High accuracy angle of arrival estimation using estimated range to target node

Patent metadata

Field	Value
Publication number	US-2020011956-A1
Application number	US-201916555623-A
Country	US
Kind code	A1
Filing date	Aug 29, 2019
Priority date	Oct 18, 2017
Publication date	Jan 9, 2020
Grant date	—

Abstract

An angle of arrival system can be self-calibrating. The angle of arrival system can continuously estimate imperfections caused by the analog RF components and dynamically apply corrections based on these estimates. As a result, an angle of arrival system can employ inexpensive components, will not require factory calibration, but can still perform geolocation with high precision.

First claim

What is claimed:

1 . A method, performed by an angle of arrival node in an angle of arrival system, for estimating an angle of arrival of a signal emitted by a node at an unknown location, the method comprising:
receiving, at each of a plurality of antennas of an antenna array, a first signal emitted by a calibration node having a known location relative to the antenna array, the antennas being coupled to a modem via an RF chain; generating, by the modem, a first covariance matrix representing phase differences of the first signal received at each of the antennas; based on the known location of the calibration node, calculating a correction matrix that represents phase rotation caused by the RF chain; receiving, at each of the plurality of antennas of the antenna array, a second signal emitted by a node at an unknown location; generating, by the modem, a second covariance matrix representing phase differences of the second signal received at each of the antennas; applying the correction matrix to the second covariance matrix to generate a corrected second covariance matrix, the correction matrix at least partially removing the phase rotation caused by the RF chain; correlating the corrected second covariance matrix with a steering vector for each angle of interest, the steering vector including an estimated range from the antenna array to the node at the unknown location, wherein the angle of interest that corresponds to the largest correlation between the corrected second covariance matrix and the steering vector is chosen to be the estimated angle of arrival.

2 . The method of claim 1 , wherein calculating the correction matrix comprises:
calculating a first component of the first covariance matrix that represents phase differences caused by a known angle of arrival of the first signal; and applying the first component to the first covariance matrix to produce a second component of the first covariance matrix that represents the phase rotation caused by the RF chain.

3 . The method of claim 2 , wherein applying the first component to the first covariance matrix comprises performing an element by element product of the first covariance matrix and the conjugate of the first component.

4 . The method of claim 2 , wherein the first component is calculated using a known position of each antenna in the antenna array and the known location of the calibration node.

5 . The method of claim 2 , wherein calculating the correction matrix further comprises:
creating a vector from a first column of the second component; normalizing each element in the vector; multiplying the normalized vector with the conjugate transpose of the normalized vector; and conjugating the results of the multiplication.

6 . The method of claim 1 , further comprising:
receiving input that defines the known location of the calibration node.

7 . The method of claim 1 , wherein the known location of the calibration node is relative to a boresight vector of the antenna array.

8 . The method of claim 7 , wherein the known location comprises an elevation angle and an azimuth angle relative to the boresight vector of the antenna array.

9 . The method of claim 1 , further comprising:
updating the correction matrix to reflect a change in the phase rotation caused by the RF chain; and applying the updated correction matrix to another covariance matrix that is generated to represent phase differences of the second signal received at a later time at each of the antennas.

10 . The method of claim 1 , wherein the first signal is repeatedly received and the correction matrix is repeatedly updated to reflect updates to the first covariance matrix that occur as a result of changes in the phase rotation caused by the RF chain.

11 . The method of claim 1 , wherein the steering vector for each angle of interest is calculated in a time period before the second signal is received.

12 . The method of claim 1 , wherein the steering vector for each angle of interest is calculated in the same time period as the second signal is received.

13 . The method of claim 1 , wherein the node at the unknown location comprises an aircraft, a vehicle, a projectile, or an individual.

14 . An angle of arrival system comprising:
an angle of arrival node that includes an antenna array, a modem, and an RF chain that couples each antenna of the antenna array to the modem; and a calibration node that is configured to emit a calibration signal for reception by the antenna array; wherein the angle of arrival node is configured to: generate, based on a known location of the calibration node and the received calibration signal, a correction matrix that represents phase rotation caused by the RF chain; calculate a covariance matrix for a signal received from a node at an unknown location and to apply the correction matrix to the covariance matrix to remove the phase rotation caused by the RF chain; and correlate the corrected covariance matrix with a steering vector for each angle of interest, the steering vector including an estimated range from the antenna array to the node at the unknown location, wherein the angle of interest that corresponds to the largest correlation between the corrected second covariance matrix and the steering vector is chosen to be the estimated angle of arrival.

15 . The angle of arrival system of claim 14 , wherein the angle of arrival node
generates the correction matrix by: generating a calibration covariance matrix representing phase differences of the calibration signal received at each of the antennas; calculating a first component of the calibration covariance matrix that represents phase differences caused by a known angle of arrival of the first signal; and applying the first component to the calibration covariance matrix to produce a second component of the calibration covariance matrix that represents the phase rotation caused by the RF chain.

16 . The angle of arrival system of claim 14 , wherein the angle of arrival node generates the correction matrix by:
creating a vector from a first column of the second component; normalizing each element in the vector; multiplying the normalized vector with the conjugate transpose of the normalized vector; and conjugating the results of the multiplication.

17 . The angle of arrival system of claim 14 , wherein the correction matrix is repeatedly generated to reflect a current phase rotation caused by the RF chain.

18 . The angle of arrival system of claim 14 , wherein the modem is configured to receive the known location of the calibration node as input.

19 . A method, performed by an angle of arrival node in an angle of arrival system, for estimating an angle of arrival of a signal emitted by a node at an unknown location, the method comprising:
repeatedly receiving, at each of a plurality of antennas of an antenna array, a first signal emitted by a calibration node having a known location relative to the antenna array, the antennas being coupled to a modem via an RF chain; repeatedly generating, by the modem, a first covariance matrix representing phase differences of the first signal received at each of the antennas; based on the known location of the calibration node, repeatedly calculating a correction matrix that represents a current phase rotation caused by the RF chain; receiving, at each of the plurality of antennas of the antenna array, a second signal emitted by a node at an unknown location; generating, by the modem, a second covariance matrix

Assignees

• L3 Tech Inc

Inventors

• Zarubica Radivoje
• Thomson Larry S
• Shen Bing
• Reimschussel Cory A

Classifications

• G01S3/023 Primary

  Monitoring or calibrating · CPC title

• G01S3/46 Primary

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

• G01S3/12

  Means for determining sense of direction, e.g. by combining signals from directional antenna or goniometer search coil with those from non-directional antenna (determining direction by amplitude comparison of signals derived by combining directional and non-directional signals G01S3/24, G01S3/34) · CPC title