Dissertations / Theses: 'Multiparty models'

1

Dielmann, Alfred. "Automatic recognition of multiparty human interactions using dynamic Bayesian networks." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4022.

Full text

Abstract:

Relating statistical machine learning approaches to the automatic analysis of multiparty communicative events, such as meetings, is an ambitious research area. We have investigated automatic meeting segmentation both in terms of “Meeting Actions” and “Dialogue Acts”. Dialogue acts model the discourse structure at a fine grained level highlighting individual speaker intentions. Group meeting actions describe the same process at a coarse level, highlighting interactions between different meeting participants and showing overall group intentions. A framework based on probabilistic graphical models such as dynamic Bayesian networks (DBNs) has been investigated for both tasks. Our first set of experiments is concerned with the segmentation and structuring of meetings (recorded using multiple cameras and microphones) into sequences of group meeting actions such as monologue, discussion and presentation. We outline four families of multimodal features based on speaker turns, lexical transcription, prosody, and visual motion that are extracted from the raw audio and video recordings. We relate these lowlevel multimodal features to complex group behaviours proposing a multistreammodelling framework based on dynamic Bayesian networks. Later experiments are concerned with the automatic recognition of Dialogue Acts (DAs) in multiparty conversational speech. We present a joint generative approach based on a switching DBN for DA recognition in which segmentation and classification of DAs are carried out in parallel. This approach models a set of features, related to lexical content and prosody, and incorporates a weighted interpolated factored language model. In conjunction with this joint generative model, we have also investigated the use of a discriminative approach, based on conditional random fields, to perform a reclassification of the segmented DAs. The DBN based approach yielded significant improvements when applied both to the meeting action and the dialogue act recognition task. On both tasks, the DBN framework provided an effective factorisation of the state-space and a flexible infrastructure able to integrate a heterogeneous set of resources such as continuous and discrete multimodal features, and statistical language models. Although our experiments have been principally targeted on multiparty meetings; features, models, and methodologies developed in this thesis can be employed for a wide range of applications. Moreover both group meeting actions and DAs offer valuable insights about the current conversational context providing valuable cues and features for several related research areas such as speaker addressing and focus of attention modelling, automatic speech recognition and understanding, topic and decision detection.

APA, Harvard, Vancouver, ISO, and other styles

2

Bangalore, Kantharaju Reshmashree. "Modelling Cohesive Behaviours for Virtual Agents in Multiparty Interactions." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS230.

Full text

Abstract:

Les interactions de groupe sont une forme de communication couramment utilisée entre humains. Souvent, les membres d'un groupe sont impliqués dans la discussion, la prise de décisions et l'échange d'idées, dans différents contextes (par exemple, réunion, conférence, fête, etc.). La cohésion de groupe décrit le lien partagé qui pousse les membres à rester ensemble et à vouloir travailler ensemble pour atteindre les objectifs du groupe. Dans les interactions de groupe, les humains communiquent et se coordonnent via un certain nombre de comportements verbaux et non verbaux. Dans ce travail de recherche, dans un premier temps, nous reconnaissons la relation entre la cohésion de groupe et certains signaux sociaux d'intérêt non verbaux. Ensuite, nous présentons les résultats sur l'estimation automatique des niveaux de cohésion dans les groupes en utilisant différentes caractéristiques et techniques de représentation des caractéristiques pour les groupes. Les agents virtuels, un personnage animé généré par ordinateur avec des comportements non verbaux de type humain, ont été largement utilisés pour les interactions homme-machine dans diverses applications, par exemple des agents éducatifs, des entraîneurs de santé, des assistants de formation, etc. La plupart des applications jusqu'à présent se sont concentrées sur le développement d'agents pour des interactions dyadiques, c'est-à-dire un seul agent et utilisateur. Un groupe d'agents (multipartite) peut être potentiellement efficace pour persuader, motiver et éduquer les utilisateurs à travers des discussions interactives. Dans l'étape suivante, nous développons un modèle multipartite impliquant plusieurs agents autonomes capables d'afficher un comportement de groupe cohérent, c'est-à-dire un engagement partagé envers les tâches de groupe et une relation positive entre les agents. Compte tenu de l'augmentation du nombre d'applications utilisant des agents virtuels, il est important d'étudier les interactions entre plusieurs agents et l'utilisateur et de comprendre les effets de l'utilisation d'un tel système. Nous émettons l'hypothèse que l'utilisation d'un système multi-agents permettrait à l'utilisateur d'être plus engagé dans la discussion et fournirait différentes perspectives sur le même problème et faciliterait aux utilisateurs de prendre des décisions éclairées. Par conséquent, dans la dernière étape, nous menons plusieurs études d'évaluation des utilisateurs pour comprendre les effets des interactions multipartites sur l'utilisateur et ses perceptions, par exemple le niveau de confiance, la persuasion. Nous présentons des informations sur la forme d'interactions la plus efficace pour promouvoir un changement de comportement ou persuader l'utilisateur à l'aide de différents sujets de conversation de groupe. En résumé, dans cette thèse, nous reconnaissons l'association entre certains signaux sociaux non verbaux et la cohésion de groupe, présentons la précision de l'estimation à l'aide de caractéristiques extraites de ces signaux, développons un modèle multipartite pour simuler un groupe cohésif d'agents affichant des signaux sociaux importants et enfin évaluons l'efficacité d'un tel modèle dans un contexte de changement de comportement et ses effets sur les perceptions des utilisateurs
Group interactions are a commonly used form of communication among humans. Often the members of a group are involved in discussing, making decisions and exchanging ideas, under different settings (e.g., meeting, conference, party etc.). Group Cohesion describes the shared bond that drives the members to stay together and to want to work together to achieve group goals. In group interactions, humans communicate and coordinate with each other via a number of verbal and nonverbal behaviours. In this research work, as a first step we recognise the relation between group cohesion and certain non-verbal social signals of interest. Next, we present the results on automatic estimation of cohesion levels in groups using different features and feature representation techniques for groups. Virtual agents, a computer-generated animated character with human-like non-verbal behaviours, have been widely used for human-computer interactions in various applications e.g., educational agents, health coaches, training assistants etc. Most of the applications so far have focused on developing agents for dyadic interactions i.e., a single agent and user. A group of agents (multiparty) can be potentially effective in persuading, motivating and educating the users through interactive discussions. In the next step, we develop a multiparty model involving multiple autonomous agents that are capable of displaying cohesive group behaviour i.e., shared commitment to group tasks and positive relationship among the agents. Considering the surge in the range of applications using virtual agents, it is important to study the interactions between multiple agents and the user and understand the effects of using such a system. We hypothesise that the use of a multi-agent system would allow the user to be more engaged in the discussion and provide different perspectives on the same issue and facilitate the users to make informed decisions. Therefore, in the final step we conduct multiple user evaluation studies to understand the effects of multiparty interactions on the user and their perceptions e.g., the level of trust, persuasion. We present insights into the most effective form of interactions for promoting behaviour change or persuading the user using different group conversational topics. To summarise, in this thesis we recognise the association between certain non-verbal social signals and group cohesion, present the estimation accuracy using features extracted from these signals, develop a multiparty model to simulate a cohesive group of agents displaying prominent social signals and finally evaluate the effectiveness of such a model in the context of behaviour change and its effects on user’s perceptions

APA, Harvard, Vancouver, ISO, and other styles

3

Malik, Muhammad Usman. "Learning multimodal interaction models in mixed societies A novel focus encoding scheme for addressee detection in multiparty interaction using machine learning algorithms." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR18.

Full text

Abstract:

Les travaux de recherche proposés se situe au carrefour de deux domaines de recherche, l'interaction humain-agent et l'apprentissage automatique. L’interaction humain-agent fait référence aux techniques et concepts impliqués dans le développement des agents intelligents, tels que les robots et les agents virtuels, capables d'interagir avec les humains pour atteindre un objectif commun. L’apprentissage automatique, d'autre part, exploite des algorithmes statistiques pour apprendre des modèles de donnée. Les interactions humaines impliquent plusieurs modalités, qui peuvent être verbales comme la parole et le texte, ainsi que les comportements non-verbaux, c'est-à-dire les expressions faciales, le regard, les gestes de la tête et des mains, etc. Afin d'imiter l'interaction humain-humain en temps réel en interaction humain-agent, plusieurs modalités d'interaction peuvent être exploitées. Avec la disponibilité de corpus d'interaction multimodales humain-humain et humain-agent, les techniques d'apprentissage automatique peuvent alors être utilisées pour développer des modèles interdépendants participant à l'interaction humain-agent. À cet égard, nos travaux de recherche proposent des modèles originaux pour la détection de destinataires d'énoncés, le changement de tour de parole et la prédiction du prochain locuteur, et enfin la génération de comportement d'attention visuelle en interaction multipartie. Notre modèle de détection de destinataire prédit le destinataire d'un énoncé lors d'interactions impliquant plus de deux participant. Le problème de détection de destinataires a été traité comme un problème d'apprentissage automatique multiclasse supervisé. Plusieurs algorithmes d'apprentissage ont été entrainés pour développer des modèles de détection de destinataires. Les résultats obtenus montrent que ces propositions sont plus performants qu'un algorithme de référence. Le second modèle que nous proposons concerne le changement de tour de parole et la prédiction du prochain locuteur dans une interaction multipartie. La prédiction du changement de tour est modélisée comme un problème de classification binaire alors que le modèle de prédiction du prochain locuteur est considéré comme un problème de classification multiclasse. Des algorithmes d'apprentissage automatique sont entraînés pour résoudre ces deux problèmes interdépendants. Les résultats montrent que les modèles proposés sont plus performants que les modèles de référence. Enfin, le troisième modèle proposé concerne le problème de génération du comportement d'attention visuelle (CAV) pour les locuteurs et les auditeurs dans une interaction multipartie. Ce modèle est divisé en plusieurs sous-modèles qui sont entraînés par l'apprentissage machine ainsi que par des techniques heuristiques. Les résultats attestent que les systèmes que nous proposons sont plus performants que les modèles de référence développés par des approches aléatoires et à base de règles. Le modèle de génération de comportement CAV proposé est mis en œuvre sous la forme d’une série de quatre modules permettant de créer différents scénarios d’interaction entre plusieurs agents virtuels. Afin de l’évaluer, des vidéos enregistrées pour les modèles de génération de CAV pour les orateurs et les auditeurs, sont présentées à des évaluateurs humains qui évaluent les comportements de référence, le comportement réel issu du corpus et les modèles proposés de CAV sur plusieurs critères de naturalité du comportement. Les résultats montrent que le comportement de CAV généré via le modèle est perçu comme plus naturel que les bases de référence et aussi naturel que le comportement réel
Human -Agent Interaction and Machine learning are two different research domains. Human-agent interaction refers to techniques and concepts involved in developing smart agents, such as robots or virtual agents, capable of seamless interaction with humans, to achieve a common goal. Machine learning, on the other hand, exploits statistical algorithms to learn data patterns. The proposed research work lies at the crossroad of these two research areas. Human interactions involve multiple modalities, which can be verbal such as speech and text, as well as non-verbal i.e. facial expressions, gaze, head and hand gestures, etc. To mimic real-time human-human interaction within human-agent interaction,multiple interaction modalities can be exploited. With the availability of multimodal human-human and human-agent interaction corpora, machine learning techniques can be used to develop various interrelated human-agent interaction models. In this regard, our research work proposes original models for addressee detection, turn change and next speaker prediction, and finally visual focus of attention behaviour generation, in multiparty interaction. Our addressee detection model predicts the addressee of an utterance during interaction involving more than two participants. The addressee detection problem has been tackled as a supervised multiclass machine learning problem. Various machine learning algorithms have been trained to develop addressee detection models. The results achieved show that the proposed addressee detection algorithms outperform a baseline. The second model we propose concerns the turn change and next speaker prediction in multiparty interaction. Turn change prediction is modeled as a binary classification problem whereas the next speaker prediction model is considered as a multiclass classification problem. Machine learning algorithms are trained to solve these two interrelated problems. The results depict that the proposed models outperform baselines. Finally, the third proposed model concerns the visual focus of attention (VFOA) behaviour generation problem for both speakers and listeners in multiparty interaction. This model is divided into various sub-models that are trained via machine learning as well as heuristic techniques. The results testify that our proposed systems yield better performance than the baseline models developed via random and rule-based approaches. The proposed VFOA behavior generation model is currently implemented as a series of four modules to create different interaction scenarios between multiple virtual agents. For the purpose of evaluation, recorded videos for VFOA generation models for speakers and listeners, are presented to users who evaluate the baseline, real VFOA behaviour and proposed VFOA models on the various naturalness criteria. The results show that the VFOA behaviour generated via the proposed VFOA model is perceived more natural than the baselines and as equally natural as real VFOA behaviour

