京都大学 / 新制・課程博士 / 博士(医学) / 甲第23086号 / 医博第4713号 / 新制||医||1050(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 斎藤 通紀, 教授 藤田 恭之, 教授 近藤 玄 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

This work deals with the description of the communication using the VSAT satellite network. A used network topology, frequency bands, satellite orbits and also an access technology are defined. The next part is focused on the VSAT terminal, where the block diagram is shown. A model of the indoor unit IDU is designed in the system background of Ansoft Designer. Individual parts of the system model are analyzed in terms of input variables. The results of the simulation are shown. The curves of BER before Viterbi decoding and after Viterbi decoding are shown too.

Space time block codes (STBC) are a type of multiple input multiple output (MIMO) communications system that encode blocks of information into symbol sequences sent simultaneously from multiple antennas. MIMO communications systems have shown channel capacity improvement in multipath digital communications environments. The STBC class of MIMO communications systems can be easily decoded using linear combination and is resilient in the face of multipath channel effects. MIMO systems have traditionally been studied using theoretical analyses, simulations and real signal based experiments. Probabilistic models simulate channel effects as random variables, but are only estimates of actual conditions. Real signal experiments evaluate system performance under real-world conditions, but are not readily repeatable. Both modeling methods evaluate system performance in terms of the aggregate results. This dissertation research presents an approach that introduces controlled attenuation and delay to probabilistic channel models. This method allows the evaluation of MIMO system performance under specific channel conditions. The approach is demonstrated with a hardware accelerated STBC system model that is used to evaluate the performance of a MIMO system under controlled path conditions. The STBC system model utilizes a Xilinix® programmable gate array (PGA) device as a hardware accelerator. The model exploits the parallel processing capability of the PGA to simulate a nine path channel model and a three antenna rate ½ STBC. Novel implementations are developed for the additive white Gaussian noise (AWGN) sources and the linear MIMO decoding in PGA hardware. The model allows specification of overall noise and multipath fading effects for the channel as well as attenuation and phase delay for each channel path. Performance of the communications system is evaluated in terms of bit error rate (BER) versus signal-to-noise ratio (SNR). Hardware acceleration greatly reduces the time required to obtain simulation results. Reduced simulation time improves the use of the model by allowing evaluation of system performance under a greater number of conditions, greater performance curve resolution and evaluation at lower BER. The processing rate of the hardware accelerated model is compared to an equivalent software model. The model also provides an extensible platform for future research in communications theory. / Engineering

This research investigates robust demodulation of Gaussian Minimum Shift Keying (GMSK) signals, using demodulator diversity and real-time bit-error-rate (BER) estimation. GMSK is particularly important because of its use in promi- nent wireless standards around the world (GSM, DECT, CDPD, DCS1800, and PCS1900). The dissertation begins with a literature review of GMSK demodu- lation techniques (coherent and noncoherent) and includes an overview of single- channel interference rejection techniques in digital wireless communications. Vari- ous forms of GMSK demodulation are simulated, including the limiter discrimina- tor and di erential demodulator (i.e., twenty-five variations in all). Ten represent new structures and variations. The demodulator performances are evaluated in realistic wireless environments, such as additive white Gaussian noise, co-channel interference, and multipath environments modeled by COST207 and SMRCIM. Certain demodulators are superior to others for particular channel impairments, so that no demodulator is necessarily the best in every channel impairment. This research formally introduces the concept of demodulator diversity, a new idea which consists of a bank of demodulators which simultaneously demodulate the same signal and take advantage of the redundancy in the similar signals. The dissertation also proposes practical real-time BER estimation techniques which have tremendous ramifications for communications. Using Parzen's estimator for probability density functions (pdfs) and Gram-Charlier series approximation for pdfs, BER can be estimated using short observation intervals (10 to 500 training symbols) and, in some cases, without any training sequence. We also introduce new variations of Gram-Charlier estimation using robust estimators. BER (in place of MSE) can now drive adaptive signal processing. Using a cost function and gradient for Parzen's estimator (derived in this paper), BER estimation is applied to demodulator diversity with substantial gains of 1-10 dB in carrier- to-interference ratio over individual receivers in realistic channels (with adaptive selection and weighting). With such gains, a BER-based demodulator diversity scheme can allow the employment of a frequency reuse factor of N = 4, instead of N = 7, with no degradation in performance. A lower reuse factor means more channels are available in a cell, thus increasing overall capacity. The resulting techniques are simple and easily implemented at the mobile. BER estimation techniques can also be used in BER-based equalization and dynamic allocation of resources. / Ph. D.

