IEEE 802.11 networks successfully satisfy high data demands and are cheaper compared to cellular networks. Modern mobile computers and phones are equipped with 802.11 and are VoIP capable. Current network designs do not dynamically accommodate changes in the usage. We propose a dynamic power control algorithm that provides greater capacity within a limited geographic region. Most other power algorithms necessitate changes in 802.11 requiring hardware changes. Proposed algorithm only requires firmware updates to enable dynamic control of APs transmit power. We use earlier studies to determine the limit of the number of users to optimize power. By lowering transmit power of APs with large number of users, we can effectively decrease the cell size. The resulting gap is then covered by dynamically activating additional APs. This also provides greater flexibility and reduces the network planning costs. / by Serkan Dural. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

El reciente aumento en la implementación de redes inalámbricas nos obliga a contemplar con más cuidado el aspecto de la seguridad en este tipo de redes. Así como en el caso de las típicas redes de datos con cables (siendo la tecnología Ethernet la más utilizada para estos casos), tiene que asegurarse que los usuarios de una red inalámbrica se encuentren conectados a ésta de una manera segura, teniendo en cuenta que ahora el medio de transmisión ya no se restringe a un cable, sino que se encuentra en todo el ambiente que lo rodea. Debe de comprobarse que el usuario sea quien dice ser (autenticación), que solo tenga acceso a los recursos que le corresponda (autorización) y también llevar a cabo un registro de las actividades que haga dentro de la red (contabilidad); realizando todo esto de una manera segura y sin que sujetos ajenos a la red puedan estar leyendo información confidencial ni mucho menos tratar de modificarla. En esta tesis se tiene pensado explicar el diseño e implementación que se debería de llevar a cabo dentro de un escenario dado para la instalación de una red inalámbrica segura que contemple la administración de sus usuarios por medio de una plataforma de gestión Web basada en PHP, integrada a un servidor de directorios LDAP con compatibilidad hacia implementaciones libres y cerradas de dicho protocolo, un servidor de autenticación RADIUS y un servidor de base de datos MySQL. Se estudiarán los principales aspectos aplicados en redes inalámbricas Wi-Fi, poniendo especial énfasis en la seguridad de la red y de sus usuarios con mecanismos tales como: WPA2 (IEEE 802.11i), 802.1X, EAP, RADIUS, entre otros. / Tesis

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2018. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). / Inúmeras tecnologias promissoras foram desenvolvidas desde a concepção da Internet das Coisas (IoT, do inglês Internet of Things) que poderão modificar diferentes aspectos em nosso cotidiano. Tendo em vista o rápido crescimento da IoT, foi criado o grupo de tarefa IEEE 802.11ah para o desenvolvimento de uma nova norma Wi-Fi para lidar com os principais desafios da IoT, que são a conectividade de muitos dispositivos com recursos de energia limitados a um único ponto de acesso e o aumento do alcance das transmissões para distâncias muito maiores do que aquelas tipicamente utilizadas em redes locais sem fio. Assim, esse padrão traz novos mecanismos nas camadas física e de enlace para atender aos requisitos da IoT. Na camada física, houve modificações para operação em faixas de frequências abaixo de 1 GHz e, na camada MAC, o padrão traz novos mecanismos de economia de energia para ter um melhor desempenho em redes densas, sendo um deles o acesso restrito ao canal (RAW, do inglês Restricted Access Window). Recentemente, há muitos trabalhos sobre o IEEE 802.11ah, entretanto, a maior parte deles trazem ideias de agrupamento ou modelagem analítica para descobrirem o tamanho ótimo do RAW para obter maior desempenho da rede. No entanto, para um melhor entendimento dos efeitos dos diversos parâmetros e mecanismos do IEEE 802.11ah, esta dissertação apresenta um modelo analítico da função de coordenação distribuída do IEEE 802.11ah para o caso em que as estações estão distribuídas uniformemente em diversos slots RAW e possuem a mesma prioridade de tráfego, sob condições de tráfego saturado e canal ideal. Em nosso modelo, consideramos que cada intervalo de beacon possui somente um RAW o qual é dividido em slots RAW, e estudamos o impacto no desempenho da vazão ao variar o número de slots RAW e o número de estações na rede. Além disto, introduzimos ao modelo Markoviano uma probabilidade de término do slot RAW e propomos duas expressões empíricas para o cálculo desta probabilidade. Por fim validamos o modelo analítico com simulações no simulador de redes NS3 e, a partir das simulações computacionais, encontramos uma constante de ajuste para aproximar o modelo das simulações. / Many promising technologies have been developed since the conception of the Internet of Things (IoT) that can modify different aspects of our daily lives. In light of the rapid growth of IoT, it was created the IEEE 802.11ah Task Group to develop a newWi-Fi standard to address IoT’s key challenges, which are the connectivity of many devices with limited power resources to a single access point and the increase in the transmissions range for distances much greater than those typically used in wireless local area networks. Thus, this standard brings new mechanisms in the physical and link layers to meet IoT requirements. In the physical layer, there were modifications to permit the operation in frequency bands below 1 GHz and, in the MAC layer, the standard brings new power saving mechanisms to perform better in dense networks, one of which is the restricted access to the channel (RAW). Recently, there have been a lot of work on IEEE 802.11ah, however, most of them bring grouping or analytical modeling ideas to find out the optimal RAW size for a higher network performance. On the other hand, for a better understanding of the effects of the various IEEE 802.11ah parameters and mechanisms, this dissertation presents an analytical model of the distributed coordination function of IEEE 802.11ah for the case where the stations are evenly distributed in several RAW slots and have the same traffic priority, under conditions of saturated traffic and ideal channel. In our model, we consider that each beacon interval has only one RAW which is divided into RAW slots, and we study the impact on throughput performance by varying the number of RAW slots and the number of stations in the network. In addition, we introduce to the Markovian model a probability of reaching the end of a RAW slot and propose two heuristic expressions for this probability calculation. Finally we validate the analytical model with simulations in the networks simulator NS3 and, from the computational simulations, we find an adjustment constant to approximate the model of the simulations.

