With the increasing demand for more wireless multimedia applications, it is desired to design a wireless system with higher data rate. Furthermore, the frequency spectrum has become a limited and valuable resource, making it necessary to utilize the available spectrum efficiently and coexist with other wireless systems. Orthogonal frequency division multiplexing (OFDM) modulation is widely used in communication systems to meet the demand for ever increasing data rates. The major advantage of OFDM over single-carrier transmission is its ability to deal with severe channel conditions without complex equalization. However, OFDM systems suffer from a high peak to average power ratio, and they are sensitive to carrier frequency offset and Doppler spread. This dissertation first focuses on the development of intercarrier interference (ICI) reduction and signal detection algorithms for OFDM systems over time-varying channels. Several ICI reduction algorithms are proposed for OFDM systems over doubly-selective channels. The OFDM ICI reduction problem over time-varying channels is formulated as a combinatorial optimization problem based on the maximum likelihood (ML) criterion. First, two relaxation methods are utilized to convert the ICI reduction problem into convex quadratic programming (QP) problems. Next, a low complexity ICI reduction algorithm applicable to $M$-QAM signal constellations for OFDM systems is proposed. This formulates the ICI reduction problem as a QP problem with non-convex constraints. A successive method is then utilized to deduce a sequence of reduced-size QP problems. For the proposed algorithms, the QP problems are solved by limiting the search in the 2-dimensional subspace spanned by its steepest-descent and Newton directions to reduce the computational complexity. Furthermore, a low-bit descent search (LBDS) is employed to improve the system performance. Performance results are given to demonstrate that the proposed ICI reduction algorithms provide excellent performance with reasonable computational complexity. A low complexity joint semiblind detection algorithm based on the channel correlation and noise variance is proposed which does not require channel state information. The detection problem is relaxed to a continuous non-convex quadratic programming problem. Then an iterative method is utilized to deduce a sequence of reduced-size quadratic programming problems. A LBDS method is also employed to improve the solution of the derived QP problems. Results are given which demonstrate that the proposed algorithm provides similar performance with lower computational complexity compared to that of a sphere decoder. A major challenge to OFDM systems is how to obtain accurate channel state information for coherent detection of the transmitted signals. Thus several channel estimation algorithms are proposed for OFDM systems over time-invariant channels. A channel estimation method is developed to utilize the noncircularity of the input signals to obtain an estimate of the channel coefficients. It takes advantage of the nonzero cyclostationary statistics of the transmitted signals, which in turn allows blind polynomial channel estimation using second-order statistics of the OFDM symbol. A set of polynomial equations are formulated based on the correlation of the received signal which can be used to obtain an estimate of the time domain channel coefficients. Performance results are presented which show that the proposed algorithm provides better performance than the least minimum mean-square error (LMMSE) algorithm at high signal to noise ratios (SNRs), with low computational complexity. Near-optimal performance can be achieved with large OFDM systems. Finally, a CS-based time-domain channel estimation method is presented for OFDM systems over sparse channels. The channel estimation problem under consideration is formulated as a small-scale $l_1$-minimization problem which is convex and admits fast and reliable solvers for the globally optimal solution. It is demonstrated that the magnitudes as well as delays of the significant taps of a sparse channel model can be estimated with satisfactory accuracy by using fewer pilot tones than the channel length. Moreover, it is shown that a fast Fourier transform (FFT) matrix of extended size can be used as a set of appropriate basis vectors to enhance the channel sparsity. This technique allows the proposed method to be applicable to less-sparse OFDM channels. In addition, a total-variation (TV) minimization based method is introduced to provide an alternative way to solve the original sparse channel estimation problem. The performance of the proposed method is compared to several established channel estimation algorithms. / Graduate

Den 10 mars år 2000 blev det tillåtet för publika aktiebolag att förvärva sina egna aktier i Sverige. Många bolag har det sett den nya möjligheten att genomföra återköp av egna aktier, av olika anledningar, vilket har lett till att flera publika aktiebolag genomför återköpsprogram. Syftet med denna studie är undersöka hur återköp påverkar aktiernas likviditet genom att studera spreaden och volatiliteten i de perioder som företaget inte får genomföra återköp. Tidsperioden som studeras är åren 2010 till 2013. Resultatet visar att det inte finns någon signifikant skillnad i spread och volatilitet mellan de perioder som återköp får ske och de peioder som inte tillåter återköp.

The goal of this study is to assess the potential of using bench-scale fire testing to screen materials for the Steiner tunnel fire test. It is hypothesized that the chemical and physical changes made to a material to improve its fire performance in small scale fire tests will have a predictable response in the Steiner tunnel. This hypothesis is based on the observation that fire test results can, in some cases, provide insight on a material's relative fire hazard, and the assumption that the relative hazard should be consistent across scale. The ASTM E84 Steiner tunnel test provides a relative ranking of material hazard in two categories. The horizontal Flame Spread Index (FSI) is used to rank the flame hazard of a material, and the Smoke Developed Index (SDI) is used to rank the smoke hazard of a material. Two fire tests are proposed to independently assess each hazard at the bench-scale. The ASTM E1354 cone calorimeter test measures a material's open-flaming heat release rate; it is proposed that the cone calorimeter test can be used to assess a material's relative flame hazard. The ISO 5659-2 smoke density chamber test measures a material's closed-environment smoke development; it is proposed that the smoke density chamber test can be used to assess a material's relative smoke hazard. The material selected for this study is fire-retarded sprayed polyurethane foam (FRSPF) insulation. Specific details of the foam chemistry, fire retardants, and the manufacturer are confidential. Generally, the foam can be described as medium-density (approximately 2 lbs/ft³), closed-celled, and semi-rigid. The fire retardant additives are comprised of differing ratios and concentrations of phosphorous- and halogen-containing compounds. A series of 30 Steiner tunnel tests is conducted on 20 different formulations. Repeated testing is conducted on several formulations in order to assess variability in the Steiner tunnel test results. Cone calorimeter and smoke density chamber tests are conducted on a subset of those formulations, in sets of 3-5 tests per formulation. Key performance indicators are identified from each fire test, relationships between those indicators are examined, and correlations are presented where strong relationships are apparent. Empirical prediction models are proposed for FSI and SDI based on the success rate of prediction, and minimization of error between experimental (measured) and modelled (predicted) results. It is concluded that for the materials tested in this study, there is sufficient evidence of consistency in relative performance to recommend bench-scale screening tests as a cost-effective alternative to repeated Steiner tunnel testing.

This study adopts Markov-switching ARCH model proposed by Hamilton and Susmel (1994) to explore the behavior of credit spreads for different bond ratings. Specifically, this paper examines the properties of credit spreads and the co-movements of spreads among different durations and credit ratings. The consideration of the population makes the outcome more precise. The contribution of this study is to add to the investors a knowledge as to the credit spread behavior and help them understand the lower rating or longer maturity bonds by the observation of the investment-graded bonds while there are more risks and uncertainties conceal in these high yield bonds or D-rated bonds. The conclusion of this paper may help investors understand credit risk management and thus build appropriate portfolios.

No description available.

In this dissertation, three related issues concerning empirical time series models for energy financial markets and the stock market were investigated. The purpose of this dissertation was to analyze the interdependence of price movements, focusing on the forecasting models for crude oil prices and the hedging models for gasoline prices, and to study the change in the contemporaneous causal relationship between investors' activities and stock price movements in the Korean stock market. In the first essay, the nature of forecasting crude oil prices based on financial data for the oil and oil product market is examined. As crack spread and oil-related Exchange-Traded Funds (ETFs) have enabled more consumers and investors to gain access to the crude oil and petroleum products markets, I investigated whether crack spread and oil ETFs were good predictors of oil prices and attempted to determine whether crack spread or oil ETFs were better at explaining oil price movements. In the second essay, the effectiveness of diverse hedging models for the unleaded gasoline price is examined using futures and ETFs. I calculated the optimal hedge ratios for gasoline futures and gasoline ETF utilizing several advanced econometric models and then compared their hedging performances. In the third essay, the contemporaneous causal relationship between multiple players' activities and stock price movements in the Korean stock market was investigated using the framework of a DAG model. The causal impacts of three players' activities in regard to stock return and stock price volatility are examined, concentrating on foreign investor activities. Within this framework, two Korean stock markets, the KSE and KOSDAQ markets, are analyzed and compared. Recognizing the global financial crisis of 2008, the change in casual relationships was examined in terms of pre- and post-break periods. In conclusion, when a multivariate econometric model is developed for multi-markets and multi-players, it is necessary to consider a number of attributes on data relations, including cointegration, causal relationship, time-varying correlation and variance, and multivariate non-normality. This dissertation employs several econometric models to specify these characteristics. This approach will be useful in further studies of the information transmission mechanism among multi-markets or multi-players.

