A fixed terrestrial wireless system such as the Microwave Multi-channel Distribution Service (MMDS) can be used as the ``last mile' to provide a high speed Internet connection from a base station to a home in a rural or suburban residential area. Such a broadband wireless system works very well under line-of-sight transmission. It works quite well even if the line-of-sight is obstructed with a large number of trees. However, when trees obstruct the line-of-sight, under conditions of wind, the user may experience loss of the RF signal from time to time. This is especially true under gusty conditions. As part of this research a high precision DSP-based measuring system is devised to accurately measure and characterize the distortions caused by tree foliage on the RF line-of-sight signal. The approach is to digitally generate a signal composed of several tones, up-convert the signal to 2.5 GHz and send it through tree foliage to a receiver where the signal is down-converted and sampled for a duration of five seconds. The samples collected are processed using Matlab to compute the temporal amplitude and phase variations of the tones. The measurement system provides estimates of the amplitude and phase of the receive tones with a time resolution of 3.2 ms. The standard deviation of the amplitude estimates is 0.3\% of the actual amplitude of the tones and the standard deviation of the phase estimates is 0.23 degree. This accuracy is obtained when the signal-to-noise ratio of the receive signal is greater than 20 dB. Measurement in the field with tree foliage in the line-of-sight shows that the swaying of the branches in the wind can cause rapid signal fading. This research determines the type of fade, the depth and duration of the fade, as well as the fading rate.

In this thesis, we address the statistics of mutual information of amplify-and-forward (AF) multiple-input multiple-output (MIMO) two-hop relay channels, where the source terminal (ST), relay terminal (RT) and destination terminal (DT) are equipped with a number of correlated antennas and there is a line-of-sight (LOS) component (Rician fading) of each link. To the best of our knowledge, deriving analytical expressions for the statistics of mutual information of the relay channel is difficult and still unsolvable. To circumvent the mathematical difficulties, we consider this problem under the large-system regimen in which the numbers of antennas at the transmitter and receiver go to infinity with a fixed ratio. In the large-system regimen, this thesis has made the following contributions: 1) We get the mean and the variance of the mutual information of the concerned relay channel. 2) We show that the mutual information distribution converges to the Gaussian distribution. The analytical results are derived by mean of two powerful tools developed in the context of theoretical physics: emph{saddle-point approximation} and emph{superanalysis}. The derived analytical results are very general and can degenerate to several previously results as special cases. From a degenerated case, we realize that the previous result by Wagner {em et al.} cite{Wag-08} is wrong and thus we provide the corrected result. Finally, Simulation results demonstrate that even for a moderate number of antennas at each end, the proposed analytical results provide undistinguishable results as those obtained by Monte-Carlo results.

