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

In the following years, the European GNSS programs 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. Services usable by communities requiring integrity are within the objectives of the European Satellite Navigation Programs, thus the European Commission (EC) is currently working in this area, as well as in the definition of the future ARAIM (Advanced RAIM) standard in international fora. The objective of this paper is to summarize a comparative analysis of ARAIM user algorithms performed by GMV under the frame of a Support Contract to the EC. The paper analyzes and compares the performances achieved with GEAS ARAIM (2008 and 2010 versions) and IBPL techniques for aviation users. At the time the analyses were performed, the principal consolidated reference for the ARAIM avionics algorithm was that described in GEAS Phase II (2010) report. Further versions of ARAIM have been presented, but they are based on GEAS Phase II ARAIM principles ([REF.10] and [REF.1]) The ARAIM algorithm references used for this study 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). 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 is aimed to 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. Since the US GEAS concluded (2010), the U.S.-EU Working Group C-ARAIM Technical Subgroup has taken the lead to further develop the ARAIM concept. The work of the group so far confirms that 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 provides a very simple and robust solution to the multi-constellation integrity problem, in principle without the need of a specific ground segment, as claimed by its developers. 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. In this context, the MSIL project analyzed the performance of IBPL for aviation users (LPV-200 target mission), comparing it with the ARAIM performance as a reference. The results of this comparison were considered as a useful benchmarking exercise in the development and analysis of multi-GNSS integrity solutions for aviation. In order to adequately develop the analysis of the performances obtained using ARAIM and IBPL techniques a specific strategy has been followed: Identification of a set of scenarios to analyse the performances achieved using the different techniques; Adaptation of the available infrastructure tools to generate the feared event scenarios; Execution of the selected scenarios using ARAIM 2008, ARAIM 2010 and IBPL; Analysis and comparison of the performances obtained with each technique; and Identification of conclusions. The main results for each scenario and technique are presented in this paper, including a summary of the performances achieved.