Studien syftar till att analysera mätningar av tidsfördröjningar i inbyggda system som använder externa Wi-Fi-moduler och Network Time Protocol (NTP) för tidssynkronisering. Mätning i detta sammanhang innebär att man tar mätbara data som kan representera tidsfördröjningarna i numerisk form, vilket gör det möjligt att analysera och jämföra dem på ett objektivt sätt. Genom en grundlig litteraturstudie identifierades de olika elementen involverade i tidssynkroniseringsprocessen, inklusive egenskaper hos Wi-Fi-moduler, NTP-protokollet och andra systemkomponenter. Insamlad data analyserades för att upptäcka mönster och tendenser i tidsfördröjning. Det övergripande målet med studien var att bidra med specifika insikter som kan förbättra konfigurationen och prestandan hos inbyggda system. Genom att jämföra prestanda hos olika dataenheter och visa på variationer i tidsfördröjning, har studien gett konkreta mätdata i form av tid, dess genomsnitt och standardavvikelse. Dessa insikter kan användas för att designa mer tillförlitliga inbyggda system med förbättrad tidssynkronisering, vilket är avgörande för mcu som kräver hög precision och stabilitet. / The study aims to analyze the measurements of time delays in embedded systems that use external Wi-Fi modules and the Network Time Protocol (NTP) for time synchronization. Measurement in this context means taking measurable data that can represent time delays in numerical form, making it possible to analyze and compare them objectively. Through a thorough literature review, the various elements involved in the time synchronization process were identified, including the characteristics of Wi-Fi modules, the NTP protocol, and other system components. Collected data were analyzed to detect patterns and trends in time delays. The overall goal of the study was to contribute specific insights that can improve the configuration and performance of embedded systems. By comparing the performance of different data units and showing variations in time delays, the study provided concrete guidelines and recommendations for engineers and developers. These insights can be used to design more reliable embedded systems with improved time synchronization, which is crucial for mcu requiring high precision and stability.

A proliferação de dispositivos móveis e de redes sem fio tem encorajado um crescente interesse em sistemas e serviços baseados na localização de dispositivos portáteis, especialmente em ambientes internos, como edifícios e residências. A localização de um dispositivo portátil é um parâmetro crítico em aplicações baseadas no contexto, as quais requerem grande precisão na estimativa de localização. Entretanto, projetar e desenvolver sistemas de localização em interiores, com crescente precisão na estimação e decrescente custo de instalação, é um problema desafiador. Uma abordagem bastante interessante para satisfazer os requisitos de baixo custo consiste em utilizar as infra-estruturas existentes de redes locais sem fio (WLAN) no padrão IEEE 802.11, que já estão instaladas em muitos ambientes. A maioria das abordagens para localização usando WLAN propostas na literatura é baseada em técnicas probabilísticas, que apresentam bom desempenho e estão cada vez mais populares. Estas técnicas usam um mapa com a informação da potência recebida do sinal (RSSI) juntamente com a freqüência de presença de sinal coletada de múltiplos pontos de acesso Wi-Fi, em diferentes localizações físicas no ambiente. Porém, a informação sobre freqüência de presença de sinal pode ser muito ruidosa devido à natureza imprevisível das falhas de transmissão, as quais podem ocorrer decorrentes de diversos fatores. Este trabalho propõe um novo sistema de localização Wi-Fi, o WBLS (Wireless Based Location System), que não considera a informação sobre freqüência de presença de sinal no processo de estimação, visando eliminar os ruídos a ela associados. O WBLS explora o fato da potência do sinal Wi-Fi variar com a localização e usa um HMM descrito em um grafo onde os nós representam as localizações e as arestas, as probabilidades de transição em função da topologia do ambiente e das velocidades esperadas de um pedestre portando um dispositivo móvel. Investiga-se em que situações a eliminação da informação sobre freqüência de presença de sinal devido a seus ruídos associados aumenta a exatidão da estimativa de localização, apesar do descarte da informação em si. Os experimentos realizados demonstram que a característica mais importante do WBLS é uma particular robustez ao lidar com desligamentos de pontos de acesso, os quais podem ocorrer sem nenhum aviso ou previsão em um ambiente onde pouco controle se tem sobre sua infra-estrutura. / The proliferation of mobile computing devices and wireless networks has fostered a growing interest in location-based systems and services for Portable Wireless Devices, specially in indoor environments. The location of a handheld device is a critical parameter in context-aware applications, which require high degree of accuracy of location estimation. However, designing and developing indoor location systems with increasing estimation accuracy and decreasing cost installation is a challenging problem. A very interesting approach to reach low-cost requirements consists in using the pre-existing IEEE 802.11 wireless local area network (WLAN) infrastructure that is already installed in many places. Most of the WLAN indoor location approaches proposed in the literature are based on probabilistic techniques which show good performance and are becoming increasingly popular. Such approaches use a map of received signal strength information and signal presence frequency collected from multiple Wi-Fi access points at different physical locations in the environment. However, the signal presence frequency information can be very noisy due to the unpredictable nature of transmissions failures, which can be caused by several factors. This work proposes a new probabilistic-based Wi-Fi location system, WBLS (Wireless Based Location System), which doesn\'t take the signal presence frequency information into account in the estimation process, in an attempt to eliminate its associated noise. WBLS exploits the fact that Wi-Fi signal strength vary with location, and uses an HMM on a graph of location nodes whose transition probabilities are a function of the building\'s floor plan and expected speeds of a pedestrian holding a portable device. We investigate if eliminating signal presence frequency information due to its associated noise increases the accuracy of the location estimation, despite the amount of information about the signal presence that is discarded. Experiments show that the most important feature of WBLS is a particular robustness while dealing with access points shutdowns that may happen without any warning in an environment where there is little control over the infrastructure.

