Satellite Selection in the Operational GBAS Context

Kurzfassung

When incorporating multiple constellations into future Ground Based Augmentation Systems (GBAS) a problem with limited VDB (VHF Data Broadcast) capacity might arise. Apart from that, the number of airborne receiver tracking channels could be insufficient to use all satellites in view as well. One way to overcome these issues is to perform any kind of satellite selection to limit the number of used satellites with least possible influence on performance. While the general process of how to select most useful satellites efficiently has been largely covered lately, this paper focuses on the incorporation of such algorithms into GBAS. It investigates different factors that constrain the approach of simply selecting "the best set in every epoch independently" and shows how to overcome some limitations. These constraints include limitations in satellite visibility, loss of satellites during approach (i.e. in curves) and convergence times in the airborne processing until satellites are of use. Various protection level simulations are performed to show the influence of the named factors on the nominal performance. Additionally, this paper describes methods how airborne users can perform stand-alone selection in a most efficient way and later transition into GBAS, which requires using the satellites actually provided with corrections from the ground. Taking into account all these contextual influences on top of the selection process, results show satellite selection is still applicable in GBAS ground stations.