Organizational Unit: Department of Electrical and Electronics Engineering
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Master ThesisPublication Metadata only Analysis of firmness in renewable energy sources with energy storageYılmaz, Samet; Poyrazoğlu, Göktürk; Poyrazoğlu, Göktürk; Bebek, Özkan; Erdinç, O.; Department of Electrical and Electronics EngineeringRenewable energy has gained renewed attention due to recent developments in the energy sector, particularly as a potential solution to global warming and for reducing dependence on imported energy sources. This study focuses on the firm capacity that hybrid systems can provide to support the transition from thermal to renewable energy systems. The aim is to determine the required size of an energy storage system, such as a battery, to replace a 1 MW diesel generator or any other thermal system. A linear programming model was developed to minimize the size of the energy storage system required and lower the capital investment costs. Then the results of the mathematical model are used as inputs for another system called the Metric Calculator. The results obtained by the sensitivity analyses applied to the developed model such as different locations and different renewable energy technologies are analyzed and presented as case studies in this study. Case studies were presented to illustrate the results of the analyses. The findings indicate that it is possible to transition to renewable energy while maintaining firmness at its maximum by utilizing an energy storage system like a battery.Master ThesisPublication Metadata only Performance analysis of vertical underwater visible light communication link(2018-07) Yılmaz, Anıl; Uysal, Murat; Uysal, Murat; Durak, Kadir; Yılmaz, F.; Department of Electrical and Electronics Engineering; Yılmaz, AnılDemand for high-bandwidth underwater applications such as image and real-time video transmission, has been increasing parallel to the increase in maritime activities such as environment monitoring, navigation, ocean-pollution control, tactical surveillance, oil and gas field exploration, and coastal security. To satisfy this demand, underwater visible light communication (UVLC) has emerged as a high-capacity alternative to acoustic and RF signaling. One of the major impairments in UVLC systems is turbulence-induced fading as a result of temporal variations in temperature and salinity. Furthermore, unlike the horizontal links modeled with fixed turbulence strength, vertical links experience varying turbulence strength based on the depth-dependent temperature and salinity profiles. In this thesis, we consider a multiple-input multiple-output (MIMO) UVLC link over a vertical turbulence channel, which is modeled as the concatenation of multiple layers. Under the assumption of cascaded log-normal channel model, we derive the outage probability of vertical MIMO UVLC links and provide a quantitative analysis for the diversity gain in terms of the number of transmitter/receivers.Master ThesisPublication Metadata only Performance improvement strategies for 802.11 network(2017-08) Çakmak, Kıvanç; Ercan, Ali Özer; Uğurdağ, Hasan Fatih; Kaya, O.; Department of Electrical and Electronics Engineering; Çakmak, Kıvanç802.11 networks have enabled and are fueled by the proliferation of connected mobile devices with a wide variety of applications, which have been integral parts of our daily lives. Currently, IEEE 802.11ac is a state-of-art protocol that provides higher data rates than its predecessors to accommodate the increasing demands of users with more bandwidth, spatial streams, modulation schemes, and downlink multi-user MIMO (MU-MIMO). In addition, 802.11ac protocol inherits aggregation and QoS prioritization, from 802.11n and 802.11e, respectively. On the other hand, some new features of the latest 802.11 standard may cause adverse affects to the co-existing legacy nodes. For example, the MU-MIMO feature may result in the deafness problem, and QoS prioritization and MAC layer aggregation cause significantly lower performance in classical hidden node scenario - even with the RTS/CTS handshake mechanism. Also, delay and/or packet loss in TCP significantly decreases end-to-end throughput due to congestion control. This thesis studies and verifies these problems, proposes a methodology to mitigate the deafness problem in MU-MIMO, analyzes experimentally the effectiveness of multiple TCP connections to improve TCP throughput, and finally provides a framework via multiple-synced-sniffing methodology to diagnose hidden-node problems.Master ThesisPublication Restricted Lgp (light guide plate) pattern