Master's Theses

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Fire protection performance of different industrial intumescent coatings for steel beams
(01.07.2022) Kocapınar, Serkan; Altay, Gülay; Altay, Gülay; Erkmen, Bülent; Çeribaşı, S.; Department of Civil Engineering; Kocapınar, Serkan
This study covers comparison of fire protection performance efficiencies of two commercially available different intumescent coatings on two 1-meters steel beams which have S275 steel grade and UPN 200 steel sections for 2 hours by following ISO 834 fire curve in a furnace in Turkish Standards Institute (TSE) laboratory. Each beam was insulated with different industrial intumescent coatings to explore the efficiency of these intumescent coatings. Hence, all variables containing workmanship quality, period of application of intumescent coatings, steel grade, steel sections, furnace type, fire type and period of the experiment were kept constant except the type of intumescent coatings. First intumescent coating which is the Product A complies to BS 476-20,22 and EN 13381-8 and has an ISO Standards certificate. The Product B complies to ASTM UL-94 and EN 13381-8 and has a TSE certificate. 12 thermocouples were applied on each steel beams before the intumescent coatings performed to get temperature-time curves to determine the time to reach the critical temperatures of steel beams which were isolated. Fin EC software was used for the preliminary analysis to determine the critical temperatures and ABAQUS software was used to define the critical temperatures of each insulated steel beam and heat transfer analysis to compare with the temperature-time curves with experimental ones to have a better understanding of intumescent coating's thermal barrier duty in a case of ISO 834 fire type.
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Performance analysis and optimization of relay-assisted free space optical communication systems
(2012-07) Kashani, Mohammadreza Amini; Uysal, Murat; Uysal, Murat; Ercan, Ali Özer; Pusane, A. E.; Kashani, Mohammadreza Amini
Free-space optical (FSO) communication has received an increasing attention in recent years with their ability to achieve ultra-high data rates (at the order of multiple gigabits per second) over unlicensed optical spectrum. A major degrading factor, particularly in long links, is the atmospheric turbulence induced fading. Smartly exploiting the fact that fading variance is distance-dependent in FSO channel, relay assisted transmission takes advantage of the resulting shorter hops and yields significant performance improvements. In this thesis, we make several contributions to the performance analysis and design of relay-assisted FSO systems. In the first part, we investigate how to determine optimal relay locations in serial and parallel FSO relaying as to minimize the outage probability and quantify performance improvements obtained through optimal relay placement. In the second part, we investigate the combined use of serial and parallel relaying for FSO mesh networks. We derive the outage probability expressions of FSO mesh networks and demonstrate performance improvements with respect to both stand-alone serial and parallel relaying schemes. We also present a diversity gain analysis and quantify the achievable diversity orders in terms of the number of relays and turbulence channel parameters. Finally, we investigate the use of all-optical relaying removing the need for optical-electrical and electrical-optical conversions. Building on all-optical relay assumption, we investigate the outage performance of a dual-hop FSO link taking into account practical limitations such as amplifier noise and filtering effects.
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Multi-pick round robin arbiter
(2012-08) Temizkan, Fatih; Uğurdağ, H. Fatih; Uğurdağ, H. Fatih; Erdem, Tanju; Aktemur, Tankut Barış; Department of Electrical and Electronics Engineering; Temizkan, Fatih
In this thesis, we propose two multi(m)-pick Round Robin Arbiter (RRA) architectures. An m-pick RRA selects the m topmost requests out of n inputs with priority order indicated by an internally kept pointer (with an update policy that ensures fairness among requestors). The architectures that we propose are m-pick Thermo Coded-Parallel Prefix Arbiter (TC-PPA) and Three-Dimensional Programmable m-Selector RRA (3DPmS-RRA). Prior to this thesis, these two architectures existed in the literature as 2-pick and 1-pick arbiters, respectively. Our main contribution to the literature is the generalization of these architectures to m-pick. A logic building block that we call ?Saturated Adder? plays a key role in this generalization, which makes the 1-pick and 2-pick architectures simply special cases. We developed six different variants of 3DPmS-RRA and eight different variants of m-pick TC-PPA. We wrote automated HDL code generators for all variants as well as Cascade Architecture, which is a straight-forward way of implementing a multi-pick RRA using 1-pick Programmable Priority Encoders. Then, all multi-pick architectures were verified and synthesized. Our experimental results show that 3DPmS-RRA architecture is the best choice for all pick sizes (except 2-pick) when timing is the primary design criterion. However, when area is more critical, TC-PPA architecture performs better. It is worthwhile to note that in terms of timing 3DPmS-RRA is better than TC-PPA by a mere 8% at the most based on our synthesis results. However, when we consider area, TC-PPA has significant improvements over 3DPmS-RRA, up to 53%.
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Induction cooker design and experimental results with quasi resonant topology and jitter method
(2012-08) Tülü, Mehmet Emin; Yıldırım, D.; Uğurdağ, H. Fatih; Yıldırım, D.; Uğurdağ, H. Fatih; Sunay, M. Oğuz; Uysal, Murat; Arık, Mehmet; Department of Electrical and Electronics Engineering; Tülü, Mehmet Emin
This thesis presents an induction cooker design and its detailed experimental results. The design is based on Quasi Resonant Topology and is unique in terms of the particular Jitter Method it employs to drive the semiconductor switches (IGBTs). Most induction cookers are based on Half Bridge Topology. Although Quasi Resonant Topology offers a more cost effective implementation, it introduces more EMI problems. However, we solve these problems with our Jitter Method. Although there are other works in the literature that solve the EMI issues by some sort of jitter methods (i.e., spread spectrum methods), these methods do not address the high voltage stress created across the IGBTs. However, the Jitter Method proposed in this thesis also reduces collector-emitter voltage stress besides improving EMI. Note that jitter methods also prevent mechanical vibration (i.e., resonance), which cause audible noise. Another thing that makes this thesis unique in the literature is the rich set of experimental results it contains ? based on an experimental prototype we built with a power rating of 2300W. While the existing literature mostly contains theoretical treatment, we have produced detailed experimental results for Quasi Resonant Topology and show that the current harmonics (drawn from the utility) stay within the published standards (TS EN 61000-3-2). We also include experimental results for Delivered Power Detection, Pan Detection, and Protection Circuits.
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A simulation study of cooperative underwater acoustic communication
(2012-08) Sökün, Hamza Ümit; Uysal, Murat; Uysal, Murat; Şenol, H.; Erdem, Tanju; Department of Electrical and Electronics Engineering; Sökün, Hamza Ümit
Cooperative communication promises significant performance gains in terms of link reliability, spectral efficiency, system capacity, and transmission range. Due to its indisputable advantages for high-speed underwater applications with size and power limitations, cooperative transmission is a promising physical layer solution for next generation underwater acoustic (UWA) communication systems. Although a rich literature already exists on cooperative communication for terrestrial wireless radio frequency (RF) systems, there are only sporadic results reported for UWA applications. In this thesis, we consider cooperative UWA communication and investigate the performance of relay selection in underwater for multi-carrier and single-carrier systems with various selection criteria. In the first part, we consider a multi-carrier multi-relay cooperative UWA communication system based on orthogonal frequency division multiplexing (OFDM) and investigate both amplify-and-forward (AaF) and decode-and-forward (DaF) relaying in half-duplex mode. We adopt different relay selection criteria which rely either on the maximization of signal-to-noise ratio (SNR), the minimization of probability of error (PoE), or the maximization of capacity for relay selection. These are utilized in conjunction with diverse approaches such as per-subcarrier, all-subcarriers, or subcarrier grouping. We provide an extensive Monte Carlo simulation study to evaluate the error rate performance of relay selection schemes. In the second part of the research, in order to increase spectral efficiency, we consider OFDM-based multi-relay systems with two-way relaying and study the performance of relay selection in UWA channels. In the final part of the thesis, we consider single-carrier frequency-domain equalization (SC-FDE) and present the performance of relay assisted SC-FDE schemes providing comparisons with uncoded OFDM counterparts.
