Use of High Altitude Platform Systems to augment ground based APNT systems

An Alternative Position Navigation and Timing (APNT) service is needed to backup satellite navigation for civil aviation in case of a radio frequency interference. Current APNT services rely on legacy systems and range sources based on ground stations and therefore, present limitations in terms of geometric diversity due to poor visibility. Moreover, there is still no straight forward solution how to maintain the correct synchronization of the ranging sources in case of GNSS outage. In this work, we propose the potential use of High Altitude Platform Systems (HAPS) first as pseudolites to enhance a ground APNT system. We evaluate the coverage of the platform and the enhancement in terms of dilution of precision. This lead to a ground-stratospheric APNT system with increased navigation service area. Besides, we propose these platforms for time synchronization and for integrity monitoring of the ground stations.