Advanced RAIM System Architecture with a Long Latency Integrity Support Message

Advanced Receiver Autonomous Integrity Monitoring is a promising concept enabling aviation safety of life operations, in particular approaches with vertical guidance [1]. The benefits of ARAIM would include a reduced ground infrastructure, a reduced dependency on any one GNSS core constellation, and, in general, a lesser exposure to single points of failure. In ARAIM, as in RAIM, the aircraft compares the various ranging measurements that it makes to different satellites to ensure that they are consistent with each other. However, for the aircraft to meet its integrity requirement, the satellites must perform within a certain set of expectations. Current GNSS ground segments deployed or under deployment may not offer sufficient guarantees that these expectations will always be met. For this reason, ARAIM will require an independent ground monitor that would provide an Integrity Support Message to the users. Each threat would need to be mitigated by a combination of three elements: the ground segments of the constellations, an independent ground monitoring network, and the user receiver. The European Union (EU) and the United States (US) have an agreement establishing cooperation between GPS and Europe’s Galileo system. As part of this cooperative agreement a subgroup was formed to investigate the benefits of Advanced Receiver Autonomous Integrity Monitoring (ARAIM) [1]. This EU-US ARAIM subgroup has developed a reference airborne algorithm [2] and identified key issues affecting the potential use of ARAIM [1]. Among these key issues are the reliance on the core constellations’ providers for the characterization of the nominal and faulted behavior, the possible persistence of faults, the possibility of faults affecting all constellations simultaneously (due to erroneous Earth Orientation Parameters), as well as sovereignty and liability issues. In order to advance in the design of ARAIM, a set of representative ARAIM system architectures was introduced in [3]. In this paper we describe an architecture that minimizes the ground requirements and is closer to today’s Receiver Autonomous Integrity Monitoring (RAIM). We will give a more detailed description of this architecture. We will specify, among other elements, the reference network, the role of offline monitoring, the level of trust given to core constellation providers, and the ISM delivery method. Then, we will outline a possible path from current horizontal RAIM to ARAIM both for the receiver and the Air Navigation Service Provider. REFERENCES [1] Blanch, J., Walter, T. , Enge, P., Wallner, S. , Fernandez, F. , Dellago, R. , Ioannides, R. , Pervan, B. , Hernandez, I. , Belabbas, B. , Spletter, A. , and Rippl, M. , “Critical Elements for Multi-Constellation Advanced RAIM for Vertical Guidance,” to appear in Navigation, Journal of the Institute of Navigation. [2] Blanch, J., Walter, T. , Enge, P., Lee, Y. , Pervan, B. , Rippl, M. , Spletter, A. , "Advanced RAIM user Algorithm Description: Integrity Support Message Processing, Fault Detection, Exclusion, and Protection Level Calculation," Proceedings of the 25th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. -. [3] Walter, T. , Blanch, J., Enge, P., "A Framework for Analyzing Architectures that Support ARAIM," Proceedings of the 25th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. -.