The ever-increasing demand for higher information-transfer rates in wireless data networks invokes the need to develop more spectrally-efficient communication strategies. Techniques such as MIMO and turbo-coded CDMA are well known and obvious candidates for improving the spectral efficiency of next generation wireless networks, and addressing the limitations of currently implemented technologies. Correspondingly, such methods are finding their way into wireless network standards such as 3GPP and IEEE 802.20. / One measure of the size of a communication system is the number of independent data streams being transmitted simultaneously through a channel, assuming tight constraints on available bandwidth and signal power. Such data streams may originate from different users all wishing to communicate at once. In addition, each user may wish to transmit independent data on more than one antenna simultaneously in order to increase his or her own data rate. Although strategies for such multi-dimensional signalling have seen significant improvements in recent years, most of the techniques proposed in the literature still suffer from either poor performance or prohibitive complexity when the size of the system grows large. / This thesis is concerned primarily with supporting high system spectral-efficiencies in very large systems, while maintaining strong resistance to data errors with manageable complexity. / Iterative decoding, or Bayesian message-passing, is demonstrably able to approach closely the performance of an optical decoder for certain families of single-user error correction codes, with low computational complexity. The topic of this work, iterative list detection, is a technique for jointly decoding many independent data streams from multiple users and/or antennas, using powerful iterative decoding strategies developed for such single-user codes. The receiver strategies presented are based on the premise that iterative Bayesian decoding is capable of achieving performance very close to that of an optimal decoder for a multi-dimensional system, given certain assumptions on the system model. Other than this, iterative list detection makes no assumptions about the statistics of the interfering signals, linearity, or any other simplifying impositions. Rather, the method seeks only to approximate closely the probabilistic quantities dictated by the rules of the iterative decoding paradigm, which is by now well understood. / List detection itself refers to the computationally efficient calculation of signal probabilities conditioned on a noise-and-interference corrupted signal at the receiver, computed for each simultaneously transmitted signal. The calculation is the key step in the implementation of an iterative receiver for such a system. / After introducing the list detection strategy in the context of iterative receivers for multi-user MIMO channels, algorithms for optimal list detection are described. A new optimal list detection algorithm with some superior properties to other implementations in the literature is proposed. While still very computationally complex, performance results for optimal list detection are presented that demonstrate the effectiveness and utility of the paradigm, and provide a performance benchmark for any sub-optimal list detection technique. The performance is also compared with other techniques such as linear filters, providing an appreciation of the benefits of list detection. / An asymptotic large-systems analysis is then undertaken in order to determine the behaviour of a fundamental parameter that determines the complexity of list detection, specifically the number of terms in a certain summation. The minimum number of terms is derived under an accuracy constraint on the signal probabilities. Results demonstrate that the number of terms does not necessarily increase with the size of the system, and the conditions under which this is true are indicated. / The main contribution of the thesis is the development of a number or computationally efficient sub-optimal list detection algorithms. Various strategies are proposed for different system scenarios, resulting in near-optimal performance with complexity that adapts automatically to cope with changing channel conditions and interference. The performance of the new techniques is demonstrated via simulation in channels with various statistics, dimensionality and interference, showing significant improvements in terms of both error resistance and complexity over other proposed methods. / Thesis (PhDTelecommunications)--University of South Australia, 2004.

Thesis (PhD)--University of South Australia, 1999

Bibliography: leaves 181-201. / ix, 201 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis investigates non-binary spread-spectrum multiple-access communications. The research considers wide generation techniques, system performance, how performance is influenced by the different properties of the codes, and how those properties relate to the code generation technqiue. The research refines the code design philosophy and investigates this by developing a novel code generation technique. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1995?

Bibliography: leaves [205]-213 / viii, 214 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1991