Trier, Univ., Diplomarb., 2009.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Kartik Gopalan, Florida State University, College of Arts and Sciences, Dept. of Computer Science. Title and description from dissertation home page (viewed June 6, 2006). Document formatted into pages; contains ix, 43 pages. Includes bibliographical references.

Code division multiple access (CDMA) is a well-known radio communication technique that allows multiple users to share the same spectrum simultaneously. It is an alternative to frequency division and time division multiple access scheme. Its numerous advantages have merited being the main air-interface choice for the third generation (3G) mobile communication system. Nevertheless, due to the use of same frequency, the capacity of CDMA air-interface is interference limited. This problem is minimised by use of power control scheme. Power Control reduces the interference in the system by adjusting the transmitted power according to the received Signal-to-Interference (SIR) ratio. The main difficulty to achieve this scheme is that mobile terminals experience different radio propagation channel. For success completion of this task, two objectives have been identified for power control. First assure that the received signal matches the required SIR at physical layer and secondly adjust the required SIR of users at system layer to an acceptable value so that the terminals in the system are capable of achieving. In this thesis both objectives are discussed and analysed through analytical and simulation methods. At physical layer, two analytical methods based on non-linear control theory are proposed to combat the fast fading channel propagation. The proposed methods are a fast solution to assess the performance of the Closed Loop Power Control compared to the usual lengthy simulation process. At system level, a new distributed power algorithm for reverse link that adjusts the SIR target of the mobile terminal at the base station is proposed. This algorithm brings the performance of the distributed algorithm closer to the optimal solution provided by the non-feasible centralised power control algorithm in current technology.

The goal for the third generation (3G) of mobile communications system is to seamlessly integrate a wide variety of communication services such as high-speed data, video and multimedia traffic as well as voice signals for transmission on a Wideband Code Division Multiple Access (WCDMA) air interface. CDMA suffers from interference and in this thesis multiuser detection for the mobile uplink has been considered. A thorough comparative study for different multiuser detection methods is done. RAKE-IC as an architecture for mixing the ideas of RAKE receiver, and parallel Interference Cancellation, are introduced. The basic concept is to maximize the signal to noise ratio of all users in the system by using adaptive algorithms. The structure of RAKE-IC has been extended to multi-stages and several adaptive algorithms are implemented. An iterative method for interference cancellation has been considered and its convergence issue has been analytically studied. An improvement in convergence using the Rayleigh-Ritz theorem is proposed which in consequence increases the convergence speed in synchronous scenarios. Using analytical methods another improvement using the Gershgorin theorem has been proposed which does not impose a great complexity in the system, yet works well even in asynchronous environments. A suboptimum search algorithm for correcting the reliable detected information has been introduced with the property that its structure can be combined well with the iterative detectors. This combination achieves a better performance than partial parallel interference cancellation method even in rather low interference regions of operation. The structure of the sub-optimum search algorithm has been extended to multiple stages and its performance in terms of bit error rate has been analytically derived in closed form that shows good agreement with the simulation results. Considering the power profile of the users and by sacrificing a little performance, the suboptimum search structure has been further simplified. Key words: Multiuser Detection, WCDMA and Interference Cancellation.

Access to Personal Health Information (PHI) is a valuable part of the modern health care model. Timely access to relevant PHI assists care providers in making clinical decisions and ensure that patients receive the highest quality of care. PHI is highly sensitive and unauthorized disclosure of PHI has potential to lead to social, economic, or even physical harm to the patient. Traditional electronic health (eHealth) tools are designed for the needs of care providers and are insufficient for the needs of patients. Our research goal is to investigate the requirements of electronic health care systems which place patient health and privacy above all other concerns. Control of secure resources is a well established area of research in which many techniques such as cryptography, access control, authentication, and organizational policy can be combined to maintain the confidentiality and integrity of data. Access control is the dominant data owner facing privacy control. To better understand this domain we conducted a scoping literature review to rapidly map the key concepts underpinning patient facing access controls in eHealth systems. We present the analysis of that corpus as well as a set of identified requirements. Based on the identified requirements we developed Circle of Health based Access Control (CoHBAC), a patient centered access control model. We then performed a second scoping review to extend our research beyond just access controls, which are insufficient to provide reasonable privacy alone. The second review yielded a larger, more comprehensive, set of sixty five requirements for patient centered privacy systems. We refined CoHBAC into Privacy Centered Access Control (PCAC) to meet the needs of our second set of requirements. Using the conceptual model of accountability that emerged from the reviewed literature we present the identified requirements organized into the Patient Centered Privacy Framework. We applied our framework to the Canadian health care context to demonstrate its applicability. / Graduate

