Les travaux présentés dans ce mémoire se placent dans le contexte des réseaux sans fil sans infrastructure (Ad Hoc) impliquant l’utilisation d’antennes sectorielles simples dans le canal radio à 60 GHz. L’antenne est constituée de plusieurs antennes simples, chacune destinée à un secteur particulier et susceptible d’être commutée mécaniquement pour activer un seul secteur. Il est ainsi possible de choisir le secteur d’émission ou de réception des données. Ce type d’antenne souffre néanmoins d’un problème lié à cette commutation mécanique : elle ne peut pas se faire instantanément. À chaque changement de secteur, une petite quantité de temps est perdue, ce qui diminue l’efficacité de l’ensemble. Ce problème est d’autant plus important lorsque le temps de commutation avoisine le temps d’émission d’un paquet : plus de la moitié de la bande passante peut être gâchée. Les solutions de l’état de l’art permettant de supporter les antennes sectorielles ne prennent généralement pas en compte ce temps de commutation et ne sont donc pas adaptées au problème. La thèse défendue est qu’en prenant en compte ce temps de commutation, il est possible de produire une pile protocolaire performante et adaptée à ce type d’antennes. Nous proposons donc une nouvelle pile protocolaire optimisée comprenant les deux couches basses du modèle OSI. Elle reste donc interopérable avec les systèmes actuels. / The work presented in this paper are placed in the context of wireless networks without infrastructure (Ad Hoc) involving the use of sector antennas in a 60 GHz radio channel. The antenna consists of several simple antennas; each intended for a particular sector and may be mechanically switched to activate a single sector. It is thus possible to choose the area of transmitting or receiving data. This type of antenna nevertheless suffers from a problem with this mechanical switching: it cannot be done instantly. At each change of sector, a small amount of time is lost, which reduces the efficiency. This problem is particularly important when the switching time is around the time needed to send a packet: more than half of the bandwidth can be wasted. The state of the art solutions for supporting sector antennas generally do not take into account this switching time and therefore are not adapted to this problem. The thesis is that by taking into account the switching time, it is possible to produce an efficient and adapted protocol stack to this type of antennas. We therefore propose a new optimized protocol stack including the two lower layers of the OSI model. It then remains interoperable with other systems.

Les villes actuelles sont de plus en plus connectées. Les compteurs sont relevés sans-fil et à distance. Les luminaires des villes communiquent pour économiser l’énergie tandis que les engins de ramassage communiquent avec les poubelles pour planifier les tournées. Ces réseaux sont sans infrastructure et les nœuds capteurs puisent leur énergie dans une batterie limitée.Dans cette thèse j'analyse les problématiques des réseaux sans-fil muti-sauts dans les villes intelligentes. J’étudie dans un premier temps l’importance et l’impact de la topologie sur les performances réseau. Plus précisément, au travers de simulations et d’études expérimentales, je démontre que le placement des nœuds impacte les performances des algorithmes de routage géographique. Je propose ensuite une famille d’algorithmes de clustering pour réseaux de capteurs sans-fil reposant sur l’hypothèse qu’un chef de cluster consomme plus d’énergie que les autres nœuds. L’idée principale de ces algorithmes est que le rôle de cluster-head doit être attribué en fonction du niveau d’énergie des nœuds et de leur voisinage. Ces algorithmes ont été testés grâce à des simulations sur des topologies de villes réalistes avec des paramètres de simulation tirés du monde réel. Enfin, je propose un algorithme de routage pour les villes intelligentes ayant pour base deux techniques de routage. Il repose sur l'hypothèse que seulement une partie des nœuds dispose de l'information de sa position. Je montre qu’il est possible d’obtenir des performances proches des algorithmes de routage géographique, même sous cette hypothèse. / In recent years, cities have become more and more connected. Readings of the electricity usage are being performed wirelessly. In order to reduce the energy consumption, lampposts became intelligent, while the garbage trucks communicate with dust bins in order to plan the garbage collection tours. These networks often lack the infrastructure and sensor nodes rely on a battery with a limited capacity. In this thesis, I analyze the issues of multi-hop wireless networks in smart cities. First, I study the significance and impact of network topologies on network performance. More precisely, through simulations and an experimental study, I show that the placement of nodes impacts the performance of geographic routing algorithms. Then, I propose a set of clustering algorithms for wireless sensor networks that optimize the lifetime of the network. The key hypothesis is that a cluster-head is consuming more energy than a regular node. This set of algorithms, named BLAC, creates multi-hop clusters in which each cluster-head is the root of a tree. The main idea is that the role of each cluster-head should be assigned regarding the remaining energy of nodes and their neighborhood. These algorithms have been tested through simulations based on realistic city topologies with simulation parameters resembling the real world.In the end, I propose a routing algorithm for large scale smart cities that combines two geographic routing techniques. It relies on the hypothesis that only a fraction of nodes in the network are aware of their positions. I show that it is possible to achieve the performance close to classical routing algorithms, even under this hypothesis.

