Bilgisayar Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12469/45

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Citation - WoS: 4
Citation - Scopus: 8
Accurate Indoor Positioning With Ultra-Wide Band Sensors
(Tubitak, 2020) Arsan, Taner
Ultra-wide band is one of the emerging indoor positioning technologies. In the application phase, accuracy and interference are important criteria of indoor positioning systems. Not only the method used in positioning, but also the algorithms used in improving the accuracy is a key factor. In this paper, we tried to eliminate the effects of off-set and noise in the data of the ultra-wide band sensor-based indoor positioning system. For this purpose, optimization algorithms and filters have been applied to the raw data, and the accuracy has been improved. A test bed with the dimensions of 7.35 m x 5.41 m and 50 cm x 50 cm grids has been selected, and a total of 27,000 measurements have been collected from 180 test points. The average positioning error of this test bed is calculated as 16.34 cm. Then, several combinations of algorithms are applied to raw data. The combination of Big Bang-Big Crunch algorithm for optimization, and then the Kalman Filter have yielded the most accurate results. Briefly, the average positioning error has been reduced from 16.34 cm to 7.43 cm.
Amplitude and Frequency Modulations With Cellular Neural Networks
(Springer, 2015) Tander, Baran; Özmen, Atilla
Amplitude and frequency modulations are still the most popular modulation techniques in data transmission at telecommunication systems such as radio and television broadcasting gsm etc. However the architectures of these individual systems are totally different. In this paper it is shown that a cellular neural network with an opposite-sign template can behave either as an amplitude or a frequency modulator. Firstly a brief information about these networks is given and then the amplitude and frequency surfaces of the generated quasi-sine oscillations are sketched with respect to various values of their cloning templates. Secondly it is proved that any of these types of modulations can be performed by only varying the template components without ever changing their structure. Finally a circuit is designed simulations are presented and performance of the proposed system is evaluated. The main contribution of this work is to show that both amplitude and frequency modulations can be realized under the same architecture with a simple technique specifically by treating the input signals as template components.
Citation - WoS: 1
Citation - Scopus: 1
Bayesian Estimation of Discrete-Time Cellular Neural Network Coefficients
(TUBITAK Scientific & Technical Research Council Turkey, 2017) Özer, Hakan Metin; Özmen, Atilla; Şenol, Habib
A new method for finding the network coefficients of a discrete-time cellular neural network (DTCNN) is proposed. This new method uses a probabilistic approach that itself uses Bayesian learning to estimate the network coefficients. A posterior probability density function (PDF) is composed using the likelihood and prior PDFs derived from the system model and prior information respectively. This posterior PDF is used to draw samples with the help of the Metropolis algorithm a special case of the Metropolis--Hastings algorithm where the proposal distribution function is symmetric and resulting samples are then averaged to find the minimum mean square error (MMSE) estimate of the network coefficients. A couple of image processing applications are performed using these estimated parameters and the results are compared with those of some well-known methods.
Citation - WoS: 4
Citation - Scopus: 6
Channel Estimation for Realistic Indoor Optical Wireless Communication in Aco-Ofdm Systems
(Springer, 2018) Özmen, Atilla; Şenol, Habib
In this paper channel estimation problem in a visible light communication system is considered. The information data is transmitted using asymmetrical clipped optical orthogonal frequency division multiplexing. Channel estimation and symbol detection are performed by the Maximum Likelihood and the Linear Minimum Mean Square Error detection techniques respectively. The system performance is investigated in realistic environment that is simulated using an indoor channel model. Two different channels are produced using the indoor channel model. Symbol error rate (SER) performance of the system with estimated channels is presented for QPSK and 16-QAM digital modulation types and compared with the perfect channel state information. As a mean square error (MSE) performance benchmark for the channel estimator Cramer-Rao lower bound is also derived. MSE and SER performances of the simulation results are presented.
