Dissertations / Theses: 'Radio opportuniste'

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Oularbi, Mohamed Rabie. "Identification de Systèmes OFDM et Estimation de la QoS : Application à la Radio Opportuniste." Phd thesis, Ecole Nationale Supérieure des Télécommunications de Bretagne - ENSTB, 2011. http://tel.archives-ouvertes.fr/tel-00661753.

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Le schéma de modulation OFDM est très répandu de nos jours (WiFi, WiMAX, \dots) et préconisé comme couche physique pour de nombreux réseaux futurs (3GPP/LTE, IEEE 802.22). Ainsi cette coexistence de réseaux OFDM fait que l'environnement radio est de nos jours hétérogène. Afin de tirer partie de cette hétérogénéité et de satisfaire le concept de ''\textit{Always Best connected}'', il a été imaginé des terminaux multistandards capables de basculer de manière transparente d'un réseau à un autre à la recherche du réseau offrant la qualité de service la plus satisfaisante. Ce processus de basculement entre standards est appelé ''\textit{vertical handover}''. Avant de déclencher un \textit{vertical handover} le terminal se doit d'identifier les réseaux actifs qui l'entourent et estimer la qualité de service disponible sur chaque réseau. Ainsi, dans le cadre de cette thèse nous proposons dans un premier temps des algorithmes d'identification de systèmes OFDM. Dans un second temps, nous nous intéressons à la qualité de service disponible sur les réseaux détectés, nous avons ainsi proposé des estimateurs de métriques de qualité de service dédiés à des réseaux basés sur les schémas d'accès multiples OFDMA et CSMA/CA. Certaines de ces métriques ont été validées expérimentalement sur la plate-forme RAMMUS de TELECOM Bretagne. Toutes les techniques proposées dans le cadre de cette thèse, sont des approches passives à faible coût de calcul qui ne nécessitent aucune connexion au point d'accès, permettant ainsi une économie en temps et en énergie.

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2

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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3

Collot, Ludovic. "Étude de nouvelles architectures de filtres RF intégrés dans le contexte de la radio opportuniste." Limoges, 2011. https://aurore.unilim.fr/theses/nxfile/default/790e39b6-b073-4378-9625-215ed53b5b21/blobholder:0/2011LIMO4020.pdf.

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Ce travail de thèse porte sur la conception de fonctions filtrantes passe-bandes microondes à la fois intégrables en technologie MMIC, accordables et différentielles. L’objectif principal est de réaliser des structures filtrantes et accordables utilisables dans un context de radio opportuniste. Le second objectif est de montrer que l’utilisation d’inductances ferromagnétiques dans ces structures en améliore les performances. Les chaînes de reception actuelles sont figées de part leurs architectures et les composants utilisés (SAW filter, LNA par exemple). Nous proposons de concevoir de nouveaux circuits intégrés : LNA filtrant et filtres à 1, 2 et 3 pôles permettant de rendre la chaîne RF agile en fréquence. Ces circuits reposent sur une topologie très simple de résonateurs LC compensés et permettent d’obtenir une accordabilité continue de la bande passante et de la fréquence centrale sur une octave. Les résultats obtenus, et principalement ceux du LNA filtrant, montent qu’il est possible de concilier fonction de filtrage accordable, gain et faible facteur de bruit sur une unique puce MMIC, ce qui constitue un premier pas vers la conception d’une chaîne de reception opportuniste
This work concerns the conception of microwaves filtering functions at the same time band-pass, MMIC technology compliant, tunable and differential. The main objective is to realize filtering structures compatible with opportunist radio. The second objective is to demonstrate that ferromagnetics inductors improves the performance of such devices. Commersialised RF receivers are deadlocked due to their topologies and used components (SAW filter, LNA for example). We put forward new integrated circuits : filtering LNA and 1, 2 and 3 poles filters usable in fully frequency tunable receivers. These circuits are Q-enhanced resonator based. They have a continuous frequency and bandwidth tunability over an octave. The observed results at first for filtering LNA mixe wide tunablility, gain and low noise figure on a unique MMIC circuit. This contribution is a first step toward opportunists receivers

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4

Jouini, Wassim. "Contribution to learning and decision making under uncertainty for Cognitive Radio." Thesis, Supélec, 2012. http://www.theses.fr/2012SUPL0010/document.

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L’allocation des ressources spectrales à des services de communications sans fil, sans cesse plus nombreux et plus gourmands, a récemment mené la communauté radio à vouloir remettre en question la stratégie de répartition des bandes de fréquences imposée depuis plus d’un siècle. En effet une étude rendue publique en 2002 par la commission fédérale des communications aux Etats-Unis (Federal Communications Commission - FCC) mit en évidence une pénurie des ressources spectrales dans une large bande de fréquences comprise entre quelques mégahertz à plusieurs gigahertz. Cependant, cette même étude expliqua cette pénurie par une allocation statique des ressources aux différents services demandeurs plutôt que par une saturation des bandes de fréquences. Cette explication fut par la suite corroborée par de nombreuses mesures d’occupation spectrale, réalisées dans plusieurs pays, qui montrèrent une forte sous-utilisation des bandes de fréquences en fonction du temps et de l’espace, représentant par conséquent autant d’opportunité spectrale inexploitée. Ces constations donnèrent naissance à un domaine en plein effervescence connu sous le nom d’Accès Opportuniste au Spectre (Opportunistic Spectrum Access). Nos travaux suggèrent l’étude de mécanismes d’apprentissage pour la radio intelligente (Cognitive Radio) dans le cadre de l’Accès Opportuniste au Spectre (AOS) afin de permettre à des équipements radio d’exploiter ces opportunités de manière autonome. Pour cela, nous montrons que les problématiques d’AOS peuvent être fidèlement représentées par des modèles d’apprentissage par renforcement. Ainsi, l’équipement radio est modélisé par un agent intelligent capable d’interagir avec son environnement afin d’en collecter des informations. Ces dernières servent à reconnaître, au fur et à mesure des expériences, les meilleurs choix (bandes de fréquences, configurations, etc.) qui s’offrent au système de communication. Nous nous intéressons au modèle particulier des bandits manchots (Multi-Armed Bandit appliqué à l’AOS). Nous discutons, lors d’une phase préliminaire, différentes solutions empruntées au domaine de l’apprentissage machine (Machine Learning). Ensuite, nous élargissons ces résultats à des cadres adaptés à la radio intelligente. Notamment, nous évaluons les performances de ces algorithmes dans le cas de réseaux d’équipements qui collaborent en prenant en compte, dans le modèle suggéré, les erreurs d’observations. On montre de plus que ces algorithmes n’ont pas besoin de connaître la fréquence des erreurs d’observation afin de converger. La vitesse de convergence dépend néanmoins de ces fréquences. Dans un second temps nous concevons un nouvel algorithme d’apprentissage destiné à répondre à des problèmes d’exploitation des ressources spectrales dans des conditions dites de fading. Tous ces travaux présupposent néanmoins la capacité de l’équipement intelligent à détecter efficacement l’activité d’autres utilisateurs sur la bande (utilisateurs prioritaires dits utilisateurs primaires). La principale difficulté réside dans le fait que l’équipement intelligent ne suppose aucune connaissance a priori sur son environnement (niveau du bruit notamment) ou sur les utilisateurs primaires. Afin de lever le doute sur l’efficacité de l’approche suggérée, nous analysons l’impact de ces incertitudes sur le détecteur d’énergie. Ce dernier prend donc le rôle d’observateur et envoie ses observations aux algorithmes d’apprentissage. Nous montrons ainsi qu’il est possible de quantifier les performances de ce détecteur dans des conditions d’incertitude sur le niveau du bruit ce qui le rend utilisable dans le contexte de la radio intelligente. Par conséquent, les algorithmes d’apprentissage utilisés pourront exploiter les résultats du détecteur malgré l’incertitude inhérente liée à l’environnement considéré et aux hypothèses (sévères) d’incertitude liées au problème analysé
During the last century, most of the meaningful frequency bands were licensed to emerging wireless applications. Because of the static model of frequency allocation, the growing number of spectrum demanding services led to a spectrum scarcity. However, recently, series of measurements on the spectrum utilization showed that the different frequency bands were underutilized (sometimes even unoccupied) and thus that the scarcity of the spectrum resource is virtual and only due to the static allocation of the different bands to specific wireless services. Moreover, the underutilization of the spectrum resource varies on different scales in time and space offering many opportunities to an unlicensed user or network to access the spectrum. Cognitive Radio (CR) and Opportunistic Spectrum Access (OSA) were introduced as possible solutions to alleviate the spectrum scarcity issue.In this dissertation, we aim at enabling CR equipments to exploit autonomously communication opportunities found in their vicinity. For that purpose, we suggest decision making mechanisms designed and/or adapted to answer CR related problems in general, and more specifically, OSA related scenarios. Thus, we argue that OSA scenarios can be modeled as Multi-Armed Bandit (MAB) problems. As a matter of fact, within OSA contexts, CR equipments are assumed to have no prior knowledge on their environment. Acquiring the necessary information relies on a sequential interaction between the CR equipment and its environment. Finally, the CR equipment is modeled as a cognitive agent whose purpose is to learn while providing an improving service to its user. Thus, firstly we analyze the performance of UCB1 algorithm when dealing with OSA problems with imperfect sensing. More specifically, we show that UCB1 can efficiently cope with sensing errors. We prove its convergence to the optimal channel and quantify its loss of performance compared to the case with perfect sensing. Secondly, we combine UCB1 algorithm with collaborative and coordination mechanism to model a secondary network (i.e. several SUs). We show that within this complex scenario, a coordinated learning mechanism can lead to efficient secondary networks. These scenarios assume that a SU can efficiently detect incumbent users’ activity while having no prior knowledge on their characteristics. Usually, energy detection is suggested as a possible approach to handle such task. Unfortunately, energy detection in known to perform poorly when dealing with uncertainty. Consequently, we ventured in this Ph.D. to revisit the problem of energy detection limits under uncertainty. We present new results on its performances as well as its limits when the noise level is uncertain and the uncertainty is modeled by a log-normal distribution (as suggested by Alexander Sonnenschein and Philip M. Fishman in 1992). Within OSA contexts, we address a final problem where a sensor aims at quantifying the quality of a channel in fading environments. In such contexts, UCB1 algorithms seem to fail. Consequently, we designed a new algorithm called Multiplicative UCB (UCB) and prove its convergence. Moreover, we prove that MUCB algorithms are order optimal (i.e., the order of their learning rate is optimal). This last work provides a contribution that goes beyond CR and OSA. As a matter of fact, MUCB algorithms are introduced and solved within a general MAB framework

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Ezzaouia, Mahdi. "Allocation de ressource opportuniste dans les réseaux sans fil multicellulaires." Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2018. http://www.theses.fr/2018IMTA0098/document.

