Interferometric time delay of arrival

Patent metadata

Field	Value
Publication number	US-10422847-B2
Application number	US-201715492694-A
Country	US
Kind code	B2
Filing date	Apr 20, 2017
Priority date	Apr 20, 2017
Publication date	Sep 24, 2019
Grant date	Sep 24, 2019

Abstract

Systems and methods for determining an angle of arrival (AoA) of a signal received from an emitters at a pair of antennas spaced apart by more than one half wavelength of the received signal. Features of the signal are determined, including a phase difference between signal components detected at the antennas, and a time difference of arrival (TDOA) having a known measurement error. A set of TDOA possibilities bounded by the known TDOA measurement error and a set of AoA estimates using phase interferometry (PI) within the range are calculated. The TDOA set is iteratively reduced to determine a precise AoA estimate for the emitter.

First claim

What is claimed is:

1. A method for determining an angle of arrival (AoA) of one or more RF signals received from an emitter at an antenna pair, comprising:
receiving at a processor corresponding first and second components of a first signal detected at first and second antenna elements of the antenna pair, the antenna elements spaced apart by more than one half wavelength of the received signal components;
determining one or more features of the received signal, including a phase difference between corresponding phases of the first and second signal components detected at the first and second antenna elements, and a time difference of arrival (TDOA) between the signal components arriving at the first and second antenna elements, the TDOA having a known measurement uncertainty or error range;
performing a TDOA angle calculation using the TDOA to obtain a TDOA error boundary comprising a range of TDOA AoA possibilities centered at a solution to the TDOA angle calculation and bounded by the known TDOA measurement error range;
calculating a set of AoA estimates using phase interferometry (PI) based on the phase difference of the first and second signal components measured at the first and second antenna elements, and within the TDOA AoA error boundary; and
determining a precise AoA estimate by iteratively performing the steps of receiving signal components at the first and second antenna elements, determining the received signal component features, averaging the TDOA measurements, using the averaged TDOA measurements to re-compute the TDOA AoA error boundary with smaller error bounds, and, optionally, averaging the signal component phase differences and re-calculating the PI AoA estimate for one or more additional signals associated with the emitter.

2. The method of claim 1 , further comprising:
if the set of PI AoA estimates contains only one AoA estimate within the TDOA AoA error boundary, reporting that AoA estimate as the precise AoA estimate.

3. The method of claim 1 , further comprising reporting as the precise AoA estimate the PI AoA estimates remaining within the TDOA AoA error boundary.

4. The method of claim 3 , further comprising:
calculating a probability weight for each remaining PI AoA estimate; and
reporting the calculated probability weights associated with the PI AoA estimates.

5. The method of claim 1 , wherein determining the precise AoA estimate further comprises:
determining whether a frequency of the one or more additional signals associated with the emitter differs from a frequency of the first signal;
if the frequency of the one or more additional signals differs from the frequency of the first signal, reporting as the precise AoA estimate the common PI AoA estimate associated with the first signal and the one or more additional signals within the TDOA AoA error boundary; and
if the frequency of the one or more additional signals does not differ from the frequency of the first signal, disassociating PI AoA estimates no longer within the TDOA AoA error boundary with smaller error bounds, until the set of PI AoA estimates has been reduced such that a probability of the PI AoA estimates remaining in the set being the correct AoA achieves a predetermined threshold, and reporting the acceptably reduced set of PI AoA estimates.

6. The method of claim 1 , wherein prior to averaging the TDOA measurements, the initial TDOA AoA error boundary is reduced to extend only across the angles spanned by the PI AoA estimates included within the TDOA AoA error boundary.

7. The method of claim 5 , further comprising, if the frequency of the one or more additional signals does not differ from the frequency of the detected first signal, monitoring the TDOA measurement error and spacing of the PI AoA estimates to determine when a sufficient number of additional signals have been collected to achieve the predetermined probability threshold.

8. The method of claim 5 , wherein additional signals are collected for tens of microseconds to milliseconds.

9. The method of claim 1 , wherein the first signal and one or more additional signals are pulsed signals.

10. The method of claim 1 , wherein:
the first and second antenna elements comprise directional antennas having known gain patterns and have peak gain in different directions; and
adjusting the TDOA AoA error boundary based on an amplitude comparison calculation using the first and second signal components of the first signal and the one or more additional signals.

11. A system for determining an angle of arrival (AoA) of one or more RF signals received from an RF emitter at an antenna pair, comprising:
an antenna pair for detecting first and second components of a first signal at corresponding first and second antenna elements spaced apart by more than one half wavelength of the detected first signal;
one or more signal processors in communication with the antenna pair to receive the first and second components, and configured to:
determine one or more features of the received signal, including a phase difference between corresponding phases of the first and second signal components detected at the first and second antenna elements, and a time difference of arrival (TDOA) between the signal components arriving at the first and second antenna elements, the TDOA having a known measurement uncertainty or error range;
perform a TDOA angle calculation using the TDOA to obtain a TDOA AoA error boundary centered at a solution to the TDOA angle calculation and bounded by the known TDOA measurement error range;
calculate a set of AoA estimates using phase interferometry (PI) based on the phase difference of the first and second signal components measured at the first and second antenna elements, and within the TDOA AoA error boundary; and
determine a precise AoA estimate by iteratively performing the steps of receiving signal components at the first and second antenna elements, determining the received signal component features, averaging the TDOA measurements, using the averaged TDOA measurements to re-compute the TDOA AoA error boundary with smaller error bounds, and, optionally, averaging the signal component phase differences and re-calculating the PI AoA estimate for one or more additional signals associated with the emitter.

12. The system of claim 11 , wherein the one or more processor is further configured to report as the precise AoA estimate the PI AoA estimates remaining within the TDOA AoA error boundary.

13. The system of claim 12 , wherein the one or more processors is further configured to:
calculate a probability weight for each remaining PI AoA estimate; and
report the calculated probability weights associated with the PI AoA estimate(s).

14. The system of claim 11 , wherein the one or more processor is further configured, if the set of PI AoA estimates contains only one AoA estimate, report that AoA estimate as the precise AoA estimate.

15. The system of claim 11 , wherein the one or more processors is further configured to determine the precise AoA estimate by
determining whether a frequency of the one or more additional signals associated with the emitter differs from a frequency of the first signal;
if the frequency of the one or more additional signals differs from the frequency of the first signal, reporting as the precise AoA estimate the PI AoA estimate associated with the first signal and the one or more additional signals; and
if the frequency of the one or more additional signals does not differ from the frequency of the first signal, disassociating PI AoA estimates no longer within the TDOA AoA error boundary with smaller err

Assignees

• Raytheon Co

Inventors

• Robinson Ian S
• Flanders Bradley A
• Kilfoyle Daniel

Classifications

• G01S3/46 Primary

  using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems · CPC title

• G01S3/48 Primary

  the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured · CPC title

• G01S3/465

  the waves arriving at the aerials being frequency modulated and the frequency difference of signals therefrom being measured · CPC title

• G01S3/50

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