Method and Apparatus for Integrity Communication in a Navigation Satellite System

A system for integrity communication in a navigation satellite system having i) a space segment with a plurality of satellites that emit navigation signals for reception and analysis by user systems for the position determination, and ii) a ground segment with a plurality of observation stations which monitor the satellites;

• wherein:
• the system is constructed for controlling the integrity communication such that it distributes integrity information concerning the satellites to user systems with the navigation signals;
• the integrity information for a satellite has a first SISMA value and a second broadcast SISMA value for the accuracy of the satellite monitoring by the ground segment,
• the second broadcast SISMA value, in contrast to the first SISMA value, takes into account a failure of an observation station of the ground segment;
• a threshold value is provided for the second broadcast SISMA value;
• and
• the system is configured to carry out the steps of,
• transmitting the threshold value with the integrity information for a satellite instead of the second broadcast SISMA value when the latter exceeds the threshold value and the first SISMA value is lower than the threshold value for the satellite;
• and
• changing the integrity information to be transmitted as soon as the second broadcast SISMA value and the first SISMA value for the satellite each exceed the threshold value.