O desenvolvimento da tecnologia de telecomunicação móvel ensejou a implantação massiva de ERBs (Estações rádio base) para o atendimento da crescente demanda ocorrida na última década. As ERBs, por sua vez, constituem fontes emissoras de radiação não ionizante. Os estudos científicos concluídos nos últimos anos indicam que a exposição à radiação não ionizante, principalmente em longo prazo, pode produzir consequências negativas para a saúde humana, por essa razão, mister se faz a aplicação do Princípio da Precaução que vem evocar cautela diante do risco. Das principais normas existentes no planeta, nem todas adotaram o princípio da precaução ao fixar seus limites; em decorrência, a maioria das normas que determinam limites máximos de exposição teve como base apenas os efeitos biológicos danosos da exposição à radiação não ionizante já conhecidos pela comunidade científica e relacionados à exposição aguda. Dessa maneira, diante do risco resultante da exposição, surge outra questão de grande importância o gerenciamento dessas ERBs. Haveria, na cidade de São Paulo, um sistema de gerenciamento das ERBs que garanta o cumprimento dos limites e padrões definidos na legislação local? Nesse cenário, este estudo pretende: (i) elaborar um levantamento junto aos três órgãos públicos responsáveis pelo gerenciamento das ERBs na cidade de São Paulo, sobre o atual estágio dos sistemas de gerenciamento praticado por cada entidade pública legalmente competente para o respectivo exercício; (ii) desenvolver uma análise das características básicas dos sistemas de gerenciamento das ERBs no município de São Paulo, estudando a evolução ocorrida entre os anos de 2006 e 2011; e, (iii) avaliar as possibilidades de melhoria na proposta atual de gerenciamento das ERBs, no município de São Paulo. Esta pesquisa parte dos dados levantados no ano de 2006, na cidade de São Paulo, que na ocasião indicaram a existência de um sistema de gerenciamento das ERBs incipiente e frágil por parte dos órgãos públicos competentes (Secretaria Estadual da Saúde, Secretaria Municipal do Verde e Meio Ambiente e ANATEL). A partir deste cenário, elabora-se uma análise das características básicas dos sistemas de gerenciamento das ERBs no município de São Paulo, estudando a evolução ocorrida entre os anos de 2006 e 2011. Dessa avaliação, são identificadas falhas e possibilidades de melhoria nos sistemas de gerenciamento das ERBs praticados no município de São Paulo na atualidade. A metodologia adotada constitui-se de pesquisa de campo, por meio de entrevista estruturada, aplicada aos representantes dos órgãos públicos responsáveis pelo gerenciamento das ERBs no município de São Paulo. Finalmente, é desenvolvida a interpretação dos dados, global e individualmente, de forma que os resultados obtidos possibilitaram as considerações e propostas formuladas no capítulo conclusivo desta pesquisa. / The development of mobile telecommunication technology gave rise to the massive deployment of RBSs (Radio base stations) to attend the growing demand occurred in the last decade. The RBSs in turn, are emitting sources of non-ionizing radiation. Scientific studies concluded in the recent years indicate that exposure to non-ionizing radiation, especially in the long term, can produce negative consequences for human health, therefore, it becomes important to apply the Precautionary Principle that evokes caution in risk situation. Of the main rules in the world, not all adopted the precautionary principle in setting its limits; as a result, most of the rules that determine maximum exposure limits were based only on the harmful biological effects of exposure to ionizing radiation already known by the scientific community and related to acute exposure exclusively. Thus, with the risk resulting from exposure, there is another major issue - the management of these RBSs. Would it exist, in São Paulo city, a management system of RBSs to ensure compliance with the limits and standards defined by local law? In this scenario, this study aims to: (i) develop a survey along the three entities responsible for managing the RBSs in São Paulo, on the current stage of respective management systems practiced by each public entity legally responsible for the exercise thereof; (ii) develop an analysis of the basic features of the RBSs management systems in São Paulo, studying the evolution that occurred between the years 2006 and 2011; and, (iii) assess the possibilities for improvement in the current proposal for the RBSs management in São Paulo. This survey starts from the data collected in 2006, in São Paulo, which at the time indicated the existence of an incipient and fragile RBSs management system, by the public agencies (Secretaria Estadual da Saúde, Secretaria Municipal do Verde e Meio Ambiente e Anatel). From this scenario, it is drawn up an analysis of the basic features of the RBSs management systems in São Paulo, studying the evolution that occurred between the years 2006 and 2011. From this evaluation, are identified gaps and opportunities for improving the RBSs management systems practiced in São Paulo at present. The methodology consisted of field survey through structured questionnaires, applied to representatives of public agencies responsible for RBSs management in São Paulo. Finally, it is developed the interpretation of the data, overall and individually, so that the results enabled the considerations and proposals made in the concluding chapter of this research.

