Multilateration algorithm for time arrival estimation and target location in airports

The "Multilateration" system is a Surveillance and Identification element of the Air Traffic Management able to estimate, in real time and with high precision, the aircraft position on the airport surface with all the related information as transmitted by the on-board transponder (e.g. aircraft identification code, status, etc.). In airport traffic management (A-SMGCS) applications the Multilateration system, called MLAT in this paper, can provide the same data for targets on the airport surface and nearby the airport area (within a radius of approximately 10-15 nautical miles-nm). Moreover, with the adoption of an appropriate on-board "non-transponder device", it's possible to identify and locate cars and other service mobiles on the airport surface. The MLAT subsystem uses the transponder reply (Mode S reply/squitter and Mode A/C reply) time of arrival as obtained by a suitable number of ground stations. In detail, the target position estimation is obtained by the TDOA technique (Time Difference Of Arrival), which exploits the time differences between the arrival time in many ground stations of a signal transmitted by a transponder and the time of arrival of the same signal at ground station taken as the reference station. In this work a new TOA (Time Of Arrival) estimation method is described and compared with the standard method (based on edge threshold crossing).