PhD Students

The 1st Scientific Days

As a Resarch Lab, one of the TeSA priorities is to welcome PhD students.

In what follows, you will find the list of the current PhD students with a short summary of their work and the past TeSA PhDs.

Since most of the PhDs are written in French, the French title has been kept.

Current PhD Students

StartNameThesis Topic
Jan. 2017Thibaud AdrienEtude du transport pour les ICN dans un contexte satellite
Funding: TAS
Oct. 2016Zamoum SelmaMéthodes d'accès aléatoires pour les communications par satellite.
Funding: TAS - CNES
Oct. 2016Ortega Espluga LorenzoEtudes et Optimisations des signaux pour les évolutions Galileo.
Funding: TAS - CNES
Mar. 2016Urbano SimoneDétection et diagnostic de phénomènes oscillants dans les systèmes de commandes de vol
Funding: Airbus
Jan. 2016Lesouple JulienTechniques de séparation de sources appliquées aux traitements des signaux et mesures GNSS
Funding: CNES + M3 SYSTEMS
Oct. 2015Piat-Durozoi Charles-UgoNouvelles formes d'onde et récepteur avancé pour la télémesure des futurs lanceurs
Funding: CNES + INP
Oct. 2015Couble YoannOptimisation de la gestion des ressources voie retour
Funding: CNES + TAS
Oct. 2015Tauran BastienInteraction protocoles de transport / fiabilisation MAC pour services mobiles par satellite
Funding: CNES + TAS
Oct. 2015Chayot RomainSynchronisation temporelle et fréquentielle appliquée au cas de modulations continues codées dans des canaux sélectifs en temps et en fréquence avec Doppler
Funding: CNES + TAS
Oct. 2015Cluzel SylvainSystèmes M2M/loT par satellite
Funding: CNES + TAS
Feb. 2015Canuet LucienFiabilisation des transmissions optiques satellite-sol
Nov. 2014Bouttier ElieSystèmes de distribution de contenu hybride terrestre / satellite
Funding: TAS CNES
Oct. 2014Kbayer NabilSPRING Usage for Modelling Multipath Effects on a Receiver (SUMMER)
Funding: CNES
Oct. 2014Manzoni Vieira FábioSatellite AIS and Radar data fusion for high performance maritime surveillance
Funding: TAS
Apr. 2014Asselin ÉricSystèmes de détection et de prévention d'intrusion adaptés au monde aéronautique embarqué
Funding: RCF

Past PhD Students

PhD DefenceNameThesis Topic
Nov. 2016Zidane KarineImproving Synchronous Random Access Schemes for Satellite Communications
Funding: TAS - CNES
With the need to provide the Internet access to deprived areas and to cope with constantly enlarging satellite networks, enhancing satellite communications becomes a crucial challenge. In this context, the use of Random Access (RA) techniques combined with dedicated access on the satellite return link, can improve the system performance. However conventional RA techniques like Aloha and Slotted Aloha suffer from a high packet loss rate caused by destructive packet collisions. For this reason, those techniques are not well-suited for data transmission in satellite communications. Therefore, researchers have been studying and proposing new RA techniques that can cope with packet collisions and decrease the packet loss ratio. In particular, recent RA techniques involving information redundancy and successive interference cancellation, have shown some promising performance gains. With such methods that can function in high load regimes and resolve packets with high collisions, channel estimation is not an evident task. As a first contribution in this dissertation, we describe an improved channel estimation scheme for packets in collision in new RAmethods in satellite communications. And we analyse the impact of residual channel estimation errors on the performance of interference cancellation. The results obtained show a performance degradation compared to the perfect channel knowledge case, but provide a performance enhancement compared to existing channel estimation algorithms. Another contribution of this thesis is presenting a method called Multi-Replica Decoding using Correlation based Localisation (MARSALA). MARSALA is a new decoding technique for a recent synchronous RAmethod called Contention Resolution Diversity Slotted Aloha (CRDSA). Based on packets replication and successive interference cancellation, CRDSA enables to significantly enhance the performance of legacy RA techniques. However, if CRDSA is unable to resolve additional packets due to high levels of collision, MARSALA is applied. At the receiver side, MARSALA takes advantage of correlation procedures to localise the replicas of a given packet, then combines the replicas in order to obtain a better Signal to Noise plus Interference Ratio. Nevertheless, the performance of MARSALA is highly dependent on replicas synchronisation in timing and phase, otherwise replicas combination would not be constructive. In this dissertation, we describe an overall framework ofMARSALA including replicas timing and phase estimation and compensation, then channel estimation for the resulting signal. This dissertation also provides an analytical model for the performance degradation of MARSALA due to imperfect replicas combination and channel estimation. In addition, several enhancement schemes forMARSALA are proposed likeMaximum Ratio Combining, packets power unbalance, and various coding schemes. Finally, we show that by choosing the optimal design configuration for MARSALA, the performance gain can be significantly enhanced.
June 2016Ali Ahmad RamiMécanismes de fiabilité bi-directionnels “couches basses” pour les communications par satellite
Funding: TAS - CNES
As part of a satellite communications system, the characteristics of the communication links make it difficult to set up telecommunications systems. For certain applications and protocols (TCP for example), the main problem is the propagation delay which reaches 500 ms for the round trip of the signal via a geostationary satellite. Another problem is the loss of data due to the characteristics of the transmission channel. For these reasons, protocols that ensure the reliability of communications must be set up on a satellite link. The aim of this thesis is to propose a mechanism that ensures the reliability of communication and maximize the utilization efficiency of the available bandwidth. HARQ protocol (Hybrid Automatic Repeat reQuest) is known for its ability to achieve the best compromise reliability/throughput. However, this mechanism which is now used in most terrestrial standards, is not well adapted for a satellite link. First, we propose a reliability method based on static HARQ. This method is specifically for services that tolerate some delay before the reception of the message. It consists in defining the probability of decoding at each transmission, using an optimization algorithm that we propose. The number of bits to be sent is calculated based on these probabilities and the distribution of the mutual information, assuming knowledge of the statistical distribution of the channel attenuation. Secondly, we introduce an adaptive version of the proposed method. Unlike the method proposed previously, this new approach calculates the number of bits to be sent by taking into account variations of the channel state during the communication. In fact, instead of sending a fixed number of bits at each transmission, the receiver calculates the number of bits to be sent depending on the channel state during the current transmission. Finally, we propose a frame structure for a physical layer that implements the proposed mechanisms and evaluate their performance by varying the system parameters. The aim is to find the optimal order of frame sizes and codes to be used and also to define the best strategy of transmission to be adopted by the transmitter.
Jan. 2016Vernhes Jean-AdrienEchantillonnage Non Uniforme : Application aux filtrages et aux conversions CAN/CNA (Convertisseurs Analogique-Numérique et Numérique-Analogique) dans les télécommunications par satellite
Funding: TAS - CNES
The theory of uniform sampling, developed among others by C. Shannon, is the foundation of today digital signal processing. Since then, numerous works have been dedicated to non uniform sampling schemes. On the one hand, these schemes model uniform sampling device imperfections. On the other hand, sampling can be intentionally performed in a non uniform way to benefit from specific properties, in particular simplifications concerning the choice of the mean sampling frequency. Most of these works have focused on theoretical approaches, adopting simplified models for signals and sampling devices. However, in many application domains, such as satellite communications, analog-to-digital conversion is submitted to strong constraints over the involved bandwidth due to the very high frequencies used. These operational conditions enhance the imperfections of the involved electronic devices and require the choice of particular signal models and sampling schemes. This thesis aims at proposing sampling models suitable for this context. These models apply to random band-pass signals, which are the classical models for telecommunication signals. They must take into account technological, economical factors and on-board complexity constraints and allow to integrate particular functionalities useful for telecommunication applications. This thesis first contribution is to develop non uniform sampling formulas that can digitally integrate functionalities that appear to be tricky in the analog domain at the considered frequencies. The thesis second contribution consists in applying non uniform sampling theory to the estimation and compensation of synchronization errors encountered in particular sampling devices, the time-interleaved analog-to-digital converters. This estimation will be performed through supervised or blind methods.
Dec. 2015Benaddi TarikSparse Graph-Based Coding Schemes for Continuous Phase Modulations
Funding: TAS - CNES
The use of the continuous phase modulation (CPM) is interesting when the channel represents a strong non-linearity and in the case of limited spectral support ; particularly for the uplink, where the satellite holds an amplifier per carrier, and for downlinks where the terminal equipment works very close to the saturation region. Numerous studies have been conducted on this issue but the proposed solutions use iterative CPM demodulation/decoding concatenated with convolutional or block error correcting codes. The use of LDPC codes has not yet been introduced. Particularly, no works, to our knowledge, have been done on the optimization of sparse graph-based codes adapted for the context described here. In this study, we propose to perform the asymptotic analysis and the design of turbo-CPM systems based on the optimization of sparse graph-based codes. Moreover, an analysis on the corresponding receiver will be done.
Dec. 2015Trang Si Quoc VietFLOWER, an Innovative Fuzzy Lower-than-Best-Effort Transport Protocol
Funding: TAS - CNES
In this thesis, we look at the possibility to deploy a Lower-than-Best-Effort (LBE) service over long delay links such as satellite links. The objective is to provide a second priority class dedicated to background or signaling traffic. In the context of long delay links, an LBE service might also help to optimize the use of the link capacity. In addition, an LBE service can enable a low-cost or even free Internet access to remote communities via satellite communication. Two possible deployment levels of an LBE approach exists : either at the MAC layer or at the transport layer. In this thesis, we are interested in an end-to-end approach and thus specifically focus on transport layer solutions. We first propose to study LEDBAT (Low Extra Delay Background Transport) because of its potential. Indeed, LEDBAT has been standardized by the IETF and is widely deployed within the official BitTorrent client. Unfortunately, the tuning of LEDBAT parameters is revealed to highly depend on network conditions. In the worst case scenario, LEDBAT flows can starve other traffic such as commercial traffic performing over a satellite link. LEDBAT also suffers from an intra-unfairness issue, called the latecomer advantage. These reasons often prevent operators from using LBE protocols over wireless and long-delay links as a misconfiguration can overload link capacity. Therefore, we design FLOWER, a new delay-based transport protocol, as an alternative to LEDBAT. By using a fuzzy controller to modulate the sending rate, FLOWER aims to solve LEDBAT issues while fulfilling the role of an LBE protocol. Our simulation results show that FLOWER can carry LBE traffic not only in the long delay context, but in a wide range of network conditions where LEDBAT usually fails.
Oct. 2015Prendes JorgeNew statistical modeling of multi-sensor images with application to change detection
Remote sensing images are images of the Earth surface acquired from satellites or airborne equipment. These images are beco-ming widely available nowadays, with many commercial and non-commercial services pro-viding them. The technology of the sensors required to capture this kind of images is evol-ving fast. Not only classical sensors are impro-ving in terms of resolution and noise level, but also new kinds of sensors are proving to be useful. Multispectral image sensors are stan-dard nowadays, synthetic aperture radar (SAR) images are very popular, and hyperspectral sen-sors are receiving more and more attention in many applications. One of the main applications of remote sensing images is the detection of changes in multitem-poral datasets, i.e., detecting changes in images of the same area acquired at different times. Change detection for images acquired by ho-mogeneous sensors has been of interest for a long time. However the wide range of different sensors found in remote sensing makes the de-tection of changes in images acquired by hete-rogeneous sensors an interesting challenge. The main interest of this thesis is to study statistical approaches to detect changes in images acquired by heterogeneous sensors.
Oct. 2015Dupé Jean-BaptisteOrdonnancement et gestion des ressources pour un système de Télécommunications haut débit : Optimisation de la bande passante satellite
Funding: TAS - CNES
Satellite telecommunications have seen a tremendous increase in interest, due to its ability to reduce the digital divide. In fact, a geostationary satellite can take advantage of its very wide coverage and high capacity to reach areas where deployment of a terrestrial network would not be possible, such as transports, or too expensive to be profitable, as in remote areas. Traditionally focused on digital television broadcasting, the latest generation of standards have evolved to reflect those new needs, dealing extensively with the transmission of interactive data, particularly by natively supporting Internet protocols. Scheduling has arisen as a major issue of those modern systems, since it has to deal with to highly uncorrelated processes : demand and capacity. Demand, on one side, evolves with user's needs, and therefore with the applications they are using : video, voice or data. Capacity, on the other side, depends on meteorological conditions over the satellite's cover, as the frequencies used in such systems are very sensitive to wet atmosphere attenuation. This thesis aims to study the problem of scheduling and resource allocation, hoping to achieve a service that can match with terrestrial networks in terms of services, while showing the best possible performances. If numerous solutions were proposed on this topic, none is taking into account all of the current system's constraints. In addition to the variable nature of system's capacity, the conjunction of variable demand and quality of service constraints constitutes an additional issue. Furthermore, we have to consider the practicability of our solution in a real-time context, necessary if we aim for industrial use. We have first developed a scheduler architecture for the Forward link, based on utility functions, thus allowing a simple formulation of the capacity versus demand compromise. We show, through a detailed low-complexity implementation and accurate simulations, how our algorithm could be used eciently in an industrial context. We then focus on the Return link, where we propose a resource allocation method, taking into account quality of service and quality of transmission jointly to deliver an ecient yet consistent resource allocation. Simulations show that our algorithm achieves a better efficiency and traffic handling than reference solutions presented in the literature.
Apr. 2015Garcia NilMéthodes d'optimisation pour la localisation active et passive des cibles
Funding: TESA
Active and passive localization employing widely distributed sensors is a problem of interest in various fields. In active localization, such as in MIMO radar, transmitters emit signals that are reflected by the targets and collected by the receive sensors, whereas, in passive localization the sensors collect the signals emitted by the sources themselves. This dissertation studies optimization methods for high precision active and passive localization. In the case of active localization, multiple transmit elements illuminate the targets from different directions. The signals emitted by the transmitters may differ in power and bandwidth. Such resources are often limited and distributed uniformly among the transmitters. However, previous studies based on the well known Crámer-Rao lower bound have shown that the localization accuracy depends on the locations of the transmitters as well as the individual channel gains between different transmitters, targets and receivers. Thus, it is natural to ask whether localization accuracy may be improved by judiciously allocating such limited resources among the transmitters. Using the Crámer-Rao lower bound for target localization of multiple targets as a figure of merit, approximate solutions are proposed to the problems of optimal power, optimal bandwidth and optimal joint power and bandwidth allocation. These solutions are computed by minimizing a sequence of convex problems. The quality of these solutions is assessed through extensive numerical simulations and with the help of a lower-bound that certifies their optimality. Simulation results reveal that bandwidth allocation policies have a stronger impact on performance than power. Passive localization of radio frequency sources over multipath channels is a diffcult problem arising in applications such as outdoor or indoor geolocation. Common approaches that combine ad-hoc methods for multipath mitigation with indirect localization relying on intermediary parameters such as time-of-arrivals, time difference of arrivals or received signal strengths, are unsatisfactory. This dissertation models the localization of known waveforms over unknown multipath channels in a sparse framework, and develops a direct approach in which multiple sources are localized jointly, directly from observations obtained at distributed sources. The proposed approach exploits channel properties that enable to distinguish line-of-sight (LOS) from non-LOS signal paths. Theoretical guarantees are established for correct recovery of the sources'locations by atomic norm minimization. A second-order-conebased algorithm is developed to produce the optimal atomic decomposition, and it is shown to produce high accuracy location estimates over complex scenes, in which sources are subject to diverse multipath conditions, including lack of LOS.
Mar. 2015Artero Gallardo GuillaumeQualité de service dans des environnements réseaux mobiles, contraints et hétérogènes
Funding: RCF
The unprecedented success of wireless telecommunication systems has resulted in the wireless spectrum becoming a scarce resource. At the same time, extensive measurements conducted in the early 2000’s have shown that a significant part of the licensed spectrum, for instance that dedicated to TV broadcast services, is under-utilized. Cognitive Radio systems have been proposed as the enabling technology allowing unlicensed equipments, referred to as secondary users, to opportunistically access the licensed spectrum when not in use by the licensed users, referred to as primary users. Obviously, changing decades-old policies on spectrum access in the civilian and military domain will not happen overnight and many issues, technological and legal, will have to be ironed out first. However, the fundamental principle that we expect to underlie all solutions is that of access while doing no harm – secondary users should not interfere with primary users. The focus of this thesis is on heterogeneous tactical networks deploying cognitive radios in parts or in their entirety. Such networks can be organized in multiple sub-networks, each characterized by a specific topology, medium access scheme and spectrum access policy. As a result, providing end-to-end Quality of Service guarantees in terms of bandwidth, delay and jitter, emerges as a key challenge. We first address the admission control in multi-hop cognitive radio networks. We show that for this type of networks there is no algorithm capable of estimating the available end-to-end bandwidth in a distributed fashion. Therefore, we fill the gap by introducing a polynomial time algorithm that lands itself to a distributed implementation. Then, we focus on routing and propose a new metric that takes into account the specifics of such networks. Using empirical data from a USRP testbed we show that ETX, the de facto standard metric for wireless networks, fails in the cognitive radio context. Therefore, we revisit ETX by considering the effects of primary user activity and the implications of the principle of access while doing no harm. Finally, as quality of service requirements can be expressed using multiple metrics, we turn our attention to multi-constrained quality of service routing. With the underlying problem being NP-complete, we review the proposed heuristics and approximation algorithms. Our research reveals a trade-off between utilizing theoretically-proven but computably expensive algorithms and solutions that are fast but have poor worstcase bounds. To test the feasibility of solving multi-constrained routing in practice, we implement on a real testbed low complexity algorithms that extend the Dijkstra’s shortest path algorithm. We show that these algorithms can be incorporated in link state routing protocols, such as OSPF and OLSR. While these solutions suffer from poor worst-case performance bounds, in practice, they lead to satisfactory results when compared to exact but non tractable solutions.
Jan. 2015Roudier MarionAnalysis and Improvement of GNSS Navigation Message Demodulation Performance in Urban Environments
Funding: TAS - CNES
Global Navigation Satellite Systems (GNSS) are increasingly present in our everyday life. New users are emerging with further operational needs implying a constant evolution of the current GNSS systems. A significant part of the new applications are found in environments with difficult reception conditions such as urban areas, where there are many obstacles such as buildings or trees. Therefore, in these obstructed environments, the signal emitted by the satellite is severely degraded. The signal received by the user has suffered from attenuations, as well as refractions and diffractions, making difficult the data demodulation and the user position calculation. GNSS signals being initially designed in an open environment context, their demodulaton performance is thus generally studied in the associated AWGN propagation channel model. But nowadays, GNSS signals are also used in degraded environments. It is thus essential to provide and study their demodulation performance in the urban propagation channel models. Nevertheless, GNSS modernization with new signals design such as GPS L1C or Galileo E1 OS, takes into account these new obstructed environments constraints. Since they have been designed especially for urban propagation channels [1], they are expected to have better demodulation performance compared with current GNSS signals. It is thus particularly interesting to firstly provide their demodulation performance in urban environments (not available in the literature) and secondly to compare it with the new GNSS signal designed in this PhD research context. In this way, their performance could be used as a benchmark for the future signals design. However these modernized signals are not yet available for this moment (for example, GPS L1C is expected to be operational over the entire constellation in 2026). It is thus essential to provide and study their demodulation performance in urban environments through simulations. It is in this context that this PhD thesis is related, the final goal being to improve GNSS signals demodulation performance in urban areas, proposing a new signal. In order to be able to provide and study GNSS signals demodulation performance in urban environments, a simulation tool has been developed : SiGMeP for "Simulator for GNSS Message Performance". It allows simulating the entire emission/reception GNSS signal chain in urban environment getting away from dependence of real signals availability, controlling the simulation parameters and testing new configurations. Existing and modernized signals demodulation performance has thus been computed with SiGMeP in urban environments. Since the classical way to compute and represent GNSS signals demodulation performance assumes an AWGN propagation channel model, and since the urban environments are really different from the AWGN channel, this classical method is not satisfactory in our urban context. Thus, in order to represent GNSS signals demodulation performance faithfully to reality, a new methodology more adapted to the user environment is proposed. It is based on the fundamental characteristics of a GNSS system, as well as on the urban environment impact on the received signal analysis. GNSS signals demodulation performance is thus provided in urban environments thanks to this new methodology, and compared with the classic methodology used in the AWGN case. Then, to improve GNSS signals demodulation performance in urban environments, many strategies are possible. However, the research axis on this thesis focuses on the "Channel Coding" aspect. It is thus this field which will be privileged to improve GNSS signals demodulation performance in urban environments. Each message, in addition to containing the useful information, carries redundant informaton, which is in fact the channel coding result, applying to the useful information. The message thus needs to be decoded at the reception. In order to decode the transmitted useful information, the receiver computes a detection function at the decoder imput. But the detection function used in classic receivers correspond to an AWGN propagation channel. This dissertation thus proposes an advanced detection function which is adapting to the propagation channel where the user is moving. This advanced detection function computation considerably improves demodulation performance, just in modifying the receiver part system. Finally, in order to design a new signal with better demodulation performance in urban environments than one of existing and future signals, a new LDPC channel code profile has been proposed, optimizing for a CSK modulation in an AWGN channel for iterative decoding. Indeed, the CSK modulation is a promising modulation in the spread signals world, which permits to free from limitations in terms of data rate implied by current GNSS signals modulations. Moreover, LDPC codes belong to the modern codes family, the first being able to approach the channel capacity.They thus represent promising achievable performance.
Sept. 2014Dion ArnaudRécepteur de navigation reconfigurable pour applications spatiales
Funding: TAS ISAE
The orbit of a satellite around the earth is constantly disturbed by various factors, such as variations in the gravitational field and the solar wind pressure. The drift of the satellite position can compromise the mission, and even lead to a crash or a fall in the atmosphere. The station-keeping operations therefore consist in performing an accurate measurement of the satellite trajectory and then in using its thrusters to correct the drift. The conventional solution is to measure the position with the help of a ground based radar. This solution is expensive and does not allow to have the satellite position permanently : the trajectory corrections are therefore infrequent. A positioning and autonomous navigation system using constellations of navigation satellites, called Global Navigation Satellite System (GNSS), allows a significant reduction in design and operational maintenance costs. Several studies have been conducted in this direction and the first navigation systems based on GPS receivers, are emerging. A receiver capable of processing multiple navigation systems, such as GPS and Galileo, would provide a better service availability. Indeed, Galileo is designed to be compatible with GPS, both in terms of signals and navigation data. Continuous knowledge of the position would then allow a closed loop control of the station keeping. Initially, we defined what the specifications of a multi-mission space receiver are. Indeed, the constraints on such a receiver are different from those for a receiver located on the surface of the Earth. The analysis of these constraints, and the performance required of a positioning system, is necessary to determine the specifications of the future receiver. There are few studies on the subject. Some of them are classified ; others have, in our view, an analytical bias that distorts the determination of specifications. So we modeled the system : GNSS and receivers satellite orbits, radio frequency link. Some parameters of this link are not given in the specification or manufacturers documents. Moreover, the available theoretical data are not always relevant for realistic modeling. So we had to assess those parameters using the available data. The model was then used to simulate various scenarios representing future missions. After defining analysis criteria, specifications were determined from the simulation results. Calculating a position of a satellite navigation system involves three main phases. For each phase, there are several possible algorithms, with different performance characteristics, the circuit size or the computation load. The development of new applications based on navigation also drives the development of new adapted algorithms. We present the principle for determining a position, as well as GPS and Galileo navigation signals. From the signal structure, we explain the phases of the demodulation and localization. Through the use of GPS and Galileo constellations, standard algorithms achieve the performance required for space applications. However, these algorithms need to be adapted, thus some parts were specifically designed. In order to validate the choice of algorithms and parameters, we have simulated the various operating phases of the receiver using real GPS signals. Finally, impact and prospects are discussed in the conclusion.