This master’s thesis is the design of the system of the differential GPS, creation of the software for basic wireless communication between 2 GPS receivers, and practical tests of the designed system. Parameters and characteristics of system were determined and they should inform us better about the appropriateness of the designed system for navigation of a mobile robot in outside conditions.

L'augmentation massive du trafic cellulaire pose de sérieux défis à tous les acteurs concernés par la diffusion de contenu sans fil. Alors que la densification du réseau permet d’accéder à des utilisateurs supplémentaires, les liaisons de transport à grande vitesse et à grande capacité sont coûteuses. La mise en cache du contenu populaire en bordure du réseau permettra de décharger le trafic utilisateur de ces connexions, susceptibles d'être encombrées, ainsi que des centres de données du réseau fédérateur. Cette thèse propose un modèle économique dans lequel un opérateur de réseau mobile (Mobile Network Operator, MNO) pré-installe et entretient des caches sur son équipement sans fil (stations de base avec cache, CBS). L’espace mémoire ainsi que les capacités de calcul sont ensuite loués aux fournisseurs de contenu (CP) qui souhaitent rapprocher leur contenu de l'utilisateur. Pour une compensation financière, un CP peut alors décharger le trafic de son centre de données et améliorer la qualité de service des utilisateurs. Le CP prend des décisions de placement de contenu en fonction des données prédictives sur le trafic des utilisateurs et la popularité du contenu. Dans la phase de livraison, un utilisateur peut être desservi à partir des caches pour le cas où il serait associé à une station sur laquelle le contenu demandé est mis en cache. Ce travail examine trois aspects du modèle économique proposé : La première question de recherche porte sur l'association des utilisateurs en tant qu'élément central du schéma de mise en cache à la bordure du réseau. Les stratégies d'association des utilisateurs prenant en compte le cache peuvent permettre aux utilisateurs dans des zones de chevauchement de couverture d'être associés à une CBS contenant le contenu demandé plutôt que conventionnellement à celui qui fournit le signal le plus puissant. La thèse propose un algorithme décentralisé original pour une association d'utilisateurs appelée Generalized Bucket-filling qui permet des gains au-delà de la maximisation du taux de réussite. Les mesures de performance telles que le débit du réseau et l'équilibrage de la charge des utilisateurs parmi les CBS sont prises en compte. Les expériences montrent que l'association des utilisateurs au cache augmente le taux de réussite sans surcharger les CBS uniques tout en fournissant un débit élevé du système. Le deuxième problème traité concerne un seul CP qui doit décider de l'espace de cache à louer à chaque CBS pour un prix fixe et du contenu à placer. Ses choix doivent être basés sur des estimations de la popularité des fichiers ainsi que sur la politique d'association des utilisateurs du MNO. Le problème de leasing et de placement du contenu du cache est formulé sous la forme d'un problème non linéaire mixte en nombres entiers (NLMIP). Dans sa solution, le problème est séparé en un sous-problème linéaire discret et un sous-problème continu non linéaire utilisant la décomposition de Benders. Le CP et le MNO coopèrent, aidant le CP à prendre des décisions optimales qui profitent aux deux parties : Le CP maximise ses économies grâce à la mise en cache tandis que le MNO peut trouver le prix de cache optimal et recevoir la compensation financière maximale. Une troisième question de recherche élargit la portée de l'interaction entre plusieurs CPs et un opérateur de réseau mobile. Désormais, le MNO ne fixe pas de prix fixe par unité de mémoire, mais réagit aux demandes des CPs en matière d'espace mémoire en fonction des économies réalisées grâce à la mise en cache. / The massive increase in cellular traffic poses serious challenges to all actors concerned with wireless content delivery. While network densification provides access to additional users, high-speed and high-capacity backhaul connections are expensive. Caching popular content at the network edge promises to offload user traffic from these congestion prone connections as well as from the data centers in the backbone network. This thesis proposes a business model in which a mobile network operator (MNO) pre-installs and maintains caches at its wireless