Satellite radio navigation operations monitoring system and method

1 . A method for monitoring GNSS based navigation operations, the method comprising:

receiving a plurality of reports comprising at least one respective report from each respective station in a plurality of stations, each respective report comprising:

a respective indication of a respective determined location, as determined by a respective GNSS receiver, of the respective station at a respective time;

a respective indication of a respective reported location of a vehicle, where the respective reported location is determined by a GNSS receiver and is communicated in a respective location reporting signal transmitted by the vehicle; and

a respective indication of a respective received signal strength, at the respective station, of the respective location reporting signal, wherein the respective indication of a respective signal strength comprises a respective estimated distance between the respective station and the vehicle that is determined based on a respective received signal strength of the respective location reporting signal at the respective station;

determining, for each respective report, a respective calculated distance between the respective station and the vehicle based on a difference between the respective determined location and the respective reported location;

determining, based on inconsistencies between respective indications of respective reported locations of the vehicle and respective indications of respective received signal strengths within the plurality of reports comprising the respective calculated distance differing from the respective estimated distance by more than a threshold, a likelihood of GNSS based navigation abnormality in a vicinity of at least one of the stations in the plurality of stations or the vehicle; and

reporting, based on determining the likelihood of GNSS based navigation abnormality, a geographic location of the likelihood of GNSS based navigation abnormality.

2 . The method of claim 1 , wherein the plurality of stations comprises a plurality of floating stations each configured to at least:

determine the respective determined location of the respective station;

determine the respective received signal strength;

determine the respective calculated distance; and

send a report within the plurality of reports, wherein the report comprises the respective determined location, the respective calculated distance and the respective reported location.

3 . The method of claim 1 , further comprising;

determining, for at least one respective station in the plurality of stations, a time sequence of signal-to-noise ratios of GNSS signals over a first time duration as a function of at least one of azimuth or elevation of a GNSS satellite relative to the respective station;

determining, for the at least one respective station at a monitoring time subsequent to the first time duration, respective monitored azimuth and elevation values to at least one GNSS satellite from the respective station;

measuring a respective measured signal-to-noise ratio for a GNSS signal received at the respective station from the at least one GNSS satellite at the monitoring time;

determining that the respective measured signal-to-noise ratio differs from signal-to-noise ratios in the vicinity of the time sequence of signal-to-noise ratios of GNSS satellites that are at the respective monitored azimuth and elevation; and

sending an interference report indicating that the respective measured signal-to-noise ratio differs from signal-to-noise ratios in the vicinity of the time sequence of signal-to-noise ratios of GNSS satellites that are at the respective monitored azimuth and elevation.

4 . The method of claim 3 , wherein the at least one respective report further comprises a respective indication of a respective signal-to-noise ratio of a GNSS signal received by the GNSS receiver at the monitoring time, and

wherein the determining that the respective measured signal-to-noise ratio differs from signal-to-noise ratios in the vicinity of the time sequence of signal-to-noise ratios of GNSS satellites that are at the respective monitored azimuth and elevation is performed at the respective station, and

wherein sending the interference report comprises sending the interference report from the respective station.

5 . The method of claim 1 , comprising:

comparing, for each respective report, the respective reported location of the respective vehicle indicated in the respective report to locations that are consistent with the respective determined location of the respective station and the respective estimated distance that are indicated in each respective report;

identifying, based on the comparing, at least one selected report in the plurality of reports that has a distance between its indicated respective reported location and respective determined location that is consistent with the respective determined location and the respective estimated distance;

based on identifying the at least one selected report, identifying spoofed location reports in the plurality of reports where the spoofed location reports are reports other than the selected report that are reports that indicate GNSS spoofing in a respective area that is one of the respective determined location and a likely location of the vehicle corresponding to the spoofed location reports;

determining an area of GNSS spoofing based on overlaps of respective areas indicated in the spoofed location reports; and

sending a report indicating the area of GNSS spoofing.

6 . The method of claim 1 , further comprising:

receiving radio frequency energy within a GNSS radio frequency band with a general radio receiver;

characterizing the radio frequency energy; and

determining, based on characterizing the radio frequency energy, that the radio frequency energy received in the GNSS radio frequency band comprises interference signals.

7 . The method of claim 1 ,

wherein the plurality of stations are distributed over a geographic area,

wherein the method further comprises determining, based on the plurality of stations being distributed over a geographic area and based on inconsistencies between respective indications of respective reported locations of the vehicle and respective indications of respective received signal strengths within the plurality of reports, a likelihood that the respective reported location differs from an actual location of the vehicle,

wherein the reporting comprises reporting the likelihood that the respective reported location differs from an actual location of the vehicle.

