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Yayın Cooperative strategies, achievable rates and resource allocation for OFDMA channels(Işık Üniversitesi, 2011-07-28) Bakım, İsmail Sezi; Kaya, Onur; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Doktora ProgramıThe design of next generation wireless communication systems brings along new challenges, since the degrading factors such as fading and multi-user interference become harder to deal with as the number of users and the bandwidth require- ments increase. Orthogonal Frequency Division Multiple Access (OFDMA) is a multiple accessing technique which provides a solution to both of the problems above: it provides a relatively simple way of assigning available bandwidth to users, while avoiding interference; and at the same time, it converts a frequency selective fading channel, to parallel flat fading subchannels, hence reducing the effects of intersymbol interference. However, in wireless channels, what is tradi- tionally considered as interference is in fact side information, and combined with the diversity created by the orthogonal subchannels in OFDMA, this side infor»mation can be carefully taken advantage of to increase the rates achievable by the users. In our thesis, without imposing any prior constraints on subchannel allocation, we investigate cooperation strategies, achievable rates and resource allocation for OFDMA channels. We propose new cooperative encoding strategies for wireless communication net- works över OFDMA channels. We particularly focus on a two user cooperative OFDMA system, based on block Markov superposition encoding (BMSE). We obtain expressions of the resulting achievable rate regions for ali proposed coroperative encoding strategies. We show that, by allowing for re-partitioning and re-encoding of the cooperative messages across subchannels, it is possible to better exploit the diversity created by OFDMA, and higher rates can be achieved. In order to take full advantage of the diversity created by OFDMA, we then introduce a channel adaptive cooperation strategy for OFDMA, and optimize the transmit powers as a function of the channel states. We provide the optimality conditions that need to be satisfied by the powers associated with the users' codewords and derive the closed form expressions for the optimal powers.Yayın Positive solutions for a sum-type singular fractional integro-differential equation with m-point boundary conditions(Politechnica University of Bucharest, 2017) Aydoğan, Seher Melike; Nazemi, Sayyedeh Zahra; Rezapour, ShahramWe study the existence and uniqueness of positive solutions for a sum-type singular fractional integro-differential equation with m-point boundary condition. Also, we provide an example to illustrate our main result.Yayın EOQ model with transportation cost under deterministic demand(Işık Üniversitesi, 2012-12-24) Kars, Cihan; Altunbay, Seyhun; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Endüstri Mühendisliği - Yöneylem Araştırması Yüksek Lisans ProgramıInventory planning issues are one of the most important aspects of the companies. To have optimal stock level both for production planning and low stock holding cost with successful demand forecast is also very important. If the companies work with high stock level, it causes the increase of the unused capital and it hinders to use the money for more effective operations. In global world, the companies purchase goods, semi-finished goods or materials from different regions of the world. They purchase the goods with variable quantities from different regions and directly affect the stock level of the companies. Furthermore it is essential to take transportation cost into account with the consumption quantity of material and the purchase price of unit material while determining inventory stock levels. There are also different payment options in purchasing of materials. The cash payment or the payment after receiving goods have also role in determining stock levels. When we take into account the transportation options and the payment options of purchasing materials the classical economic order quantity model is inadequate. The aim of this thesis is to have a new approach of economic order quantity model by considering the transportation cost and different payment options when we have deterministic demand. By the calculation of all possible transportation and payment alternatives, it becomes possible to find the optimum options of transportation and payment. The new model was implemented for a specific material of company X, for deterministic demand and the aim is to have optimal stock level for the specific material. The program MINITAB is used to find the appropriate method among different forecasting methods. The consumption of specific materials is evaluated and a sample group is composed to implement the new model. The all possible transportation modes, transportation durations and the historical demand data of 2010 and 2011 are collected and analyzed. Demand forecasting methods are applied on historical demand data and the results are accepted as deterministic and transportation modes and times are investigated in excel and used in problem. The process of the model is shown for the material WTR910R and the results are compared with the old system of company X.Yayın Evolving strategies for web crawler(Işık Üniversitesi, 2009-05-06) Küçük, Kamil; Perdahçı, Nazım Ziya; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Enformasyon Teknolojileri Yüksek Lisans ProgramıWith the rapid growth of Internet and Internet-based information, it becomes the largest and publicly accessible data source in the world. Every day millions of information available so to achieve information becomes harder. To get the correct information trusted web sites and search engines are used. Trusted web sites have links between themselves, and users can reach correct and relevant information. Search engines are using crawler to follow links between pages. The context available to such crawlers can guide the navigation of links with the goal of efficiently locating highly relevant target pages. Crawler takes seed pages from search engines and follows these links using multi-agents. After first search, the results are inserted to database and they are used for seed pages for another search. The aim is the get access more reliable information using more seed pages in a short time.Yayın Author identification of newspaper columns using style and semantic features(Işık Üniversitesi, 2016-05-17) Yıldız, Ergin Doğan; Solak, Ercan; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Bilgisayar Mühendisliği Yüksek Lisans ProgramıThis study has two major purposes : to implement and compare the author classification results of di erent Naive Bayes Classi ers, and to investigate whether merging individual methods will increase classi cation success or not. The subjects of this study were newspaper columnists. Data was collected from well known public newspapers. This study first investigates Numeric, Nominal, Multinominal NBC, and their various merged versions. We then address each method using cross-validation. The results of the experiments show that merging multiple classi cation methods can increase classifi cation success. Additionally, it depends on how well individual classifi cation models are