MLAT Impact Analysis / Part 1 - Introduction and Simplified Assessment: Analysis of mutual interference od surveillance systems using 1030 / 1090 MHz signals

This study investigates the occupancy of the SSR frequencies 1030 and 1090 MHz due to interrogation of and replies from aircraft transponders caused by various sensors like SSR, Mode-S radar, MLAT system or ACAS systems. A special focus lies on the additional transponder load due to the introduction of a MLAT in addition to or as a replacement of one or more existing radar systems.
The assessment presented here is done in a simple way based on the calculation of the occupancy of a single transponder (either Mode A/C-only or Mode S) situated in a location which is covered by all the given interrogators. The investigated scenarios are on the one hand simple scenarios given by AustroControl GmbH. And on the other hand scenarios with more sensors which represent the situation in the vicinity of Zürich.
But in the next step a follow-up is intended, which will consist of software package allowing a more sophisticate evaluation including the real positions of the sensors and their coverage volumes. Furthermore, it will also incorporate traffic scenarios.
The result of the assessment conducted in this paper confirms that the transponder occupancy caused by MLAT depends mainly on the number of aircraft inside the coverage of a transmitter and should be no problem under normal conditions. The limit where MLAT causes a 2 % transponder occupancy lies at about 315 aircraft. In heavily populated airspace the transmit coverage of MLAT should therefore be split between a larger number of transmitters with lower ranges.