Philosophiae Doctor - PhD / Wireless sensor networks (WSNs) have become a popular research area that is widely gaining the attraction from both the research and the practitioner communities due to their wide area of applications. These applications include real-time sensing for audio delivery, imaging, video streaming, and remote monitoring with positive impact in many fields such as precision agriculture, ubiquitous healthcare, environment protection, smart cities and many other fields. While WSNs are aimed to constantly handle more intricate functions such as intelligent computation, automatic transmissions, and in-network processing, such capabilities are constrained by their limited processing capability and memory footprint as well as the need for the sensor batteries to be cautiously consumed in order to extend their lifetime. This thesis revisits the issue of the energy efficiency in sensor networks by proposing a novel clustering approach for routing the sensor readings in wireless sensor networks. The main contribution of this dissertation is to 1) propose corrective measures to the traditional energy model adopted in current sensor networks simulations that erroneously discount both the role played by each node, the sensor node capability and fabric and 2) apply these measures to a novel hierarchical routing architecture aiming at maximizing sensor networks lifetime. We propose three energy models for sensor network: a) a service-aware model that account for the specific role played by each node in a sensor network b) a sensor-aware model and c) load-balancing energy model that accounts for the sensor node fabric and its energy footprint. These three models are complemented by a load-balancing model structured to balance energy consumption on the network of cluster heads that forms the backbone for any cluster-based hierarchical sensor network. We present two novel approaches for clustering the nodes of a hierarchical sensor network: a) a distance-aware clustering where nodes are clustered based on their distance and the residual energy and b) a service-aware clustering where the nodes of a sensor network are clustered according to their service offered to the network and their residual energy. These approaches are implemented into a family of routing protocols referred to as EOCIT (Energy Optimization using Clustering Techniques) which combines sensor node energy location and service awareness to achieve good network performance. Finally, building upon the Ant Colony Optimization System (ACS), Multipath Routing protocol based on Ant Colony Optimization approach for Wireless Sensor Networks (MRACO) is proposed as a novel multipath routing protocol that finds energy efficient routing paths for sensor readings dissemination from the cluster heads to the sink/base station of a hierarchical sensor network. Our simulation results reveal the relative efficiency of the newly proposed approaches compared to selected related routing protocols in terms of sensor network lifetime maximization.

A presente tese de doutorado propõe uma arquitetura de cloud broker para ambientes de computação em nuvem híbrida. Um cloud broker tem o objetivo de executar a mediação entre clientes e provedores, recebendo requisições dos clientes e encaminhando-as ao serviço do provedor que melhor se adaptar aos requisitos de qualidade de serviço (QoS) solicitados. A arquitetura de broker de serviços com QoS proposta denomina-se QBroker, características de implementação de seu modo de operação bem como sua interação com os recursos virtuais de um ambiente de nuvem são apresentadas. O modelo de nuvem considerado foi o de nuvem híbrida com uma caracterização de arquitetura orientada a serviços (SOA) na qual serviços remotos são disponibilizados aos clientes. A política de escalonamento de tarefas desenvolvida para o QBroker foi a de intermediação de serviços, considerando tratativas de QoS, diferenciação das instâncias de serviços (SOA) e alocação dinâmica de serviços. Além disso, toda a caracterização do modo de operação do QBroker foi baseada no conceito de intermediação do modelo de referência de nuvem do NIST. O componente QBroker foi introduzido numa arquitetura de computação em nuvem BEQoS (Bursty Energy and Quality of Service), desenvolvida no Laboratório de Sistemas Distribuídos e Programação Concorrente do ICMC-USP de São Carlos. Avaliações de desempenho para a implementação da arquitetura QBroker foram conduzidas por meio de programas de simulação com uso da API do simulador CloudSim e da arquitetura CloudSim-BEQoS. Três cenários experimentais foram avaliados e, segundo a análise de resultados efetuada, foi possível validar que as características arquiteturais implementadas no QBroker resultaram em significativo impacto nas variáveis de resposta consideradas. Assim, foi possível comprovar que o uso do QBroker como mecanismo de mediação em ambientes de nuvem híbrida com SOA promoveu ganhos em desempenho para o sistema de nuvem e permitiu melhoria na qualidade dos serviços oferecidos. / This doctoral thesis proposes a cloud broker architecture for hybrid cloud computing environments. A cloud broker aims to perform mediation between clients and providers, receiving customer requests and forwarding them to the service provider that best suits the requested QoS requirements. The broker architecture services with QoS proposal is called QBroker. Implementation features of its mode of operation as well as its interaction with the virtual resources from a cloud environment are presented. The cloud deployment model was considered a hybrid cloud with a characterization of service-oriented architecture (SOA) in which remote services are available to customers. The task scheduling policy developed for QBroker was the intermediation of services, considering negotiations of QoS, differentiation of services instances and dynamic allocation of services. Moreover, the entire characterization of QBroker operation mode is based on the intermediation concept of the NIST cloud reference model. The QBroker component was introduced into a cloud computing architecture BEQoS (Bursty, Energy and Quality of Service), developed in the Laboratory of Distributed Systems and Concurrent Programming at ICMC-USP. Performance evaluations analysis the of results of QBroker architecture were conducted through simulation programs using the CloudSim simulator API and CloudSim-BEQoS architecture. Three experimental scenarios were evaluated and, according to analysis of the results, it was possible to validate that the architectural features implemented in QBroker resulted in significant impact on response variables considered. Thus, it was possible to prove that the use of QBroker as mediation mechanism in hybrid cloud environments with SOA promoted performance gains for the cloud system and allowed improvement in the quality of services offered.