APA, Harvard, Vancouver, ISO, and other styles

4

Skowronek, Janto [Verfasser], Alexander [Akademischer Betreuer] Raake, Alexander [Gutachter] Raake, Sebastian [Gutachter] Möller, and Callet Patrick [Gutachter] Le. "Quality of experience of multiparty conferencing and telemeeting systems : methods and models for assessment and prediction / Janto Skowronek ; Gutachter: Alexander Raake, Sebastian Möller, Patrick Le Callet ; Betreuer: Alexander Raake." Berlin : Technische Universität Berlin, 2017. http://d-nb.info/1156176972/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Menemenlis, Nickie. "Stochastic models for multipath fading channels." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38505.

Full text

Abstract:

The main contribution of this work is to extend the present multi-path fading channel (MFC) models in two directions.
First, the wireless communication system is viewed as a dynamical system where the channel constitutes the main plant of such a system. The random variables characterizing the magnitude of each multi-path component are generalized to random processes with time-varying statistics. It is claimed that the dynamics of both the log-normal shadowing and short-term fading channels is captured by the use of stochastic diffusion processes which emerge from mean-reverting Ornstein-Uhlenbeck processes, implying that signal envelope variations can be modeled using stochastic differential equations. Explicit expressions for signal envelope distributions and second order statistics of the received signal are derived.
Further, the short-term dynamical model is cast into a state-space representation and a nominal model is derived, based on which robust analysis and design can be performed in order to capture additional channel uncertainties.
The dynamical channel models introduced here are in accordance of the physical principles of electromagnetic wave propagation, they are parametric and able to describe diverse propagation environments.
Second, a unified statistical analysis framework is introduced in order to compute the various statistics, second-order properties and densities of the overall received signal of the MFC's. To this end, the MFC model is formulated as a general shot-noise process brought forward by Rice. By extending and adapting the shot-noise analysis to complex signals the statistics of the overall received signal are derived, with explicit computations of the various moments and second-order statistics. The analysis includes the case of moving scatters (i.e. rain droplets) which it is shown to affect the dynamical temporal characteristics of the channel. It is also shown here that samples of the received signal approach a jointly Gaussian density, as certain parameters tend to their limits. Further, when the density of the received signal does not approach the Gaussian density, the Edgeworth series expansion is employed to compute the non-Gaussian density. This analysis brings forward the parameters responsible for Gaussianity of the received signal, parameters which designers can use in order to tailor their transmitter/receiver design. (Abstract shortened by UMI.)

APA, Harvard, Vancouver, ISO, and other styles

6

Abbas, Syed Aun. "Multipath mobile wireless channel, models, interpretations and applications." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ26842.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Abbas, Syed A. (Syed Aun) Carleton University Dissertation Engineering Systems and Computer. "Multipath mobile wireless channel; models, interpretations and applications." Ottawa, 1997.

Find full text

APA, Harvard, Vancouver, ISO, and other styles

8

Chalaça, João Pedro Gonçalves. "Multipath policy routing in packet switched networks." Master's thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/10716.

Full text

Abstract:

Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e Tecnologia
Nowadays, the continuous operations of large networks, under multiple ownerships, are of tremendous importance and as a result, routing protocols have gained numerous extensions and accumulated complexity. Policy-based routing can be of signi cance for common networks when the cost of transporting a bit is no longer the biggest pressure point. The best path problem is a generalization of the shortest path problem that suits policy based routing. This means that preferences for the paths depend on semantically rich characteristics, in which two di erent paths may have the same preference. However, current policy-based routing models cannot take full advantage of the multiplicity of connections to a given destination and are single path in nature. Therefore multipath can bring several advantages in policy based routing. Designing multipath routing protocols based on policies seem to be a problem of interest. To model routing problems, algebraic structures and graph theory are used. Through variants of classical methods of linear algebra routing problems can be solved. The objective of this dissertation is to devise a multipath policy-based routing protocol using a simple destination-based hop-by-hop protocol with independent forwarding decisions. Networks featuring these characteristics can be more resilient to failures, provide better tra c distribution and maintain a simple forwarding paradigm. The dissertation concludes with the trade-o 's between the exibility of the proposed solution, the amount of multiple paths that can be used simultaneously and the network restrictions that must be applied.

APA, Harvard, Vancouver, ISO, and other styles

9

Rice, Michael, and Qiang Lei. "SHF MULTIPATH CHANNEL MODELING RESULTS." International Foundation for Telemetering, 2005. http://hdl.handle.net/10150/604799.

Full text

Abstract:

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada
This paper presents the results of land-based SHF channel modeling experiments. Channel modeling data were collected at Edwards AFB, California at S-Band, X-Band and Ku-band. Frequency domain analysis techniques were used to evaluate candidate channel models. A graphical user interface (GUI) was developed to search for the optimum channel parameters. The model parameters corresponding to different frequencies were compared for multipath events captured at approximately the same locations. A general trend was observed where the magnitude of the first multipath reflection decreased as frequency increased and the delay remained relatively unchanged.

APA, Harvard, Vancouver, ISO, and other styles

10

EDWARDS, KARLA ROBERTA LISA. "Site-Specific Point Positioning and GPS Code Multipath Parameterization and Prediction." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1300860715.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Amaral, Pedro Miguel Figueiredo. "Multipath inter-domain policy routing." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2012. http://hdl.handle.net/10362/8797.

Full text

Abstract:

Dissertação submetida para a obtenção do grau de Doutor em Engenharia Electrotécnica e de Computadores
Routing can be abstracted to be a path nding problem in a graph that models the network. The problem can be modelled using an algebraic approach that describes the way routes are calculated and ranked. The shortest path problem is the most common form and consists in nding the path with the smallest cost. The inter-domain scenario introduces some new challenges to the routing problem: the routing is performed between independently con gured and managed networks; the ranking of the paths is not based on measurable metrics but on policies; and the forwarding is destination based hop-by-hop. In this thesis we departed from the Border gateway Protocol (BGP) identifying its main problems and elaborating on some ideal characteristics for a routing protocol suited for the inter-domain reality. The main areas and contributions of this work are the following: The current state of the art in algebraic modeling of routing problems is used to provide a list of possible alternative conditions for the correct operation of such protocols. For each condition the consequences in terms of optimality and network restrictions are presented. A routing architecture for the inter-domain scenario is presented. It is proven that it achieves a multipath routing solution in nite time without causing forwarding loops. We discuss its advantages and weaknesses. A tra c-engineering scheme is designed to take advantage of the proposed architecture. It works using only local information and cooperation of remote ASes to minimize congestion in the network with minimal signalling. Finally a general model of a routing protocol based on hierarchical policies is used to study how e cient is the protocol operation when the correctness conditions are met. This results in some conclusions on how the policies should be chosen and applied in order to achieve speci c goals.
Portuguese Science and Technology Foundation -(FCT/MCTES)grant SFRH/BD/44476/2008; CTS multi-annual funding project PEst OE/EEI/UI0066/2011; MPSat project PTDC/EEA TEL/099074/2008; OPPORTUNISTICCR project PTDC/EEA-TEL/115981/2009; Fentocells project PTDC/EEA TEL/120666/2010

APA, Harvard, Vancouver, ISO, and other styles

12

Martens, Walter. "Multipath propagation models for near line-of-sight conditions." Mémoire, École de technologie supérieure, 2009. http://espace.etsmtl.ca/68/1/MARTENS_Walter.pdf.

Full text

Abstract:

Cette thèse porte sur le comportement d’un canal à propagation par trajets multiples dont le lien est en visibilité directe ou dont les pertes additionnelles dues aux obstacles sont très faibles. Ce type de canal existe dans les banlieues ou les régions presque rurales. L’objectif de ce projet de recherche est de caractériser le comportement à large bande de ce type de canal. La thèse comporte cinq parties majeures : la problématique et revue de la littérature, une analyse théorique, des mesures expérimentales pour valider l’analyse, des applications aux canaux pratiques et une étude des effets d’un tel canal sur les signaux typiques. Les amplitudes et l’étalement du délai pour un modèle de propagation à trajets multiples réaliste de cet environnement sont étudiés. Ceci se base sur une analyse théorique de la réflexion des surfaces plates finies qui représentent des murs de bâtiments. À partir de cette analyse, un modèle à large bande est proposé. La partie suivante de la thèse présente les résultats des mesures expérimentales pour les canaux de propagation à trajets multiples dans les banlieues et les régions presque rurales. Dans ces conditions, les liens sont en visibilité directe ou encore, les pertes additionnelles dues aux obstacles sont très faibles. Les résultats confirment l’analyse théorique. Selon les régions mises à l’essai, on observe un canal soit très bon ou encore très mauvais. Un canal mauvais se trouve généralement près d’un bâtiment où il existe une seule réflexion dominante dont le délai relatif est de moins d’une microseconde. Cette réflexion cause des évanouissements est des distorsions sévères du signal qui rend le canal souvent inutilisable. L’aire de la région pour laquelle le canal est mauvais dépend de la largeur du bâtiment. Après les résultats expérimentaux, la thèse décrit quelques applications du modèle à large bande et analyse les effets du modèle proposé sur les signaux typiques de communication comme la modulation en quadrature de phase, QPSK, la modulation par étalement du spectre en séquence directe et la modulation utilisant des sous-porteuse orthogonales, OFDM. Pour le signal QPSK, les effets d’une seule réflexion dominante sur les circuits pour la récupération de l’horloge et de la porteuse d’un démodulateur sont étudiés. Une méthode est aussi présentée pour déterminer les endroits dans lesquels les liens seront sévèrement dégradés.

APA, Harvard, Vancouver, ISO, and other styles

13

Ribaud, Florian. "Analysis of Multipath Channel Reduction Models for the Testing of Realistic GNSS Receivers." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17680/1/Ribaud_Florian.pdf.

Full text

Abstract:

This PhD work relates the development of multipath channel reduction methods, putting the emphasis on the preservation of the signal tracking performances of satellite navigation systems. It aims at adapting the land mobile channel models to the realistic testing of GNSS receivers, by reducing drastically the number of multipaths of the original channel model (from thousands to less than 10 typically) all by conserving the pseudo-range error. Three types of methods have been investigated in order to cover all different possibilities of reduction processes. As a first approach, a multipath aggregation method has been considered, through the clustering of the multipaths according to the delay and Doppler dimensions, weighted by their power. Even if this method allows a good preservation of the delay and Doppler characteristics of the original channel, a second approach has been investigated, oriented toward the optimization of the parameters of the reduced channel (delay, Doppler shift, phase and amplitude) in order to minimize the difference between the original channel correlation function and the reduced one. Even if this approach gives good performances in terms of pseudorange error preservation, it leads to the instability of the reduced channel echoes. Therefore, a statistical method has been implemented, considering that the delays of the reduced channel evolve according to a first order Markov process. These three approaches have been compared through the preservation of the discriminator open loop error. In particular conditions concerning the number of echoes in the reduced channel or the elevation of the emitter satellite, the clustering technique implemented in first approach appears to equal the performances of the parametric method, the statistical approach giving systematically the worst performances. The invariance of this hierarchy as adding tracking loops to the simulation or changing the signal model (modulation and RF bandwidth) allows extending the conclusion. Being given the significant advantage of the clustering on the parametric method in terms of computation time, the use of this method is preconized to address the channel reduction problem. In particular, the weighted clustering technique developed in this thesis offers the possibility to reproduce the wide-band characteristics of a channel model composed of thousands of multipaths with less than 10 echoes. Moreover, it constitutes an interesting tradeoff between computational effort and GNSS systems pseudo-range error conservation, approaching the performances of parametric methods, and even overcoming them in some conditions, with a computation time close to the real time.

APA, Harvard, Vancouver, ISO, and other styles

14

Ben, Hassine Seif. "Multipath and receiver models for assessing the VOR bearing error : application to wind farms." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30047.

Full text

Abstract:

L'implémentation des éoliennes à proximité des systèmes VOR (VHF Omnidirectional Range) est une préoccupation importante pour l'aviation civile. Les éoliennes constituent une source de multitrajets qui peuvent produire des erreurs sur l'information d'azimut estimée par le récepteur d'avion. Dans la littérature, l'erreur VOR est calculée à partir de paramètres multitrajets en utilisant l'expression analytique proposée par Odunaiya et Quinet. Dans cette thèse de doctorat, nous avons développé un modèle d'un récepteur IQ numérique qui peut reproduire la réponse d'un récepteur VOR lorsque les multitrajets varient dans le temps tout au long d'une trajectoire réaliste d'avion. Le Chapitre 1 présente les principes de base des systèmes : VOR conventionnel (VORC) et VOR Doppler (VORD). Le phénomène de multitrajets générés par les éoliennes à proximité des stations VOR est détaillé en présentant ses paramètres et certaines méthodes de modélisation associées qui existent dans la littérature. Un aperçu des récepteurs VOR est présenté en décrivant la structure classique d'un récepteur VOR et les étapes du traitement du signal appliquées afin d'extraire l'information d'azimut. Les expressions de l'erreur VOR proposées par Odunaiya et Quinet pour les systèmes VORC et VORD sont données et illustrées. Dans le Chapitre 2, nous présentons notre modèle de récepteur IQ numérique. Un générateur de séries temporelles au long d'une trajectoire réaliste d'avion est présenté. Un critère échantillonnage est également proposé pour être sûr de capturer toutes les variations de multitrajets dans l'espace. Le modèle de récepteur IQ numérique est détaillé en décrivant ses composantes. Afin d'analyser l'effet et dynamique de multitrajets sur le récepteur VOR, un test d'illustration est donné en comparant la réponse du modèle avec l'expression d'Odunaiya. Dans le Chapitre 3, le comportement de notre modèle de récepteur IQ numérique est analysé en le comparant avec un récepteur de calibration (R&S EVS300) à l'aide de deux mesures de laboratoire. La première mesure est effectuée dans la bande des fréquences VHF en traitant un multitrajet canonique. La seconde mesure est effectuée en utilisant des signaux en bande de base IQ générées à partir d'une simulation d'un scénario complexe. Les résultats des mesures montrent un bon accord entre les récepteurs. Une analyse critique de récepteur VOR est présentée dans le Chapitre 4. Pour le VORC, nous présentons une méthode permettant de déterminer le domaine de validité de l'expression statique d'Odunaiya afin de calculer l'erreur VOR. Pour le VORD, nous montrons que l'erreur VOR est sensible au type de démodulateur FM en développant et en validant une expression alternative de l'erreur Doppler analytique qui est cohérente avec notre démodulateur FM. Enfin, nous évaluons l'analyse de Bredemeyer qui indique que l'effet et des multitrajets sur le signal de référence doit être pris en compte dans le calcul de l'erreur VORD. Dans le Chapitre 5, nous proposons un modèle statistique d'erreur VOR dont les seuls paramètres sont les positions de l'avion et de l'éolienne et les autres paramètres suivent des distributions statistiques. Ce modèle permet de réduire le temps de simulation électromagnétique. Tout d'abord, nous déterminons les distributions statistiques associées aux paramètres multitrajets. Ensuite, la distribution statistique associée à l'erreur VOR est déduite. Enfin, nous effectuons des simulations de Monte Carlo pour évaluer les paramètres des distributions statistiques
The implementation of wind turbines close to VHF Omnidirectional Range (VOR) systems is an important concern for civil aviation. The wind turbines constitute a source of multipath that can yield bearing errors in the azimuth estimated by aircraft receivers. In the literature, the bearing error is computed from the multipath characteristics by means of the analytic expression proposed by Odunaiya and Quinet. In this PhD thesis, we have developed a digital IQ receiver model which can reproduce the response of a VOR receiver when the multipath change in time along a realistic aircraft trajectory. In Chapter 1, the basic principle of the Conventional VOR (CVOR) and Doppler VOR (DVOR) is pre-sented. The multipath phenomenon generated by the wind turbines in the vicinity of VOR stations is detailed by presenting its parameters and some associated modeling methods that exist in the literature. An overview of the VOR receivers is presented by describing the standard structure of a VOR receiver and the signal processing steps to extract the azimuth information. The analytical expressions proposed by Odunaiya and Quinet for the CVOR and DVOR systems are given and illustrated. In Chapter 2, we present our digital IQ receiver model. A time series generator along a realistic aircraft trajectory is presented. A sampling criterion is also proposed to be sure to capture all the multipath variations in space. The digital IQ receiver model is detailed by describing its components. In order to analyze the effect of multipath dynamics on the VOR receiver, an illustration test is given by comparing the receiver model response with the Odunaiya expression. In Chapter 3, the behavior of our digital IQ receiver model is analyzed by comparing with a calibration receiver (R&S EVS300) from two laboratory measurements. The first one is performed in the VHF frequency band for one canonical multipath. The second one is performed using baseband IQ signals in a complex scenario. The measurements results are shown a good agreement between receivers. A CVOR and DVOR analysis are given in Chapter 4. For CVOR, we present a method to determine the validity domain of the static Odunaiya expression for computing the bearing error. For DVOR, we show that the bearing error is sensitive to the type of FM demodulator by developing and validating an alternative expression of the analytic Doppler error which is consistent with our FM demodulator. Finally, we evaluate the analysis of Bredemeyer which indicates that the effect of multipath on the reference signal must be considered in the DVOR error computation. In Chapter 5, we propose a statistical model for the bearing error with which the only parameters are the aircraft and wind turbine positions and the other parameters follow statistical distributions. This model allows to reduce the electromagnetic simulation time. Firstly, we determine the statistical distributions associated with the multipath parameters. Secondly, the statistical distribution associated with the bearing error is deduced. Finally, we perform Monte Carlo simulations to assess the parameters of the statistical distributions

APA, Harvard, Vancouver, ISO, and other styles

15

Sung-hoon, Jang, Han Sung-hee, and Kim Heung-bum. "Auto-tracking antenna pattern effects on multipath channel model at test range." International Foundation for Telemetering, 2001. http://hdl.handle.net/10150/607672.

Full text

Abstract:

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada
Telemetry propagation channel is modeled to predict PCM/FM telemetry receiving signal level at APG(Anheung Proving Ground), ADD(Agency for Defense Development). Channel model is composed of direct wave and reflected wave in sea surface, so-called 2-ray model. Our 2-ray model includes transmitting antenna radiation pattern, auto-tracking antenna radiation pattern, sea surface reflection coefficient and phase depending on incident angle. Vertical and horizontal polarized receiving signal strength is obtained from pre-calculated flight trajectory of transmitter. Calculated results are compared with measured data in real flight test. 2-ray channel model can predict almost identical receiving signal level and calculate starting point of multi-path fading effect. Using these results, receiving system can be moved to more proper position before flight test.

APA, Harvard, Vancouver, ISO, and other styles

16

Rice, Michael, Adam Davis, and Christian Bettwieser. "A WIDEBAND CHANNEL MODEL FOR AERONAUTICAL TELEMETRY — PART 2: MODELING RESULTS." International Foundation for Telemetering, 2002. http://hdl.handle.net/10150/606289.

Full text

Abstract:

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California
This paper is the second of two papers that present a multipath channel model for wideband aeronautical telemetry. Channel sounding data were collected at Edwards AFB, California at both L-Band and lower S-Band. Frequency domain analysis techniques were used to evaluate candidate channel models. The channel model is composed of three propagation paths: a line-of-sight path, and two specular reflections. The first specular reflection is characterized by a relative amplitude of 70% to 96% of the line-of-sight amplitude and and a delay of 10 – 80 ns. This path is the result of “ground bounces” off the dry lake bed at Edwards and is a typical terrain feature at DoD test ranges located in the Western USA. The amplitude and delay of this path are defined completely by the flight path geometry. The second path is a much lower amplitude path with a longer delay. The gain of this path is well modeled as a zero-mean complex Gaussian random variable. The relative amplitude is on the order of 2% to 8% of the line-of-sight amplitude. The mean excess delay is 155 ns with an RMS delay spread of 74 ns.

APA, Harvard, Vancouver, ISO, and other styles

17

Dimopoulos, Peter, and dimpet@gmail com. "Modeling and Improving the Performance of Interactive TCP Traffic in Computer Networks." RMIT University. Computer Science and Information Technology, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080208.150856.