Submitted by Samira Prince (prince@ufpa.br) on 2012-05-22T14:49:02Z No. of bitstreams: 2 Dissertacao_ArcaboucoAprovisionamentoQos.pdf: 2402283 bytes, checksum: 538c75b15b62e851587e9c898048d628 (MD5) license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) / Approved for entry into archive by Samira Prince(prince@ufpa.br) on 2012-05-22T14:49:50Z (GMT) No. of bitstreams: 2 Dissertacao_ArcaboucoAprovisionamentoQos.pdf: 2402283 bytes, checksum: 538c75b15b62e851587e9c898048d628 (MD5) license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) / Made available in DSpace on 2012-05-22T14:49:50Z (GMT). No. of bitstreams: 2 Dissertacao_ArcaboucoAprovisionamentoQos.pdf: 2402283 bytes, checksum: 538c75b15b62e851587e9c898048d628 (MD5) license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Previous issue date: 2011 / Recentemente a sociedade está vivendo em meio a um aglomerado de dispositivos móveis com múltiplas interfaces sem fio que permitem que clientes móveis domésticos e corporativos solucionem problemas rotineiros no menor espaço de tempo e em diversas localizações. Por outro lado, a disponibilidade de diversas tecnologias de acesso sem fio como: Wi-Fi (Wireless Fidelity), WiMAX (Worldwide Interoperability for Microwave Access) e LTE (Long Term Evolution), proporcionam um cenário heterogêneo com diversas oportunidades de conectividade para o usuário de dispositivos com múltiplas interfaces. Alguns dos desafios atuais no contexto da concepção da então denominada NGN (Next Generation Networks) são o desenvolvimento de arcabouços e mecanismos que viabilizem tanto o suporte adequado à Qualidade de Serviço (QoS – Quality of Service) e à Qualidade de Experiência (QoE – Quality of Experience) para aplicações multimídia, quanto a garantia de equidade entre vazões de diferentes aplicações em ambiente heterogêneo. Esta dissertação propõe um arcabouço para o aprovisionamento de QoS e QoE em redes sem fio heterogêneas formada por redes WiMAX e Wi-Fi. Especificamente, nossa solução provê mapeamento estático de QoS entre as classes de serviços WiMAX e categorias de acesso Wi-Fi. Além disso, nossa proposta também combina funcionalidades de equidade entre vazões com a solução de mapeamento, a fim de alcançar um bom compromisso tanto para o operador da rede, quanto para o usuário, através de uma nova metodologia de coleta e calculo de vazão agregada e algoritmo de decisão de handover vertical. A avaliação quantitativa da proposta foi realizada através de modelos de simulação no ns-2 (Network Simulator). Os resultados de desempenho demonstram a eficiência da arquitetura em termos de métricas de QoS (vazão, vazão média e atraso) e QoE (PSRN - Peak Signal to Noise Ratio, SSIM - Structural Similarity Index e VQM - Video Quality Metric). / Recently, the society is living amid an agglomerate of mobile devices with multiple wireless interfaces that allow mobile customers home and business solve routine problems in the shortest time and in several locations. On the other hand, the availability of various wireless access technologies such as Wireless Fidelity (Wi-Fi), Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE), provide a heterogeneous scenario with several connectivity opportunities for the user of devices with multiple interfaces. Some of the current challenges in framing the so called Next Generation Networks (NGN) are the development of frameworks and mechanisms that enable both adequate support for Quality of Service (QoS) and Quality of Experience (QoE) for multimedia applications, and assurance equity among throughputs of different applications in a heterogeneous environment. This dissertation proposes a framework for provisioning of QoS and QoE in heterogeneous wireless networks consisting of WiMAX and Wi-Fi networks. Specifically, our solution provides static mapping of QoS between classes of service WiMAX and access categories Wi-Fi. In addition, our proposal also combines features of equity among throughputs with the mapping solution in order to achieve a good tradeoff for both, for the network operator and for the user, through a new methodology for collection and calculation of aggregate throughput and algorithm for Vertical Handover Decision (VHD). The quantitative evaluation of the proposal was carried out using simulation models in Network Simulator (NS-2). The performance results demonstrate the efficiency of the framework in terms of QoS (throughput, average throughput and delay) and QoE (Peak Signal to Noise Ratio, Structural Similarity Index and Video Quality Metric) metrics.

