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

In this thesis, we propose a number of distributed schemes for wireless communications in the cross layer design context, considering an uplink random access network in which multiple users communicate with a common base station. In addition, we perform a comprehensive study on a splitting based multiuser selection algorithm which is simple, effective, and scales with the network size. First, we investigate a reservation-type protocol in a channel aware ALOHA system. Various Markovian models are used to describe the system and to capture the temporal correlation of the channel evolution. The average throughput of the system is obtained using the Markov Analysis technique and we show that the reservation protocol can achieve better performance than the original channel-aware ALOHA by reducing the collision probability. Second, for better resource utilization in the Opportunistic Multichannel ALOHA scheme, we propose a simple extension to the transmission policy that exploits the idle channels. Performance analysis shows that, theoretically, the maximum system throughput can be improved by up to 63% in the asymptotic case. Through numerical results, it can be seen that a significant gain is achieved even when the system consists of a small number of users. Third, we consider a splitting based multiuser selection algorithm in a probabilistic view. Asymptotic analysis leads to a functional equation, similar to that encountered in the analysis of the collision resolution algorithm. Subject to some conditions, the solution of the functional equation can be obtained, which provides the approximations for the expected number of slots and the expected number of transmissions required by the algorithm in a large system. These results shed light on open design problems in choosing parameters for the algorithm when considering the delay and the overhead jointly. A typical example is to optimize the parameters that minimize the weighted sum of these measures of interest.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2008. Includes bibliographical references (leaves 67-72). / Distributed wireless sensor networks (DWSNs) are applied in a variety of applications that can enhance the quality of human life or even save lives, such as in fire monitoring, where DWSN microsensors relay the exact location of the fire to water sprinkler actors to automatically extinguish the fire. Batteries are currently the predominant source of energy in DWSNs. one of the key obstacles in the adoption of DWSN technology is the limited lifetime of batteries in microsensors. Recharging or replacing depleted batteries can significantly increase costs in DWSNs. The aim of this study is to address the power challenge in DWSNs by proposing a sixteen-element equiangular spiral rectenna to ahrvest ambient microwave energy to supply indoor DWSNs. The study concludes that this rectenna model has the potential to generate power that enables long periods of operation of the DWSNs without human intervention in the power manageement process, thus reducing maintenance and administration costs. The efficiency of the rectenna model was tested in an anechoic chamber. Efficiency test results indicated that the highest efficiency of 2% for the rectenna model was achieved as 2 GHz for an ambient power of -6 dBm across a 1 K ohm load resistence. The study further concludes that the current rectenna model size of sixteen elements is a limiting factor for the deployment of DWSNs.

Orientador: Paulo Cardieri / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-23T21:03:39Z (GMT). No. of bitstreams: 1 Nardelli_PedroHenriqueJuliano_D.pdf: 1436293 bytes, checksum: cb00e855f5094f65e4ad9f206f58cfd1 (MD5) Previous issue date: 2013 / Resumo: O Resumo poderá ser visualizado no texto completo da tese digital / Abstract: The complete Abstract is available with the full electronic document / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Magister Scientiae - MSc / This thesis proposed and presented technical details of new probabilistic metrics of trust in the links wireless ad hoc networks for unobservable communications. In covert communication networks, only the end nodes are aware of the communication characteristics of the overall path. The most widely used protocols of ad hoc networks was overviewed. The routing protocols of ad hoc networks with trust considerations and select Destination Sequence Routing, a protocol that can be used in distributed ad hoc network settings for path discovery, was also reviewed. It establishes a path through which all packets sent by a source must pass to the destination. The end nodes are responsible for examining the statistics of the received packets and deriving inferences on path feature variations which are used for computing new trust metrics. When a path is judged not trustworthy based on the metrics, the Destination Sequence Routing is informed to undertake a new trusted path discovery between the end points. The thesis added a new feature based on the quality of service parameters of the path to create trust in the links in recognition of attacks. / South Africa

