Features of Decoding Transponder Signal of an Aircraft Using FPGA

At the end of the 20th century, even with the use of various flight safety systems such as IFF, ATCRBS and ACAS, there were a significant number of airplanes and other aircraft crushes in the air, which necessitated the improvement of these systems. These improvements were reflected in the MODE-S technology. Nowadays every civilian aircraft is equipped with a special transmitter, the so-called ADS-B transponder. This device sends special data packages at the frequency of 1090 MHz containing the main flight parameters, type of aircraft, its coordinates, destination, etc. One of the drawbacks of using this system is the inaccuracy of the transmitted location and speed of flight data. The article describes a solution of this problem with the help of a specialized block of automatic decoding and modification of the incoming message. In addition, it describes a rather simple and efficient way of processing a digitized signal, which has some distortions due to a number of factors, such as the error of the receiving-transmitting equipment, the presence of interference in the air and the signal reflections, the effect of various electromagnetic fields, etc. A variant of circuit design and firmware implementation of the decoding unit are considered. Because the transponder itself is based on the FPGA, both embodiments are effective and do not interfere with the operation of other transponder modules in the MODE-S mode. This is important because this technology is used not only by the airport control services to identify aircraft, but also on the aircrafts themselves to prevent crushes with other aircraft.