Adaptive Least Mean Square (LMS) equalizers are widely used in digital communication systems primarily for their ease of implementation and lack of dependence on a priori knowledge of input signal statistics. LMS equalizers exhibit non-Wiener characteristics in the presence of a strong narrowband interference and can outperform the optimal Wiener equalizer in terms of both mean square error (MSE) and bit error rate (BER). There has been significant work in the past related to the analysis of the non-Wiener characteristics of the LMS equalizer, which includes the discovery of the shift in the mean of the LMS weights from the corresponding Wiener weights and the modeling of steady state MSE performance. BER performance is ultimately a more practically relevant metric than MSE for characterizing system performance. The present work focuses on modeling the steady state BER performance of the normalized LMS (NLMS) equalizer operating in the presence of a strong narrowband interference. Initial observations showed that a 2 dB improvement in MSE may result in two orders of magnitude improvement in BER. However, some differences in the MSE and BER behavior of the NLMS equalizer were also seen, most notably the significant dependence (one order of magnitude variation) of the BER behavior on the interference frequency, a dependence not seen in MSE. Thus, MSE cannot be used as a predictor for the BER performance; the latter further motivates the pursuit of a separate BER model. The primary contribution of this work is the derivation of the probability density of the output of the NLMS equalizer conditioned on a particular symbol having been transmitted, which can then be leveraged to predict its BER performance. The analysis of the NLMS equalizer, operating in a strong narrowband interference environment, resulted in a conditional probability density function in the form of a Gaussian Sum Mixture (GSM). Simulation results verify the efficacy of the GSM expression for a wide range of system parameters, such as signal-to-noise ratio (SNR), interference-to-signal (ISR) ratio, interference frequency, and step-sizes over the range of mean-square stable operation of NLMS. Additionally, a low complexity approximate version of the GSM model is also derived and can be used to give a conservative lower bound on BER performance. A thorough analysis of the MSE and BER behavior of the Bi-scale NLMS equalizer (BNLMS), a variant of the NLMS equalizer, constitutes another important contribution of this work. Prior results indicated a 2 dB MSE improvement of BNLMS over NLMS in the presence of a strong narrowband interference. A closed form MSE model is derived for the BLMS algorithm. Additionally, BNLMS BER behavior was studied and showed the potential of two orders of magnitude improvement over NLMS. Analysis led to a BER model in the form of a GSM similar to the NLMS case but with different parameters. Simulation results verified that both models for MSE and BER provided accurate prediction of system performance for different combinations of SNR, ISR, interference frequency, and step-size. An enhanced GSM (EGSM) model to predict the BER performance for the NLMS equalizer is also introduced, specifically to address certain cases (low ISR cases) where the original GSM expression (derived for high ISR) was less accurate. Simulation results show that the EGSM model is more accurate in the low ISR region than the GSM expression. For the situations where the derived GSM expression was accurate, the BER estimates provided by the heuristic EGSM model coincided with those computed from the GSM expression. Finally, the two-interferer problem is introduced, where NLMS equalizer performance is studied in the presence of two narrowband interferers. Initial results show the presence of non-Wiener characteristics for the two-interferer case. Additionally, experimental results indicate that the BER performance of the NLMS equalizer operating in the presence of a single narrowband interferer may be improved by purposeful injection of a second narrowband interferer. / PHD

