Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaf 92-96).

Thesis (M. Phil.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 58-63).

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves vi-vii, 122-131).

Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 67-73).

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 47-51).

Thesis (M.Phil.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 116-121) Also available in print.

Thesis (M. Eng.)--Carleton University, 2001. / Includes bibliographical references (p. 86-91). Also available in electronic format on the Internet.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009. / Full text also available. Scroll down for electronic link.

In this dissertation, three multiuser detectors are developed for different application scenarios in direct-sequence code-division multiple access systems. The first detector is an overlapping widow decorrelating detector aimed at asynchronous reverse links. In companion with the design of this detector, a study on the decay property of the ideal decorrelating impulse response is presented, resulting in a quantitative description of the decay rate as a function of the Cholesky factors of the cross-correlation matrix of user signature signals. This result can serve as a guide for determining window length of decorrelating or minimum mean-squared error multiuser detection in asynchronous multiuser systems. Based on this result, a signal-adapted window-length determination algorithm is developed for the proposed detector. Several supporting utilities for efficient implementation of the proposed detector are also described. The second detector is a linear multiuser detector that is also aimed at the reverse links. Particularly, it is desirable for cases where the number of users is small and, thus, significant performance gain over the existing linear multiuser detectors is possible. Unlike in the decorrelating and MMSE detectors, minimizing the bit-error rate is taken as the optimization objective in the proposed detector. To avoid undesired local minima of the highly nonlinear BER cost function, a set of convex constraints is proposed for the optimization problem. It is shown that this constrained optimization problem has a unique solution once the decorrelating detector exists. It is also shown that the proposed detector achieves the best performance among linear detectors for most realistic situations. In addition, a Newton barrier method is developed for efficiently calculating the coefficient vector of the proposed detector (i.e., the solution of the constrained optimization problem). The third detector is an adaptive detector that is aimed at the forward link where information about interfering users is often unavailable. The proposed detector consists of a bank of blind adaptive filters, one for each resolvable path, followed by a channel estimator and a coherent diversity combiner. To allow blind adaptation, the impulse response of each filter is decomposed into two orthogonal parts: one part is fixed as the decorrelating coefficient vector for the path in the absence of interfering users and the other is free to be adapted according to the mean-squared error criterion. Assuming perfect adaptation, the performance of the proposed detector is shown to be between those of the decorrelating detector and the minimum mean-squared error detector. Other studies conducted include the effects of fading on the performance of the proposed detector and the behavior of the proposed blind adaptation algorithm. / Graduate

The initial code Acquisition Techniques of Direct Sequence Spread Spectrum Systems for two categories of serial and parallel search strategies is investigated. A simple and economic scheme for coarse code acquisition of Reverse Link for UMTS (FDD-WCDMA) application is presented. The emphasis is on the performance of a new scheme (using a Surface Acoustic Wave Matched Filter) as a term of probability of false detection (pf) in code division multiple access (CDMA) systems. Knowledge of initial code uncertainty phases help to reduce the overhead of preamble on the access channel and a very simple scheme for acquisition to be determined. In the reverse link this uncertainty is due to the cell radius only. Acquisition time required for a simple serial search scheme may therefore be unacceptably large. On the other hand, for parallel acquisition using parallel branches in accordance with the chip uncertainty time region leads to a lot of hardware complexity. Initially, the effect of multiple access interference and spreading sequence length are determined for models applicable to the reverse link of a mobile communications system. Then the acquisition performance is derived using a model of a cellular mobile communication channel, which includes the effects of multiple access interference, adjacent cell interference, frequency selective Rician channel, shadowing, power control error, and vehicle speed. It is shown that the most significant factors in determining the acquisition performance are the acquisition observation interval, the number of users, and the specular to diffuse power ratio. Numerical results based on analysis of acquisition performance in mobile channel show that the proposed acquisition scheme is efficient, robust, fast and suitable for real time low cost implementation.