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Fast, secure, and remote multiboot of FPGAs
(2012-09) Yıldız, Abdullah; Gören Uğurdağ, S.; Uğurdağ, H. Fatih; Uğurdağ, H. Fatih; Gören Uğurdağ, S.; Aktemur, Tankut Barış; Küçük, G.; Arı, İsmail; Department of Electrical and Electronics Engineering; Yıldız, Abdullah
The purpose of this thesis is to develop an efficient framework to implement secure FPGA-based (Field Programmable Gate Array) systems. An FPGA is a reconfigurable device that has the ability to adapt the hardware during runtime by loading a new circuit on the reconfigurable fabric. However, a circuit design formed as configuration data (bitstream) can be easily counterfeited and needs to be protected against the risks of cloning, overbuilding, and reverse-engineering. Although many applications could be implemented on low-cost FPGAs, protection schemes and dedicated hardware are mostly available on high-end FPGAs. In addition to this, only high-end FPGAs support dynamic partial self reconfiguration (DPSR), which is the ability to change a part of a design at runtime. This thesis focuses on developing a security scheme leveraging hardware intrinsic features on low-cost FPGAs by using physical unclonable functions (PUFs). A PUF provides a way to extract security keys which are unique to each device. This thesis combines PUFs with another security scheme called obfuscation. Obfuscation is the act of intentionally modifying the description or structure of a circuit in order to conceal its functionality. Obfuscation is implemented in this thesis at RTL-level and is used to authenticate and control the device by using the keys by exploiting the PUF technique within a finite state machine (FSM). These methods are further used to implement ?secure MultiBoot?. The MultiBoot feature allows to reconfigure the FPGA fully at runtime as opposed to DPSR for devices which do not support partial reconfiguration. This thesis also establishes a framework that enables secure remote MultiBoot. A bitstream compression technique is applied to reduce the transmission time over the network. A proof-of-concept example is implemented using the proposed framework.
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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, Koray
Currently, 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.
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P2P live scalable video streaming with ALTO service
(2012-10) Kırkgül, İsmail Serkan; Sunay, M. Oğuz; Sunay, M. Oğuz; Arı, İsmail; Erdem, Tanju; Ercan, Ali Özer; Department of Electrical and Electronics Engineering; Kırkgül, İsmail Serkan
It has been measured that, as high as 80% of the average Internet traffic is now from peer-to-peer (P2P) applications, and upwards of 90% during peak hours. These results tell us that a significant portion of the traffic that ISPs route is P2P traffic. However, since the typical P2P application overlay network model is network-oblivious, due to its nature, it causes inefficient network utilization, and low quality of experience, from the perspective of the network providers and the end users, respectively. This inefficient resource utilization increases inter-ISP traffic, and leads to serious disruptions on ISP economics as well as lower QoE by the users. A significant portion of the P2P traffic on the Internet is for video applications. Furthermore, real networks are heterogeneous in link rates. Thus a live video streaming service should support streams with different qualities for users using different data rates. A possible solution to this problem is achieved by creating a different video file for each quality level. However, this solution is inefficient due to data duplication. To improve ISP economics, improve network efficiency and achieve acceptable QoE performance, we implement a P2P Live Scalable Video Streaming Mechanism and Application Layer Traffic Optimization (ALTO) Server, by using different peer ranking algorithms in this thesis. The main objective of this thesis, to show that the ALTO protocol reduces the inter-ISP traffic significantly while maintaining the application performance. Results reveal that, placing an ALTO Server decreases the inter-ISP traffic dramatically while maintaining a satisfactory QoE performance for the streaming video application.
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Application-based scheduling for indoor femtocell networks
(2013-01) Mungan, Devin; Sunay, M. Oğuz; Sunay, M. Oğuz; Ercan, Ali Özer; Arı, İsmail; Department of Electrical and Electronics Engineering; Mungan, Devin
This thesis is concerned with designing a QoS-enabled, application-based scheduler for indoor femtocell networks. For this purpose, a novel scheduler is proposed which takes into account the quality of service (QoS) requirements of each active application as well as whether their sustainability is at risk at a given time. The scheduler aims to maintain an efficient use of the wireless radio resources and strives to achieve a user and application specific notion of fairness of service reception. Unlike current so- lutions, the scheduler differentiates between not only different users but also between applications of each user, and schedules data transmission amongst these applications so that QoS requirements for all applications are satisfied.
