Galileo HAS Availability Analysis Using the Internet Data Distribution Service

This paper evaluates the availability and outages of Galileo High Accuracy Service (HAS) corrections received over the Networked Transport of RTCM via Internet Protocol (NTRIP). We evaluate the service's performance across three distinct locations: within the HAS service area at a university building in Winterthur, Switzerland (station ZHAW), and outside the service area in Daejeon, South Korea (station DAEJ), and on Mauna Kea, Hawaii (station MKEA). The study evaluates a four-week period from November 19 to December 16, 2023, assessing the degradation of HAS service availability due to the geographic location of the station and examining the impact of HAS corrections on code-based position solutions using an dual frequency, dual constellation ionosphere-free combination. Our methodology involved collecting and analyzing GNSS code and carrier measurements, satellite ephemeris data, HAS clock and orbit corrections, and code biases for GPS and Galileo satellites of the L1 and L2C signals and E1 and E5, respectively. The analysis revealed that clock and orbit corrections were unavailable in 1.88% for GPS and 1.31% of the time for Galileo, equating to approximately 20 hours (GPS) and 15 hours (GAL) of downtime over the study period. Furthermore, we examined the effect of HAS corrections on positional accuracy by comparing lateral, longitudinal, and vertical deviations from a classic standalone position (referred to as DFMC Ifree) and a HAS augmented position (referred to as HAS Ifree) to the respective reference position at each station. The results indicated a slight reduction in standard deviations at station ZHAW for HAS Ifree compared to DFMC Ifree, although inconsistencies were observed at station DAEJ and station MKEA, attributed to fluctuations in the number of usable satellites. The study concludes with recommendations for enhancing HAS service reliability and positional accuracy. This includes extending HAS correction validity and exploring the use of more robust signals such as GPS L5 instead of GPS L2C, to mitigate multipath effects, and the use of a carrier based position solution.