Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Investigation of Factors Affecting Noise Robustness in Voice Activity Detectors(Gazi Univ, Fac Engineering Architecture, 2023) Ozaydin, SelmaIn this manuscript, some voice activity detectors (VADs) in the literature were examined in terms of factors affecting their robustness under different acoustic noise conditions and in this context, the changes in detection accuracy rates according to changing noise conditions were tested. In this scope, the effect of situations such as whether the threshold value used in the decision phase in VAD methods is fixed or adaptive, the analysis window is short or long, the use of more than one feature vector together has been evaluated and analyzed comparatively. While three of the four different VAD detectors examined in this manuscript use feature vectors within the short-term analysis window while generating the decision result, one decides according to the measurement result of long-term spectral vectors. The VAD detectors in the article have been tested using the NOIZEUS noisy speech database. Thus, the performance of the analyzed VADs has been evaluated under different acoustic conditions using an extensive database that has already taken place in the literature. During the testing of the analyzed VADs, different input noise speech signals with environmental background noises between [15-0dB] such as restaurant, car, street, or station were tested. Tests were carried out using objective test measurement methods and the detection accuracy rate of each VAD method was measured. The results showed that each method gave different endurance performance in adverse environmental conditions.Article Citation - WoS: 5Citation - Scopus: 5Bessel Beam Diffraction by an Aperture in an Opaque Screen(Hindawi Ltd, 2015) Basdemir, Husnu DenizThe scattering of the Bessel beam by a circular aperture in an opaque screen is investigated by the geometrical theory of diffraction approach. The geometrical optics and diffracted and scattered fields are obtained. The effect of the aperture to the scattering process is analyzed. The uniform versions of field expressions are derived. The geometrical optics and diffracted and scattered fields are examined numerically.Article Citation - WoS: 7Citation - Scopus: 22Joint Next-hop/Relay Selection for Distributive Multihop Cooperative Networks(Hindawi Ltd, 2015) Alkhayyat, AhmedCooperative networks that use adjacent nodes to relay hearing data are employed as an effective technique to deal with channel fading, thereby enhancing the network performances. Next-hop and relay nodes selection schemes determine the optimal next-hop node toward the destination and relay node between the source and the optimal next-hop and/or destination. Offering joint next-hop and relay node selection in distributive multihop cooperative networks will enable the source to select the optimal next-hop node and relay node that can improve the system performance. In this paper, we propose a joint next-hop node and relay node selection (JNRS) protocol for wireless distributive multihop cooperative networks. The goal of JNRS is to reduce the spectral efficiency loss and outage probability. Analysis results show that JNRS can enhance the cooperative networks performance under general conditions compared to cooperative networks without the JNRS protocol.Article Citation - WoS: 24Citation - Scopus: 24Molecular Dynamics Simulation of the Melting Behaviour of 12-, 13-, 14-Atom Icosahedral Platinum Clusters(Iop Publishing Ltd, 2004) Sebetci, A; Guvenc, ZBUsing the molecular dynamics simulation technique, we have studied the melting behaviour of free, icosahedral Pt-N clusters in the size range of N = 12-14. The Voter and Chen version of an embedded-atom model, derived by fitting to experimental data of both the diatomic molecule and bulk platinum simultaneously, has been employed in this study. We present an atom-resolved analysis method that includes physical quantities such as the root mean square bond-length fluctuation and coordination number for individual atoms as functions of temperature. The results show that while the 13-atom icosahedron and the 12-atom cluster with a vacancy on the icosahedral surface exhibit one-stage melting, the 14-atom cluster with an adatom on the icosahedral surface undergoes two-stage melting, as the temperature increases.Editorial Citation - WoS: 6Citation - Scopus: 6Applications of Cognitive Radio Networks: Recent Advances and Future Directions(Sage Publications inc, 2016) Pan, Miao; Joshi, Gyanendra Prasad; Gazi, Orhan; He, Jianhua; Coupechoux, Marceau; Kim, Sung W.Article Citation - WoS: 3Citation - Scopus: 6Decoding of Lt-Like Codes in the Absence of Degree-One Code Symbols(Electronics Telecommunications Research inst, 2016) Gazi, Orhan; Abdulkhaleq, Nadhir I.Luby transform (LT) codes were the first practical rateless erasure codes proposed in the literature. The performances of these codes, which are iteratively decoded using belief propagation algorithms, depend on the degree distribution used to generate the coded symbols. The existence of degree-one coded symbols is essential for the starting and continuation of the decoding process. The absence of a degree-one coded symbol at any instant of an iterative decoding operation results in decoding failure. To alleviate this problem, we proposed a method used in the absence of a degree-one code symbol to overcome a stuck decoding operation and its continuation. The simulation results show that the proposed approach provides a better performance than a conventional LT code and memory-based robust soliton distributed LT code, as well as that of a Gaussian elimination assisted LT code, particularly for short data lengths.Article Citation - WoS: 6Citation - Scopus: 6Field Correlations for Off-Axis Gaussian Laser Beams in Atmospheric Turbulence(Amer Geophysical Union, 2014) Baykal, YahyaThe absolute field correlations in atmospheric turbulence are evaluated for the off-axis optical Gaussian beam incidence. Evaluations in the practical range of the source and the turbulent medium parameters show that an increase in the diagonal length at the receiver plane causes the absolute field correlations of the off-axis Gaussian beam to decrease. At a fixed receiver diagonal length, the off-axis Gaussian beams having smaller displacement parameters and larger source sizes exhibit larger absolute field correlations. Comparing the absolute field correlations of the off-axis Gaussian beams in atmospheric turbulence with their no turbulence counterparts, it is observed that the behavior of the absolute field correlation variations remains the same; however, the diminishing of the absolute field correlations in turbulence occurs at smaller diagonal lengths.Article Citation - WoS: 17Citation - Scopus: 22Turbo Product Codes Based on Convolutional Codes(Wiley, 2006) Yilmaz, Ali Ozgur; Gazi, OrhanIn this article, we introduce a new class of product codes based on convolutional codes, called convolutional product codes. The structure of product codes enables parallel decoding, which can significantly increase decoder speed in practice. The use of convolutional codes in a product code setting makes it possible to use the vast knowledge base for convolutional codes as well as their flexibility in fast parallel decoders. Just as in turbo codes, interleaving turns out to be critical for the performance of convolutional product codes. The practical decoding advantages over serially-concatenated convolutional codes are emphasized.