Citation - WoS: 13
Citation - Scopus: 17
Contraction and Deletion Blockers for Perfect Graphs and H-Free Graphs
(Elsevier Science, 2018) Diner, Öznur Yaşar; Paulusma, Daniel; Picouleau, Christophe; Ries, Bernard
We study the following problem: for given integers d k and graph G can we reduce some fixed graph parameter pi of G by at least d via at most k graph operations from some fixed set S? As parameters we take the chromatic number chi clique number omega and independence number alpha and as operations we choose edge contraction ec and vertex deletion vd. We determine the complexity of this problem for S = {ec} and S = {vd} and pi is an element of{chi omega alpha} for a number of subclasses of perfect graphs. We use these results to determine the complexity of the problem for S = {ec} and S = {vd} and pi is an element of{chi omega alpha} restricted to H-free graphs. (C) 2018 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Cosmic Ray Intensity Variation During a Cme
(Pergamon-Elsevier Science Ltd, 2002) Kandemir, Gulcın; Geçkinli, Melih; Fırat, Coşkun; Yılmaz, Melek; Özuğur, B
The June 6 2000 coronal mass ejection was an exceptional full halo which made it possible to measure cosmic ray (CR) decrease with a simple experimental set-up. Variation in the local secondary cosmic ray density has been investigated by means of gamma rays. The experiment site was located in Istanbul (41.1N 29.0E). CR electrons and slow gamma rays have been eliminated. The CR density has dropped drastically starting on June 8 2000. The counts have been compared with the pre-shock levels and some other cases of CMEs. During strong solar modulation the local counts of secondary CR intensity values dropped down as much as 24%. (C) 2002 Elsevier Science Ltd. All rights reserved.
Citation - WoS: 11
Citation - Scopus: 11
Derivation of the Optical Constants of Spin Coated Ceo2-Tio2 Thin Films Prepared by Sol-Gel Route
(Pergamon-Elsevier Science Ltd, 2011) Ghodsi, Farhad E.; Tepehan, Fatma Zehra; Tepehan, Galip Gültekin
Ternary thin films of cerium titanium zirconium mixed oxide were prepared by the sol-gel process and deposited by a spin coating technique at different spin speeds (1000-4000 rpm). Ceric ammonium nitrate ce(NO3)(6)(NH4)(2) titanium butoxide Ti[O(CH2)(3)CH3](4) and zirconium propoxide Zr(OCH2CH2CH3)(4) were used as starting materials. Differential calorimetric analysis (DSC) and thermogravimetric analysis (TGA) were carried out on the CeO2-TiO2-ZrO2 gel to study the decomposition and phase transition of the gel. For molecular structural elemental and morphological characterization of the films Fourier Transform Infrared (FTIR) spectral analysis X-ray diffraction (XRD) energy dispersive X-ray spectroscopy (EDS) cross-sectional scanning electron microscopy (SEM) and atomic force microscopy (AFM) were carried out. All the ternary oxide thin films were amorphous. The optical constants (refractive index extinction coefficient band gap) and thickness of the films were determined in the 350-1000 nm wavelength range by using an nkd spectrophotometer. The refractive index extinction coefficient and thickness of the films were changed by varying the spin speed. The oscillator and dispersion energies were obtained using the Wemple-DiDomenico dispersion relationship. The optical band gap is independent of the spin speed and has a value of about E-g approximate to 2.82 +/- 0.04 eV for indirect transition. (C) 2011 Published by Elsevier Ltd.
Citation - WoS: 1
Citation - Scopus: 1
A Framework for Combined Recognition of Actions and Objects
(Springer-Verlag Berlin, 2012) Ar, İlktan; Akgül, Yusuf Sinan
This paper proposes a novel approach to recognize actions and objects within the context of each other. Assuming that the different actions involve different objects in image sequences and there is one-to-one relation between object and action type we present a Bayesian network based framework which combines motion patterns and object usage information to recognize actions/objects. More specifically our approach recognizes high-level actions and the related objects without any body-part segmentation hand tracking and temporal segmentation methods. Additionally we present a novel motion representation based on 3D Haar-like features which can be formed by depth color or both images. Our approach is also appropriate for object and action recognition where the involved object is partially or fully occluded. Finally experiments show that our approach improves the accuracy of both action and object recognition significantly.
