Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Prunable collision free random interleaver design(Springer, 2012) Gazi, OrhanIn this article we introduce a new collision free prunable random interleaver. The suggested interleaver is a joint structure involving rectangular and S-random interleaver. It comprises a general model for all kind of collision free prunable random interleavers. In addition, it can be designed for any number of parallel processors and any length of information sequence vector and can be considered also as a template for collision free prunable interleavers. The proposed interleaver can be used with all kind of turbo-like codes. The performance of the proposed interleaver is measured with parallel decodable serially concatenated convolutional codes (PDSCCCs) and compared to the PDSCCCs' performance with collision full S-random interleaver.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: 15Citation - Scopus: 16Binary Phase Shift Keying-Subcarrier Intensity Modulation Performance in Weak Oceanic Turbulence(Elsevier, 2019) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerThe performance analysis of underwater wireless optical communication (UWOC) system that employs binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) is investigated in weak oceanic turbulence. BPSK-SIM Gaussian beam and finite sized positive-intrinsic-negative (PIN) photodetector are employed at the transmitter and at the receiver, respectively. Bit error rate (BER) is taken as the performance indicator and in the evaluation of the BER, the required signal power and the aperture averaged scintillation index are obtained respectively by the use of the extended Huygens-Fresnel principle and the Rytov theory. Considering various noise types in underwater turbulence, BER variations are examined versus the oceanic turbulence parameters and the photodetector parameters, namely receiver aperture diameter, PIN-responsivity, noise factor, load resistor, and the electronic bandwidth. (c) 2019 Elsevier B.V. All rights reserved.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: 27Citation - Scopus: 28Beam Wander of J 0- and I 0-Bessel Gaussian Beams Propagating in Turbulent Atmosphere(Springer, 2010) Eyyuboglu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.; Cil, C. Z.Root mean square (rms) beam wander of J (0)-Bessel Gaussian and I (0)-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J (0)-Bessel Gaussian and the I (0)-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameter.Article Citation - WoS: 6Citation - Scopus: 7Bombardment of Ni(100) Surface With Low-Energy Argons: Molecular Dynamics Simulations(Elsevier Science Sa, 2005) Güvenç, ZB; Hippler, R; Jackson, BResults of molecular dynamics simulations of the sputtering of Ni(100) by Ar atoms are reported. The solid is described by an embedded atom potential, and the interaction between the projectile and the metal atoms is modelled by a Morse-like function. Processes leading to Ni atom emissions from the lattice are analysed over the energy range of 70-80 eV In this energy range cluster (larger than three atoms) emission is not observed. The maximum penetration depth of Ar, the kinetic energy and angular distributions of the reflected Ar, and the sputtered Ni atoms are evaluated as functions of the impact energy and sputtering time. The computed sputtering yield is compared with the available theoretical and experimental data. (C) 2004 Elsevier B.V. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 3Collisionless Fragmentation of Non-Rotating Nin (n=4-14) Clusters: a Molecular Dynamics Study(Iop Publishing Ltd, 2003) Avci, H; Çivi, M; Güvenç, ZB; Jellinek, JCollisionless fragmentation of non-rotating Ni-n (n = 4-14) clusters is studied using micro-canonical molecular dynamics (MD) computer simulations. The clusters are modelled by an embedded-atom potential energy surface. The distributions of the channel-specific fragmentation probabilities, and the global and channel-specific fragmentation rate constants are computed and analysed as functions of the internal energy and size of the clusters. The trends derived from the dynamical calculations are compared to the fragmentation energy patterns, those of the Rice-Ramsperger-Kassel (RRK) and statistical approaches. The rate constants are an order of magnitude smaller for the RRK model than with both the MD and transition-state theory approaches. The results are also compared with the other multi-channel fragmentation works.Article Citation - WoS: 27Citation - Scopus: 31The Effects of Lattice Motion on Eley-Rideal and Hot Atom Reactions: Quasiclassical Studies of Hydrogen Recombination on Ni(100)(Amer Chemical Soc, 2002) Guvenc, ZB; Sha, XW; Jackson, BQuasiclassical methods are used to simulate the interactions of H or D atom beams with D- or H-covered Ni(100) surfaces. The Ni substrate is treated as a multilayer slab, and the Ni atoms are allowed to move. The model potential energy surface is fit to the results of detailed total-energy calculations based on density functional theory. Most of the incident atoms trap to form hot atoms, which can eventually react with an adsorbate, or dissipate their energy and stick. The incident atom is found to lose several tenths of an eV of energy into the metal, upon initially colliding with the surface. This limits reflection to a few percent, at all coverages, and secondary reactions between adsorbates are significantly lowered. Long time hot atom reactions are also found to be damped out by the inclusion of lattice motion, leading to increased sticking, even at high coverages where dissipation into the adsorbates should be the primary energy loss mechanism. Overall, the inclusion of lattice motion is found to improve agreement with experiment.Article Citation - WoS: 60Citation - Scopus: 65Degree of Polarization for Partially Coherent General Beams in Turbulent Atmosphere(Springer, 2007) Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.The degree of polarization is found for optical excitations of cosh-Gaussian, cos-Gaussian and annular-Gaussian beams in a turbulent atmosphere. The related formulation is based on the beam coherence polarization matrix. The self and mutual coherence functions appearing in the beam coherence polarization matrix are evaluated, when the above mentioned excitations exhibit partial source coherence for self and cross fields. Plots showing the variation of the degree of polarization are provided versus the propagation length when the source size, displacement parameter, structure constant and the degree of source coherence for self and cross fields change.Article Citation - WoS: 31Citation - Scopus: 36Beam Wander of Dark Hollow, Flat-Topped and Annular Beams(Springer Heidelberg, 2008) