Global Performance Assessment of DFMC SBAS

Abstract

Single Frequency Satellite Based Augmentation Systems (SFSBAS) systems such as WAAS, EGNOS, MSAS and GAGAN have been providing differential corrections and integrity bounds for the L1 GPS C/A and L1 SBAS ranging signals. These SBAS corrections have been used in computing SBAS corrected position solutions and SBAS based protection levels in aviation receivers. The single frequency SBAS based position and integrity is used in all phases of the flight including when performing precision RNP (Required Navigation Performance) operations and LPV (Localizer Performance with Vertical guidance) approaches. Recently the concept of operations of Dual-Frequency, Multi-Constellation (DFMC) SBAS (also referred to as SBAS L5) has been introduced and the first version of the DFMC SBAS receiver performance document (ED259) has been published. DFMC SBAS is designed to augment both GPS and Galileo constellations and it works on the assumption that the on-board GNSS receivers can track both L1 and L5 band signals. ED-259 specifies the airborne receiver requirements for the integration of DFMC SBAS augmenting GPS and Galileo constellations. DFMC SBAS primarily corrects for the GNSS satellite clock and ephemeris errors. Since iono-free pseudo range measurements are required to be used by the receiver, DFMC SBAS does not need to provide ionospheric corrections. All current and future SBAS providers have DFMC SBAS in their roadmap. The objective of this paper is to study the potential benefits of DFMC SBAS from the perspective of an aviation certified GNSS receiver manufacturer. Collins Aerospace has been working on a project funded by the EUSPA (European Union Agency for the Space Programme) known as MUlti-mode GPS and Galileo (MUGG). The objective of the MUGG project is to develop a DFMC SBAS GNSS aviation receiver with real-time SBAS L5 and H-ARAIM functions in order to validate the ED-259 Revision A MOPS ([1]) requirements currently in development. The MUGG prototype is based on an aviation certified (TSO) Collins Multi-Mode Receiver (MMR), the GLU-2100 whose hardware already integrates the DFMC growth capability. This MMR hardware has been certified on multiple Boeing and Airbus platforms. The potential benefits of DFMC SBAS are expected to be the availability of lower protection levels, faster time to compute a full SBAS precision approach (PA mode) solution (since the single frequency SBAS ionospheric corrections grid does not need to be downloaded) and the potential to expand SBAS service to new areas with limited infrastructure. This paper will begin by briefly describing the main differences between the SFSBAS and DFMC SBAS systems and their impact to receiver processing. Next, real historical broadcast data from WAAS, EGNOS, MSAS and GAGAN satellites will be used to compute SBAS horizontal and vertical protection levels (HPL and VPL) and this will be compared against a hypothetical dual-frequency SBAS system that utilizes on-board iono-free GPS pseudo range measurements. The historical contribution of the ionospheric component to the overall SBAS based protection level will be studied and analyzed. Further the benefits of adding Galileo to DFMC SBAS positions will be studied by modelling Galileo satellite clock and ephemeris corrections and determining its impact to the SBAS performance. Additionally, world-wide availability analysis will be performed using the historical broadcast data. It is expected that this paper will provide insight into the expected benefits of DFMC SBAS and provide a means to perform a cost-benefit analysis for the introduction and adoption of DFMC SBAS for receiver manufactures, air navigation service providers, aircraft manufacturers and airlines.