Full text

Abstract:

The Internet has become one of the most widely used forms of communication available. Many applications used on the Internet require the user to interact constantly with the network. For example web browsing where the user will expect the browser to respond quickly, to finish loading pages quickly and to do all of this at an equal level for all users. The network's performance is dependant on the protocols it uses and how the resources of the network are distributed. This is why TCP (Transmission Control Protocol) is one of the most important protocols, because it controls the amount of data entering the network and provides reliability to most interactive applications. The thesis starts by introducing a basic TCP model which is later extended to model the effects of burstiness produced by TCP. Burstiness can cause a routers buffer to unnecessarily overflow. These overflows cause TCP connections to under-utilise link bandwidth because of unnecessary packet retransmissions. A model to define a quantitative measure of both burstiness and throughput of a system of TCP connections is introduced. The model gives insight into how the TCP protocol causes burstiness and can be used to find scenarios where burstiness is decreased. This helps to improve the utilization of links by reducing the burstiness of protocols. An important performance metric for interactive traffic is user perceived delay, the delay that an end user would encounter when using an application. An example of user perceived delay is the time a user waits before a HTML web page starts loading. The retransmission delays are the most important type of delay for interactive traffic because they are usually very large. A dynamic priority RED Queue (DPRQ) is introduced which changes the priority of the queues based on the goodput (throughput of succesfully transmitted packets) threshold of the interactive traffic. Using dynamic priority allows packet loss to be reduced by up to eight times for interactive traffic, which intern reduces retransmission delay. Fairness measures how equally network resources are allocated amongst different connections. When a link with TCP connections is overloaded each connection on the link will reduce its throughput to allow all the connections to have approximately equal load. This does not take into account that other links may be under utilized. The fairness issue is addressed by introducing Multipath TCP (MATCP) which allows path selection to occur at the TCP layer. This allows each unique flow to take a different path, instead of all the flows of one source using the same path. Using MATCP, a finer grain of load-balancing can be achieved and the complexity and state required in the network is greatly reduced. Two analytic models are provided in chapters three and four, which investigate slow start and TCP burstiness. In chapter five the DPRQ queue is introduced to reduce user perceived delay. An analytic model of the DPRQ is provided and verified through experimental simulation. In chapter six an analytic model of Multipath TCP is provided, which is also verified by simulation.

APA, Harvard, Vancouver, ISO, and other styles

18

Rice, Michael, Adam Davis, and Christian Bettwieser. "A WIDEBAND CHANNEL MODEL FOR AERONAUTICAL TELEMETRY — PART 1: GEOMETRIC CONSIDERATIONS AND EXPERIMENTAL CONFIGURATION." International Foundation for Telemetering, 2002. http://hdl.handle.net/10150/606288.

Full text

Abstract:

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California
This paper is the first of two papers that present a multipath channel model for wideband aeronautical telemetry. Channel sounding data, collected at Edwards AFB, California at both L-Band and lower S-Band, were used to generate channel model. In Part 1, analytic and geometric considerations are discussed and the frequency domain modeling technique is introduced. In Part 2, the experimental results are summarized and a channel model composed of three propagation paths is proposed.

APA, Harvard, Vancouver, ISO, and other styles

19

Teal, Paul D., and p. teal@irl cri nz. "Real Time Characterisation of the Mobile Multipath Channel." The Australian National University. Research School of Information Sciences and Engineering, 2002. http://thesis.anu.edu.au./public/adt-ANU20020722.085502.

Full text

Abstract:

In this thesis a new approach for characterisation of digital mobile radio channels is investigated. The new approach is based on recognition of the fact that while the fading which is characteristic of the mobile radio channel is very rapid, the processes underlying this fading may vary much more slowly. The comparative stability of these underlying processes has not been exploited in system designs to date. Channel models are proposed which take account of the stability of the channel. Estimators for the parameters of the models are proposed, and their performance is analysed theoretically and by simulation and measurement. Bounds are derived for the extent to which the mobile channel can be predicted, and the critical factors which define these bounds are identified. Two main applications arise for these channel models. The first is the possibility of prediction of the overall system performance. This may be used to avoid channel fading (for instance by change of frequency), or compensate for it (by change of the signal rate or by power control). The second application is in channel equalisation. An equaliser based on a model which has parameters varying only very slowly can offer improved performance especially in the case of channels which appear to be varying so rapidly that the convergence rate of an equaliser based on the conventional model is not adequate. The first of these applications is explored, and a relationship is derived between the channel impulse response and the performance of a broadband system.

APA, Harvard, Vancouver, ISO, and other styles

20

Montaquila, Roberto V., Ivan Iudice, and Vittorio U. Castrillo. "Design of a Radio channel Simulator for Aeronautical Communications." International Foundation for Telemetering, 2012. http://hdl.handle.net/10150/581633.

Full text

Abstract:

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California
The goal of this paper is to implement a model of multipath fading in a radio channel simulator for aeronautical applications. When developing a wireless communications system, it is useful to perform simulations of the radio context in which the system has to operate. A radio link is substantially composed by three parts: transmitting segment, transmission channel and receiving segment. We focus our attention on the radio channel propagation. We proposed two geometrical models of a territory corresponding to a determined flight area and, after importing the data needed to estimate our parameters, we compared our results with the channel soundings in literature, obtaining comparable values.

APA, Harvard, Vancouver, ISO, and other styles

21

Mwangi, Patricia A. W., Amr Haj-Omar, and Kishan Montaque. "SIMULATION OF THE AERONAUTICAL RADIO CHANNEL FOR TELEMETRY APPLICATIONS." International Foundation for Telemetering, 2006. http://hdl.handle.net/10150/604033.

Full text

Abstract:

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California
The aeronautical channel is an air to ground channel characterized by multipath, high doppler shifts, Rayleigh fading and noise. Use of a channel sounder ensures proper estimation of the parameters associated with the impulse response of the channel. These estimates help us to characterize the radio channels associated with aeronautical telemetry. In order to have a satisfactory channel characterization, the amplitudes, phase shifts and delays associated with each multipath component in the channel model must be determined.

APA, Harvard, Vancouver, ISO, and other styles

22

Betaille, David Francois. "Assessment and improvement of the capabilities of a window correlator to model GPS multipath phase errors." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446495/.

Full text

Abstract:

This thesis is concerned with the modelling of Global Positioning System (GPS) phase multipath. GPS is increasingly used for very high precision (centimetre level) engineering surveying applications such as setting out on construction sites and the control of major civil engineering plant (e.g. bulldozers, graders and pavement layers). In such applications the phase of the carrier signal is the basic observable and the dominant error source is muldpath (electromagnetic reflections of the carrier waves from surfaces in the surroundings of the antennas). The work contained in the thesis has been carried out in collaboration with the LCPC (Laboratoire Central des Ponts et Chaussees) in Nantes, France, which made available its test facility and Leica Geosystems, Heerbrugg, Switzerland, a GPS manufacmrer, which funded the work and which made available modified equipment for testing. The specific subject of the research is the assessment and improvement of the capabilities of a Phase Multipath Mitigation Window correlator (PMMW) to model GPS multipath phase errors. The phase window correlator is a new sampling technique dedicated to the estimation of multipath errors in phase measurements. The thesis contains background material on GPS multipath mitigation and on several existing patents related to the PMMW technique. The main contribution of the work relates to:The rigorous mathematical modelling of multipath, starting from the physics of the phenomenon, right through to the phase measurement process itself, particularly that based on the PMMW correlator. The design of a general testing methodology in a controlled environment to assess the efficacy of multipath mitigation techniques. The carrying out of full-scale experiments at the LCPC in both static and kinematic modes and the assessment of the performances and limitations of the PMMW correlator. Initial investigations into the design of a new real-time correction strategy for phase multipath phase errors based on a combination of multipath observables including the signal-to-noise ratio, the output from the PMMW correlator and an estimation of the code multipath errors from dual frequency phase data. A key feature of the new strategy is its ability to overcome the major limitation of the PMMW technique, i.e. its insensitivity to multipath caused by very close reflectors. It enables the multipath corrupted phase measurements to be improved by 10 % in average in this case, whereas the PMMW corrections on their own had almost no effect.

APA, Harvard, Vancouver, ISO, and other styles

23

Nelson, N. Thomas. "Probability of Bit Error on a Standard IRIG Telemetry Channel Using the Aeronautical Fading Channel Model." International Foundation for Telemetering, 1994. http://hdl.handle.net/10150/611662.

Full text

Abstract:

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California
This paper analyzes the probability of bit error for PCM-FM over a standard IRIG channel subject to multipath interference modeled by the aeronautical fading channel. The aeronautical channel model assumes a mobile transmitter and a stationary receiver and specifies the correlation of the fading component. This model describes fading which is typical of that encountered at military test ranges. An expression for the bit error rate on the fading channel with a delay line demodulator is derived and compared with the error rate for the Gaussian channel. The increase in bit error rate over that of the Gaussian channel is determined along with the power penalty caused by the fading. In addition, the effects of several channel parameters on the probability of bit error are determined.

APA, Harvard, Vancouver, ISO, and other styles

24

Adesemowo, A. Kayode. "Affective gesture fast-track feedback instant messaging (AGFIM)." Thesis, University of Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&amp.

Full text

Abstract:

Text communication is often perceived as lacking some components of communication that are essential in sustaining interaction or conversation. This interaction incoherency tends to make text communication plastic. It is traditionally devoid of intonation, pitch, gesture, facial expression and visual or auditory cues. Nevertheless, Instant Messaging (IM), a form of text communication is on the upward uptake both on PCs and on mobile handhelds. There is a need to rubberise this plastic text messaging to improve co-presence for text communications thereby improving synchronous textual discussion, especially on handheld devices.

One element of interaction is gesture, seen as a natural way of conversing. Attaining some level of interaction naturalism requires improving synchronous communication spontaneity, partly achieved by enhancing input mechanisms. To enhance input mechanisms for interactive text-based chat on mobile devices, there is a need to facilitate gesture input. Enhancement is achievable in a number of ways, such as input mechanism redesigning and input offering adaptation. This thesis explores affective gesture mode on interface redesign as an input offering adaptation. This is done without a major physical reconstruction of handheld devices.

This thesis presents a text only IM system built on Session Initiation Protocol (SIP) and SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE). It was developed with a novel user-defined hotkey implemented as a one-click context menu to &ldquo
fast-track&rdquo
text-gestures and emoticons.

A hybrid quantitative and qualitative approach was taken to enable data triangulation. Results from experimental trials show that an Affective Gesture (AG) approach improved IM chat spontaneity/response. Feedback from the user trials affirms that AG hotkey improves chat responsiveness, thus enhancing chat spontaneity.

APA, Harvard, Vancouver, ISO, and other styles

25

Odunaiya, Simbo Ajayi. "A mathematical model to aid in the design of ameliorating cosmetics for conducting surfaces that ordinarily produce derogative multipath for the ILS localizer course." Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1174610226.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Vyčítal, Jaroslav. "Šíření signálů bezdrátových komunikačních systémů IEEE 802.11." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2018. http://www.nusl.cz/ntk/nusl-377156.

Full text

Abstract:

This paper deals with the propagation of waves. Here is the wavelength distribution according to the wavelength. It focuses on the UHF and SHF band in which IEEE802.11n operates. Contains model breakdown by cell type. Describes which propagation methods are dominant in the cell type. Several propagation patterns are presented, which are then modeled in Matlab environment.The models are then compared to experimental measurements.

APA, Harvard, Vancouver, ISO, and other styles

27

Newhall, William George. "Wideband Propagation Measurement Results, Simulation Models, and Processing Techniques for a Sliding Correlator Measurement System." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35678.

Full text

Abstract:

Radio wave propagation measurements provide a way to accurately and reliably characterize environments to assist in the development and optimization of wireless communication systems. As digital radio systems occupy wider bandwidths and use multipath signal combining to enhance quality of service, knowledge of time dispersion and the multipath structure of radio channels become increasingly important. The wideband measurement system presented herein provides a practical means to precisely measure the delays and strengths of individual multipath components which arrive at a radio receiver.