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La forte croissance du trafic dans les réseaux mobiles s'accompagne d'une augmentation de son hétérogénéité, tant dans l'espace qu'au cours du temps. Cette thèse porte sur des algorithmes d’ordonnancement adaptés à des trafics avec des zones à forte concentration et variables dans le temps. Nous proposons un mécanisme de prêt de la ressource spectrale d'une cellule en sous-charge à une voisine en surcharge combinée à un ordonnancement réactif au sein de chaque cellule. Nous nous intéressons aussi à l’architecture Cloud Radio Access Network qui sépare les têtes de transmission radio (Remote Radio Heads, RRHs) des unités de traitement en bande de base (Baseband Units, BBUs). L’interconnexion entre les BBUs et les RRHs se fait selon deux modes. Le premier est appelé association bi-univoque et consiste à allouer les unités de ressources de la trame radio d’une BBU à une seule RRH. Dans le second mode, appelé association multiple, une BBU peut gérer plusieurs RRHs. Nous proposons un mode d’association hybride dans lequel les unités de ressource de chaque trame sont réparties en deux tranches. La première constitue une tranche non partagée qui est allouée aux utilisateurs centraux selon l’association bi-univoque afin d’augmenter le débit notamment à haute charge de trafic. La deuxième tranche est constituée par une quantité d’unités de ressources partagées par un groupe de RRHs appartenant au même BBU. Cette tranche commune est configurée en association multiple et est allouée aux utilisateurs frontaliers et mobiles. Nous montrons que le mode hybride réduit les interférences intercellulaires, diminue le nombre de handover inter-BBU et améliore la consommation énergétique
The exponential growth of traffic in mobile networks is accompanied by an increase in its heterogeneity, both in space and over time. This thesis deals with scheduling algorithms adapted to highly concentrated and time-varying traffic zones. We propose a spectrum borrowing mechanism from an under-loaded cell to an overloaded one combined with a reactive intra-cellular scheduling algorithm. We are also interested in the Cloud Radio Access Network architecture that separates the Radio Head(RRH) from the Baseband Unit (BBU). The BBU is connected to the RRU according to two modes. The first one is called a one-to-one association and consists in allocating the resource units of the BBU radio frame to a single RRH. In the second mode which is called multiple association, a BBU can handle multiple RRHs. We propose a hybrid association mode in which the resource units of each frame are divided into two slices. The first one constitutes an unshared slice and is allocated to central users according to the one-to-one association in order to increase the throughput, especially at high traffic load. The second slice contains a quantity of resource units that are shared by a group of RRHs belonging to the same BBU. This common slice is configured according to the multiple association mode and is allocated to the edge and mobile users. We show that the hybrid mode reduces the inter-cell interferences, decreases the number of inter-BBU handovers and improves the energy consumption

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6

Jouini, Wassim. "Contribution à l'apprentissage et à la prise de décision, dans des contextes d'incertitude, pour la radio intelligente." Phd thesis, Supélec, 2012. http://tel.archives-ouvertes.fr/tel-00765437.

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L'allocation des ressources spectrales à des services de communications sans fil, sans cesse plus nombreux et plus gourmands, a récemment mené la communauté radio à vouloir remettre en question la stratégie de répartition des bandes de fréquences imposée depuis plus d'un siècle. En effet une étude rendue publique en 2002 par la commission fédérale des communications aux Etats-Unis (Federal Communications Commission - FCC) mit en évidence une pénurie des ressources spectrales dans une large bande de fréquences comprise entre quelques mégahertz à plusieurs gigahertz. Cependant, cette même étude expliqua cette pénurie par une allocation statique des ressources aux différents services demandeurs plutôt que par une saturation des bandes de fréquences. Cette explication fut par la suite corroborée par de nombreuses mesures d'occupation spectrale, réalisées dans plusieurs pays, qui montrèrent une forte sous-utilisation des bandes de fréquences en fonction du temps et de l'espace, représentant par conséquent autant d'opportunité spectrale inexploitée. Ces constations donnèrent naissance à un domaine en plein effervescence connu sous le nom d'Accès Opportuniste au Spectre (Opportunistic Spectrum Access). Nos travaux suggèrent l'étude de mécanismes d'apprentissage pour la radio intelligente (Cognitive Radio) dans le cadre de l'Accès Opportuniste au Spectre (AOS) afin de permettre à des équipements radio d'exploiter ces opportunités de manière autonome. Pour cela, nous montrons que les problématiques d'AOS peuvent être fidèlement représentées par des modèles d'apprentissage par renforcement. Ainsi, l'équipement radio est modélisé par un agent intelligent capable d'interagir avec son environnement afin d'en collecter des informations. Ces dernières servent à reconnaître, au fur et à mesure des expériences, les meilleurs choix (bandes de fréquences, configurations, etc.) qui s'offrent au système de communication. Nous nous intéressons au modèle particulier des bandits manchots (Multi-Armed Bandit appliqué à l'AOS). Nous discutons, lors d'une phase préliminaire, différentes solutions empruntées au domaine de l'apprentissage machine (Machine Learning). Ensuite, nous élargissons ces résultats à des cadres adaptés à la radio intelligente. Notamment, nous évaluons les performances de ces algorithmes dans le cas de réseaux d'équipements qui collaborent en prenant en compte, dans le modèle suggéré, les erreurs d'observations. On montre de plus que ces algorithmes n'ont pas besoin de connaître la fréquence des erreurs d'observation afin de converger. La vitesse de convergence dépend néanmoins de ces fréquences. Dans un second temps nous concevons un nouvel algorithme d'apprentissage destiné à répondre à des problèmes d'exploitation des ressources spectrales dans des conditions dites de fading. Tous ces travaux présupposent néanmoins la capacité de l'équipement intelligent à détecter efficacement l'activité d'autres utilisateurs sur la bande (utilisateurs prioritaires dits utilisateurs primaires). La principale difficulté réside dans le fait que l'équipement intelligent ne suppose aucune connaissance a priori sur son environnement (niveau du bruit notamment) ou sur les utilisateurs primaires. Afin de lever le doute sur l'efficacité de l'approche suggérée, nous analysons l'impact de ces incertitudes sur le détecteur d'énergie. Ce dernier prend donc le rôle d'observateur et envoie ses observations aux algorithmes d'apprentissage. Nous montrons ainsi qu'il est possible de quantifier les performances de ce détecteur dans des conditions d'incertitude sur le niveau du bruit ce qui le rend utilisable dans le contexte de la radio intelligente. Par conséquent, les algorithmes d'apprentissage utilisés pourront exploiter les résultats du détecteur malgré l'incertitude inhérente liée à l'environnement considéré et aux hypothèses (sévères) d'incertitude liées au problème analysé.

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Modi, Navikkumar. "Machine Learning and Statistical Decision Making for Green Radio." Thesis, CentraleSupélec, 2017. http://www.theses.fr/2017SUPL0002/document.

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Cette thèse étudie les techniques de gestion intelligente du spectre et de topologie des réseaux via une approche radio intelligente dans le but d’améliorer leur capacité, leur qualité de service (QoS – Quality of Service) et leur consommation énergétique. Les techniques d’apprentissage par renforcement y sont utilisées dans le but d’améliorer les performances d’un système radio intelligent. Dans ce manuscrit, nous traitons du problème d’accès opportuniste au spectre dans le cas de réseaux intelligents sans infrastructure. Nous nous plaçons dans le cas où aucune information n’est échangée entre les utilisateurs secondaires (pour éviter les surcoûts en transmissions). Ce problème particulier est modélisé par une approche dite de bandits manchots « restless » markoviens multi-utilisateurs (multi-user restless Markov MAB -multi¬armed bandit). La contribution principale de cette thèse propose une stratégie d’apprentissage multi-joueurs qui prend en compte non seulement le critère de disponibilité des canaux (comme déjà étudié dans la littérature et une thèse précédente au laboratoire), mais aussi une métrique de qualité, comme par exemple le niveau d’interférence mesuré (sensing) dans un canal (perturbations issues des canaux adjacents ou de signaux distants). Nous prouvons que notre stratégie, RQoS-UCB distribuée (distributed restless QoS-UCB – Upper Confidence Bound), est quasi optimale car on obtient des performances au moins d’ordre logarithmique sur son regret. En outre, nous montrons par des simulations que les performances du système intelligent proposé sont améliorées significativement par l’utilisation de la solution d’apprentissage proposée permettant à l’utilisateur secondaire d’identifier plus efficacement les ressources fréquentielles les plus disponibles et de meilleure qualité. Cette thèse propose également un nouveau modèle d’apprentissage par renforcement combiné à un transfert de connaissance afin d’améliorer l’efficacité énergétique (EE) des réseaux cellulaires hétérogènes. Nous formulons et résolvons un problème de maximisation de l’EE pour le cas de stations de base (BS – Base Stations) dynamiquement éteintes et allumées (ON-OFF). Ce problème d’optimisation combinatoire peut aussi être modélisé par des bandits manchots « restless » markoviens. Par ailleurs, une gestion dynamique de la topologie des réseaux hétérogènes, utilisant l’algorithme RQoS-UCB, est proposée pour contrôler intelligemment le mode de fonctionnement ON-OFF des BS, dans un contexte de trafic et d’étude de capacité multi-cellulaires. Enfin une méthode incluant le transfert de connaissance « transfer RQoS-UCB » est proposée et validée par des simulations, pour pallier les pertes de récompense initiales et accélérer le processus d’apprentissage, grâce à la connaissance acquise à d’autres périodes temporelles correspondantes à la période courante (même heure de la journée la veille, ou même jour de la semaine par exemple). La solution proposée de gestion dynamique du mode ON-OFF des BS permet de diminuer le nombre de BS actives tout en garantissant une QoS adéquate en atténuant les fluctuations de la QoS lors des variations du trafic et en améliorant les conditions au démarrage de l’apprentissage. Ainsi, l’efficacité énergétique est grandement améliorée. Enfin des démonstrateurs en conditions radio réelles ont été développés pour valider les solutions d’apprentissage étudiées. Les algorithmes ont également été confrontés à des bases de données de mesures effectuées par un partenaire dans la gamme de fréquence HF, pour des liaisons transhorizon. Les résultats confirment la pertinence des solutions d’apprentissage proposées, aussi bien en termes d’optimisation de l’utilisation du spectre fréquentiel, qu’en termes d’efficacité énergétique
Future cellular network technologies are targeted at delivering self-organizable and ultra-high capacity networks, while reducing their energy consumption. This thesis studies intelligent spectrum and topology management through cognitive radio techniques to improve the capacity density and Quality of Service (QoS) as well as to reduce the cooperation overhead and energy consumption. This thesis investigates how reinforcement learning can be used to improve the performance of a cognitive radio system. In this dissertation, we deal with the problem of opportunistic spectrum access in infrastructureless cognitive networks. We assume that there is no information exchange between users, and they have no knowledge of channel statistics and other user's actions. This particular problem is designed as multi-user restless Markov multi-armed bandit framework, in which multiple users collect a priori unknown reward by selecting a channel. The main contribution of the dissertation is to propose a learning policy for distributed users, that takes into account not only the availability criterion of a band but also a quality metric linked to the interference power from the neighboring cells experienced on the sensed band. We also prove that the policy, named distributed restless QoS-UCB (RQoS-UCB), achieves at most logarithmic order regret. Moreover, numerical studies show that the performance of the cognitive radio system can be significantly enhanced by utilizing proposed learning policies since the cognitive devices are able to identify the appropriate resources more efficiently. This dissertation also introduces a reinforcement learning and transfer learning frameworks to improve the energy efficiency (EE) of the heterogeneous cellular network. Specifically, we formulate and solve an energy efficiency maximization problem pertaining to dynamic base stations (BS) switching operation, which is identified as a combinatorial learning problem, with restless Markov multi-armed bandit framework. Furthermore, a dynamic topology management using the previously defined algorithm, RQoS-UCB, is introduced to intelligently control the working modes of BSs, based on traffic load and capacity in multiple cells. Moreover, to cope with initial reward loss and to speed up the learning process, a transfer RQoS-UCB policy, which benefits from the transferred knowledge observed in historical periods, is proposed and provably converges. Then, proposed dynamic BS switching operation is demonstrated to reduce the number of activated BSs while maintaining an adequate QoS. Extensive numerical simulations demonstrate that the transfer learning significantly reduces the QoS fluctuation during traffic variation, and it also contributes to a performance jump-start and presents significant EE improvement under various practical traffic load profiles. Finally, a proof-of-concept is developed to verify the performance of proposed learning policies on a real radio environment and real measurement database of HF band. Results show that proposed multi-armed bandit learning policies using dual criterion (e.g. availability and quality) optimization for opportunistic spectrum access is not only superior in terms of spectrum utilization but also energy efficient

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Kouassi, Boris Rodrigue. "Stratégies de coopération dans les réseaux radio cognitif." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00921559.