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Fault masking as a service
(2013-01) Gülcü, Koray; Sözer, Hasan; Aktemur, Tankut Barış; Sözer, Hasan; Aktemur, Tankut Barış; Ercan, Ali Özer; Yolum, P.; Arı, İsmail; Department of Computer Science; Gülcü, Koray
In service-oriented architectures, composite services depend on a set of partner services to perform their tasks. These partner services may become unavailable due to system and/or network faults, leading to an increased error rate for the composite service. In this dissertation, we propose an approach to prevent the occurrence of errors that result from the unavailability of partner services. We introduce an external Web service, FAS (Fault Avoidance Service), to which composite services can register at will. After registration, FAS periodically checks the partner links, detects unavailable partner services, and updates the composite service with available alternatives. Thus, in case of a partner service error, the composite service will have been updated before invoking the partner service. We provide mathematical analysis regarding the error rate and the ratio of false positives with respect to the monitoring frequency of FAS for various partner service availability rates. We obtain empirical results regarding these metrics based on several tests we performed using the Amazon Elastic Compute Cloud. We use these results to evaluate our mathematical analysis. We also introduce an industrial case study for improving the quality of a service-oriented system from the broadcasting and content delivery domain.
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Joint frequency allocation and power control for minimum downlink interference in femtocellular networks
(2013-01) Ferazoğlu, Gülden; Sunay, M. Oğuz; Sunay, M. Oğuz; Ercan, Ali Özer; Arı, İsmail; Department of Electrical and Electronics Engineering; Ferazoğlu, Gülden
Due to the fact that the most of data services and more than half of calls are requested indoors, it has been dramatically important and even a must for cellular operators to provide more than adequate indoor coverage. Instead of expensive traditional approach which is to use outdoor macrocell base stations to provide good indoor coverage, indoor systems for the cases of small offices and homes are found more convenient and efficient. Femtocell is one of the developing technologies as a recent solution to aforementioned problems. They offer to improve the indoor coverage and reduce the cellular network load. However, in case of the most feasable solution, co-channel deployment of the femtocell network over the existing macrocell network, a closed access approach could result in serious co-channel interference problems. In this thesis, improvements to the performances of both femtocell and indoor macrocellular users in terms of average achieved data rates are considered. A joint spectrum and power control algorithm is proposed to mitigate the co-tier and cross-tier interferences. The algorithm aims to save the indoor macrocell subscribers from the violation of femtocells whilst providing throughput to femtocell subscribers as higher as possible. Simulations including physical layer and system level are conducted to determine the performance of the proposed method. Results reveal that an algorithm that combines the management of two important resources, spectrum and power, performs really well in two-tier networks, even better than the techniques managing only one resource, in terms of overall system performance.
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Comparison of text-independent speaker verification systems in a multi-class, semi-automatic detection scenario
(2013-06) Yeşil, Fatih; Demiroğlu, Cenk; Demiroğlu, Cenk; Aktemur, Tankut Barış; Uğurdağ, H. Fatih; Department of Electrical and Electronics Engineering; Yeşil, Fatih
Performance of the speaker veri cation systems is typically measured based on their binary decision accuracy. Soft outputs of the systems are used mostly for calibration or multiple system combination purposes. However, in speaker veri cation applications where close to 100% accuracy is required, such as the systems that are used in the call centers of nance companies, it is not possible to rely on the binary decisions of the existing veri cation systems. Still, in such cases, multi-class veri cation outputs (for example, high, medium and low veri cation score) returned by the speaker veri cation systems can be used by a human agent to either reduce the veri cation time and/or increase the veri cation accuracy compared to a human-only scenario. In this thesis, an overview of a speaker veri cation system is given explaining in detail the algorithms that are implemented. Particularly the details about a classi- er, GDA, which was rstly used by us for a veri cation purpose are given. It does relatively better job than state of the art algorithms for non-linear data like in our case. In the experiments section, some of the most popular speaker veri cation systems are compared in terms of the classical performance metric used in the literature. Then, multi-class output performance of them is compared when a human agent is assumed to be in the veri cation loop. Performance is measured by the reduction in the number of questions used by the human agent for verifying the identity of the caller without compromising the security. Experiments are performed using the NIST 2006 and 2008 databases. Eight and one conversation sides (5 minutes each) enrollment data and 1 side and 10 seconds veri cation data conditions are used.