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In recent years, a plethora of wireless applications such as Bluetooth and Ultra-wide band (UWB) radio have emerged. This drastic increase has overly congested the spectrum. So, new networks such as cognitive radios that can solve the spectrum congestion have emerged. But in such networks, interference is introduced at the physical layer. We study and develop an interference model capable of capturing the intrinsic characteristics of the coexistence of such wireless applications. We investigate the effect of interference using device isolation probability or outage probability in presence Rayleigh and Nakagami-m fading at the physical layer and the impact of lognormal shadowing. We assume that the devices are either deterministically placed or randomly distributed according to a Poisson point process. We derive explicit expressions for the isolation probability and outage probability that give insight into how these channel impairments affect communication in these applications. We use computer simulations to validate our analytical results. / by Constantine Mukasa. / Thesis (M.S.C.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

by Chiu Kwok-Yee, Louie Hon-Kuen. / Thesis (M.B.A.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves [97-98]). / ABSTRACT --- p.i / TABLE OF CONTENTS --- p.ii / LIST OF TABLES --- p.v / LIST OF FIGURES --- p.vii / ACKNOWLEDGMENTS --- p.viii / CHAPTER / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 1.1 --- Reason for Study --- p.1 / Chapter 1.2 --- An Overview of the Local Market --- p.2 / Chapter 1.2.1 --- Market Size and Growth --- p.4 / Chapter 1.2.2 --- Market Competitors --- p.6 / Chapter 1.2.3 --- Strategies --- p.8 / Chapter 1.2.3.1 --- Low Price Strategy --- p.3 / Chapter 1.2.3.2 --- Service Differentiation Strategy --- p.9 / Chapter 1.2.3.3 --- Market Development Strategy --- p.11 / Chapter 1.3 --- Research Objectives --- p.13 / Chapter 1.3.1 --- Decision Problems --- p.13 / Chapter 1.3.2 --- Research Problems --- p.13 / Chapter 1.3.3 --- Research Objectives --- p.14 / Chapter 2. --- LITERATURE REVIEW --- p.15 / Chapter 2.1 --- Definition --- p.15 / Chapter 2.2 --- Segmentation Options --- p.15 / Chapter 2.3 --- Advantages of Market Segmentation --- p.17 / Chapter 2.4 --- Prerequisites for a Segmentation Scheme --- p.18 / Chapter 2.5 --- Segmentation Bases --- p.20 / Chapter 2.5.1 --- Geographic Segmentation --- p.20 / Chapter 2.5.2 --- Demographic Segmentation --- p.20 / Chapter 2.5.3 --- Psychographic Segmentation --- p.21 / Chapter 2.5.4 --- Behaviouristic Segmentation --- p.24 / Chapter 3. --- RESEARCH METHODOLOGY --- p.27 / Chapter 3.1 --- Research Design --- p.27 / Chapter 3.2 --- Sampling --- p.27 / Chapter 3.3 --- Data Collection --- p.28 / Chapter 4. --- LIMITATIONS --- p.30 / Chapter 5. --- IDENTIFICATION OF MARKET SEGMENTS FOR PSYCHOGRAPHIC AND BENEFIT SEGMENTATION --- p.32 / Chapter 5.1 --- Psychographic Segmentation --- p.32 / Chapter 5.1.1 --- Factor Analysis --- p.32 / Chapter 5.1.2 --- Cluster Analysis --- p.38 / Chapter 5.2 --- Benefit Segmentation --- p.41 / Chapter 5.2.1 --- Factor Analysis --- p.42 / Chapter 5.2.2 --- Cluster Analysis --- p.45 / Chapter 6. --- INTERPRETATION AND PROFILING OF MARKET SEGMENTS --- p.47 / Chapter 6.1 --- Demographic Segmentation Analysis --- p.47 / Chapter 6.2 --- Usage Segmentation Analysis --- p.52 / Chapter 6.2.1 --- Demographic Profile --- p.52 / Chapter 6.2.2 --- Psychographic Profile --- p.55 / Chapter 6.2.3 --- Media Preference and Product Usage Profile --- p.56 / Chapter 6.2.4 --- Benefit Profile --- p.56 / Chapter 6.2.5 --- Service-Needs Profile --- p.58 / Chapter 6.3 --- Psychographic Segmentation Analysis --- p.61 / Chapter 6.3.1 --- Interpretation of Segments --- p.61 / Chapter 6.3.2 --- Media Preference and Product Usage Profile --- p.69 / Chapter 6.3.3 --- Benefit Profile --- p.71 / Chapter 6.3.4 --- Service-Needs Profile --- p.72 / Chapter 6.4 --- Benefit Segmentation Analysis --- p.76 / Chapter 6.4.1 --- Interpretation of Segments --- p.76 / Chapter 6.4.2 --- Psychographic Profile --- p.81 / Chapter 6.4.3 --- Media Preference and Product Usage Profile --- p.82 / Chapter 6.4.4 --- Service-Needs Profile --- p.83 / Chapter 7. --- IMPLICATIONS FOR MARKETING STRATEGIES --- p.86 / Chapter 7.1 --- Discussion --- p.86 / Chapter 7.1.1 --- General Demographics of Pager Users --- p.86 / Chapter 7.1.2 --- Services Needed by Pager Users --- p.87 / Chapter 7.1.3 --- An Evaluation of the Four Segmentation Bases Usedin the Study --- p.88 / Chapter 7.1.4 --- Similar Segments Identified by Both Usage and Benefit Segmentation --- p.90 / Chapter 7.2 --- Implications for Marketing Strategy --- p.92 / Chapter 7.2.1 --- Target Market --- p.92 / Chapter 7.2.2 --- Product Strategy --- p.92 / Chapter 7.2.3 --- Price Strategy --- p.93 / Chapter 7.2.4 --- Promotional Strategy --- p.94 / Chapter 7.2.5 --- Distribution Strategy --- p.94 / Chapter 8. --- CONCLUSION --- p.95 / BIBLIOGRAPHY / APPENDICES / APPENDIX A Questionnaire (English Version) / APPENDIX B Questionnaire (Chinese Version) / APPENDIX C List of AIO Questions / APPENDIX D Varimax Rotated Component Analysis Factor Matrix / APPENDIX E Psychographic Profile of the Two Usage Segments / APPENDIX F Psychographic Profile of the Six Psychographic Segments / APPENDIX G Demographic Profile of the Six Psychographic Segments / APPENDIX H Demographic Profile of the Two Benefit Segments / APPENDIX I Psychographic Profile of the Two Benefit Segments

