Evaluations of Low-Cost Decoding Methods for 1090 MHz SSR Signals

l,090 MHz secondary surveillance radar (SSR) signals received at airports from Mode A/C and S transponders suffer mostly from garbling, fading and multipath. Due to these radio wave propagation effects, the received overlapped signals result in pulse distortion and inter-symbol interferences (lSI) and eventually they cause bit errors. To cope with these issues, decoding methods based on threshold and edge detection principles are evaluated in this work. Herein we have shown new evaluations of decoding methods in the time domain with the corresponding signal filtering and validated with real-world data from the Salzburg airport in Austria. Each of the installed receiving stations uses a dipole antenna with a single receiving stream. Especially, the multilevel threshold detection decoding technique, which exploits multilevel thresholding for peak detection, leads to a significant lower bit error rate (BER) compared to the common known decoding method of Mode S secondary radars. Furthermore, occurring bit errors are marked and all methods are low-cost implementable on a field programmable gate array (FPGA) and digital signal processor.