A presente tese de doutorado propõe uma arquitetura de cloud broker para ambientes de computação em nuvem híbrida. Um cloud broker tem o objetivo de executar a mediação entre clientes e provedores, recebendo requisições dos clientes e encaminhando-as ao serviço do provedor que melhor se adaptar aos requisitos de qualidade de serviço (QoS) solicitados. A arquitetura de broker de serviços com QoS proposta denomina-se QBroker, características de implementação de seu modo de operação bem como sua interação com os recursos virtuais de um ambiente de nuvem são apresentadas. O modelo de nuvem considerado foi o de nuvem híbrida com uma caracterização de arquitetura orientada a serviços (SOA) na qual serviços remotos são disponibilizados aos clientes. A política de escalonamento de tarefas desenvolvida para o QBroker foi a de intermediação de serviços, considerando tratativas de QoS, diferenciação das instâncias de serviços (SOA) e alocação dinâmica de serviços. Além disso, toda a caracterização do modo de operação do QBroker foi baseada no conceito de intermediação do modelo de referência de nuvem do NIST. O componente QBroker foi introduzido numa arquitetura de computação em nuvem BEQoS (Bursty Energy and Quality of Service), desenvolvida no Laboratório de Sistemas Distribuídos e Programação Concorrente do ICMC-USP de São Carlos. Avaliações de desempenho para a implementação da arquitetura QBroker foram conduzidas por meio de programas de simulação com uso da API do simulador CloudSim e da arquitetura CloudSim-BEQoS. Três cenários experimentais foram avaliados e, segundo a análise de resultados efetuada, foi possível validar que as características arquiteturais implementadas no QBroker resultaram em significativo impacto nas variáveis de resposta consideradas. Assim, foi possível comprovar que o uso do QBroker como mecanismo de mediação em ambientes de nuvem híbrida com SOA promoveu ganhos em desempenho para o sistema de nuvem e permitiu melhoria na qualidade dos serviços oferecidos. / This doctoral thesis proposes a cloud broker architecture for hybrid cloud computing environments. A cloud broker aims to perform mediation between clients and providers, receiving customer requests and forwarding them to the service provider that best suits the requested QoS requirements. The broker architecture services with QoS proposal is called QBroker. Implementation features of its mode of operation as well as its interaction with the virtual resources from a cloud environment are presented. The cloud deployment model was considered a hybrid cloud with a characterization of service-oriented architecture (SOA) in which remote services are available to customers. The task scheduling policy developed for QBroker was the intermediation of services, considering negotiations of QoS, differentiation of services instances and dynamic allocation of services. Moreover, the entire characterization of QBroker operation mode is based on the intermediation concept of the NIST cloud reference model. The QBroker component was introduced into a cloud computing architecture BEQoS (Bursty, Energy and Quality of Service), developed in the Laboratory of Distributed Systems and Concurrent Programming at ICMC-USP. Performance evaluations analysis the of results of QBroker architecture were conducted through simulation programs using the CloudSim simulator API and CloudSim-BEQoS architecture. Three experimental scenarios were evaluated and, according to analysis of the results, it was possible to validate that the architectural features implemented in QBroker resulted in significant impact on response variables considered. Thus, it was possible to prove that the use of QBroker as mediation mechanism in hybrid cloud environments with SOA promoted performance gains for the cloud system and allowed improvement in the quality of services offered.

