The researchers of the Space and Navigation Technologies Area, in collaboration with their colleagues of Politecnico di Torino, investigated as “Galileo users” the technical aspects of the Galileo outage that hit the Galileo satellite navigation system in the last few days.
All the posts related to the Galileo outage are available on the NavSAS website (www.navsas.eu). In particular, the last post www.navsas.eu/node/614 summarizes what our researchers observed from July 15th to today, July 18th. NavSAS is the joint research group of LINKS and Politecnico di Torino focused on satellite navigation technology.
The above mentioned researchers, through their scientific tools and receivers started observing what is happening to Galileo from the point of view of the users. And some interesting observations came out.
For example, the short-term behavior of the computed position has an interesting “snake-like” trend, suggesting a temporal correlation of the SIS induced error (no temporal correlation is introduced by the PVT solution algorithm used by the receiver), possibly in the form of a clock drift. The receiving antenna was fixed on our rooftop. The figure hereafter reports this observation (blue points: without carrier smoothing, red points: with carrier smoothing; the temporal correlation introduced by carrier smoothing is negligible with respect to the one brought by the SIS). By processing 4 minutes of GNSS signal taken at 09:10 UTC, our software receiver provided a severely biased position solution by means of a Least Mean Square (LMS) algorithm. The first estimation is located about 1158 meters from the georeferenced antenna, and the solutions are drifting towards the South-West direction. In particular, shifts of 21 m and 58 m on respectively E-W and N-S coordinates are experienced during the observation time. A comparison between non-smoothed and very-smoothed positioning solutions is shown in the figure. Even without the use of carrier-smoothing the sequence of estimations shows a remarkable level of correlation along the time. Nevertheless, it has to be remarked that Galileo is usable since December 2016, but its services are still in the Initial phase, and the full operation capability has not been declared yet.
The whole news is available on www.navsas.eu/node/610