Teses / dissertações sobre o tema "Loss of sight"

Theories on the impact of visual loss tend to generalise and can simplify complex issues. Two extreme views are challenged that portray the impact of visual loss as catastrophic or as a minor inconvenience. The argument is put forward that the impact of visual loss can lessen with improved interaction, and this theory is tested by the author questioning and modifying her own interaction. The following themes are explored: limbo status and self-acceptance; the common stresses experienced when asking for help; and discriminatory attitudes. The research is action based, and the emphasis is on how individuals adjust and adapt to loss, rather than the stresses experienced.
Master of Science (Hons)

This thesis presents a model to predict signal strength for frequencies between 902 MHz and 28 GHz. The model approximates diffraction using the knife-edge concept and equations proposed by Lee (1985). LOS pathways are calculated using the Bresenham algorithm and the corresponding elevations are obtained from a 30m DEM base map. The base map was generated by the procedure outlined in Rose (2001) and includes building elevations. The effect of Fresnel zones on prediction accuracy is considered. The effect of interpolating elevations along the Bresenham line is also considered. An Inverse Distance Weighting algorithm was used to interpolate the elevations. The accuracy of the model was evaluated using received signal strength data compiled from studies conducted at 902 MHz, 24.12 GHz and 27.525 GHz. In addition to the compiled data, data was also collected for this study at 2.4 GHz. 257 receiver locations were evaluated; 70 samples were Line-of-Sight. The study area incorporates the Virginia Polytechnic Institute and State University campus. Incorporating Fresnel zones, Interpolating elevations and calculating double blockages do not have an effect on the program's overall ability to predict signal strength. However, for obstructed pathways, it is not adequate to simply use path loss as an estimate of signal strength. Accurate estimates of diffraction gain are crucial for obstructed pathways. In addition, examination of the standard deviation for the data sets indicates that the model is independent of frequency. The average error across the frequencies is positively correlated with frequency, indicating that the model predicts signal strength better for higher frequencies. The smaller wavelengths associated with the higher frequencies require a more directional antenna and are therefore less sensitive to multipath interference. In addition, the smaller wavelengths are less able to diffract around buildings and terrain features.
Master of Science

At present, the current 4G systems provide a universal platform for broadband mobile services; however, mobile traffic is still growing at an unprecedented rate and the need for more sophisticated broadband services is pushing the limits on current standards to provide even tighter integration between wireless technologies and higher speeds. This has led to the need for a new generation of mobile communications: the so-called 5G. Although 5G systems are not expected to penetrate the market until 2020, the evolution towards 5G is widely accepted to be the logical convergence of internet services with existing mobile networking standards leading to the commonly used term “mobile internet” over heterogeneous networks, with several Gbits/s data rate and very high connectivity speeds. Therefore, to support highly increasing traffic capacity and high data rates, the next generation mobile network (5G) should extend the range of frequency spectrum for mobile communication that is yet to be identified by the ITU-R. The mm-wave spectrum is the key enabling feature of the next-generation cellular system, for which the propagation channel models need to be predicted to enhance the design guidance and the practicality of the whole design transceiver system. The present work addresses the main concepts of the propagation channel behaviour using ray tracing software package for simulation and then results were tested and compared against practical analysis in a real-time environment. The characteristics of Indoor-Indoor (LOS and NLOS), and indoor-outdoor (NLOS) propagations channels are intensively investigated at four different frequencies; 5.8 GHz, 26GHz, 28GHz and 60GHz for vertical polarized directional, omnidirectional and isotropic antennas patterns. The computed data achieved from the 3-D Shooting and Bouncing Ray (SBR) Wireless Insite based on the effect of frequency dependent electrical properties of building materials. Ray tracing technique has been utilized to predict multipath propagation characteristics in mm-wave bands at different propagation environments. Finally, the received signal power and delay spread were computed for outdoor-outdoor complex propagation channel model at 26 GHz, 28 GHz and 60GHz frequencies and results were compared to the theoretical models.

