The spectacular growth in wireless services imposes scarcity in term of the available radio spectrum. A solution to overcome this scarcity is to adopt what so called cognitive radio based on dynamic spectrum access. With dynamic spectrum access, secondary (unlicensed) users can access  spectrum owned by primary (licensed) users when it is temporally and/or geographically unused. This unused spectrum is termed as spectrum opportunity. Finding these spectrum opportunities related aspects are studied in this thesis where two approaches of finding spectrum opportunities, namely spectrum sensing and geo-locations databases are considered. In spectrum sensing arena, two topics are covered, blind spectrum sensing and sensing time and periodic sensing interval optimization. For blind spectrum sensing, a spectrum scanner based on maximum minimum eigenvalues detector and frequency domain rectangular filtering is developed. The measurements show that the proposed scanner outperforms the energy detector scanner in terms of the probability of detection. Continuing in blind spectrum sensing, a novel blind spectrum sensing technique based on discriminant analysis called spectrum discriminator has been developed in this thesis. Spectrum discriminator has been further developed to peel off multiple primary users with different transmission power from a wideband sensed spectrum. The spectrum discriminator performance is measured and compared with the maximum minimum eigenvalues detector in terms of the probability of false alarm, the probability of detection and the sensing time. For sensing time and periodic sensing interval optimization, a new approach that aims at maximizing the probability of right detection, the transmission efficiency and the captured opportunities is proposed and simulated. The proposed approach optimizes the sensing time and the periodic sensing interval iteratively. Additionally, the periodic sensing intervals for multiple channels are optimized to achieve as low sensing overhead and unexplored opportunities as possible for a multi channels system. The thesis considers radar bands and TV broadcasting bands to adopt geo-locations databases for spectrum opportunities. For radar bands, the possibility of spectrum sharing with secondary users in L, S and C bands is investigated. The simulation results show that band sharing is possible with more spectrum opportunities offered by C band than S and L band which comes as the least one. For the TV broadcasting bands, the thesis treats the power assignment for secondary users operate in Gävle area, Sweden. Furthermore, the interference that the TV transmitter would cause to the secondary users is measured in different locations in the same area. / <p>QC 20130114</p> / QUASAR

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The power industry is currently in the process of re-inventing itself. The unbundling of the traditional monopolistic structure that gave birth to a deregulated electricity market, the mass tendency towards a greener use of energy, the new emphasis on distributed generation and alternative renewable resources, and new emerging technologies have revolutionized the century old industry. Recent blackouts offer testimonies of the crucial role played by protection relays in a reliable power system. It is argued that embracing the paradigm shift of adaptive protection is a fundamental step towards a reliable power grid. The adaptive philosophy of protection systems acknowledges that relays may change their characteristics in order to tailor their operation to prevailing system conditions. The purpose of this dissertation is to present methodology to implement a security/dependability adaptive protection scheme. It is argued that the likelihood of hidden failures and potential cascading events can be significantly reduced by adjusting the security/dependability balance of protection systems to better suit prevailing system conditions. The proposed methodology is based on Wide Area Measurements (WAMs) obtained with the aid of Phasor Measurement Units (PMUs). A Data Mining algorithm known as Decision Trees is used to classify the power system state and to predict the optimal security/dependability bias of a critical protection scheme. / Ph. D.

Traditional methods for predicting transient stability of power systems such as the direct method, the time domain approach, and the energy function methods do not work well for online transient stability predictions problems. With the advent of Phasor Measurement Units (PMUs) in power systems, it is now possible to monitor the behavior of the system in real time and provide important information for transient stability assessment and enhancement. Techniques such as the rotor oscillation prediction method based on time series have made the prediction of system stability possible for real-time applications. However, methods of this type require more than 300 milliseconds after the start of a transient event to make reliable predictions. The dissertation provides an alternate prediction method for transient stability by taking advantage of the available PMUs data. It predicts transient stability using apparent impedance trajectories obtained from PMUs, decision trees, and FLDSD method. This method enables to find out the strategic locations for PMUs installation in the power system to rapidly predict transient stability. From the simulations performed, it is realized that system stability can be predicted in approximately 200 milliseconds (12 cycles). The main advantage of this method is its simplicity as the PMUs can record the apparent impedance trajectories in real-time without any previous calculations. Moreover, using decision trees built in CART, transient stability prediction becomes straightforward and computationally very fast. The optimum locations for PMUs placement can also be determined using this technique. After the transient instability prediction by the apparent impedance trajectories, a slow- coherency based intelligent controlled islanding scheme is also developed to restore the stability of system. It enables the generators in the same island to stay in synchronism and the imbalance between the generators and load demand is minimized. / Ph. D.

Yes / Purpose: Inter-individual variance in optic nerve head (ONH) position, axial length and location of the temporal raphe suggest that customizing mapping between visual field locations and optic nerve head sectors for individuals may be clinically useful. Here we quantify the proportion of the population predicted to have structure-function mappings that markedly deviate from “average”, and thus would benefit from customized mapping. Design: Database study and case report Participants: Population database of 2836 eyes from the Beijing Eye Study; single case report of an individual with primary open angle glaucoma Methods: Using the morphometric fundus data of the Beijing Eye Study on 2836 eyes and applying a recently developed model based on axial length and ONH position relative to the fovea, we determined for each measurement location in the 24-2 Humphrey visual field the proportion of eyes for which, in the customized approach as compared to the generalized approach, the mapped ONH sector was shifted into a different sector. We determined the proportion of eyes for which the mapped ONH location was shifted by 15°, 30° or 60°. Main outcome measures: Mapping correspondence between locations in visual field space to localized sectors on the optic nerve head Results: The largest inter-individual differences in mapping are in the nasal step region where the same visual field location can map to either the superior or inferior ONH depending on other anatomical features. For these visual field locations, approximately 12% of eyes showed a mapping opposite to conventional expectations. Conclusions: Anatomically customised mapping shifts the map markedly in approximately 12% of the general population in the nasal step region where visual field locations can map to the opposite pole of the ONH than conventionally considered. Early glaucomatous damage commonly affects this region, hence individually matching structure to function may prove clinically useful for the diagnosis and monitoring of progression within individuals. / Australian Research Council Linkage Project 130100055 (industry partner, Heidelberg Engineering, GmBH, Germany).

Multifunktionella aspekter och flerdimensionella problem öppnar upp för användandet av geografiska informationssystem (GIS) vid beslutsfattande. Ett användningsområde i GIS är möjligheten att ta fram lämpliga områden, det innebär områden där flera lämpliga aspekter stämmer överens med varandra. Denna typ av lämplighetsanalys påverkas i hög grad av författaren samt beroende på analysmetod vilket i sin tur påverkar beslutsfattande. Denna studie syftar till att undersöka hur de val författaren gör påverkar metoden samt vilka konsekvenser det får för beslutsprocessen. Utifrån tidigare forskning har två analysmetoder identifierats, Analytic Hierarchy Process (AHP) och Weighted Linear Combination (WLC). För att kunna jämföra de två metoderna tar studien stöd i en exempelstudie från Linköpings tätort. Utifrån denna studie går det att se att författaren påverkar resultatet av kriterier och viktning men där det skiljer sig olika mycket mellan de två analysmetoderna AHP och WLC. AHP och WLC har både styrkor och svagheter som gör dem lämpliga för denna sorts studie. / Multifunctional aspects and multidimensional problems open up the use of geographic information systems (GIS) in decision-making. One area of ​​use in GIS is the site selection, the site selection combines areas with several suitable aspects. This type of suitability analysis is greatly influenced by the author and depending on the analysis method, which in turn affects decision-making. This study aims to investigate how the choices the author makes affect the method and what consequences it has for the decision-making process. Based on previous research, two analysis methods have been identified, Analytic Hierarchy Process (AHP) and Weighted Linear Combination (WLC). In order to compare the two methods, the study is supported by an example study from Linköping City. Based on this study, it can be seen that the author influences the results of criteria and weighting. However the two analysis methods AHP and WLC affect the study in different ways. AHP and WLC both have strengths and weaknesses that make them suitable for site selection studies.

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