Frequency difference of arrival (FDOA) for geolocation

Patent metadata

Field	Value
Publication number	US-9702960-B2
Application number	US-201313946217-A
Country	US
Kind code	B2
Filing date	Jul 19, 2013
Priority date	Mar 15, 2013
Publication date	Jul 11, 2017
Grant date	Jul 11, 2017

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.

First claim

What is claimed is:

1. A method for determining a frequency difference of arrival (FDOA) with respect to a pulsed waveform comprising a plurality of pulses received from a remote emitter by two spaced apart sensors located on a same moveable platform, the method comprising:
(a) obtaining, by a multichannel receiver, and for each sensor, a respective plurality of a number (m) of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform taken over a sampling period T s ;
(b) determining, by a time difference of arrival (TDOA) detector, an approximation of a leading edge time difference of arrival (LE_TDOA) responsive to the plurality of (m) IQ samples and as a function of a leading edge of a common sampled pulse of the received pulsed waveform;
(c) obtaining, by a cross correlator, and for each pulse of the plurality of pulses, a first complex cross correlation of IQ samples at a first delay (d c ) closest to the approximation of the LE_TDOA, and respective second and third complex cross correlations at a second delay (d c +1) and a third delay (d c −1), respectively, on either side of the first delay (d c ), where the first delay (d c )=(LE_TDOA/T s ), rounded to the nearest whole sample estimate of LE_TDOA;
(d) refining, by the TDOA detector, for each pulse of the plurality of pulses, the approximation of the LE_TDOA according to an interpolation of amplitudes of the first complex cross-correlation;
(e) determining, by a phase processor, for each pulse of the plurality of pulses, a respective rate of change (dΔφ/dt) of a cross-correlation phase (Δφ);
(f) approximating, by a frequency difference of arrival (FDOA) processor, a straight line fit to the rates of change of cross-correlation phase (dΔφ/dt) determined for the plurality of pulses, wherein a slope of the straight line is the FDOA;
(g) receiving, at a navigation system, navigation information indicative of a velocity and relative bearing of the moveable platform; and
(h) determining, by a geolocation processor, a geolocation of the remote emitter as a function of the received navigation information and the determined FDOA.

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

3. The method of claim 1 , wherein the interpolation of amplitudes of the first complex cross-correlation for each pulse comprises:
fitting a parabola to amplitudes of the first, second and third complex 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 , wherein obtaining for each sensor, a respective plurality of IQ samples comprises:
downconverting, at the multichannel receiver, the received pulsed waveform; and
coherently detecting the pulse envelope of the downconverted pulsed waveform.

7. The method of claim 1 , further comprising repeating (a) through (h) for a subsequent plurality of received pulses.

8. A system for determining a frequency difference of arrival (FDOA) with respect to a pulsed waveform comprising a plurality of pulses emanating from a remote emitter, comprising:
at least two spaced apart sensors disposed on a same moveable platform, each of the at least two sensors configured to receive the pulsed waveform from the remote emitter;
a multichannel receiver having a respective receiver channel in communication with each of the at least two sensors, the multichannel receiver configured to provide a respective plurality of a number (m) of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform taken over a sampling period T s ;
a time difference of arrival (TDOA) detector configured to determine an approximation of a leading edge time difference of arrival (LE_TDOA) responsive to the plurality of m IQ samples and as a function of a leading edge of a common sampled pulse of the received 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 first delay (d c ) closest to the approximation of the LE_TDOA, and respective second and third complex cross correlations a second delay (d c +1) and a third delay (d c −1), respectively, on either side of the first delay (d c ), where the first delay (d c )=(LE_TDOA/T s ), rounded to the nearest whole sample estimate of LE_TDOA;
a phase processing module, in communication with the cross correlator, configured to determine for each pulse of the plurality of pulses, a respective rate of change (dΔφ/dt) of a cross-correlation phase (Δφ);
an FDOA processing module, in communication with the phase processing module, configured to determine the FDOA as a slope of a straight line approximation of the rates of change of cross-correlation phase (dΔφ/dt) determined for the plurality of pulses;
a navigation system configured to provide updated estimates of at least a velocity and a relative bearing of the mobile platform; and
a geolocation processing module, in communication with the FDOA processing module and the navigation system, configured to determine an estimate of a geolocation of the remote emitter.

9. The system of claim 8 , further comprising a buffer, in communication with the multichannel receiver, configured to store at least IQ samples obtained from each of the respective channels for at least some of the plurality of pulses.

10. The system of claim 8 , wherein the moveable platform is selected from the group consisting of: an aircraft; a ship; a missile; and a spacecraft.

11. The system of claim 8 , wherein the at least two spaced apart sensors are adapted to detect electromagnetic radiation.

12. The system of claim 8 , wherein the remote emitter is a radar source.

13. A system for determining a frequency difference of arrival (FDOA) with respect to a pulsed waveform comprising a plurality of pulses received from a remote emitter by two spaced apart sensors located on a same moveable platform, comprising:
means for obtaining for each sensor, a respective plurality of a number (m) of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform taken over a sampling period T s ;
means for determining an approximation of a leading edge time difference of arrival (LE_TDOA) responsive to the plurality of (m) IQ samples and as a function of 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 complex cross correlation of IQ samples at a first delay (d c ) closest to the approximation of the LE_TDOA, and respective second and third complex cross correlations at a second delay (d c +1) and a third delay (d c −1), respectively, on either side of the first delay (d c ), where the first delay (d c )=(LE_TDOA/T s ), rounded to the nearest whole sample estimate of LE_TDOA;
means for refining for each pulse of the plurality of pulses, the approximation of the LE_TDOA according to an interpolation of amplitudes of the first complex cross-correlation;
means for determining for each pulse of the plurality of pulses, a respective rate of change (dΔφ/dt) of a cross-correlation phase (Δφ);
means for determining a FDOA as a slope of a straight line approximation of the rates of change of cross-correlation phase (dΔφ/dt) determined for the plurality of pulses;
means for providing

Assignees

• Raytheon Co

Inventors

• Broad John T
• Savage Lee M

Classifications

• G01S5/0249

  Determining position using measurements made by a non-stationary device other than the device whose position is being determined · CPC title

• G01S5/12

  by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial · CPC title

• G01S3/50 Primary

  the waves arriving at the antennas being pulse modulated and the time difference of their arrival being measured · CPC title

• G01S5/06 Primary

  Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements (G01S5/12 takes precedence) · CPC title

• G01S7/021

  Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals · CPC title