This is a narrative account of a cohesive programme of research carried out between 2010 and 2016, which resulted in ten peer-reviewed, published papers that provide an empirical basis for my thesis. The impetus for this academic exploration was provided by my personal experience of acquired sight loss, where my medical and functional needs were prioritised but my emotional needs were overlooked. The first study I undertook confirmed that people experienced negative emotional effects attributable to acquired sight loss. Subsequent studies explored the experience of social exclusion in health and education for blind and partially sighted people. Difficulties were evident across the lifespan, starting with undiagnosed refractive errors in childhood, moving to perceptions of inclusion in high school and on to experiences of exclusion in health care and engagement with leisure activities in adulthood. These papers offer a context for understanding the social and emotional effects of sight loss. Two supporting papers examined how inclusion in healthcare might be increased through nurse education and how accessible games might aid inclusion in entertainment. The thesis as a whole focuses on the development of Counselling for Sight Loss, a pluralistic practice framework for responding holistically to the emotional effects of sight loss, which are compounded by social exclusion. My theoretical model explaining the transition from sight to blindness provided a theoretical context for the thesis, advocating that different people benefit from different types of emotional support at different times in their sight loss journey. This has implications for the nature and timing of emotional support offered to blind and partially sighted people. Counselling for Sight Loss is based around a menu of therapeutic tasks, identified from analysis of systematic case study data in which clients identified helpful aspects of their therapy. These tasks provide an empirical basis for working therapeutically with clients who have visual impairment and will act as a foundation for the development of training materials. The findings of my most recent study have highlighted the need for a national framework for the provision of emotional support services for blind and partially sighted people within the United Kingdom. Currently, emotional support and counselling services are being delivered by staff with varying degrees of relevant training, including those with none. My research has contributed to the development of quality standards and training, based on my Counselling for Sight Loss data, to benefit UK service delivery. Thus my thesis represents a systematic commitment to using research to generate real-world solutions to a real-world problem: designing and delivering effective emotional support and counselling for adults with sight loss in the United Kingdom.

Theories on the impact of visual loss tend to generalise and can simplify complex issues. Two extreme views are challenged that portray the impact of visual loss as catastrophic or as a minor inconvenience. The argument is put forward that the impact of visual loss can lessen with improved interaction, and this theory is tested by the author questioning and modifying her own interaction. The following themes are explored: limbo status and self-acceptance; the common stresses experienced when asking for help; and discriminatory attitudes. The research is action based, and the emphasis is on how individuals adjust and adapt to loss, rather than the stresses experienced.

The objective of this work is to enhance the awareness of the indoor propagation behaviour, by a set of investigations including simulations and measurements. These investigations include indoor propagation behaviour, local mean power estimation, proposing new indoor path loss model and introducing a case study on 60 GHz propagation in indoor environments using ray tracing and measurements. A summary of propagation mechanisms and manifestations in the indoor environment is presented. This comprises the indoor localization techniques using channel parameters in terms of angle of arrival (AOA), time of arrival (TOA) and received signal strength (RSS). Different models of path loss, shadowing and fast fading mechanisms are explored. The concept of MIMO channels is studied using many types of deterministic channel modelling such as Finite Difference Time Domain, Ray tracing and Dominant path model. A comprehensive study on estimating local average of the received signal strength (RSS) for indoor multipath propagation is conducted. The effect of the required number of the RSS data and their Euclidian distances between the neighbours samples are investigated over 1D, 2D and 3D configurations. It was found that the effect of fast fading was reduced sufficiently using 2D horizontal’s arrangement with larger spacing configuration. A modified indoor path loss prediction model is presented namely effective wall loss model (EWLM). The modified model with wall correction factors is compared to other indoor path loss prediction models using simulation data (for 2.4, 5, 28, 60 and 73.5 GHz) and real-time measurements (for 2.4 and 5 GHz). Different operating frequencies and antenna polarizations are considered to verify the observations. In the simulation part, EWLM shows the best performance among other models. Similar observations were recorded from the experimental results. Finally, a detailed study on indoor propagation environment at 60 GHz is conducted. The study is supported by Line of Sight (LoS) and Non-LoS measurements data. The results were compared to the simulated ones using Wireless-InSite ray tracing software. Several experiments have confirmed the reliability of the modelling process based on adjusted material properties values from measurements.

While scholars of ruin have long foregrounded the importance of imagination in encountering sites of ruin, they have failed to provide concrete examples of their own imaginative experiences. This dissertation is a collection of aesthetically rendered moments at various sites of ruined landscapes and of the autobiographical (in)sights of loss I have gleaned in their presence. In speaking from a concept I refer to as the autobiographical imaginative--a performative exchange between land and self where life narratives are summoned as a result of land's presence--this project weaves biographical stories of landscapes and others with stories of my own autobiography. As such, the work utilizes multiple interpretive, ethnographic methods and representational strategies, including documentary ethnography, autoethnography, performative writing, and performance auto/ethnography, as a means of illustrating the dialogic, reflexive, evocative, and fluid relationship among researched and researcher, site and self. In doing so, it reveals how land can signify lived experience, extending the traditional geography-centered notion of landscapes toward the creation of memoryscapes, bodyscapes, and mediascapes.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Ingram, Mary Ann; Committee Member: Durgin, Greg; Committee Member: Kenney, Steve; Committee Member: Landgren, Jack; Committee Member: Li, Ye. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This research looks at the contributions made by some Indian women photographers to the representation of privacy. Indian women photographers have enjoyed a privileged access in their bid to depict privacy, or the quality or state of being apart from observation, and that access can often be attributed to their gender. I propose to analyse the parallelisms and divergences in the representation of privacy by pioneer women photographers -with special attention to the phenomenon of zenana photography- as well as three contemporary practitioners: Dayanita Singh, Gauri Gill and Ketaki Sheth. I will argue that each of them has pushed, in her own way, the boundaries of representing privacy through photography and ensured that certain forms of privacy -often related to intimacy and the domestic domain- did not get “lost to human sight”.
La presente tesis doctoral analiza las contribuciones de algunas fotógrafas indias a la representación de la privacidad. Desde 1840 las fotógrafas indias han disfrutado de un acceso privilegiado a retratar lo privado -aquello que se ejecuta en soledad o a la vista de unos pocos- y ese acceso se explica frecuentemente en razón de su género. En este estudio se analizan las correspondencias y divergencias en la representación de la privacidad de las primeras fotógrafas indias -prestando especial atención al fenómeno de la fotografía zenana - y tres fotógrafas contemporáneas: Dayanita Singh, Gauri Gill y Ketaki Sheth. El argumento es que, en cada uno de los casos de estudio propuestos, la fotógrafa ha explorado los límites de representación de la privacidad en fotografía, impidiendo que algunas de sus formas o manifestaciones, a menudo relacionadas con lo doméstico y la intimidad, “se escaparan a la mirada humana”.

The ultra-wideband (UWB) technology has a vast unlicensed frequency spectrum, which can support precise indoor positioning in orders of centimeters. The features of UWB signals can be utilized for variety of applications. In this project first we present an empirical channel models to analyze the localization accuracy of the UWB technology for interactive electronic gaming (Ping-Pong) in Line-of-Sight (LOS) and Obstructed LOS (OLOS) scenarios. Then we introduce a new concept that we refer to as micro-gesture detection to handle the more refined motions of the hand, such as rotation, while one antenna is held by the user using features of UWB signal. We use four specific features of the UWB signals: time of arrival, power of the first peak, total power, and the Root-Mean Square (RMS) of the delay spread, for this purpose. As the hand rotates the position of the antenna in the hand and the external antenna changes from LOS to OLOS. We demonstrate that features of the UWB signals are more useful than the RSS signal of the Wi-Fi to detect this class of micro-gestures. We foresee this micro-gesture detection capabilities become helpful for the people with limited ability or visually impaired for implementation of simplified sign language to communication with electronic devices located away from a person. We compare gesture detection using multiple features of the UWB signal with traditional gesture detection using the received signal strength (RSS) of the Wi-Fi signal.

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
The terminal phase telemetry data acquisition has always been a challenging task especially for long and medium range test launches. The task becomes more complicated if the article under test describes a very low altitude cruise terminal phase trajectory. Generally, for long and medium range missions test fired into sea the terminal phase data is acquired by deploying instrumented ships in the vicinity of impact point but beyond the safety corridor. But for long range missions with low altitude cruise terminal phase trajectory and wide safety corridor this conventional approach will not work out because of limitation of LOS from the ship platforms. Hence, for such applications an air borne telemetry receiving system is also to be added to the down range instrumentation network. This paper describes a typical and cost effective air borne system realized utilizing the Commercial Off The Shelf (COTS) products and technology. This paper also addresses as to how the signal scattering problems are tackled in the design implementation.

