Strict extensions in pointfree topology

Extensions of spaces have been constructed and used since the 19th century, for example, to form the complex sphere from the complex plane by adding a point at in nity. Once topological spaces were invented in the 20th century, completions and compactications became important examples of extensions. Banaschewski wrote that extension problems have a """"philosophical charm"""" in that they seem to ask the question: """"What possibilities in the unknown are determined by the known?"""" Strict extensions were first defined for topological spaces by Stone. The idea was initially translated into the pointfree setting by Hong, and has since been extensively studied. Just recently, interest has been shown in studying strict extensions in the asymmetric setting of biframes, for example, by Frith and Schauerte. The intention of this dissertation is to provide a systematic and detailed exposition of strict extensions of frames and nearness frames, which can be used as a reference on this topic. For instance, someone interested in pursuing strict extensions of biframes might obtain the relevant background from reading this text, although the topic of strict extensions of biframes itself will not be discussed here

Faculty of Sciences

A comprehensive study of fuzzy rough sets and their application in data reductio

A novel MAC Protocol for Cognitive Radio Networks

In Partial Fulfilment of the Requirements for the Degree Doctor of Philosophy from the University of BedfordshireThe scarcity of bandwidth in the radio spectrum has become more vital since the demand for wireless applications has increased. Most of the spectrum bands have been allocated although many studies have shown that these bands are significantly underutilized most of the time. The problem of unavailability of spectrum bands and the inefficiency in their utilization have been smartly addressed by the cognitive radio (CR) technology which is an opportunistic network that senses the environment, observes the network changes, and then uses knowledge gained from the prior interaction with the network to make intelligent decisions by dynamically adapting transmission characteristics. In this thesis, recent research and survey about the advances in theory and applications of cognitive radio technology has been reviewed. The thesis starts with the essential background on cognitive radio techniques and systems and discusses those characteristics of CR technology, such as standards, applications and challenges that all can help make software radio more personal. It then presents advanced level material by extensively reviewing the work done so far in the area of cognitive radio networks and more specifically in medium access control (MAC) protocol of CR. The list of references will be useful to both researchers and practitioners in this area. Also, it can be adopted as a graduate-level textbook for an advanced course on wireless communication networks. The development of new technologies such as Wi-Fi, cellular phones, Bluetooth, TV broadcasts and satellite has created immense demand for radio spectrum which is a limited natural resource ranging from 30KHz to 300GHz. For every wireless application, some portion of the radio spectrum needs to be purchased, and the Federal Communication Commission (FCC) allocates the spectrum for some fee for such services. This static allocation of the radio spectrum has led to various problems such as saturation in some bands, scarcity, and lack of radio resources to new wireless applications. Most of the frequencies in the radio spectrum have been allocated although many studies have shown that the allocated bands are not being used efficiently. The CR technology is one of the effective solutions to the shortage of spectrum and the inefficiency of its utilization. In this thesis, a detailed investigation on issues related to the protocol design for cognitive radio networks with particular emphasis on the MAC layer is presented. A novel Dynamic and Decentralized and Hybrid MAC (DDH-MAC) protocol that lies between the CR MAC protocol families of globally available common control channel (GCCC) and local control channel (non-GCCC). First, a multi-access channel MAC protocol, which integrates the best features of both GCCC and non-GCCC, is proposed. Second, an enhancement to the protocol is proposed by enabling it to access more than one control channel at the same time. The cognitive users/secondary users (SUs) always have access to one control channel and they can identify and exploit the vacant channels by dynamically switching across the different control channels. Third, rapid and efficient exchange of CR control information has been proposed to reduce delays due to the opportunistic nature of CR. We have calculated the pre-transmission time for CR and investigate how this time can have a significant effect on nodes holding a delay sensitive data. Fourth, an analytical model, including a Markov chain model, has been proposed. This analytical model will rigorously analyse the performance of our proposed DDH-MAC protocol in terms of aggregate throughput, access delay, and spectrum opportunities in both the saturated and non-saturated networks. Fifth, we develop a simulation model for the DDH-MAC protocol using OPNET Modeler and investigate its performance for queuing delays, bit error rates, backoff slots and throughput. It could be observed from both the numerical and simulation results that when compared with existing CR MAC protocols our proposed MAC protocol can significantly improve the spectrum utilization efficiency of wireless networks. Finally, we optimize the performance of our proposed MAC protocol by incorporating multi-level security and making it energy efficient

Doctoral Dissertation Design and Implementation of Linear Logic Programming Languages

to my wife, Megumi iii Acknowledgments I would like to thank Prof. Naoyuki Tamura for his advice, help, patience, and understanding. I would also like to thank Prof. Yuzuru Kakuda who have encourage me to make a great effort since I was an undergraduate student at Kobe University. I would like to thank Prof. Yukio Kaneda and Prof. Toshiyasu Arai for their advice. I would like to thank Prof. Kenichi Aragane, Masaru Teranishi, and Naoshi Kanazawa at Nara National College of Technology for their kindness. I would like to thank Eiji Sugiyama and Kyoung-Sun Kang who had spent pleasant days together at the Graduate School of Science and Technology of Kobe University. I would like to thank Kenichiro Shii who attracted me by his remarkable programming sense. I would like to thank Makoto Kikuchi for his great deal of advice, Christopher Barney for his English support, and CS32 laboratory. I thank my parents Yoshiyuki and Yuko, my younger sister Yoshiko, and my wife Megumi. I could not finish this dissertation without their emotional support. In particular, I thank my grandfather Masayoshi in heaven, who said me you must give up trying to get a Ph.D. Finally, I would also like to thank my friends for sharing interesting times

Contents

I have written this thesis independently, solely based on the literature and tools mentioned in the chapters and the appendix. This document – in the present or a similar form – has not and will not be submitted to any other institution apart from the Karlsruhe University of Applie