Analysis of Multi-GNSS Service Performance Assessment: ARAIM vs. IBPL Performances Comparison

A. Cezón, M. Cueto, I. Fernández

Abstract:	In the following years, the European GNSS programmes will face critical events and decisions crucial for the successful implementation of their initial objectives and the definition of new strategic missions in line with the principles of the European Community treaties. Safety-of-Life services of EGNOS and Galileo within the objectives of the European Satellite Navigation Programmes. The European Commission is currently working on the on-going activities in the area of integrity service provision, as well as in the definition of the future ARAIM (Advanced RAIM) standard in international fora. The current ARAIM algorithm references are based on the US GNSS Evolutionary Architecture Study (GEAS), aimed at the provision of LPV-200 service performances worldwide using two or more constellations transmitting on two frequencies (L1 and L5). GEAS ARAIM techniques are an evolution of the single-frequency Receiver Autonomous Integrity Monitoring (RAIM) based on an airborne comparison of each satellite measurement to the consensus of the rest of the available satellite measurements. ARAIM would support LPV-200 and therefore it is subject to a deeper scrutiny than the former RAIM, going beyond the system development into the operation of the system. Furthermore, ARAIM requires the support of a ground segment to provide the user with an Integrity Support Message (ISM). The Isotropy-Based protection level (IBPL) technique represents an alternative protection level computation technique which makes no assumption on the statistical behavior or the size of individual measurement errors. As in case of ARAIM, it does not rely on the one-fault-at-a-time assumption that has been one of the key hypotheses of conventional RAIM-based protection level computation techniques. The IBPL technique was developed by GMV in the framework of terrestrial liability-critical applications to cope with local degraded environment characteristics, though it turns out to be of potential interest for safety-of-life applications. It also provides a very simple and robust solution to the multi-constellation integrity problem, in principle without the need of a specific ground segment. The EC launched the Mission and Service Implementation Lot 2 (MSIL2) project “Technical Support to Mission and Services Evolution”, with the objective of providing support for different GNSS aspects. GMV is the prime of MSIL2 consortium. One of the objectives of this activity is to support the EC on the analysis of multi-GNSS Safety-of-life service performances, including ARAIM. In this context, the MSIL project analysed the performance of IBPL for aviation users (LPV-200 target mission), comparing it with the ARAIM performance as a reference. The objective of this paper is to summarize the analysis performed in MSIL2. The paper will analyze and compare the performances achieved with GEAS ARAIM (2008 and 2010 versions) and IBPL techniques for aviation users. In order to adequately develop the analysis of the performances obtained using ARAIM and IBPL techniques a specific strategy has been followed: - First of all, a set of scenarios has been identified and specified to analyse the performances achieved using the different techniques. Three fault-free scenarios (considering Galileo and GPS constellations) as well as two feared event scenarios (with single faulty satellite and an entire faulty constellation) were taken into account; - Secondly, the available infrastructures were adapted to generate the feared event scenarios previously identified; - Thirdly, the selected scenarios were executed using each of the aforementioned algorithms: ARAIM2008, ARAIM 2010 and IBPL. The analysis was focused on vertical availability and accuracy in the fault-free scenarios and integrity in the feared-event scenarios. a) Output performances for the fault-free scenarios will be presented in terms of VPL CDF distributions, VPL Stanford Diagrams and VPL 99% global maps. b) As far as the feared events are concerned, the analysis was focused on checking the integrity failures, proving VPE/VPL ratio CDF plots, VPL CDF plots and VPL Stanford Diagrams. - Next, the performances obtained with each technique were analysed and compared. ARAIM 2008 results are provided only for information, since nowadays this algorithm is ruled out and has evolved to ARAIM 2010. - And finally a set of conclusions and recommendations are identified. The main results for each scenario and technique are presented in this paper, including a summary of the performances achieved. To sum up, the following conclusions can be provided from the analysis developed in this study: - IBPL performances are in line with ARAIM 2010's, for selected scenarios. - However, IBPL may enjoy a higher degree of flexibility and autonomy, as it does not need external information to ensure integrity. This hypothesis needs to be confirmed through a broader analysis including all LPV-200 requirements. - IBPL does not need to fix the maximum number of simultaneous satellite failures as it occurs in ARAIM. - ARAIM performance is driven by the bounding parameters and the number of satellites available, whereas IBPL performance is driven by the GNSS SIS accuracy and the number of satellites available. Further information on the comparison of the results achieved using each technique and scenario will be deeply analysed and provided in the paper. New results related to potential new activities could also be included in the paper.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2654 - 2663
Cite this article:	Cezón, A., Cueto, M., Fernández, I., "Analysis of Multi-GNSS Service Performance Assessment: ARAIM vs. IBPL Performances Comparison," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 2654-2663.
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