The use of High-Frequency (HF) radio-wave propagation in the ionosphere remains prevalent for applications such as long-range communication, target detection and commercial broadcasting. The ionosphere presents a challenging channel for radio-wave propagation as it is a varying medium dependent on a number of external factors. Of the many adverse effects of ionospheric propagation, signal fading is one of the most difficult to eliminate due to its unpredictable nature. Increase in the knowledge of how the ionospheric channel affects the propagating signals, in particular fading of the signals, will drive the continual improvements in the reliability and performance of modern wide-bandwidth HF systems. This is the underlying motivation for the study of signal fading of HF radio-waves propagating through the ionosphere, from both the theoretical and experimental perspectives, with the focus of application to modern wide bandwidth HF systems. Furthermore, it is the main objective of this investigation to address the lacking in the current literature of a simple analytical signal fading model for wideband HF systems that relates the physics of the ionospheric irregularities to the observable propagation effects due to the irregularities, and one that is verified by experimental observations. An original approach was taken in the theoretical investigation to develop an analytical model that combines the effects of signal fading and directly relating them to the ionospheric irregularities that are causing the fading. The polarisation fading model (PFM) is a combination of geometric optics, perturbation techniques and frequency offset techniques to derive expressions for the Faraday rotation of the radio-wave propagating in the ionosphere. Using the same notation as the PFM, the amplitude fading model (AFM) extends the Complex Amplitude concept using perturbation techniques and Green’s functions solution to arrive at a set of expressions that describes the focussing and defocussing effects of the wave. The PFM and AFM, together with expressions for combining the effects of multiple propagation paths, provide a simple analytic model that completely describes the fading of the signal propagating in the ionosphere. This theoretical model was implemented into an efficient ionospheric propagation simulator (IPS) from which simulations of wide bandwidth HF signals propagating through the ionosphere can be undertaken. As an example of the type of results produced by the IPS, for a typical 1200km path in the north-south direction with the ionospheric channel under the influence of a travelling ionospheric disturbance (TID), a 10 MHz radio-wave signal in one-hop path is shown to be affected by polarisation fading with fading periods in the order of minutes, and a fading bandwidth in the order of 100 kHz. Further results generated by the IPS have shown to be consistent with the results reported elsewhere in the literature. The experimental investigation involves the study of signal fading from observations of real signals propagating in the ionosphere, a major part of which is the development of a digital compact channel probe (CCP) capable of operating in dual-polarisation mode, and the characterisation of such systems to ensure that data collected are not compromised by the non-idealities of the individual devices contained within the system. The CCP was deployed in experiments to collect transmissions of HF frequency-modulated continuouswave (FMCW) radio signals from the Jindalee Over-the-Horizon radar (OTHR) in dualpolarisation. Analyses of the collected data showed the full anatomy of fading of signals propagating in the ionosphere for both horizontal and vertical polarisations, the results of which are consistent with that from the IPS and thus verifying the validity of the theoretical model of fading. Further experimental results showed that in majority of the observations polarisation fading is present but can be masked by multi-path fading, and confirming that periods of rapid signal fading are associated with rapid changes in the ionospheric channel. From the theoretical and experimental investigations, the major achievement is the successful development of an efficient propagation simulator IPS based on the simple analytical expressions derived in the PFM and AFM theoretical models of signal fading, which has produced sensible signal fading results that are verified by experimental observations. One of the many outcomes of this investigation is that polarisation diversity has the potential to bring improvements to the quality of wide-bandwidth HF signals in a fading susceptible propagation channel. The combination of an efficient propagation simulator IPS based on theoretical signal fading model and the experimental data collection by the dual-polarisation CCP is a major step in allowing one to fully understand the different aspects of fading of signals propagating in the ionosphere, which sets a solid foundation for further research into the design of wide bandwidth HF systems and the possible fading mitigation techniques. / Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2008