Citation - WoS: 1
Citation - Scopus: 1
Hybrid Mpi Plus Upc Parallel Programming Paradigm on an Smp Cluster
(TUBITAK Scientific & Technical Research Council Turkey, 2012) Bozkuş, Zeki
The symmetric multiprocessing (SMP) cluster system which consists of shared memory nodes with several multicore central processing units connected to a high-speed network to form a distributed memory system is the most widely available hardware architecture for the high-performance computing community. Today the Message Passing Interface (MPI) is the most widely used parallel programming paradigm for SMP clusters in which the MPI provides programming both for an SMP node and among nodes simultaneously. However Unified Parallel C (UPC) is an emerging alternative that supports the partitioned global address space model that can be again employed within and across the nodes of a cluster. In this paper we describe a hybrid parallel programming paradigm that was designed to combine MPI and UPC programming models. This paradigm's objective is to mix the MPI's data locality control and scalability strengths with UPC's fine-grain parallelism and ease of programming to achieve multiple-level parallelism at the SMP cluster which itself has multilevel parallel architecture. Utilizing a proposed hybrid model and comparing MPI-only to UPC-only implementations this paper presents a detailed description of Cannon's algorithm benchmark application with performance results of a random-access benchmark and the Barnes-Hut N-Body simulation. Experiments indicate that the hybrid MPI+UPC model can significantly provide performance increases of up to double in comparison with UPC-only implementation and up to 20% increases in comparison to MPI-only implementation. Furthermore an optimization was achieved that improved the hybrid performance by an additional 20%.
Citation - WoS: 12
Citation - Scopus: 15
Improving Opencl Programmability With the Heterogeneous Programming Library
(Elsevier Science Bv, 2015) Vinas, Moises; Fraguela, Basilio B.; Bozkuş, Zeki; Andrade, Diego
The use of heterogeneous devices is becoming increasingly widespread. Their main drawback is their low programmability due to the large amount of details that must be handled. Another important problem is the reduced code portability as most of the tools to program them are vendor or device-specific. The exception to this observation is OpenCL which largely suffers from the reduced programmability problem mentioned particularly in the host side. The Heterogeneous Programming Library (HPL) is a recent proposal to improve this situation as it couples portability with good programmability. While the HPL kernels must be written in a language embedded in C++ users may prefer to use OpenCL kernels for several reasons such as their growing availability or a faster development from existing codes. In this paper we extend HPL to support the execution of native OpenCL kernels and we evaluate the resulting solution in terms of performance and programmability achieving very good results.
Citation - WoS: 5
Citation - Scopus: 5
Information Theoretical Performance Limits of Single-Carrier Underwater Acoustic Systems
(Inst Engineering Technology-IET, 2014) Nouri, Hatef; Uysal, Murat; Panayırcı, Erdal; Şenol, Habib
In this study the authors investigate the information theoretical limits on the performance of point-to-point single-carrier acoustic systems over frequency-selective underwater channels with intersymbol interference. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise the authors derive an expression for channel capacity and demonstrate the dependency on channel parameters such as the number location and power delay profile of significant taps as well as environmental parameters such as distance temperature salinity pressure and depth. Then the authors use this expression to determine the optimal carrier frequency input signalling and bandwidth for capacity maximisation.
