Browsing by Subject "Signal processing -- Digital techniques"
Now showing 1 - 20 of 20
Results Per Page
Sort Options
Item A high-resolution charge-redistribution analog-to-digital converter(1985-12) Yung, Henry T.; Chao, Kwong Shu; Gustafson, Donald L.; Anderson, Ronald M.Not AvailableItem A high-speed, high-resolution sigma-delta modulator analog-to-digital converter(Texas Tech University, 2004-05) Fang, LieyiSigma-delta modulators provide the means for achieving high-resolution analog-to- digital conversion. The main limitation faced in the high-resolution Sigma-Delta approach is conversion speed. A multi-stage multi-bit sigma-delta modulator with interstage gain scaling is proposed in this study, and it is designed and implemented in a 0.6 ìm CMOS process. This topology employs a second-order single-bit modulator in the main stage followed by an 8-bit quantizer in pipeline structure. The second stage of the modulator consists of a first-order single-bit modulator followed by a 5-bit quantizer. A gain stage is inserted between the two stages to scale the signal level to within the reference level. System and circuit level simulations have demonstrated that the proposed modulator is capable of achieving high speed and high resolution in analog-to-digital conversion. The detailed design considerations in circuit implementation of the proposed modulator are also analyzed and discussed. The prototype is fabricated in a 0.6 ìm CMOS process with 3.3V power supply. Experimental measurement of the prototype is performed. Several factors limiting the performance are discussed.Item Adaptive image restoration in signal-dependent noise(Texas Tech University, 1982-08) Kasturi, RangacharAn image distribution is modeled as a non-stationary stochastic process. The presence of signal-dependent noise further renders the noisy observation to be spatially nonstationary. As a consequence, spatially adaptive estimators outperform estimators based on global statistics. A number of spatially adaptive Bayesian estimators are derived using (1) maximum a posteriori probability and (2) minimization of mean square error as the optimality criteria. An estimator that compensates for the low pass filtering effects of adaptive estimators is also obtained, as is a simple nonlinear contrast manipulation technique suitable for images corrupted by signal-dependent noise. In addition to the just mentioned point estimators, multiple parameter estimators using several Markovian image covariance models are derived. Estimators for images degraded by Poisson noise are also obtained. Simple transformations that render the noise signal-independent, followed by the application of classical Wiener filtering techniques to restore the degraded images are investigated. Under low signal-to-noise ratio conditions the additional signal information contained in signal-dependent noise is recovered to obtain an estimate from the degraded image. Extensive computer simulations are carried out to evaluate the performances of the estimators on several images corrupted by different types of signal-dependent noise. In addition to the qualitative comparisons of the restored images, quantitative evaluations using several measures of image quality, some of which are based on simple models of the human visual system, are presented.Item An adaptable computing structure for cepstrum caculations(Texas Tech University, 1984-12) Fowler, James McCormickNot availableItem An optimized vector quantization for color image compression(Texas Tech University, 1998-05) Kompella, Sastry V SImage Data compression using vector quantization (VQ) has received a lot of attention in the recent years because of its optimality in rate distortion and adaptability. A fundamental goal of data compression is to reduce the bit rate for transmission or data storage while maintaining an acceptable fidelity or image quality. The combination of subband coding and vector quantization can provide a powerful method for compressing color images. Most of the existing VQ algorithms however suffer from a number of serious problems like long search process, codebook initialization, getting trapped in local minima, etc. This work investigates the development of an image compression algorithm using a variable block size vector quantization technique for generation of optimal codebook by employing a neuro-fuzzy clustering approach to ensure minimum distortion. Each color image is decomposed into R, G, and B color planes prior to application of wavelet transform and vector quantization to each color plane. Each color plane is preprocessed by performing multiresolution wavelet decomposition. The multiresolution nature of the discrete wavelet transform is utilized to decompose the images into more directionally decorrelated sub-images, which are more suitable for quantization and coding. Vector quantization is performed on each of the subimages at different resolutions and a multiresolution codebook scheme is utilized. This new approach to image compression facilitates generation of an improved globally optimal codebook, and a simpler search scheme. Finally, the codebooks generated from the three encoded color planes are entropy coded for obtaining higher compression at minimum distortion. Each color plane codebook is decoded and the reconstructed color planes are combined to form the final reconstructed image. The reconstructed images are compared with those of other standard compression algorithms, in terms of Mean square error (MSE), and Peak signal-to-noise ratio (PSNR).Item Blind source separation of speech signals using filter banks(Texas Tech University, 2002-08) Patterson, Andrew J.The aim of this thesis is to improve the perceived quality of digital hearing aids through the introduction of source segregation algorithms that attenuate undesired speech and noise into the psychoacoustic model of the human ear. It proposes the use of low-delay modulated filter banks to mimic the critical bands of the human ear to accomplish blind source separation. This thesis will cover theory and results for modulated filter banks and blind source separation.Item Cascading of DSP structures to improve performance(Texas Tech University, 1990-05) Chamon, Jorge d. C.Not availableItem Coded and filtered quadrature amplitude modulation signaling(Texas Tech University, 2001-12) Harris, JasonIn this thesis, the performance of several modified digital baseband transmission signals will be evaluated against each other with respect to their bandwidth and error probability characteristics. This is accompHshed via a transmission simulator designed specifically for this purpose. Hybrid signals incorporating a combination of signaling techniques such as Walsh