US-12627394-B1 - Angle-of-arrival open-loop frequency-hopping communication system

Abstract

A method and apparatus are provided for directional communication systems in tactical environments, utilizing frequency-hopping signals to enhance low-probability-of-intercept, -detection, and -geolocation (LPI/LPD/LPG) performance; along with anti-jamming (AJ) performance, multiple access, and performance in multipath channels. Because frequency-hopping signals vary their radio frequency from dwell-to-dwell, this prevents conventional angle-of-arrival (AOA) estimation based on phase-differences. This disclosure presents a technique for AOA estimation for frequency-hopping signals with techniques for combining phase-difference measurements from multiple frequency-hopping dwells to achieve high-performance AOA estimation.

Inventors

• Carlos J. Chavez

Assignees

• ROCKWELL COLLINS, INC.

Dates

Publication Date

20260512

Application Date

20230929

Claims (18)

1. 1 . A system comprising: a directional aperture having at least two co-located apertures configured to receive at least one frequency-hopping signal from at least one transmitting source, wherein frequencies of each said frequency-hopping signal change among a range of frequencies within a set of frequency-hopping signals, each of said frequency-hopping signals within said set having a frequency dwell; at least one signal detector configured to: detect a phase-difference between phases-of-arrival from dwells received at said co-located apertures from said transmitting source of a plurality of said dwells; and generate a signal quality metric for said plurality of said dwells; and a processor configured to: receive said phase-difference and said signal quality metric for said plurality of dwells; generate a normalized phase-difference for each dwell by multiplying each said phase-difference by a normalization factor; convert each said normalized phase-difference into a unit vector; generate a quality weighted vector by multiplying each said unit vector by said signal quality metric associated with each said dwell; and generate a vector sum as a summation of each said quality weighted vector from each dwell; wherein a magnitude of the vector sum is associated with a combined quality metric and a phase of the vector sum associated with a combined-phase difference.
2. 2 . The system of claim 1 , wherein said signal quality metric is generated by at least one of a measure of signal to noise, a measure of signal power to total power, or a signal amplitude.
3. 3 . The system of claim 1 , wherein said normalization factor is a ratio of a reference frequency and a single frequency associated with said dwell.
4. 4 . The system of claim 3 , wherein said combined phase-difference and said reference frequency are used to estimate an angle-of-arrival of said at least one frequency-hopping signal.
5. 5 . The system of claim 4 , wherein said reference frequency is one within said range of frequencies for said frequency-hopping signals.
6. 6 . The system of claim 1 , wherein said co-located apertures are sub-apertures of an aperture system.
7. 7 . The system of claim 1 , wherein said combined quality metric and said combined phase-difference are inputs to further processing.
8. 8 . The system of claim 7 , wherein said further processing comprises one of a Kalman filter closed-loop tracking solution.
9. 9 . A system comprising: an aperture having at least two co-located sub-apertures configured to receive at least one frequency-hopping signal from at least one transmitting source, wherein frequencies of each said frequency-hopping signal change among a range of frequencies within a set of frequency-hopping signals, each of said frequency-hopping signals within said set having a frequency dwell; at least one signal detector configured to: detect a phase-difference between phases-of-arrival from dwells received at said aperture from said transmitting source of a plurality of said dwells; and generate a signal-to-noise ratio for said plurality of said dwells; and a processor configured to: receive said phase-difference and said signal-to-noise ratio for said plurality of said dwells; generate a normalized phase-difference for said plurality of said dwells by multiplying each said phase-difference by a normalization factor, wherein said normalization factor is a ratio of a reference frequency and a single frequency associated with said dwell; convert each said normalized phase-difference into a unit vector; generate a quality weighted vector by multiplying each said unit vector by said signal-to-noise ratio associated with each said dwell; and generate a vector sum as a summation of each said quality weighted vector from each dwell; wherein a magnitude of the vector sum is associated with a combined quality metric and a phase of the vector sum associated with a combined phase-difference.
10. 10 . The system of claim 9 , wherein said combined phase-difference and said reference frequency are used to estimate an angle-of-arrival of said at least one frequency-hopping signal.
11. 11 . The system of claim 9 , wherein said reference frequency is one within said range of frequencies for said frequency-hopping signals.
12. 12 . The system of claim 9 , wherein said co-located apertures are sub-apertures of an aperture system.
13. 13 . The system of claim 9 , wherein said combined quality metric and said combined phase-difference are inputs to further processing.
14. 14 . The system of claim 13 , wherein said further processing comprises one of a Kalman filter closed-loop tracking solution.
15. 15 . A method for determining an angle-of-arrival, comprising: receiving via a signal detector associated with a directional aperture having at least a pair of co-located apertures or sub-apertures a phase-difference between phases-of-arrival for a plurality of dwells from a frequency-hopping signal; generating a normalized phase-difference for said plurality of dwells by multiplying each said phase-difference by a normalization factor; converting each said normalized phase-difference into a unit vector; generating a quality weighted vector by multiplying each said unit vector by a quality metric associated with each said dwells; and generating a vector sum as a summation of each said quality weighted vector from said plurality of said dwells, wherein a magnitude of the vector sum is associated with a combined quality metric and a phase of the vector sum associated with a combined phase difference.
16. 16 . The method of claim 15 , wherein said normalization factor is a ratio of a reference frequency and a single frequency associated with said dwell.
17. 17 . The method of claim 16 , wherein said combined phase-difference and said reference frequency are used to estimate angle-of-arrival.
18. 18 . The method of claim 17 , wherein said reference frequency is one within a range of frequencies for the frequency-hopping signals.

Description

FIELD This disclosure is related broadly to communication system performance, and, more particularly, to method and apparatus for measuring and correcting errors in aperture pointing without the benefit of GNSS or other navigation systems. BACKGROUND Directional apertures offer enhanced communication system performance, including increased communication range, increased data rate, spatial rejection of interference, and spatial control of emissions. To realize these benefits, a directional communication system must point the aperture (whether mechanically or electronically) in the desired direction. Global satellite navigation systems (GNSS), along with attitude information, enable open-loop aperture pointing. However, GNSS may be unavailable or unreliable in many situations (e.g., urban canyon or electronically contested environments). Angle-of-arrival (AOA) estimation offers a means to measure the error in aperture pointing for feedback into a closed-loop tracking solution (such as a Kalman filter) in the absence of GNSS or other navigation systems. For directional communication systems in tactical environments, frequency-hopping signals further enhance low-probability-of-intercept, -detection, and -geolocation (LPI/LPD/LPG) performance, anti-jamming (AJ) performance, multiple access, and performance in multipath channels. Because frequency-hopping signals vary their radio frequency from dwell to dwell, this presents a challenge for conventional AOA estimation based on phase-differences. SUMMARY The present disclosure teaches the utilization of combined phase-difference measurements from multiple frequency-hopping dwells to achieve high-performance angle-of-arrival estimation by, for example: (1) Normalizing phase-difference measurements to a common reference frequency; (2) Forming complex vectors from the normalized phase-difference measurements; and (3) Weighting the phase-difference unit vector from each dwell by its corresponding metric. Additionally, the present disclosure teaches methods and apparatus providing high-performance angle-of-arrival estimation for frequency-hopping signals by, for example: (1) Allowing measurements from disparate frequencies to be combined in kind; (2) Allowing phase-difference measurements to be combined while implicitly handling the fact that angles are defined on a circular interval; and (3) Optimizing performance by emphasizing measurements with high quality and de-emphasizing measurements with low quality. Directional apertures offer enhanced communication system performance, including increased communication range, increased data rate, spatial rejection of interference, and spatial control of emissions. To realize these benefits, a directional communication system must point the aperture (whether mechanically or electronically) in the desired direction. Global satellite navigation systems (GNSS), along with attitude information, enable open-loop aperture pointing. However, GNSS may be unavailable or unreliable in many situations (e.g., urban canyon or electronically contested environments). Angle-of-arrival (AOA) estimation offers a means to measure the error in aperture pointing for feedback into a closed-loop tracking solution (such as a Kalman filter) in the absence of GNSS or other navigation systems. From prior art, the phase-difference φ as measured between two apertures (or sub-apertures of an aperture) can be used to estimate the angle-of-arrival θ in the aperture frame, given the distance d between apertures, the radio frequency f of the received signal, and the speed of radio frequency propagation c. θ=arcsin⁡(c2⁢π⁢fd⁢ϕ) For directional communication systems in tactical environments, frequency-hopping signals further enhance low-probability-of-intercept, -detection, and -geolocation (LPI/LPD/LPG) performance, anti-jamming (AJ) performance, multiple access, and performance in multipath channels. Because frequency-hopping signals vary their radio frequency from dwell to dwell, this presents a challenge for conventional AOA estimation based on phase-differences. This disclosure presents a technique for AOA estimation for frequency-hopping signals. This technique combines phase-difference measurements from multiple frequency-hopping dwells to achieve high-performance AOA estimation. This Summary is provided solely as an introduction to subject matter that is fully described in the Detailed Description and Drawings. The Summary should not be considered to describe essential features nor be used to determine the scope of the Claims. Moreover, it is to be understood that both the foregoing Summary and the following Detailed Description are examples and explanatory only and are not necessarily restrictive of the subject matter claimed. BRIEF DESCRIPTION OF THE DRAWINGS The detailed description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar