Space-based multilateration for a GNSS-independent aircraft localisation

Modern Air Traffic Control (ATC) relies on the Automatic Dependent Surveillance–Broadcast (ADS-B) system, which transmits GNSS-based aircraft positions (computed onboard) to the ground. While ADS-B is key to future Air Traffic Management (ATM), its dependence on GNSS makes it vulnerable to failures and cyber-attacks. For this reason, ground-based systems are currently used to validate ADS-B data, but they are unavailable in remote areas, such as the ocean.This paper proposes a Low Earth Orbit (LEO) satellite constellation performing multilateration (MLAT) on ADS-B signals to provide GNSS-independent position estimates. Unlike classical ground-based multilateration, the space context introduces challenges such as limited visibility, poor geometry, ill-conditioning, and synchronisation issues. To address these limitations, two possible solutions are presented and evaluated: (i) a combination of Time of Arrival (TOA) with additional measurements, such as Frequency of Arrival (FOA) and Angle of Arrival (AOA); (ii) an improved and optimised receiver antenna to obtain larger coverage of the satellites. In both cases, the proposed architecture comprises LEO satellites equipped with ADS-B phased array antennas, useful for obtaining multiple beams with different footprints on the ground.The system localisation performance is evaluated using the Cramér–Rao Lower Bound (CRLB). Simulations over the Atlantic Ocean assess different measurement combinations and constellation configurations.The results show that, with the appropriate design, the system achieves a localisation accuracy that completely meets the requirements of air traffic control en-route (i.e., 350 m horizontal RMS error).