In 2009 a development started in the Department of Broadband Infocommunications in the laboratory V2.619. in association with HungaroControl Zrt. The goal was to develop a multilateration based positioning system, which is used for accurate position measuring and identification purposes in an airport area. The system uses the Mode S Extended Squitter protocol for data transmission. The system consists of many subsystems, which are developed at the university in the previous years. My task was to develop a decoding firmware for the base stations, which can identify the squitter messages received by the RF module, and sends them to a server. The task was realized in a FPGA based system, which finds the frame pulses of the messages and decodes the data field. The system is also be able to recognize errors (e.g. overlapped messages). The decoded data and the calculated CRC field is sent to the server subsystem, which collects the data from different receiver stations for further analysis, storage and display. The program also uses a FIFO to prevent data loss when the transfer network is busy.