Backward Compatible Physical Layer Protocol Evolution for ADS-B Message Authentication

The automatic dependent surveillance-broadcast system is a pillar of the future air traffic control system. It is a surveillance system in which air planes transmit their information (identity, position, velocity, etc.) in broadcast to any listener equipped with a receiver. Networks of ADS-B receivers have been installed all over the world, producing a clear traffic awareness for air traffic controllers. For historical reasons, this protocol does not have any authentication/encryption mechanism. The aim of this article is to improve the ADS-B system security by introducing a physical layer protocol modification for the introduction of an authentication scheme. The proposed evolution fully complies with the current standard and exploits the phase modulation to increase the number of bits that can be transmitted with a single packet of data. These additional bits can be used to carry authentication information, making the overall system more secure (and safe). The proposed protocol evolution is developed ensuring backward compatibility and respecting the ICAO and RTCA recommendations; it can be introduced and used together with the present standard in a mixed scenario, allowing a smooth transition from the present protocol to the new one. Protocol performances were evaluated by simulations and, moreover, its feasibility and compliance with recommendations were tested using a software-defined radio (as transmitter) and a laboratory ADS-B receiver.