Comparison of ADS-B Verification Methods: Direct TDOA and MLAT

Abstract

Automatic Dependent Surveillance - Broadcast (ADS-B) is an emerging means of aeronautical surveillance for air traffic control. Aircraft periodically broadcast positional updates to ground stations. Although ADS-B outperforms traditional radars in terms of accuracy and update rate, positional verification - a technique used to check the validity of the position report - is necessary to counter anomalies. In this study, two different methods were compared when the ground stations measure time difference of arrival (TDOA). One is direct; the test statistic is essentially the difference between the measurement and a prediction calculated from the position report. Another method is multilateration (MLAT)-based and two-step; the emitter position is firstly estimated, whereupon the difference between the estimated and reported positions constitutes the test statistic. As a result of the comparison, a performance difference, which depending on the number of receivers, was revealed. This is an useful suggestion for implementing ADS-B when the existing multilateration infrastructure is exploited.