design by using light tools for back light units of tft lcd tvs(2014-01) Güçbilmez, Gizem Yumuşak; Yaralıoğlu, Göksenin; Yaralıoğlu, Göksenin; Erkol, Güray; Nizamoğlu, Sedat; Department of Electrical and Electronics Engineering; Güçbilmez, Gizem YumuşakIşık kılavuzu plakalar ve desenleri arka ışık üniteleri ve dolayısıyla likit kristal panellerin parlaklıkları ve eş dağılımları üzerinde oldukça etken bir rol oynamaktadır. Parlaklık ve eş dağılım daha az veya daha ucuz bir optik yapı kullanımına izin verecek seviyeye getirilebilirse ortaya çıkacak olan panel sadece maliyet değil, üretim süreci açısından da daha rekabetçi bir pozisyona sahip olacaktır. Bu çalışmanın kapsamı, yansıtıcı polarizerler gibi daha pahalı filmlerden kurtulmak hedefine ulaşmak için, parlaklık ve dağılımı iyileştirecek bir ışık kılavuzu nokta desen dağılımı tasarlamaktır. Bu hedefi yakalamak için nokta deseni tasarlarken Light Tools optik simülasyon yazılımı kullanılacak ve simülasyon sonuçları üretim sonuçları ile karşılaştırılacaktır. Bu karşılaştırma sonucunda noktaların ve arka ışık ünitesinin optik modelleri iyileştirilecektir. Çalışma kapsamında kullanılan arka ışık ünitesi 39" bir likit kristal panele ait, 52 adet LED içeren yandan aydınlatmalı bir ünitedir. ünitenin LED'leri kısa kenar üzerine yerleştirilmiştir. Eş dağılım hedefi %75 (VESA), parlaklık hedefi ise 300 nittir. Aynı zamanda kullanımı hedeflenen optik yapıda DBEF filmi olmamalı ve güç tüketim sınıfı ise A+ olmalıdır. Boyut, LED sayısı ve yerleşimi, güç tüketimi ve optik yapının her biri başlı başına birer çalışma konusu olabilirler. İlk parametreler ile alınan baskının ve üzerinde yapılan ölçümlerin sonucunda panelin eş dağılımı %61 çıkmıştır. Bu deneme sayesinde gerçek dünya ölçüm sonuçları ile simülasyon sonuçları karşılaştırılmış ve nokta deseninin optik parametreleri optimize edilmiştir. Final tasarım hedefleri tutturmuş ve %76.63'lük bir eş dağılım ve 338 nitlik merkez parlaklığa ulaşmıştır. Nokta dağılımını deneme ? yanılma yöntemi yerine simülasyon ile finalize ederek gerek maddi olarak gerekse zaman açısından büyük bir avantaj sağlanmıştır.Master ThesisPublication Metadata only Validating android permission requests by analyzing APP descriptions(2016-07) Şahin, Mustafa Kaan; Aktemur, Tankut Barış; Aktemur, Tankut Barış; Şensoy, Murat; Çakmak, Ali; Department of Electrical and Electronics Engineering; Şahin, Mustafa KaanAndroid applications can access sensitive user data if they are granted certain permissions. Android security model gives users the responsibility to approve permission requests of applications. For this, a user needs to decide whether an app's functionality justifies the permission request. To aid users in their decision, we propose and evaluate a methodology that analyzes the description of an app and identifies unusual and unjustified permission requests. In contrast to existing techniques, our approach is not limited to a fixed set of permissions and does not need source code or binary app data to operate; yet, it is on par with the current state of the art in terms of accuracy.Master ThesisPublication Restricted Combined aes + aegis architectures for high performance and lightweight security applications(2014-08) Şahin, Furkan; Uğurdağ, H. Fatih; Uğurdağ, H. Fatih; Yalçın, T.; Gören Uğurdağ, S.; Aktemur, Tankut Barış; Ercan, Ali Özer; Department of Electrical and Electronics Engineering; Şahin, FurkanGünümüzde kriptografi banka kartlarından telefonlara, arabalardan haberleşme araçlarına ve bulut hizmetlerine kadar pek çok alana girdi. Digital bilgiyi yetkilendirilmemiş erişimlere karşı korumak için bir çok şifreleme algoritması mevcuttur. Gelişmiş Şifreleme Standardı (AES) Amerikan Ulusal Standartlar ve Teknoloji Enstitüsü (U.S. NIST) tarafından standart şifreleme algoritması olarak onaylandıktan sonra en önemli blok şifreleyici olmuştur. AES'in kanıtlanmış güvenliği ve makul donanım kullanımı onu yeni bilgi güvenliği uygulamaları için mantıklı bir seçim yapmaktadır. Bugüne kadar, yüksek performanstan düşük alan kullanımına kadar pek çok tasarım yaklaşımını hedefleyen AES versiyonları donanımsal ve yazılımsal olarak gerçeklendi. Ancak günümüz bilgi güvenliği uygulamaları hem gizlilik hem de kimlik doğrulama gerektirdiği için, kimlik doğrulamalı şifreleme giderek daha çok önem kazanmaktadır. AES, bir çok kriptografi bilimcisi tarafından kimlik doğrulamalı şifrelemenin gerçeklenmesinde mantıklı bir seçim olarak düşünülmektedir. Son zamanlarda literatürde, AES algoritmasını olduğu gibi kullanan ya da AES'te küçük değişiklikler yaparak kullanan kimlik doğrulamalı şifreleme algoritmları çokça gözükmeye başlamıştır. Bu