No description available.

No description available.

Este trabalho apresenta uma ferramenta de simulação computacional de canal de propagação para ambiente macro-celular baseada em modelos geométricos e no modelo estatístico apresentado no relatório COST 259 DCM. Para a implementação desta ferramenta é realizada, inicialmente, uma abordagem dos principais modelos de predição de perda por propagação, utilizados atualmente, assim como, um estudo dos modelos geométricos que fornecem as informações de distribuição de potência temporal e angular para diferentes tipos de distribuições estatísticas de espalhadores. A modelagem geométrica utiliza grupos independentes no qual os espalhadores são distribuídos com uma densidade Gaussiana. A utilização desta distribuição Gaussiana leva a distribuições de atraso e ângulo de chegada mais próximas dos resultados de medições do que o usando distribuição uniforme. A base geométrica define o conceito direcional e temporal. A base estatística define o número de grupo de espalhadores adicionais e suas localizações, quando estes existiram. Efeitos como: direção e potência de chegada de cada grupo de espalhadores, a presença ou não de visada direta entre transmissor e receptor a medida que a estação móvel percorre uma célula e a variação da polarização cruzada foram implementados nesse simulador. Desta forma, essa ferramenta computacional simula tanto a dispersão temporal, presente nos modelos de banda larga, como a dispersão angular, utilizadas em sistemas de comunicação móveis que exploram a diversidade espacial. / This work present a simulation tool for macro cell environment based on geometrical and statistical representation of the scatterers and on the COST 259 Directional Channel Model (DCM). A comprehensive review of the propagation prediction models for terrestrial wireless communication systems and geometric channel models, that provide, times of arrival (TOA) and the angle of arrival (AOA) for diferents statistics scatterers distribution is realized. This tool uses gaussianly distributed scatterers for each cluster. This distribution is naturally more realistic than the uniform distribution leading closer to experimental results. This geometrically based model simulates the TOA dispersion present in wide band channel models and the AOA dispersion necessary for systems that explore spatial diversity. This tool also incorporates the concept of line-of-sight and non-line-of-sight and its birth and death as the mobile station moves in a cell, as well as the appearance and disappearance of additional clusters of scatterers. The output provided by this simulation tool is comprised of all the complex amplitudes, delays and angles of arrival of all multipath components associated with each cluster of scatterers. Mean attenuation and slow fading effects are also incorporated to the model and fast fading appears as a consequence of the multipath interference.

Este trabalho apresenta uma ferramenta de simulação computacional de canal de propagação para ambiente macro-celular baseada em modelos geométricos e no modelo estatístico apresentado no relatório COST 259 DCM. Para a implementação desta ferramenta é realizada, inicialmente, uma abordagem dos principais modelos de predição de perda por propagação, utilizados atualmente, assim como, um estudo dos modelos geométricos que fornecem as informações de distribuição de potência temporal e angular para diferentes tipos de distribuições estatísticas de espalhadores. A modelagem geométrica utiliza grupos independentes no qual os espalhadores são distribuídos com uma densidade Gaussiana. A utilização desta distribuição Gaussiana leva a distribuições de atraso e ângulo de chegada mais próximas dos resultados de medições do que o usando distribuição uniforme. A base geométrica define o conceito direcional e temporal. A base estatística define o número de grupo de espalhadores adicionais e suas localizações, quando estes existiram. Efeitos como: direção e potência de chegada de cada grupo de espalhadores, a presença ou não de visada direta entre transmissor e receptor a medida que a estação móvel percorre uma célula e a variação da polarização cruzada foram implementados nesse simulador. Desta forma, essa ferramenta computacional simula tanto a dispersão temporal, presente nos modelos de banda larga, como a dispersão angular, utilizadas em sistemas de comunicação móveis que exploram a diversidade espacial. / This work present a simulation tool for macro cell environment based on geometrical and statistical representation of the scatterers and on the COST 259 Directional Channel Model (DCM). A comprehensive review of the propagation prediction models for terrestrial wireless communication systems and geometric channel models, that provide, times of arrival (TOA) and the angle of arrival (AOA) for diferents statistics scatterers distribution is realized. This tool uses gaussianly distributed scatterers for each cluster. This distribution is naturally more realistic than the uniform distribution leading closer to experimental results. This geometrically based model simulates the TOA dispersion present in wide band channel models and the AOA dispersion necessary for systems that explore spatial diversity. This tool also incorporates the concept of line-of-sight and non-line-of-sight and its birth and death as the mobile station moves in a cell, as well as the appearance and disappearance of additional clusters of scatterers. The output provided by this simulation tool is comprised of all the complex amplitudes, delays and angles of arrival of all multipath components associated with each cluster of scatterers. Mean attenuation and slow fading effects are also incorporated to the model and fast fading appears as a consequence of the multipath interference.

