Inside GNSS Media & Research

NOV-DEC 2018

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38 InsideGNSS N O V E M B E R / D E C E M B E R 2 0 1 8 red line) is reported in Figure 6. is pic- ture shows: (i) the location of GNOME sentinels (GNM labeled) belonging to the BLUEGNSS network and (ii) the positions of other external operative monitoring stations (green circles) that are approxi- mately installed in the same region. It is worth noting that some of them (such as CNT, DJA, ATH, ALY) are very close or within the BLUE-MED FAB. erefore, they can be effectively considered as fur- ther monitoring points to be connected to the BLUEGNSS network. BLUEGNSS Sentinels As previously stated, the GNSS moni- toring stations (referred to as GNOME sentinels, see V. Pellegrini et alia) devel- oped by IDS are the key elements of the BLUEGNSS network. Simply speak- ing, such units are designed to receive positioning signals and process them in order to: • check the integrity of GNSS signals (e.g., in terms of carrier-to-noise ratio, pseudorange errors, etc.) • produce statistical metrics able to characterize the GNSS performance in-situ (e.g., position accuracy, xDOP, number of used satellites, protection levels, etc.) • monitor RF spectrum and detect possible intentional/unintentional interferences • analyze the physical (PHY) and navi- gation (NAV) layers of positioning signals and record data and related metrics (according to relevant stan- dards, see Additional Resources) • investigate the cause of possible anomalies detected in-situ. Such features make sentinels able to accomplish the following tasks as rec- ommended by ICAO (see the monitor- ing concept schema shown in Figure 2 and Additional Resources): • real-time monitoring of GNSS integ- rity to provide timely alert in case of detected anomalies • post incident/accident investigation, yielding data logging and review capabilities • GNSS ground validation campaigns, aimed at characterizing GNSS site performance (e.g., for GBAS and RIMS siting). As mentioned, in the framework of BLUEGNSS, the main target is the development of a network able to carry out the global assessment of GNSS per- formance wit hin BLUE-MED FAB. erefore, in this context, BLUEGNSS sentinels have the important task of: • computing some preliminary metrics from PHY and NAV layers • sending the achieved outcomes to the CMF for the final processing and report publication. In this context four stations have been deployed and installed within the following airports (see Figure 6). • Kos Airport, Greece • Luqa Airport, Malta • Larnaca Airport, Cyprus • Linate Airport, Italy. It is worth noting that, within each airport, the installation site has been carefully chosen in order to minimize the detrimental effects of possible local factors on the reception of positioning signals (e.g., masking effects due to orog- raphy or man-made obstacles, presence of transmitters, sources of multipath, etc.). Proper choice of site is essential for accomplishing reliable GNSS per- formance assessment. Each station is made up of the fol- lowing units. • Nr. 3 rackmount chassis (i.e., a power supply unit, a processing unit, and an RF and navigation unit); typically installed within a preselected equip- ment room (see Figure 7). • Nr. 1 choke-ring multi-frequency GNSS antenna for multipath mitiga- tion; typically installed on the roof of BLUEGNSS FIGURE 6 BLUE-MED flight region (green area) and the monitoring stations used for perfor- mance assessment (GNOME and pre-existing networks) FIGURE 7 Example of IDS monitoring station installed within an equipment room (a) Front view (b) Back view

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