In large scale entity-level military force-on-force simulations it is essential to know when one entity can visibly see another entity. This visibility determination plays an important role in the simulation and can affect the outcome of the simulation. When virtual Computer Generated Forces (CGF) are introduced into the simulation these intervisibilities must now be calculated by the virtual entities on the battlefield. But as the simulation size increases so does the complexity of calculating visibility between entities. This thesis presents an algorithm for performing these visibility calculations using Graphical Processing Units (GPU) instead of the Central Processing Units (CPU) that have been traditionally used in CGF simulations. This algorithm can be distributed across multiple GPUs in a cluster and its scalability exceeds that of CGF-based algorithms. The poor correlations of the two visibility algorithms are demonstrated showing that the GPU algorithm provides a necessary condition for a "Fair Fight" when paired with visual simulations.
M.S.Cp.E.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Computer Engineering

We consider time-of-arrival based robust geolocation in harsh line-of-sight/non-line-of-sight environments. Herein, we assume the probability density function (PDF) of the measurement error to be completely unknown and develop an iterative algorithm for robust position estimation. The iterative algorithm alternates between a PDF estimation step, which approximates the exact measurement error PDF (albeit unknown) under the current parameter estimate via adaptive kernel density estimation, and a parameter estimation step, which resolves a position estimate from the approximate log-likelihood function via a quasi-Newton method. Unless the convergence condition is satisfied, the resolved position estimate is then used to refine the PDF estimation in the next iteration. We also present the best achievable geolocation accuracy in terms of the Cramér-Rao lower bound. Various simulations have been conducted in both real-world and simulated scenarios. When the number of received range measurements is large, the new proposed position estimator attains the performance of the maximum likelihood estimator (MLE). When the number of range measurements is small, it deviates from the MLE, but still outperforms several salient robust estimators in terms of geolocation accuracy, which comes at the cost of higher computational complexity.

Ces travaux sur la stabilisation de la Ligne de Visée d’un dispositif optronique s’inscrivent dans le contexte actuel de durcissement des exigences de stabilisation et de réduction du temps accordé à la synthèse des lois de commande.Ils incluent dans un premier temps l’amélioration de la performance intrinsèque de stabilisation du système. La solution proposée ici est l’ajout d’un étage de stabilisation supplémentaire à une structure de stabilisation existante. L’architecture de ce nouvel étage est définie. Les composants sont choisis parmi les technologies existantes puis caractérisés expérimentalement. Un modèle complet du système à deux étages de stabilisation est ensuite proposé.L’objectif de ces travaux comprend également la simplification des procédures d’élaboration des lois de commande par l’utilisation d’une fonction de coût F incluant notamment la Fonction de Transfert de Modulation (qui quantifie le flou introduit par l’erreur de stabilisation dans l’image) en lieu et place ducritère dérivé usuel qui nécessite des vérifications supplémentaires et qui peut s’avérer conservatif.L’évaluation de F étant coûteuse en temps de calcul, un algorithme d’optimisation bayésienne, adapté à l’optimisation des fonctions coûteuses, permet la synthèse des lois de commande du système dans un temps compatible avec les contraintes industrielles, à partir de la modélisation du système précédemment proposée
The presented work on the Line of Sight stabilization of an optronic device meets the heightened demands regarding stabilization performances that come with the reduction of the time allowed to controller tuning.It includes the intrinsinc improvement of the system stabilization. The proposed solution features a double stabilization stage built from a single stabilization stage existing system. The new architecture is specified and the new components are chosen among the existing technology and experimentally characterized. A complete double stabilization stage model is then proposed.The simplification of the controller tuning process is another goal. The designed cost function F includes a high-level optronic criterion, the Modulation Transfer Function (that quantifies the level of blur broughtinto the image by the residual motion of the platform) instead of the usual low-level and potentially conservative criterion.The function F is costly to evaluate. In order to tune the controller parameters within industrial time constraints, a Bayesian algorithm, adapted to optimization with a reduced budget of evaluations, is implemented.Controllers of both stabilization stages are simultaneously tuned thanks to the previously developped system model

El cine trabaja sobre los cuerpos porque él mismo es un cuerpo y, como todo cuerpo, opera de dos maneras: como el cine-organismo, cuerpo-engranaje en una cadena de montaje de partes ensambladas y firmes, o como el cuerpo heterogéneo cuyas partes exceden lo conjuntable, van más allá del lenguaje. El organismo cinematográfico opera convergencias en función de normas de escritura, enmascara la sutura. El Cuerpo cinematográfico sin Órganos condensa en torno a la sutura misma como punto límite, como singularidad divergente; opera la apertura del intervalo y explora las regiones entre los elementos, lo no conjuntable. Y es en esas regiones entre, en las regiones no conjuntables, donde la imagen se vuelve háptica, donde la imagen ejerce verdaderamente su “toque”, donde nos afecta verdaderamente en tanto que imagen. Donde encontramos no ya una imagen del cuerpo sino una imagen-cuerpo.
Cinema affects bodies because it is a body in itself, and as any other body works in both directions: as a cinematic organism –gears working tightly together in an assembly line– or as the heterogeneous body which parts will not match, going beyond the structure of language. Cinematic organism creates convergences around rules of discourse, disguises suture. Cinematic Body without Organs condenses around the suture as a limit, as a divergent singularity, opens the interval, explores regions in between the elements, the out of joint. It is in those in between regions where images becomes haptic, where they touch and affect us as images as such. Where we find not an image of a body but a body-image.

Publicación a texto completo no autorizada por el autor
Determina si existió variación de la presión intraocular (PIO) en pacientes no glaucomatosos sometidos a cirugía de catarata con implante de lente intraocular en la cámara posterior en el Hospital Nacional Daniel Alcides Carrión (Programa Sight First) durante los meses de enero a mayo del 2010.Fue un estudio descriptivo, tipo retrospectivo. Se identificaron 111 pacientes, 49 fueron varones (44,1%) y 62 mujeres (55,9%), predominando el grupo de 68 a 80 años (62,2%), con media de 72,9 años. La media de PIO pre quirúrgica fue 15,8 ± 1,8 mm Hg y la PIO postoperatoria fue de 14 ± 2,9 mm Hg. (p=0,000). La variación de la presión fluctuó entre -14 y 9 mm Hg, con media de - 1,8 ± 3,5 mm Hg (p=0,000), no dependió del tipo de cirugía (p=0,959) ni de la presencia de pseudoexfoliación (p=0,628); pero sí del grado de catarata (p=0,033) y del nivel de PIO preoperatoria, con la que se relacionó inversamente (p=0,0000). Hubo una tendencia con respecto a la profundidad de la cámara anterior (p=0,056). Se encontró reducción significativa de la PIO que no dependió del tipo de cirugía, pero sí del nivel de PIO prequirúrgica y grado de catarata. Hubo una tendencia con respecto a la profundidad de la cámara anterior.
Trabajo académico

博士
國立臺灣大學
外國語文學研究所
94
This thesis aims to unravel the complex struggles and interactions of diverse cultural factors, forces, and elements that determined the translations and rewriting of John Milton and Paradise Lost in China in the 1920s and 30s. Based on the view of translation as growth, derivation, and refraction across cultural systems, it attempts to reveal the ways in which Milton and Paradise Lost were portrayed, interpreted, and transformed by the Chinese translators/rewriters in order to meet specific agenda, constraints, and needs of the Chinese literary system at the time of crisis and transformation. In the first chapter, I attempt to illustrate the idea of translation with Paradise Lost as the issue of telling and retelling provide an insight into the problem of translation. I then adopted Even-Zohar’s Polysystem Theory and the systemic approach as the theoretical framework for my investigations on the literary reception of Milton in China. In the subsequent chapters, I tried to reveal both the diachronic and the synchronic relations established between Milton, Paradise Lost, and the diverse elements of the Chinese literary system as suggested by the numerous translations and rewritings. The second chapter traces the reception of Milton and Paradise Lost from its first occurrence in Chinese texts to 1949—the year when an era of open, unregulated foreign literary inputs ends. It shows the changing positions of Milton and his epic in China, as result of the increasing understanding about the West, shifts of attitudes toward reform, continuous emergences of new issues and concerns, and so forth. The third chapter examines the portrayals of Milton in Chinese rewritings in the 1920s and 30s and the ways in which the rewriters refashioned Milton as an ideal intellectual for the modern intellectuals. It looks at the language the rewriters used in depicting Milton and identifies its connection with traditional and modern criteria for ideal intellectuals. It also analyzes the ways in which the rewriters embellish on certain traits of Milton and interpreted Milton’s ideas out of its 17th-century political context. The fourth chapter analyzes Fu Donghua’s translation of Paradise Lost and the debates about the proper strategies for translating the epic between Fu and his critics. It unravels the complex issues of poetic innovation and the establishment of new verse forms involved in Fu’s translation and his debates with the critics. Finally, the last chapter sums up the significance of this study in the fields of Milton studies, Translation studies, and the study of Modern Chinese literature. It also points to the prospect of subsequent research on the intertextual and intercultural relations between the English, Japanese, and Chinese rewritings of Milton. Presenting both the diachronic and synchronic pictures of Milton in China, this thesis is expected to be more than another case study of Descriptive Translation Studies with the systemic approach. With its historical and textual analyses on the reception of Milton in China, it contributed to the understanding of Milton’s influences in non-European countries—a territory still in need of exploration in Milton Studies. Showing how the issues such as Confucian ideal of scholar-statesman, modern ideal of an intellectual, canonicity, new verse forms, traditional folk literature, foreign genres, and so forth become driving factors in the translations/rewritings of Milton and Paradise Lost, it unravel the diverse relations and potentials the translated literature may have in modern Chinese literature. By so doing, it adds new understanding not only to the functions of translated literature in modern China but also to the development of modern Chinese literature.