Citation - WoS: 14
Citation - Scopus: 17
Joint Channel Estimation and Symbol Detection for Ofdm Systems in Rapidly Time-Varying Sparse Multipath Channels
(Springer, 2015) Şenol, Habib
In this paper we propose a space-alternating generalized expectation maximization (SAGE) based joint channel estimation and data detection algorithm in compressive sensing (CS) framework for orthogonal frequency-division multiplexing (OFDM) systems in rapidly time-varying sparse multipath channels. Using dynamic parametric channel model the sparse multipath channel is parameterized by a small number of distinct paths each represented by the path delays and path gains. In our model we assume that the path gains rapidly vary within the OFDM symbol duration while the number of paths and path delays vary symbol by symbol. Since the convergency of the SAGE algorithm needs statistically independent parameter set of interest to be estimated we specifically choose the discrete orthonormal Karhunen-Loeve basis expansion model (DKL-BEM) to provide statistically independent BEM coefficients within one OFDM symbol duration and use just a few significant BEM coefficients to represent the rapidly time-varying path gains. The resulting SAGE algorithm that also incorporates inter-channel interference cancellation updates the data sequences and the channel parameters serially. The computer simulations show that our proposed algorithm has better channel estimation and symbol error rate performance than that of the orthogonal matching pursuit algorithm that is commonly proposed in the CS literature.
Citation - WoS: 4
Citation - Scopus: 6
A Low-Complexity Time-Domain Mmse Channel Estimator for Space-time/Frequency Block-Coded Ofdm Systems
(Hindawi Publishing Corporation, 2006) Şenol, Habib; Çırpan, Hakan Ali; Panayırcı, Erdal
Focusing on transmit diversity orthogonal frequency-division multiplexing (OFDM) transmission through frequency-selective channels this paper pursues a channel estimation approach in time domain for both space-frequency OFDM (SF-OFDM) and space-time OFDM (ST-OFDM) systems based on AR channel modelling. The paper proposes a computationally efficient pilot-aided linear minimum mean-square-error (MMSE) time-domain channel estimation algorithm for OFDM systems with transmitter diversity in unknown wireless fading channels. The proposed approach employs a convenient representation of the channel impulse responses based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion no matrix inversion is required in the proposed MMSE estimator. Subsequently optimal rank reduction is applied to obtain significant taps resulting in a smaller computational load on the proposed estimation algorithm. The performance of the proposed approach is studied through the analytical results and computer simulations. In order to explore the performance the closed-form expression for the average symbol error rate (SER) probability is derived for the maximum ratio receive combiner (MRRC). We then consider the stochastic Cramer-Rao lower bound(CRLB) and derive the closed-form expression for the random KL coefficients and consequently exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also analyze the effect of a modelling mismatch on the estimator performance. Simulation results confirm our theoretical analysis and illustrate that the proposed algorithms are capable of tracking fast fading and improving overall performance. Copyright (C) 2006 Hindawi Publishing Corporation. All rights reserved.
Citation - WoS: 9
Citation - Scopus: 9
Navigation of Non-Communicating Autonomous Mobile Robots With Guaranteed Connectivity
(Cambridge Univ Press, 2013) Cezayirli, Ahmet; Kerestecioğlu, Feza
We consider the connectivity of autonomous mobile robots. The robots navigate using simple local steering rules without requiring explicit communication among themselves. We show that using only position information of neighbors the group connectivity can be sustained even in the case of bounded position measurement errors and the occlusion of robots by other robots in the group. In implementing the proposed scheme sub-optimal solutions are invoked to avoid an excessive computational burden. We also discuss the possibility of deadlock which may bring the group to a standstill and show that the proposed methodology avoids such a scenario in real-life settings.
New 2-Edge Graphs From Bipartite Graphs
(Wiley-Blackwell, 2016) Çalışkan, Cafer
Let G be a graph of order n satisfying that there exists lambda epsilon Z(+) for which every graph of order n and size t is contained in exactly. distinct subgraphs of the complete graph K-n isomorphic to G. Then G is called t-edge-balanced and. the index of G. In this article new examples of 2-edge-balanced graphs are constructed from bipartite graphs and some further methods are introduced to obtain more from old. (C) 2015 Wiley Periodicals Inc.
