Nominal Performance of Future Dual Frequency Dual Constellation GBAS

Abstract

In this work an overview of numerous possible processing modes in future dual frequency, dual constellation GBAS is given and compared to the current GAST D standard. We discuss the individual error contributions to GBAS protection levels and give an overview of the general processing. Based on this the consequences when adding a second constellation as well as frequency are investigated. Geometrical implications and changes to the residual differential error bounds are studied separately first. In terms of geometry a comparison between the single and dual constellation case is presented using dilution of precision as metric. The influence on the different sigma contributions when using new satellites (Galileo) and signals (E1, L5, and E5a) is individually discussed based on recent measurements. Final simulations for different varying parameters are carried out to compare relevant processing modes in terms of achieved nominal protection levels. A concluding discussion compares the outcomes and analyzes the implications of choosing one or the other mode.

Satellite selection in the context of an operational GBAS

“…We can find again in the plots the impact on the performance that could be expected from the previous simulations. The average VPL increased by about 6% to 8% along the approach, both following the same shape (introduced by speed and height profile, see Gerbeth et al), as expected. In terms of the maximum VPLs, we see some rare outliers which exceed the unconstrained maximum by about 18% to 21%.…”

“…As mentioned earlier, the protection levels we use here as comparative measure are computed according to RTCA DO‐253D. As assumptions for σ air and σ ground , we use models developed at DLR and previously published in an open access article …”

“…and nominal future Galileo (27 sat.) almanacs for satellite orbits Aircraft velocity 70 m/s, except for the final simulation where a speed profile is used σ air and σ ground as in Gerbeth et al, 100‐second models for both GPS L1 and Galileo E1 GBAS ground station broadcasts corrections for 12 satellites from dual constellation Airborne receiver tracks 12 satellites Locations at low (0°), medium (55°), and high latitudes (75°) and 10° longitude We only compare heuristic selections: the baseline “ best sets ” are always also heuristically found and not by exhaustive search We only consider H0 protections levels, not ephemeris or H1 PL (see RTCA DO‐253D for details) The protection levels can be considered as GAST C protection levels without sigma‐inflation or GAST D protection levels without D v / D l terms No airborne geometry screening is performed, but due to the multi‐constellation setup and 12 used satellites, s vert values are almost always well below 2, far from the typical exclusion threshold of 4…”

“…Details on the computation of the protection levels can be found in RTCA DO‐253D . As the absolute value of the achieved protection levels is also not of major interest in this study, but instead the relative changes due to different modifications on the selection, we will not go into details here and refer to the standards or our previous works instead …”

Satellite Selection in the Operational GBAS Context

“…Details on the computation of the protection levels can be found in RTCA DO-253C [14]. As the absolute value of the achieved protection levels is also not of major interest in this studies, but instead the relative changes due to different modifications on the selection, we will not go into details here and refer to the standards of our previous works instead [11,15].…”