This dissertation contributes to the literature and current discussions on the European postal markets and the universal service obligations (USO). It consists of three independent chapters.<p><p>In chapter one, we investigate the consumers' preferences for various kinds of postal services. As such, we begin by reviewing the market and regulatory conditions for Europe and for our case study, Belgium. Then using data provided by the incumbent provider, the Belgian post (Bpost), we estimate demand price elasticities. The data comprises customer transactional information on letter mail, direct mail, parcels & express services, press delivery and value added services for the 2008-2009 period. These categories constitute not only the important lines of services that Bpost offers to its clients but also the main segments that constitute the whole Belgian postal market. As such, and using standard methods, we estimate for each service an equation that explains demand by prices, product varieties (i.e. mixes or combinations of volume, weight, priority and destination, inter alia), income, regulation proxies and other socioeconomic variables. The estimated price elasticities for regulated and partially regulated services are around -1.1, whereas for unregulated segments they fluctuate between -2.1 and -2.8. The lowest price elasticity is obtained for direct mail services (-1.0); the highest ones are associated with value added services (-2.1) and registered mail (-3.3). Price elasticities may be influenced by the cyclical effects during the period of analysis. Therefore, elasticities are higher when compared with the empirical evidence obtained for other countries and through the various methodologies applied over the last decades. The fact that technological substitutes, such as expenditures on telephony and internet access for daily and administrative mail services and, radio and television advertising for direct mail services, could not be accounted for (because there were no data available) may however be considered as a major limitation for the scope of our results. <p><p>In the second chapter, we explore theoretically the effects of the USO on unregulated markets. In particular, we are interested in investigating its welfare effects when the provision of services cannot be technologically separated. We present a model in which there is an incumbent who provides two services: a universal service and a non-USO service, the latter opened to competition. This is the case of letter mail and direct (or bulk) mail, services which have quite different purposes and regulatory frameworks (i.e. the former is fully regulated whereas the latter is liberalized under the current European Internal Market framework), but are jointly produce at some stages of the postal value chain. The USO is simplified to two dimensions, affordability and quality, implemented as a price cap and a minimum quality standard (MQS) for the provision of letter mail services. The latter involves the technological aspects that we are interested in. We find that the definition of the USO plays an important role in organizing markets that are open to competition. When it imposes few quality requirements (low MQS), the incumbent is not cost efficient enough to provide the high-quality variant of bulk mail, allowing its competitors to cream-skim the segment. However, because there are cost economies, the firm's participation in the segment yields a higher average quality of mail services at lower prices. When the USO is too comprehensive (high MQS), the incumbent exhibits large cost economies that ensure a dominant position in the provision of bulk mail services. Consumers are worse off as competition induces too much service differentiation in order to make profitable the provision. Relaxing the definition of the USO mitigates the competitive advantage of the USP and so, yields improvements in welfare. In the absence of access costs, firms will find profitable to participate in the bulk mail segment. However, foreclosure happens if the USO induces the incumbent to exhibit significant fixed costs. Therefore, the USP may end up as the sole supplier of bulk mail services if the definition of the USO imposes too many quality requirements (high MQS). In that case, the authority must balance the welfare gains of defining USO with the welfare losses of the consumers of the contested service. <p><p>Finally, in the third chapter we consider the ownership aspect of the provision of universal services as an incentive to introduce competition. One can further segment the provision between services for customers located in high-cost areas and services for customers located in low-cost areas. Additionally, under the current EU legislation, the supply is divided between upstream activities (e.g. collection and sorting) and downstream activities (i.e. delivery). The provision of upstream activities in high-cost areas remains in hands of the incumbent firm or the owner of the downstream (delivery) network. The upstream provision in low-cost areas is open to competition, but a retailer may be vertically integrated/separated or legally unbundled with the