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Towards a reliable seamless mobility support in heterogeneous IP networksKhan, Shoaib January 2009 (has links)
Next Generation networks (3G and beyond) are evolving towards all IP based systems with the aim to provide global coverage. For Mobility in IP based networks, Mobile IPv6 is considered as a standard by both industry and research community, but this mobility protocol has some reliability issues. There are a number of elements that can interrupt the communication between Mobile Node (MN) and Corresponding Node (CN), however the scope of this research is limited to the following issues only: • Reliability of Mobility Protocol • Home Agent Management • Handovers • Path failures between MN and CN First entity that can disrupt Mobile IPv6 based communication is the Mobility Anchor point itself, i.e. Home Agent. Reliability of Home Agent is addressed first because if this mobility agent is not reliable there would be no reliability of mobile communication. Next scenario where mobile communication can get disrupted is created by MN itself and it is due to its mobility. When a MN moves around, at some point it will be out of range of its active base station and at the same time it may enter the coverage area of another base station. In such a situation, the MN should perform a handover, which is a very slow process. This handover delay is reduced by introducing a “make before break” style handover in IP network. Another situation in which the Mobile IPv6 based communication can fail is when there is a path failure between MN and CN. This situation can be addressed by utilizing multiple interfaces of MN at the same time. One such protocol which can utilize multiple interfaces is SHIM6 but it was not designed to work on mobile node. It was designed for core networks but after some modification in the protocol , it can be deployed on mobile nodes. In this thesis, these issues related to reliability of IPv6 based mobile communication have been addressed.
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Techniques et métriques non intrusives pour caractériser les réseaux Wi-Fi / Metrics and non-intrusive techniques to characterize Wi-Fi networksMolina Troconis, Laudin Alessandro 05 July 2018 (has links)
Aujourd’hui, les appareils mobiles sont présents dans le monde entier. Ces appareils permettent aux utilisateurs d'accéder à l’Internet notamment par l'intermédiaire des réseaux WiFi. La diversité et le nombre de déploiements sans coordination centrale (y compris les utilisateurs à leur domicile) conduit à des déploiements qu’on peut qualifier de chaotiques. En conséquence, les réseaux WiFi sont largement déployés avec une forte densité dans les zones urbaines. Dans ce contexte, les utilisateurs et les opérateurs tentent d’exploiter ces déploiements pour obtenir une connectivité omniprésente, et éventuellement d'autres services. Cependant, pour tirer parti de ces déploiements, il faut des stratégies pour identifier les réseaux utilisables et choisir les plus adaptés aux besoins. Pour cela, nous étudions le processus de découverte des réseaux dans le contexte de ces déploiements. Ensuite, nous présentons une plateforme de partage de mesures sans fil, un système d'information collaboratif où les stations mobiles recueillent des mesures du réseau et les envoient à un système central. En rassemblant mesures provenant de différents utilisateurs, la plateforme donne accès à des caractéristiques du déploiement précieuses. Nous évaluons l'utilité de cette plateforme collaborative grâce à deux applications : (1) l’ensemble minimal de points d'accès, afin de réduire l'énergie nécessaire pour offrir une couverture WiFi dans une zone donnée. (2) l'optimisation des paramètres de recherche de réseau, afin de réduire le temps nécessaire pour découvrir les réseaux existants. Ensuite, nous étudions une méthode passive pour déterminer si un réseau fonctionne dans un canal saturé. / Nowadays, mobile devices are present worldwide, with over 4.40 Billion devices globally. These devices enable users to access the Internet via wireless networks. Different actors (e.g., home users, enterprises) are installing WiFi networks everywhere, without central coordination, creating chaotic deployments. As a result, WiFi networks are widely deployed all over the world, with high accesspoint (AP) density in urban areas. In this context, end-users and operators are trying to exploit these dense network deployments to obtain ubiquitous Internet connectivity, and possibly other services. However, taking advantage of these deployments requires strategies to gather and provide information about the available networks. In this dissertation, we first study the network discovery process within the context of these deployments. Then, we present the Wireless Measurements Sharing Platform, a collaborative information system, to which mobile stations send simple network measurements that they collected. By gathering and processing several network measurements from different users, the platform provides access to valuable characteristics of the deployment. We evaluate the usefulness of this collaborative platform thanks to two applications: (1) the minimal access point set, to reduce the energy needed to offer WiFi coverage in a given area.(2) The optimization of the scanning parameters,to reduce the time a mobile station needs for the network discovery. Finally, we describe a method to identify whether an AP operates ina saturated channel, by passively monitoring beacon arrival distribution.
