The return link of broadband satellite systems has recently received more attention due to the spread of multi-beam antennas which enable spatial frequency reuse, and thus increase drastically the number of users that can potentially be served by one satellite. While interference isolation has so far been the way to go, with regular four-color frequency reuse scheme, there is a growing interest in densifying the frequency usage as is being done in cellular networks. In this paper, we address the return link radio resource allocation challenges, from spectral resource allocation to user scheduling, including modulation and coding scheme (MODCOD) selection. Our contributions highlight the potential gains of a two-color scheme and shed light on several levers to reap its benefits through interference management. We first consider the possibility to use a two-color scheme, while keeping the MODCOD selection and the scheduling local to each beam and we show that even though it yields a potential performance gain (+16%) with respect to the state of the art (SoA) (based on four colors), it is not viable due to a very high-block loss rate. Therefore, we propose a simple-yet fast and efficient-coordinated MODCOD selection process that alleviates the need of estimating interference and reduces drastically decoding failures. This coordination step offers significant gains (+58%) over the SoA, while leaving the per beam scheduler unchanged. Finally, we formulate a joint user scheduling and MODCOD selection problem across all beams and propose an offline heuristic to solve it efficiently. We obtain a 83% gain with respect to the SoA, but with higher computational complexity. Still, it confirms the great potential of coordinated scheduling.

In the current framework of Galileo and thanks to the flexibility of the I/NAV message, introducing new pages in order to propose an optimization of the E1-B Galileo signal has been proposed [1]. This optimization process pursues two different objectives. The first objective aims to reduce the Time To First Fix (TTFF), achieved by shortening the time to retrieve the Clock and Ephemerides Data (CED). The second objective aims to improve the resilience and robustness of the CED, particularly under hostile environments. Under the backward compatibility precondition, new outer channel error correction solutions for Galileo I/NAV are proposed in this paper. Especially, a new family of codes called Lowest Density Maximum Distance Separable codes (LD-MDS) is proposed to be used in this paper, thus in GNSS context. This family of codes, along with an enhanced performance decoding method based on the use of a soft serial iterative decoding, provides an optimal solution in order to reduce the TTFF as well as to improve the robustness of the CED.

Optical wavelengths are an alternative to radio-frequency links for future satellite-to-ground transmissions. They are envisioned in the framework of payload/telemetry data transfer (optical downlinks from LEO satellites) or communication (bi-directional optical links with GEO satellites). However, as it propagates through the atmosphere, the optical wave can be deeply affected by atmospheric turbulence which induces randomspatial and temporal variations of its amplitude and phase. Variations in amplitude translate into fluctuations of the collected power (scintillation). The phase distortions affect the spatial distribution of the power at the focal plane of the telescope causing deleterious losses when the incident flux needs to be coupled to an optoelectronic detector or to a single-mode optical fiber. Such losses result in dynamical attenuations of the received signal-called fading- and hence potentially to the loss of information. The most recent feasibility studies highlight the use of two types of fading mitigation techniques : adaptive optics systems and digital techniques (coding and interleaving). To limit the complexity and cost of such systems, the optimization of these mitigation techniques should be conducted jointly. The main objective of this thesis is therefore the investigation of the complementarity of physical (adaptive optics) and digital data reliability mechanisms (interleaving, correcting and erasure codes in a cross-layer approach).

Optical wavelengths are an alternative to radio-frequency links for future satellite-to-ground transmissions. They are envisioned in the framework of payload/telemetry data transfer (optical downlinks from LEO satellites) or communication (bi-directional optical links with GEO satellites). However, as it propagates through the atmosphere, the optical wave can be deeply affected by atmospheric turbulence which induces randomspatial and temporal variations of its amplitude and phase. Variations in amplitude translate into fluctuations of the collected power (scintillation). The phase distortions affect the spatial distribution of the power at the focal plane of the telescope causing deleterious losses when the incident flux needs to be coupled to an optoelectronic detector or to a single-mode optical fiber. Such losses result in dynamical attenuations of the received signal -called fading- and hence potentially to the loss of information. The most recent feasibility studies highlight the use of two types of fading mitigation techniques : adaptive optics systems and digital techniques (coding and interleaving). To limit the complexity and cost of such systems, the optimization of these mitigation techniques should be conducted jointly. The main objective of this thesis is therefore the investigation of the complementarity of physical (adaptive optics) and digital data reliability mechanisms (interleaving, correcting and erasure codes in a cross-layer approach).

This paper studies the performance of the generalized likelihood ratio test (GLRT) for the conditional signal model. By conditional signal model, we mean that under both hypotheses, the observations are a linear superposition of unknown deterministic signals corrupted by additive noise, with a mixing matrix depending on an unknown deterministic parameter vector. The contribution of this work is the derivation of closed form expressions for the probabilities of false alarm and of detection of the GLRT at high signal-to-noise ratio, allowing the receiver operating characteristic of the GLRT to be computed analytically. The most general case is tackled, i.e., when the number of unknown signals and the number of unknown deterministic parameters of the mixing matrix are allowed to be different under the two hypotheses.

Les systèmes dits Sensor Webs sont des middlewares informatiques assurant la communication entre les capteurs et les applications. En tant que véritables médiateurs, la popularité de ces systèmes n’a cessé de grandir depuis l’apparition des tout premiers capteurs. Plus récemment, l’émergence de nouveaux paradigmes tels que l’Internet des Objets (IoT) a complètement révolutionné les systèmes basés sur les capteurs en général. Parmi eux, les Sensor Webs ne dérogent pas à cette règle et doivent maintenant répondre à de nouveaux défis, notamment en termes d’intégration, de Qualité des Observations (QoO) et d’adaptation système. Dans le cadre de ma thèse, j'ai proposé une nouvelle génération de Sensor Webs capables d’adapter la QoO distribuée de manière autonomique et spécifique à chaque application (QASWS). Premièrement, j'introduirai un framework générique destiné aux chercheurs et développeurs souhaitant concevoir leur propre solution QASWS. Dans un deuxième temps, je montrerai comment j'ai utilisé ce framework afin de développer une plateforme d’intégration pour l’évaluation de la QoO à la demande (iQAS). Après avoir évalué ses performances, je présenterai trois cas d’utilisation pour la plateforme iQAS. Finalement, je conclurai ma présentation en imaginant l’apport de certains paradigmes transverses vis-à-vis de la QoO dans un futur proche.

Les réseaux de capteurs type LPWAN (grande autonomie, grande couverture, faible débit) sont en plein essor. Ces réseaux, qui ont pour but de connecter des milliers de capteurs sans fils de la manière la plus efficace possible, seraient un maillon indispensable à l’internet des objets tel qu’il est imaginé dans les années à venir. Dans le but d’augmenter la couverture de ces services, un lien satellite est envisagé. Cette thèse étudie les contraintes liées à l’utilisation d’un lien satellite unidirectionnel dans un système terrestre étendu, sans modifications du matériel, supposé bas-coût. Après une rapide présentation du milieu de l’IoT et des solutions LPWAN terrestres, nous présenterons la solution et le système choisis, compatible LTE NB-IoT. L’utilisation d’un lien satellite limite le système en termes de bilan de liaison et d’interférences. On cherchera alors à quantifier ces interférences et à obtenir les performances d’un tel réseau.