Inside GNSS Media & Research

SEP-OCT 2018

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46 Inside GNSS S E P T E M B E R / O C T O B E R 2 0 1 8 2 . Performance metrics and calcula- tion methods have been harmonized to a large extent to those established in GNSS international standards, following the guidelines provided by the United Nations International Committee on GNSS (ICG). Nevertheless, as system architect, ESA is also conducting in-field tests to demonstrate the system and signals usability in real environments, from open sky conditions to urban canyons, exploiting both professional and mass- market receiver technolog y. Ty pical Position, Velocity, and Time (PVT) results will be provided for illustration purposes as an indication of attainable performance in the positioning domain. ese figures of merit along with the committed Minimum Performance Lev- els (MPL) are currently being revised for the upcoming Galileo Enhanced Service provision phase, targeted in 2019 (see presentations by E. Chatre and A. Mozo in Additional Resources). In addition to the results presented in this article, the Initial Services Quarterly Performance Reports published by GSA on the European GNSS Service Centre website can be referred to for a routine and detailed review of the full set of fig- ures of merit presented in Table 2. Navigation Message Data Accuracy e broadcast navigation message accu- racy is measured through the Signal In Space Ranging Error (SISE), defined as the difference of the satellite position and time as broadcast by the navigation message and the true satellite position and time, projected on the user-satellite direction. In agreement with the Gali- leo OS-SDD, the ranging accuracy is calculated as the 95th percentile, per satellite and per constellation, of the instantaneous SISE time series over a 30-day period. Additional conditions include the computation of the error as an epoch-wise global average with- in each satellite footprint, the usage of healthy Signal In Space only, and exclusion of propagation and receivers effects. More details about the SISE cal- culation methodology can be found in Additional Resources. SISE is one of the most important GNSS figures of merit, conveying the system driven accuracy of the orbit and clock predictions in the broadcast navigation message. e long term historical SISE plots shown in Figure 4 and Figure 5 , respec- tively, computed per satellite and con- stellation over 30-day sliding windows, showed a non-stationary behavior with constant improvement over time, span- ning a period of almost four years, from September 1, 2014 to May 31, 2018. SISE has only recently reached a stabilization plateau with a constellation value of about 0.45 meters (95%, global average). is has been achieved through a com- bination of several factors, including the increased number of operational satel- lites, enhanced versions of the Ground Performance Figure of Merit Performance metrics Initial Open Service target P1 Signal In Space ranging accuracy for single and dual frequency users 95th percentile Global Average over all Age of Data. ≤7 m for any healthy SIS, ≤2 m over all healthy SIS P2 Availability of OS SIS ranging service for single and dual frequency users % of time ≥ 87% P3 Per Satellite availability of OS SIS for single and dual frequency users % of time ≥ 87% P4 HDOP availability % of time ≥ 50% P5 Horizontal positioning service availability % of time ≥ 50% P6 OS UTC time dissemination accuracy 95th percentile <30 ns P7 OS UTC frequency dissemination accuracy 95th percentile <3E-13 P8 Availability of UTC determination service % of time ≥ 87% P9 GST-GPS time offset dissemination accuracy 95th percentile <20 ns P10 Availability of GGTO determination availability % of time ≥ 80% Table 2 Galileo system performance figures of merit set for Initial Open Service FIGURE 4 Per satellite SISE 95% Global Average history (FNAV), 30 days moving average (1 day time step), September 1, 2014 – May 31, 2018 10 3 10 2 10 1 10 0 10 –1 Feb-15 Aug-14 Aug-15 Feb-16 Aug-16 Feb-17 Aug-17 Feb-18 SISE 95% (FNAV DF) [m] MEASURING G ALILEO PERFORMANCE

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