There has been a growing interest in Mobile Ad hoc Networks (MANETs) motivated by the advances in wireless technology and the range of potential applications that might be realised with such technology. Due to the lack of an infrastructure and their dynamic nature, MANETs demand a new set of networking protocols to harness the full benefits of these versatile communication systems. Great deals of research activities have been devoted to develop on-demand routing algorithms for MANETs. The route discovery processes used in most on-demand routing algorithms, such as the Dynamic Source Routing (DSR) and Ad hoc On-demand Distance Vector (AODV), rely on simple flooding as a broadcasting technique for route discovery. Although simple flooding is simple to implement, it dominates the routing overhead, leading to the well-known broadcast storm problem that results in packet congestion and excessive collisions. A number of routing techniques have been proposed to alleviate this problem, some of which aim to improve the route discovery process by restricting the broadcast of route request packets to only the essential part of the network. Ideally, a route discovery should stop when a receiving node reports a route to the required destination. However, this cannot be achieved efficiently without the use of external resources; such as GPS location devices. In this thesis, a new locality-oriented route discovery approach is proposed and exploited to develop three new algorithms to improve the route discovery process in on-demand routing protocols. The proposal of our algorithms is motivated by the fact that various patterns of traffic locality occur quite naturally in MANETs since groups of nodes communicate frequently with each other to accomplish common tasks. Some of these algorithms manage to reduce end-to-end delay while incurring lower routing overhead compared to some of the existing algorithms such as simple flooding used in AODV. The three algorithms are based on a revised concept of traffic locality in MANETs which relies on identifying a dynamic zone around a source node where the zone radius depends on the distribution of the nodes with which that the source is “mostly” communicating. The traffic locality concept developed in this research form the basis of our Traffic Locality Route Discovery Approach (TLRDA) that aims to improve the routing discovery process in on-demand routing protocols. A neighbourhood region is generated for each active source node, containing “most” of its destinations, thus the whole network being divided into two non-overlapping regions, neighbourhood and beyond-neighbourhood, centred at the source node from that source node prospective. Route requests are processed normally in the neighbourhood region according to the routing algorithm used. However, outside this region various measures are taken to impede such broadcasts and, ultimately, stop them when they have outlived their usefulness. The approach is adaptive where the boundary of each source node’s neighbourhood is continuously updated to reflect the communication behaviour of the source node. TLRDA is the basis for the new three route discovery algorithms; notably: Traffic Locality Route Discovery Algorithm with Delay (TLRDA D), Traffic Locality Route Discovery Algorithm with Chase (TLRDA-C), and Traffic Locality Expanding Ring Search (TL-ERS). In TLRDA-D, any route request that is currently travelling in its source node’s beyond-neighbourhood region is deliberately delayed to give priority to unfulfilled route requests. In TLRDA-C, this approach is augmented by using chase packets to target the route requests associated with them after the requested route has been discovered. In TL-ERS, the search is conducted by covering three successive rings. The first ring covers the source node neighbourhood region and unsatisfied route requests in this ring trigger the generation of the second ring which is double that of the first. Otherwise, the third ring covers the whole network and the algorithm finally resorts to flooding. Detailed performance evaluations are provided using both mathematical and simulation modelling to investigate the performance behaviour of the TLRDA D, TLRDA-C, and TL-ERS algorithms and demonstrate their relative effectiveness against the existing approaches. Our results reveal that TLRDA D and TLRDA C manage to minimize end-to-end packet delays while TLRDA-C and TL-ERS exhibit low routing overhead. Moreover, the results indicate that equipping AODV with our new route discovery algorithms greatly enhance the performance of AODV in terms of end to end delay, routing overhead, and packet loss.