A proliferação de dispositivos móveis e de redes sem fio tem encorajado um crescente interesse em sistemas e serviços baseados na localização de dispositivos portáteis, especialmente em ambientes internos, como edifícios e residências. A localização de um dispositivo portátil é um parâmetro crítico em aplicações baseadas no contexto, as quais requerem grande precisão na estimativa de localização. Entretanto, projetar e desenvolver sistemas de localização em interiores, com crescente precisão na estimação e decrescente custo de instalação, é um problema desafiador. Uma abordagem bastante interessante para satisfazer os requisitos de baixo custo consiste em utilizar as infra-estruturas existentes de redes locais sem fio (WLAN) no padrão IEEE 802.11, que já estão instaladas em muitos ambientes. A maioria das abordagens para localização usando WLAN propostas na literatura é baseada em técnicas probabilísticas, que apresentam bom desempenho e estão cada vez mais populares. Estas técnicas usam um mapa com a informação da potência recebida do sinal (RSSI) juntamente com a freqüência de presença de sinal coletada de múltiplos pontos de acesso Wi-Fi, em diferentes localizações físicas no ambiente. Porém, a informação sobre freqüência de presença de sinal pode ser muito ruidosa devido à natureza imprevisível das falhas de transmissão, as quais podem ocorrer decorrentes de diversos fatores. Este trabalho propõe um novo sistema de localização Wi-Fi, o WBLS (Wireless Based Location System), que não considera a informação sobre freqüência de presença de sinal no processo de estimação, visando eliminar os ruídos a ela associados. O WBLS explora o fato da potência do sinal Wi-Fi variar com a localização e usa um HMM descrito em um grafo onde os nós representam as localizações e as arestas, as probabilidades de transição em função da topologia do ambiente e das velocidades esperadas de um pedestre portando um dispositivo móvel. Investiga-se em que situações a eliminação da informação sobre freqüência de presença de sinal devido a seus ruídos associados aumenta a exatidão da estimativa de localização, apesar do descarte da informação em si. Os experimentos realizados demonstram que a característica mais importante do WBLS é uma particular robustez ao lidar com desligamentos de pontos de acesso, os quais podem ocorrer sem nenhum aviso ou previsão em um ambiente onde pouco controle se tem sobre sua infra-estrutura. / The proliferation of mobile computing devices and wireless networks has fostered a growing interest in location-based systems and services for Portable Wireless Devices, specially in indoor environments. The location of a handheld device is a critical parameter in context-aware applications, which require high degree of accuracy of location estimation. However, designing and developing indoor location systems with increasing estimation accuracy and decreasing cost installation is a challenging problem. A very interesting approach to reach low-cost requirements consists in using the pre-existing IEEE 802.11 wireless local area network (WLAN) infrastructure that is already installed in many places. Most of the WLAN indoor location approaches proposed in the literature are based on probabilistic techniques which show good performance and are becoming increasingly popular. Such approaches use a map of received signal strength information and signal presence frequency collected from multiple Wi-Fi access points at different physical locations in the environment. However, the signal presence frequency information can be very noisy due to the unpredictable nature of transmissions failures, which can be caused by several factors. This work proposes a new probabilistic-based Wi-Fi location system, WBLS (Wireless Based Location System), which doesn\'t take the signal presence frequency information into account in the estimation process, in an attempt to eliminate its associated noise. WBLS exploits the fact that Wi-Fi signal strength vary with location, and uses an HMM on a graph of location nodes whose transition probabilities are a function of the building\'s floor plan and expected speeds of a pedestrian holding a portable device. We investigate if eliminating signal presence frequency information due to its associated noise increases the accuracy of the location estimation, despite the amount of information about the signal presence that is discarded. Experiments show that the most important feature of WBLS is a particular robustness while dealing with access points shutdowns that may happen without any warning in an environment where there is little control over the infrastructure.