8 . The method of claim 1 , further comprising receiving a second plurality of reports, where each report in the second plurality of reports comprises:

a respective indication of a respective determined location, as determined by a respective GNSS receiver, of the respective station at a respective time;

a respective indication of a respective reported location of a respective vehicle within a plurality of vehicles, where the respective reported location is determined by a GNSS receiver and is communicated in a respective location reporting signal transmitted by the respective vehicle; and

a respective indication of a respective received signal strength, at the respective station, of the respective location reporting signal;

determining that a subset of vehicles within the plurality of vehicles report respective indications of respective reported locations of the vehicle that are inconsistent with respective indications of respective received signal strengths within the plurality of reports in combination with the respective determined location;

determining that each vehicle in the subset of vehicles is within an affected geographic area;

determining, that vehicles in the plurality of vehicle that are outside of the affected geographic area report respective indications of respective reported locations of the vehicle that are consistent with respective indications of respective received signal strengths within the plurality of reports in combination with the respective determined location; and

determining that the affected geographic area is an area of GNSS spoofing based on determining that a subset of vehicles within the plurality of vehicles report respective indications of respective reported locations of the vehicle that are inconsistent with respective indications of respective received signal strengths within the plurality of reports in combination with the respective determined location, that the subset of vehicles are within an affected geographic area, and that that vehicles in the plurality of vehicle that are outside of the affected geographic area report respective indications of respective reported locations of the vehicle that are consistent with respective indications of respective received signal strengths within the plurality of reports in combination with the respective determined location,

wherein the reporting comprises reporting, based on determining that the affected geographic area is an area of GNSS spoofing, the affected geographic area is an area of likely GNSS spoofing.

9 . A GNSS based navigation operations monitoring system, comprising:

a processor;

a memory, communicatively coupled to the processor; and

a report receiver, communicatively coupled to the processor and the memory, the report receiver configured to, when operating, receive a plurality of reports comprising at least one respective report from each respective station in a plurality of stations, each respective report comprising:

a respective indication of a respective determined location, as determined by a GNSS receiver, of the respective station at a respective time;

a respective indication of a respective reported location of a vehicle, where the respective reported location is determined by a GNSS receiver and is communicated in a respective location reporting signal transmitted by the vehicle; and

a respective indication of a respective received signal strength, at the respective station, of the respective location reporting signal, wherein the respective indication of a respective signal strength comprises a respective estimated distance between the respective station and the vehicle that is determined based on a respective received signal strength of the respective location reporting signal at the respective station, wherein the processor, when operating, is configured to:

determine, for each respective report, a respective calculated distance between the respective station and the vehicle based on a difference between the respective determined location and the respective reported location;

determine, based on inconsistencies between respective indications of respective reported locations of the vehicle and respective indications of respective received signal strengths within the plurality of reports comprising the respective calculated distance differing from the respective estimated distance by more than a threshold, a likelihood of GNSS based navigation abnormality in a vicinity of at least one of the stations in the plurality of stations or the vehicle; and

report, based on determining the likelihood of GNSS based navigation abnormality, a geographic location of the likelihood of the GNSS based navigation abnormality.

10 . The GNSS based navigation operations monitoring system of claim 9 , further comprising the plurality of stations, wherein the plurality of stations comprises a plurality of floating stations each configured to at least:

determine the respective determined location of the respective station;

determine the respective received signal strength;

determine the respective calculated distance; and

send a report within the plurality of reports, wherein the report comprises the respective determined location, the respective calculated distance and the respective reported location.

11 . The GNSS based navigation operations monitoring system of claim 9 , wherein the processor, when operating, is further configured to;

determine, for at least one respective station in the plurality of stations, a time sequence of signal-to-noise ratios of GNSS signals over a first time duration as a function of at least one of azimuth or elevation of a GNSS satellite relative to the respective station;

determine, for the at least one respective station at a monitoring time subsequent to the first time duration, respective monitored azimuth and elevation values to at least one GNSS satellite from the respective station;

measure a respective measured signal-to-noise ratio for a GNSS signal received at the respective station from the at least one GNSS satellite at the monitoring time;

determine that the respective measured signal-to-noise ratio differs from signal-to-noise ratios in the vicinity of the time sequence of signal-to-noise ratios of GNSS satellites that are at the respective monitored azimuth and elevation; and

send an interference report indicating that the respective measured signal-to-noise ratio differs from signal-to-noise ratios in the vicinity of the time sequence of signal-to-noise ratios of GNSS satellites that are at the respective monitored azimuth and elevation.

12 . The GNSS based navigation operations monitoring system of claim 9 ,

wherein the GNSS based navigation operations monitoring system further comprises the plurality of stations, wherein the plurality of stations comprises a plurality of floating stations comprising at least a part of the processor, and wherein the processor of the floating stations is configured to, when operating, perform the:

compare, for each respective report, the respective reported location of the respective vehicle indicated in the respective report to locations that are consistent with the respective determined location of the respective station and the respective estimated distance that are indicated in each respective report;

identify, based on a comparison of the respective reported location of the respective vehicle indicated in the respective report to locations that are consistent with the respective determined location of the respective station and the respective estimated distance that are indicated in each respective report, at least one selected report in the plurality of reports that has a distance between its indicated respective reported location and respective determined location that is consistent with the respective determined location and the respective estimated distance;

identify, based on identifying the at least one selected report, spoofed location reports in the plurality of reports, the spoofed location reports being reports other than the selected report and are reports that indicate GNSS spoofing in a respective area that is one of the respective determined location and a likely location of the vehicle corresponding to the spoofed location reports;

determine an area of GNSS spoofing based on overlaps of respective areas indicated in the spoofed location reports; and

send a report indicating the area of GNSS spoofing.

13 . The GNSS based navigation operations monitoring system of claim 9 , further comprising a GNSS based navigation operations monitoring station, the GNSS based navigation operations monitoring station comprising:

a second processor;

a second memory, communicatively coupled to the second processor,

wherein the GNSS receiver is communicatively coupled to the second processor and to the second memory, wherein the GNSS receiver, when operating, is configured to:

receive GNSS signals from one or more GNSS constellations; and

process the GNSS signals to determine a second determined location of the GNSS based navigation operations monitoring station; and the GNSS based navigation operations monitoring station further comprising:

a location reporting signal receiver, communicatively coupled to the second processor and the second memory, wherein the location reporting signal receiver, when operating, is configured to:

receive a second location reporting signal transmitted by a second vehicle, the second location reporting signal comprising an indication of a reported location of the second vehicle; and

determine a signal strength of the second location reporting signal, and wherein the second processor, when operating, is configured to:

determine a calculated distance between the second determined location and a location of the reported location of the second vehicle; and

determine, based on inconsistencies between the indication of reported location of the second vehicle and the signal strength of the second location reporting signal, a second likelihood of GNSS based navigation abnormality in a vicinity of at least one of the GNSS based navigation operations monitoring station or the second vehicle; and

send an anomaly report comprising an indication of the second likelihood of GNSS based navigation abnormality in a vicinity of at least one of the GNSS based navigation operations monitoring station or the second vehicle.

14 . The GNSS based navigation operations monitoring station of claim 13 ,

wherein the second processor, when operating, is further configured to determine, based on the signal strength of the second location reporting signal, an estimated distance between the GNSS based navigation operations monitoring station and the second vehicle, and

wherein the second likelihood of GNSS based navigation abnormality is based on an inconsistency between the calculated distance and the estimated distance.

15 . The GNSS based navigation operations monitoring station of claim 13 , wherein the second processor, when operating, is further configured to:

determine a time sequence of signal-to-noise ratios of GNSS signals over a first time duration as a function of at least one of azimuth or elevation of a GNSS satellite relative to the GNSS based navigation operations monitoring station;

determine, at a monitoring time subsequent to the first time duration, respective monitored azimuth and elevation values to at least one GNSS satellite from the GNSS based navigation operations monitoring station;

measure a respective measured signal-to-noise ratio for a GNSS signal received at the GNSS based navigation operations monitoring station from the at least one GNSS satellite at the monitoring time;

determine that the respective measured signal-to-noise ratio differs from signal-to-noise ratios in the vicinity of the time sequence of signal-to-noise ratios of GNSS satellites that are at the respective monitored azimuth and elevation; and

send an interference report indicating that the respective measured signal-to-noise ratio differs from signal-to-noise ratios in the vicinity of the time sequence of signal-to-noise ratios of GNSS satellites that are at the respective monitored azimuth and elevation.

16 . The GNSS based navigation operations monitoring station of claim 13 , wherein the anomaly report further comprises the second determined location, the calculated distance, the reported location of the second vehicle.