Method for improving the continuity in a dual frequency satellite navigation system

摘要

A continuity improving method for use in two-frequency navigation satellite system (10) involves observing the ionosphere by measurements in at least two frequency bands containing the frequencies of two-frequency navigation satellite system. An alert message which informs user systems (18) of a change of ionosphere is transmitted when at least one measurement indicates a change of ionosphere that deviates from at least one predefined condition. An independent claim is also included for the method of processing alert message.