Automatic Dependent Surveillance – Broadcast (ADS-B) is an operational enhancement as part of next-generation air transportation systems in Air Traffic Control. It enables aircraft and airport vehicles to periodically broadcast the information from their on-board equipment, like their identification, GPS location, velocity, and intent. Compared to classical radar surveillance, the service implementation has increased the renewal time, reduced costs, and increased safety and accuracy already. Nowadays, Mode S 1090 Extended Squitter is the most predominant adopted technology ADS-B service implementation.
However, the ATC system has not been developed with security in mind and is vulnerable to a number of different radio frequency attacks by malicious parties. ADS-B is planned for long-term use but lacks the minimal and necessary inherent security mechanisms.
This study suggests a possible and cost-effective solution that improves the security and integrity of raw ADS-B signals by designing a tool which can verify and validate the low-level signal. In this study, in order to mitigate the threat of maliciously injected signals, a method is proposed where two variables of direction of arrival are independently determined using a multi-channel coherent receiver. First, a calculated angle using signal decoding and trigonometry and secondly, an estimated angle using phase relationships and spatial correlation. Finally, an integrity verification method has been proposed and successfully applied.

Automatic Dependent Surveillance-Broadcast (ADS-B) enables aircraft to periodically broadcast their flight states such as position and velocity. Compared to classical radar surveillance, it increases update rate and accuracy. Currently, Mode S Extended Squitter is the most common implementation for ADS-B. Due to the simplicity of Mode S design, ADS-B signals are prone to injections. This study proposes a cost-effective solution that verifies the integrity of ADS-B signals using coherent receivers. We design the verification approach by combining the signal’s direction of arrival, estimated from the multi-channel data, with the target bearing calculated from ADS-B messages. By using another high-performance software-defined radio transceiver, we also conduct real signal injection experiments to validate our approaches