yeni kimlik doğrulamalı şifreleme algoritmalarının bazılarında daha iyi performans ve daha az kaynak kullanımı başarılabileceği iddia edilmektedir. Ancak bu algoritmalar henüz yeni literatüre girdiği için bu iddiaları destekleyen çok az donanım gerçeklemesi mevcuttur, hatta bazıları donanımsal olarak henüz gerçeklenmemiştir. Bu tezde AES'i, çok yakın zamanda literatüre giren AES tabanlı kimlik doğrulamalı şifreleme algoritması olan AEGIS ile aynı donanımda birleştiren mimariler tasarlanmıştır. Buradaki amacımız iki algoritmanın tek bir devrede gerçeklenmesine örnek teşkil edecek bir mimari sunmak, birleşik performans ve donanım kaynağı kullanımını analiz etmek ve AEGIS'ın tasarımcılarının kaynak kullanımı konusundaki iddialarının tartışılabileceği sentez sonuçları elde etmektir. Ayrıca bilgilerimize göre literatürde AEGIS'ın donanımda gerçeklenmesini sunan bir çalışma henüz yapılmamıştır ve AEGIS ilk kez bu çalışmada donanımsal olarak gerçeklenmiştir. Bu tezde yüksek performans ve az donanım kaynağı kullanan olmak üzere iki değişik, birleşik AES + AEGIS donanım mimarisi sunulmuş ve bu devreler Verilog donanım tanımlama dilinde (Verilog HDL) yazmaç transfer seviyesinde (RTL) kodlanmıştır. Ayrıca sadece AES şifrelemesi yapan devreler de gerçeklenip, her iki birleşik mimarinin kaynak kullanımı bu devreler ile kendi kategorisinde kıyaslanmıştır. Devreler UMC 90nm standart hücre kütüphanesiyle ve Cadence RTL derleyicisi kullanılarak gerçeklenmiştir. Sentez sonuçları raporlanmış ve değerlendirilmiştir.Master ThesisPublication Restricted Analysis of ALTO protocol over P2P networks(2012-10) Kökten, Koray; Sunay, M. Oğuz; Sunay, M. Oğuz; Arı, İsmail; Erdem, Tanju; Tan, A. S.; Ercan, Ali Özer; Department of Electrical and Electronics Engineering; Kökten, KorayCurrently, for distributed applications such as Peer-to-Peer (P2P) and Content Delivery Networks (CDNs), the most important challenge is to determine the optimal peer or node selection process, since it sometimes causes low Quality of Experience and affects the economics of the Internet Service Providers (ISPs) negatively. Therefore, in recent years significant research has been conducted in this area. However, since these protocols operate on Layer 7 (Application Layer) according to the Open Systems Interconnection (OSI) model, they are network-oblivious. Therefore, without a co-operation between service or network providers (i.e. ISPs) and applications, obtaining an optimal solution is not easy or even possible. Since P2P applications are one of the most widely used applications on the Internet, Internet Engineering Task Force (IETF) has started to work on a protocol, commonly referred to as the Application Layer Traffic Optimization (ALTO) Protocol, in order to enable a standartized interface between applications and network providers. With this protocol, both applications and service providers have a chance to interact using a common interface via the ALTO Server and share the necessary information in order to calculate the costs of communication between peers, so that a better-than-random peer or node selection is possible. In this thesis, we implement an ALTO Server for several ISPs, describe several(either novel or from the literature) cost calculation methods and try to improve the performance of the communication network from the perspectives of both applications and service providers. We analyse the implemented ALTO Server using a P2P BitTorrent-Like file sharing application, a P2P real-time scalable video streaming application and a CDN application running on a Software DefinedNetwork (SDN) with an OpenFlow Controller. Simulation results and demos show that, with carefully designed peer selection algorithms used in the ALTO Service, the performance of the applications can be sustained (even can be improved), while the inter-ISP traffic rates can be reduced dramatically.Master ThesisPublication Metadata only Speaker adaptation with minimal data in statistical speech synthesis systems(2014-09) Mohammadi, Amir; Demiroğlu, Cenk; Demiroğlu, Cenk; Yaralıoğlu, Göksenin; Sözer, Hasan; Department of Electrical and Electronics Engineering; Mohammadi, AmirStatistical speech synthesis (SSS) systems have the ability to adapt to a target speaker with a couple of minutes of adaptation data. Developing adaptation algorithms to further reduce the number of adaptation utterances to a few seconds of data can have substantial effect on the deployment of the technology in real life applications such as consumer electronics devices. The traditional way to achieve such rapid adaptation is the eigenvoice technique which works well in speech