ENAC
Location
Haute Garonne (31) | France
Job description
Mission: Founded 70 years ago, ENAC, École Nationale de l'Aviation Civile, is Europe's largest aeronautical Grandes Écoles or university. It provides initial and advanced training for managers and key players in the civil aviation industry: engineering, air navigation, piloting, airport management, research, expertise and international development. ENAC is a public scientific, cultural and professional establishment, under the supervision of the DGAC (Direction Générale de l'Aviation Civile ), the French civil aviation authority. ENAC has a main campus in Toulouse and 8 sites in France. This PhD thesis is co-funded by CNES and THALES ALENIA SPACE (pending final acceptance by the CNES PhD selection committee). This PhD thesis can only be applied through the following online application: The interest in Low Earth Orbit (LEO) mega constellation systems providing either high data-rate communications (high-speed internet) or Position Navigation and Timming (PNT) services, which is commonly referred to as LEO PNT, has grown in the last years with a significant acceleration of the research and development of such systems [1]. To provide some examples, China is planning on deploying 3 LEO mega constellation systems; Geospace which is a commercial system providing PNT services for autonomous vehicles, CentiSpace which is an hybrid commercial and governmental system proving augmentation to Beidou (Precise Point Positioning and integrity) and Satnet which is a commercial system providing high-speed internet services [2]. US is planning on deploying, is deploying or has deployed several LEO mega constellation systems, Blackjack which is a governmental system for researching LEO constellations capacities, XONA Space System which is a commercial system proving PNT services, TrustPoint which is a commercial system providing PNT services, Satelles which is a commercial system proving PNT services using the IRIDIUM constellation, and Starlink which is a commercial system providing high-speed internet services [2]. Finally, Europe is preparing two projects, LEO PNT (which follows the ELCANO project funded by ESA on a system study on potential LEO-PNT capabilities for potential future space-based PNT infrastructures [1]) and IRIS2 which is funded by the European Commission and is designed to tackle a wide variety of services, from high-speed internet to even PNT [2]. The advantages to use LEO mega constellation for PNT services are quite numerous and the driving force of the constant interest growth in these systems [1]. First of all, the increase of satellites in view, even in constrained environments such as urban canyons, increase the DOP (Dilution of Precision) of the navigation solution with the consequence increase on the final accuracy performance. Moreover, the fast change in the LEO satellites position makes the propagation channel to vary very fast and, for example, it makes obstructed Line-Of-Sight (LOS) signals to become unobstructed in a relative short of amount of time in comparison with MEO GNSS signals. Second, LEO satellites being closer to Earth have low Free Space Losses (FSL) in comparison to MEO GNSS satellites; for example a LEO satellite have about 20dB less of FSL at the 600km (Edge-of-Coverage). Third, the improved link budget can allow for the use of non-typical RNSS frequency bands to provide more specifically targeted PNT services, such as Ka/Ku frequency bands for high precision PNT services due to the large available bandwidth which can be offered to the navigation signal, and such as UHF frequency band to obtain deep signal penetration for indoor, canopy or urban canyons positioning. Fourth, the high dynamics of the LEO satellites increase the importance of Doppler frequency/speed measurements and thus the overall quality of the PVT (position velocity Time) solution; indeed, the first operational global positioning system, TRANSIT, was based only on Doppler positioning with LEO Satellites; moreover, the high dynamics of the satellite will also change the correlation time of the signal distortions, such as the ionosphere, and will allow reduced convergence time for high-accuracy GNSS positioning. Fifth, the high number of LEO satellites expected in a mega constellation and the proximity of the satellites allow for two-way PNT signals enhancing their timing and ranging capabilities. Finally, LEO PNT systems can be less complex than GNSS due to the reuse of GNSS services (LEO satellites can determine its position and time synchronization from GNSS ) with the consequent reduction of Size, Weight and Power consumption of the satellite payload. The goal of this thesis is to conduct the analysis of LEO mega constellations focusing on the first stages of the receiver, the Radio-Frequency Front End (RFFE) block and mainly the signal processing block, by proposing acquisition and tracking algorithms specifically adapted to LEO PNT signals, by providing theoretical thresholds and by providing mathematical models of at least the noise component distorting the code delay and phase delay pseudorange measurements associated to the developed acquisition and tracking algorithms. The outputs of this PhD, mainly the code delay and phase delay pseudorange error models could be used for further LEO PNT analysis focused on PVT performance. The proposed thesis will focus on the LEO PNT being currently developed by ESA and its different proposed signals. The first phase of the thesis will consists in selecting 2 or 3 signal candidates depending on the targeted applications. Indeed, as previously said, depending on the frequency band, the targeted services vary; UHF band targets indoor or urban positioning, L, S or C bands target typical GNSS PNT services and Ka/Ku band targets PPP services. Therefore, in this PhD thesis, the analyzed signals will depend on the needs of CNES and the needs of the cofunding partner, Thales Alenia Space, after a first high-level analysis of all the proposed signals in the ESA LEO PNT ICD. For example, one typical band (e.g. L band) and one experimental band (Ka band) could be selected. The second phase of the thesis will consists in analyzing in-depth the identified signal of the first phase. The following tasks will be conducted and constitute the research core of the PhD thesis:
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