Texture characterization of natural images using the mathematical framework of multifractal (MF) analysis, enables the study of the fluctuations in the regularity of image intensity. Although successfully applied in various contexts, the use of MF analysis has so far been limited to the independent analysis of a single image, while the data available in applications are increasingly multivariate. This paper addresses this limitation and proposes a joint Bayesian model and associated estimation procedure for MF parameters of multivariate images. It builds on a recently introduced generic statistical model that enabled the Bayesian estimation of MF parameters for a single image and relies on the following original key contributions : First, we develop a novel Fourier domain statistical model for a single image that permits the use of a likelihood that is separable in the MF parameters via data augmentation. Second, a joint Bayesian model for multivariate images is formulated in which prior models based on gamma Markov random fields encode the assumption of the smooth evolution of MF parameters between the image components. The design of the likelihood and of conjugate prior models is such that exploitation of the conjugacy between the likelihood and prior models enables an efficient estimation procedure that can handle a large number of data components. Numerical simulations conducted using sequences of multifractal images demonstrate that the proposed procedure significantly outperforms previous univariate benchmark formulations at a competitive computational cost.

Trellis-based detector is an effective method to demodulate non-coherent continuous-phase modulated sequences. Most of them have been derived for the maximum likelihood sequence estimation setting, while only few contributions have been proposed for the maximum a posteriori (MAP) symbol detection, required when soft information is needed for iterative detection and decoding. In this letter, we derive a new symbol MAP non-coherent receiver with reduced state space representation compared with the existing extended state-space-based approaches. While having the same performance, it enables a lower complexity.

Multipath remains the main source of error when using global navigation satellite systems (GNSS) in constrained environment, leading to biased measurements and thus to inaccurate estimated positions. This paper formulates the GNSS navigation problem as the resolution of an overdetermined system, which depends nonlinearly on the receiver position and linearly on the clock bias and drift, and possible biases affecting GNSS measurements. The extended Kalman filter is used to linearize the navigation problem whereas sparse estimation is considered to estimate multipath biases. We assume that only a part of the satellites are affected by multipath, i.e., that the unknown bias vector is sparse in the sense that several of its components are equal to zero. The natural way of enforcing sparsity is to introduce an `1 regularization associated with the bias vector. This leads to a least absolute shrinkage and selection operator (LASSO) problem that is solved using a reweighted-l1 algorithm. The weighting matrix of this algorithm is designed carefully as functions of the satellite carrier to noise density ratio and the satellite elevations. The smooth variations of multipath biases versus time are enforced using a regularization based on total variation. An experiment conducted on real data allows the performance of the proposed method to be appreciated.

The increase and reinforcement of Internet uses make necessary to improve existing networks. However, we observe strong inequalities between urban areas, well served and which concentrate the major part of investments, and rural areas, underserved and forkasen. To face this situation, users in underserved areas are moving to others Internet access, and in particular satellite Internet access. However, the latter suffer from a limitation which is the long delay induced by the propagation time between the earth and the geostationnary orbit. In this thesis, we are interresed in the simultaneous use of a terrestrial access network, characterized by a low delay and a low throughput, and a satellite access network, characterized by a high throughput and an long delay. Elsewhere, Content Delivery Networks (CDNs), consisting of a large number of cache servers, bring an answer to the increase in trafic and needs in terms of latency and throughput. However, located in core networks, cache servers stay far from end users and do not reach access networks. Thus, Internet Service Providers (ISPs) have taken an interest in deploying their own CDNs, which will be referred to as TelCo CDNs. The content delivery ideally needs the interconnection between CDN operators and TelCo CDNS, allowing the delegation of the content delivery to the TelCo CDNs. The latter are then able to optimize the content delivery on their network, for which they have a better knowledge. Thus, we will study the optimization of the contents delivery on a hybrid satellite / terrestrial network, integrated in a CDN delivery chain. We will initially focus on the description of a architecture allowing, thanks to a CDN interconnection, handling contents delivery on the hybrid network. In a second stage, we will study the value of the information provided by the CDN context in the routing on such architecture. In this framework, we will propose a routing mechanism based on contents size. Finally, we will show the superiority of our approach over the multipath transport protocol MP-TCP.

A new sparse estimation method was recently introduced in a previous work to correct biases due to multipath (MP) in GNSS measurements. The proposed strategy was based on the resolution of a LASSO problem constructed from the navigation equations using the reweighted-l1 method. This strategy requires to adjust the regularization parameters balancing the data fidelity term and the involved regularizations. This paper introduces a new Bayesian estimation method allowing the MP biases and the unknown model parameters and hyperparameters to be estimated directly from the GNSS measurements. The proposed method is based on BernoulliLaplacian priors, promoting sparsity of MP biases.