Presented in this Thesis are fundamental theory, practical implementation, and simulation models for a sliding correlator measurement system. The sliding correlator technique is explained in detail and large-scale measurement survey is presented. Techniques for statistically quantifying the characteristics of propagation using the sliding correlator measurements are presented and compared. The development of simulations of the sliding correlator system is described, and simulation results are used to test conventional and newly developed post-processing algorithms.

This Thesis presents a practical view of the sliding correlator measurement system, but its foundations are rooted in the theoretical results which are explained and derived herein. Propagation researchers and students in the wireless communication field may find this work and the cited references useful for continued study of wideband propagation measurements or for application of the sliding correlator system as a wideband measurement solution.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

28

Bradbury, Jody Neil. "The integration of city models and GNSS for the simulation and modelling of multipath and availability : paving the way for new applications." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1445208/.

Full text

Abstract:

Positioning in the urban environment, using Global Navigation Satellite Systems (GNSS), is hampered by poor satellite availability due to signal obstruction and disruption caused by both manmade and natural features of the urban environment. In addition, range measurement to satellites for positioning and for navigation, is severely degraded by the presence of reflected and diffracted signals. The arrival and continuous enhancement of computerised geometric environment models, makes it possible to tackle these problems through mathematical modelling. Environment models have been used by architects and town planners for around thirty years. Within the last decade city model quality in terms of coverage, level of detail and geometric accuracy, has increased. Consequently, the number of applications for such models is continuously increasing and this ensures their continued availability and future usage. Currently, accurate prediction of satellite availability, particularly in cities, is extremely problematic. This thesis presents research undertaken into the use of environment models for the accurate prediction of satellite availability. A software simulator has been developed in order to accurately predict satellite availability, taking as input any environment model. Line of sight (LOS), Fresnel zone, diffracted propagation and reflected signal propagation models have been implemented in the simulator. Validation of each signal propagation model has been performed by comparison of observed data with corresponding simulated outputs. Successful validation of the Fresnel and diffracted propagation models, presented in this thesis, clearly indicate an enhancement over the use of conventional LOS propagation models alone. The reflected propagation model provides a potentially significant enhancement to the area of multipath modelling. It is certain that this work is of importance for mobile positioning devices. With the arrival of greater computational resources inside GNSS receivers, this research is likely to provide a means of reducing positioning errors due to multipath.

APA, Harvard, Vancouver, ISO, and other styles

29

Bradáč, Lubomír. "Model distribuční energetické sítě." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219469.

Full text

Abstract:

The thesis is focused on PLC technology issues and thus the data transmission over a power-line. This work describes characteristics of the PLC technology, its usage, functional principles and used modulation techniques. The main part of the work describes individual kinds of interferences in the network. The method of necessary steps against these interferences by using the right modulation and relevant coding is also described in the thesis. On the basis of theoretical knowledge, the models of interferences are realized in Matlab/Simulink. The simulative model of power-lines with random parameters is designed and realized for each elected techniques of modulation (BPSK, QPSK, ASK, FSK). The method of PLC channels modeling is chose as a multipath signal spreading for topology with one and two branching and the dependence of their transmission functions are inquired too. The analysis of interference influence on the data transmission is performed via the created models. All acquired results are compared and evaluated in the conclusion of this thesis.

APA, Harvard, Vancouver, ISO, and other styles

30

Hallmén, Mathias. "Map-Aided GPS Tracking in Urban Areas : Application to Runner Tracking in Sprint Orienteering." Thesis, Linköpings universitet, Reglerteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-121649.

Full text

Abstract:

The GPS tracking in sprint orienteering is often a poor supplement to the viewer experience during events taking place in urban areas because of multipath effects. Since the GPS tracking of runners is an important means to making the sport more spectator friendly, it is of interest to make it more accurate. In this thesis project, the information provided by the map of a competition is fused with the GPS tracker position measurements and punch time data in a particle filter to create estimates of the runner trajectories. The map is used to create constraints and to predict motion of runners, as well as to create a model of the GPS reliability depending on map position. A simple observation model is implemented, using the map to decide if a GPS measurement is reliable or not depending on the distance to the closest building. A rather complex motion model is developed to predict the runner motion within the constraints given by the map. The results show that given certain conditions the improvements are vast compared to the traditional GPS tracking. The estimates are bound to possible routes, and they are often very good given that alternative route choices are easily separable. It is however principally difficult to generally improve the tracking using this method. Better measurements or observation models are needed in order to receive a fully satisfying tracking.

APA, Harvard, Vancouver, ISO, and other styles

31

Aloi, Daniel Nicholas. "Development and verification of a mathematical model to investigate the effects of earth-surface-based multipath reflections at a differential global positioning system ground reference site." Ohio : Ohio University, 1999. http://www.ohiolink.edu/etd/view.cgi?ohiou1175264170.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Nuckols, John Eric. "Implementation of Geometrically Based Single-Bounce Models for Simulation of Angle-of-Arrival of Multipath Delay Components in the Wireless Channel Simulation Tools, SMRCIM and SIRCIM." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/35989.

Full text

Abstract:

As the demand for wireless communication systems has exploded over the past few years, many researchers have taken on the challenge to model wireless channels more accurately. These models are very useful for enhancing the design of all aspects of wireless communications. Smart antennas and systems used in position location are among the most popular new studies that require signal information such as the amplitude, phase, and angle-of-arrival (AOA) of multipath delay spreads. For proper and efficient implementation of future systems, emerging wireless systems must be able to exploit processing of spatial information. The goal of the work presented in this thesis is to further improve two channel modeling tools, SMRCIM and SIRCIM, by implementing new geometrical models that provide users with angle-of-arrival information as well as amplitude and phase data for wideband wireless communication channels. The new angle-of-arrival models are explained and pseudo code is provided to demonstrate the software implementation of the models. Likewise, the channel models are explained and the usage and results of the simulation tools are described. The SMRCIM and SIRCIM tools are currently being used by researchers throughout the world.

[Vita removed March 5, 2012. GMc]
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

33

Queiroz, Diego Véras de. "Simulação realista de redes de sensores sem fio industriais." Universidade Federal da Paraíba, 2016. http://tede.biblioteca.ufpb.br:8080/handle/tede/9248.

Full text

Abstract:

Submitted by Fernando Souza (fernandoafsou@gmail.com) on 2017-08-14T10:56:32Z No. of bitstreams: 1 arquivototal.pdf: 4889368 bytes, checksum: 2154a6772c98f0f2fb36fa3148dc4a24 (MD5)
Made available in DSpace on 2017-08-14T10:56:32Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 4889368 bytes, checksum: 2154a6772c98f0f2fb36fa3148dc4a24 (MD5) Previous issue date: 2016-02-29
A Wireless Sensor Network (WSN) can be characterized by the use of sensor nodes in varied environments for many different applications, e.g., monitoring and control systems applications in industrial environments. The use of WSNs in industrial applications must deal with typical problems of wireless networks, such as high attenuation and obstructions. In these environments, different characteristics of the channels can be observed due to its multipath profile. Changes in the topology may also cause changes in the channel characteristics as the time goes on, and it may cause differences in the average value of the received power. An alternative to deal with it and with the variation of channel quality is the development of protocols that use multiple channels. Its use allows, e.g., to achieve better use of the channel, increasing the network transmission capacity. However, there is a difficulty in evaluating and comparing different approaches due to the lack of simulators which have more accurate models. To assess the real benefits of these protocols, one should take into account a more realistic propagation model. This work presents a realistic simulation model that captures the effects of fading on a large and small scale, log-normal shadowing, the non-stationary characteristics of the channel for a long time, and the different characteristics of the different IEEE 802.15.4 standard channels. The model was then built into the open-source discrete event simulator Castalia and tested, comparing it with the default stationary model of the simulator. After integration, the protocol Tree-based Multi-Channel Protocol (TMCP) was evaluated using the proposed model. In the experiments it was possible to identify good accuracy in both the model and the TMCP protocol.
Uma Rede de Sensores sem Fio (RSSF) pode ser caracterizada pela utilização de nós sensores em variados ambientes para as mais diversas aplicações, por exemplo, para monitoramento e controle em ambiente industrial. O uso de RSSFs para implementar aplicações industriais precisa lidar com problemas típicos das redes sem fio, como alta atenuação e obstruções. Nesses ambientes, diferenças nas características dos canais podem ser observadas dado o seu perfil de multipercurso. Mudanças na topologia também podem provocar mudanças nas características dos canais ao longo do tempo, podendo causar diferença no valor médio da potência recebida. Uma alternativa para lidar com isso e com a variação da qualidade dos canais é o desenvolvimento de protocolos que utilizam múltiplos canais. Seu uso permite, por exemplo, alcançar uma melhor utilização do canal, aumentando a capacidade de transmissão da rede. No entanto, existe uma dificuldade em avaliar e comparar as diferentes abordagens devido à carência de simuladores que apresentem modelos mais precisos. Para avaliar os reais benefícios desses protocolos deve-se levar em consideração um modelo de propagação mais próximo da realidade. Esse trabalho apresenta um modelo de simulação que captura os efeitos de desvanecimento em larga escala, atenuação em pequena escala, sombreamento log-normal, as características não-estacionárias do canal em longos períodos de tempo, e as características distintas dos diferentes canais do padrão IEEE 802.15.4. O modelo foi então integrado ao simulador de eventos discretos de código aberto Castalia e testado, comparando-o com o modelo estacionário padrão do próprio simulador. A partir da integração, o protocolo Tree-based Multi-Channel Protocol (TMCP) foi implementado e avaliado utilizando o modelo proposto. Com os experimentos foi possível identificar uma ótima precisão do modelo e do protocolo TMCP.

APA, Harvard, Vancouver, ISO, and other styles

34

Motiwala, Murtaza. "An architecture for network path selection." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43576.

Full text

Abstract:

Traditional routing protocols select paths based on static link weights and converge to new paths only when there is an outright reachability failure (such as a link or router failure). This design allows routing scale to hundreds of thousands of nodes, but it comes at the cost of functionality: routing provides only simple, single path connectivity. Networked applications in the wide-area, enterprise, and data center can all beneﬁt from network protocols that allow trafﬁc to be sent over multiple routes en route to a destination. This ability, also called multipath routing, has other signiﬁcant beneﬁts over single-path routing, such as more efﬁciently using network resources and recovering more quickly from network disruptions. This dissertation explores the design of an architecture for path selection in the network and proposes a "narrow waist" interface for networks to expose choice in routing trafﬁc to end systems. Because most networks are also business entities, and are sensitive to the cost of routing trafﬁc in their network, this dissertation also develops a framework for exposing paths based on their cost. For this purpose, this dissertation develops a cost model for routing trafﬁc in a network. In particular, this dissertation presents the following contributions: * Design of path bits, a "narrow waist" for multipath routing. Our work ties a large number of multipath routing proposals by creating an interface (path bits) for decoupling the multipath routing protocols implemented by the network and end systems (or other network elements) making a choice for path selection. Path bits permit simple, scalable, and efﬁcient implementations of multipath routing protocols in the network that still provide enough expressiveness for end systems to select alternate paths. We demonstrate that our interface is ﬂexible and leads to efﬁcient network implementations by building prototype implementations on different hardware and software platforms. * Design of path splicing, a multipath routing scheme. We develop, path splicing, a multipath routing technique, which uses random perturbations from the shortest path to create exponentially large number of paths with only a linear increase in state in a network. We also develop a simple interface to enable end systems to make path selection decisions. We present various deployment paths for implementing path splicing in both intradomain and interdomain routing on the Internet. * Design of low cost path-selection framework for a network. Network operators and end systems can have conﬂicting goals, where the network operators are concerned with saving cost and reducing trafﬁc uncertainty; and end systems favor better performing paths. Exposing choice of routing in the network can thus, create a tension between the network operators and the end systems. We propose a path-selection framework where end systems make path selection decisions based on path performance and networks expose paths to end systems based on their cost to the network. This thesis presents a cost model for routing trafﬁc in a network to enable network operators to reason about "what-if " scenarios and routing trafﬁc on their network.

