by Yiu-ming Cheung. / "July 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. 98-106). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

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published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

by Wai-kuen Lai. / Thesis (Ph.D.)--Chinese University of Hong kong, 1997. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

by Yeung Wai Leung. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (p. 248-[259]). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

In this thesis, we also investigated various conversion techniques concerning how to improve the performance of multiplierless fast 1-D DCT, and row column 2-D DCT fast algorithms. We have explored a number of choices of conversion techniques having an impact on the performance of multiplierless fast DCT algorithms. Based on our analytical analysis, and experiment results, we have the following findings: (1) a transform based on a reversible inverse generally performs better than a version based on a traditional inverse; (2) a transform with a delayed uniform normalization step can achieve a much better performance; (3) a lifting structure transform can usually achieve better performance than its non-lifting structure version; (4) using an optimized configuration of non-zero digits to approximate the coefficients can help to achieve a much better performance than using a non-optimized configuration. / This thesis proposes effective methods to convert fast DCT algorithms, including 1-D DCT, row column 2-D DCT, and direct 2-D DCT, into their multiplierless versions. The basic conversion techniques used include: (1) to convert any butterfly structures in a DCT algorithm into lifting steps; (2) to use an optimized configuration of non-zero digits to approximate the coefficients so that multiplications can be converted into shift and add operations. We devised an effective algorithm based on the remainder theorem for finding an MSD representation, with minimum wordlength, of any float constant. As the approximation errors of different coefficients often affect the MSE of an approximated fast DCT algorithm differently, we developed an efficient search algorithm for finding an optimized configuration of non-zero digits for approximating each of the coefficients with an appropriate number of non-zero signed digits so that the approximated algorithm could achieve a minimum MSE. / When compared to those multiplierless fast 1-D DCT algorithms developed by others, the multiplierless 1-D DCT fast algorithms developed via our proposed conversion method can achieve similar or better performance in terms of MSE and PSNR. While the published methods were use to approximate only the kernels of the 1-D DCT fast algorithms with butterfly structures, our proposed methods can approximate both the kernels and the normalization steps of any 1-D DCT, row column 2-D DCT, and direct 2-D DCT fast algorithms. / Chan, Kwong Wing Raymond. / "February 2007." / Adviser: Lee Moon Chuen. / Source: Dissertation Abstracts International, Volume: 68-09, Section: B, page: 6172. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 110-117). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

Sensor arrays have been successfully applied to many engineering fields and the theoretical as well as applied aspects of senor array processing have received intensive research interest. Practically, sensor array systems usually suffer from uncertainties such as unknown gains and phases, mutual coupling, and look direction mismatch. In this thesis, problems of direction finding and beamforming in the presence of array uncertainties are addressed, and new algorithms to tackle these problems are developed. In certain applications, senor arrays are only partly calibrated. Hence, the exact responses of some sensors are unknown, which degrades the performance of traditional direction finding techniques. To tackle this problem, a new method for direction finding with partly calibrated uniform linear arrays (ULAs) is proposed. It generalizes the estimation of signal parameters via rotational invariance techniques (ESPRIT) by modeling the imperfection of the ULA as gain and phase uncertainties. For a fully calibrated array, it reduces to the standard ESPRIT algorithm. In this method, the direction-of-arrivals (DOAs), unknown gains and phases of the uncalibrated sensors can be estimated in closed-form without performing spectral grid search. Moreover, it can be further improved by a refining scheme proposed. Its superiority over existing methods is demonstrated by simulation results. Apart from unknown gains and phases, the mutual coupling caused by interactions among sensors also seriously deteriorate the performance of array processing techniques. In ULAs, the mutual coupling matrix (MCM) can be approximated as a banded symmetric Toeplitz matrix. Using this specific property, a new parameterization of the steering vector is proposed and the corresponding method for joint estimation of DOAs and MCM is derived. Compared with the conventional subarray-based method, the proposed one makes use of the whole array and achieves better performance especially for weak signals. On the other hand, the specific property is further employed to develop a new approach to calibrate the steering vector. By incorporating the calibrated steering vector with a diagonally loaded robust beamformer, a new adaptive beamformer for ULAs with mutual coupling is obtained. It is found that the resultant steering vector estimate considerably improves the robustness of the beamformer against mutual coupling. Another common uncertainty in sensor array systems is the look direction mismatch. Though numerous robust beamformers have been developed accordingly, most of them cannot offer sufficient robustness against large look direction errors. To this end, a new robust beamforming method which can flexibly control the magnitude response in the look direction is proposed. By linearizing the nonconvex constraints in the original problem, the resultant problem is convex and can be solved using second-order cone programming (SOCP). Moreover, to further improve the robustness against array covariance uncertainties, this method is extended by optimizing its worst-case performance. Unlike some conventional methods restricted to specific arrays, the proposed method is applicable to arbitrary array geometries. Simulation results show that the proposed method offers comparable performance to the optimal solution for uniform linear arrays, and also achieves good results under different array specifications and geometries. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

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