Through a thorough review of existing literature, and extensive study of two large ubicomp systems, problems are identified with current mobile design practices, infrastructures and a lack of required software. From these problems, a set of guidelines for the design of mobile, peer-to-peer, context-aware systems are derived. Four key items of software infrastructure that are desirable but currently unavailable for mobile systems are identified. Each of these items of software are subsequently implemented, and the thesis describes each one, and at least one system in which each was used and trialled. These four items of mobile software infrastructure are: An 802.11 wireless driver that is capable of automatically switching between ad hoc and infrastructure networks when appropriate, combined with a peer discovery mechanism that can be used to identify peers and the services running and available on them. A hybrid positioning system that combines GPS, 802.11 and GSM positioning techniques to deliver location information that is almost constantly available, and can collect further 802.11 and GSM node samples during normal use of the system. A distributed recommendation system that, in addition to providing standard recommendations, can determine the relevance of data stored on the mobile device. This information is used by the same system to prioritise data when exchanging information with peers and to determine data that may be culled when the system is low on storage space without greatly affecting overall system performance. An infrastructure for creating highly adaptive, context-aware mobile applications. The Domino infrastructure allows software functionality to be recommended, exchanged between peers, installed, and executed, at runtime.

The use of small-world graphs as interconnection networks of multicomputers is proposed and analysed in this work. Small-world interconnection networks are constructed by adding (or modifying) edges to an underlying local graph. Graphs with a rich local structure but with a large diameter are shown to be the most suitable candidates for the underlying graph. Generation models based on random and deterministic wiring processes are proposed and analysed. For the random case basic properties such as degree, diameter, average length and bisection width are analysed, and the results show that a fast transition from a large diameter to a small diameter is experienced when the number of new edges introduced is increased. Random traffic analysis on these networks is undertaken, and it is shown that although the average latency experiences a similar reduction, networks with a small number of shortcuts have a tendency to saturate as most of the traffic flows through a small number of links. An analysis of the congestion of the networks corroborates this result and provides away of estimating the minimum number of shortcuts required to avoid saturation. To overcome these problems deterministic wiring is proposed and analysed. A Linear Feedback Shift Register is used to introduce shortcuts in the LFSR graphs. A simple routing algorithm has been constructed for the LFSR and extended with a greedy local optimisation technique. It has been shown that a small search depth gives good results and is less costly to implement than a full shortest path algorithm. The Hilbert graph on the other hand provides some additional characteristics, such as support for incremental expansion, efficient layout in two dimensional space (using two layers), and a small fixed degree of four. Small-world hypergraphs have also been studied. In particular incomplete hypermeshes have been introduced and analysed and it has been shown that they outperform the complete traditional implementations under a constant pinout argument. Since it has been shown that complete hypermeshes outperform the mesh, the torus, low dimensional m-ary d-cubes (with and without bypass channels), and multi-stage interconnection networks (when realistic decision times are accounted for and with a constant pinout), it follows that incomplete hypermeshes outperform them as well.