APA, Harvard, Vancouver, ISO, and other styles

35

Franek, Lešek. "Vícevodičový model komunikace po venkovním elektrickém vedení." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-256566.

Full text

Abstract:

PLC - power line communication is not new. It has been known for many years. But It never be used in massive scale. There were only sporadic applications, for example ripple control system HDO used in the Czechoslovakia. PLC currently experiencing a renaissance thanks to the advent of Smart Grid. PLC offering relatively low bit rates and relatively unreliable transmission, but these disadvantages compensates very low costs to build a communication infrastructure and it offers specific functionalities for Smart Grid. The question is whether the declared parameters will be met in the real world. This thesis tries to find an answer.

APA, Harvard, Vancouver, ISO, and other styles

36

Mota, Susana de Jesus. "Channel modelling for MIMO systems." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14961.

Full text

Abstract:

Doutoramento em Engenharia Electrotécnica
Systems equipped with multiple antennas at the transmitter and at the receiver, known as MIMO (Multiple Input Multiple Output) systems, offer higher capacities, allowing an efficient exploitation of the available spectrum and/or the employment of more demanding applications. It is well known that the radio channel is characterized by multipath propagation, a phenomenon deemed problematic and whose mitigation has been achieved through techniques such as diversity, beamforming or adaptive antennas. By exploring conveniently the spatial domain MIMO systems turn the characteristics of the multipath channel into an advantage and allow creating multiple parallel and independent virtual channels. However, the achievable benefits are constrained by the propagation channel’s characteristics, which may not always be ideal. This work focuses on the characterization of the MIMO radio channel. It begins with the presentation of the fundamental results from information theory that triggered the interest on these systems, including the discussion of some of their potential benefits and a review of the existing channel models for MIMO systems. The characterization of the MIMO channel developed in this work is based on experimental measurements of the double-directional channel. The measurement system is based on a vector network analyzer and a two-dimensional positioning platform, both controlled by a computer, allowing the measurement of the channel’s frequency response at the locations of a synthetic array. Data is then processed using the SAGE (Space-Alternating Expectation-Maximization) algorithm to obtain the parameters (delay, direction of arrival and complex amplitude) of the channel’s most relevant multipath components. Afterwards, using a clustering algorithm these data are grouped into clusters. Finally, statistical information is extracted allowing the characterization of the channel’s multipath components. The information about the multipath characteristics of the channel, induced by existing scatterers in the propagation scenario, enables the characterization of MIMO channel and thus to evaluate its performance. The method was finally validated using MIMO measurements.
Os sistemas equipados com múltiplas antenas no emissor e no recetor, conhecidos como sistemas MIMO (Multiple Input Multiple Output), oferecem capacidades mais elevadas, permitindo melhor rentabilização do espectro e/ou utilização de aplicações mais exigentes. É sobejamente sabido que o canal rádio é caracterizado por propagação multipercurso, fenómeno considerado problemático e cuja mitigação tem sido conseguida através de técnicas como diversidade, formatação de feixe ou antenas adaptativas. Explorando convenientemente o domínio espacial os sistemas MIMO transformam as características multipercurso do canal numa mais-valia e permitem criar vários canais virtuais, paralelos e independentes. Contudo, os benefícios atingíveis são condicionados pelas características do canal de propagação, que poderão não ser sempre as ideais. Este trabalho centra-se na caracterização do canal rádio para sistemas MIMO. Inicia-se com a apresentação dos resultados fundamentais da teoria da informação que despoletaram todo o entusiamo em torno deste tipo de sistemas, sendo discutidas algumas das suas potencialidades e uma revisão dos modelos existentes para sistemas MIMO. A caracterização do canal MIMO desenvolvida neste trabalho assenta em medidas experimentais do canal direcional adquiridas em dupla via. O sistema de medida é baseado num analisador de redes vetorial e numa plataforma de posicionamento bidimensional, ambos controlados por um computador, permitindo obter a resposta em frequência do canal rádio nos vários pontos correspondentes à localização dos elementos de um agregado virtual. As medidas são posteriormente processadas com o algoritmo SAGE (Space-Alternating Expectation-Maximization), de forma a obter os parâmetros (atraso, direção de chegada e amplitude complexa) das componentes multipercurso mais significativas. Seguidamente, estes dados são tratados com um algoritmo de classificação (clustering) e organizados em grupos. Finalmente é extraída informação estatística que permite caracterizar o comportamento das componentes multipercurso do canal. A informação acerca das características multipercurso do canal, induzidas pelos espalhadores (scatterers) existentes no cenário de propagação, possibilita a caracterização do canal MIMO e assim avaliar o seu desempenho. O método foi por fim validado com medidas MIMO.

APA, Harvard, Vancouver, ISO, and other styles

37

Roivainen, A. (Antti). "Three-dimensional geometry-based radio channel model:parametrization and validation at 10 GHz." Doctoral thesis, Oulun yliopisto, 2017. http://urn.fi/urn:isbn:9789526215549.

Full text

Abstract:

Abstract This dissertation presents complete parameterizations for a three-dimensional (3-D) geometry-based stochastic radio channel model (GSCM) at 10 GHz based on measurement campaigns. The thesis is divided into the following main parts: radio channel measurements, the characterization of model parameters, and model validation. Experimental multiple-input multiple-output (MIMO) channel measurements carried out in two-story lobby and urban small cell scenarios are first described. The measurements were performed with a vector network analyzer and dual polarized virtual antenna arrays with a bandwidth over 500 MHz. The measurement data was post-processed using the ESPRIT algorithm and the post-processed data was verified using a semi-deterministic map-based model. The results showed a good match between estimated and modeled multipath components (MPCs). In addition, single-input single-output outdoor-to-indoor measurements were executed through a standard multi-pane glass window and concrete wall. A statistical analysis was carried out for defining full 3-D characterization of the propagation channel in both line-of-sight (LOS) and non-line-of-sight (NLOS) propagation conditions. The delay and angular dispersions of MPCs are smaller in comparison to lower frequency bands due to the higher attenuation of the delayed MPCs. Moreover, specular reflection is observed to be the more dominant propagation mechanism in comparison to diffuse scattering, leading to smaller cluster angle spreads in comparison to lower frequency bands. The penetration loss caused by a standard multi-pane glass window is on the same level as in the lower frequency bands, whereas the loss caused by the concrete wall is a few dBs higher than at lower frequency bands. Finally, the GSCM with determined parameters is validated. A MIMO channel was reconstructed by embedding 3-D radiation patterns of the antennas into the propagation path estimates. Equivalently the channel simulations were performed with a quasi deterministic radio channel generator (QuaDRiGa) using the defined parameters. The channel capacity, Demmel condition number, and relative condition numbers are used as the comparison metrics between reconstructed and modeled channels. The results show that the reconstructed MIMO channel matches the simulated MIMO channel well
Tiivistelmä Tämä väitöskirja esittää parametroinnit kolmiulotteiselle geometriaan perustuvalle stokastiselle radiokanavamallille 10 GHz:n taajuusalueella perustuen mitattuun radiokanavaan. Väitöskirja koostuu kolmesta pääalueesta: radiokanavamittaukset, radiokanavamallin parametrien määrittäminen ja mallin validointi. Aluksi kuvataan kaksikerroksisessa aula ja kaupunkipiensolu ympäristöissä monilähetin monivastaanotin (MIMO) järjestelmällä tehdyt kanavamittaukset. Mittaukset tehtiin vektoripiirianalysaattorilla ja kaksoispolaroiduilla virtuaaliantenniryhmillä 500 MHz kaistanleveydellä. Mittausdata jälkikäsiteltiin käyttämällä ESPRIT-algoritmia ja jälkikäsitelty data varmennettiin osittain deterministisellä mittausympäristön karttaan pohjautuvalla radiokanavamallilla. Tulokset osoittivat hyvän yhteensopivuuden mitattujen ja mallinnettujen moniteiden välillä. Lisäksi toteuttiin yksi-lähetin yksi-vastaanotin mittaukset ulko-sisä etenemisympäristössä monikerroksisen lasin ja betoniseinän läpi. Tilastollinen analyysin avulla määritettiin täysi kolmiulotteinen kuvaus radioaallon etenemiskanavasta näköyhteys ja näköyhteydettömässä tilanteissa. Moniteiden suuremmista vaimennuksista johtuen viive ja kulmahajonnat ovat pienemmät verrattaessa matalempiin taajuuksiin. Peiliheijastus on diffuusisirontaa merkittävämpi radioaallon etenemismekanismi johtaen pienempiin klustereiden kulmahajeisiin matalempiin taajuuksiin verrattuna. Monikerroksisen lasin läpäisyvaimennus on samankaltainen kuin alemmilla taajuuksilla, kun sitä vastoin betoniseinän vaimennus on muutaman desibelin suurempi kuin alemmilla taajuuksilla. Lopulta geometriaan perustava stokastinen radiokanavamalli validoidaan määritellyillä parametreilla. MIMO kanava uudelleen rakennetaan lisäämällä kolmiulotteiset antennien säteilykuviot estimoituihin radioaallon etenemisteihin. Vastaavasti radiokanava simuloidaan näennäisesti deterministisellä radiokanavageneraattorilla (QuaDRiGa) käyttäen määriteltyjä mallin parametreja. Kanavakapasiteettia, Demmel ehtolukua ja suhteellista ehtolukua käytetään vertailumittareina uudelleen rakennetun ja simuloidun kanavan välillä. Tulosten perusteella uudelleen rakennettu MIMO kanava on yhteensopiva simuloidun radiokanavan kanssa

APA, Harvard, Vancouver, ISO, and other styles

38

IMAM, RAYAN MOHAMED ELMUBARAK ALI. "Global Navigation Satellite Systems as Signals of Opportunity for Environmental Applications: Reflectometry and Scintillation." Doctoral thesis, Politecnico di Torino, 2022. https://hdl.handle.net/11583/2973801.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Hunter, Brandon. "Channel Probing for an Indoor Wireless Communications Channel." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/64.

Full text

Abstract:

The statistics of the amplitude, time and angle of arrival of multipaths in an indoor environment are all necessary components of multipath models used to simulate the performance of spatial diversity in receive antenna configurations. The model presented by Saleh and Valenzuela, was added to by Spencer et. al., and included all three of these parameters for a 7 GHz channel. A system was built to measure these multipath parameters at 2.4 GHz for multiple locations in an indoor environment. Another system was built to measure the angle of transmission for a 6 GHz channel. The addition of this parameter allows spatial diversity at the transmitter along with the receiver to be simulated. The process of going from raw measurement data to discrete arrivals and then to clustered arrivals is analyzed. Many possible errors associated with discrete arrival processing are discussed along with possible solutions. Four clustering methods are compared and their relative strengths and weaknesses are pointed out. The effects that errors in the clustering process have on parameter estimation and model performance are also simulated.

