Time signal verification and distribution

• US 9,813,173 B2
• Filed: 10/05/2015
• Issued: 11/07/2017
• Est. Priority Date: 10/06/2014
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Achanta, Shankar V., Achanta, Srinivas, Whitehead, David E.
• Primary Examiner(s): Perez, James M
• Application Number:
  US14/875,453
• Publication Number:
  US 20160099803A1
• Time in Patent Office: 764 Days
• Field of Search: 375354-376
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43
• CPC Class Codes: H04J 3/0644 External master-clock
• CPC Class Codes: H04L 63/14 for detecting or protecting against malicious traffic

Abstract

The time signal verification and distribution device disclosed herein verifies and distributes a time signal to consuming devices. The device determines a time quality status of a first and second time signal, calculates a difference between a first and a second time signal, and compares the difference to a predetermined threshold. Based on the time quality status and the comparison, the time signal verification and distribution device distributes a time signal to a plurality of time signal consuming devices. Exceeding the predetermined threshold may indicate a spoofing attack or other problem with the time signals.

Claims

1. A time signal verification and distribution device, comprising:

a time signal receiver for receiving time signals;

a time input in communication with the time signal receiver, configured to receive from the time signal receiver a first time signal from a first time source and a second time signal from a second time source;

a time signal quality module in communication with the time input, configured to determine a time quality of the first time signal and the second time signal;

a time signal difference module in communication with the time input, configured to calculate a difference between the first time signal and the second time signal, and compare the difference to a predetermined threshold;

a time signal output module in communication with the time signal quality module and the time signal difference module, configured to determine an output time signal based on the comparison and the determined time quality of the first time signal and the second time signal; and

a time signal output in communication with the time signal output module, configured to output the output time signal to a plurality of time signal consuming devices.

2. The device of claim 1, wherein the time signal quality module is further configured to determine whether the first and second time signals include a quality indication.

3. The device of claim 1, wherein the time signal output module is configured to determine the output time signal as the first time signal when the first time signal quality is not suspect and the second time signal quality is suspect.

4. The device of claim 1, wherein the time signal output module is configured to determine the output time signal as a holdover time signal when the first time signal quality is suspect and the second time signal quality is suspect.

5. The device of claim 1, wherein the time signal output module is configured to determine the output time signal as a holdover time signal when the difference exceeds the predetermined threshold.

6. The device of claim 1, wherein the time signal output module is configured to determine the output time signal as the first time signal when the first time signal quality is not suspect, the second time signal quality is not suspect, and the difference does not exceed the predetermined threshold.

7. The device of claim 1, wherein the first time signal is a GNSS time signal.

8. The device of claim 1, wherein the second time signal is a network time signal.

9. The device of claim 1, wherein the first time signal is derived from a GNSS time signal obtained at a first location and the second time signal is derived from a GNSS time signal obtained at a second location.

10. The device of claim 9, wherein the first location and the second location are separated by 200 m.

11. The device of claim 1, wherein:

the time input is further configured to receive a third time signal, the time signal

the time signal quality module is further configured to determine the time quality of the third time signal; and

,

the time signal output module is further configured to determine an output signal based on the determined time quality of the third time signal.

12. A time signal communication system, comprising:

a first receiver configured to receive a first time signal at a first location, and transmit the first time signal across a wide-area communications network;

a second receiver configured to receive a second time signal at a second location remote from the first location;

a time signal verification and distribution device in communication with the wide-area communications network and the second receiver, configured to receive the first time signal and the second time signal, the time signal verification and distribution device comprising;

a time signal quality module in communication with the time input, configured to determine a time quality of the first time signal and the second time signal;

a time signal difference module in communication with the time input, configured to calculate a difference between the first time signal and the second time signal, and compare the difference to a predetermined threshold;

a time signal output module in communication with the time signal quality module and the time signal difference module, configured to determine an output time signal based on the comparison and the determined time quality of the first time signal and the second time signal; and

,

a time signal output in communication with the time signal output module and the plurality of consuming devices, configured to output the output time signal to the plurality of consuming devices

the plurality of consuming devices in communication with the time signal verification and distribution device, configured to receive and use the output time signal from the time signal verification and distribution device.

13. The system of claim 12, wherein the time signal quality module, time signal difference module, and time signal output module comprise a single module.

14. The system of claim 12, wherein the time signal output module is configured to determine the output time signal as the first time signal when the first time signal quality is not suspect and the second time signal quality is suspect.

15. The system of claim 12, wherein the time signal output module is configured to determine the output time signal as a holdover time signal when the first time signal quality is suspect and the second time signal quality is suspect.

16. The device of claim 12, wherein the time signal output module is configured to determine the output time signal as a holdover time signal when the difference exceeds the predetermined threshold.

17. The device of claim 12, wherein the time signal output module is configured to determine the output time signal as the first time signal when the first time signal quality is not suspect, the second time signal quality is not suspect, and the difference does not exceed the predetermined threshold.

18. The device of claim 12, wherein the first time signal is a GNSS time signal.

19. The device of claim 12, wherein the second time signal is a network time signal.

20. The device of claim 12, wherein the first time signal is derived from a GNSS time signal obtained at a first location and the second time signal is derived from a GNSS time signal obtained at a second location.

21. The device of claim 20, wherein the first location and the second location are separated by 200 m.

22. The time signal communication system of claim 12, further comprising a third receiver configured to receive a third time signal at a third location remote from the first and second locations;

and wherein;

the time signal quality module is further configured to determine the time quality of the third time signal; and

,

the time signal output module is further configured to determine an output signal based on the determined time of the third time signal.

23. A method comprising:

receiving, at a time signal receiver of a time distribution device, a first time signal;

receiving, at the time distribution device, a second time signal;

determining a time quality status of the first time signal and the second time signal;

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

comparing the difference to a predetermined threshold;

distributing an output time signal to a plurality of consuming devices based on the determination of the time quality status of the first time signal and the second time signal and the comparison of the difference to the predetermined threshold, wherein the output time signal comprises one selected from the group consisting of the first time signal, the second time signal, and a holdover time.