A high throughput does not necessarily translate to a good Quality of Experience, especially in a satellite context. The round trip time, for instance, also has a tremendous impact on the reactivity of applications and thus on the Quality of Experience. Content delivery networks are massively used for over‐the‐top services in terrestrial network: They reduce the load of network and the delay as they draw the content closer to the end user. In a satellite system, the content delivery network presents a good opportunity for enhancing the end users' Quality of Experience and can change the conventional use of performance‐enhancing proxies. This paper investigates the satellite as access link for home networks or a backhaul link for small cells for a 5G perspective. We analysed the impact of caching on both gateway side and satellite terminal side for 2 on‐trend services: web browsing and adaptive video streaming (dynamic adaptive streaming over HTTP). The main contribution is an evaluation of transparent caching through a satellite platform. The caching policy is out of the scope of this paper. One large part of the testbed is based on an open‐source platform, OpenSAND that emulates the satellite system. To confirm the results, some real experiments have been conducted on a commercial satellite link. As expected, the transparent caching at the satellite terminal side can increase the Quality of Experience to its upper border as long as the content is available in the cache. For the satellite gateway cache, the performances exceed the expectations. Although the application experiences the satellite delay in this case, the traversal time of different Internet service provider networks also delays the delivery of content. Then it may have a greater impact on reactivity than the satellite itself. Through careful analysis of the different results, we noticed some issues. Transparent caching is unable to cache encrypted or dynamic content. Moreover, a misuse of caching can provoke bad behaviour of dynamic adaptive streaming over HTTP mechanisms and severely decrease the Quality of Experience. We designed a solution that in addition to solving the issue, alleviates the storage space of satellite terminal caches.

Machine-Type Communications are meeting a growing interest on the consumer market. Dedicated technologies arise to support more robust communications involving a massive number of low cost, low energy-consuming devices This paper discusses the coverage extension of a Low-Powered Wide Area Network using a Low Earth Orbit satellite constellation, benefiting from the improved performance of a recent standard. The transmission complies with the user equipment specifications standardized as NB-IoT by 3GPP in Release 13. This radio technology is an update on LTE standard with enhanced performances : the supported path loss can be 20 dB higher than with legacy LTE. This improvement makes satellite-compatible the small and energy-constrained devices. A specific unidirectional system is defined, and a link budget is derived. Also, a receiver architecture is presented, that takes into consideration satellite channel specific impairments.

Aujourd’hui, le satellite géostationnaire propose à ses clients un accès Internet haut débit (de l’ordre de 20Mbit/s). Cependant le délai induit engendre une baisse de réactivité pour la plupart des applications. En particulier, le protocole de streaming vidéo adaptatif DASH ne parvient pas à s’y adapter. Au contraire, il sous-évalue les capacités du réseau et fournit le service minimal disponible. Pour réduire les délais, le CDN rapproche les données de l’utilisateur final grâce à la mise en place de caches. Ce service a fait ses preuves pour la navigation web et le téléchargement de fichiers dans Internet. Cet article propose d’analyser l’impact du CDN pour un service de streaming vidéo adaptatif et dans un contexte satcom, deux points qui, ensemble, divergent de l’utilisation habituelle du CDN. De cette première analyse, nous pouvons différentier trois situations. La première propose des performances optimales. Dans la deuxième, le CDN n’apporte rien. Enfin, dans la dernière situation, le CDN a un impact néfaste sur les performances. Ces deux derniers cas sont induits par une mauvaise politique de mise en cache qui leurre le client DASH sur les qualités à demander. Nous résolvons ce problème par le déploiement d’un proxy transparent indiquant les qualités disponibles dans les caches.

In the sake of modernization, aviation stakeholders decided that the future aviation network infrastructure, in particular for air-ground communica- tion systems, will move towards IP based networks. It has been referred to in the International Civil Aviation Organization as Aeronautical Telecommunication Network/Internet Protocol Suite. Due to the heterogeneous communication envi- ronment, it is necessary to support handover between different access technolo- gies and access networks. In this article, we first define the very specific aero- nautical communication environment. Our main contribution is a performance assessment of the most deployed network protocols capable of managing IP mo- bility within the aeronautical environment. We focus our analysis on the Mobile IPv6 protocol and implementation issues of a representative aeronautical network in Omnet++.

As Internet usages expand quickly, access networks are modernized with new technologies like fiber-optic communications. However, upgrade costs are prohibitive in sparsely populated areas, the latter turning notably towards satellite connection. Indeed, this technology allows deploying a high-throughput Internet access quickly in these regions. Nevertheless, GEO satellites induce a long delay, not experienced on terrestrial infrastructures despite their low throughput. In this paper, we consider a heterogeneous network with both a satellite and a terrestrial path. This kind of architecture is known to be difficult to operate because of the important differences between used technologies. The emerging MP-TCP transport protocol, whose design enables to aggregate disparate paths properly, brought new hopes for heterogeneous networks. However, it does not take user Quality of Experience (QoE) into account as it focuses on maximizing the links occupancy. This paper propose an intelligent path selector using the content size to maximize users QoE in heterogeneous networks. Before detailing this method, we describe the architecture able to retrieve the size of delivered contents thanks to Content Delivery Network Interconnection (CDNI). Finally, we implement a testbed to evaluate the behavior of the proposed routing method. The results show a significant improvement of the delivery performance, outperforming MP-TCP.