Baigiamajame magistro darbe nagrinėjami su duomenų perdavimo sparta susiję ryšio kanalo parametrai. Pirmojoje darbo dalyje apžvelgiami užsienio ir Lietuvos mokslininkų atliekami tyrimai kanalo parametrų, susietų su duomenų perdavimo sparta, tematika, analizuojama mobilaus tinklo kanalo parametrų matavimams skirta iranga. Kituose darbo skyriuose išskiriami konkretūs su duomenų pralaidumu sąveikaujantys parametrai. Naudojant šiuos parametrus darbe kuriami modeliai, skirti duomenų perdavimo spartai prognozuoti tikrinamas modelių tinkamumas bei tikslumas. Tiesinės prognozės atveju pasiektas 77,83%, o netiesinės prognozės atveju – 76,19% tikėtinos duomenų perdavimo spartos prognozės tikslumas. Atsižvelgiant į vartotojų interesus siūlomi jų įrangai pritaikyti prognozės modeliai. Darbo pabaigoje tikrinamas sukurtų modelių adekvatumas realiomis ryšio salygomis. / This work analyzes communication channel settings of UMTS technology which are related with a data transfer throughput. Further course of study includes the most specific parameters selection, that arethe most crucial for data speed. Using these parameters it is developed the models suitable for data transfer throughput prediction. To build the model the linear and nonlinear forecasting methods are applied. The linear prediction is made by using linear regression, nonlinear – neural networks. Using linear prediction model 77.83% forecast accuracy has been achieved, while the nonlinear forecast expected transmission rate forecast accuracy is 76.19%.These prediction models accuracy obtained by using eight parameters of the communication channel. Finally in this paper are built the data throughput prediction models that allow to predict data speed using only standard terminal presented channel parameters. At the end all built prediction models are checked in real communication environment.

[pt] A ocorrência de erros em surto é observada principalmente em canais sem fio. Para a análise e melhor entendimento deste tipo de erro, a fim de se melhorar os projetos de sistemas de comunicações digitais, uma modelagem mais precisa, de canais com esta característica, torna-se necessária. Uma diversidade de métodos de estimação de parâmetros tem sido estudada, principalmente aquelas baseadas nos Modelos Escondidos de Markov (HMM do ingês). Em geral cada método é focado em um sistema de comunicações específico, sobre uma camada específica. Neste trabalho é proposto um novo método baseado em um HMM com uma estrutura particular, que permite a dedução de expressões analíticas para todas as estatísticas de interesse. A estrutura do modelo proposto permite a geração de eventos que ocorrem numa sequência binária de dados sujeita a surtos de erro, de acordo com a definição de surtos de erro do CCITT. O modelo proposto possui um número fixo de apenas sete parâmetros, mas o seu número de estados cresce com um de seus parâmetros, que aumenta a precisão, mas não a complexidade. Este trabalho adotou técnicas de otimização, associadas aos métodos de Máxima Verossimilhança e Particle Swarm Optimization (PSO) a fim de realizar a estimação dos parâmetros do modelo proposto. Os resultados demonstram que o modelo proposto permite a caracterização precisa de canais com memória de diversas origens. / [en] The occurrence of error busts is mainly observed in wireless channels. For analysis and a better understanding of such errors, in order to improve the design of communication systems, an accurate modeling of channels with this characteristic is necessary. A lot of parameter estimation methods have been studied, mainly the ones based on Hidden Markov Models (HMM). In general each method is focused in a specific communication system, on a specific layer. In this work it is proposed a new method based on a HMM with particular structure that allows the deduction of analytical expressions for all statistics of interest. The structure of the proposed model permits the generation of events that occur in a binary data sequence subject to bursts of error concerning CCITT error burst definition. The proposed model has a fixed number of only seven parameters but its number of states increase with one of those parameters that increase the accuracy but not the complexity. This work adopted techniques of optimization associated to Maximum Likelihood (ML) and Particle Swarm Optimization (PSO) to perform the parameter estimation to the proposed model. The results show that the proposed model achieves accurate characterization of channels with memory from many different sources.

