No description available.

No / Two training schemes namely the orthogonal pilot scheme (OPS) and the superimposed pilot scheme (SPS) are compared in terms of achievable rates in multiple-antenna fading channels with memory. For both schemes, we show that the achievable rate depends on the number of antennas, signal-to-noise ratio (SNR) and fading speed via the channel estimation error variance and the fraction of time for data transmission. To guarantee positive achievable rates, we show that for the OPS the number of transmit antennas that can be accommodated is limited by the fading speed whereas for the SPS the number of antennas can be arbitrary. For most antenna configurations, we observe that while the SPS is superior in the low-SNR and fastfading regimes, the OPS is superior in other regimes. However, for a few number of antennas (e.g., single antenna), the SPS may also be superior in the low-SNR and slow-fading regimes.

No / Multi-antenna(MIMO) techniques are reported to improve the performance of radio communication systems in terms of their capacity and spectral efficiency. In combination with appropriate receiver technologies they can also provide savings in the required transmit power with respect to target bit error rate. Long Term Evolution(LTE), one of the candidates for fourth generation(4G) mobile communication systems has MIMO as one of its underlying technologies and ITU defined channel models for its propagating environment. This paper undertakes a comprehensive verification of the performance of transmit diversity MIMO in the downlink sector of LTE. It uses models built using MATLAB to carry out simulations. It is deduced that generally increasing transmit diversity configuration from 2x2 to 4x4 offers SNR savings in flat fading channels though with a user equipment moving at 30km/hr, deploying 2x2 offers higher SNR saving below 7dB. Furthermore bandwidth variation has minimal effect on the BER performance of transmit MIMO except at SNR values above 9dB while the gains of higher modulation schemes come with a transmit power penalty.

Opportunistic selection and rate adaptation play a vital role in improving the spectral and power efficiency of current multi-node wireless systems. However, time-variations in wireless channels affect the performance of opportunistic selection and rate-adaptation in the following ways. Firstly, the selected node can become sub-optimal by the time data transmission commences. Secondly, the choice of transmission parameters such as rate and power for the selected node become sub-optimal. Lastly, the channel changes during data transmission. In this thesis, we develop a comprehensive and tractable analytical framework that accurately accounts for these effects. It differs from the extensive existing literature that primarily focuses on time-variations until the data transmission starts. Firstly, we develop a novel concept of a time-invariant effective signal-to-noise ratio (TIESNR), which tractably and accurately captures the time-variations during the data transmission phase with partial channel state information available at the receiver. Secondly, we model the joint distribution of the signal-to-noise ratio at the time of selection and TIESNR during the data transmission using generalized bivariate gamma distribution. The above analytical steps facilitate the analysis of the outage probability and average packet error rate (PER) for a given modulation and coding scheme and average throughput with rate adaptation. We also present extensive numerical results to verify the accuracy of each step of our approach and show that ignoring the correlated time variations during the data transmission phase can significantly underestimate the outage probability and average PER, whereas it overestimates the average throughput even for packet durations as low as 1 msec.

Seismic methods have been used in sedimentary environment for almost 80 years. During that time, exploration geophysicists have developed a number of techniques to handle specific aspects of working in sedimentary areas. This is not the case for studies in the hardrock environment, where significantly less time and money have been invested on seismic investigations. Therefore, there is still a need to develop the right techniques appropriate for working in hardrock environments. The research presented here, covers aspects of acquisition, processing and interpretation in hardrock environments. A cost-effective alternative for two-dimensional data acquisition is presented. Acquisition parameters are also discussed and recommendations for future work are given. The main effort of this thesis, however, was to find appropriate processing methods to address some of the different problems present in datasets acquired in the hardrock environment. Comparison of two computer programs for first arrival seismic tomography was performed in order to find the most suitable one for processing crooked line geometries. Three-dimensional pre-stack depth migration was also tested to find a detailed near-surface image. A processing method geared to enhance the signal-to-noise ratio was applied to the dataset with the lowest signal amplitudes to improve the quality of the stack. Finally, cross-dip analysis and corrections were performed on two of the three datasets included in this thesis. Cross-dip analysis was also applied as an interpretation tool to provide the information needed for estimation of the true dip of some of the reflectors related to geological structures. The results presented in this thesis indicate that cross-dip analysis and corrections are one of the most powerful tools for processing and interpretation in the presence of complex geology. Therefore, it is recommended to include this method as a standard step in the processing and interpretation sequence of data acquired in hardrock environments.

Photoconductive antenna (PCA) array based THz near-field imager incorporating Hadamard multiplexing method is developed in this work. By using a 2 × 2 dipole antenna array as the THz transmitter, the system signal-to-noise ratio (SNR) is demonstrated to be improved by a factor of 2 as the theory predicts. Additionally, a 2-D scanning of a metallic structure on a THz-transparent substrate (with a total scanning area of 1 × 1 mm2) is experimentally implemented. Correlation coefficient estimation is made afterwards to quantify the reconstructed image quality.

