A system with at least one device obtains assistance data for Galileo for a current time from at least one terrestrial apparatus. The system predicts assistance data for Galileo for a plurality of subsequent time instants based on the obtained assistance data for Galileo and associates for each subsequent time instant a separate message authentication code with the predicted assistance data. The system causes transmission of information comprising at least the predicted assistance data for Galileo and the associated message authentication codes to a satellite signal receiver.