Super-imposed Mode S signals: Single-antenna Projection Algorithm and processing architecture

This paper presents an effective algorithm to discriminate and separate superimposed SSR (secondary surveillance radar) mode S signals. The algorithm is an adaptation of the PA (projection algorithm) [1,3,4] that perform a blind separation of the multiple SSR sources using a single channel receiver. As present-days SSR stations only have a single-channel receiver, the proposed algorithm is operatively useful, specially for multilateration and wide area multilateration applications, (M-LAT, WAM). The algorithm is evaluated with real recorded data and also simulated signals generated by a complete simulation of a typical MLAT Rx station, from the RF to the digital section. We discuss as well the estimation of the time of arrival for each overlapped signal, that is necessary for the timing. Finally we propose a possible architecture for the signals separation block of the digital processor of the receiving station.