Les Technologies d'Information et de Communication (TIC) facilitent la collecte et le traitement d'informations numériques, aussi nombreuses que variées, et sont de plus en plus sollicitées dans différents domaines (géographie, informatique, économie, statistiques etc.). La thèse a pour objectif de montrer les apports des TIC dans l'étude d'objets ou phénomènes géographiques dont la distribution est variable dans l'espace. Dans un premier temps, des inégalités territoriales de diffusion d'infrastructures Internet sont observées à différentes échelles, ce qui est communément appelé " la fracture numérique ". Pour remédier à ces inégalités, en particulier dans des espaces peu densément peuplés, la solution proposée est d'envisager une desserte maximale du territoire par la technologie non-filaire (Wi-Fi). Cette solution a été appliquée pour une commune drômoise (La Roche-sur-le-Buis). Les données (bâti) sont de type images et nécessitent un dispositif de repérage et de collecte approprié qui fait l'objet du second temps de la recherche. L'objectif a été de trouver une méthode relativement simple et accessible d'extraction de données du bâti sous un logiciel de géo-localisation en accès libre (type Google Earth). Ce logiciel permet d'accéder à des bases de données d'images raster grand public couvrant le monde entier. A une échelle fine, les méthodes habituelles de télédétection n'étant pas assez satisfaisantes, une autre méthode basée sur une stratégie de choix de la cible, de l'image (bonne résolution spatiale) et de la méthode de détection de l'objet spatial (bâti) à l'aide d'un Système d'Information Géographique (SIG) est proposée en mode vecteur. Elle est testée en France et en Syrie à différentes échelles. Les résultats montrent que la qualité de cette approche semi-automatique, voire automatique, est liée à certains paramètres dans les trois phases de la méthode : phase de choix des données, phase de traitement et phase d'analyse

Avec l'arrivée des systèmes radio mobiles de troisième et de quatrième génération, les standards de communications ont tendance à occuper plus de bande pour pouvoir assurer des services de voix, de données et de multimédia. En parallèle, le terminal mobile doit être reconfigurable pour couvrir à la fois le service cellulaire et la connectivité de données. Dans ce contexte, la tendance est d'intégrer les fonctions radio et bandes de base sur le même substrat en utilisant la technologie CMOS afin de réduire la surface, le coût de fabrication et la consommation des terminaux sans fils. Récemment, de nouvelles architectures de réception radio dites " échantillonnées " sont apparues (TexasInstruments, STMicroelectronics, UCLA). Dans ce cas, l'échantillonnage est fait directement sur le signal RF et la majorité du traitement de signal se fait en temps-discret par des capacités commutées. L'évolution de la technologie CMOS et la miniaturisation des transistors rendent la conception analogique de plus en plus difficile (capacités parasites, bruit, linéarité, etc.). De nouveaux effets parasites apparaissent comme la fuite de grille qui inquiète désormais les technologues et les concepteurs de circuits. D'un autre côté, des contraintes de dynamique surgissent avec la diminution des tensions d'alimentation et le bruit des circuits numériques de plus en plus denses augmente considérablement. Le but de ce travail de thèse est de répondre à la question de la portabilité de la solution échantillonnée, en étudiant l'impact des différents effets parasites cités précédemment sur les performances radio de la solution. Ainsi, les critères de portabilité qui sont considérés sont la reconfigurabilité, l'immunité aux effets parasites, l'adaptation à la baisse des tensions d'alimentation, la surface, la consommation et la facilité de conception. Ce travail de thèse a été basé sur des études théoriques et sur des simulations d'une solution échantillonnée de réception radio. Afin d'affronter réellement les problématiques de portabilité, un portage d'une chaîne de réception échantillonnée Wi-Fi/WiMAX de CMOS 65nm à 45nm a été réalisé. Les résultats de mesures obtenus sur ce circuit donnent une grande confiance vis-à-vis des performances radio de la solution échantillonnée et constituent un premier élément de réponse concret à la question de portabilité étudiée.