Neste trabalho é apresentada uma nova geometria e os critérios de projeto para dispositivos de espectrometria de mobilidade iônica, com objetivo de aumentar a relação entre sinal e ruído detectados pelos eletrômetros que compõem a região de detecção, quando associado à ionização baseada em descargas elétricas que tipicamente emitem maior interferência eletromagnética em relação a outros tipos de ionização. A geometria e os critérios de projeto foram estabelecidos com o auxílio do simulador de trajetórias iônicas SIMION versão 8.1 e comparada com espectrômetros de mobilidade iônica do estado-da-arte. Os resultados das simulações dos dispositivos foram avaliados por meio dos testes estatísticos não-paramétricos de Iman-Davenport e Holm. O resultado indicou que a geometria proposta apresentou compatibilidade com as melhores características dos espectrômetros atuais com confiança estatística a 95 %. Na sequência a geometria proposta foi simulada, fabricada e testada para detecção dos íons de: tolueno - C7H8 (C5H5+, C6H5+, C7H7+), propanol - C3H8O (CH3+, CH3O+, C2H3+, C2H4O+, C2H5O+, C3H6+, C3H7+, C3H7O+) e água - H2O (H+, HO+, H2+, O+). Os picos de corrente iônica detectada nos eletrômetros indicaram coerência com as trajetórias simuladas para estes conjuntos de íons. Além disso, os resultados experimentais apresentaram um aumento na relação entre sinal e ruído para a nova geometria proposta que foi validada pelo teste de comparação pareada não-paramétrico de Wilcoxon a 95 % de confiança estatística. / In this work, a new geometry and a design criteria for ion mobility spectrometry devices was presented, aiming to increase the signal-to-noise ratio detected by electrodes of the detection region, when associated with ionization based on electrical discharges. The new geometry and the design criteria were established in the SIMION version 8.1 (an ionic trajectory simulator) and compared with the state-of-art ion mobility spectrometers. The results from device simulations were evaluated using the non-parametric statistical test of Iman-Davenport and Holm. The result indicated that the proposed design criteria presented compatibility with the best characteristics of current spectrometers with statistical evidence at 95%. The proposed geometry was simulated, fabricated and tested for the following solvents: toluene - C7H8 (C5H5+, C6H5+, C7H7+), propanol - C3H8O (CH3+, CH3O+, C2H3+, C2H4O+, C2H5O+, C3H6+, C3H7+, C3H7O+) and water - H2O (H+, HO+, H2+, O+). The peaks of ion current detected in the electrometers occurred at approximate positions of the simulated trajectories for these sets of ions. In addition, the experimental data showed an increase in the signal-to-noise ratio for the proposed new geometry that was validated by the test statistic of Wilcoxon signed rank at 95% statistical confidence.

Neste trabalho é apresentada uma nova geometria e os critérios de projeto para dispositivos de espectrometria de mobilidade iônica, com objetivo de aumentar a relação entre sinal e ruído detectados pelos eletrômetros que compõem a região de detecção, quando associado à ionização baseada em descargas elétricas que tipicamente emitem maior interferência eletromagnética em relação a outros tipos de ionização. A geometria e os critérios de projeto foram estabelecidos com o auxílio do simulador de trajetórias iônicas SIMION versão 8.1 e comparada com espectrômetros de mobilidade iônica do estado-da-arte. Os resultados das simulações dos dispositivos foram avaliados por meio dos testes estatísticos não-paramétricos de Iman-Davenport e Holm. O resultado indicou que a geometria proposta apresentou compatibilidade com as melhores características dos espectrômetros atuais com confiança estatística a 95 %. Na sequência a geometria proposta foi simulada, fabricada e testada para detecção dos íons de: tolueno - C7H8 (C5H5+, C6H5+, C7H7+), propanol - C3H8O (CH3+, CH3O+, C2H3+, C2H4O+, C2H5O+, C3H6+, C3H7+, C3H7O+) e água - H2O (H+, HO+, H2+, O+). Os picos de corrente iônica detectada nos eletrômetros indicaram coerência com as trajetórias simuladas para estes conjuntos de íons. Além disso, os resultados experimentais apresentaram um aumento na relação entre sinal e ruído para a nova geometria proposta que foi validada pelo teste de comparação pareada não-paramétrico de Wilcoxon a 95 % de confiança estatística. / In this work, a new geometry and a design criteria for ion mobility spectrometry devices was presented, aiming to increase the signal-to-noise ratio detected by electrodes of the detection region, when associated with ionization based on electrical discharges. The new geometry and the design criteria were established in the SIMION version 8.1 (an ionic trajectory simulator) and compared with the state-of-art ion mobility spectrometers. The results from device simulations were evaluated using the non-parametric statistical test of Iman-Davenport and Holm. The result indicated that the proposed design criteria presented compatibility with the best characteristics of current spectrometers with statistical evidence at 95%. The proposed geometry was simulated, fabricated and tested for the following solvents: toluene - C7H8 (C5H5+, C6H5+, C7H7+), propanol - C3H8O (CH3+, CH3O+, C2H3+, C2H4O+, C2H5O+, C3H6+, C3H7+, C3H7O+) and water - H2O (H+, HO+, H2+, O+). The peaks of ion current detected in the electrometers occurred at approximate positions of the simulated trajectories for these sets of ions. In addition, the experimental data showed an increase in the signal-to-noise ratio for the proposed new geometry that was validated by the test statistic of Wilcoxon signed rank at 95% statistical confidence.