APA, Harvard, Vancouver, ISO, and other styles

40

Nahimana, Donnay Fleury. "Impact des multitrajets sur les performances des systèmes de navigation par satellite : contribution à l'amélioration de la précision de localisation par modélisation bayésienne." Phd thesis, Ecole Centrale de Lille, 2009. http://tel.archives-ouvertes.fr/tel-00446552.

Full text

Abstract:

De nombreuses solutions sont développées pour diminuer l'influence des multitrajets sur la précision et la disponibilité des systèmes GNSS. L'intégration de capteurs supplémentaires dans le système de localisation est l'une des solutions permettant de compenser notamment l'absence de données satellitaires. Un tel système est certes d'une bonne précision mais sa complexité et son coût limitent un usage très répandu.Cette thèse propose une approche algorithmique destinée à améliorer la précision des systèmes GNSS en milieu urbain. L'étude se base sur l'utilisation des signaux GNSS uniquement et une connaissance de l'environnement proche du récepteur à partir d'un modèle 3D du lieu de navigation.La méthode présentée intervient à l'étape de filtrage du signal reçu par le récepteur GNSS. Elle exploite les techniques de filtrage statistique de type Monte Carlo Séquentiels appelées filtre particulaire. L'erreur de position en milieu urbain est liée à l'état de réception des signaux satellitaires (bloqué, direct ou réfléchi). C'est pourquoi une information sur l'environnement du récepteur doit être prise en compte. La thèse propose également un nouveau modèle d'erreurs de pseudodistance qui permet de considérer les conditions de réception du signal dans le calcul de la position.Dans un premier temps, l'état de réception de chaque satellite reçu est supposé connu dans le filtre particulaire. Une chaîne de Markov, valable pour une trajectoire connue du mobile, est préalablement définie pour déduire les états successifs de réception des satellites. Par la suite, on utilise une distribution de Dirichlet pour estimer les états de réception des satellites

APA, Harvard, Vancouver, ISO, and other styles

41

Kamali, Kaivan. "Multiparty proactive communication a perspective for evolving shared mental models /." 2007. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-1982/index.html.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Vitorino, Tiago Miguel Mendes Ferreira. "Planning and verification of multipath routing protocols." Master's thesis, 2014. http://hdl.handle.net/10362/14110.

Full text

Abstract:

Conventionally the problem of the best path in a network refers to the shortest path problem. However, for the vast majority of networks present nowadays this solution has some limitations which directly affect their proper functioning, as well as an inefficient use of their potentialities. Problems at the level of large networks where graphs of high complexity are commonly present as well as the appearing of new services and their respective requirements, are intrinsically related to the inability of this solution. In order to overcome the needs present in these networks, a new approach to the problem of the best path must be explored. One solution that has aroused more interest in the scientific community considers the use of multiple paths between two network nodes, where they can all now be considered as the best path between those nodes. Therefore, the routing will be discontinued only by minimizing one metric, where only one path between nodes is chosen, and shall be made by the selection of one of many paths, thereby allowing the use of a greater diversity of the present paths (obviously, if the network consents). The establishment of multi-path routing in a given network has several advantages for its operation. Its use may well improve the distribution of network traffic, improve recovery time to failure, or it can still offer a greater control of the network by its administrator. These factors still have greater relevance when networks have large dimensions, as well as when their constitution is of high complexity, such as the Internet, where multiple networks managed by different entities are interconnected. A large part of the growing need to use multipath protocols is associated to the routing made based on policies. Therefore, paths with different characteristics can be considered with equal level of preference, and thus be part of the solution for the best way problem. To perform multi-path routing using protocols based only on the destination address has some limitations but it is possible. Concepts of graph theory of algebraic structures can be used to describe how the routes are calculated and classified, enabling to model the routing problem. This thesis studies and analyzes multi-path routing protocols from the known literature and derives a new algebraic condition which allows the correct operation of these protocols without any network restriction. It also develops a range of software tools that allows the planning and the respective verification/validation of new protocols models according to the study made.

APA, Harvard, Vancouver, ISO, and other styles

43

Singh, Ankit. "Multipath Probabilistic Early Response TCP." Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11723.

Full text

Abstract:

Many computers and devices such as smart phones, laptops and tablet devices are now equipped with multiple network interfaces, enabling them to use multiple paths to access content over the network. If the resources could be used concurrently, end user experience can be greatly improved. The recent studies in MPTCP suggest that improved reliability, load balancing and mobility are feasible. The thesis presents a new multipath delay based algorithm, MPPERT (Multipath Probabilistic Early response TCP), which provides high throughput and efficient load balancing. In all-PERT environment, MPPERT suffers no packet loss and maintains much smaller queue sizes compared to existing MPTCP, making it suitable for real time data transfer. MP-PERT is suitable for incremental deployment in a heterogeneous environment. It also presents a parametrized approach to tune the amount of traffic shift off the congested path. Multipath approach is benefited from having multiple connections between end hosts. However, it is desired to keep the connection set minimal as increasing number of paths may not always provide significant increase in the performance. Moreover, higher number of paths unnecessarily increase computational requirement. Ideally, we should suppress paths with low throughputs and avoid paths with shared bottlenecks. In case of MPTCP, there is no efficient way to detect a common bottleneck between subflows. MPTCP applies a constraint of best single-path TCP throughput, to ensure fair share at a common bottleneck link. The best path throughput constraint along with traffic shift, from more congested to less congested paths, provide better opportunity for the competing flows to achieve higher throughput. However, the disadvantage is that even if there are no shared links, the same constraint would decrease the overall achievable throughput of a multipath flow. PERT, being a delay based TCP protocol, has continuous information about the state of the queue. This information is valuable in enabling MPPERT to detect subflows sharing a common bottleneck and obtain a smaller set of disjoint subflows. This information can even be used to switch from coupled (a set of subflows having interdependent increase/decrease of congestion windows) to uncoupled (independent increase/decrease of congestion windows) subflows, yielding higher throughput when best single-path TCP constraint is relaxed. The ns-2 simulations support MPPERT as a highly competitive multipath approach, suitable for real time data transfer, which is capable of offering higher throughput and improved reliability.

APA, Harvard, Vancouver, ISO, and other styles

44

WanLee and 李宛. "Research of Indoor Positioning Based on Discrete Multipath Signal Model with Neural Network." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/2zyn8j.

Full text

Abstract:

碩士
國立成功大學
工程科學系
106
Global positioning system (GPS) is affected by many factors in the indoor environment and cannot provide accurate positioning. How to accurately locate in indoor environments has become very popular in recent years. In order to solve the multipath effects of wireless signal on indoor positioning, this paper proposes a discrete multipath signal model (DMS). Particularly, the multipath signals received at each point in space are not the same. Using this feature, the DMS model is used as a fingerprint for location fingerprinting. The ray tracing is used to calculate the electric field intensity of each grid point in the free space to establish the DMS fingerprint database. Subsequently, the back-propagation neural network (BPNN) and the generalized regression neural network (GRNN) are used to estimate the position. Various factors affecting the indoor positioning are evaluated, such as the size of the room, the number of access points (APs), and the number of hidden neurons in BPNN. The experimental results show that the number and arrangement of APs will significantly affect the results. Simulating a small room scenario (10 m×8 m×4 m), the error percentage is about 5%. Moreover, the distance error for the 90% error probability is within 1 m. In a large room scenario (100 m×80 m×4 m), the distance error for the 90% error probability is 2 m. Compared with conventional positioning methods, the positioning results of the proposed DMS using BPNN and GRNN are better than other methods.

APA, Harvard, Vancouver, ISO, and other styles

45

Teal, Paul D. "Real Time Characterisation of the Mobile Multipath Channel." Phd thesis, 2001. http://hdl.handle.net/1885/48207.

Full text

Abstract:

In this thesis a new approach for characterisation of digital mobile radio channels is investigated. The new approach is based on recognition of the fact that while the fading which is characteristic of the mobile radio channel is very rapid, the processes underlying this fading may vary much more slowly. The comparative stability of these underlying processes has not been exploited in system designs to date. ¶ Channel models are proposed which take account of the stability of the channel. Estimators for the parameters of the models are proposed, and their performance is analysed theoretically and by simulation and measurement. ¶ Bounds are derived for the extent to which the mobile channel can be predicted, and the critical factors which define these bounds are identified. ¶ Two main applications arise for these channel models. The first is the possibility of prediction of the overall system performance. This may be used to avoid channel fading (for instance by change of frequency), or compensate for it (by change of the signal rate or by power control). The second application is in channel equalisation. An equaliser based on a model which has parameters varying only very slowly can offer improved performance especially in the case of channels which appear to be varying so rapidly that the convergence rate of an equaliser based on the conventional model is not adequate. ¶ The first of these applications is explored, and a relationship is derived between the channel impulse response and the performance of a broadband system.

APA, Harvard, Vancouver, ISO, and other styles

46

Adesemowo, Kayode. "Affective Gesture Fast-track Feedback Instant Messaging (AGFIM)." Thesis, 2005. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6988_1370595481.

Full text

Abstract:

Text communication is often perceived as lacking some components of communication that are essential in sustaining interaction or conversation. This interaction incoherency tends to make
text communication plastic. It is traditionally devoid of intonation, pitch, gesture, facial expression and visual or auditory cues. Nevertheless, Instant Messaging (IM), a form of text communication is on the upward uptake both on PCs and on mobile handhelds. There is a need to rubberise this plastic text messaging to improve co-presence for text communications thereby improving
synchronous textual discussion, especially on handheld devices. One element of interaction is gesture, seen as a natural way of conversing. Attaining some level of interaction naturalism
requires improving synchronous communication spontaneity, partly achieved by enhancing input mechanisms. To enhance input mechanisms for interactive text-based chat on mobile devices,
there is a need to facilitate gesture input. Enhancement is achievable in a number of ways, such as input mechanism redesigning and input offering adaptation. This thesis explores affective gesture mode on interface redesign as an input offering adaptation. This is done without a major physical reconstruction of handheld devices. This thesis presents a text only IM system built on
Session Initiation Protocol (SIP) and SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE). It was developed with a novel user-defined hotkey implemented as a one-click context menu to &ldquo
fast-track&rdquo
text-gestures and emoticons. A hybrid quantitative and qualitative approach was taken to enable data triangulation. Results from experimental trials show that an
Affective Gesture (AG)approach improved IM chat spontaneity/response. Feedback from the user trials affirms that AG hotkey improves chat responsiveness, thus enhancing chat spontaneity.

APA, Harvard, Vancouver, ISO, and other styles

47

Sarkar, Pratik. "Adaptively Secure Primitives in the Random Oracle Model." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5449.