equipment (Cache-equipped Base Stations, CBSs). Memory space together with computational capabilities is then leased to content providers (CPs) that want to bring their content closer to the user. For a financial compensation, a CP can then offload traffic from its data center and improve user Quality of Service. The CP makes content placement decisions based on predictive user traffic and content popularity data. In the delivery phase, users can be served from the caches in case they are associated to stations that have the requested content cached. This work investigates three aspects of the proposed business model: The first research question focuses on user association as a central element to the edge caching scheme. Cache-aware user association policies can allow for users in coverage overlap areas to be associated to a CBS that holds the requested content rather than conventionally to the one that provides the strongest signal. The thesis proposes an original decentralized algorithm for user association called Generalized Bucket-filling that allows gains beyond maximizing the hit ratio. Performance metrics such as network throughput and load balancing of users among CBSs are taken into account. Experiments show that cache-aware user association a) increases the hit ratio b) without overloading single CBSs while c) providing high system throughput. The second problem treated considers a single CP that needs to decide how much cache space to lease at each CBS for a fixed price, and what content to place. Its choices should be based on estimates of file popularity as well as MNO user association policy. The cache leasing and content placement problem is formulated as a non-linear mixed-integer problem (NLMIP). In its solution, the problem is separated into a linear discrete CP subproblem and a nonlinear continuous subproblem using Benders decomposition. The CP and the MNO cooperate, helping the CP to make optimal decisions that benefit both parties: The CP maximizes its savings from caching while the MNO can find the optimal cache price and receive the maximum financial compensation. A third research question widens the focus to the interaction between several CPs and one MNO. Now, the MNO does not set a fixed price per memory unit but instead reacts to CP demands for memory space that depend on the savings they can achieve from caching.

No description available.

With the emergence of Fifth Generation (5G) mobile networks, the employment ofhigher frequencies in the millimeter-wave (mmWave) range and the realization of agreat number of beams in 5G radio base stations (RBS) make the electromagnetic (EM)simulation of RBS products very costly in terms of hardware and time requirements.In order to compute the electromagnetic field (EMF) exposure in close proximity of theRBS, more efficient simulation methods are required.The move to mmWave frequencies enables the use of the so-called high frequencymethods for EM simulation with RBS antennas. In this thesis, conventional fullwavesimulation solvers and different implementations of hybridization of highfrequency methods with conventional methods are used with different commercial EMsimulation tools, and their performance is evaluated for the purpose of EMF exposureassessment in close proximity of 5G mmWave RBS.Among all the investigated methods, the hybrid scheme with Finite IntegrationTechnique (FIT) and Shooting and Bouncing Rays (SBR) methods, e.g., thatimplemented in CST Studio Suite 2020, outperforms in terms of hardwarerequirements and time costs, although the accuracy is compromised on the side andbehind the mmWave RBS. The Multilevel Fast Multipole Method (MLFMM), e.g.,that implemented in Altair FEKO 2019, though not a hybrid method, also has goodperformance but requires very large Random Access Memory (RAM), and it cannothandle very exquisite details of RBS. The Finite Difference Time Domain (FDTD)method implemented in EMPIRE XPU can also handle the investigated problemseffciently, but for extremely large problems, its requirements on RAM may become thebottleneck. In the thesis, many other hybrid implementations are also investigated,but it is found that they are not suitable for the EMF exposure assessment in closeproximity of the mmWave RBS with evaluation on a planar area of 0.42 m × 1 m at 28 GHz due to various reasons. / För den femte generationens (5G) mobilnät kommer användningen av millimetervågoroch det stora antalet lober som en radiobasstation (RBS) kan hantera