Coding, Pre-filtering, and QAM signaling will be simulated and analyzed with a focus on Walsh Coded Gaussian QAM signals.Item Digital signal processing for seismic inverse problem(Texas Tech University, 1983-05) Yuan, Kai-chih JohnNot availableItem Digital signal processing of multi-echo interference(Texas Tech University, 1981-05) Chiu, Peter Ge-MingNot availableItem Digital signal processing of multi-echo interference for angle modulated signal(Texas Tech University, 1982-08) Jain, Gwo-hannNot availableItem DSP-enhanced vision recognition(Texas Tech University, 1990-12) Sharbutt, Albert CThis thesis addresses the problem of the time involved in performing image recognition or image processing. Digital signal processing chips can be used alone or as additions to existing processors to increase the throughput and versatility of these systems. This thesis does not seek to develop a vision recognition system, but examines several common vision recognition tasks to determine how much improvement could be offered by a digital signal processing chip and how much effort is required to achieve this benefit.Item Efficient realization of biorthoganal [sic] fixed point cosine modulated filter banks(Texas Tech University, 2002-12) Casey, Ryan B.Cosine modulated filter banks are widely researched and used in signal compression because they can provide perfect reconstruction (PR) while maintaining a low computational cost. Their ability to provide PR can be hindered by the device that they are implemented on. Fixed-point digital signal processors require that the filter coefficients be quantized, force resultants to be rounded, and are subject to overflow. All three can lead to reconstruction errors. For the filter bank to preserve its PR properties, its realization structure must be robust to these three sources of error. This structure is then implemented on a fixed-point device, such as a TI C6201 DSP without losing a valuable property. This is validated in this thesis along with showing that the frequency response of the filters is upheld by this structure through the use of Matlab simulations supported by a DSP implementationItem Implementation and comparison of cosine modulated filter banks on a fixed point digital signal processor(Texas Tech University, 2004-05) Bhate, Kedar RavindraCosine Modulated Filter Banks have an efficient structure with respect to the number of multiplication and delay elements required. They also provide another desirable feature, perfect reconstruction (PR). However, their ability to provide PR can be affected due to various parameters, such as fixed-point constraints, imperfect modulation matrix, etc. In this thesis, effects of these parameters on the ability of the filter bank to provide PR are studied. To demonstrate the use of the filter bank in a real- time application, it is implemented using a TMS320C6211 Fixed-point Digital Signal Processor (DSP). The implementation uses the TLC320AD535 audio Encoder/Decoder (CODEC), the Multichannel Buffered Serial Port (McBSP) and the Enhanced Direct Memory Access (EDMA) controller on the DSK6211 board to continuously process and reconstruct digitized audio data.Item Implementation of FFT on a multimicrocomputer system(Texas Tech University, 1982-08) Yen, Yi-Yih WilliamNot availableItem Real time digital signal processing(Texas Tech University, 1982-05) Londono, Luis EduardoNot availableItem Robust image estimation in signal-dependent noise(Texas Tech University, 1983-08) Chen, Sin-horngNot availableItem Sigma-delta modulators with interstage gain scaling(Texas Tech University, 1999-12) Zheng, ZhongqiangThis thesis work describes the efforts made on a new sigma-delta modulator. This unique topology employs an algorithm called interstage gain scaling to depress quantization errors and improve the signal-to-noise ratio (SNR). It consists of two stages: one is a single bit sigma-delta modulator, which is the main stage and the other is a feedback loop stage. At the output of the modulator, the quantization error from the main stage is cancelled while the quantization error from the quantizer in the feedback loop is scaled down by a factor of K. Depending upon the input swing of comparators and operational amplifiers (Opamps) used in the circuits, K can be chosen as 2, 4, 6... For instance, if K is equal to 2, the SNR can be increased by 6 dB or 1 bit compared to the corresponding traditional structure. Successful MATLAB system simulation and PSpice transistor-level simulation in a standard 1.2-um CMOS technology have verified that the proposed sigma-delta modulator is an effective and practicable architecture.Item Simulation of communication time for a space-time adaptive processing algorithm on a parallel embedded system(Texas Tech University, 1998-08) West, Jack M.This thesis involves the investigation of parallelization and performance improvement for a class of radar signal processing techniques known as space-time adaptive processing (STAP). The assumed platform, which consists of multiple DSPs, is the commercially available Mercury RACE System. The main contribution of the thesis is the design and implementation of a network simulator for the RACE system. This simulator allows for the performance of various parallel STAP algorithm implementations to be predicted for existing or future RACE system configurations. A major challenge of implementing parallel STAP algorithms on multiprocessor systems is determining the best method for distributing the 3-D data cube across CEs of the multiprocessor system (i.e., the mapping strategy) and the scheduling of communication within each phase of computation. It is important to understand how mapping and scheduling strategies affect overall performance. The network simulator developed in this thesis is used to evaluate the performance of various mapping and scheduling strategies.Item Speaker independent real-time speech recognition system(Texas Tech University, 1998-08) Jindani, Abid MThis thesis attempts to develop a real-time speaker-independent Automatic Speech Recognition (ASR) system. The system recognizes isolated utterances from a limited vocabulary, and is small and cost-efficient to be incorporated into a consumer appliance. The recognition is based on zero crossings and energy content measurement on the speech waveforms. The algorithm is based on segmenting the speech waveform into ten equally spaced intervals and performing a match with the patterns in a reference template. The system was implemented on an IBM Personal Computer and achieved an error rate of 0% on a vocabulary of four words from an initial ten-word database of 16 speakers (8 male and 8 female). The system recognized unknown utterances in less than 0.3 seconds.