Manipulation resilient time distribution network

• US 9,400,330 B2
• Filed: 05/17/2013
• Issued: 07/26/2016
• Est. Priority Date: 10/19/2012
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Achanta, Shankar V., Zweigle, Gregary C., Huntley, Christopher R.
• Primary Examiner(s): Liu, Harry
• Application Number:
  US13/896,999
• Publication Number:
  US 20140111377A1
• Time in Patent Office: 1,166 Days
• Field of Search: 342/357.58, 342/357.25
• 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 19/215 issues related to spoofing

Abstract

Disclosed herein is a system for detecting manipulation of a global time source such as a Global Navigational Satellite System (GNSS) signal and mitigating against such manipulation. A plurality of receivers with geographical diversity receive GNSS signals, and calculate a time signal to be distributed to consuming devices. The receivers also communicate calculated time signals with other receivers. The receivers compare the time signals, and when a difference between the time signals exceeds a predetermined threshold, the receivers indicate that manipulation is likely. Such indication is shared across the network of receivers. The indication is further shared with consuming devices of the time signal from the compromised receiver. A second time signal that is not compromised may be shared with the consuming devices and/or used by the consuming devices. The consuming devices may modify their behavior when in receipt of the indication.

Claims

1. A system for detecting and mitigating against manipulated time signals, comprising:

a first receiver at a first location configured to receive a first plurality of radio signals from a global time source and calculate a first time signal from the first plurality of radio signals; and

a second receiver at a second location configured to receive a second plurality of radio signals from the global time source and calculate a second time signal from the second plurality of radio signals, the second receiver further configured to;

receive the first time signal from the first receiver;

calculate a time difference between the first time signal and the second time signal;

compare the time difference with a defined time difference threshold; and

communicate a manipulation alarm to the first receiver in response to determining that the time difference exceeds the defined time difference threshold.

2. The system of claim 1, wherein the first receiver is further configured to calculate a signal integrity based on the first plurality of radio signals and transmit the signal integrity to the second receiver.

3. The system of claim 2, wherein the second receiver is further configured to communicate the second time signal to the first receiver.

4. The system of claim 3, wherein the first receiver is configured to distribute the second time signal when the time difference exceeds the defined time difference threshold.

5. The system of claim 2, wherein the first receiver is further configured to calculate the signal integrity using a signal-to-noise ratio.

6. The system of claim 2, wherein the global time source is a Global Navigational Satellite System (“

GNSS”

).

7. The system of claim 6, wherein, to calculate the signal integrity, the first receiver is further configured to:

determine a location of the first receiver using the first plurality of radio signals; and

compare the location with a known location of the first receiver.

8. The system of claim 7, wherein the known location is calculated using a plurality of radio signals from the GNSS during a time of signal integrity.

9. The system of claim 6, wherein the first receiver is further configured to calculate the signal integrity using historical satellite data.

10. The system of claim 2, wherein, to calculate the signal integrity, the first receiver is further configured to:

measure a rate of change of the first time signal; and

compare the rate of change with a holdover performance threshold of the first receiver.

11. A time distribution device comprising:

an antenna configured to receive a plurality of radio signals from a global time source at a first location;

a receiver configured to determine a first time from the plurality of radio signals;

a communication component configured to transmit and/or receive data; and

a manipulation detection component configured to;

receive a time signal from a remote time distribution device at a second location;

determine a second time from the time signal;

calculate a time difference between the first time and the second time;

compare the time difference with a defined time difference threshold; and

transmit a manipulation alarm to the remote time distribution device in response to determining that the time difference exceeds the defined time difference threshold.

12. The time distribution device of claim 11, wherein the manipulation detection component is further configured to determine a signal integrity based on the plurality of radio signals.

13. The time distribution device of claim 12, wherein the manipulation detection component is further configured to determine the signal integrity based on a signal-to-noise ratio of the plurality of radio signals.

14. The time distribution device of claim 12, wherein the receiver is a Global Navigational Satellite System (“

GNSS”

) receiver.

15. The time distribution device of claim 14, wherein the manipulation detection component is further configured to determine the signal integrity based on a location calculated by the GNSS receiver using the plurality of radio signals and a known location of the time distribution device.

16. The time distribution device of claim 12, wherein, to calculate the signal integrity, the manipulation detection component is further configured to:

measure a rate of change of the first time; and

compare the rate of change with a holdover performance threshold of the time distribution device.

17. The time distribution device of claim 14, wherein the manipulation detection component is further configured to determine the signal integrity based on historical satellite data.

18. The time distribution device of claim 11, wherein, in response to determining that the time difference exceeds the defined time difference threshold, the time distribution device is configured to transmit a local holdover time signal to downstream devices.

19. A time distribution device comprising:

an antenna suitable for receiving a first plurality of radio signals from a global time source;

a global time source receiver suitable for determining a first time from the first plurality of radio signals; and

a manipulation detection component configured to;

determine a first signal integrity of the first plurality of radio signals;

receive a time signal, including a second time and a second signal integrity, from a remote time distribution device;

in response to determining that the first signal integrity and the second signal integrity are greater than a defined signal integrity threshold;

calculate a time difference between the first time and the second time;

compare the time difference with a defined time difference threshold; and

transmit a manipulation indication to the remote time distribution device in response to determining that the time difference exceeds the defined time difference threshold.

20. The time distribution device of claim 19, wherein:

the defined time difference threshold comprises a warning threshold and an alarm threshold; and

the manipulation indication is a warning when the time difference exceeds the warning threshold but not the alarm threshold and an alarm when the time difference exceeds the alarm threshold.

21. The time distribution device of claim 19, wherein the manipulation detection component is configured to determine the first signal integrity based on a signal-to-noise ratio of the first plurality of radio signals.

22. The time distribution device of claim 19, wherein the global time source receiver is a Global Navigational Satellite System (“

GNSS”

) receiver.

23. The time distribution device of claim 22, wherein the manipulation detection component is configured to determine the first signal integrity based on a location calculated by the GNSS receiver using the first plurality of radio signals and a known location of the time distribution device.

24. The time distribution device of claim 19, wherein, to calculated the first signal integrity, the manipulation detection component is further configured to:

measure a rate of change of the first time; and

compare the rate of change with a holdover performance threshold of the time distribution device.

25. The time distribution device of claim 22, wherein the manipulation detection component is configured to determine the first signal integrity based on historical satellite data.