Dissertations / Theses: 'Communications opportunistes'

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Shikfa, Abdullatif. "Sécurité des communications opportunistes." Paris, Télécom ParisTech, 2010. http://www.theses.fr/2010ENST0045.

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Dans cette thèse, nous étudions la sécurité des communications opportunistes. Dans ce nouveau type de communication, la mobilité des nœuds implique que les solutions de sécurité doivent être dynamiques et locales. Par ailleurs l’absence de connectivité bout-en-bout compromet toute solution de sécurité interactive. En outre, contrairement au routage traditionnel basé sur des adresses, les nouvelles stratégies de transmission opportunistes utilisent des informations comme le contexte d'un nœud ou le contenu d'un message pour prendre les décisions de transfert. Contexte et contenu sont des informations sensibles que les utilisateurs pourraient ne pas vouloir révéler aux autres afin de préserver leur vie privée, par conséquent, ces informations doivent être manipulées avec soin pour assurer leur confidentialité. Le conflit entre les exigences de sécurité et de routage justifie la recherche de nouveaux mécanismes de sécurité qui permettent certaines opérations sur des données chiffrées. Après avoir analysé les problèmes de sécurité dans les communications opportunistes, nous proposons une solution de sécurité complète pour la communication basée sur le contexte. Cette solution garantit non seulement la confidentialité des données et le respect de la vie privée des utilisateurs, mais aussi la correction des opérations, ce qui procure une résistance face aux attaques visant à perturber ou à endiguer la communication. Nous proposons aussi un protocole de routage basé sur le contenu qui préserve la vie privée des utilisateurs via un système de chiffrement multicouches, et une solution associée de gestion de clés, qui est locale et dépendante de la topologie
In this thesis, we investigate security in opportunistic communications. This new communication paradigm involves storing and carrying messages in addition to forwarding and impacts all security aspects of communication. Indeed, nodes’ high mobility implies that security solutions should be dynamic and local. Furthermore, delay tolerance, which is one of the main characteristics of opportunistic networks, has a strong impact from a security perspective as it amounts to the infeasibility of interactive protocols. Moreover, radically new forwarding strategies have been proposed to enable communication in opportunistic networks: parting from traditional network addresses, these enriched forwarding strategies use information such as context of a node or content of a message to take forwarding decisions. Context or content are sensitive information that users might not want to reveal to others in order to preserve their privacy, hence these information should be carefully handled to ensure their secrecy. The conflicting requirements between security and forwarding motivate the need for new security mechanisms that enable computation on encrypted data. After analyzing the security challenges in opportunistic communications, we propose a complete security framework for context-based communication. This framework features not only data confidentiality and user privacy, but also computation assurance, which provides resilience against malicious entities aiming at disrupting or subverting the communication. We also propose a privacy-preserving content-based protocol which relies on multiple encryption layers, and an associated local and topology-dependent key management solution

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Koteich, Jana. "Routage opportuniste tenant compte du contexte dans les réseaux sans fil." Electronic Thesis or Diss., Université de Lille (2022-....), 2024. http://www.theses.fr/2024ULILB018.

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Aujourd'hui, le partage des données et du contenu numérique est essentiel dans diverses applications, notamment dans les domaines de la santé, de l'éducation et de l'agriculture. Les réseaux câblés traditionnels et les réseaux sans fil sont les deux principaux modes de communication, ces derniers présentant davantage de difficultés en raison de l'absence de chemin physique guidé. Le routage opportuniste apparaît comme une solution prometteuse dans les régions dépourvues d'infrastructures de communication, en particulier dans les pays les moins avancés.Dans cette thèse, nous proposons une solution alternative aux approches basées sur l'infrastructure pour fournir des données indépendamment de toute infrastructure existante. Cette solution repose sur des dispositifs de communication et de stockage peu coûteux qui peuvent intégrer différentes technologies de communication, ce qui permet de créer un système global de partage de données préservant la vie privée et basé sur la mobilité naturelle des foules. Pour ce faire, nous analysons les schémas de mobilité de la foule afin d'attribuer une probabilité de livraison à un message en fonction de son schéma de mobilité. Tout d'abord, nous avons généré l'ensemble de données PILOT, une collection de données préservant la confidentialité des technologies de communication sans fil. L'ensemble de données se compose de quatre types d'informations collectées conjointement dans différents contextes de mobilité. Il comprend trois technologies de communication sans fil : les réponses des sondes WiFi, les balises BLE (Bluetooth Low Energy) et les paquets LoRa (Long Range Radio), ainsi que des informations supplémentaires sur l'accélération, le roulis et le tangage, toutes collectées simultanément. L'ensemble des données a été collecté pendant environ 90 heures, avec une taille de 200 Mo, en utilisant les dispositifs FiPy de Pycom. Nous avons fourni les clés permettant de reproduire cette collecte de données et partagé les ensembles de données déjà collectés sur GitHub. Après avoir généré l'ensemble de données, nous avons traité les traces collectées de WiFi et de BLE pour générer un modèle de classification capable d'estimer la situation réelle d'un appareil. Le premier modèle créé, appelé modèle B, vise à identifier si un appareil est stationnaire ou mobile. Par la suite, un modèle complémentaire, le modèle M, a été créé pour déterminer une situation plus précise de l'appareil dans la vie réelle, comme à la maison, au bureau, dans un bus, un train, etc. Enfin, nous avons exploité l'ensemble des données collectées et les modèles d'apprentissage automatique entraînés pour concevoir un protocole de routage en établissant des probabilités de livraison conditionnées par le contexte déterminé de l'appareil. Nous testons et validons notre approche en utilisant le simulateur ONE, qui est conçu pour un environnement de réseau opportuniste
Today, sharing data and digital content is essential across various applications, particularly in health, education, and agriculture. Traditional wired networks and wireless networks are the two main modes of communication, with the latter presenting more challenges due to the absence of a guided physical path.Opportunistic routing emerges as a promising solution in regions lacking communication infrastructure, especially in Least Developed Countries.In this thesis, we propose an alternative solution to infrastructure-based approaches for delivering data independently of any existing operated infrastructure. This solution relies on low-cost communication and storage devices that can embed different communication technologies, resulting in a global privacy-preserving data-sharing system based on natural crowd mobility. To achieve this, we analyze crowd mobility patterns to assign a delivery probability for a message based on its mobility pattern. First, we generated the PILOT dataset, a privacy-preserving data collection of wireless communication Technologies. The dataset consists of four types of jointly collected information in different mobility contexts. It includes three wireless communication technologies: WiFi probe responses, BLE (Bluetooth Low Energy) beacons, and LoRa (Long Range Radio) packets, as well as additional information on acceleration, roll, and pitch, all collected simultaneously. The dataset was collected over approximately 90 hours, with a size of 200 MB, using FiPy devices from Pycom. We provided the keys to reproduce such data collection and shared the datasets already collected on GitHub. After generating the dataset, we processed the collected traces of WiFi and BLE to generate a classification model that can estimate the real-life situation of a device. The first created model, called the B-model, aims to identify whether a device is stationary or mobile. Subsequently, a complementary model, the M-model, was created to determine a more precise real-life situation of the device, such as being at home, in the office, on a bus, train, etc. Finally, we exploited the collected dataset and the trained machine learning models todesign a routing protocol by setting delivery probabilities conditioned by the determined context of the device. We are testing and validating our approach using the ONE simulator, which is designed for an opportunistic network environment

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Benchi, Abdulkader. "Middleware Systems for Opportunistic Computing in Challenged Wireless Networks." Thesis, Lorient, 2015. http://www.theses.fr/2015LORIS372/document.

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Les réseaux mobiles opportunistes (ou OppNets, pour Opportunistic Networks) constituent une solution séduisante pour compléter les réseaux fixes d’infrastructure, voire compenser leur absence dans des zones sinistrées ou défavorisées. Les recherches menées ces dernières années ont principalement visé à permettre les transmissions dans les OppNets, mais ceci ne peut être qu’un premier pas vers une réelle exploitation de tels environnements contraints. L’informatique opportuniste (Opportunistic Computing) dépasse le cadre des seules transmissions, et introduit un nouveau paradigme d’exécution de tâches collaboratives dans de tels environnements. Dans ce domaine qu’est l’informatique opportuniste, la conception, la mise en œuvre et le déploiement d’applications distribuées sont des objectifs majeurs. Une application pour OppNet doit pouvoir fonctionner et assurer un niveau de service satisfaisant, tout en supportant les diverses contraintes propres aux OppNets, telles qu’une connectivité fluctuante, un partitionnement chronique du réseau, de longs délais de transmissions, de fréquents échecs de transmission, et des équipements hétérogènes offrant des ressources limitées. La complexité et le coût du développement d’applications pour OppNets peuvent être réduits de manière significative en utilisant des modèles de programmation appropriés. De tels modèles peuvent être fournis par des systèmes intergiciels capables de supporter de manière transparente les contraintes évoquées plus haut. Le travail rapporté dans ce mémoire a porté sur l’étude des contraintes inhérentes aux OppNets, et sur la proposition de solutions appropriées. Parmi les modèles de programmation usuels, certains ont été identifiés comme pouvant être utilisés dans le cadre des OppNets. Sur la base de ces divers modèles de programmation, des systèmes intergiciels opportunistes ont été mis en oeuvre. Ces systèmes supportent respectivement le modèle de messagerie distribuée (sur la base de files d’attentes et de "topics"), le modèle du tuple-space, et la résolution de consensus. Des implémentations complètes ont été réalisées, et le code source est distribué sous licence GPL (GNU General Public License). Ces systèmes ont été évalués par le biais d’expérimentations menées en conditions réelles et par simulation
Opportunistic networks (OppNets) constitute an appealing solution to complement fixed network infrastructures –or make up for the lack thereof– in challenged areas. Researches in the last few years have mostly addressed the problem of supporting networking in OppNets, yet this can only be a first step towards getting real benefit from these networks. Opportunistic computing goes beyond the concept of opportunistic networking, and provides a new paradigm to enable collaborative computing tasks in such environments. In the realm of opportunistic computing, properly designing, implementing and deploying distributed applications are important tasks. An OppNet-dedicated application must be able to operate and maintain an acceptable level of service while addressing the many problems that can occur in these networks, such as disconnections, partitioning, long transmission delays, transmission failures, resource constraints, frequent changes in topology, and heterogeneous devices. Much of the complexity and cost of building OppNet-dedicated applications can be alleviated by the use of high-level programming models. Such models can be supported by middleware systems capable of transparently addressing all the above-mentioned problems. The work reported in this dissertation focused on providing insight into the fundamental problems posed by OppNets, so as to analyze and solve the problems faced by application developers while dealing with these environments. The research focused on identifying well-known high-level programming models that can be satisfactorily implemented for OppNets, and that can prove useful for application developers. In order to demonstrate the feasibility of application development for OppNets, while assessing the benefits brought about by carefully designed middleware systems, a couple of such systems have been designed, implemented, and evaluated as part of this work. These middleware systems respectively support distributed messaging (through message queues and topics), the tuple-space model, and consensus solving in OppNets. They are supplemented with fully-functional implementations, that can be used in real settings, and that are all distributed under the terms of the GNU General Public License (GPL). Real-life experiments and simulations have been realized so as to evaluate the effectiveness and efficiency of these systems in real conditions

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Belouanas, Salah-Eddine. "Dissémination de contenus populaires et tolérants au délai dans les réseaux cellulaires." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066230/document.

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Les ressources cellulaires sont précieuses et doivent être préservées dès que possible. Dans cette thèse, nous abordons le problème de la dissémination de contenus dans un réseau cellulaire surchargé. La première partie présente SCoD (Scheduled Content Delivery), une stratégie de dissémination purement cellulaire qui exploite la mobilité des utilisateurs ainsi que leur tolérance aux délais afin d’effectuer des transmissions différées. SCoD attend que les utilisateurs se rassemblent autour d’un minimum de points d’accès afin que le nombre total de transmissions soit réduit. Pour déclencher des transmissions, SCoD repose sur différentes fonctions de décision qui déclenchent aux instants opportuns une transmission en multicast. La deuxième partie de cette thèse traite également le problème d’économie de ressources cellulaires, mais en l’attaquant sous un autre angle. Nous exploitons des communications D2D que nous associons au multicast pour réduire la charge sur l’infrastructure. Nous analysons les avantages des communications opportunistes dans le contexte d’un service de diffusion de contenus basé sur les abonnements des utilisateurs. Nous présentons nos résultats pour deux cas de figure. Tout d’abord, nous illustrons le bénéfice des communications D2D dans le cadre d’un processus de diffusion, où le coût d’une transmission opportuniste est négligeable par rapport à celui d’une transmission cellulaire. Nous considérons ensuite le cas où les utilisateurs doivent être indemnisés pour leur participation au processus de diffusion, et où il y a donc un compromis à trouver. Nous fournissons des lignes directrices dans ce sens et nous montrons la variation d’un tel compromis en fonction de plusieurs paramètres du réseau
Cellular resources are valuable and must be saved whenever possible. In this thesis, we address the problem of content dissemination within an overloaded cellular network. Firstly, we propose SCoD (Scheduled Content Delivery), a purely cellular dissemination strategy that exploits the mobility of users and their delay tolerance in order to postpone transmissions. SCoD waits for users to gather around a minimum number of access points so that the total number of transmissions is reduced. To trigger transmissions, SCoD relies on different decision functions which launch, if necessary, a multicast transmission. The second part of this thesis deals with the same problem of saving cellular resources, but from another angle. We use D2D (Device-to-Device) communications with multicast to mitigate the traffic load on the infrastructure. We study the benefits of opportunistic communications in the context of a content distribution service based on user subscriptions. We present our results in two ways. First, we illustrate the benefits of D2D communications in a content dissemination process where the cost of opportunistic transmission is negligible compared to that of cellular transmission. Then, we consider the case where users must be compensated for their participation in the dissemination process. Therefore, there is a tradeoff to be found, we thus provide guidelines in this direction and show the variation of such a tradeoff as a function of several network parameters

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Belouanas, Salah-Eddine. "Dissémination de contenus populaires et tolérants au délai dans les réseaux cellulaires." Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066230.pdf.

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Les ressources cellulaires sont précieuses et doivent être préservées dès que possible. Dans cette thèse, nous abordons le problème de la dissémination de contenus dans un réseau cellulaire surchargé. La première partie présente SCoD (Scheduled Content Delivery), une stratégie de dissémination purement cellulaire qui exploite la mobilité des utilisateurs ainsi que leur tolérance aux délais afin d’effectuer des transmissions différées. SCoD attend que les utilisateurs se rassemblent autour d’un minimum de points d’accès afin que le nombre total de transmissions soit réduit. Pour déclencher des transmissions, SCoD repose sur différentes fonctions de décision qui déclenchent aux instants opportuns une transmission en multicast. La deuxième partie de cette thèse traite également le problème d’économie de ressources cellulaires, mais en l’attaquant sous un autre angle. Nous exploitons des communications D2D que nous associons au multicast pour réduire la charge sur l’infrastructure. Nous analysons les avantages des communications opportunistes dans le contexte d’un service de diffusion de contenus basé sur les abonnements des utilisateurs. Nous présentons nos résultats pour deux cas de figure. Tout d’abord, nous illustrons le bénéfice des communications D2D dans le cadre d’un processus de diffusion, où le coût d’une transmission opportuniste est négligeable par rapport à celui d’une transmission cellulaire. Nous considérons ensuite le cas où les utilisateurs doivent être indemnisés pour leur participation au processus de diffusion, et où il y a donc un compromis à trouver. Nous fournissons des lignes directrices dans ce sens et nous montrons la variation d’un tel compromis en fonction de plusieurs paramètres du réseau
Cellular resources are valuable and must be saved whenever possible. In this thesis, we address the problem of content dissemination within an overloaded cellular network. Firstly, we propose SCoD (Scheduled Content Delivery), a purely cellular dissemination strategy that exploits the mobility of users and their delay tolerance in order to postpone transmissions. SCoD waits for users to gather around a minimum number of access points so that the total number of transmissions is reduced. To trigger transmissions, SCoD relies on different decision functions which launch, if necessary, a multicast transmission. The second part of this thesis deals with the same problem of saving cellular resources, but from another angle. We use D2D (Device-to-Device) communications with multicast to mitigate the traffic load on the infrastructure. We study the benefits of opportunistic communications in the context of a content distribution service based on user subscriptions. We present our results in two ways. First, we illustrate the benefits of D2D communications in a content dissemination process where the cost of opportunistic transmission is negligible compared to that of cellular transmission. Then, we consider the case where users must be compensated for their participation in the dissemination process. Therefore, there is a tradeoff to be found, we thus provide guidelines in this direction and show the variation of such a tradeoff as a function of several network parameters

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Gorbil, Gokce. "Opportunistic communications for emergency support." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/14674.

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In this thesis, we consider the problem of providing emergency support when existing communication infrastructure is unavailable. We propose using opportunistic communications (oppcomms) among mobile devices carried by civilians for the dissemination of emergency information. With oppcomms, devices exchange mes- sages at a close range of a few to tens of meters with limited or no infrastructure and messages are carried over multiple hops in a "store-carry-forward" manner by exploiting human mobility. We specifically look at the evacuation component of emergency response and propose an emergency support system (ESS) based on oppcomms to provide evacuation guidance to civilians in small-scale and large-scale urban emergencies in the absence of other means of communication. We evaluate the evacuation performance of ESS and investigate the communication characteristics of oppcomms for emergency support by simulation experiments. Our evaluations show that ESS improves evacuation by up to 31% and 14% compared to shortest path evacuation in large and small scale emergencies, respectively, and by up to 9% compared to a static-node based building evacuation system. We also investigate the resilience and security of oppcomms for emergency support under node failures and network attacks. We consider insider attacks where some nodes participating in oppcomms are compromised and misbehave. We investigate three different types of misbehaviour, including dropping packets, signal jamming and a hybrid attack on routing and evacuation that uses data falsification. Our evaluations show that node failures up to 20% are well-tolerated, and that data falsification has the most significant effect on evacuation by decreasing performance by up to 54%. In order to improve resilience of the system to such attacks, we propose a collaborative defense mechanism that combines identity-based cryptography and content-based message verification, and show that our defense mechanism improves performance by up to 50% in the presence of attacks.

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To, Toan. "Distributed opportunistic scheduling algorithms for wireless communications." Thesis, Swansea University, 2012. https://cronfa.swan.ac.uk/Record/cronfa42588.

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In this thesis, we propose a number of distributed schemes for wireless communications in the cross layer design context, considering an uplink random access network in which multiple users communicate with a common base station. In addition, we perform a comprehensive study on a splitting based multiuser selection algorithm which is simple, effective, and scales with the network size. First, we investigate a reservation-type protocol in a channel aware ALOHA system. Various Markovian models are used to describe the system and to capture the temporal correlation of the channel evolution. The average throughput of the system is obtained using the Markov Analysis technique and we show that the reservation protocol can achieve better performance than the original channel-aware ALOHA by reducing the collision probability. Second, for better resource utilization in the Opportunistic Multichannel ALOHA scheme, we propose a simple extension to the transmission policy that exploits the idle channels. Performance analysis shows that, theoretically, the maximum system throughput can be improved by up to 63% in the asymptotic case. Through numerical results, it can be seen that a significant gain is achieved even when the system consists of a small number of users. Third, we consider a splitting based multiuser selection algorithm in a probabilistic view. Asymptotic analysis leads to a functional equation, similar to that encountered in the analysis of the collision resolution algorithm. Subject to some conditions, the solution of the functional equation can be obtained, which provides the approximations for the expected number of slots and the expected number of transmissions required by the algorithm in a large system. These results shed light on open design problems in choosing parameters for the algorithm when considering the delay and the overhead jointly. A typical example is to optimize the parameters that minimize the weighted sum of these measures of interest.

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Bjurefors, Fredrik. "Measurements in opportunistic networks." Licentiate thesis, Uppsala universitet, Avdelningen för datorteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-227626.

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Opportunistic networks are a subset of delay tolerant networks where the contacts are unscheduled. Such networks can be formed ad hoc by wireless devices, such as mobile phones and laptops. In this work we use a data-centric architecture for opportunistic networks to evaluate data dissemination overhead, congestion in nodes' buffer, and the impact of transfer ordering. Dissemination brings an overhead since data is replicated to be spread in the network and overhead leads to congestion, i.e., overloaded buffers. We develop and implement an emulation testbed to experimentally evaluate properties of opportunistic networks. We evaluate the repeatability of experiments in the emulated testbed that is based on virtual computers. We show that the timing variations are on the order of milliseconds. The testbed was used to investigate overhead in data dissemination, congestion avoidance, and transfer ordering in opportunistic networks. We show that the overhead can be reduced by informing other nodes in the network about what data a node is carrying. Congestion avoidance was evaluated in terms of buffer management, since that is the available tool in an opportunistic network, to handle congestion. It was shown that replication information of data objects in the buffer yields the best results. We show that in a data-centric architecture were each data item is valued differently, transfer ordering is important to achieve delivery of the most valued data.
WISENET

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Kouyoumdjieva, Sylvia T. "System Design for Opportunistic Networks." Doctoral thesis, KTH, Kommunikationsnät, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176479.

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Device-to-device communication has been suggested as a complement to traditional cellular networks as a means of offloading cellular traffic. In this thesis we explore a solution for device-to-device communication based on opportunistic content distribution in a content-centric network. Communication opportunities arise as mobile nodes roam around in an area and occasionally enter in direct communication range with one another. We consider a node to be a pedestrian equipped with a mobile device and explore the properties of opportunistic communication in the context of content dissemination in urban areas. The contributions of this thesis lie in three areas. We first study human mobility as one of the main enablers of opportunistic communication. We introduce traces collected from a realistic pedestrian mobility simulator and demonstrate that the performance of opportunistic networks is not very sensitive to the accurate estimation of the probability distributions of mobility parameters. However, capturing the space in which mobility occurs may be of high importance. Secondly, we design and implement a middleware for opportunistic content-centric networking, and we evaluate it via a small-scale testbed, as well as through extensive simulations. We conclude that energy-saving mechanisms should be part of the middleware design, while caching should be considered only as an add-on feature. Thirdly, we present and evaluate three different energy-saving mechanisms in the context of opportunistic networking: a dual-radio architecture, an asynchronous duty-cycling scheme, and an energy-aware algorithm which takes into account node selfishness. We evaluate our proposals analytically and via simulations. We demonstrate that when a critical mass of participants is available, the performance of the opportunistic network is comparable to downloading contents directly via the cellular network in terms of energy consumption while offloading large traffic volumes from the operator.

QC 20151120

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Dillon, PJ. "Enabling tetherless care with context-awareness and opportunistic communication." Thesis, University of Pittsburgh, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3690742.

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Tetherless care is a novel healthcare delivery paradigm that enables an interaction between caregivers and patients beyond the confines of traditional points of care. This thesis presents a synthesis of recent advances in wearable, ubiquitous sensing; mobile computing; wireless networks; and health information technology into a cohesive framework that enables and supports the tetherless care concept. Tetherless care is formally defined and modeled in a higher order logical framework. The model distills three relations between several classes in the model’s domain of discourse. A prototype implementation is developed and evaluated to capture and represent the logical classes of tetherless care and provide the development infrastructure upon which the relational logic outlined by the model can be implemented. An algorithm is presented and evaluated to support the delivery of traffic between mobile devices and servers despite intermittent connectivity given the changing urgency of the patient’s situation. And an example tetherless care application is presented, developed for the framework, and compared with its deployment on a similar platform. Results show that contemporary mobile devices supply sufficient power to support 24 hours of operation and that, at least, some patient environments provide sufficient opportunities for connectivity to reliably meet the demands of some tetherless care applications, ultimately leading to a conclusion of proof-of-concept for tetherless care.

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Eltayeb, Mohammed. "Opportunistic Scheduling with Limited Feedback in Wireless Communication Networks." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1414874159.

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Khan, Sardar Kashif Ashraf. "Message forwarding techniques in Bluetooth enabled opportunistic communication environment." Thesis, Middlesex University, 2015. http://eprints.mdx.ac.uk/17327/.