Sept. 2014Sallantin RenaudOptimisation de bout-en-bout du démarrage des connexions TCP
Funding: TAS - CNES
Undoubtedly, the idea of global network is the founding concept of the next generation of communication systems. In the future, a user should therefore be able to maintain an excellent quality of communication regardless of where he is or moves without noticing the underlying technology changes. As a niche market of communications, be part of this dynamic is crucial for satellite communications. However, in the recent years, many studies have shown that the integration of the satellite segment in a global context was complicated by the different characteristics of considered technologies. In fact, some of the most important protocols such as TCP that warranty the quality of a communication are strongly suffering from the RTT duration and so are inadequate for the satellite link. Since the 2000s, satellite community therefore deployed specific solutions in the form of TCP-PEP. They offer very good performance, but marginalize the satellite link from the others by breaking the essential concept of end-to-end communication, and then make its integration among other technologies difficult. Also, if a solution that enables a better integrability and efficiency is not found, the satellite may be excluded from this ambitious project, despite its numerous strengths. We first conducted an extensive set of studies regarding the behavior of TCP latest flavors initiated by the main Operating Systems. They suggest that relevant end-to-end solutions, designed to fit terrestrial networks, can eventually offer similar performance in a satellite environment than the TCP-PEP solution. However, these optimisations only improve long-lived connections. The poor performance of short-lived connections, that are a majority in the Internet, continues therefore to justify the use of TCP-PEP. Consequently, we focused on improving end-to-end transport protocols for short-lived connections and proposed a mechanism called Initial Spreading that allows significant performance improvements regardless of the context. Its simple concept aims to overcome the RTT dependence that strongly damages the short-lived flows by emitting a large amount of data segments just after the connection establishment. We pay close attention to the consequences of releasing a large group of segments (burst) in a congested network. So while solutions such as RFC 6928, proposed by Google, see their performance sharply deteriorated in such an environment, our mechanism ensures very good performance using an accurateand regulated spreading of the first sent segments. Many simulations in NS2 first allowed us to validate the usefulness and scope of our mechanism. A mathematical model of short-lived TCP connections then allowed us to corroborate these results and to understand in an accurate way the consequences of the transmission of bursts of segments on the average performance of a communication. Finally, we implemented the Initial Spreading in the Linux kernel in order to test its behavior and efficiency in terrestrial and satellite networks and show the merits of our proposal in a real environment. All these evaluations allowed us to refine our mechanism to significantly improve the performance of short-lived TCP connections regardless of the context in question and the state of the network. We finally submitted our proposal to the IETF in the form of an “Internet Draft”.
June 2014Raveneau PatriceSatellites d'observation et réseaux de capteurs autonomes au service de l'environnement
Funding: TESA
Data gathering and transmission through a communicating network can be obtained thanks to wireless sensor networks and observation satellites. Using both these technologies will allow mankind to build a sustainable future by understanding the world around. In recent years, space actors have demonstrated a will to reuse the developped technologies by creating multiple programs platforms and defining context-agnostic protocols. The goal of this thesis is to study the characteristics of several observation technologies to exploit their similarities. We analyse the existing technologies and architectures in several contexts. Then, we propose a networking architecture handling constraints of most commonly used systems in such a context. The main constraints of observation scenarios are due to the links intermittence and lack of network connectivity. We focus on a solution using the delay tolerant networking concept. In such a context, a path between source and destination might not exist at all time. That is why most proposed protocols send multiple copies of a message to increase the delivery ratio. We wanted to decrease network resource use while keeping a similar performance to increase network efficiency. After having proposed a common architecture, we focused on particularities of each network segment to solve problems locally. Concerning the satellite part, we focused specifically on memory management techniques. We considered a low earth orbit satellite with a limited on-board buffer, gathering data from gateways. The goal is then to select the most urgent messages even though the least urgent ones are sent back to the ground. On the terrestrial sensor network part, we focused on the decrease of network resource use. We used the history of encounters between nodes and analysed the influence of the proportion of memory allocated to acknowledgements on network performance. We achieved better performance than existing solutions and at lower cost. The proposed solutions can be deployed and applied in several applications.
May 2014Esteves PauloHigh-Sensitivity Adaptive GNSS Acquisition Schemes
Funding: CNES
Satellite navigation (GNSS) is a constant in our days. The number of applications that depend on it is already remarkable and is constantly increasing. With new applications, new challenges have also risen: much of the new demand for signals comes from urban areas where GNSS signal processing is highly complex. In this thesis the issue of weak GNSS signal processing is addressed, in particular at the first phase of the receiver processing, known as signal acquisition. The first axe of research pursued deals with the analysis and compensation of the Doppler effect in acquisition. The Doppler shift that is experienced by a user is one of the main design drivers for the acquisition module and solutions are proposed to improve the sensitivity-complexity trade-off typical of the acquisition process. The second axe of research deals with the characterization of differential GNSS detectors. After a first step of coherent integration, transition to postcoherent (noncoherent or differential) integration is required for acquiring weak signals. The quantification of the sensitivity of differential detectors was not found in literature and is the objective of this part of the research. Finally, the third axe of research is devoted to multi-constellation Collective Detection (CD). CD is an innovative approach for the simultaneous processing of all signals in view. Several issues related to CD are addressed, including the improvement of the CD search process and the hybridization with standard acquisition. Finally, the application of this methodology in the context of a multi-constellation receiver is also addressed, by processing simultaneously real GPS and Galileo signals.
Jan. 2014Bissoli Nicolau VictorPerformances de détection et de localisation des terminaux SAR dans le contexte de transition MEOSAR
Funding: TAS - CNES
Cospas-Sarsat is an international search and rescue system that operates using low-orbit satellites and geostationary satellites. The current satellite constellation is being replaced by medium Earth orbit satellites which will cover larger areas of the surface of the Earth, permitting almost instantaneous alerts. The objective of this thesis is to study the localization performance of this new system, named MEOSAR (Medium Earth Orbit Search and Rescue). We first study the quality of the link between the beacon, the satellite and the ground receiving station through a link budget. Then, we propose a signal model based on sigmoidal functions to model the smooth transitions of the distress signal. For this model, the localization performance (in terms of Cramér-Rao bounds and estimator variances) is studied for the estimation of the beacon position and for different parameters including the time of arrival, the frequency of arrival and the symbol width. Then, we study the impact of adding prior information on the symbol width and the signal rise time, which are constructed from the allowed tolerances on the beacon specifications. We also investigate the error introduced by the addition of oscillator phase noise, and we show how the position estimation can be improved by taking into account multiple emissions of the beacon. Finally, the localization performance of the MEOSAR system is studied for second generation beacons, which are being developed using spread spectrum modulation.
Dec. 2013Roche SébastienMéthodes de poursuite de phase pour signaux GNSS multifréquence en environnement dégradé
Funding: TAS CNES
This thesis aims to introduce multifrequency phase tracking algorithms operating in low C/N0 environment. The objective is to develop new structures whose tracking limits are lower than that of current algorithms used in mass market receivers. Phase tracking suffers from a lack of robustness due to the cycle slip phenomenon. Works have thus been focused on elaborating new phase unwrapping systems. To do so, two different tracking approaches were studied. First, we have developed new monofrequency tracking loops based on a conventional DPLL. These structures aim at predicting the discriminator output by analyzing, thanks to a polynomial model, the last output samples of either the discriminator or the loop filter. Once the discriminator output is predicted, the estimated value is pre-compensated so that the phase dynamics to be tracked is reduced as well as the cycle slip rate. Then, the unwrapping structure analyzing the loop filter outputs has been extended to multifrequency signals. Using a data fusion step, the new multifrequency structure takes advantage of the frequency diversity of a GNSS signal (i.e., proportionality of Doppler frequencies) to improve the tracking performances. Secondly, studies have been focused on developing a new multifrequency tracking algorithm using variational Bayesian filtering technique. This tracking method, which also uses the GNSS frequency diversity, assumes a Markovian phase dynamics that enforces the smoothness of the phase estimation and unwraps it.
Dec. 2013Bourdeau AudeApproches avancées de navigation par signaux GNSS en environnement urbain utilisant un modèle 3D
Funding: TAS - DGA
The use of Global Navigation Satellites System, better known by the acronym GNSS, in an urban environment has grown signi cantly, especially with the advent of GNSS chips in mobile phones. However, the urban environment introduces many diculties in GNSS signal reception that can lead to position ?s errors of several tens of meters. We chose to answer these problems by using a 3D city model allowing to simulate a realistic propagation of the GNSS signal in urban environment. The rst part of our work regards the Non Line Of Sight problem, where we propose a navigation solution based on a 3D city model to estimate geometrical properties of NLOS measured by the receiver. In a second part, the 3D city model is used to estimate the bias coming from the multipath on the pseudorange measurement. Finally, the last part of our study provides a solution coupling the GNSS signal vectorial tracking method to the information produced from the 3D city model in order to improve the tracking in the context of strong GNSS signal power attenuation.
May 2013Liu ZhongxunModélisation des signatures radar des tourbillons de sillage par temps de pluie
Funding: ONERA
In recent years, wake vortex monitoring in real time has emerged as one of the key challenges in air trac control at landing or taking-o . In clear air, several experimental tests have demonstrated that Lidar is an e ective sensor for wake vortex monitoring. In rainy weather, Lidar becomes blind and Radar is a candidate sensor to detect the motion of raindrops in wake vortices. Thus, investigation on radar monitoring of wake vortices in rainy weather is of both scienti c and practical interests. This topic has been tackled through three successive steps during thisthesis. Firstly, the motion of raindrops in wake vortices has been modeled and simulated. The equation of the motion has been derived and the methodology to compute the raindrops' trajectory and distribution in the flow induced by the wake vortices has been proposed. Secondly, two simulators have been developed for evaluating the radar signatures of raindrops in wake vortices. One simulator is based on the simulation of radar signal time series, by superimposing the radar backscattered signal from each raindrop in the wake vortex region. The other one is based on the raindrops' number concentration and velocity distribution in wake vortices, enabling the computation of radar signatures much more eciently. Those simulators have been used to reproduce experimental configurations and the comparison between measured and simulated signature has shown an interesting agreement at X and W band. Lastly, the interpretation of radar signatures of raindrops in wake vortices has been presented. Based on the computation of three spectral moments, the dependence of radar signatures on rain rate, vortex circulation and radar parameters has been studied for vortices generated by different aircraft types. A wake vortex detection method based on the analysis of Doppler spectrum width of raindrops has been proposed. Considering radar scanning under flight path, a methodology to estimate the wake vortex characteristics has been proposed. Preliminary simulation results have shown its effectiveness. The radar signatures of wake vortices in rainy weather have been modeled and analyzed in this thesis. The simulation results have demonstrated the capability of radar to detect wake vortex in rainy weather. The methodologies developed in this thesis can be further exploited for designing new wake vortex radar systems.
Mar. 2013Cazes FlorianMéthodes de traitement innovantes pour les systèmes de commandes de vol
Funding: AIRBUS
From the 80’s to today, all AIRBUS civil aircraft are equipped with electrical flight control systems (EFCS). This technology now constitutes an industrial standard for commercial applications. This allows a more sophisticated aircraft control (advanced flight laws, more available autopilot...) and the setting up of specific protection functions of the flight enveloppe. In the framework of a global aircraft optimisation, for future and upcoming programs, current research efforts are dedicated to a more easy-to-handle aircraft, more efficient and so on more environmentally-friendly, resulting in augmented EFCS availability. The industrial state of practice, for all aircraft manufacturers, is to develop high levels of hardware redundancy. Therefore several sensors (for instance three angle of attack probes, three pitot probes) provide flight parameter measurements which are necessary for the computation of the flight laws, as an example. For each of these measurements, a choice or computation is performed to provide a unique and valid value among the redundant sensors. In parallel, a monitoring is done to discard a measure in case of a failure. Both processes are called « consolidation ». The aim of the Ph.D. is to provide new detection strategies to detect a failure on each sensor (monosensor monitoring) and then to design new data fusion methods to act as the actual « consolidation » process. The main idea proposes to create « software » sensors which actually are flight parameter estimators (measured by external sensors) created thanks to other dissimilar flight parameters (in our case inertial parameters, measured by inner sensors, from a different technology). The partial least squares regression (PLS) is used to perform this estimation. Detection strategies and fusion methods are following from its properties.
Feb. 2013Carcanague SébastienAlgorithmes de réception GNSS multifréquence pour positionnement précis
Funding: M3 SYSTEMS
GNSS and particularly GPS and GLONASS systems are currently used in some geodetic applications to obtain a centimeter-level precise position. Such a level of accuracy is obtained by performing complex processing on expensive high-end receivers and antennas, and by using precise corrections. Moreover, these applications are typically performed in clear-sky environments and cannot be applied in constrained environments. The constant improvement in GNSS availability and accuracy should allow the development of various applications in which precise positioning is required, such as automatic people transportation or advanced driver assistance systems. Moreover, the recent release on the market of low-cost receivers capable of delivering raw data from multiple constellations gives a glimpse of the potential improvement and the collapse in prices of precise positioning techniques. However, one of the challenge of road user precise positioning techniques is their availability in all types of environments potentially encountered, notably constrained environments (dense tree canopy, urban environments…). This difficulty is amplified by the use of multi-constellation low-cost receivers and antennas, which potentially deliver lower quality measurements. In this context the goal of this PhD study was to develop a precise positioning algorithm based on code, Doppler and carrier phase measurements from a low-cost receiver, potentially in a constrained environment. In particular, a precise positioning software based on RTK algorithm is described in this PhD study. It is demonstrated that GPS and GLONASS measurements from a low-cost receivers can be used to estimate carrier phase ambiguities as integers. The lower quality of measurements is handled by appropriately weighting and masking measurements, as well as performing an efficient outlier exclusion technique. Finally, an innovative cycle slip resolution technique is proposed. Two measurements campaigns were performed to assess the performance of the proposed algorithm. A horizontal position error 95th percentile of less than 70 centimeters is reached in a beltwayenvironment in both campaigns, whereas a 95th percentile of less than 3.5 meters is reached in urban environment. Therefore, this thesis demonstrates the possibility of precisely estimating the position of a road user using low-cost hardware.
Dec. 2012Goy Jean-PhilippeDétection d'obstacles et de cibles de collision par un radar FMCW aéroporté
Funding: RCF
This thesis, in collaboration with Rockwell-Collins France, forms part of the development of an X-band FMCW airborne radar designed for obstacles detection and collision avoidance. More precisely, this thesis deals with the problem of detecting targets which exhibit a collision trajectory with the radar carrier, in presence of ground clutter. Target detection performances are highly degraded when the targets of interest fall into ground clutter. The main goal of this thesis is to develop signal processing methods to increase radar detection capacities and recognition for collision targets inside ground clutter. First, we give a brief review of signal processing methods for target detection using an airborne FMCW radar : conventional beamforming, range migration compensation, double-FFTs for Range-Doppler Map visualization. We then derive an adaptive antenna array processing to separate ground clutter and fixed hazardous obstacles above the ground (cables, pylons, buildings, ...) using their difference in elevation angle. In the second part of this thesis, we use a long integration time and include extra information on the time model of a range cell signal : Doppler frequency variation. A collision target does not exhibit Doppler frequency ariation, whereas fixed obstacle or ground clutter exhibits a known variation depending on the carrier velocity and the aspect angle. We take advantage of this variation first to separate a cable from a pylon, and then separate collision target from ground clutter. We finally tackle the problem of adaptively detecting a collision mobile spread target in ground clutter region. The proposed algorithms in this thesis have been successively tested on experimental data.
Dec. 2012Diana RémiLe routage dans les réseaux DTN : du cas pratique des réseaux satellitaires quasi-déterministes à la modélisation théorique
Funding: TAS - CNES
Satellite communication is the achievement of more than 50 years of research in the fields of telecommunications and space technologies.First satellites had exorbitant costs for very limited performances. Technological advances occurred in these areas have helped them to become commercially feasible and satisfying. This enable the increase of satellite launches and thus, building complete satellite networks.Today, there are many GEO or LEO satellite constellations used for civilian or military applications. In general, routing in these constellations is done by pre-computing existing routes. These routes are then used for a given period and refreshed if needed. This type of routing is optimal only on deterministic topologies as a consequence we need to consider other solutions if we relax this assumption. The objective of this thesis is to explore alternatives to pre-computed routing. As a potential solution, we propose to assess the suitability of replication based routing protocols issued from the world of delay tolerant networks, DTN. To provide a relevant framework to study this topic, we focus on a particular constellation that present a quasi-deterministic nature and do not provide direct connectivity between all nodes of the system. In a second part, we focus on the modeling of the Binary Spray and Wait, routing protocol. We develop a model that can theoretically determine the distribution of end-to-end delay for any type of network, homogeneous and heterogeneous. Finally, we present a possible use of this model to conduct more in-depth theoretical analysis.
Nov. 2012Meric HugoCodage par superposition pour les communications par satellite
Funding: TAS - CNES
Modern satellite communication systems mainly rely on time sharing to optimize the throughput. Each receiver uses the channel during a given fraction of time. During this period, the transmission parameters (i.e., the modulation and the coding rate) are chosen in order to transmit as much information as possible. The scheme is easy to implement which explains its popularity. However, it is today well established that time sharing is not optimal in terms of spectrumefficiency offered to the receivers. Indeed, the scheme that consists in sending superposed data offers better performance than the time sharing. This thesis investigates the application of superposition coding in satellite communication systems. First of all, we study the performance of hierarchical modulation which is an implementation of superposition coding at the modulation level.We propose a performance evaluation method for such modulations.We also compare the performance of hierarchical and non hierarchical modulations in terms of spectrum efficiency and link unavailability. These two criteria are very important for broadcast system and we show that hierarchical modulations often offer better performance than non hierarchical modulations. Then, we study the performance improvement in terms of spectrum efficiency when using hierarchical modulation in satellite communication systems. Two issues are addressed. The first one is how to group the receivers in pairs in order to transmit data with a hierarchical modulation. The second issue is the computation of the spectrumefficiency.We show that significant gains are possible depending on the system configuration. The last part considers a system where multiple users communicate through a satellite. The satellite acts as a relay in our scenario.We propose a communication scheme where several users emit at the same time with appropriate transmitting power. Thus the signals naturally superpose and generate interference. The receivers use two mechanisms for decoding the signals : physical layer network coding and demodulation of superposed constellations. Finally, we explain how the performance improvements obtained by superposition coding in several scenarios open perspectives for future work.
Nov. 2012Serant DamienAlgorithmes avances de traitement du signal pour réception des signaux GNSS et OFDM
Funding: TAS - CNES
Oct. 2012Prévost RaoulDécodage et localisation AIS par satellite
Funding: CNES - DGA
The automatic identification system (AIS) is a system allowing ships and coast stations to exchange some information by VHF radio. This information includes the identifier, status, location, direction and speed of the emitter. The aim of this thesis is to allow the reception of AIS messages by low Earth orbit satellites without modifying the existing ship equipments. With this system, it becomes possible to know the position of all ships over the Earth. As a consequence, several new services become available, such as global traffic monitoring or determining boat location (for ship-owners). Satellite reception of AIS signals is subjected to a higher noise level when compared to ground level reception. This noise makes classical demodulation and decoding methods unusable. A first contribution of this thesis is to develop new demodulators using error correction methods. These demodulators take advantage of the presence of a cyclic redundancy check (CRC) block in the messages as well as known information about the structure of messages and data. Generalizations of the proposed receiver have also been studied in order to take into account the phase noise of the received signals and the possible collision of messages sent simultaneously by several vessels. The last part of this thesis is devoted to the study of localization methods for ships that do not transmit their location in AIS messages. This localization takes advantage of information contained in the received messages such as the propagation delay and the carrier frequency shift due to the Doppler effect, and a ship movement model.
Oct. 2012Dudal ClémentEtude de la forme d'onde et d'un récepteur pour des systèmes de diffusion par satellite haute capacité
Funding: TAS - TESA
This thesis focuses on jointly improving the spectral efficiency and the power efficiency of satellite transmission schemes. The emergence of new services and the increasing number of actors in this field involve higher transmission rates with increasingly limited resources. Recent progress in the embedded technologies and in digital communications offered to consider transmission schemes with higher spectral and power efficiency. Nevertheless, the major current challenge consists in making efficient use of resources. The study developed in this thesis explores the possibilities of jointly improving the spectral and power efficiency by offering a combination of the Cyclic- Code-Shift Keying modulation (CCSK), which power efficiency increases with the degree of modulation, with a multiplexing technique such as Code-Division Multiplexing (CDM) to offset the deterioration on the spectral efficiency due to the spread spectrum induced by CCSK. Two approaches based on the use of Gold sequences of length N are defined : • a multi-stream approach with an optimal receiver implemented through sphere decoding. The complexity due to the receiver optimality leads to limited spectral efficiencies but the study of performance, confirmed by simulations, shows an increase in power efficiency with spectral efficiency. • a single-stream approach justified by the appearance of redundancy in the patterns following the sequences multiplexing. The single-stream approach offers spectral efficiencies equivalent to the adopted schemes in the DVB-S2 standard, with improved power efficiency from a certain level of signal to noise ratio compared to those schemes. Subsequently, the study focuses on the implementation of several modulation symbols on the subcarriers of an OFDM modulator and the benefits and advantages of such an approach. It concludes with the contribution of channel coding based on nonbinary block codes such as Reed-Solomon and LDPC codes. The proposed waveform offers operating points with high spectral efficiency and high power efficiency with attractive perspectives. In the current context, its application is limited by its amplitude fluctuations but is possible in a multicarrier transmission context, as expected in the years to come.
July 2012Salos Carlos DanielContrôle d’intégrité appliqué à la réception des signaux GNSS en environnement urbain
Funding: TAS - CNES
Global Navigation Satellite Systems (GNSS) integrity is defined as a measure of the trust that can be placed in the correctness of the information supplied by the navigation system. Although the concept of GNSS integrity has been originally developed in the civil aviation framework as part of the International Civil Aviation Organization (ICAO) requirements for using GNSS in the Communications, Navigation, and Surveillance / Air Traffic Management (CNS/ATM) system, a wide range of non-aviation applications need reliable GNSS navigation with integrity, many of them in urban environments. GNSS integrity monitoring is a key component in Safety of Life (SoL) applications such as aviation, and in the so-called liability critical applications like GNSS-based electronic toll collection, in which positioning errors may have negative legal or economic consequences. At present, GPS integrity monitoring relies on different augmentation systems (GBAS, SBAS, ABAS) that have been conceived to meet the ICAO requirements in civil aviation operations. For this reason, the use of integrity monitoring techniques and systems inherited from civil aviation in non-aviation applications needs to be analyzed, especially in urban environments, which are frequently more challenging than typical aviation environments. Each application has its own requirements and constraints, so the most suitable integrity monitoring technique varies from one application to another. This work focuses on Electronic Toll Collection (ETC) systems based on GNSS in urban environments. Satellite navigation is one of the technologies the EU recommends for the European Electronic Toll Service (EETS), and it is already being adopted: as of 2012, toll systems for freight transport that use GPS as primary technology are operational in Germany and Slovakia, and France envisages to establish a similar system from 2013. This dissertation begins presenting first the concept of integrity in civil aviation in order to understand the objectives and constraints of existing GNSS integrity monitoring systems. The derivation of the GNSS integrity requirements and the appropriate integrity monitoring techniques capable to meet them needs a deep knowledge of the targeted application and of its needs and constraints. Consequently, a thorough analysis of GNSS-based ETC systems and of GNSS navigation in urban environments is done in Chapter 2 with the aim of identifying the most suitable road toll schemes, GNSS receiver configurations and integrity monitoring mechanisms. In this case, the need of integrity is not given by safety reasons as in civil aviation, but rather as requirements of economic nature (overcharging and undercharging). Geo-fencing is selected as the method for developing GNSS-based ETC systems over a given area or road network, dividing the tolled region in geo-objects which are the basic pricing sections. A simple user detection (geo-object recognition) algorithm is proposed to charge a user the price of a section whenever it is detected inside it. Receiver autonomous integrity monitoring (RAIM) is chosen among other integrity monitoring systems due to its design flexibility and adaptability to urban environments. Finally, the most promising GNSS receivers are retained, giving special emphasis to dual constellation GPS & Galileo users. The use of SBAS corrections is optionally considered for reducing pseudorange errors. An accurate pseudorange measurement model is a key input in the derivation of the GNSS integrity requirements and the evaluation of RAIM performance. A nominal pseudorange measurement model suitable for integrity-driven applications in urban environments has been obtained following a methodology similar to that of civil aviation, splitting the total pseudorange error into five independent error sources which can be modeled independently: broadcasted satellite clock corrections and ephemeris errors, ionospheric delay, tropospheric delay, receiver thermal noise (plus interferences) and multipath. Nominal errors are modeled as zero-mean Gaussian variables, which is consistent with the error models and integrity monitoring systems used in civil aviation, as well as with SBAS corrections. In this work the fault model that includes all non-nominal errors consists only of major service failures. Once the ETC scheme and the fault model are known, the GNSS integrity requirements with which design the RAIM can be calculated. First, the top level requirements of toll applications are defined in terms of maximum allowable probabilities of missed and false geo-object recognition. Afterwards, the relationship between positioning failures and incorrect geo-object recognition is studied, resulting in maximum allowed probabilities of missed and false alarm values that depend on the number of independent positions with available RAIM employed to decide whether the user is or not inside a pricing section. Two RAIM algorithms are studied. The first of them is the Weighted Least Squares Residual (WLSR) RAIM, widely used in civil aviation and usually set as the reference against which other RAIM techniques are compared. Since one of the main challenges of RAIM algorithms in urban environments is the high unavailability rate because of the bad user/satellite geometry, a new RAIM is proposed. The novel algorithm, based on the WLSR RAIM, is designed with the premise of providing a trade-off between the false alarm probability and the RAIM availability in order to maximize the probability that the RAIM declares valid a fault-free position. Finally, simulations have been carried out to study the performance of the different RAIM and ETC systems in rural and urban environments. Electronic toll collection by means of GNSS in urban environments with geo-objects shorter than 500 m and road topologies that allow a Horizontal Alert Limit (HAL) of 25 or 50 meters has been demonstrated to be feasible with certain signal combinations of dual constellation GPS & Galileo users. Single constellation users only attain the requirements in rural environments with some receiver configurations. In all cases, the availability obtained with the novel RAIM improve those of the standard WLSR RAIM. The main contributions of this thesis are a detailed analysis of GNSS-based ETC systems, a numerical pseudorange nominal error model due to ionospheric delay in Galileo single-frequency receivers, a pseudorange nominal error model due to multipath in urban environments suitable for applications with GNSS integrity, the failure tree that leads to geo-object misleading positions, the derivation of the and of fault detection RAIM algorithms for GNSS-based ETC in the case of a threat model consisting on major service failures, a novel RAIM, based on the WLSR RAIM, that increments the number of valid positions within the integrity requirements in urban environments, the derivation of the analytical expression of the chi-squared non-centrality parameter in the WLSR RAIM and the derivation of the null correlation between the test statistic and the navigation solution error in the WLSR RAIM.
July 2012Lin ChaoAnalyse des ondes P et T des signaux ECG à l'aide de méthodes Bayésiennes
Funding: TeSA
The subject of this thesis is to study Bayesian estimation/detection algorithms suitable for P and T wave analysis in ECG signals. In this work, different statistical models and associated Bayesian methods are proposed to solve simultaneously the P and T wave delineation task (determination of the positions of the peaks and boundaries of the individual waves) and the waveform-estimation problem. These models take into account appropriate prior distributions for the unknown parameters (wave locations and amplitudes, and waveform coefficients). These prior distributions are combined with the likelihood of the observed data to provide the posterior distribution of the unknown parameters. Due to the complexity of the resulting posterior distributions, we propose to use Markov chain Monte Carlo algorithms for (sample-based) detection/estimation.
Mar. 2012Ferrandiz ThomasMaîtrise des latences de communication dans les réseaux bord SpaceWire
Funding: TAS - CNES
The SpaceWire network standard is promoted by the ESA and is scheduled to be used as the sole onboard network for future satellites. SpaceWire uses a wormhole routing mechanism to reduce memoryconsumption and the associated costs. However, wormhole routing can lead to packet blocking in routerswhich creates large variations in end-to-end delays. As the network will be shared by real-time and nonreal-time traffic, network designers require a tool to check that temporal constraints are verified for allthe critical messages. The metric we chose for this tool is an upper-bound on the worst-case end-to-enddelay of a packet traversing a SpaceWire network. This metric is simpler to compute than the exact delayof each packet and provide enough guarantee to the network designers. During the thesis, we designed three methods to compute this upper-bound. The three methods use different assumptions and have different advantages and drawbacks. On the one hand, the first two methods are very general and do not require strong assumptions on the input traffic. On the other hand, the third method requires more specific assumptions on the input traffic. Thus, it is less general but usually gives tighter bounds than the two other methods. In the thesis, we apply those methods to a case study provided by Thales Alenia Space and compare the results. We also compare the three methods on several smaller networks to study the impact of various parameters on their results.
Sept. 2011Hobaya FabriceConvergence vers IP des systèmes de télécommunication par satellite
Funding: TAS - CNES
The world of telecommunications converging towards IP, the telecommunication satellite systems have to follow the trend to stay competitive and to be integrated to the Internet world. We first remind the issues of convergence in satellite communications, then we list the different convergence architectures conceivable in satellite systems and describe the limits of current systems in term of IP convergence. Our choice is devoted to the IP/GSE architecture for the forward link. Then, we specify the GSE-Alt protocol, inspired from GSE but adapted to the return link. The deployment of new services and the evolution of existing services are possible and made easier thanks to the IP layer. Both layers GSE and GSE-Alt optimize the transport of the IP packets. In order to propose a communication support allowing various quality of service (QoS) needs, we specify several mechanisms allowing a great coherence of the quality of service treatments at the different protocol levels. Finally, to allow an interconnection and an integration of the satellite world to the Internet world, we study the requirements in term of IP routing deployment. Therefore, we specify an architecture allowing the satellite to make the switching at the IP level. This convergence of the satellite towards an "all IP" system is the base required to its transparent insertion to the rest of the telecommunication world.
Sept. 2011Pradas DavidConception et méthodologie cross-layer pour les réseaux satellite à haut débit
Funding: CNES
Communication satellites emerge as an attractive solution in providing broadband connectivity to a variety of users thanks to its inherent global coverage. The broadcast nature of satellites (with higher frequency bands Ku/Ka) makes them the natural choice for multicasting services, for interconnecting geographically high-speed networks, and for providing multimedia services. However, this higher frequency band imposes challenging channel conditions. To avoid such problem, upcoming broadband satellite networks have adopted the adaptive coding and modulation at the physical layer. This is the main driver of this thesis due to the crucial fact that such adaptivity makes traditional satellite system design totally inefficient. In this thesis, we focus on a different paradigm to address such new challenges, based on a joint optimization across layers of the protocol stack. The fundamental idea behind this concept is the fact that adaptivity at the physical layer should be followed at upper layers in order to achieve efficient management of the system resources, and in order to comply with the stringent QoS of new applications services. We cover several aspects related to the networking optimization; allocating resources efficiently, maximizing the throughput and assuring fairness among all the users, according to channel condition. Our efforts have been also focused on choosing the best methodology in terms of selecting; efficient mathematical tools, most suitable architecture, novel adaptive technologies at higher layers, the best approach to the cross-layer design, and truly available standardized tools.
Apr. 2011Giraldo Rodriguez CarlosManet Routing Assisted by Satellites
Funding: TAS Telecom Bretagne
Since no similar studies has been proposed, this work intends to present the first conclusions about the possibilities of satellite communications in the distribution of MANET routing signaling. The improvements on MANET routing protocols will be evaluated to figure out if it is interesting or not to introduce this new role for satellites. For that purpose we shall delimit the applicative context. Mobile ad hoc networks are suitable for a wide range of applications. However, the presence of satellite terminals are not always guaranteed. One of the objectives of this work is to identify the applicative contexts where the hybrid terrestrial-satellite signaling distribution is suitable. Another point is the routing protocol itself. A lot of MANET routing protocols are available from the literature. Therefore we need to analyze the different routing solutions so to identify the most adaptable to a hybrid terrestrialsatellite signaling distribution. Finally, we intend to describe the steps and the crucial points of MANET routing protocol evaluation. Several tasks are involved: network modeling, scenario and performance metrics, output analysis techniques, etc. Therefore we highlight the complexity of MANET routing evaluation and present guidelines to achieve valid and representative results
Mar. 2011Fares FaresTraitement des signaux ARGOS 4
Funding: TAS - CNES
In our thesis, we investigate the application of multi user detection techniques to a Low Polar Orbit (LPO) satellite used in the Argos system. Argos is a global satellite-based location and data collection system dedicated for studying and protecting the environment. User platforms, each equipped with a Platform Transmitter Terminal (PTT), transmit data messages to a 850 km LPO satellite. An ARGOS satellite receives, decodes, and forwards the signals to ground stations. All PTTs transmit at random times in a 100 kHz bandwidth using different carrier frequencies. The central carrier frequency f0 is 401.65 MHz. Due to the relative motion between the satellite and the platforms, signals transmitted by PTTs are affected by both a different Doppler shift and a different propagation delay. Thus, the Argos satellite receives overlapping signals in both frequency and time domains inducing Multiple Access Interference (MAI). One common approach to mitigate the MAI problem is to implement Multi User Detection (MUD) techniques at the receiver. To tackle this problem, several MUD techniques have been proposed for the reception of synchronous and asynchronous users. In particular, the Successive Interference Cancelation (SIC) detector has been shown to offer a good optimality-complexity trade-off compared to other common approaches such as the Maximum Likelihood (ML) receiver. In an Argos SIC receiver, users are decoded in a successive manner, and the signals of successfully decoded users are subtracted from the waveform before decoding the next user. This procedure involves a parameter estimation step and the impact of erroneous parameter estimates on the performance of Argos SIC receiver has been studied. Argos SIC receiver has been shown to be both robust to imperfect amplitude and phase estimation and sensitive to imperfect time delay estimation. The last part of our work focuses on the implementation of digital estimators for the Argos system. In particular, we propose a time delay estimator, a frequency estimator, a phase estimator and an amplitude estimator. These estimators are derived from the ML principle and they have been already derived for the single user transmission. In our work, we adapt successfully these estimators for the multi user detector case. These estimators use the Non Data Aided (NDA) cases in which no a priori information for the transmitted bits is required. The performance of these different estimators are compared to the Cramer Rao Bound (CRB) values. Finally, we conclude in our work by showing the different results obtained during this dissertation. Also, we give some perspectives for future work on Argos system.
Dec. 2010Bouabdallah AmineContributions à la fiabilisation du transport de la vidéo
Funding: TAS - CNES
Video applications are growing more and more successful in the new communication networks. Their utilization in growing harder context as lossy packet network (Interne), satellitemobile broadcasting wireless channel, call for the developments of more ecient and well adapted solutions. The work done in this thesis is an attempt to answer those new needs. The proposed solutions can be grouped into two sets : solutions based on new works developed for medium context and solutions based on the improvement and optimization of existing works developed for extremes contexts. The Bernoulli channel represented the working environment to develop new solutions. So for video streaming application, we targeted unequal protection mechanisms and developed dependency-aware unequal protection codes (DA-UEP). This mechanism is located near the source application and adapt the protection level to the importance of the data. Its originality comes from its ability to integrate video data dependencies into the protection generator. In a forward work of improvement and exploration, we combined DA-UEP unequal protection from high layers with hierarchical-modulation unequal protection from lower layer. The system optimization achieves substantial gains and validate the righteous of this research area. For conversational video applications, we evaluated the performances of Tetrys in the video communication context. This On-the-y coding mechanism with acknowledgment integration achieves performances as high as those obtained by unequal protection in streaming context. Those performances also advances the high potential of this mechanism. The land mobile satellite channels represented the working environment to improve and optimize existing solutions. We particulary focus on satellite to mobile video broadcasting applications. In this context, we evaluated mechanisms such as forward errors correcting codes (FEC), data interleaving at physical or link layers and forward erasures correcting codes at intermediates layers. The evaluation is made on a realistic satellite channel and takes into account practical constraints such as the maximum zapping time and the user mobility at several speeds. We reveal the existing relations between user velocity, data spreading and reception quality. Consequently, We identied the combinations of mechanisms that give the best performance in terms of reliability and zapping time in this particular framework.
Nov. 2010Thevenon PaulInterface air pour systèmes de navigation en bande S : étude détaillée des signaux OFDM
Funding: TAS - CNES
Positioning in urban or indoor environment is a hot topic, either due to regulations such as the E911 requiring US mobile telecommunication operators to be able to locate their subscribers in case of emergency, or due to the market development, with the extension of location-based services targeting the mass market concentrated in metropolitan areas. In urban or indoor areas, it is generally recognized that satellite-based positioning systems are not suitable (alone) to provide a continuous, reliable and accurate position to the user. Therefore, alternative positioning techniques may be useful to complement or replace satellite positioning in these environments. This PhD study has studied the possibility of using a mobile TV system based on the DVB-SH standard as system of opportunity for positioning. The advantages of using a DVB-SH system for positioning are multiple. First, such system has a good availability in metropolitan areas, including indoor. Secondly, the emitters are synchronized and their density should be sufficient to track signals from several emitters simultaneously. This opens the possibility of using timing measurements from several emitters to find a position by tri-lateration. Also, the large bandwidth of the TV signal, required for the transmission of video content, should be beneficial for the accuracy of the timing measurements and for the robustness against multipaths. Therefore, DVB-SH system seems to be an interesting candidate as system of opportunity for positioning. However, several challenges are to be solved for such a solution to be relevant. First, the signals propagate in the urban environment, which creates challenging conditions for positioning such as strong power fading, blockage of the desired line-of-sight signal or large echoes. Secondly, the DVB-SH standard uses an OFDM modulation, which has not been studied for positioning purpose. Therefore, techniques for fine tracking of the first received signal replica will have to be developed. Finally, a particularity of modern broadcast system is the use of a Single Frequency Network, in which all emitters send the same signal on the same carrier frequency. Therefore emitter identification in a Single Frequency will be another issue to be solved. This PhD study has proved the feasibility of positioning using DVB-SH signals. The main contributions of this work are the propositions of (1) an OFDM signal delay tracking method working in urban propagation channels, and (2) a modification to the network deployment permitting emitter identification and (3) a first assessment of the position accuracy using the proposed algorithms. These two methods have very low impact on the initial TV broadcasting service if the right set of signal parameters is chosen: no signal modification is required and the network deployment modification uses a feature already present in the DVB-SH standard. The positioning method was simulated using real urban propagation channel measurements. The obtained position has root mean square error of 40m. The main error contribution comes from tracking a non-line-of-sight signal. Further work would be required to deal with this issue, which would lower the position root mean square error to 7m, which has been locally observed in the simulation for good tracking conditions.
Oct. 2010Garcia Pena AxelOptimisation de la Performance de Démodulation des Messages de Navigation GPS et GALILEO
Funding: TAS - CNES
The demodulation performance achieved by any of the existing GNSS signals, such as GPS L1 C/A, GPS L2C or GPS L5, is satisfactory in open environments where the available C/N0 is quite high. However, in indoor and in urban environments, several characteristics degrade the demodulation performance. In particular, in these environments, the C/N0 level of the received signal is often very low. Also, when the receiver is in motion, the C/N0 suffers additional fast variations due to changing diffraction conditions which can further affect the GNSS messages demodulation. Therefore, since the mass-market applications being conceived nowadays are aimed at indoor and urban environments, it is necessary to study and to search alternative demodulation/decoding methods which improve the GNSS messages demodulation performance in these environments. It is also needed to consider new GNSS signals, such as GPS L1C and GALILEO E1, which were developed recently. These signals aim at providing satellite navigation positioning service in any kind of environment, giving special attention to indoor and urban environments. Therefore, this dissertation also analyses the demodulation performances of the new GNSS signals as they are defined in the current public documents. Moreover, new GALILEO E1 message structures are proposed and analysed in order to optimize the demodulation performance as well as the quantity of broadcasted information. Therefore, the main goal of this dissertation is to analyse and to improve the demodulation performance of the GPS L1 C/A, GPS L2C, GPS L5, GPS L1C and GALILEO E1 signals, specifically in indoor and urban environments, and to propose new navigation message structures for GALILEO E1. A detailed structure of the sections of this dissertation is given next. First, the subject of this thesis is introduced, original contributions are highlighted, and the outline of the report is presented. Second, this dissertation begins by a description of the current structure of the different analysed GNSS signals, paying special attention to the navigation message structure and the implemented channel code. Also, the different channel code decoding techniques used in subsequent sections of this dissertation are fully described. In the third section, two types of transmission channel models are presented. These models represent the correlator outputs as used for carrier tracking and demodulation in the two environments, assuming ideal code tracking. On one hand, the open environments, and even some indoor environments, are modelled by an AWGN channel. Therefore, this report describes the AWGN channel mathematical model and presents its effects on the signal carrier phase tracking process, since the phase tracking performance altogether with the code tracking performance condition the demodulation performance. On the other hand, the urban environments and some indoor environments are modelled as a mobile channel. In this case, there exists several possible mathematical mobile channel models, and thus one of them is selected and this choice is justified. Moreover, the problems affecting the signal carrier phase tracking process are also presented, altogether with two techniques employed during the simulations in order to track the signal carrier phase. These techniques are the PLL and the channel estimation. Additionally, for both transmission channels, the structure implemented during the simulations in order to reproduce the channel characteristics is presented. In the fourth and fifth sections, efforts to improve the demodulation performance of the existing GNSS signals are presented. In the fourth section, a tentative to make a binary prediction of a part of the GPS L1 C/A navigation message is presented. Note that the binary prediction introduced is a prediction of the bits forming the navigation message, not a prediction of the physical magnitude of different message fields. More specifically, the prediction of the broadcasted satellite ephemeris is tried using the GPS L1 C/A almanacs data, a long term orbital prediction program provided by TAS-F, and some signal processing methods. These signal processing methods can be separated in two types. The first type searches the ephemeris data prediction by using the past ephemeris data values, or, in other words, the history of the ephemeris data. The methods tried are the ephemeris data spectral estimation, the PRONY method, and a neural network. The second type of methods tries to exploit the correlation between the different GPS satellite orbits. More precisely, these methods try to exploit the fact that some GPS satellites share the same orbit with their position delayed in time. Then, in the fifth section, improvements to the GPS L2C and GPS L5 navigation message demodulation performance are brought by using their channel codes in a non-traditional way. The proposed method consists in combining the navigation message inner and outer channel codes in order to correct more received words. The technique is such that the receiver accepts as the transmitted word the most probable word provided by the Viterbi decoding, or inner channel code, which meets the outer channel code verification. In fact, this technique follows the same principle as the list Viterbi decoding method although the proposed algorithm is completely different. Also, the technique solves some additional problems due to the GPS navigation messages. The proposed algorithm is described, its advantages and drawbacks presented, some possible modifications are given and its performance is compared with the performance obtained by traditional GPS L2C and GPS L5 decoding methods. Additionally, another method used to improve this performance is presented. This method consists in using the ephemeris data probabilities in order to improve the traditional Viterbi decoding. In the sixth section, the GPS L1C and GALILEO E1 Open Service demodulation performance is analysed in different environments. More specifically, this section presents a brief study of the structure of both signals to determine the received C/N0 in an AWGN channel. Then, the demodulation performance of these signals is analysed through simulations in different environments. The environments analysed are the open, indoor and urban environments modelled by the AWGN channel and the mobile channel. Therefore, this section presents the demodulation performance obtained when the GNSS signals are transmitted through an AWGN channel assuming perfect tracking, an AWGN channel with thermal noise affecting the PLL tracking, an AWGN channel with thermal noise and dynamic stress error affecting the PLL tracking, and a mobile channel with a GNSS receiver travelling at 5km/h, 30 km/h and 50 km/h. In this last case, the carrier phase tracking is achieved either by using a PLL or by applying a channel estimation technique. In the seventh section, efforts to improve the different GALILEO E1 signal performances are presented. Specifically, this dissertation presents a new navigation message structure which improves the demodulation performance and increases the signal information transmission rate. The new proposed navigation message structure consists in adopting a message structure similar to the GPS L1C message structure but also in including a signalling technique known as Code Shift Keying, or CSK, which increases the information transmission rate. In fact, the CSK technique consists in shifting the PRN code of each transmitted symbol in order to map for each code shift a fixed quantity of bits. This results into an increased quantity of bits transmitted during a symbol length, from one to the number of mapped bits. The CSK implementation into a navigation signal analysis is detailed next. First, the drawbacks introduced by the CSK implementation are analysed, and mainly the problems due to the fact that the data channel PRN code is no longer synchronized with the pilot channel PRN code. This induces that the data channel can no longer be used to acquire or to track the signal in the signal parts where the CSK is implemented. Therefore, the new acquisition performance is analysed. The optimal source mapping code shifts which reduce the acquisition false alarm arte when the data channel is employed are also presented. Initial conclusions concerning the impact of CSK on the tracking performance is also presented. Second, this dissertation searches for the demodulation performance of different CSK source mapping configurations. The CSK source mapping configuration refers to the bits and their distribution into packets to be transmitted by the same CSK symbol. Therefore, in order to analyse the different CSK source mapping options, the following points are studied. First, the interest in using the CSK polarity in order to encode an extra bit is analysed. Second, the study determines whether it is best to transmit bits belonging to several packets inside the same CSK symbol, or if it is best to transmit only bits belonging to the same packet. Third, the theoretical BER curves for different numbers of bits forming a CSK are shown. Fourth and last, figures depicting the BER and WER of different CSK source mapping configurations are presented. Additionally, since some of the packets transmitted by the CSK symbols implement channel codes with soft inputs, the theoretical expressions of the likelihood ratios of the bits coded by a CSK symbol have been calculated and verified. Finally, we conclude this study.