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A hybrid statistical/unit-selection text-to-speech synthesis system for morphologically rich languages
(2013-06) Güner, Ekrem; Demiroğlu, Cenk; Demiroğlu, Cenk; Erdem, Tanju; Bozkurt, B.; Department of Electrical and Electronics Engineering; Güner, Ekrem
Two most prominent examples of Text-to-Speech (TTS) systems are Unit Selection based TTS (UTTS) and the Hidden Markov Model (HMM) based TTS (HTTS). UTTS has been the dominant approach of the last decade while HTTS has been increasingly getting more attention from the TTS research community. Both systems have distinct pros and cons. Despite its success, UTTS has some disadvantages such as the sudden discontinuities in speech which cause distraction whereas HTTS lacks of those artifacts. However, UTTS systems offer high quality speech given a huge unit database where the storage is not a problem. On the other hand, the small memory footprint requirement of HTTS systems makes them attractive for embedded devices. Here, a novel hybrid statistical/unit selection TTS system for morphologically rich languages is proposed. The proposed hybrid system aims at improving the quality of the baseline HTTS system while keeping the memory footprint small. First, the motivation of the proposed hybrid system is given after the comparison of both systems. Then the proposed hybrid system is presented along with the details of the baseline HTTS system. In order to assess the performances of proposed and baseline systems, the subjective and objective tests are conducted. Intelligibility and quality scores of the baseline system are comparable to the MOS scores of English reported in the Blizzard Challenge tests. Results of the AB preference tests revealed the listeners' preference for the hybrid system over the baseline system.
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Design and implementation of a data stream management system with advanced complex event processing capabilities
(2013-06) Ölmezoğulları, Erdi; Arı, İsmail; Arı, İsmail; Sözer, Hasan; Duman, Ekrem; Ergüt, S.; Department of Computer Science; Ölmezoğulları, Erdi
The world has seen proliferation of data stream applications over the last years. These applications include computer network monitoring, Radio Frequency Identication (RFID)-based supply chain and traffic management systems, e-trading, online financial transactions, web click-streams, some mobile communication applications, and civilian or military applications using sensor networks. All of these applications are considered ?mission-critical? by related organizations and require real-time stream processing to detect simple or complex events, so that strategic decisions can be made quickly. An emerging system architecture called Data Stream Management System (DSMS) is well-suited to address the analysis needs of emerging data stream applications. DSMS forms the basis for our project and allows processing of high-speed data streams with different continuous queries. In this thesis, we present design and implementation details of a data stream management system with advanced Complex Event Processing (CEP) capabilities. Specifically, we add ?online? Association Rule Mining (ARM) and testing capabilities on top of an open-source DSMS system and demonstrate its capabilities over fast data streams. Our most important findings show that online ARM can generate (1) more unique rules, (2) with higher throughput, (3)much sooner (lower latency) than online rule mining. In addition, we have found many interesting and realistic musical preference rules such as ?If a person listens to George Harrison, then s/he also listens to The Beatles?. We demonstrate a sustained rate of 15K rows/sec per core. We hope that our findings can shed light on the design and implementation of other fast data analytics systems in the future.
