Multi-Constellation System as Augmentation to GPS Performance in Difficult Environment or Critical Applications

The GPS Standard Positioning Service (SPS) does not provide suitable performance in all environment conditions or in every possible applications. In severely signal degraded environments, e.g. mountainous or urban areas, where a lot of GPS signals are blocked by buildings or natural obstacles, the positioning is inaccurate because of bad satellite configuration or impossible owing to lack of minimum number of visible satellites. Otherwise GPS SPS is inadequate for critical safety applications like aircraft take-off or landing, because does not satisfy the Required Navigation Parameters (RNP) relative to these flight phases. To solve the GPS gap on regional scale, space-based augmentations could be employed. In this study a simulation is carried out, considering GLONASS and EGNOS GEO constellations and a set of 3 geosynchronous satellites (similar to QZSS space segment). A software for constellation analysis is developed in MATLAB® environment to evaluate the considered augmentations performances in critical conditions (urban canyon or critical phase of flight). The used indicators to evaluate coverage performance are the VSN (Visible Satellites Number), DOP (Dilution of Precision) and the probability that integrity is available to be computed in autonomous.