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Les réseaux radio actuelles utilisent le spectre inefficacement, car une bande de fréquence est allouée de façon permanente à une technologie spécifique. Vu que le spectre est une ressource limitée, cette attribution statique ne pourra bientôt plus combler les besoins des systèmes de transmission qui ne cessent de croître. On peut toutefois optimiser l'utilisation du spectre en permettant des transmissions secondaires (SU) dans les espaces libres du primaire (PU). Cette vision constitue l'objectif principal de la radio cognitive. Nous proposons d'évaluer les stratégies de transmission pour la coexistence des systèmes primaires (PU) et SU dans les mêmes réseaux. Plus concrètement, nous nous focalisons sur un scénario spatial interweave en émettant les signaux SU dans les espaces vides du PU à l'aide d'un précodeur linéaire. Néanmoins, ce précodage nécessite une connaissance a priori des canaux interférents. L'échange d'informations entre le PU et le SU étant proscrit, nous exploitons l'hypothèse de la réciprocité du canal. Cette hypothèse compense l'absence de coopération, mais elle n'est pas si évidente à exploiter en pratique à cause des perturbations des circuits radio fréquence. Nous suggérons de compenser ces perturbations par des méthodes de calibration relative. Nous proposons ensuite une implémentation temps-réel des solutions sur une plateforme LTE. Pour finir, nous généralisons l'approche RC à un système de transmission multi-utilisateurs, à travers une combinaison des techniques RC et massive MIMO, cette approche constitue s'établit comme une solution à la progression exponentielle du trafic.

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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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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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Hirve, Sachin C. "Multihop Transmission Opportunistic Protocol on Software Radio." Cleveland State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1254976381.

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Xie, Qing Yan. "Performance Analysis of Opportunistc Spectrum Access on Cognitive Radio." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1273173530.

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13

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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14

Rehmani, Mubashir Husain. "Opportunistic Data Dissemination in Ad-Hoc Cognitive Radio Networks." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2011. http://tel.archives-ouvertes.fr/tel-00630214.

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Les progrès récents des technologies de communication et la prolifération de l'informatique sans fil et des dispositifs de communication, ont induit 'a une surcharge dans l'utilisation du spectre radio. Cependant, les expériences de la Commission Fédérale de Communication (FCC) ont révélé que l'utilisation du spectre varie entre 15% et 85%. Par conséquent, les réseaux radios cognitifs (Cognitive Radio Networks ou CRNs) sont proposés afin d'utiliser le spectre radio d'une manière opportuniste. Dans ce type de réseaux radios cognitifs, où les fréquences de transmission sont sélectionnées d'une manière opportuniste - également sont appelés réseaux Ad-Hoc à radios cognitives -, la fiabilité de la dissémination des données est difficile 'a réaliser. D'abord, en plus des défis déjà connus dans les environnements sans fils, la diversité dans le nombre de fréquences qu'un noeud à radio cognitif a droit d'utiliser ajoute un autre défi, en limitant l'accessibilité à ses noeuds voisins. Deuxièmement, les noeuds à radio cognitif (CR) doivent conquérir les ressources de fréquences résiduelles avec les noeuds à radio primaire (PR), tout en essayent de les exploiter d'une manière opportuniste. En outre, les noeuds CR ne devraient pas perturber la qualité de réception des noeuds PR durant leur communication, et ce en limitant les interférences entre les deux de noeuds. Par conséquent, une nouvelle méthode de sélection de fréquences est requise afin de réduire le nombre d'interférences nuisibles aux noeuds PR, et maximiser les chances de délivrance des messages aux voisins récepteurs des noeuds CR, et augmenter ainsi la fiabilité des données disséminées. Dans cette thèse nous proposons SURF, une nouvelle méthode distribuée de sélection de fréquences pour la dissémination fiable de données dans un réseau radio cognitif multi-sauts. SURF classifie les fréquences radio disponibles en fonction de l'occupation des fréquences des noeuds à radio primaire et le nombre de noeuds 'a radio cognitive utilisant ces fréquences. Les résultats de simulation obtenus par NS-2 confirment que SURF est une stratégie efficace dans la sélection des meilleures fréquences de diffusion de données, comparée aux autres approches liées. Nous avons aussi constaté que les stratégies de sélection de fréquences sont considérablement influencées par l'activité des noeuds 'a radio primaire. Dans la suite ce cette thèse, nous étudierons et analyserons l'impact des modèles d'activités des noeuds PR sur les différentes stratégies de sélection de fréquences à travers des simulations basées NS-2. Nous avons remarqué que l'activité intermittente de PR est le cas où les solutions intelligentes doivent opérées. C'est dans ce cas où SURF donne les meilleures résultats et la région ciblée se serve des opportunités de communication. Enfin, dans cette thèse, nous allons encore plus loin en vérifiant l'applicabilité et la faisabilité de SURF. Dans cette perspective, d'abord, nous proposons une architecture d'accès à internet basse sur la radio cognitive pour les réseaux partiellement endommagés. Nous discutons les détails architecturaux et le principe de fonctionnement de l'architecture proposée. Nous avons également passé en revue les enjeux et les défis de déploiement de cette nouvelle architecture. Deuxièmement, nous discutons l'applicabilité de SURF dans le contexte de l'agrégation de fréquences et à cet égard, nous discutons une stratégie d'interférence basée sur l'agrégation de fréquences pour les réseaux radios cognitifs.

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Bany, Salameh Haythem Ahmad Mohammed. "Channel Access Mechanisms and Protocols for Opportunistic Cognitive Radio Networks." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/193865.

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High traffic load over the unlicensed portion of the radiospectrum (a.k.a., ISM bands) along with inefficient usage of thelicensed spectrum gave impetus for a new paradigm in spectrumallocation, whose main purpose is to improve spectrum efficiencythrough opportunistic access. Cognitive radios (CRs) havebeen proposed as a key enabling technology for such paradigm.Operating a CR network (CRN) without impacting the performance oflicensed (primary) users requires new protocols for informationexchange as well as mathematical tools to optimize thecontrollable parameters of the CRN. In this dissertation, wetarget the design of such protocols. First, we develop adistributed CRN MAC (COMAC) protocol that enables unlicensed usersto dynamically utilize the spectrum while limiting theinterference they inflict on primary (PR) users. The main noveltyin COMAC lies in not assuming a predefined CR-to-PR power mask andnot requiring coordination with PR users. Second, we propose anovel distance-dependent MAC protocol for CRNs in whicheach CR is equipped with multiple transceivers. Our protocol(called DDMAC) attempts to maximize the CRN throughput byfollowing a novel probabilistic channel assignment mechanism. Thismechanism exploits the dependence between the signal's attenuationmodel and the transmission distance while considering the trafficprofile. We show that through its distance- and traffic-aware,DDMAC significantly improves network throughput. Finally, weaddress the problem of assigning channels to CR transmissions,assuming one transceiver per CR. The main goal of our design is tomaximize the CRN throughput with respect to both spectrumassignment and transmission power. Specifically, we presentcentralized and distributed solutions that leverage the uniquecapabilities of CRs. Compared with previously proposed protocols,our schemes are shown to significantly improve network throughput.

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Shu, Tao. "Efficient Radio Resource Management and Routing Mechanisms for Opportunistic Spectrum Access Networks." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/194747.

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Opportunistic spectrum access (OSA) promises to significantly improve the utilization of the RF spectrum. Under OSA, an unlicensed secondary user (SU) is allowed to detect and access under-utilized portions of the licensed spectrum, provided that such operation does not interfere with the communication of licensed primary users (PUs). Cognitive radio (CR) is a key enabling technology of OSA. In this dissertation, we propose several radio resource management and routing mechanisms that optimize the discovery and utilization of spectrum opportunities in a cognitive radio network (CRN). First, we propose a sequential channel sensing and probing mechanism that enables a resource-constrained SU to efficiently identify the optimal transmission opportunity from a pool of potentially usable channels. This mechanism maximizes the SUs expected throughput by accounting for the tradeoff between the reward and overhead of scanning additional channels. The optimal channel sensing and probing process is modeled as a maximum-rate-of-return problem in optimal stopping theory. Operational parameters, such as sensing and probing times, are optimized by exploiting the problem's special structure. Second, we study the problem of coordinated spectrum access in CRNs to maximize the CRNs throughput. By exploiting the geographic relationship between an SU and its surrounding PUs, we propose the novel concept of microscopic spectrum opportunity, in which active SUs and PUs are allowed to operate in the same region, subject to power constraints. Under this framework, we formulate the coordinated channel access problem as a joint power/rate control and channel assignment optimization problem. Centralized and distributed approximate algorithms are proposed to solve this problem efficiently. Compared with its macroscopic counterpart, we show that the microscopic-spectrum-opportunity framework offers significant throughput gains. Finally, at the network layer, we study the problem of truthful least-priced-path (LPP) routing for profit-driven CRNs. We design a route selection and pricing mechanism that guarantees truthful spectrum cost reporting from profit-driven SUs and that finds the cheapest route for end users. The problem is investigated with and without capacity constraints at individual nodes. In both cases, polynomial-time algorithms are developed to solve the LPP problem. Extensive simulations are conducted to verify the validity of the proposed mechanisms.

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Mansfield, Thomas Oliver. "Data communication signals of opportunity for navigation." Thesis, University of Plymouth, 2017. http://hdl.handle.net/10026.1/10169.

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Mobile devices with wireless networking capabilities are used in a wide range of environments. Geolocation information increases the value of the data generated by a device and is vital in the development of a wide range of applications from autonomous vehicles to the Internet of things. Systems that generate signals specifically for geolocation have become widely adopted but, due to fundamental constraints, lack coverage and accuracy in complex urban and indoor environments. In addition to this, the reliance on a single signal source is not desirable in many applications that value the integrity of the geolocation estimate. A direction of research aiming to improve geolocation in indoor and urban environments measures signals of opportunity in order to generate a more robust estimate. While this approach improves signal availability, the unpredictable nature of these variable and uncontrolled signals leads to poor geolocation estimates, which are typically not suitable for use in many applications. This project aims to improve on the accuracy, resilience and integrity of a geolocation estimate obtained from signal of opportunity measurements in indoor and urban environments while reducing hardware requirements. This has been achieved by efficiently coupling signals of opportunity within the radio environment with other system signals, such as those from an inertial measurement unit. Research has been carried out to optimise the coupling of these data sources resulting in techniques to allow the identification and removal of key error drivers from both the radio environment and other system sensors. This thesis proposes a specifically designed extended Kalman filter to improve on the signal coupling. The filter aims to optimise the accuracy of radio environment measurements while also providing the ability to identify signal error sources in urban and indoor environments, leading to both greater accuracy and resilience of the geo-location estimate. Further, the proposed extended Kalman filter may use the radio environment as a source of geolocation data. The ability of the filter to recognise and mitigate leading radio environment error sources such as multipath and interference allowed the design of filters to obtain detailed and accurate signal strength and time of arrival information. The thesis also presents a thorough set of simulation and modelling experiments to investigate and optimise the efficiency of the proposed solutions in a range of environments. Validation testing confirmed that in the urban and indoor environments, the average error of geo-location estimates has been reduced from 10 m to 3 m without improvement to the hardware surrounding infrastructure. The improvements presented in this thesis allow networked devices to improve the value of their data by incorporating the context that comes from increased geolocation accuracy and resilience. In turn, this allows the development of a wide range of new location based applications for mobile devises in indoor and urban environments.