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These days, most of the mobile phones are smart enough with computer like intelligence and equipped with multiple communication technologies such as Bluetooth, wireless LAN, GPRS and GSM. Different communication medium on single device have unlocked the new horizon of communication means. Modern mobile phones are not only capable of using traditional way of communication via GSM or GPRS; but, also use wireless LANs using access points where available. Among these communication means, Bluetooth technology is very intriguing and unique in nature. Any two devices equipped with Bluetooth technology can communicate directly due to their unique IDs in the world. This is opposite to GSM or Wireless LAN technology; where devices are dependent on infrastructure of service providers and have to pay for their services. Due to continual advancement in the field of mobile technology, mobile ad-hoc network seems to be more realised than ever using Bluetooth. In traditional mobile ad-hoc networks (MANETs), before information sharing, devices have partial or full knowledge of routes to the destinations using ad-hoc routing protocols. This kind of communication can only be realised if nodes follow the certain pattern. However, in reality mobile ad-hoc networks are highly unpredictable, any node can join or leave network at any time, thus making them risky for effective communication. This issue is addressed by introducing new breed of ad-hoc networking, known as opportunistic networks. Opportunistic networking is a concept that is evolved from mobile ad-hoc networking. In opportunistic networks nodes have no prior knowledge of routes to intended destinations. Any node in the network can be used as potential forwarder with the exception of taking information one step closer to intended destination. The forwarding decision is based on the information gathered from the source node or encountering node. The opportunistic forwarding can only be achieved if message forwarding is carried out in store and forward fashion. Although, opportunistic networks are more flexible than traditional MANETs, however, due to little insight of network, it poses distinct challenges such as intermittent connectivity, variable delays, short connection duration and dynamic topology. Addressing these challenges in opportunistic network is the basis for developing new and efficient protocols for information sharing. The aim of this research is to design different routing/forwarding techniques for opportunistic networks to improve the overall message delivery at destinations while keeping the communication cost very low. Some assumptions are considered to improved directivity of message flow towards intended destinations. These assumptions exploit human social relationships analogies, approximate awareness of the location of nodes in the network and use of hybrid communication by combining several routing concept to gain maximum message directivity. Enhancement in message forwarding in opportunistic networks can be achieved by targeting key nodes that show high degree of influence, popularity or knowledge inside the network. Based on this observation, this thesis presents an improved version of Lobby Influence (LI) algorithm called as Enhanced Lobby Influence (ELI). In LI, the forwarding decision is based on two important factors, popularity of node and popularity of node’s neighbour. The forwarding decision of Enhanced Lobby Influence not only depends on the intermediate node selection criteria as defined in Lobby Influence but also based on the knowledge of previously direct message delivery of intended destination. An improvement can be observed if nodes are aware of approximate position of intended destinations by some communication means such as GPS, GSM or WLAN access points. With the knowledge of nodes position in the network, high message directivity can be achieved by using simple concepts of direction vectors. Based on this observation, this research presents another new algorithm named as Location-aware opportunistic content forwarding (LOC). Last but not least, this research presents an orthodox yet unexplored approach for efficient message forwarding in Bluetooth communication environment, named as Hybrid Content Forwarding (HCF). The new approach combines the characteristics of social centrality based forwarding techniques used in opportunistic networks with traditional MANETs protocols used in Bluetooth scatternets. Simulation results show that a significant increase in delivery radio and cost reduction during content forwarding is observed by deploying these proposed algorithms. Also, comparison with existing technique shows the efficiency of using the new schemes.

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Kurth, Mathias. "Contention techniques for opportunistic communication in wireless mesh networks." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2012. http://dx.doi.org/10.18452/16458.

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Auf dem Gebiet der drahtlosen Kommunikation und insbesondere auf den tieferen Netzwerkschichten sind gewaltige Fortschritte zu verzeichnen. Innovative Konzepte und Technologien auf der physikalischen Schicht (PHY) gehen dabei zeitnah in zelluläre Netze ein. Drahtlose Maschennetzwerke (WMNs) können mit diesem Innovationstempo nicht mithalten. Die Mehrnutzer-Kommunikation ist ein Grundpfeiler vieler angewandter PHY Technologien, die sich in WMNs nur ungenügend auf die etablierte Schichtenarchitektur abbilden lässt. Insbesondere ist das Problem des Scheduling in WMNs inhärent komplex. Erstaunlicherweise ist der Mehrfachzugriff mit Trägerprüfung (CSMA) in WMNs asymptotisch optimal obwohl das Verfahren eine geringe Durchführungskomplexität aufweist. Daher stellt sich die Frage, in welcher Weise das dem CSMA zugrunde liegende Konzept des konkurrierenden Wettbewerbs (engl. Contention) für die Integration innovativer PHY Technologien verwendet werden kann. Opportunistische Kommunikation ist eine Technik, die die inhärenten Besonderheiten des drahtlosen Kanals ausnutzt. In der vorliegenden Dissertation werden CSMA-basierte Protokolle für die opportunistische Kommunikation in WMNs entwickelt und evaluiert. Es werden dabei opportunistisches Routing (OR) im zustandslosen Kanal und opportunistisches Scheduling (OS) im zustandsbehafteten Kanal betrachtet. Ziel ist es, den Durchsatz von elastischen Paketflüssen gerecht zu maximieren. Es werden Modelle für Überlastkontrolle, Routing und konkurrenzbasierte opportunistische Kommunikation vorgestellt. Am Beispiel von IEEE 802.11 wird illustriert, wie der schichtübergreifende Entwurf in einem Netzwerksimulator prototypisch implementiert werden kann. Auf Grundlage der Evaluationsresultate kann der Schluss gezogen werden, dass die opportunistische Kommunikation konkurrenzbasiert realisierbar ist. Darüber hinaus steigern die vorgestellten Protokolle den Durchsatz im Vergleich zu etablierten Lösungen wie etwa DCF, DSR, ExOR, RBAR und ETT.
In the field of wireless communication, a tremendous progress can be observed especially at the lower layers. Innovative physical layer (PHY) concepts and technologies can be rapidly assimilated in cellular networks. Wireless mesh networks (WMNs), on the other hand, cannot keep up with the speed of innovation at the PHY due to their flat and decentralized architecture. Many innovative PHY technologies rely on multi-user communication, so that the established abstraction of the network stack does not work well for WMNs. The scheduling problem in WMNs is inherent complex. Surprisingly, carrier sense multiple access (CSMA) in WMNs is asymptotically utility-optimal even though it has a low computational complexity and does not involve message exchange. Hence, the question arises whether CSMA and the underlying concept of contention allows for the assimilation of advanced PHY technologies into WMNs. In this thesis, we design and evaluate contention protocols based on CSMA for opportunistic communication in WMNs. Opportunistic communication is a technique that relies on multi-user diversity in order to exploit the inherent characteristics of the wireless channel. In particular, we consider opportunistic routing (OR) and opportunistic scheduling (OS) in memoryless and slow fading channels, respectively. We present models for congestion control, routing and contention-based opportunistic communication in WMNs in order to maximize both throughput and fairness of elastic unicast traffic flows. At the instance of IEEE 802.11, we illustrate how the cross-layer algorithms can be implemented within a network simulator prototype. Our evaluation results lead to the conclusion that contention-based opportunistic communication is feasible. Furthermore, the proposed protocols increase both throughput and fairness in comparison to state-of-the-art approaches like DCF, DSR, ExOR, RBAR and ETT.

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Perez-Ramirez, Javier. "An Opportunistic Relaying Scheme for Optimal Communications and Source Localization." International Foundation for Telemetering, 2012. http://hdl.handle.net/10150/581448.

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ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California
The selection of relay nodes (RNs) for optimal communication and source location estimation is studied. The RNs are randomly placed at fixed and known locations over a geographical area. A mobile source senses and collects data at various locations over the area and transmits the data to a destination node with the help of the RNs. The destination node not only needs to collect the sensed data but also the location of the source where the data is collected. Hence, both high quality data collection and the correct location of the source are needed. Using the measured distances between the relays and the source, the destination estimates the location of the source. The selected RNs must be optimal for joint communication and source location estimation. We show in this paper how this joint optimization can be achieved. For practical decentralized selection, an opportunistic RN selection algorithm is used. Bit error rate performance as well as mean squared error in location estimation are presented and compared to the optimal relay selection results.

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Huang, Wen, and 黄文. "Opportunistic scheduling in wireless data networks." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B45895235.

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Nasif, Ahmed O. "Opportunistic spectrum access using localization techniques." Fairfax, VA : George Mason University, 2009. http://hdl.handle.net/1920/4572.

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Thesis (Ph.D.)--George Mason University, 2009.
Vita: p. 146. Thesis director: Brian L. Mark. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Title from PDF t.p. (viewed Oct. 11, 2009). Includes bibliographical references (p. 138-145). Also issued in print.

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Cao, Yaofu. "Modélisation du contexte social : application aux réseaux opportunistes." Thesis, Troyes, 2017. http://www.theses.fr/2017TROY0002/document.

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Cette thèse traite de l’adaptation automatique des applications sensibles au contexte par l’utilisation d’informations liées à l’environnement social des utilisateurs afin d’enrichir le service rendu par les applications. Pour cela, notre contribution s’articule autour de la modélisation multidimensionnelle des différents niveaux de contextes sociaux, notamment le poids de la relation entre les acteurs. Plus spécifiquement, nous synthétisons des contextes sociaux non seulement liés à la familiarité mais aussi liés à la similitude des communautés statiques et dynamiques. Deux modèles basés respectivement sur les graphes et les ontologies sont proposés afin de satisfaire l’hétérogénéité des réseaux sociaux de la vie réelle. Nous utilisons les données réelles recueillies sur les réseautages sociaux en ligne pour conduire nos expérimentations et analysons les résultats en vérifiant l’efficacité de ces modèles. En parallèle nous traitons le point de vue de l’application, et nous présentons deux algorithmes utilisant des contextes sociaux pour améliorer la stratégie de transmission des données dans le réseau opportuniste, et particulièrement la contre-mesure aux nœuds égoïstes. Les simulations des scénarios réels confirment les avantages liés à l’introduction des contextes sociaux, en termes de taux de succès et de délais de transmission. Nous effectuons une comparaison avec d'autres algorithmes de transmission traditionnellement décrits dans la littérature pour compléter notre démonstration
This thesis deals with the dynamic adaptation of context-aware applications using information related to the social environment of users to enrich the service rendered by the applications. To achieve this goal our contribution mobilizes multidimensional modeling of the different levels of social contexts, especially the weight of the relationship between the actors. Particularly, we synthesize not only social contexts related to familiarity but also social contexts reasoned from the similarity of static and dynamic communities. Two models based on respectively graphs and ontologies are proposed in order to satisfy the heterogeneity of the social networks in real life. We use the actual data gathered on online social networking services for conducting experiments and the results are analyzed by checking the effectiveness of the models. In parallel we consider the point of view of the application, and we present two algorithms using social contexts to improve the strategy of transmission of data in the opportunistic network, particularly countermeasure against selfish nodes. The simulations of real scenarios confirm the advantages of introducing social contexts in terms of success rate and delay of transmission. We carry out a comparison with other popular transmission algorithms in the literature

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Butt, M. Majid. "On the Near-Far Gain in Opportunistic and Cooperative Multiuser Communications." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12009.

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In this dissertation, we explore the issues related to opportunistic and cooperative communications in a multiuser environment. In the first part of the dissertation, we consider opportunistic scheduling for delay limited systems. Multiuser communication over fading channels is a challenging problem due to fast varying channel conditions. On the other hand, it provides opportunities to exploit the varying nature of the channel and maximize the throughput by scheduling the user (or users) with good channel. This gain is termed as multiuser diversity. The larger the number of users, the greater is the multiuser diversity gain. However, there is an inherent scheduling delay in exploiting multiuser diversity. The objective of this work is to design the scheduling schemes which use multiuser diversity to minimize the system transmit energy. We analyze the schemes in large system limit and characterize the energy--delay tradeoff. We show that delay tolerance in data transmission helps us to exploit multiuser diversity and results in an energy efficient use of the system resources. We assume a general multiuser environment but the proposed scheduling schemes are specifically suitable for the wireless sensor network applications where saving of transmit energyat the cost of delay in transmission is extremely useful to increase the life of battery for the sensor node. In the first part of the thesis, we propose scheduling schemes withthe objective of minimizing transmit energy for a given fixed tolerable transmission delay. The fixed delay is termed as hard deadline. A group of users with channels better than a transmission threshold are scheduled for transmission simultaneously using superposition coding. The transmission thresholds depend onthe fading statistics of the underlying channel and hard deadline of the data to be scheduled. As deadline is approached, the thresholds decrease monotonically to reflect the scheduling priority for theuser. We analyze the proposed schedulers in the large system limit. We compute the optimized transmission thresholds for the proposed scheduling schemes. We analyze the proposed schemes for practically relevant scenarios when the randomly arriving packets have individual, non--identical deadlines. We analyze the case when loss tolerance of the application is exploited to further decrease the system energy. The transmitted energy is not a convex function oftransmission thresholds. Therefore, we propose heuristic optimization procedures to compute the transmission thresholds and evaluate the performance of the schemes. Finally, we study the effect of outer cell interference on the proposed scheduling schemes. The second part of the thesis investigates the problem of cooperative communication between the nodes which relay the data of other sources multiplex with their own data towards a common destination, i.e. a relay node performs as a relay and data source at the same time. This problem setting is very useful in case of some wireless sensor network (WSN) applications where all the nodes relay sensed data towards a common destination sink node. The capacity region of a relay region is still an open problem. We use deterministic network model to study the problem. We characterizethe capacity region for a cooperative deterministic network with single source, multiple relays and single destination. We also characterize the capacity region when communicating nodes have correlated information to be sent to the destination.
Cross Layer Optimization of Wireless Sensor Networks

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Kathiravelu, Thabotharan. "Towards content distribution in opportunistic networks." Licentiate thesis, Uppsala universitet, Avdelningen för datorteknik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-85837.