A má nutrição precoce gera efeitos deletérios graves no crescimento, no comportamento e nas capacidades cognitivas de ratos e crianças, sendo que a desnutrição proteica é a principal insuficiência nutricional que pode ser examinada individualmente em estudos experimentais. O objetivo deste estudo foi estabelecer discriminações condicionais em ratos, comparando-se animais controles com animais desnutridos e que passaram por recuperação nutricional, bem como testar três modificações no procedimento de Feliciano (2007). Como modificações foram empregadas um maior número de reversões da discriminação simples, antes do treino de discriminação condicional e os procedimentos de fading e correção de tentativas. No Experimento 1, foram testados o procedimento de fading e as reversões da discriminação. No Experimento 2, as reversões foram testadas junto com o procedimento de correção, mas não foram empregados animais previamente desnutridos. Por fim, no Experimento 3 os animais só passaram pela discriminação condicional e pela correção. Ao final das reversões os animais controles e desnutridos apresentaram a mesma velocidade de aprendizagem. Ao término da vigência do procedimento de fading não houve manutenção do desempenho característico da aprendizagem sem erros, indicando que o procedimento de fading utilizado não foi eficiente. A correção de tentativas facilitou a aprendizagem da discriminação simples e melhorou o desempenho dos animais. Não ocorreu curva de aprendizagem para a discriminação condicional nos três experimentos. Ainda assim, ao final do treino os animais submetidos ao procedimento de correção de tentativas apresentaram melhor desempenho do que os animais submetidos apenas ao fading, ou do que o dos animais não submetidos a qualquer dos procedimentos. Entre os fatores apontados como responsáveis pela não aprendizagem da discriminação condicional, destacam-se a programação da contingência, a disposição espacial aleatória dos estímulos de escolha e a existência de mais de duas alternativas para a resposta de escolha. / Early malnutrition leads to serious deleterious effects on growth, behavior and cognitive abilities of rats and children. Protein malnutrition is the main nutritional failure that can be examined individually in experimental studies. The aim of this study was to establish conditional discriminations in rats by comparing control animals with early malnourished animals which have received nutritional recovery and to test three changes in the procedure used by Feliciano (2007). As changes were employed a greater number of simple discrimination reversals, before the conditional discrimination training and the the procedures of fading correction. In experiment 1, we tested the procedure of fading and the discrimination reversals. In the experiment 2, the discrimination reversals were tested along with the correction procedure, but preveiously malnourished animals were not used. Finally, in experiment 3 the animals were tested only in the conditional discrimination with or without the correction procedure. At the end of reversals control and malnourished rats showed the same learning speed. At the end of the duration of the fading procedure the performance characteristics of learning without errors was not maintained, indicating that the fading procedure was not used efficiently. Correction facilitated the learning of simple discrimination and improved animal performance. There was no learning curve for the conditional discrimination in all experiments, yet at the end of training the performance of the animals subjected to correction procedure was better than the performance of rats subjected only to fading, or that of animals not submitted to any procedures. Among the factors that have prevented the learning of the conditional discrimination by the rats, we highlight the programmed contingency, the random spatial arrangement of the choice stimuli and the existence of more than two alternatives for the responses.

A literatura internacional ao investigar a durabilidade dos efeitos do Ensino Infantil se deparou com um eventual fenômeno de decaimento de tais efeitos, chamado de facing-out. Utilizando dados longitudinais coletados na cidade de Sertãozinho buscamos investigar e documentar tal fenômeno para a realidade nacional. Encontramos evidências de decaimento do benefício do EI especialmente sobre a proficiência de matemática. Além disso, mostramos que a estrutura da base de dados utilizada para fazer tal mensuração pode gerar resultados sobrestimados, especialmente se tal base contiver alto grau de seletividade. Por fim, indicamos que a qualidade das instituições de educação na primeira infância pode ser um dos determinantes da durabilidade do efeito encontrado, uma vez que crianças que frequentaram a maior parte do EI em escolas públicas estão mais sujeitas a este fênomeno. / The international literature while investigating the long term effects of early childhood education identified a decrease phenomenon of such effects, called fading-out. Using longitudinal data collected in the city of Sertãozinho our goal was to investigate and document this phenomenon for Brazilians\' reality. We found evidence of the decrease of early childhood education benefits, especially in Math proficiency. Furthermore, we show that the structure of the database used to make such measurements can generate results that overestimate the phenomenon, especially if those databases contain a high degree of selectivity. Finally, we indicate that the quality of the early childhood schoolscan be an important determinant of the effects\' durability, since children who attended most of the early childhood education in public schools are more prone to this phenomenon.

