Browsing by Subject "Signal detection"
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Item An electrocortical model of bimodal vigilance performance.(Texas Tech University, 1975-05) Schiflett, Samuel G.The purpose of this dissertation is to develop a model that is based upon physiological processes that accurately reflect changes in an organism's state that are correlated with different aspects of performance of a vigilance task. The utility of the model will then be assessed by predicting a priori effects on electrocortical activity manipulating independent variables that have well established outcomes on vigilance performance, e.g. signal/nonsignal probability ratios. The model is based primarily on the sensory evoked response averaged fron the electroencephalogram.Item Central perceptual task difficulty on peripheral detection performance(Texas Tech University, 1979-05) Dannhaus, Dale M.People cannot respond to all the stimuli which are present at any given moment. Consequently, we attend to a severely restricted selection of potential information and ignore the remainder. The process of selecting certain information, as opposed to other information impinging on the sensory receptors, has been termed selective attention (Treisman, 1969). When persons are required to perform two or more tasks at the same time, performance on at least one of the tasks usually deteriorates from that observed when the same tasks are performed separately. The results of the investigations in this experimental area served as one of the principal sources of evidence in support of the notion that man is limited in the amount of information he can process per unit of time (Broadbent, 1958; Norman, 1968; Treisman, 1969) Since there is a type of competition between signals for some limited capacity system, tasks which place demands on the central limited capacity tend to interfere with each other (Posner & Boies, 1971). A number of investigations (e.g., Welch, 1898; Welford, 1968) have used this basic idea to measure the attention demands of one task by its interference with a secondary task.Item Driver pre-emphasis for data transmission(Texas Tech University, 2001-05) Casall, John LindleyThe main focus of this thesis is to investigate improvements to data transmission. Data transmission speeds and distances are limited by the amount of jitter in the system, and signal modifications to reduce jitter are simulated. A solution is sought to reduce the amount of system jitter, enabling the increase in the transmitting speed and distance over the cable. Optimizing the pre-emphasis signal is determined by simulation different parameters. In addition, alternative signaling schemes are investigated to compare the effectiveness and find the signal that minimizes jitter.Item Polyspectral signal analysis techniques for interharmonics in shipboard power systems(2008-08) Kim, Taekhyun, 1977-; Powers, Edward J.In this dissertation, we present the theory and application of polyspectral signal analysis techniques for interharmonics in shipboard power systems. Interharmonics are generated from various kinds of adjustable speed drives (ASD) in such power systems. ASDs are highly nonlinear devices due to the use of rectifiers and inverters. Since interharmonics can seriously hamper the normal operation of electric ships in many different ways (e.g., excitation of undesirable electrical and/or mechanical resonances, misoperation of control devices, and light flicker), the detection and analysis of interharmonic-related events is a critical issue in assessing power quality in an all-electric ship. Standard signal analysis techniques for regular harmonics are not immediately applicable to interharmonics due to their small amplitude and uncertain frequency of occurrence. Hence, we propose the use of alternative polyspectral analysis techniques such as higher-order spectra (the cross bispectrum/bicoherence) for the detection and analysis of the ASD-generated interharmonics. First, we develop the interharmonic application specific definitions of the cross bispectrum and the cross bicoherence. The statistical characteristics and frequency domain symmetries are also investigated. We apply the modified cross bispectrum to interharmonic detection problems. Due to their small amplitudes, the detection of interharmonics is sensitive to many undesirable factors such as spectral leakage and measurement error. Our analysis results demonstrate that the detection performance of the conventional DFT-based method is seriously degraded in the presence of noise. Hence, we develop a constant false alarm rate (CFAR) interharmonic detector based on the modified cross bispectrum. Our analysis and experimental results show that our method can provide more robust detection performance than conventional methods in the presence of noise. We also develop an ASD condition monitoring method based on the cross bicoherence. The key idea is to diagnose the status of the load side of an ASD from observations made at the source side. In this dissertation, we apply our method to detection and analysis of phase imbalance at the load side of the ASD. Our experimental results demonstrate that the proposed method provides a unique interharmonic signature for detection and classification of asymmetric impedance associated with the phase imbalance. Furthermore, the proposed method shows a more sensitive detection performance compared to the conventional imbalance measurement method, which enables prognosis of potential faults. A novel quadratic phase coupling detector for a single data record with coherent interharmonics is developed. The traditional bicoherence definition fails when its ’phase randomization’ assumption is not satisfied. This assumption is not appropriate for certain applications such as continuous monitoring of rotating machines. Therefore, we propose a novel quadratic phase coupling detector and compare it with previous techniques. It is shown that our detector is superior to previous detectors at high SNRs, and can also address partially coherent cases which previous approaches could not properly address. Flicker issues related to interharmonics are also discussed. We present a newly found limitation of the current IEC flickermeter regarding detecting flicker caused by low frequency interharmonics. We also present observation results of flicker responses of various lamps including light-emitting-diode (LED) lamps. Our observation results confirm that compact fluorescent and LED lamps are sensitive to high frequency interharmonics, although the IEC flickmeter can not detect flicker caused by such interharmonics. Hence, we develop an alternative flicker detection method based on down-up sampling. Our experiment results show that our method can detect flicker regardless of the value of the interharmonic frequencies. Independent of interharmonic topics, we also present our additional achievement involving application of wavelet denoising techniques to network congestion monitoring problems. This was a collaboration with researchers at the Department of Computer Sciences in the University of Texas at Austin, and mainly completed before becoming engaged in the electric ship project. By applying wavelet techniques, we could drastically enhance shared congestion detection performance over previously proposed methods.Item Signal detection for OFDM systems with transmit diversity(2004) Kim, Jaekwon; Powers, Edward J.Item Task adaptation: an attempt to modify a time dependent attention deficit(Texas Tech University, 1977-05) Bohn, Carole A.NOT AVAILABLEItem Visual target detection performance as a function of similarities between signal and background display characteristics(Texas Tech University, 1974-12) Curran, Patrick M.The relevance of this study to the question of the effect of type of relevant background information on target detection performance is somewhat limited since the background was carefully selected to be entirely irrelevant, even though it has been pointed out that the background was not truly homogeneous. Also only large-scale displays (80 cm to somewhat less than 60 cm diameter) and extreme viewing distances (20 to 68 feet) were examined. What is of considerable interest is the finding that, when the array consisted of 16 figures, increasing exposure time from 12 sec. to 24 sec. resulted in no increase in performance beyond 90 per cent correct recognition.