In my thesis, the issue of utilization of cultural and historical sights in tourism was executed by means of SWOT analysis. Based on the data entry form, the analysis of strengths and weaknessses of selected cultural and historical sights in the South Bohemia Region was drawn up. The output of the analysis of external environment was applied to the analysis of opportunities and threats for Kvítkův Dvůr, another place of interest. The thesis presents proposals for the utilization of the Kvítkův Dvůr premises, moreover, it also deals with the calculation of economic impacts of a few suggested measures including quantitative documentation.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη και ο προσδιορισμός, θεωρητικός και πειραματικός, του συντελεστή Κ της Rician κατανομής σε ένα κανάλι στα 2.4 GHz. Η κατανομή Rice χρησιμοποιείται για την περιγραφή του πλάτους του λαμβανόμενου σήματος σε ένα κανάλι μετάδοσης με ισχυρή επίδραση οπτικής επαφής (Line-of-Sight) μεταξύ κεραίας πομπού και δέκτη. Ο συντελεστής Κ Rice εκφράζει τον λόγο της συνεισφοράς της ισχύος της απευθείας συνιστώσας του σήματος ως προς την συνολική λαμβανόμενη ισχύ λόγω φαινομένων διάχυσης. Χρησιμοποιείται για τον χαρακτηρισμό του καναλιού καθώς και τον υπολογισμό του BER (bit-error-ratio) και της πλέον σημαντικής παραμέτρου των τηλεπικοινωνιών SNR (Signal-to-Noise-Ratio), δηλαδή του λόγου σήματος προς θόρυβο. Στο 1ο κεφάλαιο αναλύονται και περιγράφονται μερικές από τις σημαντικότερες τεχνολογίες ασυρμάτων δικτύων, από την πρώτη στιγμή της εμφάνισής τους (δίκτυα 1ης και 2ης γενιάς) έως τα πιο σύγχρονα δίκτυα 3ης και 4ης γενιάς, και παρουσιάζονται οι ζώνες συχνοτήτων που καταλαμβάνουν αυτές οι τεχνολογίες στο διαθέσιμο ηλεκτρομαγνητικό φάσμα. Στο 2ο κεφάλαιο μελετώνται οι 3 βασικότεροι μηχανισμοί διάδοσης του ηλεκτρομαγνητικού κύματος μέσα σε ένα ασύρματο κανάλι (ανάκλαση, περίθλαση, σκέδαση), περιγράφονται οι τύποι των απωλειών που υφίσταται ένα σήμα κατά την μετάδοση του και τα φαινόμενα των διαλείψεων, που παρατηρούνται πολύ έντονα σε ένα κινητό και μεταβαλλόμενο περιβάλλον διάδοσης. Στο 3ο κεφάλαιο γίνεται περιγραφή του μοντέλου ηλεκτρομαγνητικής μετάδοσης κατά Rice, δηλαδή όταν η απευθείας συνιστώσα του σήματος είναι η ισχυρότερη διαδρομή που ακολουθεί το εκπεμπόμενο σήμα κατά την πορεία του μέχρι τον δέκτη (LoS). Αναλύεται η σημαντικότερη παράμετρος αυτού του τύπου μετάδοσης, δηλαδή ο συντελεστής Κ, και παρουσιάζονται διάφορες μέθοδοι προσδιορισμού του τόσο θεωρητικά όσο και πειραματικά. Στο 4ο κεφάλαιο παρουσιάζονται τα αποτελέσματα των πειραματικών μας μετρήσεων σε διάφορες τοπολογίες μετάδοσης με LoS για ένα δίκτυο Wi-Fi, δηλαδή για συχνότητα λειτουργίας στα 2.4 GHz. Για κάθε τοπολογία, περιγράφεται πλήρως το περιβάλλον μετάδοσης καθώς και ολόκληρη η διαδικασία εκπόνησης των μετρήσεων (μετρητικά όργανα, απαραίτητο λογισμικό, τυχόν προσεγγίσεις κτλ.). Τέλος, στο 5ο και τελευταίο κεφάλαιο, παρουσιάζεται μια μέθοδος υπολογισμού του συντελεστή Κ μέσω των μετρήσεων και με τη βοήθεια του μοντέλου ελευθέρου χώρου, που χρησιμοποιείται για τον υπολογισμό των