Citation - WoS: 1
Citation - Scopus: 1
New Infinite Families of 2-Edge Graphs
(Wiley-Blackwell, 2014) Çalışkan, Cafer; Chee, Yeow Meng
A graph G of order n is called t-edge-balanced if G satisfies the property that there exists a positive for which every graph of order n and size t is contained in exactly distinct subgraphs of Kn isomorphic to G. We call the index of G. In this article we obtain new infinite families of 2-edge-balanced graphs.
Citation - WoS: 2
Nonuniform Sampling for Detection of Abrupt Changes
(Birkhauser Boston Inc, 2003) Kerestecioğlu, Feza; Tokat, Sezai
In this work detection of abrupt changes in continuous-time linear stochastic systems and selection of the sampling interval to improve the detection performance are considered. Cost functions are proposed to optimize both uniform and nonuniform sampling intervals for the well-known cumulative sum algorithm. Some iterative techniques are presented to make online optimization computationally feasible. It is shown that considerable improvement in the detection performance can be obtained by using nonuniform sampling intervals.
Citation - WoS: 1
Citation - Scopus: 1
Partitioning 3-Arcs Into Steiner Triple Systems
(Wiley, 2017) Çalışkan, Cafer
In this article it is shown that there is a partitioning of the set of 3-arcs in a projective plane of order three into nine pairwise disjoint Steiner triple systems of order 13.
Citation - WoS: 2
Citation - Scopus: 3
Predictive Control of a Constrained Pressure and Level System
(TUBITAK Scientific & Technical Research Council Turkey, 2015) Kaplanoğlu, Erkan; Arsan, Taner; Varol, Hüseyin Selçuk
The focus of this paper is the implementation of a constrained predictive control algorithm implemented in Multi-Parametric Toolbox (MPT) which is a free MATLAB toolbox for design analysis and implementation of controllers for constrained linear nonlinear and hybrid systems. In general MPT is used for modeling systems offline. The novelty of this study is that real-time mode MPT is used in process control. We also combined the Model Predictive Control Toolbox with MPT. This novel controller is considered a real-time controller of level-pressure systems. In this study a special type of model predictive control algorithm the constrained continuous-time generalized control is used as a controller. The advantages of the controller are illustrated by comparing it to a decoupling PI control.
Citation - WoS: 2
Citation - Scopus: 2
Subchannel Allocation and Power Control for Uplink Femtocell Radio Networks With Imperfect Channel State Information
(Springer, 2019) Altabbaa, Mhd Tahssin; Arsan, Taner; Panayırcı, Erdal
Femtocell technology is emerging as a key solution for mobile operators for its advantage in coverage and capacity enhancement along with its cost effectiveness. However, densely and randomly deployed femtocells while sharing the frequency spectrum of the macrocell arises a severe interference environment. In femtocells deployment, interference coming from a femtocell user affect other femtocell users and the macrocell users, where maintaining the communication of the users in both tiers is a mandatory. In this paper, a novel power control algorithm is proposed for optimizing the uplink transmission powers of femtocell users in a TDD-OFDM communication model in the presence of a channel estimation error and intra-tier interference. We consider signal to interference and noise ratio as the objective function where the proposed constraints deal with: (1) the aggregated interference coming from femtocell tier and received at the active subchannels by the macrocell tier, and (2) the maximum uplink power a femtocell user equipment is allowed to occupy per admissible subchannel. Based on Lagrangian multipliers, the proposed power control approach grants the priority in subchannel usage for macrocell user, then it allows or prohibits frequency reuse of a subchannel with the femtocell tier. A comparison is then made with a pure isolation method that does not allow femtocell user equipments to occupy the active subchannels at the macrocell tier. The numerical results of the proposed approach show a high total rate of femtocell user equipments and the average uplink power is below the maximum allowable transmission power.

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