The rapid development of the Internet of Things (IoT) and wireless sensor network (WSN) technologies enable easy access and control of a variety forms of information and data from numerous number of smart devices, and give rise to many novel applications and research areas such as smart home, machine type communications, etc. However due to the small sizes, sophisticated environment, and large number of devices in network, it is hard to directly power the devices from grid. Hence the power connectivity remains one of the major issues that needs to be addressed for related IoT applications. Wireless power transfer (WPT) and backscatter communications are provisioned to be prominent solutions to overcome the power connectivity challenge, but they suer strong efficiency limitation which becomes the barrier to universally popularize such technologies. On the other hand, network optimization is also a research focus of such applications which significantly affects the performance of the system due to the high volume of connected devices and different features. In this thesis we propose advanced techniques to overcome the challenges on the low efficiency and network design of the wireless information and power transfer systems. The thesis consists of two parts. In the first part we focus on the power transmitter design which addresses the low efficiency issue associated with backscatter communication and WPT. In Chapter 2, we consider a backscatter RFID system with the multi-antenna reader and propose a blind transmit and receive adaptive beamforming algorithm. The interrogation range and data transmission performance are both investigated under such configuration. In Chapter 3 we study wireless power transfer by the beamspace large-scale MIMO system with lens antenna arrays. We first present the WPT model for the beamspace MIMO which is derived from the spatial MIMO model. By constraining on the number of RF chains in the transmitter, we formulate two WPT optimization problems: the sum power transfer problem and the max-min power transfer problem. For both problems we consider two different transmission schemes, the multi-stream and uni-stream transmissions, and we propose different algorithms to solve both problems in both schemes respectively. In the second part we study the network optimization problems in the WPT and backscatter systems. In Chapter 4, we study the resource allocation problem for a RF-powered network, where the objective is to maximize the total data throughput of all sensors. We break the problem into two subproblems: the sensor battery energy utilization problem and the charging power allocation problem of the central node, which is an RF power transmitter that transmits RF power to the sensors. We analyze and show several key properties of both problems, and then propose computationally efficient algorithms to solve both problems optimally. In Chapter 5, we study the time scheduling problem in RF-powered backscatter communication networks, where all transmitters can operates in either backscattering mode or harvest-then-transmit (HTT) mode. The objective is to decide the operating mode of each transmitter and minimize the total transmission time of the network. We also consider both ideal and realistic transmitters based on different internal power consumption models for HTT transmitters. Under both transmitter models we show several key properties, and propose bisection based algorithms which has low computational complexity that solves the problem optimally. The results are then extended to the massive MIMO regime.