System and method for detecting false global navigation satellite system satellite signals
Disclosed is a system and method for detecting false Global Navigation Satellite System (GNSS) satellite signals. False GNSS satellite signals can be used malevolently to take control of a body such as a vehicle or ship that is using GNSS satellite signals for navigation. In some embodiments a GNSS attitude system is used to detect the false GNSS satellite signals. The GNSS attitude system measures the code or carrier phase of the GNSS satellite signals at two or more antennas to detect the false GNSS satellite signals. In some embodiments the attitude system computes first measured and second estimated carrier phase differences in order to detect the false GNSS satellite signals. The attitude system may compute the attitude of a baseline vector between the two antennas. Once false GNSS satellite signals are detected, the method can include preventing the attitude determining system from outputting position or location data.
1. A method of using a global navigation satellite system (GNSS) attitude determining system to detect false GNSS satellite signals, the method comprising:
receiving GNSS satellite signals from a plurality of satellites at a first antenna of a GNSS attitude determining system;
receiving GNSS satellite signals from the plurality of satellites at a second antenna of the GNSS attitude determining system;
measuring in the GNSS attitude system first signal phase values for a plurality of the GNSS satellite signals received at the first antenna;
measuring in the GNSS attitude system second signal phase values for a plurality of the GNSS satellite signals received at the second antenna;
determining in the GNSS attitude system phase differences between corresponding first signal phase values and second signal phase values, wherein corresponding signal phase values are signal phase values received by the first and second antennas of the GNSS attitude system from the same satellite;
processing in the GNSS attitude system the determined phase differences to determine a residual error for the determined phase differences, wherein a baseline vector joining the antennas, and geometric terms comprising the baseline vector, are assumed to have a value of zero;
comparing in the GNSS attitude system the residual error to a predetermined threshold value to determine if the measure of residual error is below the predetermined threshold value; and
identifying the received GNSS satellite signals as spoofed signals in the GNSS attitude system if the measure of residual error is below the threshold value.
2. The method of claim 1 , wherein the step of processing in the GNSS attitude system the determined phase differences to determine a residual error for the determined phase differences comprises the steps of:
processing the determined phase differences to remove integer ambiguities;
processing the determined phase differences to remove a common bias term;
squaring the bias and ambiguity-free phase differences; and
summing the squared phase differences to provide a residual error.
3. The method of claim 2 , wherein double-differencing is used in processing the determined phase differences to remove a common bias term.