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[en] PRECODING AND RESOURCE ALLOCATION FOR CELL-FREE MASSIVE MIMO SYSTEMS / [pt] PRÉ-CODIFICAÇÃO E ALOCAÇÃO DE RECURSOS EM SISTEMAS DE MÚLTIPLAS ANTENAS MASSIVOS LIVRES DE CÉLULAS03 December 2020 (has links)
[pt] Sistemas de múltiplas antenas livres de células surgiram recentemente
como uma combinação de MIMO massivo, sistemas de antenas distribuídas
(DAS) e network MIMO. Esta dissertação explora o downlink deste cenário
com pontos de acesso (PAs) de uma ou múltiplas antenas e considerando conhecimento perfeito e imperfeito do canal. São desenvolvidos esquemas que
combinam pré-codificação, alocação de potência e seleção de PAs (SPA).
Para começar, duas estratégias de SPA foram investigadas, uma baseada
em busca exaustiva (BE-SPA) e a outra em coeficientes de desvanecimento
de larga escala (LE-SPA), com o intuito de reduzir a complexidade das redes
livres de células. Subsequentemente, apresentamos duas técnicas iterativas
de pré-codificação, todas seguindo o critério Minimum Mean-Square Error
(MMSE), combinadas à restrição de potência total. A primeira nós chamamos
de MMSE, com restrição de potência total. Nós também incorporamos
robustez ao método desenvolvido chamado RMMSE, um pré-codificador
robusto com restrição de potência total. Como terceiro elemento da configuração
proposta, esquemas de alocação de potência foram desenvolvidos,
com abordagens ótimas, adaptativas e uniformes. Um algoritmo de alocação
de potência ótima (APO) é apresentado, baseado na maximização da
mínima Signal-to-Interference-plus-Noise Ratio (SINR). A solução adaptativa
(APA) é caracterizada pelo gradiente estocástico (GE) do mean-square
error (MSE) e a alternativa uniforme (UPA) propõe a equalização de todos
os coeficientes de potência. Todas as configurações devem respeitar a restrição
de potência por antena, imposta pelo sistema. Uma análise de soma
das taxas é feita, para todas as técnicas estudadas e o custo computacional
de cada uma delas é calculado. Resultados numéricos provam que as
técnicas propostas têm performance superior à pré-codificadores Conjugate
Beamforming (CB) e Zero-Forcing (ZF), ambos com alocação de potência
uniforme e ótima, na forma de taxa de erro de bit (BER), soma das taxas
e mínima SINR. Além disso, os resultados atestam que o desempenho pode
ser mantido e até melhorado com a aplicação de SPA. / [en] Cell-Free Massive multiple-input multiple-output (MIMO) systems
have emerged in recent years as a combination of massive MIMO, distributed
antenna systems (DAS) and network MIMO. This thesis explores the
downlink channel of such scenario with single and multiple-antenna access
points (APs) and takes into account both perfect and imperfect channel
state information (CSI). We propose transmit processing schemes that
combine precoding, power allocation and AP selection (APS). To begin
with, two APS strategies have been investigated, one based on exhaustive
search (ES-APS) and the other on the large-scale fading coefficients (LSAPS),
in order to reduce the complexity of cell-free networks. Subsequently,
we present two iterative precoding techniques following the minimum meansquare
error (MMSE) criterion with total power constraint. The first we
call MMSE, with total power constraint. We also incorporate robustness
in the developed method, called RMMSE, a robust precoder with total
power constraint. As the third element of the proposed schemes, power
allocation techniques are developed, with optimal, adaptive and uniform
approaches. An optimal power allocation (OPA) algorithm is presented
based on the maximization of the minimum signal-to-interference-plus-noise
ratio (SINR). The adaptive solution (APA) is characterized by the stochastic
gradient of the mean-square error (MSE) and the uniform alternative (UPA)
proposes to equalize all power coefficients. All configurations must fulfil an
antenna power constraint, imposed by the system. A sum-rate analysis is
carried out for all studied techniques and the computational cost of each
one is calculated. Numerical results prove that the proposed techniques
outperform existing conjugate beamforming (CB) and zero-forcing (ZF)
precoders, both with uniform and optimal power allocation, in terms of
bit error rate (BER), sum-rate and minimum SINR. Furthermore, we also
attest that performance can be maintained or even improved in the presence
of APS.
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