Abstract High radio capacity is one of the main targets in wireless network planning. The characteristics of the broadband radio channel pose serious challenges for achieving this goal. This thesis views the capacity problem from two frameworks. In the first, the effective user capacity in advanced direct sequence wideband code-division multiple-access (DS-CDMA) radio networks is evaluated. Sensitivity to various imperfections in key system parameters is studied. The analysis is based on a mathematical foundation that presents complex signal models and enables evaluation of the performance losses due to parameter estimation errors and multipath fading. The effective number of users supported in a cell is restricted by the multiple access interference (MAI) in the same cell (intracell interference) and overall background noise. The studied wideband CDMA receiver structures comprise conventional rake receivers with both the maximal ratio combining (MRC) and equal gain combining (EGC) schemes that can be supplemented with either linear decorrelating or nonlinear successive cancellation-based multiuser detectors and M-antenna spatial diversity. The second framework focuses on direct sequence spread spectrum-based ultra wideband (UWB) indoor communications. Cochannel interference limited capacity is evaluated against the outage probability criterion in exponentially decaying lognormal multipath fading channels. Distance-dependence and spatial distribution of users is taken into account at different spatial cell configurations. Only moderate complexity partial rake receivers with noncoherent combining are employed. Total interference is composed of interpath, multipath, intracell, and intercell interference contributions. Lognormal sum approximations and simulations are used to evaluate distributions of the desired and interfering signals. The impact of the timing errors at the receiver monopulse correlation is studied. The numerical results for the wideband CDMA framework show that effective user capacity and sensitivity depend critically on the joint impact of nonidealities in system parameters (e.g., channel profile, severity of fading, receiver algorithms). User capacities of the studied multiuser enhanced receivers were more prone to these impairments than those of the simpler single user receivers. The results should be used for network planning and optimization. The numerical results of the UWB framework suggest that, even in the multipath rich channel, the optimal number of rake fingers can be less than half of the significant multipaths. Differences between circular, square, and hexagonal cell models proved to be minor with respect to link distance distributions. The derived link distance statistics are useful tools in the analytic piconet dimensioning and optimization.

Yes / The MIMO technology towards achieving future generation broadband networks design criteria is presented. Typical next generation scenarios are investigated. The MIMO technology is integrated with the OFDM technology for effective space, time and frequency diversity exploitations for high speed outdoor environment. Two different OFDM design kernels (fast Fourier transform (FFT) and wavelet packet transform (WPT)) are used at the baseband for OFDM system travelling at terrestrial high speed for 800MHz and 2.6GHz operating frequencies. Results show that the wavelet kernel for designing OFDM systems can withstand doubly selective channel fading for mobiles speeds up to 280Km/hr at the expense of the traditional OFDM design kernel, the fast Fourier transform.

Wavelet Modulation (WM)---also referred to as fractal modulation---simultaneously sends data at multiple rates through an unknown channel. This novel multirate diversity strategy offers improved message recovery over conventional modulation techniques: if the message is not received at one rate due to the channel disturbances, it can be received at another rate where the channel is clear. Previous research has demonstrated the performance of wavelet modulation in Gaussian channels. This paper extends the investigation to the performance of wavelet modulation in time varying channels. We show that bit error rate (BER) wavelet demodulation performance in the additive, white, Gaussian noise (AWGN) channel is comparable to theoretical binary phase shift keying. Our results depict the improvement in performance that can be realized for time varying channels by utilizing the various rates of wavelet modulation; BER versus SNR curves for each fading channel show how the message at one rate can be more accurately recovered than at another rate. Furthermore, we also present results indicating the dramatic improvement in wavelet demodulation performance when multiple rates are available and utilized for demodulation. This improvement in performance is highly visible in BER performance for the AWGN and flat fading channels. Finally, a comparison of binary phase shift keying (BPSK) and WM in a frequency selective channel is performed. The BER improvement of WM is shown when demodulation is done at rates which are least corrupted by ISI. We illustrate our new algorithm that: identifies the channel characteristics; determines which rates are maximally corrupted by ISI; and, utilizes only those uncorrupted copies in demodulation. / Master of Science