Adaptive LMS equalizers are widely used in digital communication systems for their simplicity in implementation. Conventional adaptive filtering theory suggests the upper bound of the performance of such equalizer is determined by the performance of a Wiener filter of the same structure. However, in the presence of a narrowband interferer the performance of the LMS equalizer is better than that of its Wiener counterpart. This phenomenon, termed a non-Wiener effect, has been observed before and substantial work has been done in explaining the underlying reasons. In this work, we focus on the Bit Error Rate (BER) performance of LMS equalizers. At first a model “the Gaussian Mixture (GM) model“ is presented to estimate the BER performance of a Wiener filter operating in an environment dominated by a narrowband interferer. Simulation results show that the model predicts BER accurately for a wide range of SNR, ISR, and equalizer length. Next, a model similar to GM termed the Gaussian Mixture using Steady State Weights (GMSSW) model is proposed to model the BER behavior of the adaptive NLMS equalizer. Simulation results show unsatisfactory performance of the model. A detailed discussion is presented that points out the limitations of the GMSSW model, thereby providing some insight into the non-Wiener behavior of (N)LMS equalizers. An improved model, the Gaussian with Mean Square Error (GMSE), is then proposed. Simulation results show that the GMSE model is able to model the non-Wiener characteristics of the NLMS equalizer when the normalized step size is between 0 and 0.4. A brief discussion is provided on why the model is inaccurate for larger step sizes. / Master of Science

Actuellement, les techniques multiporteuses sont largement utilisées dans les systèmes de transmission grâce à leur robustesse aux effets de trajets multiples et à leur implémentation efficace utilisant des FFTs. L'OFDM (orthogonal frequency division multiplexing) est un type de modulation multiporteuse qui consiste à subdiviser un flux de données à très haut débit en plusieurs flux élémentaires à bas-débit qui sont transmis sur différentes sous-porteuses orthogonales. Récemment, une technique multiporteuse à base de bancs de filtres (FBMC) a été proposée comme une alternative permettant d'offrir quelques avantages par rapport à l'OFDM. Un des principaux avantages est l'amélioration de l'efficacité spectrale grâce à l'absence du préfixe cyclique (CP) et aux formes d'onde bien localisées en temps et en fréquence.Contrairement à ce qui est souvent supposé dans la littérature, l'asynchronisme existe intrinsèquement dans un bon nombre de systèmes de communication à cause de multiples facteurs tels que les délais de propagation et la distribution géographique des utilisateurs. Cet asynchronisme peut engendrer une perte d'orthogonalité entre les sous-porteuses qui peut se traduire par l'apparition d'interférences asynchrones causant à leurs tours une dégradation des performances du système. La modélisation de cette interférence présente un enjeu important dans la conception des systèmes de communication.Dans cette thèse, nous analysons l'impact de la désynchronisation temporelle sur les performances de l'OFDM et de la FBMC. Tout d'abord, nous présentons un modèle global permettant la caractérisation et l'analyse de l'interférence dans les systèmes multiporteuses asynchrones. Une nouvelle famille de tables d'interférence est proposée tenant compte du décalage temporel ainsi que de la distance spectrale entre les sous-porteuses interférente et victime. Les termes de ces tables sont calculés pour CP-OFDM et FBMC avec les deux formes d'onde IOTA et PHYDYAS. L'impact de l'interférence asynchrone sur le taux d'erreur (BER) et sur l'efficacité spectrale de l'OFDM/FBMC est examiné. En se basant sur les fonctions génératrices des moments de la puissance d'interférence, nous avons établi des expressions analytiques simples du BER et de l'efficacité spectrale moyens. Ces dernières expressions réduisent d'une façon considérable la complexité de l'évaluation des performances. Cette étude théorique a été consolidée et validée par des résultats de simulation pour différents scénarios où nous avons démontré que contrairement à l'OFDM, les modulations FBMC sont moins sensible à la désynchronisation temporelle grâce à la bonne localisation des formes d'ondes utilisées. / Multicarrier systems are widely used today due to their robustness to multipath effects and efficient implementation using FFT. Orthogonal Frequency Division Multiplexing (OFDM) system is a class of multicarrier modulation which consists of splitting up a wide-band signal at a high symbol rate into several lower rate signals, each one occupying a narrower band. System performance improves because subcarriers experience flat fading channels and are orthogonal to one another. Recently, a number of papers have focused on a new alternative called Filter bank based multicarrier system (FBMC) which can offer a number of advantages over CP-OFDM system such as the improved spectral efficiency by not using a redundant CP and by having much better control of the out-of-band emission due to the time-frequency localized shaping pulses.Furthermore, asynchronism inherently exists in several communication systems due to many factors e.g. the propagation delays and the spatial distribution of users. As one of the most challenging issue in design of communication systems, the asynchronism can harmfully affect the system performance by causing the so-called asynchronous interference.In this dissertation, we investigate the impact of asynchronism on the performance of OFDM FBMC systems. First, we present a unified framework for multicarrier interference characterization and analysis in asynchronous environments. We propose a new family of interference tables that model the correlation between a given interfering subcarrier and the victim one, not only as a function of the spectral distance separating both subcarriers but also with respect to the timing misalignment between the subcarriers holders. These tables are derived for CP-OFDM, PHYDYAS-FBMC and IOTA-FBMC systems. Furthermore, the impact of the asynchronous interference on the average error rate and the average spectral efficiency of OFDM and FBMC systems is addressed. Based on computing the moment generating functions of the asynchronous interference power, simple new expressions for the exact evaluation of the average error rate and the average spectral efficiency are derived considering the frequency correlation fading between adjacent interfering subcarriers. These expressions significantly reduce the computation complexity of the performance evaluation.For each technique two scenarios are examined: fully-loaded network and partially loaded ones. The accuracy of the obtained expressions has been validated through different simulation results. In contrast to OFDM, FBMC waveforms are demonstrated to be less sensitive to timing asynchronism, due to the better frequency localization of the used prototype filters.

La maladie de Huntington (MH) est une maladie neurodégénérative fatale, causée par l’expansion des répétitions CAG du gène de Huntingtine. La longueur de l’expansion est instable et proportionnelle à la gravité de la maladie. L’instabilité varie selon les tissus, p.ex. le striatum est très instable et dégénère, alors que le cervelet a une instabilité limitée et est épargné par la maladie. Nous avons étudié le rôle des lésions oxydantes et du mécanisme de réparation par excision de base (BER) dans la sélectivité tissulaire de l'instabilité dans ces deux tissus de souris R6/1. Le niveau des lésions était similaire dans ces tissus, alors que les niveaux et les activités des principales protéines BER étaient globalement diminués dans le striatum. L’efficacité de réparation dépendait de la stoechiométrie de BER, la position de la lésion et la séquence d’ADN. Nos résultats suggèrent une faible coopération entre les activités BER associée à la spécificité tissulaire de l’instabilité de la MH. / Huntington’s disease (HD) is a neurodegenerative fatal disease caused by the expansion of CAG repeats in the Huntingtin gene. The expansion length is unstable and proportional to the disease severity. The instability affects differently several tissues, among which the striatum that shows a high instability and degenerates, whereas the cerebellum that shows limited instability is spared from the disease. We addressed the role of oxidative lesions and Base Excision Repair (BER) in the tissue-selectivity of the instability in striatum and cerebellum of R6/1 mouse model. Interestingly, we observed a similar level of oxidative lesions at both tissues. Levels and activities of main BER proteins were globally decreased in striatum relative to cerebellum. Moreover we found that repair outcome is dependent upon BER stoichiometries, lesion location and sequence. Our results suggest a poor cooperation between BER activities that could underlie tissue-specificity of somatic instability in HD.