Correction of propagation errors in Wide Area Multilateration systems

Methods to estimate and correct slow time-variant position errors due to bad synchronization and propagation in Wide Area Multilateration Systems (WAM) are presented. The procedure does not use emitters at known locations. Instead it uses opportunity traffic emissions (from the aircraft present in coverage). The need for these methods came from the difficulty to install reference beacons that can be seen simultaneously by all WAM base stations.