Determination of Integrity of Incoming Signals of Satellite Navigation System

• US 20150116147A1
• Filed: 10/31/2013
• Published: 04/30/2015
• Est. Priority Date: 10/31/2013
• Status: Active Grant

• Current Assignee: UHU Technologies, LLC
• Original Assignee: Southwest Research Institute
• Inventors: Jaeckle, Thomas H.
• Granted Patent: US 10,162,060 B2
• Time in Patent Office: Days
• US Class Current: 342/357.59
• CPC Class Codes: G01S 19/015 Arrangements for jamming, spoofing or other methods of denial of service of such systems
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/215 issues related to spoofing

Abstract

A system and method for testing the integrity of signals incoming to a satellite navigation system. The method is implemented with an array of antenna elements, and a receiver connected to each antenna element. The receivers simultaneously and continuously make measurements on all tracked signals. Each receiver measures the carrier phase of an incoming signal. Based on the carrier phase differences between antenna elements and the distance between them, the azimuth and elevation of the signal source can be calculated. This measured angle of arrival can then be compared to an expected angle of arrival to determine if the signal source is legitimate. The system and method can be also applied to determining the angle of arrival of sources of interference, and to mitigating the effects of both illegitimate and interfering signals.

Claims

1. A method for testing the integrity of signals received by a receiver of a satellite navigation system, comprising:

receiving an incoming signal with a receiver system having an array of antenna elements and a receiver associated with each antenna element;

wherein the distance between antenna elements is known;

measuring the carrier phase of the incoming signal simultaneously received by at least three antenna elements;

calculating phase differences between the antenna elements;

based on the phase differences and the distance between antenna elements, using a geometry algorithm to calculate a measured angle of arrival of the incoming signal;

determining an expected angle of arrival of the incoming signal; and

comparing the measured angle of arrival to the expected angle of arrival of the incoming signal.

2. The method of claim 1, wherein the satellite navigation system is a GPS system.

3. The method of claim 1, further comprising calculating the ratio of the projection of the ray to the satellite upon the antenna plane and the distance between antenna elements, and based on that ratio, using a geometry algorithm to determine the angle of elevation of the incoming signal.

4. The method of claim 1, wherein the at least three antenna elements are arranged on two orthogonal baselines, the baselines having a common antenna element.

5. The method of claim 1, wherein the distance between antenna elements is twenty centimeters or less.

6. The method of claim 1, further comprising mitigating the effect of the incoming signal by adjusting antenna element delays in the direction of the incoming signal.

7. The method of claim 6, wherein the adjusting is performed on digitized output of the antenna elements.

8. The method of claim 6, wherein the adjusting is performed on analog output of the antenna elements.

9. The method of claim 1, wherein the expected angle of arrival is determined by receiving data carried by the signal representing the position of the source of the signal, and using this data to calculate an expected angle of arrival of the signal.

10. The method of claim 1, wherein the expected angle of arrival is determined by obtaining data necessary to compute the expected angle of arrival data from an external source.

11. The method of claim 10, wherein the external source is ephemerides from government sources.

12. The method of claim 10, wherein the external source is broadcast ephemeris relayed to the location of the system via another communications means.

13. A receiver system for testing the integrity of signals received by a receiver of a satellite navigation system (SNS), comprising:

an array of antenna elements arranged on, or resolvable to, two orthogonal baselines, with at least one common antenna element and at least one antenna elements along each baseline;

a receiver associated with each antenna element;

wherein the distance between antenna elements is known;

wherein the receivers or a common processing unit are programmed to perform the following tasks;

measure the carrier phase of the incoming signal simultaneously received by at least three antenna elements;

calculate phase differences between the antenna elements;

based on the phase differences and the distance between antenna elements, use a geometry algorithm to calculate a measured angle of arrival of the incoming signal;

to determine an expected angle of arrival of the incoming signal; and

to compare the measured angle of arrival to the expected angle of arrival of the incoming signal.

14. The system of claim 13, wherein the satellite navigation system is a GPS system.

15. The system of claim 13, wherein the receivers or a common processing unit are further programmed to calculate the ratio of the projection of the ray to the satellite upon the antenna plane and the distance between antenna elements, and based on that ratio, to use a geometry algorithm to determine the angle of elevation of the incoming signal.

16. The system of claim 13, wherein the distance between antenna elements is twenty centimeters or less.

17. The system of claim 13, wherein the receivers or a common processing unit are further programmed to mitigate the effect of the incoming signal by adjusting antenna element delays in the direction of the incoming signal.

18. The system of claim 13, wherein the expected angle of arrival is determined by receiving data carried by the signal representing the position of the source of the signal, and using this data to calculate an expected angle of arrival of the signal.

19. A method for detecting interference in signals received by a receiver of a satellite navigation system (SNS), comprising:

receiving an incoming signal with a receiver system having an array of antenna elements and a receiver associated with each antenna element;

wherein the distance between antenna elements is known;

calculating the Fourier transform of the intermediate frequency output of each antenna element;

determining frequency bins for the Fourier transforms;

subtracting corresponding frequency bins of the antenna elements, thereby obtaining phase differences among the antenna elements;

based on the phase differences, using a geometry algorithm to calculate an angle of arrival of the energy in a frequency bin; and

comparing the angles of arrival in the frequency bins.

20. The method of claim 19, further comprising determining the angle of arrival of the interference and mitigating the effect of the interference by adjusting antenna element delays in that direction.