Development and Experimental Validation of a GNSS Receiver Simulator for Flight Missions in Hostile Environments

Abstract

The adoption of GNSS technologies for civil aviation enabled the so-called Performance Based Navigation (PBN) that results in a more efficient use of airspace (route placement, fuel efficiency and noise abatement) and, in addition, allows automatic precision approach and landing in low visibility conditions, up to touch down. Despite such potential advantages, the GNSS technology in civil aviation is still almost based on the use of a single constellation (GPS) and a single ranging frequency (L1 band) that, especially for flight operations in hostile environments close to mountains or in valleys with poor connectivity to traditional infrastructures, is not reliable. Indeed, in these conditions, such receivers have well-known vulnerabilities, such as low GPS and SBAS visibility, multipath and potential unintentional electromagnetic interferences. In order to assess and demonstrate the concept of a Dual Frequency Multi Constellation (DFMC) GNSS receiver and related advantages, this paper describes a numerical software tool that can perform a complete flight mission simulation using both a standard aviation-grade GNSS receiver with Single Frequency Single Constellation (SFSC), and an advanced one with DFMC capabilities. The tool can simulate up to three satellite constellations (GPS, Galileo and BeiDou) with a set of different integrity monitoring algorithms and can predict the behavior of such GNSS receivers when installed on helicopters during flight missions in hostiles environments. For this purpose, the proposed approach considers satellite visibility and multi-path effects by modelling the GNSS receiver antenna radiation patterns and the terrain elevation. The proposed simulator and related methods for estimating GNSS vulnerabilities has been finally tuned and validated using experimental flight data gathered during real missions of a helicopter in hostile environments. Several comparisons between simulated and flight data are performed and the accuracy of the simulator results is discussed. Finally, potential improvements and weaknesses of DFMC GNSS receivers with respect to SFSC ones are underlined.