Detection of manipulated satellite time signals
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.
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.