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Fall detection for elderly people using depth video data obtained by kinect
(2013-08) Davari, Amir Abbas; Erdem, Tanju; Erdem, Tanju; Sunay, M. Oğuz; Ercan, Ali Özer; Department of Electrical and Electronics Engineering; Davari, Amir Abbas
Automatic detection of unusual events such as falls is very important especially for elderly people living alone. Real-time detection of these events can reduce the health risks associated with a fall. There has been a series of ongoing researches in the ?eld of unusual event detection using the Microsoft`s depth sensor Kinect. It has been applied in areas like fall detection using only the depth images and features derived from skeletal data having exaggerated dimensionality. This thesis will propose a novel method for automatic detection of fall event by using depth cameras. Depth images generated by these cameras are used in estimating the skeletal data of a person. The contribution here is to use features extracted from this data to form a strong set of features which can help us achieve an increased precision at low redundancy. The achievements indicate that the calculated features which are derived from skeletal data are moderately powerful for detecting unusual events such as fall.
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Investigation of the refrigerator bottom cabinet cavity acoustic behavior
(2013-08) Öztürk, Anıl; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Bebek, Özkan; Erol, H.; Department of Mechanical Engineering; Öztürk, Anıl
This thesis investigates the computational and experimental analysis for the acoustic behavior of a bottom cabinet cavity in a refrigerator. The finite element and analytical approaches are used in order to determine the natural frequencies and associated mode shapes of the bottom cabinet cavity. The sound of bottom cabinet cavity is related to its frequencies. The noise level of the bottom cabinet, increases at the peak frequencies of the bottom cabinet cavity. The effects of sound propagation from the bottom cabinet of the refrigerator, due to vibration from the compressor in a rectangular cavity, in dictating the overall sound level of the refrigerator is considerable. For the end user, a quiet run is one of the most important criteria in refrigerator selection. Therefore, design of the bottom cabinet cavity, in where the compressor works and causes the noise problem, has a profound significance. The natural frequencies of the bottom cabinet cavity are investigated. Firstly, natural frequencies are determined with analytical method. Secondly, natural frequencies are determined with numerical analysis using the finite element model of the bottom cabinet cavity. Comparisons with the results of the analytical study verify the validity of the numerical solution. It is seen that finite element model of the bottom cabinet cavity is applicable. Finally, experimental study is carried out for validation of both models. It is seen that the sound pressure of the bottom cabinet of the refrigerator is higher at some frequencies. As a result, these frequencies are in close match with the natural frequencies of the bottom cabinet cavity of the refrigerator which can be determined with the analytical and numerical analysis.
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Experimental QOS-based comparison of olsr and B.A.T.M.A.N. mesh routing algorithms for multimedia home networks
(2013-08) Ulusoy, Sırrı Erdem; Ercan, Ali Özer; Ercan, Ali Özer; Erdem, Tanju; Sunay, M. Oğuz; Department of Electrical and Electronics Engineering; Ulusoy, Sırrı Erdem
Wireless Mesh Networks (WMNs) allow communication of two nodes via a multi-hop route, without the need for an infrastructure such as base stations. Routing has been a fundamental issue for this type of communication networks. In this thesis, we compare two well-known routing algorithms for WMNs, namely OLSR and B.A.T.M.A.N., in their achieved QoS for video streaming, on a real life WMN test-bed. Our test-bed consists of seven mesh access points (MAPs) placed on several rooms spread on two floors of Ozyegin University Engineering Building. We installed B.A.T.M.A.N.-Adv, a layer two implementation of B.A.T.M.A.N. routing algorithm, and OLSRd, a layer three implementation of OLSR routing algorithm, on the MAPs. We used a laptop as a video server and another laptop placed on the other corner of the building as a client. A test video is streamed from the server to the client using the said routing algorithms several times and the sample means and standard deviations of the PSNR values between compressed and received videos as well as between uncompressed and received videos are calculated. In the calculation of the PSNR values, we developed a novel method to overcome the problem of mismatched frames in the case of dropped frames. The experiments are repeated for varying levels of video compression rates, cross-traffic levels on the network, and by changing settings of the RTS/CTS handshaking mechanism. The PSNR values are reported and compared between the two routing algorithms for these different cases, and their effects are discussed.
