Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 137-143). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 189-194). Also available on the Internet.

Not available / text

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

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

This dissertation presents interference cancellation techniques for both the Forward Error Correction (FEC) coded and the uncoded Direct Sequence Code Division Multiple Access (DS-CDMA) systems. Analytical models are also developed for the adaptive and the non-adaptive Parallel Interference Cancellation (PlC) receivers. Results that are obtained from the computer simulations of the PlC receiver types confirm the accuracy of the analytical models that are developed. Results show that the Least Mean Square (LMS) algorithm based adaptive PlC receivers have bit error rate performances that are better than those of the non-adaptive PlC receivers. In the second part of this dissertation, a novel iterative multiuser detector for the Turbo coded DS-CDMA system is developed. The performance of the proposed receiver in the multirate CDMA system is also investigated. The developed receiver is found to have an error rate performance that is very close to the single user limit after a few numbers of iterations. The receiver is also resilient against the near-far effect. A methodology is also presented on the use of the Gaussian approximation method in the convergence analysis of iterative interference cancellation receivers for turbo coded DS-CDMA systems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2004.

This dissertation presents interference cancellation techniques for both the Forward Error Correction (FEC) coded and the uncoded Direct Sequence Code Division Multiple Access (DS-CDMA) systems. Analytical models are also developed for the adaptive and the non-adaptive Parallel Interference Cancellation (PlC) receivers. Results that are obtained from the computer simulations of the PlC receiver types confirm the accuracy of the analytical models that are developed. Results show that the Least Mean Square (LMS) algorithm based adaptive PlC receivers have bit error rate performances that are better than those of the non-adaptive PlC receivers. In the second part of this dissertation, a novel iterative multiuser detector for the Turbo coded DS-CDMA system is developed. The performance of the proposed receiver in the multirate CDMA system is also investigated. The developed receiver is found to have an error rate performance that is very close to the single user limit after a few numbers of iterations. The receiver is also resilient against the near-far effect. A methodology is also presented on the use of the Gaussian approximation method in the convergence analysis of iterative interference cancellation receivers for turbo coded DS-CDMA systems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2004.

Wireless cellular communications is witnessing a rapid growth in, and demand for, improved technology and range of information types and services. Future third generation cellular networks are expected to provide mobile users with ubiquitous wireless access to a global backbone architecture that carries a wide variety of electronic services. This thesis examines the topic of multiple access protocols and models suitable for modem third-generation wireless networks. The major part of this thesis is based on a proposed Medium Access Control (MAC) protocol for a Code Division Multiple Access (CDMA) data packet radio network, as CDMA technology is proving to be a promising and attractive approach for spectrally efficient, economical and high quality digital communications wireless networks. The proposed MAC policy considers a novel dual CDMA threshold model based on the Multiple Access Interference (MAl) capacity of the system. This protocol is then extended to accommodate a mixed voice/data traffic network in which variable length data messages share a common CDMA channel with voice users, and where the voice activity factor of human speech is exploited to improve the data network performance. For the protocol evaluation, the expected voice call blocking probability, expected data throughput and expected data message delay are considered, for both a perfect channel and a correlated Rayleigh fading channel. In particular, it is shown that a significant performance enhancement can be made over existing admission policies through the implementation of a novel, dynamic, load-dependent blocking threshold in conjunction with a fixed CDMA multiple access threshold that is based on the maximum acceptable level of MAl. / Thesis (Ph.D.)-University of Natal, Durban, 1999.

Third generation cellular communication systems based on CDMA techniques have shown great scope for improvement in system capacity. Over the last decade, there has been significant interest in DS-CDMA detectors. The conventional detector, the optimal detector and a number of sub-optimal multi-user detectors (MUD) have been extensively analyzed in the literature. Recently, the reduction of power consumption in DS-CDMA systems has also become another important consideration in both system design and in implementation. In order to support wireless multimedia services, all CDMA-based systems for third generation systems have a large bandwidth and a high data rate, therefore the power consumed by the digital signal processor (DSP) is high. This thesis focuses on power consumption in the adaptive Minimum Mean Square Error (MMSE) detector which is based on the Least Mean Square (LMS) algorithm. This thesis presents a literature survey on MUD and adaptive filter algorithms. A system model of the quantized LMS-MMSE MUD is proposed and its performance is analyzed. The quantization effects in the finite precision LMS-MMSE adaptive MUD including the steady-state weight covariance, mean square error (MSE) and bit error rate (BER) versus wordlength of data and coefficient are investigated when both the data and filter coefficients are quantized. The effects of wordlength size on power consumption are investigated and the tradeoff between the power consumption and performance degradation and the optimal allocation of bits to data and to LMS coefficients under power constraint is presented. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

Third generation wireless systems have adopted Direct-Sequence/Code-Division Multiple-Access (DS/CDMA) as the multiple access scheme of communication. This system would typically operate in a multipath fading channel. This dissertation only deals with the task of channel estimation at the base station where the multipath delays and attenuations for each user are estimated. This information is used to aid the recovery of data that was transmitted by each user. Subspace-based algorithms are popularly used to perform the task of channel estimation because they have the desirable property of perfectly estimating the channel in a noise-free environment. In this dissertation a new subspace-based channel estimation algorithm for DS/CDMA systems is presented. The proposed algorithm is based on the Parametric Subspace algorithm by Perros-Meilhac et al. for single-user systems. The main focus of this dissertation is to convert the Parametric Subspace algorithm from a single-user system to a multi-user DS/CDMA system. It has been shown in the literature that by using information of the pulse-shaping filter in the Channel Subspace algorithm, the variance of the channel estimates is decreased. However, this has only been applied to a single-user system. There are several subspace algorithms that have been proposed for DS/CDMA systems. Most of these algorithms sample the received signal at the chip rate, making it impossible to exploit knowledge of the pulse-shaping filter in the channel estimation algorithm. In this dissertation a new subspace-based channel estimation algorithm is derived for a DS/CDMA system with multiple receive antennas, where the output is oversampled with respect to the chip rate. By oversampling the received signal, knowledge of the pulse-shaping filter is used in the channel estimation algorithm. It is shown that the variance of the channel estimate for the proposed subspace algorithm is less than the Torlak/Xu subspace algorithm that does not exploit information of the pulse-shaping filter. A mathematical expression of the mean square error of estimation for the new algorithm is also derived. It was shown that the analytic expression provides a good approximation of the actual MSE for high SNR. The Parametric Subspace Delay Estimation (PSDE) algorithm was developed by Perros-Meilhac et al. to estimate the multipath delays introduced by the communications channel. The limitation of the PSDE algorithm is that the performance of the algorithm deteriorates as the power of the multipath signals decrease with increasing delay time. This dissertation proposes a modified version of the PSDE algorithm, called the Modified Parametric Subspace Delay Estimation (MPSDE) algorithm, which performs better than the PSDE algorithm in an environment where the power of the multipath signals varies. The final part of this dissertation discusses the Torlak/Xu channel estimation algorithm and the Bensley/Aazbang delay estimation algorithm. In order to compare the performance of these two subspace algorithms, the Torlak/Xu algorithm is converted to a delay estimation algorithm that is called the Parametric TX algorithm. The performance of the Bensley/Aazbang delay estimation algorithm and the proposed Parametric TX algorithm are compared and it is shown that the Parametric TX algorithm offers the better performance. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.