Inside GNSS Media & Research

JUL-AUG 2018

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Navigation

Page 42 of 59

www.insidegnss.com J U L Y / A U G U S T 2 0 1 8 Inside GNSS 43 mum AoD to 100 minutes. However, due to ongoing deploy- ment of the Galileo ground segment, improvement in the robustness of the navigation message uplink capability needs to be ensured. Furthermore, additional measures also will be taken on-board the satellites to protect the users with the automated SIS flag setting in case the navigation message is not uplinked from ground in a timely manner. Searching to the Rescue In addition to navigation services, Galileo also provides an SAR service, in the form of contribution to the Internation- al Cospas-Sarsat system, a satellite based Search and Rescue distress alert detection and information distribution system ( Figure 8 ). Galileo satellites receive signals from Cospas-Sarsat- approved 406 megahertz emergency beacons, located anywhere on Earth's surface and rebroadcast them in L-band to ground receiving terminals, called MEOLUTs (Medium Earth Orbit Local User Terminal), which detect and compute the distress beacon locations based on the measurements performed on the signals relayed by several SAR repeaters in visibility of the FIGURE 7 SISE vs Age of Data Galileo 5 (E18) and Galileo 6 (E14) message age (minutes) ODTS Error As Observed vs. Nav Msg Age nms (m) 0 20 40 60 80 100 120 160 20 18 16 14 12 10 8 6 4 2 0 FIGURE 8 Cospas-Sarsat International Satellite System for Search and Rescue

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