Method and device for detecting a decoy operation of a GNSS system

1. A method of detecting an operation to spoof a first satellite signal positioning device carried by a first vehicle moving in a zone in which at least one second vehicle carrying a second satellite signal positioning device is also moving, the method comprising:

causing at least one first positioning value to be calculated for each vehicle from initial satellite signals received by each satellite signal positioning device;

in parallel both with receiving initial satellite signals by the second satellite signal positioning device and also with calculating the first positioning value for the second vehicle, causing the second satellite signal positioning device to initiate a latching stage in order to make a new search for satellite signals and using new satellite signals received by the second satellite signal positioning device to calculate a second positioning value for the second vehicle at the same instant as the first value;

comparing the first and second positioning values relating to the second vehicle; and

issuing a warning when the two positioning values do not coincide;

at least the second satellite signal positioning device having at least first satellite signal reception channels and second satellite signal reception channels and at least one processor unit arranged:

during a latching mode to select transmitters of satellite signals on the first channels that are sufficiently powerful to be used, and during an operating mode that lasts for as long as the signals transmitted by the selected transmitters are sufficiently powerful, to calculate successive first positioning values from said signals; and

during a latching mode to select transmitters of signals on the second channels that are sufficiently powerful to be used, and during an operating mode, to calculate at least one second positioning value from said signals, the processor unit returning automatically to latching mode after calculating said at least one positioning value on the second channels regardless of the power of the signals.

2. The method according to claim 1 , wherein the warning is issued when the compared positioning values differ by a difference greater than a predetermined threshold.

3. The method according to claim 2 , wherein the threshold is determined while taking account of statistical accuracy both for calculating the first positioning value and for calculating the second positioning value when not in a spoofing situation.

4. The method according to claim 1 , wherein the warning is issued by broadcast transmission.

5. The method according to claim 1 , wherein the warning is issued to a ground station.

6. The method according to claim 5 , wherein the ground station sends a warning message to the first vehicle.

7. The method according to claim 1 , wherein the first positioning value is also calculated using non-satellite positioning data.

8. The method according to claim 1 , wherein a plurality of second vehicles are moving in the zone and the method includes the step of estimating an outline of the spoofing zone from the first positioning values of the second vehicles.

9. The method according to claim 8 , including the step of estimating a position for a transmitter of spoofing signals from the outline of the spoofing zone.

10. The method according to claim 1 , wherein the processor unit returns to latching mode on the second channels after calculating a single positioning value.

11. The method according to claim 1 , wherein the processor unit returns to latching mode on the second channels after a predetermined duration after having calculated calculating said at least one positioning value on the second channels regardless of the power of the signals.

12. A satellite signal positioning device having at least first satellite signal reception channels and second satellite signal reception channels and at least one processor unit arranged:

during a latching mode to select transmitters of satellite signals on the first channels that are sufficiently powerful to be used, and during an operating mode that lasts for as long as the signals transmitted by the selected transmitters are sufficiently powerful, to calculate successive first positioning values from said signals; and

during a latching mode to select transmitters of signals on the second channels that are sufficiently powerful to be used, and during an operating mode, to calculate at least one second positioning value from said signals, the processor unit returning automatically to latching mode after calculating said at least one positioning value on the second channels regardless of the power of the signals;

to compare the second positioning value and the corresponding first positioning values; and

to issue a warning when the two positioning values do not coincide.

13. The device according to claim 12 , wherein the processor unit returns to latching mode on the second channels after calculating a single positioning value.

14. The device according to claim 12 , wherein the processor unit returns to latching mode on the second channels after a predetermined duration.

15. The device according to claim 12 , wherein the first channels belong to a first receiver and the second channels belong to a second receiver.

16. The device according to claim 12 , wherein the first and second channels belong to a single receiver.