Before revision: It uses a minimum of six measurements which can be achieved with 6 satellites or 5 satellites with baro-aiding to not only detect a possible faulty satellite, but to exclude , a method of augmenting the GPS integrity solution by using a non-satellite input source) to detect an integrity anomaly.
After revision: At least one satellite, in addition to those required for navigation, must be in view for the receiver to perform the RAIM function; thus, RAIM needs a minimum of five satellites in view or four satellites and a barometric altimeter ( baro-aiding , a method of augmenting the GPS integrity solution by using a non-satellite input source) to detect an integrity anomaly.