Orientador: Michel Daoud Yacoub / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-15T21:02:32Z (GMT). No. of bitstreams: 1 Rabelo_GuilhermeSilveira_M.pdf: 2232654 bytes, checksum: 5ad1d7c509404a4af175e0cb18c271f9 (MD5) Previous issue date: 2010 / Resumo: Este trabalho avalia o desempenho de enlaces sem fio em condições muito severas de desvanecimento. Para isso, uma nova distribuição de probabilidade, a ?-µ Extrema, é investigada como modelo de desvanecimento para descrever o sinal propagado em tais condições. Ajustes a dados de campos publicados na literatura e coletados em um ambiente confinado e outros dados coletados pelo grupo de pesquisa do autor deste trabalho mostram que a distribuição ?-µ Extrema é flexível e apropriada para modelar ambientes severos. Medidas de desempenho de enlace são então obtidas para esquemas de modulação não-coerente, onde é mostrado que, devido a uma característica particular do canal de desvanecimento ?-µ Extremo, a taxa de erro de bit é limitada inferiormente por um valor assintótico não-nulo. Do mesmo modo, para qualquer uma das três técnicas de combinação por diversidade denominadas combinação por seleção, combinação por razão máxima e combinação por ganho igual, a taxa de erro de bit também é limitada inferiormente, embora o valor mínimo decresça com o aumento do número de ramos de diversidade. Formulações para a distribuição do sinal de saída e relação sinal-ruído média na saída dos combinadores também são obtidas. De forma bastante interessante, é mostrado que em condições extremas de desvanecimento, o desempenho do combinador por seleção pode superar o desempenho do combinador por ganho igual. Além disso, este trabalho também apresenta uma formulação inédita para a distribuição conjunta a-µ, que inclui como casos particulares as distribuições de desvanecimento largamente utilizadas Weibull, Nakagami-m e Rayleigh. Escrita em termos de funções já conhecidas na literatura, a formulação é facilmente computável e muito geral na medida em que permite um esquema de correlação e parâmetros arbitrários. Embora a formulação seja dada na forma de soma infinita, é mostrado que uma versão truncada também é uma distribuição válida. Finalmente, para demonstrar a aplicabilidade das novas formulações, a distribuição da envoltória na saída de um combinador por seleção é avaliada utilizando as abordagens exata e aproximada. Os resultados mostram que um número pequeno de termos na soma já é suficiente para prover um excelente ajuste entre os resultados exatos e aproximados / Abstract: This work evaluates the performance of a wireless link under severe fading conditions. To achieve this, a new probability distribution, the ?-µ Extreme, is investigated as a fading model to describe the propagated signal under such conditions. Adjustments to field data published elsewhere in the literature, collected in an enclosed environment, and other fading data collected by the author's team show that the ?-µ Extreme distribution is flexible and suitable to model these scenarios. Link performance measures are then obtained for non-coherent modulation schemes, where it is shown that, due to an intrinsic characteristic of the ?-µ Extreme fading channel, the bit error rate is lower-bounded by a non-nil minimum value. In the same way, for anyone of the M-branch basic diversity combining techniques, namely selection combining, maximal ratio combining, and equal gain combining, the bit error rate is still lower-bounded, although the minimum achievable value decreases exponentially with the increase in the number of diversity branches. Formulations for the outage probability as well as mean signal-to-noise ratio at the output of the combiners are also derived. Interestingly, it is shown that in extreme fading conditions, the selection combiner may outperform the equal gain combiner. In addition, this works also derives a new closed-form series-type formulation for the multivariate a-µ joint distribution, which includes as particular cases the largely used fading distributions Weibull, Nakagami-m, and Rayleigh. Written in terms of functions already available in literature, the formulation is easily computable and very general for it assumes arbitrary correlation scheme and parameters. Even though the new formulation is given in terms of an infinite series, it is shown that a truncated version is still a valid distribution. Finally, in order to demonstrate the applicability of the new results, the envelope cumulative distribution at the output of the selection combiner is evaluated using the approximate and exact approaches. The results show that that only a few terms is sufficient to provide an excellent fit between approximate and exact results / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

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.