att betydaett kraftigt ökat behov av hårdvara och större tidsåtgång för att göra beräkningarav exponeringen för elektromagnetiska fält nära utrustningen. Därför behövs mereffektiva simuleringsmetoder.Eftersom systemen opererar på millimetervåg-frekvenser kan högfrekvensmetoderanvändas i simuleringen av simuleringen av en RBS. I den här avhandlingenutvärderas konventionella metoder, samt olika hybridmetoder för beräkningenav EMF-exponeringen av millimetervågor i närheten av en RBS. De utvärderadehybridmetoderna är implementerade i olika mjukvaror och blandar användandet avhögfrekvensmetoder och konventionella metoder.Av alla utvärderade metoder fungerar hybridmetoden implementerad med finitaintegralmetoden (FIT) och ”Shooting and Bouncing Rays”-metoden (SBR) i CST bästi termer av vilken hårdvara som behövs för beräkningarna och för tidsåtgången.Dock är noggrannheten i beräkningarna på sidan av och bakom RBSen mindrebra. Multilevel Fast Multipole Method (MLFMM)”-lösaren i Feko i FEKO använderingen hybridmetod men presterar bra, men den kräver mycket RAM-minne och kaninte ta hänsyn till små detaljer i RBSen. Finita differensmetoden i tidsdomänen(FDTD) i EMPIRE kan också användas men dess RAM-krav blir en flaskhals förstora simuleringar. Ytterligare hybridmetoder är undersökta i avhandlingen men medslutsatsen att de inte är användbara (av olika anledningar) för beräkningen av EMFexponeringenfrån en RBS opererandes på frekvensen 28 GHz och över en yta som är0.42 x 1 m.

Wireless network virtualization (WNV) and millimeter wave (mmW) communications are emerging as two key technologies for cellular networks. Virtualization in cellular networks enables wireless services to be decoupled from network resources (e.g., infrastructure and spectrum) so that multiple virtual networks can be built using a shared pool of network resources. At the same time, utilization of the large bandwidth available in mmW frequency band would help to overcome ongoing spectrum scarcity issues. In this context, this dissertation presents efficient frameworks for building virtual networks in sub-6 GHz and mmW bands. Towards developing the frameworks, first, we derive a closed-form expression for the downlink rate coverage probability of a typical sub-6 GHz cellular network with known base station (BS) locations and stochastic user equipment (UE) locations and channel conditions. Then, using the closed-form expression, we develop a sub-6 GHz virtual resource allocation framework that aggregates, slices, and allocates the sub-6 Ghz network resources to the virtual networks in such a way that the virtual networks' sub-6 GHz downlink coverage and rate demands are probabilistically satisfied while resource over-provisioning is minimized in the presence of uncertainty in UE locations and channel conditions. Furthermore, considering the possibility of lack of sufficient sub-6 GHz resources to satisfy the rate coverage demands of all virtual networks, we design a prioritized sub-6 GHz virtual resource allocation scheme where virtual networks are built sequentially based on their given priorities. To this end, we develop static frameworks that allocate sub-6 GHz resources in the presence of uncertainty in UE locations and channel conditions, i.e., before the UE locations and channel conditions are revealed. As a result, when a slice of a BS serves its associated UEs, it can be over-satisfied (i.e., resources left after satisfying the rate demands of all UEs) or under-satisfied (i.e., lack of resources to satisfy the rate demands of all UEs). On the other hand, it is extremely challenging to execute the entire virtual resource allocation process in real time due to the small transmission time intervals (TTIs) of cellular technologies. Taking this into consideration, we develop an efficient scheme that performs the virtual resource allocation in two phases, i.e., virtual network deployment phase (static) and statistical multiplexing phase (adaptive). In the virtual network deployment phase, sub-6 GHz resources are aggregated, sliced, and allocated to the virtual networks considering the presence of uncertainty in UE locations and channel conditions, without knowing which realization of UE locations and channel conditions will occur. Once the virtual networks are deployed, each of the aggregated BSs performs statistical multiplexing, i.e., allocates excess resources from the over-satisfied slices to the under-satisfied slices, according to the realized channel conditions