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Opportunistic networking is a new communication paradigm. Content Distribution in opportunistic networks is challenging due to intermittent connectivity, short connection durations and a highly dynamic topology. Research is needed to develop new applications and protocols that can distribute content in opportunistic networks. This thesis explores and evaluates approaches to developing mobile P2P systems for content distribution, focusing mainly on the problem of modeling device contacts. Contact duration and patterns of connections influence routing and forwarding strategies. To model device contacts we need to capture the characteristics of the network and be able to model its behavior. Connectivity models capture the aggregated network behavior by modeling the social connectedness of the network. A model of inter-device relationships can be constructed using parameters are extracted from connectivity traces collected in the field using real devices. These traces represent how connectivity might look in an opportunistic network. Altering and fine tuning these parameters enables us to change the stochastic behavior of the network and study the behavior of applications and protocols. Another approach is mobility modeling. There are two major drawbacks to using mobility models. First, in ad hoc networks traces have been collected which estimate the connectivity of the network. Typically traces are then used to model node mobility which in turn generates nodal connectivity during a simulation. This is a wasteful process and as the network size grows it becomes a tedious job. Second, the inter-contact time distribution observed in traces differs greatly from what is generated by popular mobility models. We have developed a connectivity model to generate synthetic device contact traces for opportunistic networks. We present the preliminary validation results from a comparative study of synthetic traces and traces collected in the field.

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Rajaei, Aydin. "Efficient and flexible geocasting for opportunistic networks." Thesis, University of Sussex, 2016. http://sro.sussex.ac.uk/id/eprint/66039/.

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With the proliferation of smartphones and their advanced connectivity capabilities, opportunistic networks have gained a lot of traction during the past years; they are suitable for increasing network capacity and sharing ephemeral, localised content. They can also offload traffic from cellular networks to device-to-device ones, when cellular networks are heavily stressed. Opportunistic networks can play a crucial role in communication scenarios where the network infrastructure is inaccessible due to natural disasters, large scale terrorist attacks or government censorship. Geocasting, where messages are destined to specific locations (casts) instead of explicitly identified devices, has a large potential in real world opportunistic networks, however it has attracted little attention in the context of opportunistic networking. In this thesis, we propose Geocasting Spray And Flood (GSAF), a simple but efficient and flexible geocasting protocol for opportunistic, delay tolerant networks. GSAF follows a simple but elegant and flexible approach where messages take random walks towards the destination cast. Messages that follow directions away from the cast are extinct when the device buffer gets full, freeing space for new messages to be delivered. In GSAF, casts do not have to be pre-defined; instead users can route messages to arbitrarily defined casts. Also, the addressed cast is flexible in comparison to other approaches and can take complex shapes in the network. DA-GSAF as the direction aware version of the GSAF is proposed as well which use location information to aid routing decisions in the GSAF. Extensive evaluation shows that GSAF and DA-GSAF are significantly more efficient than existing solutions, in terms of message delivery ratio and latency as well as network overhead.

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Chen, Yuan. "Opportunistic Overlays: Efficient Content Delivery in Mobile Environments." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-04082005-002659/unrestricted/chen%5Fyuan%5F200505%5Fphd.pdf.

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Thesis (Ph. D.)--Computing, Georgia Institute of Technology, 2005.
Riley, George, Committee Member ; Zhou, Dong, Committee Member ; Pu, Calton, Committee Member ; Ahamad, Mustaque, Committee Member ; Schwan, Karsten, Committee Chair. Vita. Includes bibliographical references.

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Loke, Yong. "Sensor synchronization, geolocation and wireless communication in a shipboard opportunistic array." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Mar%5FLoke.pdf.

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Scone, Sion. "Opportunistic communication schemes for unmanned vehicles in urban search and rescue." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/7269.

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In urban search and rescue (USAR) operations, there is a considerable amount of danger faced by rescuers. The use of mobile robots can alleviate this issue. Coordinating the search effort is made more difficult by the communication issues typically faced in these environments, such that communication is often restricted. With small numbers of robots, it is necessary to break communication links in order to explore the entire environment. The robots can be viewed as a broken ad hoc network, relying on opportunistic contact in order to share data. In order to minimise overheads when exchanging data, a novel algorithm for data exchange has been created which maintains the propagation speed of flooding while reducing overheads. Since the rescue workers outside of the structure need to know the location of any victims, the task of finding their locations is two parted: 1) to locate the victims (Search Time), and 2) to get this data outside the structure (Delay Time). Communication with the outside is assumed to be performed by a static robot designated as the Command Station. Since it is unlikely that there will be sufficient robots to provide full communications coverage of the area, robots that discover victims are faced with the difficult decision of whether they should continue searching or return with the victim data. We investigate a variety of search techniques and see how the application of biological foraging models can help to streamline the search process, while we have also implemented an opportunistic network to ensure that data are shared whenever robots come within line of sight of each other or the Command Station. We examine this trade-off between performing a search and communicating the results.

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Almeida, Rodrigo Coelho. "A multi-technology network for environmental data gathering through opportunistic communication." Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/23783.

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mestrado em Engenharia Eletrónica e Telecomunicações
O conceito de Smart City surge da combinação do paradigma de Internet of Things (IoT) sobre contextos urbanos aliado à exploração de soluções de Tecnologias de Informação e Comunicação (TIC). O típico cenário de Smart City tem de lidar com desafios, tais como as elevadas quantidades de sensores e geradores de dados, dos quais alguns são colocados em dispositivos de grande mobilidade, visando a recolha e geração de todo o tipo de informações e levando ao aumento do número de dispositivos comunicantes. Esta dissertação foca o desenvolvimento e implementação de uma plataforma heterogénea de sonorização ambiental com o objectivo de servir de infraestrutura para aplicações no âmbito das Smart Cities. Esta pretende tirar proveito da utilização de múltiplas tecnologias de comunicação, nomeadamente tecnologias de longo e curto alcance. Para al em disto, visto que a plataforma visa ambientes urbanos, esta tira proveito de uma rede oportunista e tolerante a atrasos, Delay Tolerant Network (DTN), através de entidades m oveis que circulam pela cidade, nomeadamente bicicletas. Assim sendo, esta dissertação propõe: (1) o desenho e desenvolvimento da rede e dos seus constituintes; (2) uma extensão a um protocolo de controlo de acesso ao meio, Medium Access Control (MAC), para a tecnologia LoRa com o objectivo de o dotar compatível para ambientes de gateways múltiplas; (3) novas estratégias de encaminhamento para a rede tolerante a atrasos, tendo em consideração a topologia e as características apresentadas por esta. As avaliações realizadas permitiram concluir que o protocolo MAC para LoRa em ambientes de gateways múltiplas proposto contribui para um aumento da escalabilidade da rede, bem como para uma melhoria do seu desempenho. Relativamente às estratégias de encaminhamento propostas para a DTN, os testes realizados permitiram avaliar o impacto que cada estratégia tem sobre o comportamento da rede, nomeadamente a taxa de entrega dos pacotes de dados, a sobrecarga da rede, o número de pacotes transmitidos, entre outros. Com estes resultados foi possível perceber as in- suficiências que as funcionalidades propostas têm sobre a solução geral, e identificar as caraterísticas necessárias de uma solução escalável para a recolha de dados massivos num ambiente de IoT.
The Smart City concept is the combination of the Internet of Things (IoT) paradigm under an urban context with the exploitation of Information and Communication Technologies (ICT) solutions. The typical Smart City scenario has to deal with an extensive amount of sensors and data generators, some of them placed in high mobile devices, deployed to collect and generate all type of information which will increase the number of communicating machines. This dissertation focuses on the development and implementation of a heterogeneous environmental sensing platform to serve as an infrastructure for Smart City applications. It aims to take advantage of the use of multiple communication technologies, namely long and short range. Being within an urban environment, the platform bene ts from an opportunistic and Delay Tolerant Network (DTN) through mobile entities that travel over the city, such as bicycles. Therefore, this dissertation proposes: (1) the design and development of the network and its elements; (2) an extension to a LoRa Medium Access Control (MAC) protocol in order to endow it with capabilities to operate in multi-gateway environments; and lastly, (3) new forwarding strategies for the opportunistic network that takes into consideration the network topology. The performed evaluations showed that the proposed multi-gateway LoRa MAC protocol contributes to increase the LoRa network scalability, as well as its performance. The performed tests to the proposed DTN forwarding strategies evaluate the impact of each strategy on the network behavior, namely the delivery ratio, network overhead, number of transmitted packets, among others. As a result, it is possible to perceive which are the in- uences introduced by the proposed functionalities on the overall solution, and identify the characteristics of a scalable solution to collect massive data in an IoT environment.

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Trotta, Angelo <1985&gt. "Next-Generation Public Safety Systems Based on Autonomous Vehicles and Opportunistic Communications." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/8065/1/TesiDottoratoAngeloTrottaFinal.pdf.

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An emergency scenario is characterized by the unpredictability of the environment conditions and by the scarcity of the available communication infrastructures. After a natural or human disaster, the main public and private infrastructures are partially damaged or totally destroyed. These infrastructures include roads, bridges, water supplies, electrical grids, telecommunications and so on. In these conditions, the first rescue operations executed by the public safety organizations can be very difficult, due to the unpredictability of the disaster area environment and the lack in the communications systems. The aim of this work is to introduce next-generation public safety systems where the main focus is the use of unmanned vehicles that are able to exploit the self-organizing characteristics of such autonomous systems. With the proposed public safety systems, a team of autonomous vehicles will be able to overcome the hazardous environments of a post disaster scenario by introducing a temporary dynamic network infrastructure which enables the first responders to cooperate and to communicate with the victims involved. Furthermore, given the pervasive penetration of smart end-user devices, the emergence of spontaneous networks could constitute promising solutions to implement emergency communication systems. With these systems the survivors will be able to self-organize in a communication network that allows them to send alerts and information messages towards the rescue teams, even in absence of communication infrastructures.

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Klaghstan, Merza. "Multimedia data dissemination in opportunistic systems." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI125/document.

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Les réseaux opportunistes sont des réseaux mobiles qui se forment spontanément et de manière dynamique grâce à un ensemble d'utilisateurs itinérants dont le nombre et le déplacement ne sont pas prévisibles. En conséquence, la topologie et la densité de tels réseaux évoluent sans cesse. La diffusion de bout-en-bout d'informations, dans ce contexte, est incertaine du fait de la forte instabilité des liens réseaux point à point entre les utilisateurs. Les travaux qui en ont envisagé l'usage visent pour la plupart des applications impliquant l'envoi de message de petite taille. Cependant, la transmission de données volumineuses telles que les vidéos représente une alternative très pertinente aux réseaux d'infrastructure, en cas d'absence de réseau, de coût important ou pour éviter la censure d'un contenu. La diffusion des informations de grande taille en général et de vidéos en particulier dans des réseaux oppnets constitue un challenge important. En effet, permettre, dans un contexte réseau très incertain et instable, au destinataire d’une vidéo de prendre connaissance au plus vite du contenu de celle-ci, avec la meilleure qualité de lecture possible et en encombrant le moins possible le réseau reste un problème encore très largement ouvert. Dans cette thèse, nous proposons un nouveau mécanisme de diffusion de vidéos dans un réseau opportuniste de faible densité, visant à améliorer le temps d'acheminement de la vidéo tout en réduisant le délai de lecture à destination. La solution proposée se base sur le choix d'encoder la vidéo en utilisant l'encodage SVC, grâce auquel la vidéo se décline en un ensemble de couches interdépendantes (layers), chacune améliorant la précédente soit en terme de résolution, soit en terme de densité, soit en terme de perception visuelle. Notre solution se décline en trois contributions. La première consiste à proposer une adaptation du mécanisme de diffusion Spray-and-Wait, avec comme unités de diffusion, les couches produites par SVC. Les couches sont ainsi diffusées avec un niveau de redondance propre à chacune, adapté à leur degré d'importance dans la diffusion de la vidéo. Notre seconde contribution consiste à améliorer le mécanisme précédent en prenant en compte une granularité plus fine et adaptative en fonction de l'évolution de la topologie du réseau. Cette amélioration a la particularité de ne pas engendrer de coût de partitionnement, les couches vidéos dans l'encodage SVC étant naturellement déclinées en petites unités (NALU) à base desquelles l'unité de transfert sera calculée. Enfin, la troisième contribution de cette thèse consiste à proposer un mécanisme hybride de complétion des couches vidéos arrivées incomplètes à destination. Cette méthode se caractérise par le fait d'être initiée par le destinataire. Elle combine un protocole de demande des parties manquantes aux usagers proches dans le réseau et des techniques de complétion de vidéo à base d’opérations sur les frames constituant la vidéo
Opportunistic networks are human-centric mobile ad-hoc networks, in which neither the topology nor the participating nodes are known in advance. Routing is dynamically planned following the store-carry-and-forward paradigm, which takes advantage of people mobility. This widens the range of communication and supports indirect end-to-end data delivery. But due to individuals’ mobility, OppNets are characterized by frequent communication disruptions and uncertain data delivery. Hence, these networks are mostly used for exchanging small messages like disaster alarms or traffic notifications. Other scenarios that require the exchange of larger data are still challenging due to the characteristics of this kind of networks. However, there are still multimedia sharing scenarios where a user might need switching to an ad-hoc alternative. Examples are the cases of 1) absence of infrastructural networks in far rural areas, 2) high costs due limited data volumes or 3) undesirable censorship by third parties while exchanging sensitive content. Consequently, we target in this thesis a video dissemination scheme in OppNets. For the video delivery problem in the sparse opportunistic networks, we propose a solution that encloses three contributions. The first one is given by granulating the videos at the source node into smaller parts, and associating them with unequal redundancy degrees. This is technically based on using the Scalable Video Coding (SVC), which encodes a video into several layers of unequal importance for viewing the content at different quality levels. Layers are routed using the Spray-and-Wait routing protocol, with different redundancy factors for the different layers depending on their importance degree. In this context as well, a video viewing QoE metric is proposed, which takes the values of the perceived video quality, delivery delay and network overhead into consideration, and on a scalable basis. Second, we take advantage of the small units of the Network Abstraction Layer (NAL), which compose SVC layers. NAL units are packetized together under specific size constraints to optimize granularity. Packets sizes are tuned in an adaptive way, with regard to the dynamic network conditions. Each node is enabled to record a history of environmental information regarding the contacts and forwarding opportunities, and use this history to predict future opportunities and optimize the sizes accordingly. Lastly, the receiver node is pushed into action by reacting to missing data parts in a composite backward loss concealment mechanism. So, the receiver asks first for the missing data from other nodes in the network in the form of request-response. Then, since the transmission is concerned with video content, video frame loss error concealment techniques are also exploited at the receiver side. Consequently, we propose to combine the two techniques in the loss concealment mechanism, which is enabled then to react to missing data parts

