Transmitting GBAS messages via LDACS

Abstract

The Ground Based Augmentation System (GBAS)is a landing system for aircraft based on Global NavigationSatellite Systems (GNSS). It consists of a reference station at anairport that generates corrections and integrity parameters thatare transmitted to arriving aircraft. The broadcast is currentlyaccomplished via a VHF data broadcast (VDB). In recent years itturned out that proper siting and frequency planning for theVDB is a challenging task in an operational environment.Coverage, as well as signal power issues, especially at large andcomplex airports have led to a number of considerations thathave to be taken into account when installing VDB transmissionantennas. Furthermore, current GBAS only broadcastcorrections for the L1 frequency of GPS satellites. Availabilityissues, mainly due to ionospheric effects in equatorial regions,however, drive the development of expanding GBAS from asingle frequency single constellation system towards a dualfrequency multi constellation architecture. Transmittingadditional corrections and integrity parameters at the sameupdate rate is challenging due to the limited capacity of the VDBdata link. Finally, transmission should offer the potential toprovide secure transmissions with an authenticated signal inorder to be robust also from a security perspective. For all thesereasons it can be envisioned to provide the GBAS messages viaLDACS which is currently in the process of standardization. Thiscould resolve the issues mentioned and thus support GBASimplementation in the future. This paper provides an overview ofthe expected benefits mentioned above and provides a firstperformance estimation of GBAS over LDACS.