Alternative Architecture for Dual Frequency Multi-Constellation GBAS

Tim Murphy, Matt Harris, Gary McGraw, Joel Wichgers, Linda Lavik, Morten Topland, Mutaz Tuffaha, Susumu Saito

Abstract: This paper describes an alternative architecture candidate proposal for consideration for the future Dual Frequency MultiConstellation (DFMC) Ground Based Augmentation System (GBAS). The GBAS architecture candidate builds off the work done over the last 10 years by the Single European Sky Air Traffic Management Research (SESAR) program. However, the proposed alternative architecture is designed to enable more optimal airborne processing that is expected to enable better performance (e.g. higher accuracy and smaller alert limits), increased robustness to loss of civil GNSS signals on either L1/E1 or L5/E5a frequency as well as to the loss of a constellation, and higher availability for DFMC GBAS globally. The alternative architecture is envisioned to support one or more new levels of GBAS approach service. This GBAS Approach Service Type (GAST) will be referred to generically as GAST X in this paper. GAST X is envisioned as a natural extension of the currently defined GAST C and GAST D. The proposal borrows heavily in many respects from the SESAR proposal for DFMC GBAS documented in reference [1]. However, some of the processing has been reallocated to the airborne equipment in order to enable some very desirable capabilities. In the proposed GAST X DFMC GBAS concept, raw measurements from both L1/E1 and L5/E5a civil GNSS frequencies are uplinked in addition to corrections and other parameters that are already uplinked from ground stations that support the existing GAST C and D services. Uplinking raw measurements instead of corrections potentially enables the use of pure carrier phase position solutions such as Real Time Kinematic (RTK) Carrier Phase (CP) based solutions. Moreover, it allows for a low noise long baseline airborne iono gradient monitoring capability. This paper describes the basic architecture to support GAST X and gives some predicted performance results for accuracy, the size of protection levels and the availability based on a simulation study. In addition, the paper discusses a potential set of services and considers the transition between service levels that would result from loss of a frequency or total failure of a constellation.
Published in: Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021)
September 20 - 24, 2021
Union Station Hotel
St. Louis, Missouri
Pages: 1334 - 1374
Cite this article: Murphy, Tim, Harris, Matt, McGraw, Gary, Wichgers, Joel, Lavik, Linda, Topland, Morten, Tuffaha, Mutaz, Saito, Susumu, "Alternative Architecture for Dual Frequency Multi-Constellation GBAS," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 1334-1374.
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