συνολικών απωλειών διαδρομής του σήματος. Τα αποτελέσματα των υπολογισμών χρησιμοποιήθηκαν, με την βοήθεια του Matlab, για την κατασκευή της CDF των τιμών του Κ αλλά και της γραφικής παράστασης της μεταβολής του Κ συναρτήσει της απόστασης. Οι εμπειρικές CDF συγκριθήκαν και προσεγγιστήκαν με γνωστές θεωρητικές CDF, και η συνάρτηση της μεταβολής του Κ με την απόσταση προσεγγίστηκε με όρους Goodness of Fit με την βοήθεια της γενικής μορφής γνωστών συναρτήσεων. Κλείνοντας, στην τελευταία παράγραφο της εργασίας αφήνεται περιθώριο και δίνεται τροφή για μελλοντική εργασία πάνω στην μελέτη και τον προσδιορισμό του συντελεστή Κ της Rice τόσο για εσωτερικούς όσο και για εξωτερικούς χώρους.
The main purpose of this thesis, is the analysis and estimation , theoretical and empirical, of the Rician K factor for a wireless channel at 2.4 GHz. The Rician power density function is used to describe the amplitude of the received signal when there is a strong LOS component. The Rician K factor expresses the ratio of the power component due to LOS signal propagation and the received signal power due to diffuse components (reflection, scattering, diffraction etc.). It is commonly used for the channel's characterization and the estimation of BER (bit error rate) and SNR (signal to noise ratio), a very important parameter for telecommunications. In the 1st chapter, some of the most important wireless systems are described, since their very first appearance (1G & 2G networks) until the latest 3rd and 4rth generation systems. We also present the current frequency bands and how they are spread at the given electromagnetic spectrum. In the 2nd chapter, the 3 basic propagation mechanisms (reflection, scattering, diffraction) are studied. In addition, we describe all types of signal attenuation within a wireless channel and the fading phenomena that are so commonly seen in mobile and continuously changing propagation environments. In the 3rd chapter, the Rician model of electromagnetic propagation, where LOS is the strongest path of signal components, is analyzed. The most important parameter of this propagation type, the Rician K factor, is also studied. Therefore, various methods of theoretical and empirical estimation of the K factor are presented. In the 4rth chapter, we include the results of our measurements in various LOS propagation topologies for a Wi-Fi system at 2.4 GHz. For each measurement topology, the propagation environment as well as the entire measurement procedure, are thoroughly described. Lastly, in the 5th and final chapter, a K factor estimation method based on the empirical set of data and the Free Space Model, used for the average path loss calculation, is presented. The results of our measurements via the help of the Matlab software were used in order to plot the CDF of K values as well as the K values versus d (distance) curve. Using curve fitting methods, the empirical CDFs and plots were compared to theoretical ones in terms of Goodness of Fit. In the closing section, possible future research in the aforementioned fields is proposed.