downstream firm. Legal unbundling means, in our model, that the downstream firm and one upstream firm located in the low-cost area belong legally to the same entity entitled to all profits, whom does not have full control rights over the firms' decisions. That is to say, upstream activities and the downstream services will be managed separately under the same ownership. In this framework we analyze the firm's boundaries in terms of competition development and welfare. We implement two criteria to answer questions like, does vertical separation promotes competition (entry of firms) while covers a larger demand than vertical integration? Does vertical integration demand less public funds to cover demand? Does legal unbundling is worse than ownership separation to promote competition? The first criterion is the probability of entry (of the potential upstream firm), which we determine for each modes of ownership. The second criterion is the cost of public funds. It is implemented by defining a loss function as the difference between the expected consumer surplus when the downstream firm chooses an access fee that maximizes its profits and the consumer surplus when access is priced at marginal cost. The use of both criteria let us conclude that efficient entry occurs when the downstream firm is vertically separated or legally unbundled of the retailer providing services in the low-cost area. However, it is under legal unbundling that the access charge takes its lowest value. The highest cost of public transfers is obtained when firms are vertically separated, but the lowest one is attained when firms are legally unbundled. Therefore legal unbundling constitutes the preferred organizational form to induce competition and to reduce the cost of public funds. / Doctorat en Sciences économiques et de gestion / info:eu-repo/semantics/nonPublished

Depuis quelques années, la recherche dans le domaine des réseaux maillés sans fil ("Wireless Mesh Network (WMN)" en anglais) suscite un grand intérêt auprès de la communauté des chercheurs en télécommunications. Ceci est dû aux nombreux avantages que la technologie WMN offre, telles que l'installation facile et peu coûteuse, la connectivité fiable et l'interopérabilité flexible avec d'autres réseaux existants (réseaux Wi-Fi, réseaux WiMax, réseaux cellulaires, réseaux de capteurs, etc.). Cependant, plusieurs problèmes restent encore à résoudre comme le passage à l'échelle, la sécurité, la qualité de service (QdS), la gestion des ressources, etc. Ces problèmes persistent pour les WMNs, d'autant plus que le nombre des utilisateurs va en se multipliant. Il faut donc penser à améliorer les protocoles existants ou à en concevoir de nouveaux. L'objectif de notre recherche est de résoudre certaines des limitations rencontrées à l'heure actuelle dans les WMNs et d'améliorer la QdS des applications multimédia temps-réel (par exemple, la voix). Le travail de recherche de cette thèse sera divisé essentiellement en trois principaux volets: le contrôle d‟admission du trafic, la différentiation du trafic et la réaffectation adaptative des canaux lors de la présence du trafic en relève ("handoff" en anglais). Dans le premier volet, nous proposons un mécanisme distribué de contrôle d'admission se basant sur le concept des cliques (une clique correspond à un sous-ensemble de liens logiques qui interfèrent les uns avec les autres) dans un réseau à multiples-sauts, multiples-radios et multiples-canaux, appelé RCAC. Nous proposons en particulier un modèle analytique qui calcule le ratio approprié d'admission du trafic et qui garantit une probabilité de perte de paquets dans le réseau n'excédant pas un seuil prédéfini. Le mécanisme RCAC permet d‟assurer la QdS requise pour les flux entrants, sans dégrader la QdS des flux existants. Il permet aussi d‟assurer la QdS en termes de longueur du délai de bout en bout pour les divers flux. Le deuxième volet traite de la différentiation de services dans le protocole IEEE 802.11s afin de permettre une meilleure QdS, notamment pour les applications avec des contraintes temporelles (par exemple, voix, visioconférence). À cet égard, nous proposons un mécanisme d'ajustement de tranches de temps ("time-slots"), selon la classe de service, ED-MDA (Enhanced Differentiated-Mesh Deterministic Access), combiné à un algorithme efficace de contrôle d'admission EAC (Efficient Admission Control), afin de permettre une utilisation élevée et efficace des ressources. Le mécanisme EAC prend en compte le trafic en relève et lui attribue une priorité supérieure par rapport au nouveau trafic pour minimiser les interruptions de communications en cours. Dans le troisième volet, nous nous intéressons à minimiser le surcoût et le délai de re-routage des utilisateurs mobiles et/ou des applications multimédia en réaffectant les canaux dans les WMNs à Multiples-Radios (MR-WMNs). En premier lieu, nous proposons un modèle d'optimisation qui maximise le débit, améliore l'équité entre utilisateurs et minimise le surcoût dû à la relève des appels. Ce modèle a été résolu par le logiciel CPLEX pour un nombre limité de noeuds. En second lieu, nous élaborons des heuristiques/méta-heuristiques centralisées pour permettre de résoudre ce modèle pour des réseaux de taille réelle. Finalement, nous proposons un algorithme pour réaffecter en temps-réel et de façon prudente les canaux aux interfaces. Cet algorithme a pour objectif de minimiser le surcoût et le délai du re-routage spécialement du trafic dynamique généré par les appels en relève. Ensuite, ce mécanisme est amélioré en prenant en compte l‟équilibrage de la charge entre cliques. / In the last few years, Wireless Mesh Networks (WMNs) area brought a new field of advanced research among network specialized scientists. This is due to the many advantages which WMN technology offers, such as: easy and inexpensive installation, reliable connectivity and flexible interoperability with other existing networks (Wi-Fi, WiMax, Cellular, Sensors, WPAN networks, etc.). However, several problems still remain to be solved such as the scalability, the security, the quality of service (QoS), the resources management, etc. These problems persist for WMNs, therefore the researchers propose to improve the existing protocols or to conceive new protocols for WMNs. In order to solve some of the current limitations met in the wireless networks and to improve QoS of real time multimedia applications in such networks, our research will be divided primarily into three parts: traffic admission control, traffic differentiation and handoff-aware channel assignment schemes. In the first part, we propose a distributed admission control scheme for WMNs, namely, Routing on Cliques (a clique is defined as a subset of logical links that interfere with each other) Admission Control (RCAC). Particularly, we propose an analytical model to compute the appropriate acceptance ratio and guarantee that the packet loss probability in the network does not exceed a threshold value. The model also allows computing end-to-end delay to process flow requests with delay constraints. In the second part, we design an efficient scheduler for Mesh Deterministic Access (MDA) in IEEE 802.11s-based WMNs, called Enhanced Differentiated-MDA (ED-MDA) to support voice and video applications with strict requirements on delay and on blocking/dropping probability. ED-MDA together with Enhanced Admission Control, namely EAC, reserves the minimum amount of necessary resources while maintaining an acceptable handoff call dropping and high resource utilization. The final section addresses handoff-aware channel assignment (CA) problem in Multiple Radios WMNs (MR-WMNs). In this section, we first propose a multi-objective optimization model that, besides maximizing throughput, improves fairness and handoff experience of mesh clients. In this model, the Jain’s index is used to maximize users’ fairness and to allow same channel assignments to links involved in the same high handoff traffic, thus reducing handoff-triggered re-routing characterized by its high latency. Second, we solved this model to obtain exact solutions by the CPLEX software for a limited number of nodes. We therefore propose to use centralized heuristics/meta-heuristics algorithms as an offline CA process to obtain near-optimal solutions for larger instances (real size network). Moreover, in order to adapt to traffic dynamics caused especially by user handoffs, an online CA scheme is proposed that carefully re-assigns channels to interfaces with the purpose of continuously minimizing the re-routing overhead/latency during user handoffs. This online scheme is improved using load balancing.

Depuis quelques années, la recherche dans le domaine des réseaux maillés sans fil ("Wireless Mesh Network (WMN)" en anglais) suscite un grand intérêt auprès de la communauté des chercheurs en télécommunications. Ceci est dû aux nombreux avantages que la technologie WMN offre, telles que l'installation facile et peu coûteuse, la connectivité fiable et l'interopérabilité flexible avec d'autres réseaux existants (réseaux Wi-Fi, réseaux WiMax, réseaux cellulaires, réseaux de capteurs, etc.). Cependant, plusieurs problèmes restent encore à résoudre comme le passage à l'échelle, la sécurité, la qualité de service (QdS), la gestion des ressources, etc. Ces problèmes persistent pour les WMNs, d'autant plus que le nombre des utilisateurs va en se multipliant. Il faut donc penser à améliorer les protocoles existants ou à en concevoir de nouveaux. L'objectif de notre recherche est de résoudre certaines des limitations rencontrées à l'heure actuelle dans les WMNs et d'améliorer la QdS des applications multimédia temps-réel (par exemple, la voix). Le travail de recherche de cette thèse sera divisé essentiellement en trois principaux volets: le contrôle d‟admission du trafic, la différentiation du trafic et la réaffectation adaptative des canaux lors de la présence du trafic en relève ("handoff" en anglais). Dans le premier volet, nous proposons un mécanisme distribué de contrôle d'admission se basant sur le concept des cliques (une clique correspond à un sous-ensemble de liens logiques qui interfèrent les uns avec les autres) dans un réseau à multiples-sauts, multiples-radios et multiples-canaux, appelé RCAC. Nous proposons en particulier un