Discriminating closely spaced aircrafts using time difference of arrival (TDOA) based association algorithm

Abstract

A time difference of arrival (TDOA) based locating system determines the location of an aircraft by measuring the time difference between transponder emissions received at ground station antenna (GSA) pairs. To locate multiple aircrafts, the TDOAs are first grouped according to each aircraft using an association algorithm prior to the individual aircraft locating process. The ability to correctly associate the TDOAs to the right aircraft depends on the received signal to noise ratio (SNR) and the separation between the aircraft. For a given horizontal range, azimuth and altitude separation between an aircraft pair, a technique is developed to evaluate an association algorithm capability to group the measured TDOAs to the correct aircraft. The performance of the association algorithm considers three different military flying formations using emissions from the onboard weapon control radar (WCR) and replies to a secondary surveillance radar (SSR) interrogator. The simulation results show that with the technique, it is possible to determine the probability of correct association of the estimated TDOAs to the right aircraft by the association algorithm. Furthermore, based on a horizontal range and azimuth separations of 50 m and an altitude separation of 1,000 ft, the TDOA based locating system coupled with the association algorithm has the best locating performance using TDOAs obtained from emissions through the main lobe of the WCR antenna.