Satellite communication system designers are continuously struggling to improve the channel capacity. A critical challenge results from the limited power available aboard the satellite.Because of this constraint, the onboard power amplifier must work with a small power supply which limits its maximum output power. To ensure a sufficient Signal-to-Noise power Ratio (SNR) on the receiver side, the power amplifier must work close to its saturation point. This is power efficient but unfortunately adds non-linear distortions to the communication channel. The latters are very penalizing for high order modulations.In the literature, several equalization algorithms have been proposed to cope with the resulting non-linear communication channel. The most popular solution consists in using baseband Volterra series in order to build non-linear equalization filters. On the other hand, the Recurrent Neural Networks (RNNs), which come from the artificial neural network field, are also interesting candidates to generate such non-linear filters. But they are difficult to implement in practice due to the high complexity of their training. To simplify this task, the Echo State Network (ESN) paradigm has been proposed. It has the advantage of offering performances similar to classical RNNs but with a reduced complexity.The purpose of this work is, first, to compare this solution to the state-of-the-art baseband Volterra filters. We show that the classical ESN is able to reach the same performances, evaluated in terms of Bit Error Rate (BER), and has similar complexity. Secondly, we propose a new design for the ESN which achieves a strong reduction in complexity while conserving a similar BER.To compensate for the channel, the literature proposes to adapt the coefficients of these equalizers with the help of a training sequence in order to recover the transmitted constellation points. We show that, in such a case, the usual symbol detection criterion, based on Euclidean distances, is no longer optimal. For this reason, we first propose a new detection criterion which meets the Maximum Likelihood (ML) criterion. Secondly, we propose a modification of the equalizers training reference points in order to improve their performances and make the detection based on Euclidean distances optimal again. This last solution can offer a significant reduction of the BER without increasing the equalization and detection complexity. Only the new training reference points must be evaluated.In this work, we also explore the field of analog equalizers as different papers showed that the ESN is an interesting candidate for this purpose. It is a promising approach to reduce the equalizer complexity as the digital implementation is very challenging and power-hungry, in particular for high bandwidth communications. We numerically demonstrate that a dedicated analog optoelectronic implementation of the ESN can reach the state-of-the-art performance of digital equalizers. In addition, we show that it can reduce the required resolution of the Analog-to-Digital Converters (ADCs).Finally, a hardware demonstration of the digital solutions is proposed. For this purpose, we build a physical layer test bench which depicts a non-linear communication between two radios. We show that if we drive the transmitter power amplifier close to its saturation point, we can improve the communication range if the non-linear distortions are compensated for at the receiver. The transmitter and the receiver are implemented with Software Defined Radios (SDRs). / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

