METHOD TO SECURE GNSS BASED LOCATIONS IN A DEVICE HAVING GNSS RECEIVER

• US 20100117899A1
• Filed: 11/13/2009
• Published: 05/13/2010
• Est. Priority Date: 11/13/2008
• Status: Active Grant

• Current Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Original Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Inventors: JOVANOVIC, ALEKSANDAR, PAPADIMITRATOS, PANAGIOTIS
• Granted Patent: US 8,159,391 B2
• Time in Patent Office: Days
• US Class Current: 342/357.620
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/254 relating to Doppler shift of satellite signals

Abstract

A method to detect at a GNSS receiver whether the received GNSS signals and navigation messages are the product of an attack. If there is evidence, as provided by the method described here, that the received signals and messages originate from adversarial devices, then receiver equipped with an instantiation of the method notifies the user or the computing platform that integrates the GNSS receiver that the calculated via the GNSS functionality position and time correction are not trustworthy. In other words, our method enables any GNSS receiver, for example, GPS, GLONAS, or Galileo, or any other GNSS system, to detect if the received navigation messages are the legitimate ones (from the satellites) or not (e.g., from attacker devices that generate fake messages that overwrite the legitimate messages). Based on this detection, neither the user and nor any application running in the computing platform is misled to utilize erroneous position information.

Claims

1. A method to secure GNSS based locations in a device having a GNSS receiver receiving a plurality of satellite signals, processing means and a memory, said method comprising the steps of:

acquiring first positions by the GNSS receiver;

extracting trusted position relevant values of said first positions and storing the trusted position relevant values in the memory;

acquiring at least one second position by the GNSS receiver;

extracting a second position relevant value of said second position;

calculating an expected relevant value based on the trusted position relevant values;

calculating a metric representing the difference between the second position relevant value and the expected relevant value; and

setting an invalid flag when the metric is above a threshold.

2. The method of claim 1 wherein the position relevant value is a Doppler shift value representing the relative motion of a satellite with respect to the receiver, the metric being the difference between the Doppler shift values of the first positions and the Doppler shift value of the second position.

3. The method of claim 2, wherein the step of calculating the expected value is carried out by determining a variation of the Doppler shift value with at least the two last trusted position relevant values.

4. The method of claim 1, wherein the position relevant value is Doppler shift values of at least two satellites representing the relative motion of said satellite with respect to the receiver, the metric being the difference between the Doppler shift values of the first and second satellite of the first positions and the Doppler shift value of the second position of the first and second satellite.

5. The method of claim 1, wherein it comprises a further step of measuring a signal power level representing the signal power of the satellite signal and comparing the signal power with at least one maximum value.

6. The method of claim 1, wherein the position relevant value is the power signal of the received satellite signal, the metric being the difference between the power signal of the first positions and the power signal of the second position.

7. The method of claim 6, wherein the position relevant value is the ratio between two power signal of at least two satellite signal, the metric being the difference between the power signal ration of the first positions and the ratio power signal of the second position.

8. The method of claim 1, wherein the position relevant value is the location value, the trusted location values allowing to determine an expected area as expected value, the metric being the distance between the second location value and the limit of the second area.

9. The method of claim 8, wherein the expected area is further determined using actual movement detectors of the receiver.

10. The method of claim 8, wherein it comprise a step of determining the velocity of the receiver using the trusted location values, the expected area is determined based on the velocity of the receiver.

11. The method of claim 8, wherein it comprises a step of determining the velocity of the receiver using a velocity meter of the receiver, the expected area is determined based on the velocity of the receiver.

12. The method of claim 1, wherein the position relevant value is the time value bound with the satellite signal, the metric being the difference between the time value of the first positions and the time value of the second position.

13. The method of claim 11, wherein the receiver comprises a clock updated with the time of the first position and allowing to calculate elapsed time, the metric being the difference between the elapsed time and the time of the second position.

14. The method of claim 1, wherein a plurality of GNSS receivers have the capacity to communicate with each other, further comprising the steps of

transmitting the second position relevant values from a first receiver for which the invalid flag has been set to a second receiver;

and

using additionally the received second position relevant values while calculating the metric.

15. A device comprising:

a GNSS receiver for receiving a plurality of satellite signals;

a processor connected to the GNSS receiver; and

a memory connected to the processor;

wherein the processor is configured to perform the steps of

acquiring first positions by the GNSS receiver;

extracting trusted position relevant values of said first positions and storing the trusted position relevant values in the memory;

acquiring at least one second position by the GNSS receiver;

extracting a second position relevant value of said second position;

calculating an expected relevant value based on the trusted position relevant values;

calculating a metric representing the difference between the second position relevant value and the expected relevant value; and

setting an invalid flag when the metric is above a threshold.