of associated UEs. In this way, we further improve the sub-6 GHz resource utilization. Next, we steer our focus on the mmW virtual resource allocation process. MmW systems typically use beamforming techniques to compensate for the high pathloss. The directional communication in the presence of uncertainty in UE locations and channel conditions, make maintaining connectivity and performing initial access and cell discovery challenging. To address these challenges, we develop an efficient framework for mmW virtual network deployment and UE assignment. The deployment decisions (i.e., the required set of mmW BSs and their optimal beam directions) are taken in the presence of uncertainty in UE locations and channel conditions, i.e., before the UE locations and channel conditions are revealed. Once the virtual networks are deployed, an optimal mmW link (or a fallback sub-6 GHz link) is assigned to each UE according to the realized UE locations and channel conditions. Our numerical results demonstrate the gains brought by our proposed scheme in terms of minimizing resource over-provisioning while probabilistically satisfying virtual networks' sub-6 GHz and mmW demands in the presence of uncertainty in UE locations and channel conditions. / Doctor of Philosophy / In cellular networks, mobile network operators (MNOs) have been sharing resources (e.g., infrastructure and spectrum) as a solution to extend coverage, increase capacity, and decrease expenditures. Recently, due to the advent of 5G wireless services with enormous coverage and capacity demands and potential revenue losses due to over-provisioning to serve peak demands, the motivation for sharing and virtualization has significantly increased in cellular networks. Through wireless network virtualization (WNV), wireless services can be decoupled from the network resources so that various services can efficiently share the resources. At the same time, utilization of the large bandwidth available in millimeter wave (mmW) frequency band would help to overcome ongoing spectrum scarcity issues. However, due to the inherent features of cellular networks, i.e., the uncertainty in user equipment (UE) locations and channel conditions, enabling WNV and mmW communications in cellular networks is a challenging task. Specifically, we need to build the virtual networks in such a way that UE demands are satisfied, isolation among the virtual networks are maintained, and resource over-provisioning is minimized in the presence of uncertainty in UE locations and channel conditions. In addition, the mmW channels experience higher attenuation and blockage due to their small wavelengths compared to conventional sub-6 GHz channels. To compensate for the high pathloss, mmW systems typically use beamforming techniques. The directional communication in the presence of uncertainty in UE locations and channel conditions, make maintaining connectivity and performing initial access and cell discovery challenging. Our goal is to address these challenges and develop optimization frameworks to efficiently enable virtualization and mmW technologies in cellular networks.

Most times people are unprepared to face natural disasters resulting in chaos, increased number of deaths, etc.Emergency responders need an efficiently working communication network to get in touch with the emergency services like hospitals, police, fire and rescue as well as people who are stranded. Such a network is also the need of the hour for survivors to contact their near and dear ones. One of the major barriers of communication during an emergency is the destruction of network elements. In case the communication devices survive the calamity, odds of the network getting congested are certainly high because almost everyone will be trying to use the same network resources. An important factor when dealing with emergency situations is the calls for an immediate response and an efficient Emergency Communication Systems (ECS). Currently there is a capability gap between existing ECS solutions and what we dream of achieving. Most current solutions do not meet cost or mobility constraints. An inexpensive, portable and mobile system will fulfill this capability gap. The main purpose of this research is to optimize the altitude and received signal strength of an aerial base station to provide maximum radio coverage on the ground as well as propose the best fit radio propagation channel model to carry out the experiment for the current scenario.