OFDM has been recognized as a powerful multi-carrier modulation technique that provides efficient spectral utilization and resilience to frequency selective fading channels. Adaptive modulation is a concept whereby the modulation modes are dynamically changed based on the perceived instantaneous channel conditions. In conjunction with OFDM systems, adaptive modulation is a very powerful technique to combat the frequency selective nature of mobile channels, while simultaneously attempting to fully maximize the time-varying capacity of the channel. This is based on the fact that frequency selective fading affects the sub-carriers unevenly, causing some of them to fade more severely than others. The modulation modes are adaptively selected on the sub-carriers depending on the amount of fading, to maximize throughput and improve the overall BER. Transmission parameter adaptation is the response of the transmitter to the time-varying channel quality. To efficiently react to the dynamic nature of the channel, adaptive OFDM systems rely on efficient algorithms in three key areas namely, channel quality estimation, transmission parameter selection and signaling or blind detection mechanisms of the modified parameters. These are together termed as the enabling techniques that contribute to the effective performance of adaptive OFDM systems. This thesis deals with higher performance and efficient enabling parameter estimation algorithms that further improve the overall performance of adaptive OFDM systems. Traditional estimation of channel quality indicators, such as noise power and SNR, assume that the noise has a flat power spectral density within the transmission band of the OFDM signal. Hence, a single estimate of the noise power is obtained by averaging the instantaneous noise power values across all the sub-carriers. In reality, the noise within the OFDM bandwidth is a combination of white and correlated noise components, and has an uneven affect across the sub-carriers. It is this fact that has motivated the proposal of a windowing approach for noise power estimation. Windowing provides many local estimates of the dynamic noise statistics and allows better noise tracking across the OFDM transmission band. This method is particularly useful for better resource utilization and improved performance in sub-band adaptive modulation, where adaptation is performed on the sub-carriers on a group-by-group basis based on the observed channel conditions. Blind modulation mode detection is another relatively unexplored issue in regard to adaptation of OFDM systems. The receiver has to be informed of the appropriate modulation modes used at the transmitter for proper demodulation. If this can be done without any explicit signaling information embedded within the OFDM symbol, it has the advantage of improved throughput and data capacity. A model selection approach is taken, a novel statistical blind modulation detection method based on the Kullback-Leibler (K-L) distance is proposed. This algorithm takes into account the distribution of the Euclidian distances from the received noisy samples on the complex plane to the closest legitimate constellation points of all the modulation modes used. If this can be done without any explicit signaling information embedded within the OFDM symbol, it has the advantage of improved throughput and data capacity. A model selection approach is taken, and a novel statistical blind modulation detection method based on the Kullback-Leibler (K-L) distance is proposed. This algorithm takes into account the distribution of the Euclidian distances from the received noisy samples on the complex plane to the closest legitimate constellation points of all the modulation modes used.

To many, high-frequency (HF) radio communications is obsolete in this age of long distance satellite communications and undersea optical fiber. Yet despite this, the HF band is used by defence agencies for backup communications and spectrum surveillance, and is monitored by spectrum management organizations to enforce licensing. Such activity usually requires systems capable of locating distant transmitters, separating valid signals from interference and noise, and recognizing signal modulation. Research presented here targets the latter issue. The ultimate aim is to develop robust algorithms for automatic modulation recognition of real HF signals, where real means signals propagating by multiple ionospheric modes with co-channel signals and non- Gaussian noise. However, many researchers adopt Gaussian noise models for signals for the sake of convenience at the cost of accuracy. Furthermore, literature describing the probability density function (PDF) of HF noise does not abound. So an additional aim of this research is measurement of the PDF of HF noise. A simple empirical technique, not found in the literature, is described that supports the hypothesis that HF noise is generally not Gaussian. In fact, the probability density function varies with the time of day, electromagnetic environment, and state of the ionosphere. Key contributions of this work relate to the statistics of HF noise and the discrimination of real HF signals via three signal features. Through two unique experiments, the density function of natural HF noise is found to closely follow a Bi-Kappa distribution. This distribution can model natural and man-made HF noise through a single control parameter. Regarding signal features, the coherence function is found to be a brute-force technique suitable only for hard (not soft) decisions. A novel application of an entropic distance measure proves able to separate four real HF signals based on their modulation types. And, an estimator for signal-to-noise (SNR) ratio is shown to provide reasonable measures of SNR for the same real HF signals. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1330848 / Thesis (Ph.D.) - University of Adelaide, School of Electrical and Electronic Engineering, 2008