July 2010Ouzeau ChristopheDegraded Modes Resulting From the Multi Constellation Use of GNSS
Funding: DTI
The International Civil Aviation Organization (ICAO) has defined the concept of Global Navigation Satellite System (GNSS), which corresponds to the set of systems allowing to perform satellite-based navigation while fulfilling ICAO requirements. The US Global Positioning Sysem (GPS) is a satellite-based navigation system which constitutes one of the components of the GNSS. Currently, this system broadcasts a civil signal, called L1 C/A, within an Aeronautical Radio Navigation Services (ARNS) band. The GPS is being modernized and will broadcast two new civil signals: L2C (not in an ARNS band) and L5 in another ARNS band. Galileo is the European counterpart of GPS. It will broadcast three signals in an ARNS band: Galileo E1 OS (Open Service) will be transmitted in the GPS L1 frequency band and Galileo E5a and E5b will be broadcasted in the same 960-1215 MHz ARNS band than that of GPS L5. GPS L5 and Galileo E1, E5a, E5b components are expected to provide operational benefits for civil aviation use. However, civil aviation requirements are very stringent and up to now, the bare systems alone cannot be used as a means of navigation. For instance, the GPS standalone does not implement sufficient integrity monitoring. Therefore, in order to ensure the levels of performance required by civil aviation in terms of accuracy, integrity, continuity of service and availability, ICAO standards define different systems/algorithms to augment the basic constellations. GPS, Galileo and the augmentation systems could be combined to comply with the ICAO requirements and complete the lack of GPS or Galileo standalone performance. In order to take benefits of new GNSS signals, and to provide the service level required by the ICAO, the architecture of future combined GNSS receivers must be standardized. The European Organization for Civil Aviation Equipment (EUROCAE) Working Group 62, which is in charge of Galileo standardization for civil aviation in Europe, proposes new combined receivers architectures, in coordination with the Radio Technical Commission for Aeronautics (RTCA). The main objective of this thesis is to contribute to the efforts made by the WG 62 by providing inputs necessary to build future receivers architecture to take benefits of GPS, Galileo and augmentation systems. In this report, we propose some key elements of the combined receivers’ architecture to comply with approach phases of flight requirements. In case of perturbation preventing one of the needed GNSS components to meet a phase of flight required performance, it is necessary to be able to switch to another available component in order to try to maintain if possible the level of performance in terms of continuity, integrity, availability and accuracy. That is why future combined receivers must be capable of detecting the impact of perturbations that may lead to the loss of one GNSS component, in order to be able to initiate a switch. These perturbations are mainly atmospheric disturbances, interferences and multipath. In this thesis we focus on the particular cases of interferences and ionosphere perturbations. The interferences are among the most feared events in civil aviation use of GNSS. Detection, estimation and removal of the effect of interference on GNSS signals remain open issues and may affect pseudorange measurements accuracy, as well as integrity, continuity and availability of these measurements. In literature, many different interference detection algorithms have been proposed, at the receiver antenna level, at the front-end level. Detection within tracking loops is not widely studied to our knowledge. That is why, in this thesis, we address the problem of interference detection at the correlators outputs. The particular case of CW interferences detection on the GPS L1 C/A and Galileo E1 OS signals processing is proposed. Nominal dual frequency measurements provide a good estimation of ionospheric delay. In addition, the combination of GPS or GALILEO navigation signals processing at the receiver level is expected to provide important improvements for civil aviation. It could, potentially with augmentations, provide better accuracy and availability of ionospheric correction measurements. Indeed, GPS users will be able to combine GPS L1 and L5 frequencies, and future GALILEO E1 and E5 signals will bring their contribution. However, if affected by a Radio Frequency Interference, a receiver can lose one or more frequencies leading to the use of only one frequency to estimate the ionospheric code delay. Therefore, it is felt by the authors as an important task to investigate techniques aimed at sustaining multi-frequency performance when a multi constellation receiver installed in an aircraft is suddenly affected by radiofrequency interference, during critical phases of flight. This problem is identified for instance in [NATS, 2003]. Consequently, in this thesis, we investigate techniques to maintain dual frequency performances when a frequency is lost (L1 C/A or E1 OS for instance) after an interference occurrence.
Nov. 2009Montesinos JulienTraitement d'antenne SDMA pour système de télécommunications par satellite avec couverture dispersée
Funding: TAS
For national/international organisms, it is of utmost importance to own a communication mean over a wide zone able to connect, upon request, potentially dispersed users. To ensure the security of people even in areas difficult to access, to have at one’s disposal a system able to work even if surrounded by jamming stations. A satellite system with a direct radiating array (DRA) associated with a digital beamforming network (DBFN) and a space-time-position radio resource management allows to achieve these objectives thanks to a spatial division multiple access (SDMA). SDMA is the combination of a flexible resource allocation and adaptive beamforming. Given spatial constraints, low complexity and low sample support beamformers are required to use a SDMA strategy in order to allow an efficient use of frequency resources. The conditions to use such algorithms that are needed for a SDMA strategy are determined given the encountered operational context. SDMA benefits quantification shows that in peacetime the spectral efficiency and therefore the link rates are increased, while in a jammered environment, SDMA provides the ability to maintain some links that would be lost without the adaptive beamforming.
June 2009Spangeberg MarianaSafe Navigation for Vehicles
Funding: TAS
Satellite navigation has acquired an increased importance during these last years, on the one hand due to the imminent appearance of the European GALILEO system that will complement the American GPS, and on the other hand due to the great success it has encountered in the commercial civil market. An important part of this success is based on the technological development at the receiver level that has rendered satellite navigation possible even in difficult environments. Today’s objective is to prepare the utilisation of this kind of signals for land vehicle applications demanding high precision positioning. One of the main challenges within this research domain, which cannot be addressed by classical coupling techniques, is related to the system capability to provide reliable position estimations. The enhancement in dead-reckoning technologies (i.e. size reduction of MEMS-based sensors or gyroscopes) cannot all by itself reach the necessary confidence levels if exploited with classical localization and integration algorithms. Indeed, these techniques provide a position estimation whose reliability or confidence level it is very difficult to quantify. The feasibility of these applications relies not only on an extensive research to enhance the navigation algorithm performances in harsh scenarios, but also and in parallel, on the possibility to maintain, thanks to the presence of additional sensors, a high confidence level on the position estimation even in the absence of satellite navigation signals.
Mar. 2009Ho Anh TaiApplication des techniques multiporteuses OFDM pour futurs systèmes de télécommunications par satellite
Funding: TAS - CNES
This thesis studies the applicability of OFDM techniques for future satellite telecommunications systems. In particular, he treats the synchronization problem at the receiver for satellite broadcasting systems in Ka band. The system uses QAM modulation with M phase stages and works in continuous mode, at small signal to noise ratio (typically at Eb/N0 = 0dB). The main objective of this thesis is to propose a receiver synchronization structure using as least resources as possible in order to optimize spectral efficiency. Two studies are carried out. The first study consists of proposing and validating a synchronization structure in the aim of optimizing spectral efficiency. The second study evaluates the performance of this structure then, compares it with existing standards such as DVB-S and DVB-S2 in terms of spectral efficiency. For first study, synchronization errors have been identified and their impact on system performance evaluated. These results prove that excepting clock frequency error, other synchronization errors have to be estimed and corrected. The transmission in continuous mode for fixed satellite broadcasting system allows the use of NDA (Non-Data-Aided) loop structure in order to avoid the use of pilots, then improve spectral efficiency. However, these algorithms need a coarse synchronization stage in order to limit interference terms. So, the synchronization includes a coarse stage in order to limit interference terms and a finer stage in order to improve system performance. For coarse synchronization stage, simulation results prove that algorithms using guard interval give better performance than whom using pilots. The second study evaluates performance of the proposed structure. In coarse synchronization stage, this evaluation allows to specify guard interval length then, calculate and compare system performance in terms of spectral efficiency with its in DVB-S and DVB-S2 standards. Then, performance evaluation of fine synchronization stage allows to calculate degradations of the proposed structure in the absence and in presence of phase noise models, one of important parameters in a telecommunications system. This stage allows not only to define operating points of the proposed structure in presence of phase noise models in existing standards but also to define phase noise mask of Wiener model supported by this structure. Finally, a study on the hanging time of the proposed structure allows to evaluate the time neccesary to this structure, based on blind algorithms, to be converged. Another study also evaluates the complexity of this structure. This study shows that the synchronization structure proposed in this thesis uses little resources both in terms of spectral efficiency and number of calculations.
Dec. 2008Chibout BenjaminTraitement des signaux boc pour la radionavigation
Funding: TAS - CNES
Nov. 2008Delaunay XavierCompression d'images satellite par post-transformées dans le domaine ondelettes
Funding: CNES
The French Space Agency, CNES, is interested in the transforms derived from the wavelets in order to increase the image compression efficiency on-board of Earth observation satellites. In this thesis, the post-transforms are studied. They are employed after the wavelet transform. Each block of wavelet coefficients is further transformed in a basis selected among a dictionary by minimization of a rate-distortion criterion. First, we emphasize dependencies between wavelet coefficients limiting the compression efficiency. Then, we study the bandelet transform by blocks, from which the post-transforms derive, and we optimize its parameter for the compression of satellite images. Particularly, we adapt Shoham and Gersho optimization method to the problem of the selection of the best bandelet basis. We deduce from these results an expression of the optimal Lagrangian multiplier used in the rate-distortion criterion. Next, we analyze dependencies between wavelet coefficient which are not exploited by the bandelet transform and we define new post-transform bases. Bases build by PCA minimize the correlations between post-transformed coefficients and compact the energy of each block on a small number of coefficients. This feature is exploited during the entropy coding process. Last, we modify the bases selection criterion to adapt the post-transform to progressive compression schemes. We then employ the Hadamard post-transform with the CCSDS image encoder to obtain a low computational complexity yet efficient compression scheme.
Nov. 2008Dubois EmmanuelConvergence dans les réseaux satellite
Funding: TAS
Satellite networks have been built by the DVB group and dedicated to digital television service. However, in the current service convergence trend, a future satellite network architecture has to be built in a less dedicated way to fit heterogeneous services. This work begins with a description of DVB satellite networks. Then, network convergence solutions are studied for the satellite context. IP and MPLS have then been chosen to build a satellite convergent architecture. Several scenarios are examined so as to evaluate this architecture. A first one deals with the historical television service in a unidirectional, transparent satellite context. We show the feasibility of such a scenario with similar performances and better protocol organisation which simplifies satellite evolution. The next scenarios concern an interactive television service with a return link and a voice over IP service. The ability of deploying new services in a simple manner is thus highlighted. The last scenario applies our convergent approach to the ULISS industrial project of a regenerative hybrid satellite. It shows the flexibility of our architecture and expand ULISS service capabilities.
Sept. 2008Puengnim AnchaleeClassification de modulations linéaires et non-linéaires à l’aide de méthodes Bayésiennes
Funding: CNES
This thesis studies classifcation of digital linear and nonlinear modulations using Bayesian methods. Modulation recognition consists of identifying, at the receiver, the type of modulation signals used by the transmitter. It is important in many communication scenarios, for example, to secure transmissions by detecting unauthorized users, or to determine which transmitter interferes the others. The received signal is generally affected by a number of impairments. We propose several classifcation methods that can mitigate the effects related to imperfections in transmission channels. More specifcally, we study three techniques to estimate the posterior probabilities of the received signals conditionally to each modulation. The first technique estimates the unknown parameters associated with various imperfections using a Bayesian approach coupled with Markov Chain Monte Carlo (MCMC) methods. A second technique uses the Baum Welch (BW) algorithm to estimate recursively the posterior probabilities and determine the most likely modulation type from a catalogue. The last method studied in this thesis corrects synchronization errors (phase and frequency offsets) with a phase-locked loop (PLL). The classifcation algorithms considered in this thesis can recognize a number of linear modulations such as Quadrature Amplitude Modulation (QAM), Phase Shift Keying (PSK), and nonlinear modulations such as Gaussian Minimum Shift Keying (GMSK).
