Availability of Iono Gradient Detection with Alternative Architectures for DFMC GBAS

The International Civil Aviation Organization (ICAO) Ground Based Augmentation System (GBAS) Working Group (GWG) is working on development of standards for Dual-Frequency Multi-Constellation (DFMC) GBAS. In the initial stage of the development, an architecture trade study is being conducted in order to select the overall architecture and to develop the concept of operation (ConOps) for DFMC GBAS. A previous paper discussed an alternative architecture candidate proposal for consideration for the future DFMC GBAS based on uplinking raw measurements in addition to the differential corrections that are uplinked to support legacy GBAS service types. A second paper extended the work to provide greater clarity regarding proposed ionospheric gradient monitoring techniques. This paper presents the results of a simulation study done to explore the difference between 3 different strategies for position determination and Ionospheric Gradient Monitoring (IGM). Two of the strategies are based on the GBAS Approach Service Type X (GAST X) architecture and the third is based on the architecture proposed by Eurocontrol that was developed under the Single European Sky ATM Research (SESAR) program (commonly referred to as GAST F). The paper reviews the test statistics and processing for each strategy. The paper then expands on methods for bounding residual ionospheric errors and for detection and isolation of ranging sources with large iono gradients. Then a simulation tool is described where representative models of ionospheric equatorial plasma bubbles derived from imaging technology are used to induce iono gradient delays on multiple simulated satellite signals simultaneously. This modelling tool is then used to assess the effectiveness of the different proposed iono gradient monitoring techniques in a severe iono environment. Finally, the model is used in an availability study comparing the performance of the different IGM strategies and position computation methods given different combinations of satellite constellations.