Full text

Abstract:

Adaptive security embodies one of the strongest notions of security that allows an adversary to corrupt parties at any point during protocol execution and gain access to its internal state. Since it models reallife situations such as “hacking”, efficient adaptively-secure multiparty computation (MPC) protocols are desirable. Such protocols demand primitives such as zero knowledge (ZK), oblivious transfer (OT) and commitment schemes that are adaptively-secure as building blocks. Efficient realizations of these primitives have been found to be challenging, especially in the no erasure model. We make progress in this direction and provide efficient constructions that are Universally-Composable in the random oracle model. The study of efficient ZK protocols for non-algebraic statements has seen rapid progress in recent times, relying on the techniques from secure computation. Our primary contribution in ZK lies in constructing efficient constant round ZK protocols from garbled circuits that are adaptively-secure, with communication linear in the size of the statement. We begin by showing that the practically efficient ZK protocol of Jawurek et al. (CCS 2013) is adaptively-secure when the underlying OT satisfies a mild adaptive security guarantee. We gain adaptive security with little to no overhead over the static case. A conditional verification technique is then used to obtain a three-round adaptively secure zero-knowledge argument in the non-programmable non-observable random oracle model. We present the first round optimal framework for building adaptively-secure OT in the programmable random oracle (PRO) model, relying upon the framework of Peikert et al. (Crypto 2008). When instantiated with Decisional Diffie Hellman assumption, it incurs a minimal communication overhead of one bit string and computational overhead of 5 random oracle queries over its static counterpart, where is the security parameter. Additionally, we obtain a construction of adaptively-secure 1-out-of-N OT by extending the result of Naor et al. (Journal of Cryptology 2005) that transforms log N copies of 1-out-of-2 OTs to one 1-out-of-N OT in the PRO model. We complete the picture of efficient OT constructions by presenting the first adaptively secure OT Extension, extending the protocol of Asharov et al. (Eurocrypt 2015) for the adaptive setting using PRO. Our OT extension enables us to obtain adaptive OTs at an amortized cost of 3 symmetric key operations and communication of 3 bit strings. We present an adaptively secure commitment scheme solely relying on observable random oracle (ORO). Our commitment scheme has a one-time offline setup phase, where a common reference string (crs) is generated between the parties using an ORO. In the online phase, the parties use the crs and ORO to generate commitments in a non-interactive fashion. Our construction incurs communication of 4 bit strings and computation of 8 exponentiations and 4 random oracle queries for committing to an arbitrary length message. It finds applications in secure two-party computation (2PC) protocols that adopt offline-online paradigm, where the crs can be generated in the offline phase and the scheme can be used in the online phase.

APA, Harvard, Vancouver, ISO, and other styles

48

Betaille, David. "Assessment and Improvement of the Capabilities of a Window Correlator to Model GPS Multipath Phase Errors." Phd thesis, 2004. http://tel.archives-ouvertes.fr/tel-00969130.

Full text

Abstract:

This thesis is concerned with the modelling of Global Positioning System (GPS) phase multipath. GPS is increasingly used for very high precision (centimetre level) engineering surveying applications such as setting out on construction sites and the control of major civil engineering plant (e.g. bulldozers, graders and pavement layers). In such applications the phase of the carrier signal is the basic observable and the dominant error source is multipath (electromagnetic reflections of the carrier waves from surfaces in the surroundings of the antennas). The work contained in the thesis has been carried out in collaboration with the LCPC (Laboratoire Central des Ponts et Chaussées) in Nantes, France, which made available its test facility and Leica Geosystems, Heerbrugg, Switzerland, a GPS manufacturer, which funded the work and which made available modified equipment for testing. The specific subject of the research is the assessment and improvement of the capabilities of a Phase Multipath Mitigation Window correlator (PMMW) to model GPS multipath phase errors. The phase window correlator is a new sampling technique dedicated to the estimation of multipath errors in phase measurements. The thesis contains background material on GPS multipath mitigation and on several existing patents related to the PMMW technique. The main contribution of the work relates to : - The rigorous mathematical modelling of multipath, starting from the physics of the phenomenon, right through to the phase measurement process itself, particularly that based on the PMMW correlator ; - The design of a general testing methodology in a controlled environment to assess the efficacy of multipath mitigation techniques ; - The carrying out of full-scale experiments at the LCPC in both static and kinematic modes and the assessment of the performances and limitations of the PMMW correlator ; - Initial investigations into the design of a new real-time correction strategy for phase multipath phase errors based on a combination of multipath observables including the signal-to-noise ratio, the output from the PMMW correlator and an estimation of the code multipath errors from dual frequency phase data. A key feature of the new strategy is its ability to overcome the major limitation of the PMMW technique, i.e. its insensitivity to multipath caused by very close reflectors. It enables the multipath corrupted phase measurements to be improved by 10 % in average in this case, whereas the PMMW corrections on their own had almost no effect.

APA, Harvard, Vancouver, ISO, and other styles

49

Τσίνος, Χρήστος. "Τεχνικές προσανατολισμένης επικοινωνίας για συνεργατικά δίκτυα." Thesis, 2008. http://nemertes.lis.upatras.gr/jspui/handle/10889/1028.

Full text

Abstract:

Τα συστήματα που έχουν πολλαπλές κεραίες σε πομπό και δέκτη (ΜΙΜΟ) έχουν την δυνατότητα να επιτύχουν υψηλούς ρυθμούς δεδομένων και αυξημένη αξιοπιστία χωρίς να απαιτείται επιπλέον εύρος ζώνης ή ισχύς μετάδοσης. Η βασική αρχή στην οποία βασίζονται είναι ότι το σήμα που εκπέμπεται από τον πομπό διέρχεται από περισσότερα του ενός ανεξάρτητα κανάλια. Ο δέκτης εκμεταλλευόμενος τις πολλαπλές λήψεις του ίδιου σήματος μπορεί να βελτιώσει την απόδοσή του. Η εισαγωγή πολλαπλών κεραιών σε κάποια συστήματα δεν είναι δυνατό να συμβεί συνήθως λόγω του χώρου που απαιτείται. Παρόλα αυτά, σε αυτό το περιβάλλον επικοινωνίας υπάρχουν συνήθως πολλαπλοί χρήστες που μπορούν να συνεργαστούν και να δημιουργήσουν ένα κατανεμημένο σύστημα ΜΙΜΟ, που αναφέρεται στην βιβλιογραφία ως συνεργατικό (cooperative). Στα συστήματα MIMO έχουν προταθεί τεχνικές προσανατολισμένης επικοινωνίας (beamforming) με σκοπό την ακύρωση των παρεμβολών και του θορύβου στο δέκτη. Οι τεχνικές αυτές απαιτούν την γνώση της κατάστασης του καναλιού αφού πραγματοποιούν διάσπαση της μήτρας των συντελεστών του καναλιού κατά παράγοντες ώστε να εξάγουν τα διανύσματα βάρους με τα οποία θα πολλαπλασιάσουν τις ακολουθίες των συμβόλων που λαμβάνει ο δέκτης ή /και των συμβόλων που μεταδίδει ο πομπός. Συγκεκριμένα, μελετήθηκε η περίπτωση της τεχνικής προσανατολισμένης επικοινωνίας που στηρίζεται στην μέθοδο SVD η οποία πολλαπλασιάζει το διάνυσμα των προς μετάδοση συμβόλων στον πομπό και το διάνυσμα των ληφθέντων συμβόλων στο δέκτη με τα κατάλληλα ιδιάζοντα διανύσματα, επιτυγχάνοντας προσανατολισμένη επικοινωνία λήψης και εκπομπής (transmit και receive beamforming). Όπως αναφέρθηκε, η συγκεκριμένη μέθοδος απαιτεί την γνώση της κατάστασης του καναλιού σε πομπό και σε δέκτη. Για αυτό το σκοπό αρχικά θα μελετηθεί η επίδραση της εκτίμησης του καναλιού στην επίδοση της μεθόδου η οποία διεξάγεται από ένα εκτιμητή μέγιστης πιθανοφάνειας από ακολουθίες συμβόλων εκμάθησης που έχει μεταδώσει ο πομπός. Στην συνέχεια θα εξεταστεί η περίπτωση που τα κανάλια μπορούν να περιγραφούν από ένα μοντέλο πολλαπλών μονοπατιών. Ένα τέτοιο μοντέλο είναι δυνατό να εκτιμηθεί από δείγματα της κρουστικής απόκρισης του καναλιού, βελτιώνοντας περαιτέρω την επίδοση του συστήματος. Επίσης, παρέχει και την δυνατότητα της πρόβλεψης των μεταγενέστερων καταστάσεων του καναλιού, μειώνοντας αρκετά τον αριθμό των συμβόλων εκμάθησης που απαιτούνται. Η εκτίμηση των παραμέτρων του μοντέλου του καναλιού θα γίνει με την βοήθεια της μεθόδου ESPRIT. Τελικά, θα ενσωματωθεί η εκτίμηση του μοντέλου και στην τεχνική προσανατολισμένης επικοινωνίας και θα μελετηθεί η επίδοσή της. Στην συνέχεια θα εφαρμόσουμε την προηγούμενη διάταξη στην περίπτωση των συνεργατικών συστημάτων. Θα εφαρμοστεί λοιπόν, σε ένα τέτοιο σύστημα η τεχνική με την εκτίμηση του μοντέλου του καναλιού και θα αναλυθεί η επίδοσή του για τα δύο πιο γνωστά πρωτόκολλα επικοινωνίας μεταξύ του κόμβου-πηγής και των κόμβων-συνεργατών, το ενίσχυσης και προώθησης και το αποκωδικοποίησης και προώθησης.
The systems that have multiple transmit and receive antennas (MIMO) can achieve high data rates and increased reliability without the need for additional bandwidth or transmission power. The aforementioned is based on the transmission of the signal of the transmitter via multiple independent channels. The receiver can use the multiple versions of the same signal to improve its performance. The introduction of multiple antennas in some systems it is not possible due to the lack of space. On contrast, in a multi-user environment there are users of a single antenna that can cooperate to construct a distributed MIMO system, which are called in the bibliography as a cooperative system. A number of beamforming schemes have already proposed in MIMO systems with the view of interference and noise cancellation. These schemes compute the singular value decomposition of the channel matrix and use the singular vectors to extract the weight vectors that are used to multiply the sequences of symbols that transmitter transmits and the symbols that receiver receives. This scheme achieves transmit and receive beamforming and transmitter and receiver must have full channel state information (CSI). The next step is to examine the performance of this method under channel estimation errors. The estimation of the channel is carried out with a maximum likelihood estimator from training sequences that were transmitted from the transmitter. After that, we examine the case in which the channel taps can be modeled by a multipath model. The parameters of a model of this kind can be computed from noise corrupted samples with sub-space methods. In this thesis we use the ESPRIT method for the estimation of these parameters. After the estimation of the model’s parameters we can use the model to predict future values of channel taps, decreasing with this way the number of the training symbols that are needed. Then, we will use this method in the system with the beamforming scheme and we will evaluate its performance. Finally, the complete infrastructure will be applied to a cooperative system and its performance will be tested for the two most popular cooperation protocols, the amplify and forward protocol and the decode and forward protocol.

APA, Harvard, Vancouver, ISO, and other styles

50

Dabin, Jason Anthony. "A statistical ultra wideband indoor channel model and the effects of antenna directivity on multipath delay spread and path loss in ultra wideband indoor channels." Thesis, 2004. http://library1.njit.edu/etd/fromwebvoyage.cfm?id=njit-etd2004-047.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Multiparty models'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles