RAIM Algorithms Analysis for a Combined GPS/GALILEO Constellation

How far a user can rely on his navigation system is a central question for safety of life applications like air navigation especially in approach phases. For Oceanic, En route or Non Precision Approach phases, the integrity requirements as defined by the ICAO (International Civil Aviation Organization) should be fulfilled by the future Galileo Safety of Life Service. This paper presents the performances of RAIM algorithms using a covariance matrix of a single frequency absolute positioning receiver noise calculated using one year measurement data. In the configuration of combined GPS/GALILEO constellation, the user will have the possibility to track at least 10 satellites at the same time. This high availability of satellites will provide a high availability of RAIM algorithms. The original approach used in this paper is to use the IPRE (Instantaneous Pseudo Range Error) developed in [1] as the input parameter of the RAIM algorithms. This concept provides a generalized covariance matrix of pseudo range noise taking into account correlations of pseudo range errors with close elevation and azimuth angles. Thanks to a Cholesky decomposition, it is always possible to use the classical χ distribution to obtain the fault detection threshold. The advantage of generalizing the RAIM methods is not only in the simplicity of the algorithm, but it is also in its efficiency thanks to lower protection levels obtained.