Ce mémoire de thèse porte sur la conception, la validation et l'application du codage canal en mode relais dans le cadre de système WiFi. A cette fin, le modèle de transmission coopératif est introduit dans le chapitre 1 et le chapitre 2 se consacre à l'étude du décodeur MIMO intégré dans le système coopératif. Le chapitre 3 se consacre à l'étude du protocole baptisé Relais-SISO et sa mise en œuvre dans le standard IEEE802.11a à 5 GHz. De nouvelles structures de trame sont proposées en ajoutant des préambules destinés à être exploités par le mode coopératif. Des résultats de simulation démontrent l'avantage de la technique coopérative. A notre connaissance, ces travaux sont les premiers à proposer une application du codage relais au WiFi. Le chapitre 4, une stratégie hybride basée sur la solution Relais-SISO est présentée car elle améliore les performances du système Relais-SISO. Le mode hybride proposé s'appuie sur l'évaluation de la qualité du lien coopératif pour activer ce mode. Dans le chapitre 5, l'optimisation du mode coopératif de la couche physique est réalisé en mettant en œuvre la chaîne de partitionnement du Golden Code. On met en évidence le fait qu'une simple combinaison de ce dernier et d'un code convolutif, fournit un gain de codage grâce au gain du déterminant du Golden code. Le travail serait incomplet sans tenir compte du nouveau standard WiFi IEEE802.11n ratifié en Octobre 2009. C'est l'objet du chapitre 6, qui propose un protocole coopératif, baptisé Relay-MIMO, qui exploite d'une manière conjointe la diversité MIMO et la diversité de coopération.

In mobile computing systems, predicting the next location of a mobile wireless user has gained interest over the past decade. Location prediction may have a wide-range of application areas such as network load balancing, advertising and web page prefetching. In the literature, there exist many location predictors which are divided into two main classes: domain-independent and domain-specific. Song et al. compare the prediction accuracy of the domain-independent predictors from four major families, namely, Markov-based, compression-based, PPM and SPM predictors on Dartmouth&#039 / s campus-wide Wi-Fi mobility data. As a result, the low-order Markov predictors are found as the best predictor. In another work, Bayir et al. propose a domain-specific location predictor (LPMP) as the application of a framework used for discovering mobile cell phone user profiles. In this thesis, we evaluate LPMP and the best Markov predictor with Dartmouth&#039 / s campus-wide Wi-Fi mobility data in terms of accuracy. We also propose a simple method which improves the accuracy of LPMP slightly in the location prediction part of LPMP. Our results show that the accuracy of the best Markov predictor is better than that of LPMP in total. However, interestingly, LPMP yields more accurate results than the best Markov predictor does for the users with the low prediction accuracy.

Ενδιαφέρον παρουσιάζει η αυξημένη ανάγκη για εφαρμογές εσωτερικού χώρου οι οποίες να είναι σε θέση να χρησιμοποιούν την ασύρματη τεχνολογία για να εντοπίσουν την θέση των χρηστών με σκοπό την εκμετάλλευση της πληροφορίας της θέσης τους για την αποστολή διαφόρων πληροφοριών ενδιαφέροντος. Στην εργασία αυτή προτείνεται ένα σύστημα εντοπισμού θέσης του οποίου η εξαγόμενη πληροφορία χρησιμοποιείται σε m-commerce εφαρμογές (mobile commerce) μέσω τεχνικών εξόρυξης γνώσης (data mining). Το σύστημα το οποίο προτείνεται αποτελείται από δύο κεντρικά υποσυστήματα. Το πρώτο υποσύστημα αποτελεί ένα σύστημα εντοπισμού θέσης μέσα σε ένα Wi-Fi δίκτυο. Το δεύτερο υποσύστημα περιλαμβάνει την λογική για την εξόρυξη δεδομένων από το πληροφοριακό περιεχόμενο της θέσης των χρηστών ώστε να μπορεί να χρησιμοποιηθεί στον εμπορικό τομέα. / The increased need for applications of indoor localization which use wireless technology in order to locate users’ position and exploiting this position information for extracting deeper knowledge has motivated this paper. In this work it is proposed a system of localization where the exported information is used in m-commerce applications (mobile commerce) via techniques of data mining. The system which is suggested is constituted of two central sub systems. The first sub system constitutes a system of localization in a Wi-Fi network. The second sub system includes the logic of the excavation of data from the informative content of users’ position so that it can be used in the commercial sector.

No description available.