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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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19

Derakhshani, Mahsa. "Distributed opportunistic spectrum access via adaptive carrier sensing in cognitive radio networks." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119593.

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The limitations of current static spectrum management policy drive the idea of a more dynamic access policy to improve the efficiency of radio spectrum usage and accommodate the increasing demand for wireless communication applications. Known as the opportunistic spectrum access (OSA), the new paradigm allows cognitive secondary users (SUs) to access the licensed spectrum, provided that the interference to the licensed primary users (PUs) is limited. In a cognitive radio network, since SUs are intended to track and take advantage of instantaneous spectrum opportunities, adaptive learning-based spectrum access schemes are desired to optimize spectrum utilization and ensure a peaceful coexistence of licensed and unlicensed systems. This thesis deals with the modeling, development and analysis of OSA schemes in a cognitive radio network from both SU and PU perspectives. The research objective is to maximize the overall throughput of SUs, while sufficiently protecting the ongoing operation of PUs.From the SU perspective, to avoid the high-risk data loss due to the random return of PUs, we present a dynamic hopping transmission strategy for SUs to access the temporarily idle frequency slots of a licensed frequency band, with adaptive activity factors. Upon applying the dual decomposition, the optimal activity factor allocation algorithm is developed. To facilitate spectrum sharing in a decentralized manner, we propose an adaptive carrier sense multiple access (CSMA) scheme. Based on the proposed CSMA scheme, learning-based distributed access algorithms for SUs are devised, including non-game-theoretic and game-theoretic approaches. The proposed algorithms can be independently performed by each SU to learn its optimal activity factors from the locally available information. To evaluate the effects of inevitable collisions among SUs in the proposed adaptive CSMA scheme, the collision probability and saturation throughput are studied by both analysis and simulation. Simulation results show significant performance improvements in terms of the achievable throughput compared to the conventional CSMA scheme. From the PU perspective, by applying the proposed access scheme to SUs, we study the interference caused by SUs to the PU due to miss-detection, and also its effects on the capacity-outage performance of the PU in a cognitive radio network. Based on the developed statistical models for the interference distribution, closed-form expressions for the capacity-outage probability of the PU are derived to examine the effects of various system parameters on the performance of the PU in the presence of interference from SUs. The model is extended to investigate the effects of cooperative sensing on the aggregate interference and the capacity-outage performance, considering OR (logical OR operation) and maximum likelihood cooperative detection techniques.
Les limites de la politique d'utilisation statique du spectre ont conduit à l'idée d'une politique d'accès plus dynamique pour améliorer l'efficacité du spectre radio utilisé et accommoder l'augmentation de la demande des applications de communication sans fils. Connu sous le nom d'accès opportuniste au spectre (AOS), ce nouveau model permet à un utilisateur secondaire (US) cognitif d'accéder à un spectre licencié, tout en limitant l'interférence de l'utilisateur primaire (UP) licencié. Dans un réseau radio cognitif, puisque les USs sont sensés traquer et profiter des instants d'opportunité spectrale, des schémas d'accès spectral basés sur l'apprentissage adaptatif sont désirés pour optimiser l'utilisation spectrale et assurer une parfaite coexistence entre les systèmes licenciés et non licenciés. Cette thèse se consacre à la modélisation, au développement et à l'analyse des schémas d'AOS dans les réseaux radio cognitif du point de vue des UP et US. L'objectif de cette recherche est de maximiser le flux total des USs, tout en protégeant suffisamment le fonctionnement de l'UP. Du point de vue de l'US, afin d'éviter un risque élevé de perte de données causée par le retour aléatoire de l'UP, nous présentons une stratégie de transmission basée sur le saut dynamique pour les USs afin d'accéder aux blocs de fréquences temporairement libres dans une bande licenciée, avec un facteur d'activité adaptatif. Lors de l'application de la double décomposition, un algorithme d'allocation optimale des facteurs d'activité est développé. Afin de faciliter le partage du spectre de manière décentralisée, nous proposons un schéma adaptif basé sur la technique CSMA (accès multiple avec détection de porteuses). En se basant sur le schéma proposé, des algorithmes d'accès distribués pour les USs basés sur l'apprentissage sont conçus, incluant des approches basées sur la théorie des jeux et d'autres non. Les algorithmes proposés peuvent être utilisés indépendamment par chaque US pour apprendre son facteur d'activité optimal à partir de l'information localement disponible. Pour évaluer les effets de collisions inévitables entre les USs dans le schéma CSMA proposé, la probabilité de collision et le flux de saturation sont étudiés analytiquement et à travers des simulations. Les résultats des simulations démontrent une amélioration considérable de performance, particulièrement de point de vue de débit réalisé par rapport à celui réalisé selon le CSMA conventionnel.Du point de vue de l'UP, nous employons le schéma d'accès proposé pour les USs, et étudions l'interférence causée par les USs aux UPs à la suite d'une erreur de détection, ainsi que ses effets sur la capacité de coupure de l'UP dans un réseau radio cognitif. En se basant sur les modèles statistiques de la distribution de l'interférence, des expressions exactes de la probabilité de la capacité de coupure pour l'UP sont dérivées afin d'examiner les effets des différents paramètres du système sur la performance de l'UP en présence des USs interférant. Le modèle est étendu pour investiguer les effets de la détection coopérative sur l'interférence totale et la capacité de coupure, en considérant l'operateur logique OR et une détection coopérative de maximum de vraisemblance.

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Wang, Ji. "Imperfect Monitoring in Multi-agent Opportunistic ChannelAccess." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71789.

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In recent years, extensive research has been devoted to opportunistically exploiting spectrum in a distributed cognitive radio network. In such a network, autonomous secondary users (SUs) compete with each other for better channels without instructions from a centralized authority or explicit coordination among SUs. Channel selection relies on channel occupancy information observed by SUs, including whether a channel is occupied by a PU or an SU. Therefore, the SUs' performance depends on the quality of the information. Current research in this area often assumes that the SUs can distinguish a channel occupied by a PU from one occupied by another SU. This can potentially be achieved using advanced signal detection techniques but not by simple energy detection. However, energy detection is currently the primary detection technique proposed for use in cognitive radio networks. This creates a need to design a channel selection strategy under the assumption that, when SUs observe channel availability, they cannot distinguish between a channel occupied by a PU and one occupied by another SU. Also, as energy detection is simpler and less costly than more advanced signal detection techniques, it is worth understanding the value associated with better channel occupancy information. The first part of this thesis investigates the impact of different types of imperfect information on the performance of secondary users (SUs) attempting to opportunistically exploit spectrum resources in a distributed manner in a channel environment where all the channels have the same PU duty cycle. We refer to this scenario as the homogeneous channel environment. We design channel selection strategies that leverage different levels of information about channel occupancy. We consider two sources of imperfect information: partial observability and sensing errors. Partial observability models SUs that are unable to distinguish the activity of PUs from SUs. Therefore, under the partial observability models, SUs can only observe whether a channel was occupied or not without further distinguishing it was occupied by a PU or by SUs. This type of imperfect information exists, as discussed above, when energy detection is adopted as the sensing technique. We propose two channel selection strategies under full and partial observability of channel activity and evaluate the performance of our proposed strategies through both theoretical and simulation results. We prove that both proposed strategies converge to a stable orthogonal channel allocation when the missed detection rate is zero. The simulation results validate the efficiency and robustness of our proposed strategies even with a non-zero probability of missed detection. The second part of this thesis focuses on computing the probability distribution of the number of successful users in a multi-channel random access scheme. This probability distribution is commonly encountered in distributed multi-channel communication systems. An algorithm to calculate this distribution based on a recursive expression was previously proposed. We propose a non-recursive algorithm that has a lower execution time than the one previously proposed in the literature. The third part of this thesis investigates secondary users (SUs) attempting to opportunistically exploit spectrum resources in a scenario where the channels have different duty cycles, which we refer to as the heterogeneous channel environment. In particular, we model the channel selection process as a one shot game. We prove the existence of a symmetric Nash equilibrium for the proposed static game and design a channel selection strategy that achieves this equilibrium. The simulation results compare the performance of the Nash equilibrium to two other strategies(the random and the proportional strategies) under different PU activity scenarios.
Master of Science

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21

Raiss, El Fenni Mohammed. "Opportunistic spectrum usage and optimal control in heterogeneous wireless networks." Phd thesis, Université d'Avignon, 2012. http://tel.archives-ouvertes.fr/tel-00907120.

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The present dissertation deals with how to use the precious wireless resources that are usually wasted by under-utilization of networks. We have been particularly interested by all resources that can be used in an opportunistic fashion using different technologies. We have designed new schemes for better and more efficient use of wireless systems by providing mathematical frameworks. In the first part, We have been interested in cognitive radio networks, where a cellular service provider can lease a part of its resources to secondary users or virtual providers. In the second part, we have chosen delay-tolerant networks as a solution to reduce the pressure on the cell traffic, where mobile users come to use available resources effectively and with a cheaper cost. We have focused on optimal strategy for smartphones in hybrid wireless networks. In the last part, an alternative to delay-tolerant networks, specially in regions that are not covered by the cellular network, is to use Ad-hoc networks. Indeed, they can be used as an extension of the coverage area. We have developed a new analytical modeling of the IEEE 802.11e DCF/EDCF. We have investigated the intricate interactions among layers by building a general cross-layered framework to represent multi-hop ad hoc networks with asymmetric topology and traffic

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Bian, Kaigui. "Medium Access Control in Cognitive Radio Networks." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/37591.

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Cognitive radio (CR) is seen as one of the enabling technologies for realizing a new regulatory spectrum management paradigm, viz. opportunistic spectrum sharing (OSS). In the OSS paradigm, unlicensed users (a.k.a. secondary users) opportunistically operate in fallow licensed spectrum on a non-interference basis to licensed users (a.k.a. incumbent or primary users). Incumbent users have absolute priority in licensed bands, and secondary users must vacate the channel where incumbent user signals are detected. A CR network is composed of secondary users equipped with CRs and it can coexist with incumbent users in licensed bands under the OSS paradigm. The coexistence between incumbent users and secondary users is referred to as incumbent coexistence, and the coexistence between CR networks of the same type is referred to as self-coexistence. In this dissertation, we address three coexistence-related problems at the medium access control (MAC) layer in CR networks: (1) the rendezvous (control channel) establishment problem, (2) the channel assignment problem in an ad hoc CR network, and (3) the spectrum sharing problem between infrastructure-based CR networks, i.e., the 802.22 wireless regional area networks (WRANs). Existing MAC layer protocols in conventional wireless networks fail to adequately address the key issues concerning incumbent and self coexistence that emerge in CR networks. To solve the rendezvous establishment problem, we present a systematic approach, based on quorum systems, for designing channel hopping protocols that ensure a pair of CRs to "rendezvous" within an upper-bounded time over a common channel that is free of incumbent user signals. In a single radio interface, ad hoc CR network, we propose a distributed channel assignment scheme that assigns channels at the granularity of "segments" for minimizing the channel switching overhead. By taking into account the coexistence requirements, we propose an inter-network spectrum sharing protocol that enables the sharing of vacant TV white space among coexisting WRANs. Our analytical and simulation results show that these proposed schemes can effectively address the aforementioned MAC layer coexistence problems in CR networks.
Ph. D.

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23

Nilsson, Martin. "Indoor Positioning Using Opportunistic Multi-Frequency RSS With Foot-Mounted INS." Thesis, Linköpings universitet, Reglerteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-111072.

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Reliable and accurate positioning systems are expected to significantly improve the safety for first responders and enhance their operational efficiency. To be effective, a first responder positioning systemmust provide room level accuracy during extended time periods of indoor operation. This thesis presents a system which combines a zero-velocity-update (ZUPT) aided inertial navigation system (INS), using a foot-mounted inertial measurement unit (IMU), with the use of opportunistic multi-frequency received signal strength (RSS) measurements. The system does not rely on maps or pre-collected data from surveys of the radio-frequency (RF environment; instead, it builds its own database of collected rss measurements during the course of the operation. New RSS measurements are continuously compared with the stored values in the database, and when the user returns to a previously visited area this can thus be detected. This enables loop-closures to be detected online, which can be used for error drift correction. The system utilises a distributed particle simultaneous localisation and mapping (DP-SLAM) algorithm which provides a flexible 2-D navigation platform that can be extended with more sensors. The experimental results presented in this thesis indicates that the developed rss slam algorithm can, in many cases, significantly improve the positioning performance of a foot-mounted INS.

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Werquin, Arnaud. "Multiple rates multiple paths wideband digital transmitter with low spurious emissions applied to opportunistic radio." Thesis, Lille 1, 2013. http://www.theses.fr/2013LIL10027/document.

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Les terminaux de communications sans fil évoluent en des terminaux supportant plusieurs standards. L'un des challenges est d'utiliser le meilleur standard au bon moment. L'émetteur d'une radio cognitive agile en fréquence se doit d'être reconfigurable afin de transmettre l'information dans des bandes fréquentielles sous utilisées et d'avoir recours au standard offrant la meilleure qualité de communication. L'élément le plus critique dans un émetteur est l'étage de puissance et sa connexion avec l'antenne. Les principaux problèmes devant être pris en compte par l'amplificateur de puissance (PA) sont: la linéarité, la puissance délivrée à l'antenne et le rendement. Un émetteur numérique basé sur un amplificateur de puissance commandé numériquement (DPA) est étudié et un prototype a été implémenté afin de démontrer la faisabilité du concept. Le DPA est principalement utilisé dans les architectures polaires plutôt que cartésienne. L'architecture proposée est basée sur une approche à multiple voies combinée à une conversion de fréquences. La diversité introduite sur les fréquences d'échantillonnage permet de contrôler le niveau d'impuretés spectrales émisses. Celles-ci proviennent de la conversion directe numérique vers RF. Cette conversion est réalisée par le DPA sans le recours à des filtres passifs. Les émetteurs implémentés en technologies CMOS avancées ont souvent recours à une architecture à multiple voies. L'approche présentée dans ce manuscrit tire avantage de cette structure parallèle afin de générer des signaux portant la même information mais échantillonnés à des fréquences différentes. Le standard LTE a été pris comme standard de référence, et un modulateur d'enveloppe a été conçu en technologie CMOS 65nm. Les conversions de fréquences bande de base et la logique de contrôle on été implémentées sur FPGA. La recombinaison des voies est réalisée à l'aide de composants discrets. Le prototype de modulateur d'enveloppe numérique réalisé, démontre le principe d'atténuation d'images pouvant atteindre 6dB dans le cas d'un système à deux voies. Les DPAs supportent quatre fréquences d'échantillonnage {100 MS/s; 133 MS/s; 152 MS/s; 160MS/s}. L'amplificateur délivre jusqu'à 16.7dBm sur la bande 0.9 à 1.9 GHz et assure un PAE de 12.4% avec un EVMrms de -28dB. Le prototype a été testé avec des signaux LTE de 10 MHz et 802.11g de 20 MHz. La surface totale occupée par le circuit est de 1.04mm² tandis que la surface dédié aux DPAs et logique de contrôle occupent seulement 0.25mm²
Wireless communication terminals are evolving towards multi-standard terminals. One of the challenges is to use the best standard available at the right moment. The transmit part of a frequency agile cognitive radio must be highly reconfigurable in order to transmit information in an unused spectral zone and to use the suitable standard to obtain the optimum communication. The most critical element in a transmitter is the power amplifier and its interface with the antenna. Key problems that need to be addressed by the Power Amplifier (PA) are the linearity, ability to deliver power to the antenna and efficiency. In this work a digital transmitter based on a digitally controlled power amplifier (DPA) is investigated, and a prototype has been implemented to prove the feasibility of the concept. The DPA is mostly used in polar transmitters rather than Cartesian ones. The proposed architecture is based on multi-path approach with different sample rate conversions. This diversity of sample rates helps to manage the spurious emissions due to the direct digital to RF conversion performed by the DPA without the need of passive filters. The transmitters implemented in advanced CMOS process are commonly based on multiple paths architecture. The approach proposed in this work takes advantage of this parallel structure to generate several signals with the same information but with different sample rates. The LTE standard has been taken as the standard example, and a 2-path digital envelope modulator has been designed in a 65nm CMOS technology. The baseband sample rate conversions and control logic have been implemented on FPGA. The path recombination is performed with o_-board components. The fabricated prototype digital envelope modulator IC demonstrates the image attenuation principle with up to 6dB attenuation. The DPAs support four sample rates {100 MS/s; 133 MS/s; 152 MS/s; 160MS/s}. The amplifier delivers up to 16.7dBm over a 0.9 - 1.9 GHz band while providing 12.4% PAE and a -28dB EVMrms.The prototype was tested with a 10 MHz LTE and a 20 MHz 802.11g standards. The total circuit occupies 1.04mm² and the area dedicated to the DPA and control logic only occupies 0.25mm²

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25

Yusuf, Idris A. "Optimising cooperative spectrum sensing in cognitive radio networks using interference alignment and space-time coding." Thesis, University of Hertfordshire, 2018. http://hdl.handle.net/2299/21106.

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In this thesis, the process of optimizing Cooperative Spectrum Sensing in Cognitive Radio has been investigated in fast-fading environments where simulation results have shown that its performance is limited by the Probability of Reporting Errors. By proposing a transmit diversity scheme using Differential space-time block codes (D-STBC) where channel state information (CSI) is not required and regarding multiple pairs of Cognitive Radios (CR's) with single antennas as a virtual MIMO antenna arrays in multiple clusters, Differential space-time coding is applied for the purpose of decision reporting over Rayleigh channels. Both Hard and Soft combination schemes were investigated at the fusion center to reveal performance advantages for Hard combination schemes due to their minimal bandwidth requirements and simplistic implementation. The simulations results show that this optimization process achieves full transmit diversity, albeit with slight performance degradation in terms of power with improvements in performance when compared to conventional Cooperative Spectrum Sensing over non-ideal reporting channels. Further research carried out in this thesis shows performance deficits of Cooperative Spectrum Sensing due to interference on sensing channels of Cognitive Radio. Interference Alignment (IA) being a revolutionary wireless transmission strategy that reduces the impact of interference seems well suited as a strategy that can be used to optimize the performance of Cooperative Spectrum Sensing. The idea of IA is to coordinate multiple transmitters so that their mutual interference aligns at their receivers, facilitating simple interference cancellation techniques. Since its inception, research efforts have primarily been focused on verifying IA's ability to achieve the maximum degrees of freedom (an approximation of sum capacity), developing algorithms for determining alignment solutions and designing transmission strategies that relax the need for perfect alignment but yield better performance. With the increased deployment of wireless services, CR's ability to opportunistically sense and access the unused licensed frequency spectrum, without causing harmful interference to the licensed users becomes increasingly diminished, making the concept of introducing IA in CR a very attractive proposition. For a multiuser multiple-input-multiple-output (MIMO) overlay CR network, a space-time opportunistic IA (ST-OIA) technique has been proposed that allows spectrum sharing between a single primary user (PU) and multiple secondary users (SU) while ensuring zero interference to the PUs. With local CSI available at both the transmitters and receivers of SUs, the PU employs a space-time WF (STWF) algorithm to optimize its transmission and in the process, frees up unused eigenmodes that can be exploited by the SU. STWF achieves higher performance than other WF algorithms at low to moderate signal-to-noise ratio (SNR) regimes, which makes it ideal for implementation in CR networks. The SUs align their transmitted signals in such a way their interference impairs only the PU's unused eigenmodes. For the multiple SUs to further exploit the benefits of Cooperative Spectrum Sensing, it was shown in this thesis that IA would only work when a set of conditions were met. The first condition ensures that the SUs satisfy a zero interference constraint at the PU's receiver by designing their post-processing matrices such that they are orthogonal to the received signal from the PU link. The second condition ensures a zero interference constraint at both the PU and SUs receivers i.e. the constraint ensures that no interference from the SU transmitters is present at the output of the post-processing matrices of its unintended receivers. The third condition caters for the multiple SUs scenario to ensure interference from multiple SUs are aligned along unused eigenmodes. The SU system is assumed to employ a time division multiple access (TDMA) system such that the Principle of Reciprocity is employed towards optimizing the SUs transmission rates. Since aligning multiple SU transmissions at the PU is always limited by availability of spatial dimensions as well as typical user loads, the third condition proposes a user selection algorithm by the fusion centre (FC), where the SUs are grouped into clusters based on their numbers (i.e. two SUs per cluster) and their proximity to the FC, so that they can be aligned at each PU-Rx. This converts the cognitive IA problem into an unconstrained standard IA problem for a general cognitive system. Given the fact that the optimal power allocation algorithms used to optimize the SUs transmission rates turns out to be an optimal beamformer with multiple eigenbeams, this work initially proposes combining the diversity gain property of STBC, the zero-forcing function of IA and beamforming to optimize the SUs transmission rates. However, this solution requires availability of CSI, and to eliminate the need for this, this work then combines the D-STBC scheme with optimal IA precoders (consisting of beamforming and zero-forcing) to maximize the SUs data rates.

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26

Bennis, M. (Mehdi). "Spectrum sharing for future mobile cellular systems." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514260582.

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Abstract Spectrum sharing has become a high priority research area over the past few years. The motivation behind this lies in the fact that the limited spectrum is currently inefficiently utilized. As recognized by the World radio communication conference (WRC)-07, the amount of identified spectrum is not large enough to support large bandwidths for a substantial number of operators. Therefore, it is paramount for future mobile cellular systems to share the frequency spectrum and coexist in a more efficient manner. The present dissertation deals with the problem of spectrum scarcity by examining spectrum sharing paradigms where a migration from fixed to flexible resource allocation is investigated. First, a radio resource management (RRM) architecture is proposed where advanced spectrum functionalities accounting for the short-term variations of the spectrum are examined. The achievable gains are shown in a multi-cell, multi-network environment with realistic traffic patterns from a European operator, enhancing thereby spectrum utilization. Second, inter-operator resource sharing in a broadband network is considered where a packet-based cellular network is developed. It is shown that the obtained gains in terms of quality-of-service (QoS), number of operators and different data rates requirements improve the overall efficiency of the network. Besides and in order to cope with the stringent data rate requirements, direct terminal-to-terminal (T2T) communication is examined in which a realistic algorithm is proposed advocating resource reuse in a cellular system with simultaneous communications between mobiles. Numerical results confirm the advantages of resource reuse in terms of throughput, average frame delays and power consumption. In this thesis, a proposal is made as how to enhance spectrum sharing. The concept of hierarchy is proposed in which wireless competitive operators share the same spectrum band. The decentralized hierarchical approach is shown to bridge the gap between the selfish and centralized approach. Interference avoidance is studied for point-to-point communication in a selforganized network where different optimal power allocation strategies are examined along with the impact of frequency reuse on the ergodic capacity of the network.

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27

Şahin, Mustafa Emin. "Towards the Realization of Cognitive Radio: Coexistence of Ultrawideband and Narrowband Systems." Scholar Commons, 2006. http://scholarcommons.usf.edu/etd/3817.

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Ultrawideband and cognitive radio are two of the most important approaches that are shaping the future of wireless communication systems. At a first glance, the aims of UWB and cognitive radio do not seem to be overlapping significantly, however, there is a strong synergy between the capabilities of UWB and the goals of cognitive radio. One of the objectives of this thesis is to shed the first light on the marriage of these two important approaches.Ultrawideband (UWB) is a promising technology for future short-range, high-data rate wireless communication networks. Along with its exciting features including achieving high data rates, low transmission power requirement, and immunity to multipath effects, UWB is unique in its coexistence capability with narrowband systems.In this thesis, the details of practical UWB implementation are provided. Regarding the coexistence of UWB with licensed narrowband systems, narrowband interference (NBI)avoidance and cancelation techniques in the literature are investigated. It is aimed to emphasize that UWB is a strong candidate for cognitive radio, and this fact is proven by providing two different approaches in which ultrawideband is combined with cognitive radio to maximize the performance of unlicensed communications.

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28

Barnes, Simon Daniel. "Cognitive radio performance optimisation through spectrum availability prediction." Diss., University of Pretoria, 2012. http://hdl.handle.net/2263/25908.

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The federal communications commission (FCC) has predicted that, under the current regulatory environment, a spectrum shortage may be faced in the near future. This impending spectrum shortage is in part due to a rapidly increasing demand for wireless services and in part due to inefficient usage of currently licensed bands. A new paradigm pertaining to wireless spectrum allocation, known as cognitive radio (CR), has been proposed as a potential solution to this problem. This dissertation seeks to contribute to research in the field of CR through an investigation into the effect that a primary user (PU) channel occupancy model will have on the performance of a secondary user (SU) in a CR network. The model assumes that PU channel occupancy can be described as a binary process and a two state Hidden Markov Model (HMM) was thus chosen for this investigation. Traditional algorithms for training the model were compared with certain evolutionary-based training algorithms in terms of their resulting prediction accuracy and computational complexity. The performance of this model is important since it provides SUs with a basis for channel switching and future channel allocations. A CR simulation platform was developed and the results gained illustrated the effect that the model had on channel switching and the subsequently achievable performance of a SU operating within a CR network. Performance with regard to achievable SU data throughput, PU disruption rate and SU power consumption, were examined for both theoretical test data as well as data obtained from real world spectrum measurements (taken in Pretoria, South Africa). The results show that a trade-off exists between the achievable SU throughput and the average PU disruption rate. Significant SU performance improvements were observed when prediction modelling was employed and it was found that the performance and complexity of the model were influenced by the algorithm employed to train it. SU performance was also affected by the length of the quick sensing interval employed. Results obtained from measured occupancy data were comparable with those obtained from theoretical occupancy data with an average percentage similarity score of 96% for prediction accuracy (using the Viterbi training algorithm), 90% for SU throughput, 83% for SU power consumption and 71% for PU disruption rate.
Dissertation (MEng)--University of Pretoria, 2012.
Electrical, Electronic and Computer Engineering
unrestricted

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29

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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30

Yenihayat, Guven. "Opportunistic Multiple Relaying In Wireless Ad Hoc Networks." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613334/index.pdf.

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Cooperative relaying systems aim to improve weak communication links by exploiting the spatial diversity obtained by the statistically independent channels between relays and the destination. In this thesis a cooperative relaying scheme called the Opportunistic Multiple Relaying (OMR) is proposed with its special receiver structure. Unlike most relaying schemes in the literature, multiple relay nodes are allowed to transmit in nonorthogonal channels in OMR without requiring any control overhead for relay coordination. OMR is compared to a benchmark scheme called the Selection Relaying (SR) in which the relay node is preselected by the source before transmission according to the average channel quality information. It is observed that OMR performs significantly better than SR in terms of error performance.

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31

Bellm, Tilo [Verfasser], Dubravko [Gutachter] Radić, and Thorsten [Gutachter] Posselt. "Potential Biases in Service Research - Opportunity and Pitfall / Tilo Bellm ; Gutachter: Dubravko Radić, Thorsten Posselt." Leipzig : Universitätsbibliothek Leipzig, 2014. http://d-nb.info/1238788173/34.

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32

Hamid, Mohamed. "On Finding Spectrum Opportunities in Cognitive Radios : Spectrum Sensing and Geo-locations Database." Licentiate thesis, KTH, Kommunikationssystem, CoS, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-110107.

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The spectacular growth in wireless services imposes scarcity in term of the available radio spectrum. A solution to overcome this scarcity is to adopt what so called cognitive radio based on dynamic spectrum access. With dynamic spectrum access, secondary (unlicensed) users can access spectrum owned by primary (licensed) users when it is temporally and/or geographically unused. This unused spectrum is termed as spectrum opportunity. Finding these spectrum opportunities related aspects are studied in this thesis where two approaches of finding spectrum opportunities, namely spectrum sensing and geo-locations databases are considered. In spectrum sensing arena, two topics are covered, blind spectrum sensing and sensing time and periodic sensing interval optimization. For blind spectrum sensing, a spectrum scanner based on maximum minimum eigenvalues detector and frequency domain rectangular filtering is developed. The measurements show that the proposed scanner outperforms the energy detector scanner in terms of the probability of detection. Continuing in blind spectrum sensing, a novel blind spectrum sensing technique based on discriminant analysis called spectrum discriminator has been developed in this thesis. Spectrum discriminator has been further developed to peel off multiple primary users with different transmission power from a wideband sensed spectrum. The spectrum discriminator performance is measured and compared with the maximum minimum eigenvalues detector in terms of the probability of false alarm, the probability of detection and the sensing time. For sensing time and periodic sensing interval optimization, a new approach that aims at maximizing the probability of right detection, the transmission efficiency and the captured opportunities is proposed and simulated. The proposed approach optimizes the sensing time and the periodic sensing interval iteratively. Additionally, the periodic sensing intervals for multiple channels are optimized to achieve as low sensing overhead and unexplored opportunities as possible for a multi channels system. The thesis considers radar bands and TV broadcasting bands to adopt geo-locations databases for spectrum opportunities. For radar bands, the possibility of spectrum sharing with secondary users in L, S and C bands is investigated. The simulation results show that band sharing is possible with more spectrum opportunities offered by C band than S and L band which comes as the least one. For the TV broadcasting bands, the thesis treats the power assignment for secondary users operate in Gävle area, Sweden. Furthermore, the interference that the TV transmitter would cause to the secondary users is measured in different locations in the same area.

QC 20130114

QUASAR

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33

Jung, Haejoon. "Experimentation and physical layer modeling for opportunistic large array-based networks." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51798.

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The objective of this dissertation is to better understand the impact of the range extension and interference effects of opportunistic large arrays (OLAs), in the context of cooperative routing in multi-hop ad hoc networks. OLAs are a type of concurrent cooperative transmission (CCT), in which the number and location of nodes that will participate in a particular CCT cannot be known a priori. The motivation of this research is that the previous CCT research simplifies or neglects significant issues that impact the CCT-based network performance. Therefore, to develop and design more efficient and realistic OLA-based protocols, we clarify and examine through experimentation and analysis the simplified or neglected characteristics of CCT, which should be considered in the network-level system design. The main contributions of this research are (i) intra-flow interference analysis and throughput optimization in both disk- and strip-shaped networks, for multi-packet OLA transmission, (ii) CCT link modeling focusing on path-loss disparity and link asymmetry, (iii) demonstration of CCT range-extension and OLA-based routing using a software-defined radio (SDR) test-bed, (iv) a new OLA-based routing protocol with practical error control algorithm. In the throughput optimization in presence of the intra-channel interference, we analyze the feasibility condition of spatially pipelined OLA transmissions using the same channel and present numerical results with various system parameters. In the CCT link model, we provide the impact of path-loss disparity that are inherent in a virtual multiple-input-single-output (VMISO) link and propose an approximate model to calculate outage rates in high signal-to-noise-ratio (SNR) regime. Moreover, we present why link asymmetry is relatively more severe in CCT compared to single-input-single-output (SISO) links. The experimental studies show actual measurement values of the CCT range extension and realistic performance evaluation of OLA-based routing. Lastly, OLA with primary route set-up (OLA-PRISE) is proposed with a practical route recovery technique.

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34

Zhang, Ruifeng. "Analyse du compromis énergie-délai pour les transmissions radio multi-sauts dans les réseaux de capteurs." Phd thesis, INSA de Lyon, 2009. http://tel.archives-ouvertes.fr/tel-00534833.

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Dans cette thèse, le compromis entre la consommation d'énergie et le délai dans les réseaux de capteurs sans fil est étudié en exploitant efficacement les liens non fiables. Nous proposons une métrique de l'efficacité énergétique et une métrique de délai moyenne qui sont combinés avec le modèle de lien radio à erreur. En utilisant ces deux métriques et un modèle réaliste de lien radio, nous déduisons la limite inférieure et le front de Pareto du compromis Energie-Délai sont calculés pour trois types de systèmes de communication: la communication multi-saut traditionnelle, la communication opportuniste et la communication coopérative MIMO (CMIMO) dans trois différents canaux: le canal a bruit additif blanc Gaussien, le canal a évanouissements rapides de Rayleigh et le canal a évanouissement de Rayleigh par blocs. Les expressions de ces limites faibles sont obtenues et vérifiées par des simulations bidimensionnelles de réseaux de capteurs distribués aléatoirement. Sur la base de l'expression de la borne inférieure du compromis Energie-Délai, un cadre multi-couche est fourni pour optimiser les paramètres des couches physique, MAC et routage sous contrainte de délai. Les résultats obtenus montrent que pour parvenir à une meilleure performance Energie-Délai, les mécanismes de communication suivants devraient être adoptés selon le type de canal : les communications multi-saut traditionnelles sont les plus performantes pour le canal à bruit additif blanc Gaussien, alors que les communications opportunistes le sont pour les canaux à évanouissements de Rayleigh par blocs et enfin le CMIMO pour les canaux à évanouissements rapides de Rayleigh.

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35

Gao, Bo. "Coexistence of Wireless Networks for Shared Spectrum Access." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/50525.

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The radio frequency spectrum is not being efficiently utilized partly due to the current policy of allocating the frequency bands to specific services and users. In opportunistic spectrum access (OSA), the ``white spaces'' that are not occupied by primary users (a.k.a. incumbent users) can be opportunistically utilized by secondary users. To achieve this, we need to solve two problems: (i) primary-secondary incumbent protection, i.e., prevention of harmful interference from secondary users to primary users; (ii) secondary-secondary network coexistence, i.e., mitigation of mutual interference among secondary users. The first problem has been addressed by spectrum sensing techniques in cognitive radio (CR) networks and geolocation database services in database-driven spectrum sharing. The second problem is the main focus of this dissertation. To obtain a clear picture of coexistence issues, we propose a taxonomy of heterogeneous coexistence mechanisms for shared spectrum access. Based on the taxonomy, we choose to focus on four typical coexistence scenarios in this dissertation. Firstly, we study sensing-based OSA, when secondary users are capable of employing the channel aggregation technique. However, channel aggregation is not always beneficial due to dynamic spectrum availability and limited radio capability. We propose a channel usage model to analyze the impact of both primary and secondary user behaviors on the efficiency of channel aggregation. Our simulation results show that user demands in both the frequency and time domains should be carefully chosen to minimize expected cumulative delay. Secondly, we study the coexistence of homogeneous CR networks, termed as self-coexistence, when co-channel networks do not rely on inter-network coordination. We propose an uplink soft frequency reuse technique to enable globally power-efficient and locally fair spectrum sharing. We frame the self-coexistence problem as a non-cooperative game, and design a local heuristic algorithm that achieves the Nash equilibrium in a distributed manner. Our simulation results show that the proposed technique is mostly near-optimal and improves self-coexistence in spectrum utilization, power consumption, and intra-cell fairness. Thirdly, we study the coexistence of heterogeneous CR networks, when co-channel networks use different air interface standards. We propose a credit-token-based spectrum etiquette framework that enables spectrum sharing via inter-network coordination. Specifically, we propose a game-auction coexistence framework, and prove that the framework is stable. Our simulation results show that the proposed framework always converges to a near-optimal distributed solution and improves coexistence fairness and spectrum utilization. Fourthly, we study database-driven OSA, when secondary users are mobile. The use of geolocation databases is inadequate in supporting location-aided spectrum sharing if the users are mobile. We propose a probabilistic coexistence framework that supports mobile users by locally adapting their location uncertainty levels in order to find an appropriate trade-off between interference mitigation effectiveness and location update cost. Our simulation results show that the proposed framework can determine and adapt the database query intervals of mobile users to achieve near-optimal interference mitigation with minimal location updates.
Ph. D.

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36

Soydan, Yusuf. "Cluster Based User Scheduling Schemes To Exploit Multiuser Diversity In Wireless Broadcast Channels." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609941/index.pdf.

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Diversity methods are used to improve the reliability of the communication between transmitter and receiver. These methods use redundancy to reduce the errors in the communication link. Apart from the conventional diversity methods, multiuser diversity has an aim of maximizing the sum capacity of a multi-user system. To benefit from multiuser diversity, the opportunistic scheduling method grants the channel access to the user which has the best channel quality among all users. Therefore, the cumulative sum of the information sent to all users, which is the sum capacity, is maximized in the long term. Although the opportunistic scheduling maximizes the sum capacity, it has some drawbacks such as the feedback load growing with the number of users and the problem of fairness for the users which may have lower channel quality than some other users. In this thesis, these two issues are investigated for the broadcast channels. Feedback quantization, which gives partial information on the channel state, is studied to mitigate the feedback load with a goal of little loss in the sum capacity. The thresholds for the finite feedback quantization are determined to provide fairness and to reduce the feedback load at the same time. To provide fairness, users are grouped into clusters and thresholds are optimized for each cluster. A method is proposed by extending the one given by Floren et. al. to solve the mentioned problems and the proposed method is compared with some other scheduling methods in the literature.

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37

Rebecchi, Filippo. "Délestage de données en D2D : de la modélisation à la mise en oeuvre." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066234/document.

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Le trafic mobile global atteindra 24,3 exa-octets en 2019. Accueillir cette croissance dans les réseaux d’accès radio devient un véritable casse-tête. Nous porterons donc toute notre attention sur l'une des solutions à ce problème : le délestage (offloading) grâce à des communications de dispositif à dispositif (D2D). Notre première contribution est DROiD, une stratégie qui exploite la disponibilité de l'infrastructure cellulaire comme un canal de retour afin de suivre l'évolution de la diffusion d’un contenu. DROiD s’adapte au rythme de la diffusion, permettant d'économiser une quantité élevée de données cellulaires, même dans le cas de contraintes de réception très serrées. Ensuite, nous mettons l'accent sur les gains que les communications D2D pourraient apporter si elles étaient couplées avec les transmissions multicast. Par l’utilisation équilibrée d'un mix de multicast, et de communications D2D, nous pouvons améliorer, à la fois, l'efficacité spectrale ainsi que la charge du réseau. Afin de permettre l’adaptation aux conditions réelles, nous élaborons une stratégie d'apprentissage basée sur l'algorithme dit ‘’bandit manchot’’ pour identifier la meilleure combinaison de communications multicast et D2D. Enfin, nous mettrons en avant des modèles de coûts pour les opérateurs, désireux de récompenser les utilisateurs qui coopèrent dans le délestage D2D. Nous proposons, pour cela, de séparer la notion de seeders (utilisateurs qui transportent contenu, mais ne le distribuent pas) et de forwarders (utilisateurs qui sont chargés de distribuer le contenu). Avec l'aide d’un outil analytique basée sur le principe maximal de Pontryagin, nous développons une stratégie optimale de délestage
Mobile data traffic is expected to reach 24.3 exabytes by 2019. Accommodating this growth in a traditional way would require major investments in the radio access network. In this thesis, we turn our attention to an unconventional solution: mobile data offloading through device-to-device (D2D) communications. Our first contribution is DROiD, an offloading strategy that exploits the availability of the cellular infrastructure as a feedback channel. DROiD adapts the injection strategy to the pace of the dissemination, resulting at the same time reactive and relatively simple, allowing to save a relevant amount of data traffic even in the case of tight delivery delay constraints.Then, we shift the focus to the gains that D2D communications could bring if coupled with multicast wireless networks. We demonstrate that by employing a wise balance of multicast and D2D communications we can improve both the spectral efficiency and the load in cellular networks. In order to let the network adapt to current conditions, we devise a learning strategy based on the multi-armed bandit algorithm to identify the best mix of multicast and D2D communications. Finally, we investigate the cost models for operators wanting to reward users who cooperate in D2D offloading. We propose separating the notion of seeders (users that carry content but do not distribute it) and forwarders (users that are tasked to distribute content). With the aid of the analytic framework based on Pontryagin's Maximum Principle, we develop an optimal offloading strategy. Results provide us with an insight on the interactions between seeders, forwarders, and the evolution of data dissemination

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Huschens, Stefan. "Chance (odd) versus Wahrscheinlichkeit (probability)." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-222552.

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Der Zusammenhang zwischen den Begriffen "Chance" (odd) und "Wahrscheinlichkeit" (probability) und die Anwendung des Chancenverhältnisses (odds ratio) im Bereich der Biometrie und bei der logistischen Regression werden erläutert. Es wird auf mögliche Fehlinterpretationen der Begriffe Chance und Chancenverhältnis hingewiesen.

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Sahin, Mustafa. "Baseband receiver algorithms for 4G co-channel femtocells." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0003283.

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Cheng, Yu-Chun, and 鄭宇淳. "Opportunistic Transmission Schemes for Cognitive Radio Systems." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/60458350552734332723.

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博士
國立臺灣大學
資訊工程學研究所
100
With the increasing of wireless in this dissertation, Radio spectrum is a kind of limited natural resource as well as water and crude oil. Its use is licensed and assigned by governmental agencies. However, according to the statistics of the Federal Communications Commission (FCC), temporal and geographical variations in the utilization of the assigned spectrum range from 15% to 85%. The temporally unused spectrum is referred to as spectrum hole or white space. A new wireless technology called Cognitive Radio (CR) is introduced to reduce the waste of spectrum resources. CR system dynamically accesses the spectrums to improve overall spectrum usage of frequency bands. However, the access of unlicensed users to licensed spectrums causes interference to the licensed users on the bands. Therefore, the key of CR design is to improving overall spectrum usage in the constraint of avoiding harmful interference to the licensed users. To achieve our CR design, we focus on the following challenges. In the MAC layer, we have: (1) To control CR users’ traffic and channel selection for avoiding interference to licensed users. (2) To achieve fairness between heterogeneous users in different CR systems In the TCP layer, we have: (3) To analysis and solve the impact of CR link to TCP layer In this dissertation, we develop efficient CR MAC and TCP protocols to improve spectrum utilization. To th first problem, we present two functions: RTS-CTS-CRTS handshaking and active traffic control mechanisms. The RTS-CTS-CRTS handshake mechanism can select a channel with better transmission quality. Then, the active traffic control mechanism is used to control the amount of DATA packets transmitted on the selected channel. We analysis the problem and solution by Markov chains and simulate by NS2. To the second problem, we study two fairness issues: uncoordinated of PU-detection ability and uncoordinated of spectrum unit size. We propose several Markov-chain models to study the potential unfairness problems. The proposed solution is a jamming-based MAC-layer approach, called probing function, to enhance PU-detection ability and fairness feature. A MAC protocol, called CCR-MAC, is proposed based on the combination of probing function and our previous work on CR MAC to avoid hardware limitation and protect PU’s traffic at the same time. To problem (3), we verify the ineffectiveness of WTCP in CR environment by NS2 simulation. Afterward, we analysis the cause of throughput decay conditions and concluding them into three events: PU-Interference Loss, Mild-Congestion and RTT-Variance events. To improve TCP throughput, three event handlers are proposed: PU-Interference handler, Faster-Recovery mechanism and RTT-Adjustment function. By applying the three handlers, a cognitive TCP that adapting CR environment, called CR-TCP, is proposed. The results show that CR-TCP improve throughput over 50% in both stable and varying environment while WTCP solutions only improve 10% to TCP-Reno.

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Lin, Shih-Chun, and 林士鈞. "Spectrum Aware Opportunistic Routing in Cognitive Radio Networks." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/02341403129569644959.

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碩士
臺灣大學
電信工程學研究所
98
Cognitive radio (CR) emerges as a key technology to enhance spectrum efficiency and thus creates opportunistic transmissions over communication links. Supporting the routing function on top of numerous opportunistic links is a must to route packets in a general cognitive radio network (CRN) consisting of multi-radio systems. However, there lacks complete understanding of these highly dynamic available links and a reliable end-to-end transportation mechanism over CRN. Aspiring to meet this need, in this thesis, we propose novel spectrum aware opportunistic routing (SAOR) algorithm suited for the CRN under wireless fading channels. With innovative establishment of the spectrum map from local sensing information and the derivation of the routing metric for opportunistic links known as opportunistic link transmission (OLT), the opportunistic path metrics, and the CR node metrics, the promising SAOR employs a cooperative scheme to enable multi-path transmissions and maintains the dual-scale QoS guaranteed throughput (i.e. opportunistic QoS guaranteed throughput and statistical QoS guaranteed throughput) for practical applications. Results in performance evaluation confirm that SAOR enjoys less delay with guaranteed throughput, not only in CRN, but also in general wireless network.

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Luís, Nuno Miguel Abreu. "Medium access control design for distributed opportunistic radio networks." Doctoral thesis, 2015. http://hdl.handle.net/10362/16564.

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Existing wireless networks are characterized by a fixed spectrum assignment policy. However, the scarcity of available spectrum and its inefficient usage demands for a new communication paradigm to exploit the existing spectrum opportunistically. Future Cognitive Radio (CR) devices should be able to sense unoccupied spectrum and will allow the deployment of real opportunistic networks. Still, traditional Physical (PHY) and Medium Access Control (MAC) protocols are not suitable for this new type of networks because they are optimized to operate over fixed assigned frequency bands. Therefore, novel PHY-MAC cross-layer protocols should be developed to cope with the specific features of opportunistic networks. This thesis is mainly focused on the design and evaluation of MAC protocols for Decentralized Cognitive Radio Networks (DCRNs). It starts with a characterization of the spectrum sensing framework based on the Energy-Based Sensing (EBS) technique considering multiple scenarios. Then, guided by the sensing results obtained by the aforementioned technique, we present two novel decentralized CR MAC schemes: the first one designed to operate in single-channel scenarios and the second one to be used in multichannel scenarios. Analytical models for the network goodput, packet service time and individual transmission probability are derived and used to compute the performance of both protocols. Simulation results assess the accuracy of the analytical models as well as the benefits of the proposed CR MAC schemes.