The mainstay of a successful organization is a well-functioning internal communication. Good internal communication creates a positive environment, togetherness, and community within the organization. A lack of internal communication can lead to an inefficient organization and can pose a threat to the organization's relationships, which is more common in international organizations. Since digital development, the internal communication is constantly evolving, which created a need to examine the area further. The purpose of this study was to create an understanding of how members in an international organization perceive internal communication. Löfberg’s internal communications were examined from the members’ perspective because their perception could give us a more honest and clearer view of what internal communication looks like within the organization. In this thesis, we had four research questions: “How do the members perceive the organizational culture within Löfbergs?", "How do the members perceive the communication channels at Löfbergs?", "To what extent do the members' perception of Löfberg's internal communication differ depending on position? " and "To what extent do members' perceptions of Löfberg's internal communication differ depending on whether they work within or outside Sweden?"       The theoretical framework in this thesis was covered by organizational culture, dissemination of information, and communication channels. Organizational culture affected the members' sense of belonging, motivation, and inclusion. Disseminating information explains how communication moved within the organization. The channels were investigated because they are the organization's tools for disseminate the information to all members. Based on previous research, we gained an understanding of the importance of horizontal and vertical communication within organizations, and how it worked. We also presented the difference between the manager role and the employee role, and how the image of these roles had changed over time. The survey was conducted with the help of a quantitative survey, where the population was a total sample of Löfberg's organizational members. The questionnaire was sent out via e-mail where members could answer 24 questions regarding internal communication. We received a total of 148 respondents out of 325 possible, from seven different countries. After analyzing the data collected from the survey, we were able to answer our purpose and our research questions. The results of the study showed that the members’ at Löfbergs generally experienced the communication as well-functioning. The majority of members enjoyed being with their colleagues, they experienced motivation to go to their work and they experienced being included within the organization. Further, members outside Sweden experienced internal communication as more well-functioning than those stationed in Sweden. Managers considered to a greater extent than employees, that they were allowed to take part in decisions that concerned the organization as a whole. Of the nine channels that were used in this thesis, we saw that mobile, e-mail, Teams chat function and the intranet were the most used channels. The channels that were not used as frequently were Yammer and the bulletin board. With the help of our results, we gained an understanding of how members within an international organization perceive internal communication. / Grundpelaren för en framgångsrik organisation är att det finns en bra internkommunikation. En bra internkommunikation skapar en positiv miljö, samhörighet och gemenskap inom en organisation. En bristande internkommunikation kan däremot leda till en ineffektiv organisation som kan innebära hot mot organisationens relationer, vilket är vanligare i större internationella organisationer. I och med den digitala utvecklingen, är internkommunikationen i ständig förändring, vilket skapade ett behov att undersöka området vidare. Syftet med denna undersökning var att skapa en förståelse för hur medlemmar inom en internationell organisation uppfattar internkommunikationen. Löfbergs internkommunikation undersöktes ur ett medlemsperspektiv eftersom deras uppfattning kunde ge oss en mer ärlig och tydlig bild av hur internkommunikationen ser ut inom organisationen. Uppsatsen utgår från fyra frågeställningar: “Hur uppfattar medlemmarna organisationskulturen inom Löfbergs? ”, “Hur uppfattar medlemmarna kommunikationskanalerna på Löfbergs?”, “Till vilken grad skiljer sig medlemmarnas uppfattning av Löfbergs internkommunikation beroende på position?” och ”Till vilken grad skiljer sig medlemmarnas uppfattning av Löfbergs internkommunikation beroende på om de arbetar i eller utanför Sverige?”.  Det teoretiska ramverket i uppsatsen utgick från organisationskultur, informationsspridning och kommunikationskanaler. Organisationskultur berörde medlemmars samhörighetskänsla, motivation och inkludering. Informationsspridning förklarade hur kommunikationen skedde inom organisationen. Kommunikationskanaler undersöktes eftersom de är organisationens verktyg för att kunna sprida information till alla medlemmar runt om i organisationen. Utifrån tidigare forskning fick vi en förståelse för hur viktig horisontell och vertikal kommunikation är inom organisationer samt hur den fungerar. Vi presenterade även skillnaden mellan chefsrollen och medarbetarrollen, och hur bilden av dessa har förändrats över tid.  Genomförandet av undersökningen gjordes med hjälp av en kvantitativ enkätundersökning, där populationen var ett totalurval av Löfbergs organisationsmedlemmar. Enkäten skickades ut via mail där medlemmarna fick svara på 24 stycken frågor rörande internkommunikation. Vi fick totalt ihop 148 respondenter av 325 möjliga, från sju olika länder.  Efter att ha analyserat insamlad data från enkäten kunde vi svara på vårt syfte och våra frågeställningar. Studiens resultat visade att medlemmarna på Löfbergs generellt upplevde kommunikationen som välfungerande. Majoriteten av medlemmarna trivdes med sina kollegor, kände sig motiverade till att gå till arbetsplatsen och kände sig inkluderade i organisationen. Medlemmar utanför Sverige upplevde internkommunikationen som mer välfungerande än de som var stationerade i Sverige. Chefer ansåg till högre grad att de fick vara med att ta belsut som rör hela organisationen än vad medarbetare gjorde. Av de nio kanaler som studerades i undersökningen, kunde vi se att de kanaler som användes mest var mobil, e-post, Teams chattfunktion och intranätet. De kanaler som inte användes lika frekvent var Yammer och anslagstavla. Med hjälp av vårt resultat har vi fått en förståelse hur medlemmar inom en internationell organisation uppfattar internkommunikationen.