modèle analytique qui calcule le ratio approprié d'admission du trafic et qui garantit une probabilité de perte de paquets dans le réseau n'excédant pas un seuil prédéfini. Le mécanisme RCAC permet d‟assurer la QdS requise pour les flux entrants, sans dégrader la QdS des flux existants. Il permet aussi d‟assurer la QdS en termes de longueur du délai de bout en bout pour les divers flux. Le deuxième volet traite de la différentiation de services dans le protocole IEEE 802.11s afin de permettre une meilleure QdS, notamment pour les applications avec des contraintes temporelles (par exemple, voix, visioconférence). À cet égard, nous proposons un mécanisme d'ajustement de tranches de temps ("time-slots"), selon la classe de service, ED-MDA (Enhanced Differentiated-Mesh Deterministic Access), combiné à un algorithme efficace de contrôle d'admission EAC (Efficient Admission Control), afin de permettre une utilisation élevée et efficace des ressources. Le mécanisme EAC prend en compte le trafic en relève et lui attribue une priorité supérieure par rapport au nouveau trafic pour minimiser les interruptions de communications en cours. Dans le troisième volet, nous nous intéressons à minimiser le surcoût et le délai de re-routage des utilisateurs mobiles et/ou des applications multimédia en réaffectant les canaux dans les WMNs à Multiples-Radios (MR-WMNs). En premier lieu, nous proposons un modèle d'optimisation qui maximise le débit, améliore l'équité entre utilisateurs et minimise le surcoût dû à la relève des appels. Ce modèle a été résolu par le logiciel CPLEX pour un nombre limité de noeuds. En second lieu, nous élaborons des heuristiques/méta-heuristiques centralisées pour permettre de résoudre ce modèle pour des réseaux de taille réelle. Finalement, nous proposons un algorithme pour réaffecter en temps-réel et de façon prudente les canaux aux interfaces. Cet algorithme a pour objectif de minimiser le surcoût et le délai du re-routage spécialement du trafic dynamique généré par les appels en relève. Ensuite, ce mécanisme est amélioré en prenant en compte l‟équilibrage de la charge entre cliques. / In the last few years, Wireless Mesh Networks (WMNs) area brought a new field of advanced research among network specialized scientists. This is due to the many advantages which WMN technology offers, such as: easy and inexpensive installation, reliable connectivity and flexible interoperability with other existing networks (Wi-Fi, WiMax, Cellular, Sensors, WPAN networks, etc.). However, several problems still remain to be solved such as the scalability, the security, the quality of service (QoS), the resources management, etc. These problems persist for WMNs, therefore the researchers propose to improve the existing protocols or to conceive new protocols for WMNs. In order to solve some of the current limitations met in the wireless networks and to improve QoS of real time multimedia applications in such networks, our research will be divided primarily into three parts: traffic admission control, traffic differentiation and handoff-aware channel assignment schemes. In the first part, we propose a distributed admission control scheme for WMNs, namely, Routing on Cliques (a clique is defined as a subset of logical links that interfere with each other) Admission Control (RCAC). Particularly, we propose an analytical model to compute the appropriate acceptance ratio and guarantee that the packet loss probability in the network does not exceed a threshold value. The model also allows computing end-to-end delay to process flow requests with delay constraints. In the second part, we design an efficient scheduler for Mesh Deterministic Access (MDA) in IEEE 802.11s-based WMNs, called Enhanced Differentiated-MDA (ED-MDA) to support voice and video applications with strict requirements on delay and on blocking/dropping probability. ED-MDA together with Enhanced Admission Control, namely EAC, reserves the minimum amount of necessary resources while maintaining an acceptable handoff call dropping and high resource utilization. The final section addresses handoff-aware channel assignment (CA) problem in Multiple Radios WMNs (MR-WMNs). In this section, we first propose a multi-objective optimization model that, besides maximizing throughput, improves fairness and handoff experience of mesh clients. In this model, the Jain’s index is used to maximize users’ fairness and to allow same channel assignments to links involved in the same high handoff traffic, thus reducing handoff-triggered re-routing characterized by its high latency. Second, we solved this model to obtain exact solutions by the CPLEX software for a limited number of nodes. We therefore propose to use centralized heuristics/meta-heuristics algorithms as an offline CA process to obtain near-optimal solutions for larger instances (real size network). Moreover, in order to adapt to traffic dynamics caused especially by user handoffs, an online CA scheme is proposed that carefully re-assigns channels to interfaces with the purpose of continuously minimizing the re-routing overhead/latency during user handoffs. This online scheme is improved using load balancing.

