The focus of this dissertation is the study of advanced processing techniques for multiuser interference cancellation in direct sequence code division multiple access communications. Emphasis is placed on the development of efficient techniques that are practical to implement. The work begins with a study of several sub-optimal multiuser detection techniques under a variety of conditions. Multistage parallel interference cancellation is identified as a practical and robust approach for mitigating multiple access interference. In order to reduce the effect of biased decision statistics inherent to parallel cancellation, a low-complexity modification to parallel interference cancellation that significantly improves performance is derived. Based on this approach, two real-time DSP implementations are devised, one fully coherent and one non-coherent. Multi-symbol differential detection is then explored as an alternative for improving the performance of the non-coherent approach. Additionally, dual-antenna diversity techniques are also investigated as a means for improving performance in multipath environments. / Ph. D.

The Joys of Gardening is a virtual experience in which the viewers are invited to roam and explore a garden maze scattered with features including a greenhouse, a fountain, a gazebo, and a variety of personal gardening videos. One of the main attractions includes an opportunity to interact with a tomato plant and observe different stages of its growth. These elements combined are essential to the piece's purpose: to spread the passion and joys of gardening. There are many therapeutic effects to gardening such as: the sun helps people be happy, working with the soil allows a sense of giving life, and watching a plant grow can inspire the joy of gardening and the joy of discovery. As the viewer inhabits the space, they are engulfed into a world of butterflies, birds chirping, and serene lighting. This experience has a set aesthetic, narrative, and user interaction. By utilizing these elements, they are able to enjoy a relaxing stroll through the maze. This paper will discuss the influence behind the experience, stylistic choices, and user interactions. This experience continues to explore the potentials of blending the physical landscape and the digital landscape. / Master of Fine Arts / The Joys of Gardening is a virtual experience that provides the viewer an opportunity to explore a garden maze. The maze is filled with different elements with which they can interact. These include videos of my personal garden, a greenhouse with an interactive tomato plant, and a gazebo and a pond filled with koi fish. The project offers a digital space for viewers to escape into a world filled with butterflies, flowers, and the sounds of birds chirping. The purpose of this piece is to inspire and spread the joys of gardening to anyone and everyone. This paper will discuss the style, audio, and interaction choices to create the full project.

Parallel interference cancellation for DS-CDMA has been shown to suffer from biased amplitude estimates if a matched-filter estimator is used. The bias magnitude is proportional to the number of interfering users. For heavy system loads, the bias has been shown to adversely effect the accuracy of the interference cancellation process, thereby impairing BER after cancellation. Empirical simulation work has demonstrated that weighting down interference estimates can improve BER performance. This thesis substantiates these BER improvements by modelling and analyzing a soft interference cancellation technique which mitigates the effects of the bias by minimizing BER after cancellation in a bit-synchronous parallel interference cancellation CDMA receiver. We analyze system decision metrics with down-scaled interference estimates and determine both the mean and variance of the biased decision statistics. From these two metric moments, system BER is evaluated, and the optimal interference scaling function which minimizes BER is derived. We demonstrate BER performance enhancements by simulating this soft interference cancellation technique in systems under perfect power control and in the near-far situation. We further discuss the applicability of the results to asynchronous systems. / Master of Science

In Code Division Multiple Access (CDMA) systems forward error correction (FEC) is an important factor in improving system performance. Because of the multiple access interference observed in asynchronous CDMA, FEC is required to improve system capacity. Several alternative coding techniques are available, including "trellis codes" specifically designed for CDMA, very low rate convolutional codes and conventional convolutional codes. An analytic approach is developed to compare the performance of different coding techniques for CDMA on the same basis by extending several improved analysis techniques which were developed for uncoded CDMA. Analytic results are presented for additive white Gaussian noise (AWGN) channels and frequency non-selective Rician Fading (FNRF) channels. The performance of coded CDMA systems in frequency selective Rayleigh fading channels is also analyzed using simulation techniques. Both analytic and simulation results show that by using trellis codes or very low rate convolutional codes significant performance improvement is achieved over conventional convolutional codes. Trellis codes outperform very low rate convolutional codes in AWGN and FNRF channels while both codes show similar performance in frequency selective Rayleigh fading channels. / Master of Science