<div>Many important scientific, engineering, and societal challenges involve large systems of individual agents or components interacting in complex ways. For example, to understand the emergence of consciousness, we study the dendritic integration in neurons; to prevent disease and rumor outbreaks, we trace the dynamics of social networks; to perform complicated scientific experiments, we separate and control the independent variables. Collectively, the interactions between individual neurons/agents/variables are often non-linear, i.e., a subset of the agents jointly behave in a manner unlike the marginal behaviors of the individuals.</div><div><br></div><div>The goal of this thesis is to construct a theoretical framework for measuring, comparing, and representing complex interactions in stochastic systems. Specifically, tools from information theory, differential geometry, lattice theory, and linear algebra are used to identify and characterize higher-order interactions among random variables.</div><div><br></div><div>We first propose measures of unique, redundant, and synergistic interactions for small stochastic systems using information projections for the exponential family. Their magnitudes are endowed with information theoretical meanings naturally, since they are measured by the Kullback-Leibler divergence. We prove that these quantities satisfy various desired properties.</div><div><br></div><div>We next apply these measures to hypothesis testing and network communication. We interpret the unique information as the two types of error components in a hypothesis testing problem. We analytically show that there is a duality between the synergistic and redundant information in Gaussian Multiple Access Channels (MAC) and Broadcast Channels (BC). We establish a novel duality between the partial information decomposition components for MAC and BC in the general case.</div><div><br></div><div>We lastly propose a new concept of representing the partial information decomposition framework with random variables. We give necessary and sufficient conditions for the representation under the assumption of Gaussianity and develop a construction method.</div><div><br></div><div>This research has the potential to advance the fields of information theory, statistics, and machine learning by contributing novel ideas, implementing these ideas with innovative tools, and constructing new simulation methods.</div>

Dans la première partie de la thèse, on se concentre sur la conception d'un système de communication par satellite complet se basant sur la construction de faisceaux adaptatifs aux terminaux mobiles. Comparé à la construction classique de faisceaux fixes, le système à faisceaux adaptatifs peut considérablement améliorer la capacité du système en termes du nombre de STs desservies et de l'efficacité énergétique. Pour la conception du système à faisceaux adaptatifs, les informations sur l'état de canal (CSI) sont essentielles. Vu que le temps de propagation est trop long par rapport au temps de cohérence du canal, le CSI instantané est déjà périmé lorsqu'il est reçu pour la construction des faisceaux. Cependant, une partie de l'information du canal, plus particulièrement, les vecteurs de directivité ont une variation assez lente. On utilise cette connaissance partielle du CSI pour concevoir le système à base de faisceaux adaptatifs. Afin d'estimer les vecteurs de directivité, on propose un algorithme basé sur un critère de minimisation de l'erreur quadratique. Puis, basées sur l'estimation des vecteurs de directivité, on présente deux approches heuristiques pour la conception des faisceaux. En outre, on propose également deux approches qui reposent sur l'estimation de la directivité pour la détection des STs et la résolution possible des collisions sur le canal d'accès aléatoire au satellite. Comme la performance du système SDMA dépend fortement des positions spatiales des STs co-existants, on propose deux algorithmes de faible complexité pour l'attribution des fréquences dans le système de communication par satellite / In the first part of the thesis, we focus on the design of a complete satellite communication system adopting adaptive beamforming with mobile satellite terminals. Compared with conventional fixed beamforming, adaptive beamforming can signi_cantly improve the capacity of a satellite system in terms of served satellite terminals (ST) and power e_ciency. For the design of an adaptive beamforming system, channel state information (CSI) is critical. Since the propagation delay is too long compared to the coherence time of the channel, the instantaneous CSI is already stale when processed for beamforming. However, some parts of the channel, more speci_cally, directivity vectors change quite slowly. We utilize this partial knowledge of CSI to design an adaptive beamforming system. In order to estimate the directivity vectors, we propose an algorithm based on a least square error criterion. Then, based on the estimation of directivity vectors, we propose two heuristics approaches to the design of adaptive beamforming. Additionally, we also propose two approaches, based on directivity estimation for the detection of transmitting terminals and the possible resolution of collisions in the random access channel of the satellite system. Since SDMA system performance depends strongly on the spatial locations of co-existing terminals, we also propose two low complexity algorithms for frequency allocation in a satellite communication system. Finally, we simulate a complete satellite system, including a random access channel and a connection-oriented channel. We analyze the system performance and compare it to conventional fixed beamforming systems