EGNOS CPF, Evolving from GPS Single Frequency to GPS and Galileo Dual Frequency

Juan Pedro Lam, Jean Manuel Melinotte, and Francisco Javier Esteban

Abstract: In summer 2008, the European Space Agency, ESA, declared successful the qualification of EGNOS System V2 for Safety of Life purposes. The safety of the System being achieved in the service area, this milestone marked the start of several engineering activities to improve the System performance by optimising the margins of the different safety barriers. In parallel to the activities to improve EGNOS V2, ESA, in the frame of the European GNSS Evolution Programme, launched in 2008 several studies to provide augmentation to dual frequency GPS and Galileo constellations. A concept phase was followed by a preliminary analysis phase and a definition phase, which set the grounds for EGNOS V3. These phases of the project allowed confirming the preliminary design and the service improvements to be obtained with a L1/L5 GPS and Galileo augmentation. EGNOS V3 entered the Final Design and Development phase in January 2018, and will be organised in two major steps: first the delivery of a GPS L1 augmentation (EGNOS V3.1), followed by a L1/L5 GPS and Galileo augmentation system (EGNOS V3.2). In this context of continuous evolution strategy, a fundamental contributor to the improvements introduced in the System has been the Central Processing Facility (CPF). The CPF is the core of the EGNOS Ground Segment, basically responsible to: 1. Generate navigation messages for the users in the service area, including: o wide area differential (WAD) corrections for GPS satellites; o ionospheric delay information; o confidence level of a user’s position estimate; o alerts (for individual satellites or ionospheric grid points when necessary). 2. Monitor the integrity of EGNOS System, i.e. protect users from applying hazardous misleading information (detection of anomalies of all serviced satellites, checking the GPS and ionospheric correction and the integrity data, etc.). With its central position in the System, the CPF has been behind most of the services improvements introduced in EGNOS since 2008. To achieve this, the CPF have been evolving along a wide range of domains, for example: • Algorithms Modernisation (iono modelling, orbitography, error bounding, synchronisation, …); • State of the Art Architecture (Obsolescence Management, SW &HW Qualification); • Evolution from GPS L1 to GPS&Gal L1/L5 augmentation (new applicable standards, modelling of GPS and Galileo L1/L5 degraded modes, use of Galileo for iono monitoring…) This article goes through the main evolutions introduced in the CPF from the first EGNOS qualification in 2008 until the time horizon of 2024; with special emphasis on the technological/algorithmic innovations that are being developed for CPF Dual Frequency Multi-Constellation ( CPF DFMC) during the V3 Phase CD activities. The first part of the article will describe the most relevant CPF optimisations developed in V2 to improve the service and to address the singularities observed on the System, showing how the performance was improved thanks to these evolutions. In the second part, the focus will be put on the design of the CPF for V3. It will start by comparing the principal differences in the SW and HW architecture with respect to V2. This will be followed by an overview of the cutting edge development logic adopted for CPF in V3, that capitalises on the early availability of CPF models to verify exhaustively the CPF algorithms. After this, the article will present the algorithms selected both for GPS L1 augmentation and for GPS and Galileo L1/L5 augmentation, with special attention to the features that introduce an innovation with regard to V2 (Kriging, Use of Galileo for ionospheric monitoring, MT28, ODTS, …). The article will conclude with a highlight of the preliminary results achieved by these algorithms.
Published in: Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018)
September 24 - 28, 2018
Hyatt Regency Miami
Miami, Florida
Pages: 1012 - 1037
Cite this article: Lam, Juan Pedro, Melinotte, Jean Manuel, Esteban, Francisco Javier, "EGNOS CPF, Evolving from GPS Single Frequency to GPS and Galileo Dual Frequency," Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018), Miami, Florida, September 2018, pp. 1012-1037.
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