Doctor of Philosopy (PhD) / Wireless communication always attracts extensive research interest, as it is a core part of modern communication technology. During my PhD study, I have focused on two research areas of wireless communication: IEEE 802.11 network performance analysis, and wireless cooperative retransmission. The first part of this thesis focuses on IEEE 802.11 network performance analysis. Since IEEE 802.11 technology is the most popular wireless access technology, IEEE 802.11 network performance analysis is always an important research area. In this area, my work includes the development of three analytical models for various aspects of IEEE 802.11 network performance analysis. First, a two-dimensional Markov chain model is proposed for analysing the performance of IEEE 802.11e EDCA (Enhanced Distributed Channel Access). With this analytical model, the saturated throughput is obtained. Compared with the existing analytical models of EDCA, the proposed model includes more correct details of EDCA, and accordingly its results are more accurate. This better accuracy is also proved by the simulation study. Second, another two-dimensional Markov chain model is proposed for analysing the coexistence performance of IEEE 802.11 DCF (Distributed Coordination Function) and IEEE 802.11e EDCA wireless devices. The saturated throughput is obtained with the proposed analytical model. The simulation study verifies the proposed analytical model, and it shows that the channel access priority of DCF is similar to that of the best effort access category in EDCA in the coexistence environment. The final work in this area is a hierarchical Markov chain model for investigating the impact of data-rate switching on the performance of IEEE 802.11 DCF. With this analytical model，the saturated throughput can be obtained. The simulation study verifies the accuracy of the model and shows the impact of the data-rate switching under different network conditions. A series of threshold values for the channel condition as well as the number of stations are obtained to decide whether the data-rate switching should be active or not. The second part of this thesis focuses on wireless cooperative retransmission. In this thesis, two uncoordinated distributed wireless cooperative retransmission strategies for single-hop connection are presented. In the proposed strategies, each uncoordinated cooperative neighbour randomly decide whether it should transmit to help the frame delivery depending on some pre-calculated optimal transmission probabilities. In Strategy 1, the source only transmits once in the first slot, and only the neighbours are involved in the retransmission attempts in the subsequent slots. In Strategy 2, both the source and the neighbours participate in the retransmission attempts. Both strategies are first analysed with a simple memoryless channel model, and the results show the superior performance of Strategy 2. With the elementary results for the memoryless channel model, a more realistic two-state Markov fading channel model is used to investigate the performance of Strategy 2. The simulation study verifies the accuracy of our analysis and indicates the superior performance of Strategy 2 compared with the simple retransmission strategy and the traditional two-hop strategy.

La problématique de la qualité de service dans les réseaux locaux sans fils IEEE 802.11 demeure l'un des défis délicats à surmonter par la communauté scientifique. L'étude et l'évaluation des approches apportés pour le support de QoS dans ce type de réseaux que ce soit par des simulations, des modèles analytiques ou des mesures réelles montre que ces approches sont toujours insuffisantes pour apporter des vraies garanties de qualité de services aux utilisateurs sans fils. Suite à des travaux effectués au CRAN qui ont porté sur l'équilibrage des charges dans les réseaux Ethernet industriels nous avons opté pour une méthode d'équilibrage de charges dans le contexte des réseaux hotspots 802.11. L'objectif de cette approche étant d'équilibrer les charges des points d'accès pour satisfaire aux besoins en termes de qualité de service de l'ensemble des applications sans fils. Ces besoins sont exprimés en termes de disponibilité, de délais, de bande passante...Nous avons alors définis un algorithme d'équilibrage de charges pouvant établir dynamiquement des associations optimales entre les utilisateurs présents dans un hotspot et les points d'accès en service. Un protocole d'échanges entre les stations sans fils et les points d'accès et entre ces derniers et le serveur d'équilibrage de charges a été établi. Le fonctionnement de ce protocole a été vérifié et simulé en utilisant les outils SDL et MSC. Pour l'évaluation de la performance de l'approche d'équilibrage par rapport à la méthode d'accès de base du protocole, un ensemble de simulations ont été effectués. Ces simulations effectuées sur OPNET montrent que cette approche permet d'améliorer un ensemble de paramètres de qualité de service perçue par les utilisateurs d'un réseau Hotspot.

L'utilisation de la communication sans fil dans les applications de contrôle offre de nombreux avantages comme la mobilité... Toutefois, la communication sans fil souffre de nombreux inconvénients tels que la perte d'information, délais aléatoires. Ces problèmes sont essentiellement induits par le non déterministe du comportement de la communication sans fil qui peut avoir un impact négatif sur la performance du système. L'objectif de ce travail porte sur l'amélioration des performances de Systèmes Discrets Contrôlés via un Réseau Sans fil. Ses systèmes sont caractérisés par une commande logique distribuée sur des automates programmables et des boîtiers d'entrées/sorties déportés communiquant via un réseau de communication sans fil, IEEE 802.11. L'approche proposée repose sur un processus de co-conception basé : un, sur une modélisation conjointe des comportements de la commande et du réseau au travers de modèles SED déterministes pour la commande et stochastiques pour le réseau, et sur la simulation pour évaluer les performances des SDCR sans fil et notamment leur temps de réponse. Deux, la proposition d'un algorithme qui alloue dynamiquement les priorités définies par l'IEEE 802.11e sur les trafics de communication en fonction des besoins et des états de la commande; cet algorithme est évalué sur un cas d'étude, pour lequel la communication sans fil induit des risques de collision entre des équipements d'une installation industrielle, en utilisant l'environnement de simulation précédemment défini. Les simulations montrent une amélioration de la performance du système surtout dans des cas où le réseau est très chargé.

<p>The IEEE 802.11b standard is today the only commonly used standard in Europe for fast wireless networks. This makes it possible to connect computers to networks in places where it is not possible to use wires. Examples of such situations are internet access at airports, communication in emergency areas or for military communication. Common for all these situations is that network security is important. </p><p>This thesis consists of two different parts. The first part handles the security mechanisms and the second part is an evaluation of the possibilities to use IEEE 802.11b in embedded applications. The part that handles the security includes the security mechanisms found in the standard, flaws in these mechanisms and methods that try to reduce these problems.</p>

<p>The usage of Wireless Local Area Networks is increasing rapidly throughout the world. The technology today is not quality proof for the market’s demands. We want to be able to completely wireless perform our demands, such as confer via video or IP-telephony. This is what we call multimedia real-time traffic. It may be achieved over the physical infrastructure in some areas with good results. The goal of this Master’s Thesis is to analyze the possibilities and give solutions and suggestions to achieve multimedia over the wireless networks, with emphasis on the protocol Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). </p><p>This Master’s Thesis is a theoretical study and the suggested solutions have not been tested in an actual wireless network. Instead they have been tested by computer simulation to give an indication of improvements. Basic configurations are set to the same as in the IEEE 802.11 standard. </p><p>Different methods to reach possible improvements of a WLAN are studied, analyzed and simulated. Such methods are: priority, congestion management and multi-channel protocol. Simulations results show how the priority affects the wireless network and how a multi-channel protocol improves the latency and efficiency of the network. The simulation part is concentrated to show improvements of real-time traffic, which is time sensitive. With a multi- channel protocol the network can allow more users, i.e. more traffic. Also, the network will gain improvement in stability.</p>

Future Wireless Local Area Networks (WLANs) with high carrier frequencies and wide channels need a dense deployment of Access Points (APs) to provide good performance. In densely deployed WLANs associations of stations and handovers need to be managed more intelligently than today. This dissertation studies when and how a station should perform a handover and to which AP from a theoretical and a practical perspective. We formulate and solve optimization problems that allow to compute the optimal AP for each station in normal WLANs and WLANs connected via a wireless mesh backhaul. Moreover, we propose to use software defined networks and the OpenFlow protocol to optimize station associations, handovers and traffic rates. Furthermore, we develop new mechanisms to estimate the quality  of a link  between a station and an AP. Those mechanisms allow optimization algorithms to make better decisions about when to initiate a handover. Since handovers in today’s WLANs are slow and may disturb real-time applications such as video streaming, a faster procedure is developed in this thesis. Evaluation results from wireless testbeds and network simulations show that our architectures and algorithms significantly increase the performance of WLANs, while they are backward compatible at the same time.

In this thesis, we characterize the proprietary active scanning algorithm of several wireless network interface cards. Our experiments are the first of its kind to observe the complete scanning process as the wireless network interface cards probe all the channels in the 2.4GHz spectrum. We discuss the: 1) correlation of channel popularity during active scanning and access point channel deployment popularity; 2) number of probe request frames statistics on each channel; 3) channel probe order; and 4) dwell time. The knowledge gained from characterizing wireless network interface cards is important for the following reasons: 1) it helps one understand how active scanning is implemented in different hardware and software; 2) it can be useful in identifying a wireless rogue host; 3) it can help implement Active Scanning in network simulators; and 4) it can radically influence research in the familiar fields like link-layer handovers and effective deployment of access points.