Wireless communications are important in our highly connected world. The amount of data being transferred in cellular networks is steadily growing, and consequently more capacity is needed. This thesis considers the problem of downlink capacity improvement from the perspective of multicell coordination. By employing multiple antennas at the transmitters and receivers of a multicell network, the inherent spatial selectivity of the users can be exploited in order to increase the capacity through linear precoding and receive filtering. For the coordination between cells, distributed algorithms are often sought due to their low implementation complexity and robustness. In this context, the thesis considers two problem domains: base station clustering and coordinated precoding. Base station clustering corresponds to grouping the cell base stations into disjoint clusters in order to reduce the coordination overhead. This is needed in intermediate-sized to large networks, where the overhead otherwise would be overwhelmingly high. Two solution methods for the clustering problem are proposed: an optimal centralized method, as well as a heuristic distributed method. The optimal method applies to a family of throughput models and exploits the structure of the model to find bounds that can be used to focus the search for the optimal clustering into promising territories. The distributed method instead uses notions from coalitional game theory, where the base stations are modelled as rational and intelligent players in a game. By letting the players make individual deviations that benefit them in the game, i.e.\@ switching clusters, a distributed coalition formation algorithm is obtained. Coordinated precoding is the act of finding the linear precoders and receive filters that maximize the network performance, given a base station clustering. Four specific challenges are studied in this problem domain. First, coordinated precoding under intercluster interference is considered. The channels of the intercluster links are not explicitly estimated due to overhead reasons, and these links thus lead to intercluster interference. By exploiting the known statistics of the intercluster channels, a robust and distributed coordinated precoding algorithm is developed. Second, coordinated precoding under imperfect channel state information is considered. Relying on the channel reciprocity under time-division duplex operation, a distributed estimation framework is proposed. Given the estimated channels, a robust and distributed coordinated precoding algorithm is then derived. Third, coordinated precoding under imperfect radio hardware is considered. By modelling the radio frequency distortion noises, a distributed coordinated precoding method that accounts for the imperfections is proposed. Fourth, joint coordinated precoding and discrete rate selection is considered. By bounding and linearizing an originally intractable optimization problem, a heuristic algorithm is derived which selects the transmit rate from a finite set and simultaneously forms the linear precoders and receive filters. / Trådlös kommunikation är ett viktigt verktyg i dagens ständigt uppkopplade värld. Datamängden som överförs i mobilnätverk ökar stadigt och därmed behovet av mer kapacitet. För att öka kapaciteten i nedlänken så utvecklar denna avhandling nya metoder för koordinering av multicellnätverk. Med flerantenniga sändare och mottagare så kan den spatiala selektiviteten hos mottagarna utnyttjas för att separera dem, vilket ger en ökad kapacitet. För denna koordinering är distribuerade algoritmer ofta att föredra eftersom de är robusta och har låg implementeringskomplexitet. I detta sammanhang undersöker denna avhandling två problemområden: basstationsgruppering och samordnad förkodning. Basstationsgruppering innebär att basstationerna delas in i disjunkta grupper, vilket minskar overheadkostnaden för samordningen. Detta är framför allt nödvändigt i medelstora till stora nätverk, eftersom overheadkostnaden för koordineringen av dessa annars skulle bli för stor. Två lösningar för basstationsgruppering presenteras: dels en optimal och centraliserad metod samt dels en heuristisk och distribuerad metod. Den optimala och centraliserade metoden kan hantera en familj av modeller för den totala datatakten och utnyttjar strukturen i modellen för att fokusera sökandet efter den optimala grupperingen mot lovande områden. Den heuristiska och distribuerade metoden bygger på spelteori för koalitioner och modellerar basstationerna som rationella och intelligenta spelare i ett spel. En distribuerad algoritm för koalitionsformering härleds genom att låta spelarna göra individuella förflyttningar, dvs. byta grupp, när det gynnar dem under spelets regler. Vid samordnad förkodning använder de flerantenniga sändarna och mottagarna linjära förkodare och mottagningsfilter för att maximera nätverkets prestanda. Inom detta problemområde undersöks fyra olika specifika problem. Först undersöks problemet när det finns störningar mellan basstationsgrupperna. För att hålla nere mängden overhead så skattas inte kanalerna mellan grupperna, vilket ger upphov till störningar hos mottagarna. Genom att utnyttja den kända statistiska informationen för dessa okända kanaler kan en robust och distribuerade samordningsmetod för förkodningen utvecklas. Därnäst undersöks problemet då kanalkännedomen är bristfällig i allmänhet. Reciprociteten som uppstår vid tidsdelningsduplexning utnyttjas och flera distribuerade skattningsmetoder härleds. Givet den skattade kanalkännedomen föreslås en robust metod för samordnad förkodning. Därnäst undersöks problemet med samordnad förkodning då radiohårdvaran är bristfällig. En modell för det distortionsbrus som skapas av den bristfälliga hårdvaran används för att föreslå en robust distribuerad metod för samordnad förkodning för detta scenario. Slutligen undersöks valet av diskret datatakt med simultan samordnad förkodning. En heuristisk algoritm utvecklas som löser ett begränsat optimeringsproblem. Algoritmen väljer sänddatatakten från en ändlig mängd och bestämmer simultant de linjära förkodarna och mottagningsfiltrena. / <p>QC 20160407</p>

The development of the IEEE 802.22 standard is aimed at providing broadband access in rural areas by effectively utilizing the unused TV band, provided no harmful interference is caused to the incumbent operation. This thesis presents the analytical framework to evaluate the number of active customer premise equipments (CPEs) in a wireless regional area network. Initial ranging is the primary process in IEEE 802.22 networks for CPEs to access the network and establish their connections with the base station (BS). A comprehensive analysis of initial ranging mechanism is provided in this work and initial ranging request success probability is derived based on the number of contended CPEs and the initial contention window size. Further, the average ranging success delay is derived for the maximum backoff stages. The collision probability is highly dependent on the size of the initial contention window and the number of contended CPEs. To keep it at a specific level, it is necessary for the BS to schedule the required size of the initial contention window to facilitate the maximum number of CPEs to establish their connections with reasonable delay. Therefore, the optimized initial window size is proposed that meets the collision probability constraint for a particular number of contended CPEs. An analytical model is also developed to estimate the ranging request collision probability depending upon the size of initial contention window and the number of contended CPEs. Moreover, this approximation provides the threshold size for contention window to start the initial ranging process in the IEEE 802.22 network.

