D6.1 Space-based MLAT algorithms description

This document presents the theoretical formulation of the algorithms and tracking filters used in SATERA to perform a space-based multilateration (MLAT) that uses three kinds of measurements: Time of Arrival (TOA), Frequency of Arrival (FOA) and Angle of Arrival (AOA). This takes the name of Enhanced MLAT (E-MLAT). The signals received by each Low Earth Orbit (LEO) satellite produce a set of measurements that are transported via Inter-Satellite Links (ISL) to a ground station and then to a Central Processing Station (CPS). Here, the measurements are finally put together to estimate the aircraft location in a GNSS-independent way. The aim is to describe in detail all the algorithms for the initial position estimation of the aircraft and the subsequent tracking over its trajectory. Since the E-MLAT is meant to be a backup for when GNSS in unavailable, an integrity indicator is also considered, so that the Automatic Dependent Surveillance – Broadcast (ADS-B) data can be validated against the E-MLAT based position. In this way, when the ADS-B position exists, but is not correct, due to service disruptions or attacks, the system is able to identify the issue, arise an alarm and, if possible, keep tracking the aircraft. All the processing is carried out in the CPS, while the satellites only provide the measurements. The data that needs to be transmitted to the CPS are defined in this document, together with the output data, after processing. Finally, a Multi-Target-Tracking approach is proposed and described.