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M.Sc. (Computer Science) / Please refer to full text to view abstract

The initial code acquisition techniques for direct sequence code division multiple access (DS/CDMA) communication networks are investigated in this thesis. Conventional methods of code acquisition, which are basically based on the auto correlation and cross correlation properties of spreading codes, fail in the presence of multiple access interference (MAI) and the near-far effect. This fact motivates the study for interference resistant acquisition algorithms in the hostile channel environment. Training-based acquisition is investigated and the effect of training sequence structure on acquisition performance is discussed. A new training sequence architecture is proposed which results in a shorter acquisition time. Demands for high bit rate services and needs for more efficient exploitation of resources lead to the study of acquisition algorithms that do not need the preamble or training sequences. In this context, blind adaptive algorithms for code acquisition are investigated. The mismatch problem of blind algorithms is addressed and a novel method of mismatch problem handling for Constraint Minimum Output Energy (C-MOE) is proposed. The algorithm results in good acquisition performance under different channel conditions and system loadings. The idea of joint acquisition and demodulation of data, where the outcome of the acquisition mode is an interference suppressor filter, is also discussed. It is shown that in this class of receivers, a one-step constraint acquisition process is not sufficient for handling both the mismatch problem and exploiting the multi-path diversity. Therefore, a novel receiver is proposed which is able to handle the mismatch problem as well as the channel diversity. This receiver is based on a two- step constraint minimum output energy algorithm and comparatively provides a good acquisition and demodulation performance.

M.Com. (Computer Science) / The area covered in this study is that of logical security models. A logical security model refers to the formal representation of a security policy which allows the subsequent movement of rights between subjects and objects in a system. The best way to illustrate the goal of this study, is with the following abstract from the submitted article, which originated from this study. 'The original protection graph rewriting grammar used to simulate the different operations of the Take/Grant model is reviewed. The productions of the PGR-grammar is then expanded, by adding a new context which is based on the different security classes found in the Bell Grid LaPadula model [14].' The first goal of this study was to take the Take/Grant security -model and expand it. This expansion included the concept of assigning a different security class to each subject and object in the model. This concept was derived from the Bell and LaPadula model as discussed in chapter 2 of this study. The next goal that was defined, was to expand the PGR-grammar of [28], so that it would also be able to simulate .the operations of this expanded Take/Grant model. The .PGR-grammar consisted of different permitting and forbidding node and edge contexts. This PGR-grammar was expanded by adding an additional context to the formal representation. This expansion is explained in detail in chapter 5 of this study. The third goal was to take the expansions, mentioned above, and implement them in a computer system. This computer system had to make use of an expert. system in order to reach certain conclusions. Each of the operations of the Take/Grant model must be evaluated, to determine whether that rule can be applied or not. The use of the expert system is explained in chapters 6 and 7 of this study. This study consists out of eight chapters in the following order. Chapter 2 starts of with an introduction of some of the most important logical security models. This chapter gives the reader background knowledge of the different models available, which is essential for the rest of the study. This chapter, however, does not discuss the Take/Grant model in detail. This is done in chapter 3 of the study. In this chapter the Take Grant model is discussed as a major input to this study. The Send Receive model is also discussed as a variation of the Take/Grant model. In the last section of the chapter a comparison is drawn between these two models. Chapter 4 formalizes the Take/Grant model. The protection graph rewriting grammar (PGR-grammar), which is used to simulate the different operations of the Take/Grant model, is introduced...