L'évolution des télécommunications a fait des produits d'intermodulation passive (PIM) un critère de qualité et de performance du réseau mais également un problème de premier ordre pour les fournisseurs de services comme par exemple les opérateurs de téléphonie mobile. Les travaux présentés dans ce manuscrit constituent une contribution à la résolution d'une partie des problèmes de PIM dans les antennes de station de base et s'articulent autour de trois axes principaux : - la caractérisation des sources d'intermodulation passive au sein des antennes de station de base. De nombreuses études expérimentales ont été réalisées avec l'objectif de déterminer l'influence de différents paramètres sur la PIM générée par les contacts métal-métal (rugosité des surfaces, utilisation de traitement de surface, géométrie et nature des métaux) ou par les circuits imprimés de type micro-ruban (adaptation, largeur de ligne et épaisseur du substrat diélectrique). Les résultats de ces études ont permis d'améliorer les connaissances théoriques et de définir des règles permettant de réduire les niveaux de PIM induits ; - la localisation des sources d'intermodulation passive au sein de systèmes radiofréquences complexes. Pour cela, un banc de mesure PIM spécifique a été conçu. Celui-ci permet de localiser des sources de PIM, de niveau proche de la spécification 3GPP, avec une précision inférieure à 2cm. De plus, pour faciliter la détection des défauts PIM dans une antenne de station de base, différentes méthodes complémentaires ont été développées et associées à ce banc de mesure ; - la modélisation, à partir des résultats des études expérimentales réalisées, de composants non-linéaires intégrables à un simulateur de type circuit. L'utilisation de ces derniers permet aux ingénieurs d'estimer, dès la phase de conception, le comportement PIM des contacts métal-métal et des circuits imprimés de type micro-ruban et tri-plaque suspendue. / The evolution of telecommunications has made passive intermodulation products (PIM) not only a criterion of quality and network performance but also a major problem for service providers such as mobile operators. The work presented in this manuscript is a contribution to the resolution of some of PIM problems in base station antennas and is organized around three main axes : - the characterization of passive intermodulation root causes within base station antennas. Numerous experimental studies have been carried out with the aim of determining the influence of different parameters on the PIM generated by metal-to-metal contacts (roughness of surfaces, use of surface treatment, geometry and nature of metals) or by printed circuits as microstrip type (matching, line width and thickness of dielectric substrate). The results of these studies contributed to improve theoretical knowledge and to define rules to reduce induced PIM levels ; - the localization of passive intermodulation root causes within complex radio frequency systems. For this, a specific PIM measurements bench has been designed. It allows locating PIM root causes, with a level close to the current 3GPP specification, with an accuracy less than 2cm. In addition, to ease the PIM defects detection in a base station antenna, various complementary methods have been developed and associated with the measurements bench ; - the electromagnetic modeling issued from the experimental studies, carried out of non-linear components usable into a circuit-type simulator. The use of these allows designers to estimate, early during the design stage, the PIM behavior of metal-to-metal contacts, microstrip and suspended stripline printed circuits.