Inside GNSS Media & Research

SEP-OCT 2018

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50 Inside GNSS S E P T E M B E R / O C T O B E R 2 0 1 8 both single and dual frequency users will already exceed 90% with 22 satel- lites. is working point is expected to be reached soon, once the on-going commissioning activities for L10 sat- ellites are completed. e availability of posit ioning ser v ice is computed through a service volume simulation for rural environment conditions (see OS-SDD for more details). System Timing Performance Metrics e system timing performance moni- toring is currently being monitored by the TGVF Timing Validation Facil- ity (TVF), using inputs from different UTC(k) European laboratories, led by GMV Spain and the German National Metrology Institute (PTB). In addition to TGVF-TVF, an independent analysis of Galileo timing performance is provid- ed by the Istituto Nazionale di Ricerca Metrologica (INR iM, Ita ly), in t he frame of ESA system verification activi- ties. Galileo-GPS calibrated receivers are connected to the local realization of UTC(k) for the assessment of UTC and GPS to Galileo (GGTO) dissemination accuracy. The OS SIS UTC time dissemina- tion accuracy is evaluated through the measurements of a standard timing/ calibrated laboratory receiver, result- ing in minor local error contributions to the overall UTC dissemination error budget. e computation of daily UTC mean values further reduces the impact of short term variations. As shown in Figure 11 , from the start of the Initial Services on December 15, 2016 to June 30, 2018, the UTC dissemi- nation error using UTCrapid as refer- ence is around 8.4 ns (95th percentile), well below the Initial Services target of 30 ns. Similarly, the accuracy of the broad- cast GGTO is computed as the 95th percentile of the difference between the broadcast GGTO prediction conveyed by the Galileo navigation message and the estimated GGTO. As for the UTC dissemination accuracy, only system contributors are considered; user envi- ronment and receiver contributions are excluded. As shown in Figure 12 , the overall broadcast GGTO accuracy dur- ing the period December 15, 2016 – June 30, 2018 was 6.9 ns (95th percentile), also within the corresponding 20 ns specifi- cation for Initial Services. GGTO pre- dictions are currently generated using the observations of combined Galileo- GPS calibrated timing receivers located at the two Galileo Control Centers. Fur- ther optimization of the GGTO predic- tion algorithm is on-going in order to mitigate some of the outliers observed in the period reported above. Figure 13 shows t he operationa l timeline of the master clocks for the MEASURING G ALILEO PERFORMANCE FIGURE 10 Evolution of the Galileo OS Positioning Service Availability 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Availability 8 10 12 14 16 18 20 2 2 2 4 Number of Operational Satellites FIGURE 11 UTC(SIS) dissemination accuracy, December 15, 2016 – June 30, 2018 (TGVF-TVF) 20 15 10 5 0 –5 –10 [ns] 14/12/2016 24/3/2017 02/07/2017 10/10/2017 18/01/2018 28/04/2018 UTC(SIS)-UTCr offset [ns] FIGURE 12 Broadcast GGTO accuracy, December 15, 2016 – June 30, 2018 (TGVF-TVF) 20 10 0 –10 –20 –30 [ns] 14/12/2016 24/3/2017 02/07/2017 10/10/2017 18/01/2018 28/04/2018 Broadcast GGTO accuracy [ns]

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