constructed.Yayın An inverse source problem connected thermoacoustic imaging in multi-layer planar medium(Işık Üniversitesi, 2018-06-04) Yücel, Hazel; Uzun, Banu; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Matematik Doktora ProgramıIn this thesis, we mentioned imaging technics used today, and microwave induced thermoacoustic procedure and imaging. We made literature survey about solution of the thermoacoustic equation for homogeneous and inhomogeneous medium. We modelled the inhomogenity of medium as a multi-layer planar structure and de?ned initial condition, continuity conditions on the layer boundaries and radiation conditions at in?nity, then we derived analytical forward and inverse solution of the thermoacoustic wave equation for inhomogeneous medium with the source distribution existing in all layers. Our solution of inverse source problem is based on the methods of the Green’s functions for layered planar media. For qualitative testing and comparison of the point-spread functions associated with the conventional solution for homogeneous medium and our derived layered solutions, we performed numerical simulations. In numerical simulations ?rst we generated the measured data by using the derived forward solution for multi-layer planar medium and then we used conventional inverse solution and our derived inverse solution to image source distribution. Our simulation results showed that the conventional inverse solution based on homogeneous medium assumption, as expected, produced incorrect locations of point sources, whereas our inverse solution involving the multi-layer planar medium produced point sources at the correct source locations. Also, we showed that the performance of layered inverse solution is sensitive to the validity of the layer parameters and medium parameters used as prior information in the measured data. Our inverse solutions based on multi-layer planar media are applicable for cross-sectional 2 dimensional imaging of the organs such as breast, skin, and abdominal structure.Yayın Cluster based sensors scheduling in a target tracking application with particle filter method(Işık Üniversitesi, 2006) Özfidan, Özgür; Bayazıt, Uluğ; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Yüksek Lisans ProgramıIn multisensor applications, management of sensors is neccessary for the classification of data they produce and for the efficient use of sensors as well. One of the most important aspects in sensor management is the sensor scheduling. By scheduling the sensors, serious redictions can be achieved in the cost of bandwith, power and computation. In this thesis, a simple solution for the problem of sensor scheduling in a multi-sensor target tracking application is presented. Proposed method is called sensor grouping. Due to non-linearity and non-gaussianity of the problem itself, proposed solution is presented in the framework of non-linear Bayesian Estimation. For this purpose a detailedtheoretical background of the theory of Bayesian Tracking and Particle Filtering algorithm is given.Yayın Asymptotic solutions of love wave propagation in a covered half-space with inhomogeneous initial stresses G(3)(1)(Işık University Press, 2015) Hasanoğlu, Elman; Negin, MasoudThe dispersive behavior of Love waves in an elastic half-space substrate covered by an elastic layer under the effect of inhomogeneous initial stresses has been investigated. Classical linearized theory of elastic waves in initially stressed bodies for small deformations is used and the well-known WKB high-frequency asymptotic technique is applied for the theoretical derivations. Numerical results on the action of the influence of the initial stresses on the wave propagation velocity for a geophysical example are presented and discussed.Yayın A global optimal control methodology and its application to a mobile robot model(Elsevier B.V., 2016) Dinçmen, ErkinA global optimal control algorithm is developed and applied to an omni-directional mobile robot model. The aim is to search and find the most intense signal source among other signal sources in the operation region of the robot. In other words, the control problem is to find the global extremum point when there are local extremas. The locations of the signal sources are unknown and it is assumed that the signal magnitudes are maximum at the sources and their magnitudes are decreasing away from the sources. The distribution characteristics of the signals are unknown, i.e. the gradients of the signal distribution functions are unknown. The control algorithm also doesn't need any position measurement of the robot itself. Only the signal magnitude should be measured via a sensor mounted on the robot. The simulation study shows the performance of the controller.Yayın Factors encouraging and hindering a wider acceptance and more frequent utilization of mobile payment systems an empirical study among mobile phone subscribers in Turkey(Işık Üniversitesi, 2021-06-21) Coşkun, Ertan; Ferman, Murat; Işık Üniversitesi, Sosyal Bilimler Enstitüsü, Çağdaş İşletme Yönetimi Doktora ProgramıConsidering the technological development in mobile payment technology, and extensive literature of technology adoption models; the current state of the related field needs to be examined in more detail to better understand current situation. Such an investigation may be invaluable to enable further expansion, consumer acceptance, market adoption, and help to improve the existing platforms’ usability. This research deals with determining the factors that affect adoption of mobile payment technology among consumers, in Turkey. It seeks to find any patterns and connections that may be of aid in framing an implementation strategy for facilitating further adoption. It has gathered different definitions of “mobile payment” in literatüre and used a consumer side definition. This study offers a different perspective by grouping constructs from a broader literature and provides a mobile payment acceptance model based on the constructs used in other studies. Previous studies have been performed with small groups of respondents. This study aims to perform the research model in a cosmopolitan city (Istanbul) where all sorts of mobile payment options are available in the market and in the time of a pandemic when remote delivery and online purchases are widely preferred compared to offline alternatives. A survey is conducted among mobile phone subscribers in Istanbul, Turkey for primary data collection phase of this research. Istanbul is the city that holds the biggest population and has the highest amount of mobile phone subscribers in the country. Istanbul’s current population is more than 15.6million and mobile phone subscriptions are more than 22million as of 2019. Survey responses have been analysed with structural equation modeling and results are presented in the corresponding sections. Empirical findings of the research show that factors such as usefulness, security, social influence, ease of use, enjoyment and innovativeness have positive effects on use of mobile payments among consumers. Factors such as attractiveness of alternatives and new technology anxiety have negative effects on use of mobile payments. This study has also discovered that intention to use mobile payments differ among demographic parameters such as education level and gender of respondents.