La technologie OFDMA (Orthogonal frequency division multiple access) a été adoptée par les systèmes de télécommunications de 4ème génération (4G) comme technique de transmission et d'accès multiple pour ses performances supérieures en termes d'efficacité spectrale. Dans ce type de systèmes, l'adaptation dynamique du débit en fonction de la qualité du canal CQI (Channel Quality Indicator) constitue une problématique de recherche d'actualité qui attire l'attention de plusieurs acteurs académiques et industriels. Ce problème d'adaptation dynamique est encore plus complexe à gérer dans des environnements multi-utilisateurs hétérogènes et à ressources limitées tels que les systèmes OFDMA comme WiMAX Mobile et Long-term Evolution (LTE). Dans cette thèse, nous nous intéressons au problème d'allocation de ressources de l'information de feedback relative au CQI dans le cadre de systèmes OFDMA multi-porteuses multi-utilisateurs. Dans le but de réduire la charge (overhead) du feedback, nous proposons une méthode de prédiction du CQI basée sur l'exploitation de la corrélation temporelle de ce dernier et d'une solution inter-couches. L'objectif est de trouver des schémas d'allocation de ressources adaptatifs respectant les contraintes de qualité de service (QoS) applicatives.Nous proposons en premier lieu un algorithme de réduction de feedback PBF (Prediction Based Feedack) qui permet à la station de base (BS) à prédire certaines occurrences du CQI en se basant sur l'algorithme des moindres carrés récursif RLS (Recursive least-square). Les résultats de simulation montrent que l'outil de prédiction du CQI réduit sensiblement l'overhead du feedback et améliore par conséquent le débit de la liaison montante. Nous proposons, par la suite, une version opportuniste de PBF pour atténuer les éventuels effets de sur et sous estimations liées à l'algorithme de prédiction. Dans ce mécanisme, nous exploitons les informations inter-couches pour améliorer les performances des mécanismes de feedbacks périodiques dont PBF fait partie. L'approche opportuniste améliore sensiblement les performances du système pour les cas de mobilité élevée comparés aux cas de faible mobilité.Dans un second temps, nous proposons une plateforme (FEREP : feedback resource allocation and prediction) basée sur une approche inter-couches. Implémentée au niveau de la station BS, FEREP intègre les fonctionnalités de prédiction, d'adaptation dynamique du CQI et d'ordonnancement des demandes de feedback. Elle comporte trois modules. Le module FWA (feedback window adaptation) gère dynamiquement la fenêtre de feedbacks de chaque station mobile (MS) en se basant sur les messages ARQ (Automatic Repeat Request) reçus qui reflètent l'état actuel des canaux respectifs. Le module PBFS (priority-based feedback scheduling) effectue ensuite l'ordonnancement des feedbacks en tenant compte de la taille de la fenêtre de feedback, du profil de l'utilisateur sous la contrainte de la limitation des ressources globales du systèmes réservées au feedback. Afin de choisir les paramètres de transmission MCS (modulation and coding schemes), le module PBF (prediction based feedback) est utilisé pour les utilisateurs dont le feedabck n'a pas pu être ordonnancé dans la trame courante. Les résultats de simulation ont montré un gain significatif des performances de FREREP en comparaison à un mécanisme de référence, en particulier, sous de fortes contraintes de limitation des ressources du feedback.Le protocole ARQ génère un accusé de réception uniquement si l'utilisateur est sélectionné par l'ordonnanceur pour envoyer des données sur la liaison descendante. Dans le cas où la fréquence d'ordonnancement des utilisateurs sur le lien descendant est réduite, les messages ARQ s'en trouvent également réduits, dégradant par conséquent les performances de la plateforme FEREP proposée ci-dessus. En effet, dans ce cas la signalisation ARQ devient insuffisante pour adapter efficacement la fenêtre de feedback de chaque utilisateur. Pour pallier à ce problème, nous proposons l'algorithme DCRA (dynamic CQI resource allocation) qui utilise deux modes d'estimation de la fenêtre de feedback. Le premier est un mode hors-ligne basé sur des études empiriques permettant d'estimer la fenêtre moyenne optimale de feedback en utilisant les profils applicatif et de mobilité de l'utilisateur. Notre analyse de performance par simulation montre que la fenêtre de feedback peut être estimée en fonction de la classe de service des utilisateurs et de leurs profils de mobilité pour un environnement cellulaire donné. Le second mode de fonctionnement de DCRA effectue une adaptation dynamique de la fenêtre en temps réel dans le cas où la signalisation ARQ est suffisante. Une étude comparative avec les mécanismes DFS (deterministic feedback scheduling) et OFS (opportunistic feedback scheduling), a montré que DCRA arrive à réaliser un meilleur gain en ressources montantes grâce à la réduction de