Shen, Yuxiu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 61-64). / Abstracts in Chinese and English. / 摘要........Error! Bookmark not defined / Abstract --- p.iii / Acknowledgement --- p.v / Content --- p.viii / List of Figures --- p.xi / List of Tables --- p.xii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background Overview --- p.1 / Chapter 1.2 --- Motivation and Related Work --- p.2 / Chapter 1.3 --- Our Contribution --- p.3 / Chapter 1.4 --- Organization of the Thesis --- p.5 / Chapter Chapter 2 --- Preliminaries --- p.6 / Chapter 2.1 --- TDMA Technology --- p.6 / Chapter 2.1.1 --- Features of TDMA --- p.8 / Chapter 2.2 --- Previous Study on TDMA Link Scheduling --- p.8 / Chapter 2.3 --- Typical Network and Interference Models --- p.10 / Chapter Chapter 3 --- System Model --- p.14 / Chapter 3.1 --- Physical Layer Interference Model --- p.14 / Chapter 3.2 --- Objective of the Problem --- p.15 / Chapter 3.3 --- Rate Matrices for Transmission Sets --- p.17 / Chapter 3.4 --- Airtime Allocation --- p.19 / Chapter Chapter 4 --- Problem Formulation and Its Solution --- p.20 / Chapter 4.1 --- LP Formulation of Optimal TDMA Link Scheduling --- p.21 / Chapter 4.2 --- Solution to the Optimal Air Time Allocation Problem --- p.22 / Chapter 4.3 --- n-length Chain Network --- p.24 / Chapter 4.3.1 --- Adaptive Rate Transmission --- p.25 / Chapter 4.3.2 --- Fixed Rate Transmission --- p.27 / Chapter Chapter 5 --- Bad Transmission Set Removal Algorithm (BTSR) --- p.30 / Chapter 5.1 --- A 7-node Chain Example --- p.30 / Chapter 5.2 --- BTSR Algorithm --- p.32 / Chapter Chapter 6 --- Randomized Decentralized Scheduling Algorithm (RDSA) --- p.35 / Chapter 6.1 --- RDSA Algorithm --- p.35 / Chapter 6.2 --- Pseudo Code of RDSA --- p.37 / Chapter 6.3 --- The Flow Chart of RDSA --- p.39 / Chapter Chapter 7 --- Performance Evaluation --- p.41 / Chapter 7.1 --- Performance of Cross-layer TDMA Link Scheduling --- p.41 / Chapter 7.2 --- Complexity Analysis and Comparisons for BTSR+LP and LP --- p.46 / Chapter 7.2.1 --- Complexity of LP Problem --- p.47 / Chapter 7.2.2 --- Problem Size Reduced by BTSR --- p.48 / Chapter 7.2.3 --- Revised BTSR Algorithm --- p.49 / Chapter 7.2.4 --- The Complexity Issues --- p.51 / Chapter 7.3 --- Performance and Complexity Issues for RDSA --- p.52 / Chapter Chapter 8 --- Conclusion and Future Work --- p.57 / Chapter 8.1 --- Conclusions --- p.57 / Chapter 8.2 --- Future Work --- p.58 / Bibliography

Zero-Correlation-Zone (ZCZ) codes differ from traditional spreading codes because they contain a region in their correlation functions where the correlation values are null. In these regions the spreading codes are considered ideal, and because of the ZCZ the inter-symbol interference (ISI) and multiple-access interference (MAI) are reduced leading to an increase in capacity and bitrate. This thesis will present a study of ZCZ codes and then will propose a new CDMA system that employs the use of ZCZ codes in particular Loosely Synchronous (LS) codes. This new system shall have its performance compared with an equivalent existing CDMA system (IS-95) and the results shall be shown and discussed. In this comparative study the thesis will also present and examine a tracking performance comparison between ZCZ codes and a traditional spreading code such as m-sequences. It is shown that the performance of the new CDMA system employing ZCZ codes outperforms the traditional CDMA system in a multi-user multipath environment. It is also found that based on the study performed there appears to be no advantage in tracking between a ZCZ code and m-sequences however a more comprehensive study in a multi-user environment is still needed before a conclusion on tracking can be made. / Master of Engineering (Hons.)

This study is aimed at solving several important problems relating to power control in CDMA systems. Our focus is on the mobile to basestation (reverse) link. In this study, we propose a new SIR estimator for CDMA systems, using an auxiliary spreading sequence method. The proposed SIR estimator is employed at the basestation to estimate the SIR, which serves as a control parameter in the power control algorithm. The effects of system parameters (step size, power-update rate, feedback delay, SIR measurement error, and command error) on the bit error rate (BER) performance of power control are investigated. Feedback delay is found to be the most critical parameter that causes a serious problem in the loop. To solve this problem, we propose to use a channel prediction technique at the basestation. To further improve the performance of power control, we then propose to use a diversity reception technique using antenna arrays at the basestation. We show that this combination allows solving the problems linked to the use of power control in a real system affected by multiple access interference under fading conditions. / thesis (PhD)--University of South Australia, 2003.

Spread ALOHA has become one of the advanced multiple access techniques promising several advantages over existing conventional and spread spectrum based wireless systems. Spread ALOHA is currently recognised as a simplified wireless multiple access system which provides a higher bandwidth and may accommodate high number of users. This thesis investigates the employment of a unique spreading code in conjunction with Spread ALOHA as opposed to the common method of employing distinct spreading codes for all users on the communication channel. This feature of Spread ALOHA would eliminate the limitation on the number of users imposed by finding sufficient orthogonal spreading codes, and moreover it would simplify the system and reduce the receiver complexity. In this research I have investigated the state of the art on this topic, and I have modelled and simulated a Single Code Spread ALOHA system together with a conventional CDMA ALOHA system in order to analyse and compare the performance of both systems. This study has shown the viability of employing single code in Spread ALOHA systems, and hence eliminating what is considered a limiting factor in other systems such as CDMA. The performance of this proposed system is comparable with that of CDMA; however the selection of suitable PN codes is essential. The parametric study in this work was aimed to find optimum performance criteria for the Spread ALOHA system. all users on the spread spectrum system to have equal average; received power levels. / Master of Engineering (Hons)

This thesis investigates reliable data communication techniques for wireless channels. The problem of data detection at the receiver is considered and several novel detectors and parameter estimators are presented.¶ It is shown that by using a noise-limiting prefilter, with a spectral support at least equal to the signal part of the received signal, and sampling its output at the Nyquist rate, a set of sufficient statistics for maximum likelihood sequence detection (MLSD) is obtained.¶ Observing that the time-variations of the multipaths in a wireless channel are bandlimited, channel taps are closely approximated as polynomials in time. Using this representation, detection techniques for frequency-flat and frequency-selective channels are obtained. The proposed polynomial predictor based sequence detector (PPSD) for frequency-flat channels is similar in structure to the MLSD that employs channel prediction. However, the PPSD uses {\em a priori} known polynomial based predictor taps. It is observed that the PPSD, without any explicit knowledge of the channel autocovariance, performs close to the Innovations based MLSD.¶ New techniques for frequency-selective channel estimation are presented. They are based on a rectangular windowed least squares algorithm, and they employ a polynomial model of the channel taps. A recursive form of the least squares algorithm with orthonormal polynomial basis vectors is developed. Given the appropriate window size and polynomial model order, the proposed method outperforms the conventional least mean squares (LMS) and the exponentially weighted recursive least squares (EW-RLS) algorithms. Novel algorithms are proposed to obtain near optimal window size and polynomial model order.¶ The improved channel estimation techniques developed for frequency-selective channels are incorporated into sliding window and fixed block channel estimators. The sliding window estimator uses received samples over a time window to calculate the channel taps. Every symbol period, the window is moved along another symbol period and a new estimate is calculated. A fixed block estimator uses all received samples to estimate the channel taps throughout a data packet, all at once. In fast fading and at a high signal-to-noise ratio (SNR), both techniques outperform the MLSD receivers which employ the LMS algorithm for channel estimation.¶ An adaptive multiuser detector, optimal in the weighted least squares (WLS) sense, is derived for direct sequence code division multiple access (DS-CDMA) systems. In a multicellular configuration, this detector jointly detects the users within the cell of interest, while suppressing the intercell interferers in a WLS sense. In the absence of intercell interferers, the detector reduces to the well-known multiuser MLSD structure that employs a bank of matched filters. The relationship between the proposed detector and a centralized decision feedback detector is derived. The effects of narrowband interference are investigated and compared with the multiuser MLSD.¶ Since in a fast time-varying channel, the LMS or the EW-RLS algorithms cannot track the channel variations effectively, the receiver structures proposed for single user communications are extended to multiuser DS-CDMA systems. The fractionally-chip-spaced channel taps of the convolution of the chip waveform with the multipath channel are estimated. Linear equalizer, decision feedback equalizer and MLSDs are studied, and under fast fading, as the SNR increases, they are found to outperform the LMS based adaptive minimum mean squared error (MMSE) linear receivers.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed Dec. 5, 2007). PDF text: xvi, 142 p. : ill. ; 5 Mb. UMI publication number: AAT 3273188. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Frequency reuse scheme is used to enhance the spectral efficiency in a cellular system, but inevitably the system suffers from co-channel interference of other users. Signal-to-interference ratio (SIR) is often used as a quality index of communication links. Several wireless communication algorithms, such as channel assignment, handover and power control, need real-time SIR information. All of these algorithms are under the assumptions that real-time SIR is available, but the methods of obtaining real-time SIR are seldom mentioned with these algorithms. In this thesis, we investigate three simple SIR estimation methods including statistics of spreading chips method, decorrelation detection method, and orthogonal stochastic approximation method. The performance of these SIR estimation methods are evaluated by computer simulations in a WCDMA system.

Smart antenna, which weights are obtained by Wiener solution, would suppress some undesired interference signals in spatial domain. The other interference signals that cannot be suppressed by smart antenna or caused by near-far effect will be post-processed by multiuser detectors. In the proposed algorithm, the cross-correlation matrix of desired signal and received signal from smart antenna algorithm would be applied to multiuser detector to reduce the complexity. From computer simulation results, the proposed algorithm has lower complexity and better BER performance than separate smart antenna or multiuser detection algorithms. Detail derivations of complexity and BER performance are also provided in this thesis.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2003. / Thesis advisor(s): Tri T. Ha, Jovan Lebaric. Includes bibliographical references (p. 77-78). Also available online.