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Στην παρούσα εργασία γίνεται μελέτη της χρήσης του διαφορισμού στις ασύρματες επικοινωνίες. Αρχικά, γίνεται η εισαγωγή και ορίζεται το πεδίο μελέτης. Στη συνέχεια, μοντελοποιείται το ασύρματο κανάλι και παρουσιάζονται οι δυσκολίες που προκύπτουν στη μετάδοση. Συγκρίνεται το κανάλι διαλείψεων (fading channel) με το κανάλι λευκού προσθετικού Γκαουσιανού Θορύβου (AWGN). Στη συνέχεια, γίνεται εισαγωγή στην έννοια του διαφορισμού και περιγράφεται ο διαφορισμός στο χώρο με τη χρήση πολλαπλών κεραιών. Ακολουθεί η ανάλυση ενός συστήματος SIMO οπου γίνεται διαφορισμός μόνο στο δέκτη. Ύστερα, εξετάζεται ένα σύστημα MISO οπου γίνεται διαφορισμός μόνο στον πομπό. Εξετάζονται διάφοροι τρόποι μετάδοσης όπως το σχήμα Alamouti. Το επόμενο κεφάλαιο αποτελεί την εισαγωγή στα συστήματα ΜΙΜΟ και περιγράφεται η ορθογωνοποίηση ενός καναλιού ΜΙΜΟ με τη χρήση SVD. Μελετάται η βέλτιστη κατανομή ενέργειας από τον πομπό. Στη συνέχεια, αναλύονται μέθοδοι ισοστάθμισης για την ανάκτηση των δεδομένων που μεταδίδονται. Εξετάζεται ο αποσυσχετιστής (decorrelator) και ο ισοσταθμιστής ελάχιστου μέσου τετραγωνικού σφάλματος (ΜΜSE). Ακολουθεί η εξέταση μη γραμμικών ισοσταθμιστών ανάδρασης απόφασης και γίνεται αναφορά στην αρχιτεκτονική V-BLAST. Στη συνέχεια γίνεται αναφορά στο βέλτιστο δέκτη και γίνεται σύγκριση του δέκτη αυτού με τους ισοσταθμιστές. / Study of space diversity in wireless communications. The first part is the introduction and the field of study is defined. The next chapter introduces the fading channel. The performance of the Rayleigh fading channel and the AWGN channel are compared. Later, follows the introduction to diversity. We examine a SIMO and a MISO channel. In the MISO channel, emphasis is given on the Alamouti scheme. Later, MIMO channels are discussed. We talk about transmission using Singular Value Decomposition with or without waterfilling. Later, we discuss the equalizers used in MIMO communications. Zero Forcing and Minimum Mean Square Error (MMSE) equalizers are discussed. The next topic of study is decision feedback equalizers. Finally we discuss the optimal receiver architecture and compare its performance against the aforementioned equalizers.

Le contexte aéronautique a depuis plusieurs années mis en évidence le besoin croissant de technologies de sécurité permettant d'éviter des utilisations malveillantes des matériels ou services installés à bord des avions. La plupart des approches de sécurisation 'avion' se concentre sur des méthodes et techniques permettant de sécuriser les échanges au sein de l'avion. Elles sont cependant inadaptées à la sécurisation dans les cas d'interconnexion des réseaux avioniques avec le reste des réseaux de communication (réseau Internet par exemple). Le problème abordé dans ce travail de thèse vise donc à proposer une architecture de sécurité et de sûreté pour l'ensemble des communications aéronautiques et permettant une interconnexion sécurisée entre le monde 'avion' et le monde extérieur, en tenant compte de l'ensemble des critères de sécurité qui caractérisent les divers environnements traversés et considère dès le départ les divers principes de standardisation associés afin de garantir la pérennité scientifique et industrielle.La solution architecturale proposée dans ce travail de thèse repose principalement sur un composant central de routage, de filtrage et de sécurisation des flux de données aéronautiques. Le travail de conception et de développement de ce composant appelé Routeur Sécurisé de Nouvelle Génération (routeur SNG) a permis une validation expérimentale sur un système reproduisant un système embarqué. / For several years, security technology has become a growing necessity for the aeronautical world. It avoids unexpected and unauthorized access to the on-board services and the systems used by companies for their operational requirements. Most current approaches are centred on methods and systems to secure data exchanges inside the plane and to isolate airground communications on dedicated links.These approaches are mandatory but they are no longer sufficient to secure avionic data flows. The evolution from isolated to interconnected avionic networks and their opening to other data networks (the global Internet for instance) is more and more viewed as inescapable.This thesis explores a way of providing a security architecture for all aeronautical communications, in order to extend the existing safety architecture. This new architecture will enable airliners to interconnect “plane” networks and open them safely and securely with the outside world (for example the Internet).One of the main requirements in our work is standardisation: the proposed solution must integrate standardisation constraints of avionic systems as a prerequisite, and provide a secure interconnection point between the on-board segment, the ground segment and the air-ground segment.The architecture we propose in this thesis is mainly based on a central core component to route, filter and secure aeronautical data flows. We have called this system The Secure New Generation Router (SNG Router). The definition, the design and the implementation of this component are here validated on a pseudo-embedded system.