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2015. / Submitted by Albânia Cézar de Melo (albania@bce.unb.br) on 2016-02-16T14:01:50Z No. of bitstreams: 1 2015_RubenOrtegaBlanco.pdf: 78834010 bytes, checksum: 3420abfa3f7efe2d616b97f09d14ff70 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2016-02-19T21:04:29Z (GMT) No. of bitstreams: 1 2015_RubenOrtegaBlanco.pdf: 78834010 bytes, checksum: 3420abfa3f7efe2d616b97f09d14ff70 (MD5) / Made available in DSpace on 2016-02-19T21:04:29Z (GMT). No. of bitstreams: 1 2015_RubenOrtegaBlanco.pdf: 78834010 bytes, checksum: 3420abfa3f7efe2d616b97f09d14ff70 (MD5) / O objetivo do seguinte trabalho é determinar um modelo matemático que permita-nos obter a Relação Sinal Ruído mais Interferência (SNIR do Inglês Signal-to-Noise plus Interference Ratio), a Taxa de Erro de Bits (BER do Inglês Bit Error Rate) de um salto e a Taxa de Erro de Bits fim-a-fim numa rede acústica submarina. Com esse propósito foi desenvolvido um modelo matemático que permite o cálculo destes parâmetros considerando a interferência para o protocolo de acesso ao meio (MAC do Inglês Medium Access Control) ALOHA puro. Também foi necessário desenvolver antes diferentes parâmetros da rede, tais como, distância média do salto, distância média até o nó central, distância média entre os nós, número médio de saltos na rota e desvio médio. Com o uso deste modelo também é possível obter o valor da frequência ótima utilizando uma função de otimização. Comparações entre a Taxa de Erro de Bits de um salto e fim-a fim também forem feitas, para diferentes valores de máximo ângulo de desvio na topologia de rede usada. Estas comparações demonstran quando pode ser mais convenente o uso de um salto ou múltiple-salto. Simulações Monte-Carlo e modelo forem comparados com o propósito de validar os resultados obtidos. Estas comparações demostram a grande similitude entre nosso modelo e as simulações de Monte-Carlo. Além disso foi possível o estudo do comportamento da SNIR e do BER variando importante parâmetros da rede tais como frequência de transmissão, número de nós, raio da esfera e máximo ângulo de desvio. Os resultados obtidos provarem que a SNIR para um salto diminui com o aumento do número de nós e o raio da esfera, mas aumenta com o incremento da potência de transmissão. O comportamento de BER é contrário ao comportamento de SNIR. Também foi possível observar a existência da frequência ótima, onde os melhores valores de SNIR e o BER são obtidos. ______________________________________________________________________________________________ ABSTRACT / The objective of this work is to nd a mathematical model that allow us to obtain the Signal-to-Noise plus Interference Ratio (SNIR), the One-Hop Bit Error Rate (BER) and the End-to-End Bit Error Rate for an Underwater Acoustic Network (UAN). Considering this, it was developed a model that includes the interference as an important impairment and for ALOHA MAC (Medium Access Control) protocol. In addition, it was necessary to obtain before several parameters from the network, such as, average distance of the hop, average distance between nodes, average distance to the central node, average number of hops and average deviation. With this model, it is also possible to nd the optimal value of frequency using an optimization function. It was made comparisons between the One-Hop BER and the End-to-End BER for various values of maximal deviation angle. This comparison shows when it is more adequate to either use one-hop or multi-hop. Finally, we compared numerical and Monte-Carlo simulation results, giving a rst validation to our model. These comparisons show a big similitude between the developed model and the Monte-Carlo simulation. In addition, it was possible to analyse the behaviour of the SNIR and BER by varying important parameters of the network, such as, transmission frequency, number of nodes and sphere radius among others. From the obtained results it was prove that the SNIR decreases with an increase from the number of nodes and the sphere radius, but increases with the transmission power. The End-to-End BER has an contrary behavior with the SNIR.

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