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Adriman, Ramzi, and Ramzi Adriman. "PERFORMANCE ANALYSES OF OPPORTUNISTIC SPECTRUM ACCESS IN COGNITIVE RADIO NETWORK." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/90043481529484181710.

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博士
亞洲大學
資訊工程學系
103
This thesis studies the performance analysis of opportunistic spectrum access (OSA) with imperfect sensing, spectrum backup channels (BCs), and prediction scheme for cognitive radio networks (CRN). The studies have organized in to three works. At first work we study the performance of an opportunistic spectrum access (OSA) system with a general number of channels and imperfect spectrum sensing. The system is modeled as a two-dimensional continuous-time Markov chain. We specify the state-dependent transition rates due to imperfect sensing for the general channel number case by using simple recursive functions. For performance metrics, we consider blocking probability, termination probability and success probability for each type of users. On second work, we study the performance of cognitive radio networks with imperfect spectrum sensing and backup channels (BCs). In case an SU is blocked from PCs, it then checks the BCs to find a free one. The system is modeled as a three-dimensional continuous-time Markov chain. We specify the state-dependent transition rates due to imperfect sensing by simple recursive functions. On the last work we propose a hidden Markov model (HMM) with state prediction for opportunistic spectrum access (OSA) in cognitive radio (CR) networks. In contrast to the traditional scheme relying only on channel sensing for exploring spectrum opportunities, the proposed prediction scheme takes advantage of state prediction, channel sensing, and acknowledgments (ACKs) from the receiver in an attempt to maximize the utility. We impose some constraints on the system parameters and derive thresholds by which we can specify the optimal action. We then conduct simulations to compare the performance of the prediction scheme to that of the traditional scheme. Keyword: Opportunistic Spectrum Access, cognitive radio network, imperfect sensing, backup channel, prediction scheme, recursive function, two dimensional Markov, Three dimensional Markov, hidden Markov model.

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Chao, Li-Hua, and 趙梨華. "Joint Spectrum Allocation and Transmission Opportunity for Cognitive Radio Networks." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/21191417189356437377.

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碩士
國立交通大學
資訊科學與工程研究所
99
There are three main operator types and research subjects in cognitive radio systems, consisting of software define radio (SDR), channel sensing and channel management. In this paper, we focus on a channel-sensing and accessing and a synchronized channel-sensing and accessing for cognitive radio users in IEEE 802.11 wireless networks is proposed. The mechanism consists of two phases: fast channel sensing and channel vacating. A pair of cognitive radio users can search an available channel with the most success transmission probability from those available channels presently and further proceed to transmit data by fast channel sensing time-efficiently; proactive channel vacating is for the pair of cognitive radio users to be aware of the presence of primary users and vacate the occupied channel as quick as possible. We utilize the concept of channel hopping to reduce the average channel sensing time of cognitive radio users. Besides, we propose one equation to decide how to set TXQ (the bounded time interval during which a CR user can send as many frames as possible) by PU traffic load and make the caused interference to primary users within tolerable range. We further evaluate the performance of a considered cognitive radio network through simulations. From the simulation results, our proposed protocol can efficiently balance the tradeoff between throughput performance of a cognitive radio network and waiting time of primary users.

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Ozdemir, Ozgur. "Opportunistic multiple antenna systems with partial channel knowledge and limited feedback /." 2007. http://proquest.umi.com/pqdweb?did=1296105631&sid=3&Fmt=2&clientId=10361&RQT=309&VName=PQD.

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Cheng, Yu-Shin, and 鄭鈺新. "Opportunistic Cognitive Radio based on Direction of Arrival Estimation with Prototyping." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/48536182449387752827.

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碩士
國立清華大學
通訊工程研究所
101
In the future world, we require higher QoS in communication systems. How to imporve QoS efficiently with limited bandwidth has become an important issue. Recently, the concept of cognitive radio has emerged and is regard this as a solution to the limitation of bandwidth. There are cognitive users(CRs) and primary users(PUs) in a cognitive radio system.In this thesis, two kinds of users are in different communication system i.e. Digital TV and mobile system. Generally, two different communication systems need two different frequency bands for these two different systems so that we need lots of bandwidth to support them. However, in cognitive radio system these two systems can use the same frquency band as long as CRs will not cause interference to PUs. To null the interference, we used to adopt Transmit Beamforming technology with full CSI, but we cannot obtain full CSI in Cognitive Radio system since PUs and CRs are two different systems. In this thesis, we construct a Cognitive Radio system with Transmit Beamforming to reduce the interference between CRs to PUs with only DOA information without full Channel State Information(CSI). At first, MUSIC estimation algorithm is applied to estimate the Direction of Arrivals(DOAs), and then we utilize this space information to apply Transmit Beamforming. Moreover, KR-MUSIC algorithm is applied to alleviate the constraint that the number of antenna is less than the number of DOAs. The accuracy of our DOA estimation algorithm is shown by simulation, and then we verify Transmit Beamforming can indeed reduce the interference to PUs so that the BER would be lower. After verifying with simulation, in this thesis we have constructed a real-time Cognivive Radio system with Universal Software Radio Peripheral(USRP) and demonstrate its performance.

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Fazeli, Dehkordy Siavash. "Adaptive Sensing Strategies for Opportunistic Spectrum Access." Thesis, 2013. http://hdl.handle.net/1807/35819.

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To meet the ever increasing spectrum demand, developing a mechanism for dynamic spectrum access seems inevitable. Spectrum sensing enables cognitive radios (CRs) to identify and use frequency bands (channels) that are not being used by primary users (PUs) at a particular place and time. However, sensing errors and limited sensing resources, such as sensing hardware and sensing time, introduce significant technical challenges to the development of such an ideal capability. Adaptive sensing strategies allow the sensing resources to be spent on more promising primary channels. This is achieved by exploiting past sensing outcomes of one secondary user (SU), or, as proposed in this research, multiple spatially distributed SUs. We propose adaptive sensing strategies for three different scenarios. First, we assume that a SU sequentially senses a number of primary channels to find the first available channel. We propose a two-stage spectrum detection strategy that allows the spectrum detector to quickly detect and skip though most of busy channels and spend most of its time on channels that are more likely to be idle. Second, we consider the case where multiple SUs jointly try to locate idle channels within a given sensing time, which itself is divided into a number of sensing slots. We propose a cooperative spectrum search strategy that specifies the channel to be sensed by each SU in each slot in such a way to maximize the expected number of identified idle channels. Third, we consider a primary network that operates in a synchronous time-framed fashion. We assume that the occupancy state of each primary channel over different time frames follows a discrete-time Markov process. We propose a cooperative sensing strategy that decides which channel should be sensed by which SU in each frame. The goal is to maximize a utility function that accounts for both the number of detected idle channel-frames and the number of miss-detected busy channel-frames. We present analytical and numerical results to demonstrate the effectiveness of the proposed sensing strategies in increasing identified time-frequency spectrum opportunities and/or reducing interference with licensed systems.

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Hsieh, Yi-Wen, and 謝禕文. "The Competitive Opportunity of the Radio Frequency Identification Industry in Taiwan." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/59128311866513931511.

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碩士
國立交通大學
科技管理研究所
93
Wireless communications technology has been growing rapidly in wide area mobile communication, wireless local area network (WLAN) and personal area network (PAN). In addition, Radio Frequency Identification (RFID), which puts emphasis on low cost, small size, and low battery consumption, has begun to develop recently. America and Japan are pushing for their own RFID standards to be accepted to become international RFID standards. China also proposed its domestic RFID standard in an attempt to secure Chinese RFID market. Low cost IC fabrication is Taiwan’s core competence in the global RFID value chain. This thesis analyzed the current situation and development trend of RFID in America, Japan, China, and Taiwan. Porter’s Diamond Model, the Industry Value Chain Analysis Model, and the Six Forces Analysis Model were used to analyze the competitiveness and opportunities of Taiwan’s RFID industry. Government support is essential for the success of RFID in Taiwan.

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Alvarenga, Chu Sofia Cristina. "A Model for Bursty Traffic and Its Impact on the Study of Cognitive Radio Networks." 2012. http://hdl.handle.net/1993/8127.

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In this thesis, we investigate the impact of channels that have a bursty nature in a cognitive radio network scenario. Our goal is to design a general channel usage model that can handle bursty primary user channel usage. The proposed model describes idle periods with a discrete platoon arrival process and describes busy periods with a discrete phase type distribution. The performance of the proposed model is compared with two more traditionally encountered channel usage models in three different secondary user access schemes. First, we design a reactive access scheme to show the poor performance results an in- vestigator can potentially obtain when ignoring bursty data traffic. We have also analyzed two proactive secondary network access schemes. Numerical results show that the achiev- able utilization and interference probability of the network are affected when traditional channel models are used in a bursty PU channel.

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Su, Hang. "Design and Analysis of Opportunistic MAC Protocols for Cognitive Radio Wireless Networks." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8943.

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As more and more wireless applications/services emerge in the market, the already heavily crowded radio spectrum becomes much scarcer. Meanwhile, however,as it is reported in the recent literature, there is a large amount of radio spectrum that is under-utilized. This motivates the concept of cognitive radio wireless networks that allow the unlicensed secondary-users (SUs) to dynamically use the vacant radio spectrum which is not being used by the licensed primary-users (PUs). In this dissertation, we investigate protocol design for both the synchronous and asynchronous cognitive radio networks with emphasis on the medium access control (MAC) layer. We propose various spectrum sharing schemes, opportunistic packet scheduling schemes, and spectrum sensing schemes in the MAC and physical (PHY) layers for different types of cognitive radio networks, allowing the SUs to opportunistically utilize the licensed spectrum while confining the level of interference to the range the PUs can tolerate. First, we propose the cross-layer based multi-channel MAC protocol, which integrates the cooperative spectrum sensing at PHY layer and the interweave-based spectrum access at MAC layer, for the synchronous cognitive radio networks. Second, we propose the channel-hopping based single-transceiver MAC protocol for the hardware-constrained synchronous cognitive radio networks, under which the SUs can identify and exploit the vacant channels by dynamically switching across the licensed channels with their distinct channel-hopping sequences. Third, we propose the opportunistic multi-channel MAC protocol with the two-threshold sequential spectrum sensing algorithm for asynchronous cognitive radio networks. Fourth, by combining the interweave and underlay spectrum sharing modes, we propose the adaptive spectrum sharing scheme for code division multiple access (CDMA) based cognitive MAC in the uplink communications over the asynchronous cognitive radio networks, where the PUs may have different types of channel usage patterns. Finally, we develop a packet scheduling scheme for the PU MAC protocol in the context of time division multiple access (TDMA)-based cognitive radio wireless networks, which is designed to operate friendly towards the SUs in terms of the vacant-channel probability. We also develop various analytical models, including the Markov chain models, M=GY =1 queuing models, cross-layer optimization models, etc., to rigorously analyze the performance of our proposed MAC protocols in terms of aggregate throughput, access delay, and packet drop rate for both the saturation network case and non-saturation network case. In addition, we conducted extensive simulations to validate our analytical models and evaluate our proposed MAC protocols/schemes. Both the numerical and simulation results show that our proposed MAC protocols/schemes can significantly improve the spectrum utilization efficiency of wireless networks.

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Dissertations / Theses on the topic 'Radio opportuniste'

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