recognition but known to generate perceptual artifacts in statistical speech synthesis. Here, we propose three methods to both alleviate the quality problems of the baseline eigenvoice adaptation algorithm while allowing speaker adaptation with minimal data. Our first method is based on using a Bayesian eigenvoice approach for constraining the adaptation algorithm to move in realistic directions in the speaker space to reduce artifacts. Our second method is based on finding pre-trained reference speakers that are close to the target speaker and utilizing only those reference speaker models in a second eigenvoice adaptation iteration. Both techniques performed significantly better than the baseline eigenvoice method in the objective tests. Similarly, they both improved the speech quality in subjective tests compared to the baseline eigenvoice method. In the third method, tandem use of the proposed eigenvoice method with a state-of-the-art linear regression based adaptation technique is found to improve adaptation of excitation features.Master ThesisPublication Metadata only Design and characterization of continuous glucose monitoring sensorHassine, Chedia Ben Ali; Akgiray, Ahmed Halid; Akgiray, Ahmed Halid; Ünal, Ramazan; Tekin, A.; Department of Electrical and Electronics Engineering; Hassine, Chedia Ben AliThe main objective of this thesis is the development and the elaboration of a low cost continuous glucose monitor. This thesis describes the design of miniaturized continuous glucose monitoring sensor based on two needles. The sensor is based on enzymatic detection of glucose. The used enzyme is glucose oxidase entrapped inside a protecting film of chitosan. Chapter I provides a general introduction to diabetes and the different types of biosensors used for continuous glucose moni toring. “Continuous” monitoring approaches involve subcutaneous implantation of a micro-needle allowing real-time glucose level measurements in the intersti tial fluid. The working principals of continuous glucose monitors (CGM)s are introduced. An overview of electrochemical sensors is presented, and the differ ent methods of common electrode modification are also discussed in this chapter. The electrical circuits that are used for glucose sensors are reviewed. The second chapter contains the methods and materials used in the performed experiments. It describes the steps of sensor elaboration from the electrical circuit assembly on the PCB board to the electrode modification process. The measurement setup is also presented in this chapter. Chapter 3 discusses the results obtained for the sensor tests. Chapter 4 is the conclusion, it stipulates that after the tests carried on the elaborated biosensor both in the buffer solution and in the real sample, the sensor can be improved and it has potential to be used in tests on humans.Master ThesisPublication Metadata only A robust voltage control method for universal ev battery charge llc resonant convertersDaş, Yılmaz; Tekin, Ahmet; Tekin, Ahmet; Poyrazoğlu, Göktürk; Akın, Ö.; Department of Electrical and Electronics Engineering; Daş, YılmazIn this study, a novel control method for LLC resonant converter with wide output voltage range and constant switching frequency is proposed targeting wide range of Electric Vehicle (EV) battery charger standards. In conventional LLC converter control topologies, in order to reach lower output voltage levels, switching frequency happens to move away from the resonance frequency, increasing in most of the cases. However, the switching losses due to switching devices start to become the main bottleneck at high switching frequency operation. In the proposed control method, the switching losses can be reduced by changing duty ratio of PWM driver signals with constant switching frequency operation. High switching frequency operation may cause irreversible inrush current damage at the input terminals during the start-up with corresponding overshoot at the output voltage as well, risking the clients on this particular supply. During soft start, the excessive inrush current can be eliminated by controlling dead time duration of PWM signals in proposed method. The work presented in this thesis proposes a robust and reliable control solution for these particular resonant converter drawbacks. Theoretical analysis for both conventional and proposed control methods are presented in detail. In order to show the effectiveness of the proposed technique, performance metrics of the both are compared experimentally on an LLC resonant converter specification having an output voltage range of 150-500 V with a maximum output power of 7.5 kW.