May 2008Canourgues LucileAlgorithmes de Routage dans les Réseaux Mobile Ad hoc Tactique à Grande Echelle
Funding: RCF
The current Transformation of the military networks adopts the MANET as a main component of the tactical domain. Indeed, a MANET is the right solution to enable highly mobile, highly reactive and quickly deployable tactical networks. Many applications such as the Situational Awareness rely on group communications, underlying the need for a multicast service within the tactical environment where the MANET is employed as a transit network. The purpose of this thesis is to study the setting up of an optimal multicast service within this tactical environment. We firstly focus on defining the protocol architecture to carry out within the tactical network paying particular attention to the MANET. This network is interconnected with different types of networks based on IP technologies and implementing poten- tially heterogeneous multicast protocols. The tactical MANET is supposed to be made of several hundred of mobile nodes, which implies that the scalability is cru- cial in the multicast protocol architecture choice. Since the concept of clustering proposes interesting scalability features, we consider that the MANET is a clus- tered network. Thereby, we define two multicast routing protocols adapted to the MANET: firstly STAMP that is in charge of the multicast communications within each cluster and secondly SAFIR that handles multicast flows between the clusters. These two protocols that can be implemented independently, act in concert to pro- vide an efficient and scalable multicast service for the tactical MANET. Then, we study the interoperability of these multicast protocols employed within the MANET with those employed in the heterogeneous networks that it is interconnected with in order to guarantee end-to-end seamless multicast services to users. Finally, since the multicast protocols proposed in this thesis rely on underlying unicast routing protocols, we propose, in the last chapter, a scalable unicast routing protocol based on OLSR.
May 2008Cantillo JuanCodage multi-couches pour systèmes de communication par satellites
Funding: TAS
Current satellite architectures for delivering interactive IP services and broadband connectivity are based on the layered principles of the OSI reference model. There is no denying that the traditional research approach focusing on layer-specific problems faced by satellite architectures within the well-defined bounds of the layered model has been rather fruitful. Wireless-friendly adaptations of major protocols exist today, and state-of-the-art coding and modulation techniques have taken physical layers close to their theoretical performance limits. However, a number of critical issues such as end-to-end fulfillment of service-level agreements, seamless mobility or scalable support for reliable multicast have not yet found optimal solutions by means of independent layer tuning, due to the unique characteristics of satellite links. The modular approach blurs the dynamics of layers interaction with the wireless medium, hindering the overall system performance with redundancy, inefficient resource handling and suboptimal performances. Recent research has thus started to address these problems in a holistic way, by stressing the potential benefits of authorizing information exchanges across layers beyond the scope of the reference model. Multi-layers feedback and the resulting system adaptivity offer multiple possibilities for attuning the protocol stack as a whole, allowing for overall optimization and better integration of satellite links in the increasingly heterogeneous network environment. Cross-layer design has emerged as a promising research area in the satellite and wireless communications fields, characterized by a multi-disciplinary approach involving information theory, network protocol design, optimization techniques, stochastic modeling and advanced signal processing. Since recent crosslayer proposals have started tackling successfully some complex problems that layered architectures do not address properly, next-generation standards and protocols are starting to integrate crosslayer principles de facto. This thesis addresses the error control problem for satellite links from the perspective of cross-layer design. At the crossroads of QoS-related constraints, devices complexity and efficient spectrum use, error control is indeed a key aspect of wireless communications — particularly crucial in the satellite context — where cross-layer enhancements can play an important role. After a thorough introduction to cross-layer design, the first part of this work focuses specifically on the error control strategy of early DVB satellites, where redundancies between the channel decoder and the adaptation layers are set to light in order to propose a joint bandwidth-efficient error control policy. The focus then moves to second-generation DVB satellites and the definition of the novel, IPcentric and cross-layer friendly GSE encapsulation protocol, where results from the aforementioned study were successfully applied. Finally, a whole new cross-layer framework called HERACLES is introduced, offering efficient and overhead-free error correction capabilities for almost any layer of a protocol stack and being patented at the moment of writing these words. The results of the overall work show the strengths of an integrated approach to error control, and open the way for innovative cross-layer mechanisms to be deployed in next-generation communications networks.
Jan. 2008Tra FerdinandContrôle d’Admission des Connexions pour les Systèmes de Télécommunication par Satellite avec des Liaisons Physiques Adaptatives
Funding: TAS
In high frequency bands (Ka and above), multimedia satellite communication systems may suffer from deep fading caused by atmospheric phenomena. Unfortunately, those deep atmospheric losses can no longer be overcome by a static link margin. Fade Mitigation Techniques (FMT) are then used to counteract those fades by enabling link adaptation according to propagation conditions. Without sacrificing bit error rate, FMT provide high average spectral efficiency by transmitting at high speeds under favorable channels conditions and by reducing throughput as the channel degrades. This capacity variation causes some difficulties to define resource management mechanisms, in particular the Connection Admission Control (CAC). Indeed a CAC function, which only uses current capacity information, may lead to intolerable dropping of admitted connection, and thus breaches the QoS guarantees made upon connection acceptance. This thesis focuses, then, on CAC mechanisms suitable for satellite systems with varying capacity. In those kinds of systems, CAC functions should estimate the possible evolution of the capacity. Therefore connections will only be admitted if the CAC function supposes the required capacity to be available for a long period of time. This kind of CAC is called as adaptive CAC. This work deals with the variation of the capacity by analyzing the different climatic phenomena and their prediction. The current study made on attenuation spatio-temporal models and their prediction showed their unsuitability for an adaptive CAC function. In fact, either they act over a very short period of time, typically some seconds, or they are too complex to be used within the context of a real system. Therefore, a simplified approach is argued in this study. It consists in separating the configuration where the Gateway/NCC is facing atmospheric impairments from the one where some user terminals face directly rain cells. For the admission policy, one could use one of the two CAC defined in this document, according to the way the system capacity varies in comparison with the connections duration : an optimistic CAC and a pessimistic CAC. This latter supposes the variation of the channel quality to be faster than connections duration. Therefore, the system capacity, on which connection admission decisions are based, corresponds to the case when the deepest fades occur. The optimistic policy is defined in the favorable case when channel quality varies slowly w.r.t to connections duration. The system capacity is, then, supposed to remain constant during connections lifetime. Thus, connection admission decision is made upon the current system capacity and the actual transmission condition faced by any of the user terminals.
July 2007El Natour HannaTechniques avancées de traitement du signal GPS pour les services LBS
Funding: TAS
In the past, in order for GPS (Global Positioning System) to work accurately, the presence of an unobstructed LOS (Line-Of-Sight) signal was necessary. Weak signals were not suitable for use because they may have large associated noise and other errors. The expansion of GPS to LBS (Location-Based Services) and other navigation applications all over the world, such as the E-911 and the E-112 mandates in the United States and Europe respectively, changed the paradigm. Consequently a dramatic increase in the need for more and more performant positioning techniques is expected, especially in urban and indoor environments. These rising localization requirements pose a particularly difficult challenge for GPS receivers design. The thesis objective is to evaluate and enhance existing GPS signal acquisition techniques for positioning goals in harsh environments, in the context of AGPS (Assisted GPS). The AGPS system assumes that the GPS receiver is connected to or introduced in a mobile phone. This allows for the transfer of AD (Assistance Data) to the GPS receiver via the GSM (Global System for Mobile communications) cellular network. Amongst others, the AD provides the GPS receiver with the list of visible satellites and estimates of their Dopplers and code delays, thus reducing the search window of these parameters. This work consists in exploring different GPS signal acquisition to reduce the acquisition time or TTFF (Time To First Fix), without affecting the receiver sensitivity. This is done after a prior study of the GPS radio channel. The study starts out with a revue of the GPS system and the GPS transmitted and received signal structure. The acquisition process is then described in details: the classical acquisition is first described in order to proceed afterwards with the impact of the propagation environment on this stage of the signal processing. For this purpose, harsh environments (urban and indoor) are modelled and analysed. This analysis enables to study the problems which encounter the radio frequency signal propagation through such environments. Note that the urban channel is studied using an existing statistical model developed by Alexander Steingass and Andreas Lehner at the DLR (German Aerospace Center) [Steingass et al., 2005]. On the other hand, an indoor channel model was developed by the ESA (European Space Agency) in the frame of a project entitled “Navigation signal measurement campaign for critical environments” and presented in [Pérez-Fontán et al, 2004]. But this model considers a time invariant statistical channel. Consequently, we developed an Indoor model which rather considers a time variant channel, by taking into account temporal variations of some channel parameters, like the transfer function delay and phase. The initial values are however based on the statistical distributions provided by the ESA model. The channels are analysed is terms of multipaths, cross-correlations and signal masking. The multipaths replicas are particularly disturbing in urban environments while the cross-correlations and masking effects are more disturbing in indoor environments. These phenomena may induce errors in the final solution calculated by the receiver. In order to avoid this error, one solution consists in increasing the signal observation duration in order to enhance the signal to noise ratio. But this generally implies longer acquisition time, thus affecting the receiver performance, commercially speaking. Indeed, the time requirements are as important as sensitivity requirements for GPS users. However, these two requirements are not generally compatible with each other. Consequently, an ideal solution consists in reducing the acquisition time without greatly affecting the receiver sensitivity. Accordingly, such advanced methods for acquisition signal processing are described next. Most of these methods aim at reducing the total acquisition time, rather than enhancing the receiver sensitivity. This means however that longer signal blocks can be processed (thus enhancing sensitivity) without affecting the global processing duration. At first, each of these methods is evaluated through the description of its advantages and drawbacks. A performance evaluation of these algorithms, using signals generated with a Spirent STR4500, ensues as a final step of this study.
Oct. 2006Christophe EmmanuelCompression des Images Hyperspectrales et son Impact sur la Qualité des Données
Funding: TAS - CNES
Hyperspectral images present some specific characteristics that should be used by an efficient compressionsystem. This thesis focuses on the definition and the optimization of a full wavelet compression system for hyperspectral images. In compression, wavelets have shown a good adaptability to a wide range of data, while being of reasonable complexity. Zerotree based compression algorithms are among the best for image compression. Therefore, in this work, efficient compression methods based on zerotree coding (EZW, SPIHT) are adapted on a near-optimal wavelet decomposition for hyperspectral images. Performances are compared with the adaptation of JPEG 2000 for hyperspectral images. End users of hyperspectral images are often interested only in some specific features of the image (resolution, location) which depend on the application. A further adaptation of the proposed hyperspectral image compression algorithm is presented to allow random access to some part of the image, whether spatial or spectral. Resolution scalability is also available, enabling the decoding of different resolution images from the compressed bitstream of the hyperspectral data while reading a minimum amount of bits from the coded data. Final spatial and spectral resolutions are chosen independantly. Finally, any lossless compression method cannot be characterized without the definition of a distortion measure. Therefore, a group of five quality criteria presenting a good complementarity is defined. The purpose is to make sure the compression algorithm does not impact significantly the data quality. A new method using these five criteria shows a good ability to discriminate between different degradations. Application of this method to the newly defined algorithm shows that the degradation remains low for compression rate around 1.0 bit per pixel per band.
Sept. 2006Millerioux Jean-PierreTechniques de détection multi-utilisateurs pour les communications multifaisceaux par satellite
Funding: TAS - CNES
This thesis is devoted to the definition and the evaluation of multiuser detection techniques to mitigate co-channel interference on the reverse link of multibeam satellite systems. These techniques can cope with lower C/I than classical systems: they can consequently allow more capacity efficient frequency reuse strategies. The considered access and waveforms are inspired by the DVB-RCS standard. We propose iterative interference cancellation algorithms adapted to the satellite context. They include estimation of beamforming coefficients and frequency offsets of received signals. These algorithms are first evaluated in terms of bit error rate and of channel estimation error on fictitious interference configurations. We show that they lead to very limited degradations (with respect to the single user case) on interference configurations characterized by very low C/I. We then consider evaluations on a multibeam coverage. Simulation results on a multibeam coverage designed on a Focal Array Fed Reflector antenna allow comparing the algorithms in a realistic context.

TeSA in New Orleans

Charles-Ugo Piat-Durozoi (left) and Romain Chayot (right) presented papers at ICASSP 2017 last March, supported by Corinne Mailhes (center).

PhD positions available at TeSA

PhD subjects available on the CNES site.
On line application before the 31rst of March.


Welcome to our 3 new PhD students: Adrien, Lorenzo and Selma (from left to right).