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Martin-Guillerez, Damien Banâtre Michel. "Mécanismes de prise de points de reprise opportunistes pour robots mobiles autonomes." Rennes : [s.n.], 2009. ftp://ftp.irisa.fr/techreports/theses/2009/martin-guillerez.pdf.

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Erpek, Tugba. "Location-based propagation modeling for opportunistic spectrum access in wireless networks." Fairfax, VA : George Mason University, 2007. http://hdl.handle.net/1920/2934.

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Thesis (M.S.)--George Mason University, 2007.
Title from PDF t.p. (viewed Jan. 17, 2008). Thesis director: Brian L. Mark Submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering. Vita: p. 60. Includes bibliographical references (p. 58-59). Also available in print.

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Ullah, Kifayat. "On the use of opportunistic vehicular communication for roadside services advertisement and discovery." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-27102016-142325/.

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Vehicular Ad hoc Network (VANET) is a special kind of Mobile Ad hoc Network (MANET) and is a key enabling technology for Intelligent Transportation Systems (ITS). It plays an important role in the deployment of a large scale of both safety and non-safety applications. Among non-safety applications, an important and challenging area is the provision of information about roadside services advertisement and discovery. In this work, we adopted the beaconing strategy and opportunistic vehicular communications to address the problem of roadside services advertisement and discovery on the highways. Our approach offers several advantages over the traditional billboard method, e.g., low cost, targeting a large number of customers in a real time, more control over the advertisement campaign, dynamic content updating, and discovery of services far ahead of the business region. For advertising roadside services, we followed the push-based advertisement strategy and relied on Infrastructure-to-Vehicle (I2V) communications only. On the other hand, for discovering these services by the drivers, we used pull-based advertisement strategy and opportunistic Vehicle-to-Vehicle (V2V) communications. In order to contribute to the advertisement campaign, we used the store-carry-and-response mechanism. Our first contribution is the Extended Opportunistic Service Discovery Protocol (EOSDP). EOSDP implements and extends the original version of Opportunistic Service Discovery Protocol (OSDP) via simulation experiments. We used Simulation of Urban Mobility (SUMO), Objective Modular Network Testbed in C++ (OMNET++), and Vehicles in network simulation (Veins) simulators. Our second contribution is Service Advertisement Protocol (SADP). SADP is a lightweight beaconing-based services advertisement protocol for VANETs. It does not require the Internet connection for advertising the roadside services. Moreover, SADP modeling is based on VANETs standard protocols. The performance of SADP was evaluated in a congested highway scenario with varying speed of vehicles and under different broadcast frequencies. Our last contribution is Commercial Services Discovery Protocol (CSDP). Like the previous protocol, CSDP is a lightweight beaconing-based services discovery protocol for VANETs. CSDP is infrastructureless protocol which only depends on opportunistic V2V communications for roadside services discovery. The protocol was implemented in congested highway scenario and extensive set of simulation experiments were performed to evaluate its performance under different parameters, e.g., Query Interval (QI), Query Attempts (QA), and Time to Live (TTL).
Vehicular Ad hoc Network (VANET) é um tipo especial de Mobile Ad hoc Network (MANET) e é uma tecnologia chave para apoiar os Sistemas Inteligentes de Transporte (ITSs). Ela desempenha um papel importante na implantação em grande escala das aplicações do tipo safety e non-safety. Dentre as aplicações non-safety, uma área importante e desafiadora é descoberta e divulgação de informação sobre serviços. Neste trabalho, nós adotamos a estratégia de beaconing e as comunicações veiculares oportunistas para resolver o problema da descoberta e divulgação de serviços ao longo de rodovias. Nossa abordagem oferece várias vantagens em relação aos métodos tradicionais usando painéis, painéis eletrônicos digitais e outdoors, por exemplo. Baixo custo, atinge um grande número de clientes em tempo real, maior controle sobre a campanha de propaganda, atualização dinâmica de conteúdo e descoberta de serviços antes de alcançar a região de negócio são algumas delas. Para a divulgação de serviços ao longo de rodovias, seguimos a estratégia de publicidade push-based e usamos somente comunicações do tipo Infrastructure-to-Vehicle (I2V). Por outro lado, para a descoberta destes serviços pelos motoristas, utilizamos a estratégia de publicidade pull-based e comunicações oportunistas do tipo Vehicle-to-Vehicle (V2V). A fim de contribuir para a campanha de propagandas, foi utilizado o mecanismo store-carry-and-response. Nossa primeira contribuição é o Extended Opportunistic Service Discovery Protocol (EOSDP). O EOSDP implementa e estende a versão original do Opportunistic Service Discovery Protocol (OSDP) via experimentos por simulação. Nós utilizamos os simuladores Simulation of Urban Mobility (SUMO), Objective Modular Network Testbed in C++ (OMNET++) e o Vehicles in network simulation (Veins). Nossa segunda contribuição é o Service Advertisement Protocol (SADP). SADP é um protocolo leve baseado na estratégia de beaconing para divulgação de serviços em VANETs. Ele não requer conexão com a Internet para anunciar os serviços nas margens das rodovias. Além disso, a modelagem do SADP é baseada no padrão de protocolos VANETs. O desempenho do SADP foi avaliado em um cenário de rodovia congestionada, com velocidades variáveis dos veículos e sob diferentes frequências de comunicação broadcast. Por fim, apresentamos o nosso último protocolo chamado Commercial Services Discovery Protocol (CSDP). Como o protocolo anterior, o CSDP é um protocolo leve para descoberta de serviços baseado em beaconing para VANETs. O CSDP depende somente de comunicações V2V oportunistas para a descoberta de serviços ao longo de rodovias. O protocolo foi implementado no cenário de uma rodovia congestionada e avaliado com um extenso conjunto de experimentos de simulação, sob diferentes parâmetros como, por exemplo, Query Interval (QI), Query Attempts (QA) e Time to Live (TTL).

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Martin-Guillerez, Damien. "Mécanismes de prise de points de reprise opportunistes pour robots mobiles autonomes." Rennes 1, 2009. ftp://ftp.irisa.fr/techreports/theses/2009/martin-guillerez.pdf.

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Les systèmes informatiques connaissent des défaillances qui entraînent des pertes de données. Les systèmes robotiques collaboratifs, opérant de manière autonome, sont très sensibles à ces défaillances. L'usage de mécanismes de sauvegarde est alors utile. Les mécanismes de communication opportuniste reposent sur les technologies de communication sans-fil courte portée pour permettre des interactions entre deux calculateurs mobiles lorsque leur proximité physique le permet. Pour pallier l'absence d'une couverte réseau permanente, nous proposons un système de sauvegarde basé sur les communications opportunistes pour réduire les coûts des défaillances au sein d'une flotte de robots mobiles autonomes
Failures of mobile computing devices can lead to severe data loss. Collaborative robotic systems, designed to work in total autonomy, are sensitive to these failures. Usual methods relying on remote backup can no longer be used in a context of high mobility. Short-range communication media can be used to overcome data failure through opportunistic communications for data backup. When two devices enter their respective communication range, they can initiate an ephemeral data exchange. To overcome the lack of global network coverage in those system, we propose a backup system based on opportunistic communications to reduce the costs induced by failures inside a swarm of autonomous mobile robots

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Dunat, Jean-Christophe. "Allocation opportuniste de spectre pour les radios cognitives." Phd thesis, Paris : École nationale supérieure des télécommunications, 2006. http://catalogue.bnf.fr/ark:/12148/cb40978484c.

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Martínez-Vidal, Rubén. "Architectures for aeronautical opportunistic networking." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/319697.

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En els últims anys, el camp de les comunicacions aeronàutiques ha experimentat un increment en la demanda d'intercanvis de dades entre plataformes terrestres, aèries i satelitals. Els mètodes de comunicació aeronàutics convencionals han demostrat no ser suficients per manejar aquesta demanda creixent. Com a resultat, els sistemes aeronàutics han tendit cap a l'ús de comunicacions via satèl·lit, que encara que efectives, suposen un repte econòmic tant en la seva instal·lació com en el seu ús. En resposta a aquest problema, el treball acadèmic en aquesta àrea ha proposat l'ús d'alternatives basades en xarxes de comunicació en la forma de xarxes aeronàutiques ad-hoc. Aquestes xarxes usen abastos de comunicació immensos i treballen sota la premissa de les Xarxes Ad-Hoc Mòbils (MANETs) requerint l'existència de connectivitat extrem a extrem per al seu correcte funcionament. Les xarxes aeronàutiques tenen una topologia extremadament variable juntament amb enllaços de comunicació poc fiables. Amb aquestes propietats en ment, creiem que assumir connectivitat de xarxa és una elecció desafortunada. Per tant, en aquesta tesi intentem solucionar aquests reptes utilitzant un enfocament diferent. Específicament, intentarem establir una xarxa d'avions sense assumir garanties de connectivitat, enllaços de radi curts i utilitzant tan sol les trobades esporàdiques entre nodes per realitzar intercanvi de dades. Aquest enfocament oportunista ofereix una alternativa més barata que aquelles basades en enllaços de radi de llarg abast o en comunicacions via satèl·lit. Els fonaments d'aquesta proposta es basen a les xarxes oportunistes, i eventualment s'uneixen amb la tendència actual d'utilitzar enllaços via satèl·lit, per oferir una nova arquitectura de xarxa que redueix àmpliament els costos de comunicació i equipament. Les principals contribucions d'aquesta tesi són les següents. D'una banda, l'ús d'un model de mobilitat precís descrivint patrons aeronàutics basats en informació i horaris de vol reals. A més, aquest treball utilitza un model minuciós per descriure les capacitats de xarxa dels nodes incloent la representació completa de totes les capes de xarxa. Aquestes característiques realistes són molt importants per assegurar el correcte desplegament en xarxes reals. D'altra banda, aquesta tesi ofereix una sèrie de garanties en la qualitat de servei que són difícils d'obtenir en xarxes oportunistes. Fins a on sabem aquesta tesi representa el primer estudi detallat d'una xarxa aeronàutica a gran escala utilitzant comunicacions oportunistes.
En los últimos años, el campo de las comunicaciones aeronáuticas ha experimentado un incremento masivo de los intercambios de datos entre plataformas terrestres, aéreas y satelitales. Los métodos de comunicación aeronáuticos convencionales han demostrado no ser suficientes para manejar esta demanda creciente. Como resultado, los sistemas aeronáuticos han tendido hacia el uso de comunicaciones vía satélite, que aunque efectivas, suponen un reto económico tanto en su instalación como en su uso. En respuesta a este problema, el trabajo académico en esta área ha propuesto el uso de alternativas basadas en redes de comunicación en la forma de redes aeronáuticas ad-hoc. Estas redes usan alcances de comunicación inmensos y trabajan bajo la premisa de las Redes Ad-Hoc Móviles (MANETs) requiriendo la existencia de conectividad extremo a extremo para su correcto funcionamiento. Las redes aeronáuticas tienen una topología extremadamente variable juntamente con enlaces de comunicación poco fiables. Con estas propiedades en mente, creemos que asumir conectividad de red es una elección desafortunada. Por tanto, en esta tesis intentamos solucionar estos retos utilizando un enfoque diferente. Específicamente, intentaremos establecer una red de aviones sin asumir garantías de conectividad, enlaces de radio cortos y utilizando tan solo los encuentros esporádicos entre nodos para realizar intercambio de datos. Este enfoque oportunista ofrece una alternativa más barata que aquellas basadas en enlaces de radio de largo alcance o en comunicaciones vía satélite. Los fundamentos de esta propuesta se basan en las redes oportunistas, y eventualmente se unen con la tendencia actual de utilizar enlaces vía satélite, para ofrecer una nueva arquitectura de red que reduce ampliamente los costes de comunicación y equipamiento. Las principales contribuciones de esta tesis son las siguientes. Por un lado, el uso de un modelo de movilidad preciso describiendo patrones aeronáuticos basados en información y horarios de vuelo reales. Además, este trabajo utiliza un modelo minucioso para describir las capacidades de red de los nodos incluyendo la representación completa de todas las capas de red. Estas características realistas son muy importantes para asegurar el correcto despliegue en redes reales. Por otro lado, esta tesis ofrece una serie de garantías en la calidad de servicio que son difíciles de obtener en redes oportunistas. Hasta donde sabemos esta tesis representa el primer estudio detallado de una red aeronáutica a gran escala utilizando comunicaciones oportunistas.
In recent years, the aeronautical communications field has experienced increased demand for data exchanges between terrestrial, aerial and satellite platforms. Conventional aeronautical communications have proven to fall short on handling this growing demand. As a result, aeronautical systems have moved towards the use of satellite-based communications, and while effective, their deployment and later use poses an economical challenge. To deal with this problem, academic work on the topic has proposed the use of networking alternatives in the form of Aeronautical Ad-hoc Networks. These networks use large radio communication ranges and work on the premises of Mobile Ad-Hoc Networks (MANET), requiring end-to-end connectivity to function properly. Aeronautical networks have an extremely varying topology coupled with a frequently unreliable communication channel. With this in mind, we think that assuming full network connectivity is a problematic choice. Therefore, in this thesis we will approach those problems using a different method. Specifically, we will strive to establish a network of aircraft assuming no guarantees for connectivity, limited radio ranges, and relying solely on the sporadic encounters between nodes to perform data exchanges. This opportunistic approach offers a cheaper solution than those based on long-range radio links or satellite communications. The foundation of this proposal lies in opportunistic networks, and eventually merges with the current communication trend based on satellite links, to provide a new network infrastructure that greatly minimizes communication costs and equipment expenditure. The main contributions of this thesis are as follows. On one hand, the use of an accurate mobility model describing aeronautical patterns by considering on flight route and scheduling information of real flights. Additionally, this work provided accurate modeling of the network capabilities of each node including the complete representation of all layers of the network stack. These realistic features are of severe importance to ensure successful deployment in real networks. On the other hand, this thesis provides Quality of Service assurances that are hard to achieve in opportunistic networking. To the best of our knowledge, this thesis represents the first in-depth analysis of a realistic large-scale aeronautical opportunistic network.

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Tsokalo, Ievgenii [Verfasser], Ralf [Gutachter] Lehnert, and Lutz [Gutachter] Lampe. "Opportunistic Routing with Network Coding in Powerline Communications / Ievgenii Tsokalo ; Gutachter: Ralf Lehnert, Lutz Lampe." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://d-nb.info/1226811167/34.

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De, Sousa Chaves Fabiano. "Controle de potência oportunista e equalização robusta em redes de comunicação sem fio : enfoques via controle automático e teoria dos jogos." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2010. http://tel.archives-ouvertes.fr/tel-00618079.

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L'interférence est un facteur de limitation de performance individuelle et globale dans les réseaux de communication sans fil. Dans ce travail, deux techniques classiques de gestion de l'interférence sont étudiées : le contrôle de puissance d'émission et l'égalisation du canal. Trois approches sont considérées pour Le contrôle de puissance décentralisé et opportuniste. La première est basée sur la théorie des jeux non-coopératifs statiques et les théories de fonctions itératives, d'où résulte la proposition d'une classe d'algorithmes. Dans la deuxième approche, nous proposons quelques algorithmes dérivés de formulations et de solutions traditionnelles de la commande H2 et de la commande mixte H2/H-infini. Finalement, nous appliquons la théorie des jeux dynamiques sur le problème, ce qui produit deux nouveaux algorithmes de contrôle de puissance. La deuxième partie de la thèse, où le problème d'intérêt est l'égalisation du canal, est divisée en deux thèmes. Dans le premier, nous développons une analyse de "pire cas" pour le retard d'égalisation par des concepts de la théorie des jeux non-coopératifs. Dans le deuxième thème, nous présentons deux approches pour la conjugaison des caractéristiques désirables des égaliseurs H2 et H-infini : une combinaison convexe des deux filtres et un schéma d'adaptation du niveau de robustesse du filtre H-infini.

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Wang, Yufeng. "Opportunistic Scheduling and Cooperative Relaying in Wireless Networks." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4416.

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The demand for ever larger, more efficient, reliable and cost effective communication networks necessitates new network architectures, such as wireless ad hoc networks, cognitive radio, relaying networks, and wireless sensor networks. The study of such networks requires a fundamental shift from thinking of a network as a collection of independent communication pipes, to a multi-user channel where users cooperate via conferencing, relaying, and joint source-channel coding. The traditional centralized networks, such as cellular networks, include a central controller and a fixed infrastructure, in which every node communicates with each other via a centralized based station (BS). However, for a decentralized network, such as wireless ad hoc networks and wireless sensor networks, there is no infrastructure support and no central controllers. In such multi-user wireless networks, the scheduling algorithm plays an essential role in efficiently assigning channel resources to different users for better system performance, in terms of system throughput, packet-delay, stability and fairness. In this dissertation, our main goal is to develop practical scheduling algorithms in wireless ad hoc networks to enhance system performance, in terms of throughput, delay and stability. Our dissertation mainly consists of three main parts. First, we identify major challenges intrinsic to ad hoc networks that affect the system performance, in terms of throughput limits, delay and stability condition. Second, we develop scheduling algorithms for wireless ad hoc networks, with various considerations of non-cooperative relays and cooperative relays, fixed-rate transmission and adaptive-rate transmission, full-buffer traffic model and finite-buffer traffic model. Specifically, we propose an opportunistic scheduling scheme and study the throughput and delay performance, with fixed-rate transmissions in a two-hop wireless ad hoc networks. In the proposed scheduling scheme, we prove two key inequalities that capture the various tradeoffs inherent in the broad class of opportunistic relaying protocols, illustrating that no scheduling and routing algorithm can simultaneously yield lower delay and higher throughput. We then develop an adaptive rate transmission scheme with opportunistic scheduling, with the constraints of practical assumptions on channel state information (CSI) and limited feedback, which achieves an optimal system throughput scaling order. Along this work with the consideration of finite-buffer model, we propose a Buffer-Aware Adaptive (BAA) scheduler which considers both channel state and buffer conditions to make scheduling decisions, to reduce average packet delay, while maintaining the queue stability condition of the networks. The proposed algorithm is an improvement over existing algorithms with adaptability and bounded potential throughput reduction. In the third part, we extend the methods and analyses developed for wireless ad hoc networks to a practical Aeronautical Communication Networks (ACN) and present the system performance of such networks. We use our previously proposed scheduling schemes and analytical methods from the second part to investigate the issues about connectivity, throughput and delay in ACN, for both single-hop and two-hop communication models. We conclude that the two-hop model achieves greater throughput than the single-hop model for ACN. Both throughput and delay performances are characterized.

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Kurth, Mathias [Verfasser], Jens-Peter [Akademischer Betreuer] Redlich, Adam [Akademischer Betreuer] Wolisz, and Mesut [Akademischer Betreuer] Güne¸s. "Contention techniques for opportunistic communication in wireless mesh networks : a cross-layer perspective on opportunistic routing and opportunistic scheduling under carrier sensing multiple access / Mathias Kurth. Gutachter: Jens-Peter Redlich ; Adam Wolisz ; Mesut Güne¸s." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2012. http://d-nb.info/1019790008/34.

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Bhadane, Kunal. "A Cognitive Radio Application through Opportunistic Spectrum Access." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc984265/.

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In wireless communication systems, one of the most important resources being focused on all the researchers is spectrum. A cognitive radio (CR) system is one of the efficient ways to access the radio spectrum opportunistically, and efficiently use the available underutilized licensed spectrum. Spectrum utilization can be significantly enhanced by developing more applications with adopting CR technology. CR systems are implemented using a radio technology called software-defined radios (SDR). SDR provides a flexible and cost-effective solution to fulfil the requirements of end users. We can see a lot of innovations in Internet of Things (IoT) and increasing number of smart devices. Hence, a CR system application involving an IoT device is studied in this thesis. Opportunistic spectrum access involves two tasks of CR system: spectrum sensing and dynamic spectrum access. The functioning of the CR system is rest upon the spectrum sensing. There are different spectrum sensing techniques used to detect the spectrum holes and a few of them are discussed here in this thesis. The simplest and easiest to implement energy detection spectrum sensing technique is used here to implement the CR system. Dynamic spectrum access involves different models and strategies to access the spectrum. Amongst the available models, an interweave model is more challenging and is used in this thesis. Interweave model needs effective spectrum sensing before accessing the spectrum opportunistically. The system designed and simulated in this thesis is capable of transmitting an output from an IoT device using USRP and GNU radio through accessing the radio spectrum opportunistically.

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Kailas, Aravind. "Toward perpetual wireless networks: opportunistic large arrays with transmission thresholds and energy harvesting." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34720.

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Solving the key issue of sustainability of battery-powered sensors continues to attract significant research attention. The prevailing theme of this research is to address this concern using energy-efficient protocols based on a form of simple cooperative transmission (CT) called the opportunistic large arrays (OLAs), and intelligent exploitation of energy harvesting and hybrid energy storage systems (HESSs). The two key contributions of this research, namely, OLA with transmission threshold (OLA-T) and alternating OLA-T (A-OLA-T), offer an signal-to-noise ratio (SNR) advantage (i.e., benefits of diversity and array (power) gains) in a multi-path fading environment, thereby reducing transmit powers or extending range. Because these protocols do not address nodes individually, the network overhead remains constant for high density networks or nodes with mobility. During broadcasting across energy-constrained networks, while OLA-T saves energy by limiting node participation within a single broadcast, A-OLA-T optimizes over multiple broadcasts and drains the the nodes in an equitable fashion. Another important contribution of this research is the design and analysis of a novel routing metric called communications using HESS (CHESS), which extends the rechargeable battery (RB)-life by relaying exclusively with supercapacitor (SC) energy, and is asymptotically optimal with respect to the number of nodes in the network.

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Azeem, Muhammad Moazam. "Erasure Correcting Codes for Opportunistic Spectrum Access (OSA)." Electronic Thesis or Diss., Paris, CNAM, 2014. http://www.theses.fr/2014CNAM1002.

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Les années récentes ont vu l’explosion du trafic sur les réseaux mobiles depuis l’apparition de nouveaux terminaux (smartphones, tablettes) et des usages qu’ils permettent, en particulier les données multimédia, le trafic voix restant sensiblement constant. Une conséquence est le besoin de plus de spectre, ou la nécessité de mieux utiliser le spectre déjà alloué. Comme il n’y a pas de coordination entre les utilisateurs secondaire(s) et primaire, avant toute transmission les premiers doivent mettre en œuvre des traitements pour détecter les périodes dans lesquelles l’utilisateur primaire transmet, ce qui est le scénario considéré dans cette thèse. Nous considérons donc une autre approche, reposant sur l’utilisation de codes correcteurs d’effacements en mode paquet. La dernière partie de la thèse aborde un scénario dans lequel il n’y a plus d’utilisateur primaire, tous les utilisateurs ayant le même droit à transmettre dans le canal. Nous décrivons une modification de la couche MAC du 802.11 consistant à réduire les différents temps consacrés à attendre (SIFS, DIFS, backoff, . . .) afin d’accéder plus souvent au canal, au prix de quelques collisions supplémentaires qu’il est possible de récupérer en mettant en œuvre des codes correcteurs d’effacements
The emergence of new devices especially the smartphones and tablets having a lot of new applications have rocketed the wireless traffic in recent years and this is the cause of main surge in the demand of radio spectrum. There is a need of either more spectrum or to use existing spectrum more efficiently due to dramatic increase in the demand of limited spectrum. Among the new dynamic access schemes designed to use the spectrum more efficiently opportunistic spectrum access (OSA) is currently addressed when one or more secondary users (SU) are allowed to access the channel when the PU is not transmitting. The erasure correcting codes are therefore envisioned to recover the lost data due to sensing impairments. We define the parameter efficiency of SU and optimize it in-terms of spectrum utilization keeping into account sensing impairments, code parameters and the activity of PU. Finally, the spectrum access for multiple secondary users is addressed when there is no primary and each user has equal right to access the channel. The interesting scenarios are Cognitive radio networks and WiFi where 802.11 protocol gives the specification for MAC layer. The throughput curvesachieved by retransmission and using various erasure correcting codes are compared. This modification in MAC layer will reduce the long waiting time to access the channel, as the number of users are increased

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Silva, Rodrigo. "ITS-based decision making mechanism for opportunistic networking in heterogeneous network environment." Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2020. http://www.theses.fr/2020IMTA0174.

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Le nombre de véhicules connectés augmentent et pour une utilisation plus intelligente des systèmes de transport, les véhicules ont besoin d’accroître leur connaissance de l’environnement. Cela peut être atteint en permettant aux véhicules de communiquer avec leur environnement. Pour une connectivité omniprésente, il sera nécessaire d’utiliser diverses technologies sans fil, existantes. Dans un tel environnement de réseau d’accès hétérogène, il est nécessaire de fournir aux applications des mécanismes décisionnels transparents pour gérer l’affectation des flux de données sur les réseaux disponibles. Dans cette thèse, nous proposons le Ant-based Decision Maker for Opportunistic Networking (AD4ON), un Decision Maker (DM) mécanisme modulaire capable de choisir le meilleur profil de communication disponible pour chaque fluxde données dans un environnement de réseau hétérogène et dynamique. Le mécanisme proposé gère les exigences et préférences de différents acteurs (applications, utilisateurs,etc.), ainsi que les information réseaux dans un futur proche, afin de prendre des décisions plus intelligentes. C’est-à-dire, afin d’augmenter la satisfaction de chaque acteur impliqué dans le processus de communication, ainsi que d’augmenter la stabilité de la décision (par exemple, en réduisant l’effet “ping-pong“)
Demand from different actors for extended connectivity where vehicles can exchange data with other devices have pushed vehicle manufacturers to invest in embedded solutions, which paves the way towards Cooperative Intelligent Transportation Systems (C-ITS). Cooperative vehicles enable the development of an ecosystem of services around them. Due to the heterogeneousness of such services and their specific requirements, for ubiquitous connectivity it is necessary to combine existing wireless technologies, providing applications with a communication architecture that hides such underlying access technologies specificities. Moreover, due to vehicles’ high velocity it is needed a Decision Maker (DM) mechanism capable to take into account the short-term prevision about network environment in order to better manage all flow communications. Based on the Intelligent Transportation Systems (ITS) architecture proposed by International Organization for Standardization (ISO), we proposed the Ant-based Decision Maker for Opportunistic Networking (AD4ON), a modular decision maker mechanism capable to choose the best available access network for each data flow in an heterogeneous and dynamic network environment. The proposed mechanism manages requirements and preferences from different actors, taking into account the short-term prevision about the network environment. Simulations have demonstrated that the AD4ON outperforms current benchmark algorithms, by increasing decision’s stability, reducing the “ping-pong” effect and maximizing flow’s satisfaction. Moreover, we demonstrate that taking into account the short-term prevision, the AD4ON can optimize the algorithm reaction time

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Sammarco, Matteo. "Dissémination multi-contenus opportuniste : monitorage passif et adaptation aux conditions du réseau." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066573/document.

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La pénétration du marché des appareils mobiles a connu une croissance impressionnante ces dernières années. Smartphones, tablettes et ordinateurs portables sont devenus soit producteurs soit consommateurs de contenus générés par les utilisateurs. Les communications opportunistes permettent une couverture étendue dans les endroits où il n'existe aucune infrastructure réseau disponible et des stratégies de délestage de données pour aider les opérateurs à soulager la charge de leurs infrastructures. Dans cette thèse, nous considérons le cas de la diffusion opportuniste de plusieurs grands contenus d'un point de vue expérimental. Dans la première partie nous commençons par implémenter EPICS, un protocole réseau conçu pour l'échange opportuniste de grands contenus, dans des terminaux Android. Après sa évaluation nous proposons DAD, un nouveau protocole, qui envoie une rafale de paquets de données de façon adaptative. Nous comparons les deux protocoles expérimentalement et, à l'aide des traces de contacts, soit réelles, soit synthétiques, nous obtenons des gains importants avec cette nouvelle approche. La deuxième partie est dédiée au passage à l'échelle des systèmes de surveillance passive. Nous proposons deux approches. La première est basée sur la similarité des traces et des algorithmes de détection de communautés. La deuxième est basée sur des mesures collaboratives
The market penetration of mobile devices has experienced an impressive growth. Smartphones, tablets, and laptops have become both producers and consumers of user-generated contents. They also motivate novel communication paradigms such as the possibility to establish, in an opportunistic fashion, direct device-to-device links whenever two mobile nodes enter within the wireless range of each other. In this thesis, we consider the case of opportunistic dissemination of multiple large contents from an experimental point of view. This implies revisiting, among others, the common assumption that contacts have enough capacity to transfer any amount of data.In the first part of this thesis, we start from an Android implementation of EPICS, a network protocol designed for exchanging large contents in opportunistic networks, on off-the-shelf devices. After an deep analysis of application-level logs and captured wireless traces we found out limitations and uncovered improving possibilities. We then propose DAD, a new content dissemination protocol that adaptively sends bursts of data instead of the per-fragment transmission strategy of EPICS.The second part of this thesis deals with the scalability of legacy WLAN monitoring systems. We propose two original approaches. With the first one, based on trace similarity and community detection algorithms, we are able to identify how many monitor we need in a target area and where to place them. The second approach in based on collaborative measurements. In this case we face the risk of biased measures due attacks of malicious users generating adulterated traces. We then propose a method to detect such malicious behaviors

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42

Sammarco, Matteo. "Dissémination multi-contenus opportuniste : monitorage passif et adaptation aux conditions du réseau." Electronic Thesis or Diss., Paris 6, 2014. http://www.theses.fr/2014PA066573.

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La pénétration du marché des appareils mobiles a connu une croissance impressionnante ces dernières années. Smartphones, tablettes et ordinateurs portables sont devenus soit producteurs soit consommateurs de contenus générés par les utilisateurs. Les communications opportunistes permettent une couverture étendue dans les endroits où il n'existe aucune infrastructure réseau disponible et des stratégies de délestage de données pour aider les opérateurs à soulager la charge de leurs infrastructures. Dans cette thèse, nous considérons le cas de la diffusion opportuniste de plusieurs grands contenus d'un point de vue expérimental. Dans la première partie nous commençons par implémenter EPICS, un protocole réseau conçu pour l'échange opportuniste de grands contenus, dans des terminaux Android. Après sa évaluation nous proposons DAD, un nouveau protocole, qui envoie une rafale de paquets de données de façon adaptative. Nous comparons les deux protocoles expérimentalement et, à l'aide des traces de contacts, soit réelles, soit synthétiques, nous obtenons des gains importants avec cette nouvelle approche. La deuxième partie est dédiée au passage à l'échelle des systèmes de surveillance passive. Nous proposons deux approches. La première est basée sur la similarité des traces et des algorithmes de détection de communautés. La deuxième est basée sur des mesures collaboratives
The market penetration of mobile devices has experienced an impressive growth. Smartphones, tablets, and laptops have become both producers and consumers of user-generated contents. They also motivate novel communication paradigms such as the possibility to establish, in an opportunistic fashion, direct device-to-device links whenever two mobile nodes enter within the wireless range of each other. In this thesis, we consider the case of opportunistic dissemination of multiple large contents from an experimental point of view. This implies revisiting, among others, the common assumption that contacts have enough capacity to transfer any amount of data.In the first part of this thesis, we start from an Android implementation of EPICS, a network protocol designed for exchanging large contents in opportunistic networks, on off-the-shelf devices. After an deep analysis of application-level logs and captured wireless traces we found out limitations and uncovered improving possibilities. We then propose DAD, a new content dissemination protocol that adaptively sends bursts of data instead of the per-fragment transmission strategy of EPICS.The second part of this thesis deals with the scalability of legacy WLAN monitoring systems. We propose two original approaches. With the first one, based on trace similarity and community detection algorithms, we are able to identify how many monitor we need in a target area and where to place them. The second approach in based on collaborative measurements. In this case we face the risk of biased measures due attacks of malicious users generating adulterated traces. We then propose a method to detect such malicious behaviors

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43

Shatila, Hazem Sarwat. "Adaptive Radio Resource Management in Cognitive Radio Communications using Fuzzy Reasoning." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/26618.

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As wireless technologies evolve, novel innovations and concepts are required to dynamically and automatically alter various radio parameters in accordance with the radio environment. These innovations open the door for cognitive radio (CR), a new concept in telecommunications. CR makes its decisions using an inference engine, which can learn and adapt to changes in radio conditions. Fuzzy logic (FL) is the proposed decision-making algorithm for controlling the CRâ s inference engine. Fuzzy logic is well-suited for vague environments in which incomplete and heterogeneous information is present. In our proposed approach, FL is used to alter various radio parameters according to experience gained from different environmental conditions. FL requires a set of decision-making rules, which can vary according to radio conditions, but anomalies rise among these rules, causing degradation in the CRâ s performance. In such cases, the CR requires a method for eliminating such anomalies. In our model, we used a method based on the Dempster-Shafer (DS) theory of belief to accomplish this task. Through extensive simulation results and vast case studies, the use of the DS theory indeed improved the CRâ s decision-making capability. Using FL and the DS theory of belief is considered a vital module in the automation of various radio parameters for coping with the dynamic wireless environment. To demonstrate the FL inference engine, we propose a CR version of WiMAX, which we call CogMAX, to control different radio resources. Some of the physical parameters that can be altered for better results and performance are the physical layer parameters such as channel estimation technique, the number of subcarriers used for channel estimation, the modulation technique, and the code rate.
Ph. D.

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Bolas, Eduardo José Ludovico. "Broadband VHF maritime communications based on cognitive radio." Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/16285.