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Information theoretical performance analysis and optimization of underwater acoustic communication systems
(2013-08) Nouri, Hatef; Uysal, Murat; Uysal, Murat; Ercan, Ali Özer; İlhan, H.; Department of Electrical and Electronics Engineering; Nouri, Hatef
Underwater wireless communication is a rapidly growing field of research and engineering as its applications, which were once exclusively military, are extending into commercial fields. The need for underwater wireless communications exists in a wide range of applications including offshore oil field exploration/monitoring, oceanographic data collection, maritime archaeology, seismic observation, environmental monitoring, disaster preventing, port and border security among many others. Although capacity calculations for terrestrial radio-frequency channels have been extensively studied, the literature on the capacity of underwater acoustic (UWA) channels is sporadic with many remaining open questions. Aiming to fill research gaps in this growing field, this thesis makes several contributions to the information theoretical performance analysis of point-to-point and relay-assisted UWA systems. A single-carrier communication architecture and sparse Rician frequency-selective UWA channel with intersymbol interference (ISI) is considered in our work. We assume non-white Gaussian distribution to model the ambient noise and consider Francois-Garrison path loss formula to take into account the effects of environmental parameters such as temperature, salinity, pressure as well as system parameters such as distance and frequency. We develop an equivalent channel model for UWA channel with ISI under consideration and show that the capacity of the equivalent channel converges to that of the operating channel in the limit of infinite block length. Using these results, we first obtain a capacity expression for the UWA channel and demonstrate the dependency on channel parameters such as the number and location of significant taps and power delay profile, and environmental parameters such as temperature, salinity, and pressure. Then, we use this expression to determine the optimal carrier frequency, input signaling, and bandwidth. A closed-form formula for the optimum carrier frequency is further obtained. In the second part of the thesis, we extend our results to cooperative UWA systems and obtain achievable rates of single-carrier cooperative UWA systems with orthogonal decode-and-forward (DF) relaying. We take into account the effect of relay geometry in the derivations of achievable rates, and use the derived expressions to optimize the location of the relay.
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Real-time event correlation and alarm rule mining models for complex event processing systems
(2013-08) Çelebi, Ömer Faruk; Arı, İsmail; Sözer, Hasan; Arı, İsmail; Duman, Ekrem; Department of Computer Science; Çelebi, Ömer Faruk
World is creating the same quantity of data every two days, as it created from up until 2003. Evolving data streams are key factor for the growth of data created over the last few years. Streaming data analysis in real-time is becoming the fastest and most effective way to get useful information from what is happening right now, thus allowing organizations to take action quickly when problems occur or to detect new trends to improve their performance. Data stream analytics is needed to manage the data currently produced from applications such as sensor networks, measurements in network monitoring, mobile traffic management, web click streams, mobile call detail records,social media posts/blogs and many others. Stream data analytics is hard because data are temporally ordered, fast changing, massive and potentially infinite. In order to cope with the challenges of data stream mining, in this thesis two main contributions are discussed. Both of them summarize the high volume streaming data and present meaningful, actionable information to end users. The first one is finding "event correlations" over the data stream pairs on real GPS data of public transportation buses. The second one is alarm sequence rule mining, with a new parameter called "time confidence", that helps automatically set time-window values for registered rules and also reduces the generated alarm rule count.
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A smart cloud platform service for socialized travel and transportation with mobile support
(2013-09) Yazıcı, Yaprak Ayazoğlu; Arı, İsmail; Arı, İsmail; Aktemur, Tankut Barış; Kayış, Enis; Department of Computer Science; Yazıcı, Yaprak Ayazoğlu
It is now clear that social networking services are evolving towards mobile web applications and continuous location sharing is also becoming a trend. In this evolution, we believe that the next step will be complete and continuous route and experience sharing. A route-based social networking cloud platform is a service in which users share their travel routes as well as experiences and stories using their mobile devices, or search for and get matched with people with similar travel and transportation habits in real-time. This work mainly focuses on the development of an end-to-end route-based social networking cloud platform service and its client-side mobile application. First, we describe the design and implementation of our real-time taxi ride-sharing service for metropolitan areas, which is a specific application of the route-sharing service. This system is composed of 1) taxi location data collection system, 2) real-time passenger coupling service and 3) a dashboard for visualization and analysis of the results. Second, we describe our location tracking mobile application that captures rich location-based information and saves it to the cloud.

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