FREQUENCY DIFFERENCE OF ARRIVAL (FDOA) FOR GEOLOCATION

• US 20140278214A1
• Filed: 07/19/2013
• Published: 09/18/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Savage, Lee M., Broad, John T.
• Granted Patent: US 9,702,960 B2
• Time in Patent Office: Days
• US Class Current: 702/150
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 3/50 the waves arriving at the antennas being pulse modulated and the time difference of their arrival being measured
• 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
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• CPC Class Codes: G01S 7/021 Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals

Abstract

A method for determining a FDOA of a pulsed waveform received by two sensors includes obtaining a respective plurality of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform. The method includes determining a TDOA responsive to a leading edge of a pulse of the pulsed waveform and obtaining a first cross correlation of IQ samples at a delay (d_c) closest to the TDOA, and respective second and third cross correlations at least one additional delay (d_c+1 and d_c−1) on either side of the closest delay. The method includes refining the approximation of the TDOA according to an interpolation of amplitudes of the cross-correlation and determining a respective rate of change of cross-correlation phase (Δφ). The method includes approximating a straight line fit to the rates of change of cross-correlation phase (dΔφ/dt), the slope of the straight line representative of the FDOA.

Claims

1. A method for determining a frequency difference of arrival (FDOA) with respect to a pulsed waveform received from a remote source by two spaced apart sensors located on a moveable platform, the method comprising:

(a) obtaining for each sensor, a respective plurality of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform, the pulsed waveform comprising a plurality of pulses;

(b) determining an approximation of a time difference of arrival (TDOA) responsive to a leading edge of a common sampled pulse of the pulsed waveform;

(c) obtaining for each pulse of the plurality of pulses, a first cross correlation of IQ samples at a delay (d_c) closest to the approximation of the TDOA, and respective second and third cross correlations at least one additional delay (d_c+1 and d_c−

1) on either side of the closest delay;

(d) refining for each pulse of the plurality of pulses, the approximation of the TDOA according to an interpolation of amplitudes of the cross-correlation;

(e) determining for each pulse of the plurality of pulses, a respective rate of change of cross-correlation phase (Δ

φ

); and

(f) approximating a straight line fit to the rates of change of cross-correlation phase (dΔ

φ

/dt) determined for the plurality of pulses, the slope of the straight line representative of the FDOA.

2. The method of claim 1, wherein approximating the straight line comprises determining a least mean squared error.

3. The method of claim 1, wherein interpolation of amplitudes of the cross-correlation for each pulse comprises:

fitting a parabola to amplitudes of the first, second and third cross correlations; and

identifying a delay (d_m) corresponding to an apex of the parabola.

4. The method of claim 1, wherein the pulsed waveform comprises electromagnetic radiation.

5. The method of claim 1, wherein the moveable platform is selected from the group consisting of:

an aircraft;

a ship;

a missile; and

a spacecraft.

6. The method of claim 1, further comprising:

receiving navigation information indicative of a velocity and relative bearing of the moveable platform; and

determining a geolocation of the emitter responsive to the received navigation information and the FDOA.

7. The method of claim 1, wherein obtaining for each sensor, a respective plurality of IQ samples comprises:

receiving at each sensor the pulsed waveform;

downconverting the received pulsed waveform; and

coherently detecting the pulse envelope of the pulsed waveform.

8. The method of claim 1, further comprising repeating (a) through (f) for a subsequent plurality of pulses.

9. The method of claim 1, further comprising determining the delay (d_c) closest to the approximation of the TDOA by rounding the determined approximation to the TDOA.

10. A system for determining a frequency difference of arrival (FDOA) with respect to a pulsed waveform emanating from a remote emitter, comprising:

at least two spaced apart sensors disposed on a moveable platform, each of the at least two sensors adapted to receive the pulsed waveform from the remote emitter;

a respective receiver channel in communication with each of the at least two sensors, the respective receiver channel configured to provide a respective plurality of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform, the pulsed waveform comprising a plurality of pulses;

a time difference of arrival (TDOA) detector configured to determine an approximation of a TDOA responsive to IQ samples indicative of a leading edge of a common sampled pulse of the pulsed waveform;

a cross correlator configured to obtain for each pulse of the plurality of pulses, a first complex cross correlation of IQ samples at a delay (d_c) closest to the approximation of the TDOA, and respective second and third complex cross correlations at least one additional delay (d_c+1 and d_c−

1) on either side of the closest delay;

a phase processing module in communication with the cross correlator, the phase processor configured to determine for each pulse of the plurality of pulses, a respective rate of change of cross-correlation phase (Δ

φ

); and

a FDOA processing module in communication with the phase processing module, configured to determine FDOA as a slope of a straight line approximation of the rates of change of cross-correlation phase (dΔ

φ

/dt) determined for the plurality of pulses.

11. The system of claim 10, wherein the respective receiver channels are individual channels of a multichannel receiver.

12. The system of claim 10, further comprising a buffer adapted for respectively storing at least IQ samples obtained from each of the respective channels for at least some of the plurality of pulses.

13. The system of claim 10, wherein the moveable platform is selected from the group consisting of:

an aircraft;

a ship;

a missile; and

a spacecraft.

14. The system of claim 10, wherein the at least two spaced apart sensors are adapted to detect electromagnetic radiation.

15. The system of claim 10, wherein the remote emitter is a radar source.

16. The system of claim 10, further comprising a navigation system configured to provide updated estimates of at least velocity and relative bearing of the mobile platform.

17. The system of claim 16, further comprising a geolocation processing module in communication with the FDOA processing module and the navigation system, the geolocation processing module configured to determine an estimate of a geolocation of the remote emitter.

18. A system for determining a frequency difference of arrival (FDOA) with respect to a pulsed waveform received from a remote source by two spaced apart sensors located on a moveable platform, comprising:

means for obtaining for each sensor, a respective plurality of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform, the pulsed waveform comprising a plurality of pulses;

means for determining an approximation of a time difference of arrival (TDOA) responsive to a leading edge of a common sampled pulse of the pulsed waveform;

means for obtaining for each pulse of the plurality of pulses, a first cross correlation of IQ samples at a delay (d_c) closest to the approximation of the TDOA, and respective second and third cross correlations at least one additional delay (d_c+1 and d_c−

1) on either side of the closest delay;

means for refining for each pulse of the plurality of pulses, the approximation of the TDOA according to an interpolation of amplitudes of the cross-correlation;

means for determining for each pulse of the plurality of pulses, a respective rate of change of cross-correlation phase (Δ

φ

); and

means for determining a FDOA as a slope of a straight line approximation of the rates of change of cross-correlation phase (dΔ

φ

/dt) determined for the plurality of pulses.