with the first collector, the first state vector including position and velocity information associated with the first collector;

determining a relative movement between the first collector and the second collector based upon, at least in part, the first state vector; and

wherein calculating the relative timebase error includes compensating for a frequency shift based upon, at least in part, the relative movement between the first collector and the second collector.

29. The computing system of claim 28, wherein the second collector is moving relative to the source of the target signal, the processor and memory module further configured for:

determining a second state vector associated with the second collector, the second state vector including position and velocity information associated with the second collector;

wherein determining the relative movement between the first collector and the second collector is based upon, at least in part the first state vector and the second state vector; and

wherein calculating the relative timebase error includes compensating for the frequency shift based upon, at least in part, the relative movement between the first collector and the second collector.

30. The computing system of claim 21, the processor and memory module further configured for geolocating a source of the target signal based upon, at least in part, calculated time difference of arrival and frequency difference of arrival of the target signal at the first collector and at the second collector and based upon, at least in part, the calculated corrected frequency difference for the target signal.