Detection of manipulated satellite time signals

• US 9,599,719 B2
• Filed: 10/14/2013
• Issued: 03/21/2017
• Est. Priority Date: 10/19/2012
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Cooper, Francis J., Achanta, Shankar V., Whitehead, David E.
• Primary Examiner(s): McGue, Frank J
• Application Number:
  US14/053,347
• Publication Number:
  US 20140247185A1
• Time in Patent Office: 1,254 Days
• Field of Search: 342/357.58
• US Class Current: 1/1
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service

Abstract

Disclosed herein is a system for detecting manipulation of a GNSS signal and mitigating against such manipulation. A GNSS receiver receives GNSS signals from a plurality of GNSS satellites, and calculates event times for each GNSS satellite. The GNSS receiver then compares a next event time for a particular GNSS satellite with an expected next event time for the particular GNSS satellite. If the difference between the expected next event time and the next event times exceeds a predetermined threshold, then the GNSS receiver indicates that signal integrity may be compromised.

Claims

1. A Global Navigational Satellite System (GNSS) receiver for providing a time signal to consuming devices, comprising:

an antenna for receiving one or more GNSS signals from one or more GNSS satellites;

a processor;

a communications interface for communicating the time signal to the consuming devices; and

a non-transitory computer-readable storage medium comprising instructions that enable the processor to;

for a particular GNSS satellite of the one or more GNSS satellites, determine event times for a repeating event;

for the particular GNSS satellite, calculate an expected next event time from the determined event times;

for the particular GNSS satellite, determine an acceptable signal strength pattern for each event, wherein the calculated expected next event time comprises a time window based on the acceptable signal strength pattern;

detect a next event time for the particular GNSS satellite;

calculate a difference between the detected next event time with the calculated expected next event time for the particular GNSS satellite; and

indicate compromised signal integrity when the difference exceeds a predetermined threshold.

2. The GNSS receiver of claim 1, wherein the GNSS receiver communicates compromised signal integrity to the consuming devices.

3. The GNSS receiver of claim 1, wherein the repeating event comprises a particular satellite coming into view of the antenna.

4. The GNSS receiver of claim 1, wherein the repeating event comprises a particular satellite leaving view of the antenna.

5. The GNSS receiver of claim 1, wherein the consuming devices comprise intelligent electronic devices (IEDs) in communication with an electric power delivery system.

6. The GNSS receiver of claim 1, wherein the instructions further enable the processor to calculate a time signal to provide to the consuming devices.

7. The GNSS receiver of claim 6, wherein the instructions further enable the processor to not use a signal from a particular GNSS satellite when the difference exceeds a predetermined threshold.

8. The GNSS receiver of claim 1, wherein the instructions further enable the processor to:

compare a signal strength of the particular GNSS satellite during the event with the acceptable signal strength pattern for the event; and

indicate compromised signal integrity when a difference between the signal strength of the particular GNSS satellite and the acceptable signal strength pattern exceeds a predetermined threshold.

9. A method for detecting manipulation of satellite signals comprising:

recording events associated with each of one or more Global Navigational Satellite System (GNSS) satellites by a GNSS receiver;

generating, by the GNSS receiver, an expected time for a next event based on the recorded events;

determining an acceptable signal strength pattern for the next event, wherein the generated expected time comprises a time window based on the acceptable signal strength pattern for the next event;

detecting the next event;

comparing an actual time of the detected next event with the expected time for the next event; and

indicating a compromised GNSS signal in response to determining that the actual time of the detected event varies from the expected time for the next event by a defined threshold.

10. The method of claim 9, further comprising communicating the compromised GNSS signal to a consuming device.

11. The method of claim 9, wherein the events associated with each of one or more GNSS satellites comprises a particular satellite coming into view of the antenna.

12. The method of claim 9, wherein the events associated with each of one or more GNSS satellites comprises a particular satellite leaving view of the antenna.

13. The method of claim 9, wherein:

comparing the actual time with the expected time comprises comparing the actual time with the calculated time window.

14. The method of claim 9 further comprising comparing a signal strength pattern of during the event with the acceptable signal strength pattern for the event.

15. The method of claim 9, further comprising calculating a time signal from the GNSS satellites.

16. The method of claim 15, further comprising not using a signal from a particular GNSS satellite in the calculation of the time signal when the time of the detected event varies from the expected time for the next event by greater than a defined threshold.

17. A method comprising:

recording events associated with each of one or more Global Navigational Satellite System (GNSS) satellites by a GNSS receiver;

generating, by the GNSS receiver, an expected time for a next event based on the recorded events;

determining, by the GNSS receiver, an acceptable signal strength pattern for the next event, wherein the generated expected time for the next event comprises a time window based on the acceptable signal strength pattern for the next event;

comparing an actual time of the next event with the expected time for the next event; and

distributing a precision time reference based on a signal from the one or more GNSS satellites, in response to determining that the actual time of the detected event is within a threshold time of the expected time for the next event.

18. The method of claim 17, wherein the events associated with each of one or more GNSS satellites comprises a particular satellite coming into view of the antenna.

19. The method of claim 17, wherein the events associated with each of one or more GNSS satellites comprises a particular satellite leaving view of the antenna.

20. A Global Navigational Satellite System (GNSS) receiver for providing a time signal to consuming devices, comprising:

an antenna for receiving one or more GNSS signals from one or more GNSS satellites;

a processor;

a communications interface for communicating the time signal to the consuming devices; and

a non-transitory computer-readable storage medium comprising instructions that enable the processor to;

for a particular GNSS satellite of the one or more GNSS satellites, determine event times for a repeating event;

for the particular GNSS satellite, calculate an expected next event time from the determined event times;

for the particular GNSS satellite, determine an acceptable signal strength pattern for each event,

detect a next event time for the particular GNSS satellite;

calculate a signal strength difference between the signal strength pattern for the particular GNSS satellite during the event and the acceptable signal strength pattern for the event;

calculate a time difference between the detected next event time and the calculated expected next event time for the particular GNSS satellite; and

indicate compromised signal integrity when one or more of the time difference exceeds a predetermined threshold, and the signal strength difference exceeds a predetermined threshold.