l'overhead des feedbacks, sans pour autant trop dégrader le débit descendant des utilisateurs. Du point de vue des utilisateurs, DCRA améliore les contraintes de QoS tels que le taux de perte de paquets et réduit la consommation énergétique des terminaux grâce à la réduction de feedback. / Orthogonal frequency division multiple access (OFDMA) technology has been adopted by 4th generation (a.k.a. 4G) telecommunication systems to achieve high system spectral efficiency. A crucial research issue is how to design adaptive channel quality indicator (CQI) feedback mechanisms so that the base station can use adaptive modulation and coding (AMC) techniques to adjust its data rate based on the channel condition. This problem is even more challenging in resource-limited and heterogeneous multiuser environments such as Mobile WiMAX, Long-term Evolution (LTE) networks. In this thesis, we consider CQI feedback resource allocation issue for multiuser multicarrier OFDMA systems. We exploit time-domain correlation for CQI prediction and cross-layer information to reduce feedback overhead for OFDMA systems. Our aim is find resource allocation schemes respecting the users QoS constraints.Our study begins with proposing prediction based feedback (PBF) which allows the base station to predict the CQI feedbacks based on recursive least-square (RLS) algorithm. We showed that it is useful to use channel prediction as a tool to reduce the feedback overhead and improve the uplink throughput. Then, we propose an opportunistic periodic feedback mechanism to mitigate the possible under and over estimation effects of CQI prediction. In this mechanism, we exploited the cross-layer information to enhance the performance of periodic feedback mechanisms. The opportunistic mechanism improves the system performance for high mobility cases compared to low mobility cases.For OFDMA systems with limited feedback resource, we propose an integrated cross-layer framework of feedback resource allocation and prediction (FEREP). The proposed framework, implemented at the BS side, is composed of three modules. The feedback window adaptation (FWA) module dynamically tunes the feedback window size for each mobile station based on the received ARQ (Automatic Repeat Request) messages that reflect the current channel condition. The priority-based feedback scheduling (PBFS) module then performs feedback allocation by taking into account the feedback window size, the user profile and the total system feedback budget. To choose adapted modulation and coding schemes (MCS), the prediction based feedback (PBF) module performs channel prediction by using recursive least square (RLS) algorithm for the user whose channel feedback has not been granted for schedule in current frame. Through extensive simulations, the proposed framework shows significant performance gain especially under stringent feedback budget constraint.ARQ protocol receives users acknowledgement only if the user is scheduled in the downlink. The reduction in users scheduling frequency also reduces the rate of ARQ hints and degrades the performance of above contributions. In this case, it is difficult to exploit the ARQ signal to adapt the feedback window for that user. To address this issue, we propose a cross-layer dynamic CQI resource allocation (DCRA) algorithm for multiuser multicarrier OFDMA systems. DCRA uses two modes for feedback window estimation. The first one is an off-line mode based on empirical studies to derive optimal average feedback window based on user application and mobility profile. Our experimental analysis shows that the feedback window can be averaged according to users service class and their mobility profile for a given cell environment. DCRA performs a realtime dynamic window adaptation if sufficient cross-layer hints are available from ARQ signaling. DCRA increases uplink resource by reducing feedback overhead without degrading downlink throughout significantly compared to deterministic feedback scheduling (DFS) and opportunistic feedback scheduling (OFS). From the users perspective, DCRA improves QoS constraints like packet loss rate and saves users power due to feedback reduction.

This diploma work deals with marketing utilization in service sektor, concrete in legal profession. The objective was to make analysis of marketing assertion in legal office. On the basis of suitable methods was followed and evaluated actual posture of marketing literacy in legal office. Result of practical analyses was definition of barriers, handicaps, reserves and opportunities at marketing utilization in legal office. Theoretical part features information about marketing in service sektor, shows in legal profession domain and gets acquainted with used methods. Practical part analyses contemporary state in legal office. By means of suitable methods is drafted the measure, how to eliminate barriers, handicaps and reserves and to take advantage of opportunities.