<p dir="ltr">Antigenically variable pathogens (AVPs) pose a significant infectious disease burden, but vaccine development is extremely difficult due to their ability to quickly evolve beyond host immunity. Existing models of AVP spread have not been able to sufficiently account for host immune history, population mobility patterns, and pathogen evolutionary dynamics. This thesis aims at creating a computational framework built from the concept of antibody landscapes to overcome these issues, thereby increasing the understanding of how these pathogens spread and evolve in order to improve vaccine design.</p><p><br></p><p dir="ltr">Briefly, the proposed stochastic framework is built from "the ground up'' using principles of antibody landscapes, in which we begin by devising a mechanism to describe how the landscape changes due to repeated pathogen exposure. Extending this to a (sub)population-level permits integration into a meta-population model that is further parameterized by geographic influences. Virus evolution is driven by a statistically meaningful model of antigenic drift in the underlying antigenic space. While the framework is robust and, in principle, capable of modeling a variety of AVPs, we focus on influenza H3N2 as a case study due to its data availability and persistently low and unpredictable vaccine efficacy.</p><p><br></p><p dir="ltr">Experimental results demonstrate that we can statistically significantly predict various properties of H3N2 evolution and population level immunity, including prevalence level, the timing of emergence of new antigenic clusters, the positions of unseen strains in antigenic space, as well as the geographic locations where new strains and antigenic clusters emerge. Through analysis of the simulated outcomes, we identified a population level of immune protection against circulating strains (titre value of approximately 5 units), which when approached, seems to signal an upcoming antigenic drift. Using this insight, we propose a new vaccine strain selection strategy that shows notable improvements in vaccine effectiveness and stability. Additionally, we estimate that it could reduce annual morbidity by 73.4 ± 40.8 million (17% ± 9%) in the Northern Hemisphere and 56.7 ± 38.0 million (10% ± 6%) in the Southern Hemisphere. In summary, this novel framework can accurately replicate the interplay between pathogen evolution and population-level immune responses decades into the future from a mechanistic perspective, and be used to design improved vaccines.</p>

The developing field of smart structures and skins provides an application to which fiber optic sensors bring unique capabilities and benefits. The primary cost in a network of fiber sensors is in the sources, receivers and associated hardware and can be prohibitive for a large number of sensors. Multiplexing of sensors based on spread spectrum techniques offers an efficient and cost effective solution to this limitation. The system hardware developed in this research work is capable of the real time monitoring of a four sensor network. Experimental results with embedded and attached Extrinsic Fabry Perot Interferometers (EFPI) are presented. The system can be used to multiplex any type of sensor which translates the measurand into intensity variations of the light. A measure of the system efficiency is obtained using crosstalk measurements. A suppression of 40 dB has been obtained between the desired sensor signal and the interference. The effect on system performance has been observed by varying system parameters such as code length and separation between codes. Highly sensitive embedded interferometric sensors have been used in a multimeasurand environment to measure temperature and strain. A solution to the inherent 'near-far' problem in an optical COMA system has been proposed and results for the same are presented. A novel WDM/CDM hybrid (Wavelength Division Multiplexing/Code Dhtision Multiplexing) scheme has been proposed to increase the light intensity at the detector thereby increasing the number of sensors in the system. Methods to optimize and upgrade the system are discussed. / Master of Science

Lately, spread spectrum systems are being increasingly used for commercial wireless communications because of their ability to reject various types of interference. This ability allows them to be used in multiple access systems. Direct sequence and frequency hopping systems have been the primary spread spectrum techniques used in practice. One technique which has not received much attention until recently is time hopping. In time hopping, a symbol is transmitted at a random position within the symbol period using a pulse width which is much smaller than the symbol period. Ultra-wideband (UWB) technology is a radar technology which shows promise for an relatively simple implementation of a time hopping system. This thesis looks at the error probability performance of a UWB time hopping multiple access system. Previous work has led to an estimate of the performance using a Gaussian approximation similar to that used for direct sequence systems. Through the use of a fast simulation technique, it will be shown that in certain situations, the Gaussian approximation fails to accurately predict the performance. A numerical analysis which uses characteristic functions is developed and shown to correctly predict the system’s performance under a wide range of situations. This numerical analysis also contributes to the understanding of the system. / Master of Science

This thesis presents two applications of spread spectrum technology to very small aperture terminal (VSAT) satellite communication networks. It describes two spread spectrum multiple access systems which use a form of noncoherent M-ary FSK (MFSK) as the primary modulation and analyzes their throughput. The analysis considers such factors as satellite power constraints and adjacent satellite interference. It considers the effect of onâ board processing on the multiple access efficiency and investigates the feasibility of overlaying low data rate spread spectrum signals on existing satellite traffic as a form of frequency reuse. / Master of Science

We will study various quantities related to connectivity of a graph. To this end, we look at Nordhaus-Gaddum type problems, which are problems where the same quantity is studied for a graph $G$ and its complement $G^c$ at the same time. For a graph $G$ on $n$ vertices with normalized Laplacian eigenvalues $0 = \lambda_1(G) \leq \lambda_2(G) \leq \cdots \leq \lambda_n(G)$ and graph complement $G^c$, we prove that \begin{equation*} \max\{\lambda_2(G),\lambda_2(G^c)\}\geq \frac{2}{n^2}. \end{equation*} We do this by way of lower bounding $\max\{i(G), i(G^c)\}$ and $\max\{h(G), h(G^c)\}$ where $i(G)$ and $h(G)$ denote the isoperimetric number and Cheeger constant of $G$, respectively. We also discuss some related Nordhaus-Gaddum questions.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第24246号 / 農博第2525号 / 新制||農||1094(附属図書館) / 学位論文||R4||N5417(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 近藤 直, 教授 飯田 訓久, 准教授 小川 雄一 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM