Algorithms for Mode S Secondary Surveillance Radar Reply Signal Receiver

Secondary Surveillance Radar (SSR) is an important part of the air traffic control, it allowing to interrogate the airplane's transponder by the ground control equipment for various flight parameters. Mode
$S$
represents the latest SSR technology and includes as a specific functioning mode the Automatic Dependent Surveillance-Broadcast (ADS-B), in which case flight parameters are broadcasted autonomously. Reception of the ADS-B frames has generated a lot of interest, many applications on several platform being developed for the reception and decoding of these frames. The paper proposes several algorithms necessary for reception of the Mode S SSR reply frames, not limited only to the ADS-B frames. Algorithms for synchronization of the Mode
$S$
frames and for estimation of the reception quality of these frames were developed. The proposed algorithms were evaluated on a test platform developed in GNU Radio and using an ADALM Pluto SDR.