Global Integrity combining ARAIM and SBAS - Method and Operational Benefit

Abstract

Today, Satellite Based Augmentation Systems (SBASs) are in transition to support dual frequency Global Positioning System (GPS) or Galileo. With this evolution comes an architectural change, mitigating some of the time-critical requirements to provision SBAS data to the user. In particular dual frequency users will no longer need fast and continuous transmission of ionospheric corrections for the safety-of-life service. Without the need to model the ionospheric delay, future SBAS may be designed with a much sparser ground network and without a GEO link. Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is a self-reliant integrity scheme that benefits from the very same update of GNSSs to dual frequency signals, and multiple constellations. The integrity information provided to ARAIM users is the Integrity Support Message (ISM) characterizing the GNSS performance with respect to integrity. ARAIM does not apply differential corrections like SBAS. The ISM message is provided to the user on a regular basis; however in contrast to GBAS or SBAS, it is significantly longer-lived and may even be provided in the form of a pre-defined dataset to be replaced only in a multiple-month time scale or on demand. This paper extends the ARAIM integrity concept so that both GNSS measurements with an ARAIM ISM and SBAS augmented measurements can be used in a joint position solution. It discusses improvement of user integrity availability when the concept is used instead of either SBAS or ARAIM alone. To illustrate the use cases for the method, we investigate on the trade space between current geostationary-satellite (GEO) based SBAS and the proposed online ARAIM architecture; we relate the architectural commonalities and differences and finally detail the proposed combination method. The operational benefit isdemonstrated on the basis of simulated scenarios showing the Vertical Protection Level (VPL) performance of the different user algorithms in comparison.