Detecting spoofing in a global navigation satellite system (GNSS) using slant range distance

A method for detecting spoofing in a Global Navigation Satellite System (GNSS), the method comprising:

• receiving signals at a GNSS receiver that purport to be from satellites in the GNSS;
• processing the signals to determine a calculated position of the GNSS receiver searching a list of distance measuring equipment transponders (DME transponders) around the calculated position to select a set of DME transponders for testing an integrity of the signals received by the GNSS receiver;
• sorting the set of DME transponders in order based on a respective distance between the calculated position and a respective position of each of the DME transponders in the set of DME transponders;
• selecting a subset of the DME transponders from the set of DME transponders based on the sorting;
• for each DME transponder in the subset of the DME transponders, autotuning to a frequency corresponding to a frequency of the DME transponder;
• recording a real time delay for the DME transponder;
• sampling and filtering a power level of a received signal from the DME transponder for a period;
• calculating an expected time delay based on a height, position, and known location of the DME transponder;
• comparing the real time delay with the expected time delay to produce a difference;
• and when the difference exceeds a first threshold, incrementing a counter;
• when the counter exceeds a second threshold, indicating that the position is spoofed and broadcasting an indication to vehicles or ground stations.

A system for detecting Global Navigation Satellite System (GNSS) spoofing, the system comprising:

• a GNSS receiver that is configured to receive signals that purport to be from satellites in the GNSS;
• a processor, in communication with the GNSS receiver, that is configured to run a spoofing detection function, which, when executed by the processor cause the processor to perform the method including:
• calculating a position of the GNSS receiver using the signals;
• searching a list of distance measuring equipment transponders (DME transponders) around the calculated position to select a set of DME transponders for testing for GNSS spoofing;
• sorting the set of DME transponders in order based on a respective distance between the calculated position and a respective position of each of the DME transponders in the set of DME transponders;
• selecting a subset of the DME transponders based on the sorting;
• for each of the subset of the DME transponders, incrementing a counter when a difference between a real slant range, determined by communicating with the DME transponder, and an expected slant range based on a height, position and known location of the DME transponder, exceeds a first threshold;
• and
• when the counter is greater than a second threshold, indicating that the position is spoofed.