Inside GNSS Media & Research

MAY-JUN 2018

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www.insidegnss.com M A Y / J U N E 2 0 1 8 Inside GNSS 37 accurate and reliable TOA-only position estimation, it becomes interesting to use FOA measurements for beacon instanta- neous speed estimation. T h e M E O S A R s y s t e m i s a l s o improving the Cospas-Sarsat global performances thanks to the continuous increase of tracking capability on the ground stations (called MEOLUT), with the deployment of new stations in the world (12 commissioned as per today): the addition of dish-antennas to some of them, or deployment of phased-array antennas (see Figure 4 ). is last solu- tion, deployed as the operational French MEOLUT since 2016, provides the capa- bility to track in parallel all satellites in view instead of selecting some of them pointed by a few dish-antennas: as we are dealing in the end with all GNSS constellations, it will represent up to 30 satellites tracked in parallel. e gains provided by a higher num- ber of simultaneously tracked satellites are multiple: • increased probability of detection of the beacon signal through at least one satellite • higher chances to receive the beacon signal bursts through at least three satellites, enabling the computation of an independent location • More TOA/FOA measurements, and then a better accuracy on the inde- pendent location. e ground segment is then continu- ously improved to get real-time access to more satellites relaying alerts from larger areas, as part of the first and most important requirement of the MEOSAR system in Cospas-Sarsat. In the frame of ELT(DT), this objective of improving the performance is particularly important: • e beacon may only transmit a few bursts before crash: the detection and location probability per burst shall be particularly high • The beacon localization adds new unk nowns: the a ltitude (usua lly considered on ground for ot her beacons, including current ELTs that are triggered by the crash) and/ or the speed (in particular for FGB where it impacts the FOA and then the overall accuracy). Even if some default calculations can be imple- mented which provides quite satis- fying results, the access to additional measurements through a fourth sat- FIGURE 4 MEOLUT phased-array antenna for all-in-view tracking

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