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Doutoramento em Engenharia Eletrotécnica
Traditionally, maritime business is associated to transportation, which represents about 90% of global trade, and fishery, but new activities at sea, opened up by technological innovations, are transforming economical context of maritime services and resources. In the future, the massive use of technology to support endurance and ranging of maritime operations, namely in intelligent transport systems and autonomous vehicles areas, would lead to federations of maritime based embedded computing devices. Nevertheless, existing systems are not prepared to support such paradigm change. Currently, stovepiped systems rely on narrowband communications systems, where voice and low data rate are the most common used services, and specific broadband applications, such as Internet access, are supported by satellite communications (SATCOM). Unfortunately, UMTS/LTE networks do not provide consistent solutions, due their limited sea coverage, so there is a need for an additional capacity that can provide acceptable performances at low cost, which might act as a complement or even an alternative to satellite. We propose a Cognitive Radio based Broadband VHF (CR-B-VHF) communications solution to provide appropriate connectivity to support current information exchange requirements and enable future developments on maritime services and applications, thus avoiding SATCOM inconveniences. This CR-BVHF network would operate in a context of spectrum scarcity, within hierarchical spectrum access model, and use cognitive radio based concepts to implement a dynamic system that can activate and deactivated subcarriers, according to spectrum opportunities, ensuring an adequate interference level at incumbent's live services. The main contribution of this thesis work is the proposed CR-B-VHF framework and the demonstration of its suitability, feasibility and deployability. The presented relevancy analysis provides an overview of the state of the art on maritime business and its associated support communications and information systems, and prospects future requirements and applications for low-cost broadband access. The developed solutions for detection and exploitation of multiple non-contiguous narrowband spectrum opportunities in maritime VHF band, within a hierarchical spectrum access context, and their envisage performances, provide good indications regarding attainability of opportunistic BVHF systems and their future deployment. Finally, the discussion on regulatory and standardization issues intend to contribute for a shared problem solving, providing an end user perspective of hierarchical spectrum access. Despite the fact that technical aspects are nor the main issues on opportunistic systems deployment, novel proposed Spectrum Coherences Detector and its experimental demonstrated performances might be an important enabler and an additional argument to convince maritime communications stakeholders.
Tradicionalmente, a economia do mar está associada ao transporte marítimo, que representa cerca de 90% do comércio mundial, e à pesca, mas as novas atividades associadas à inovação tecnológica estão a transformar o contexto económico dos serviços e aplicações marítimas. No futuro, a utilização massiva de tecnologia no suporte às atividades desenvolvidas no mar, nomeadamente em transportes marítimos inteligentes e sistemas autónomos, conduzirá a uma federação de sistemas marítimos integrados. Contudo, as comunicações marítimas existentes não estão preparadas para dar suporte a esta alteração de paradigma. Atualmente, os sistemas dedicados baseiam-se em comunicações de banda estreita, onde a telefonia e a transmissão de dados de baixo débito são os serviços mais comuns, e aplicações de banda larga específicas, como o acesso a Internet, são disponibilizados através de comunicações por satélite (SATCOM). Infelizmente, as redes UMTS/LTE não providenciam soluções consistentes, devido à fraca cobertura sobre o mar. Por conseguinte, existe uma clara necessidade de capacidade adicional que possa disponibilizar desempenhos adequados a baixo custo e que possa constituir um complemento, ou mesmo uma alternativa, ao satélite. Nesta tese é proposta uma solução de comunicações de banda larga em VHF, baseada em rádio cognitivo (CR-B-VHF), que permite disponibilizar uma adequada conectividade de suporte aos requisitos atuais de troca de informação e a futuros desenvolvimentos nos serviços e aplicações marítimas, evitando as desvantagens da utilização do satélite. Esta rede foi concebida para operar num contexto de escassez de espectro, assumindo um modelo de acesso hierárquico, e utiliza conceitos de rádio cognitivo para implementar um sistema dinâmico que possa ativar e desativar sub-portadoras, de acordo com as oportunidades para transmitir, garantindo um adequado nível de interferência com os serviços dos incumbentes. O principal contributo deste trabalho é a proposta de um conceito de CR-B-VHF e a demonstração da sua adequabilidade, exequibilidade e aceitabilidade. A análise de relevância apresentada, proporciona uma perspetiva do estado da arte das atividades marítimas associadas à economia do mar e dos sistemas de informação e comunicação que lhes dão suporte, bem como uma perspetiva dos requisitos futuros e as aplicações para acessos de banda larga a baixo custo. As soluções desenvolvidas para a deteção e exploração de múltiplas e nãocontíguas oportunidades de banda estreita na banda marítima de VHF, e as suas previsíveis prestações, abrem boas perspetivas relativamente ao potencial dos sistemas oportunísticos na banda de VHF e a sua futura implementação. Finalmente, é apresentada uma discussão sobre questões regulatórias e de normalização, cujo objetivo é contribuir para a solução do problema da utilização partilhada do espectro, providenciando uma perspetiva de utilizador final, num modelo de acesso hierárquico ao espectro.

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Moradinia, Pourya, and Imal Sakhi. "Mobile Opportunistic Services for Experience Sharing : Via a NetInf Android Application." Thesis, KTH, Radio Systems Laboratory (RS Lab), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-104297.

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Information-Centric Networking (ICN) is a new research area concerning creating a new network architecture that would be more suitable for both current and the future's network. The MOSES (Mobile Opportunistic Services for Experience Sharing) project is part of this development. The project works with the development and demonstration of the Network of Information (NetInf) protocol, which is an implementation of the ICN concept. This Master’s thesis project is part of the MOSES project and aims to assist the MOSES project with the demonstration of a mobile opportunistic sharing concept based on the NetInf protocol. Demonstrating the MOSES concept in practice requires deep understanding of networking, localization, transport, and dissemination of digital content in an ad hoc network. This implementation requires an analysis of the previous work, development of new functionalities, and finally an analysis of a series of controlled experiments. This Master’s thesis project has designed, implemented, and evaluated an Android application within the MOSES framework by using the previously developed NetInf Android library. This prototype is used to demonstrate how mobile Android users can opportunistically share and disseminate content based on their location using the MOSES/ICN concept. The functionality and efficiency of the prototype Android application built during this thesis project has been analyzed and evaluated by conducting a series of controlled experiments under the supervision of MOSES researchers. The results of these controlled experiments has provided insight for MOSES researchers as well as explored the concept of using ICN (NetInf) for opportunistic content distribution. The experiment results aim at assisting MOSES researchers to extend and further develop the prototype application and the involved algorithms to create a fully functional mobile application for experience sharing services tailored to large-scale events.
Information-Centric Networking (ICN) är ett nytt forskningsområde för att bygga en ny nätverksarkitektur mer passande för dagens och framtida nätverk. MOSES projektet är en del av denna utveckling och arbetar med utveckling och demonstration av Network of Information (NetInf) protokollet, som är en implementering av ICN konceptet. Detta examensarbete är en del av MOSES (Mobile Opportunistic Services for Experience Sharing) projektet som syftar till att bistå MOSES projektet med demonstrationen av "mobile opportunistic sharing" konceptet som bygger på NetInf protokollet. Att demonstrera MOSES konceptet i praktiken krävs djupt förståelse om nätverk, lokalisering, transport och spridning av digitalt data i en "ad hoc" och infrastruktur miljö. Genomförandet av denna implementering kräver en analys av tidigare arbete, utveckling av nya funktioner och slutligen analys av genomförda experiment och resultaten. Detta examensarbete har utformat, genomfört och utvärderat en Android applikation inom ramen för MOSES med hjälp av tidigare utvecklat NetInf Android bibliotek. Denna prototyp används för att visa hur mobila Android användare opportunistiskt kan dela och sprida innehåll baserat på deras plats med hjälp av MOSES/ICN konceptet. Funktionaliteten och effektiviteten av prototypen byggd under detta examensarbete har analyserats och utvärderats genom att utföra en serie kontrollerade experiment under ledning av MOSES forskare. Resultaten av dessa kontrollerade experiment har gett insikt åt MOSES forskare samt utforskat konceptet att använda ICN (NetInf) för opportunistisk distribution av innehåll. Experimentens resultat syftar till att hjälpa MOSES forskare att utöka och vidareutveckla prototypen och de involverade algoritmer för att skapa en fullt fungerande mobil applikation för "experience sharing services" anpassad för stora evenemang.

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46

Murugesan, Sugumar. "Opportunistic Scheduling Using Channel Memory in Markov-modeled Wireless Networks." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1282065836.

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47

Haillot, Julien. "Définition et validation d'un modèle de communication supportant la communication basée contenus dans les réseaux mobiles ad hoc discontinus." Phd thesis, Université de Bretagne Sud, 2010. http://tel.archives-ouvertes.fr/tel-00599669.

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L'activité de recherche des dernières décennies dans le domaine des réseaux mobiles ad hoc (MANETs) a essentiellement visé à définir des méthodes de routage dynamique au sein de ces réseaux. La plupart des propositions faites dans cette optique reposent sur l'hypothèse que la communication entre deux terminaux mobiles n'est possible que si une route pour l'acheminement des messages peut être établie entre ces terminaux lorsque cela est nécessaire. Cette approche équivaut à considérer que la ommunication entre deux terminaux ne peut être réalisée que dans un réseau totalement connexe. Depuis quelques années, l'activité de recherche dans le domaine des MANETs a été étendue afin de prendre en compte les spécificités des MANETs discontinus, c'est-à-dire des MANETs apparaissant sous la forme d'une collection de sous-réseaux connexes (on parlera d'îlots de connectivité) au sein desquels les terminaux peuvent communiquer (éventuellement en utilisant du routage dynamique), mais entre lesquels aucune communication n'est a priori possible. Le routage de messages dans ce type de réseau est un sujet de recherche qui suscite un intérêt grandissant. L'approche généralement adoptée, dite de "communication opportuniste", consiste à exploiter les terminaux mobiles comme des mules de données capables de stocker, transporter et relayer des messages entre des îlots non connectés du réseau afin qu'ils puissent à terme être remis à leur destinataire. Dans cette thèse nous nous intéressons au support de la communication basée contenus dans les MANETs discontinus. La communication basée contenus est un modèle de communication dans lequel l'information circule dans le réseau en fonction de l'intérêt que les terminaux y portent plutôt que vers une destination bien établie. Nous pensons que de nombreuses applications peuvent bénéficier d'un tel modèle de communication, comme par exemple des applications de partage de fichiers, de distribution d'articles thématique, d'annonce et de découverte de services, etc. Dans ce manuscrit nous présentons le protocole de communication que nous avons conçu afin d'offrir ce style particulier de communication dans les MANETs discontinus ainsi que les résultats d'expérimentations que nous avons réalisées pour valider notre approche. Ce protocole repose sur une combinaison des concepts de communication basée contenus, de communication opportuniste et de communication multi-sauts pour prendre en compte les caractéristiques des MANETs discontinus.

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Wang, Kehao. "Multi-channel opportunistic access : a restless multi-armed bandit perspective." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00832569.

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In the thesis, we address the fundamental problem of opportunistic spectrum access in a multi-channel communication system. Specifically, we consider a communication system in which a user has access to multiple channels, but is limited to sensing and transmitting only on one at a given time. We explore how the smart user should exploit past observations and the knowledge of the stochastic properties of these channels to maximize its transmission rate by switching channels opportunistically. Formally, we provide a generic analysis on the opportunistic spectrum access problem by casting the problem into the restless multi-armed bandit (RMAB) problem, one of the most well-known generalizations of the classic multi-armed bandit (MAB) problem, which is of fundamental importance in stochastic decision theory. Despite the significant research efforts in the field, the RMAB problem in its generic form still remains open. Until today, very little result is reported on the structure of the optimal policy. Obtaining the optimal policy for a general RMAB problem is often intractable due to the exponential computation complexity. Hence, a natural alternative is to seek a simple myopic policy maximizing the short-term reward. Therefore, we develop three axioms characterizing a family of functions which we refer to as regular functions, which are generic and practically important. We then establish the optimality of the myopic policy when the reward function can be expressed as a regular function and the discount factor is bounded by a closed-form threshold determined by the reward function. We also illustrate how the derived results, generic in nature, are applied to analyze a class of RMAB problems arising from multi-channel opportunistic access. Next, we further investigate the more challenging problem where the user has to decide the number of channels to sense in each slot in order to maximize its utility (e.g., throughput). After showing the exponential complexity of the problem, we develop a heuristic v-step look-ahead strategy. In the developed strategy, the parameter v allows to achieve a desired tradeoff between social efficiency and computation complexity. We demonstrate the benefits of the proposed strategy via numerical experiments on several typical settings.

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Gungor, Onur. "INFORMATION THEORY ENABLED SECURE WIRELESS COMMUNICATION, KEY GENERATION AND AUTHENTICATION." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406298547.

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Thanayankizil, Lakshmi. "Opportunistic large array (OLA)-based routing for sensor and adhoc wireless networks." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50374.

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An Opportunistic Large Array (OLA) is a form of cooperative diversity in which a large group of simple, inexpensive relays operate without any mutual coordination, but naturally fire together in response to the energy received from a single source or another OLA. The main contributions of this thesis are the introduction of two OLA-based routing protocols: OLA Concentric Routing Algorithm (OLACRA), which is an upstream routing algorithm suitable for static wireless sensor networks (WSNs), and OLA Routing On-Demand (OLAROAD), which is a robust reactive routing scheme suitable for mobile ad hoc networks (MANETs). In fixed multi-hop wireless sensor networks with a single sink, where energy conservation is often a concern, simulations of the new algorithms show as much as 80% of the transmit energy required to broadcast data can be saved, relative to existing OLA-based broadcasting approaches. In MANETs, where robustness of the routes is an important performance indicator, OLAROAD-based cooperative routes last much longer compared to their state-of-art multi-hop non-cooperative transmission (CT)-based counterparts. However, OLACRA and OLAROAD have higher node participation, and thereby lower throughput, in comparison with the non-CT schemes. To improve the throughput, and thereby bandwidth utilization, the properties of uplink OLAs and their suppression regions are carefully studied. Based on the observations, Hop-Optimized OLACRA (HOLA), which is a variant of OLACRA, and has the maximum bandwidth utilization amongst all the OLA unicast schemes studied, is proposed. HOLA routes have bandwidth utilization comparable to non-CT schemes, but a much lower (~10 dB less) transmit power per node. The last section of this thesis treats the MAC design for OLA-based networks. In contrast to non-CT networks, a 802.11-based RTS/CTS MAC scheme is shown to reduce the reliability in OLA unicast schemes. A distributed cluster-head-based MAC scheme for channel reservation and OLA Size Adaptation Mechanism for link repair/maintenance are proposed for OLA-based networks. The performances of these protocols are shown to be comparable to a non-CT multihop scheme using the RTS/CTS/DATA/ACK handshake-based link layer design.

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Dissertations / Theses on the topic 'Communications opportunistes'

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