Secondary Surveillance Radar Transponders classification by RF fingerprinting

Secondary Surveillance Radars are Air Traffic Control systems used to obtain identity and altitude of the cooperative airplanes and, together with the Primary Radar, allow a safe air traffic flow. The Secondary Surveillance Radar protocol is also used for Traffic Alert and Collision Avoidance System and Automatic Dependent Surveillance Systems: in these applications, the aircraft transmit their own information (identity, position, velocity etc.) to any equipped listener for anti-collision and surveillance scope without the interrogation of the SSR Radar. The simple Secondary Surveillance Radar protocol doesn't provide any kind of authentication and encryption, making it vulnerable to many types of cyber-attacks. In the paper, it is proposed the use of the airplane/transmitter carrier phase as a feature to perform a classification of the aircraft and, therefore, distinguish legitimate messages from fake ones. The feature extraction process is described and different classification methods are tested by the use of real data.