Remote Sensing (Jun 2019)
Galileo Single Point Positioning Assessment Including FOC Satellites in Eccentric Orbits
Abstract
On August 2016, the Milena (E14) and Doresa (E18) satellites started to broadcast ephemeris in navigation message for testing purposes. As the Galileo constellation is not yet complete. It is very important to have two more satellites available since the position accuracy increases as the number of visible satellites increases. In this article, we examine how the inclusion of the Milena (E14) and Doresa (E18) satellites impacts the position accuracy. The analysis was carried out on 20 days of 1-Hz observations collected by a receiver placed in YEL2IGS (International GNSS service) station. Two different scenarios are considered: the first excludes the measurements coming from the analyzed satellites, while the second one includes them. The analysis was conducted by using a suitable software tool developed in the MATLAB® environment able to compute satellites position from both the broadcast and precise ephemerides, to assess DOP (Dilution Of Precision) parameters and to compute single-point positioning for all Galileo frequencies. The analyses are conducted by using both broadcast and precise ephemeris. The inclusion of the two satellites improves the system availability, varying it from 94.1−97.94%, the DOP parameters, and the percentages of achieved positioning solutions by about 5% regardless of the frequency used. Nevertheless, in the positioning domain, when the broadcast ephemerides are used, the inclusion of the satellites worsens both the horizontal and vertical accuracy of the solution. The deterioration of the horizontal accuracy goes from 0.17 m with E5a frequency measurements to 0.74 m with E1 measurements. The reduction of vertical accuracy goes from 0.68 m for E5a to 1.2 m for E1 measurements. However, if precise ephemerides are used, both the horizontal and the vertical accuracy remain stable, actually for the E5b frequency, the DRMS (Distance Root Mean Squared) improves by almost 0.5 m. The results achieved show that the real drawback to overcome is related to the quality of broadcast ephemeris as, when precise ephemeris are used, the number of solutions achieved is increased by about 5% with an accuracy similar to that obtained when the satellites are excluded.
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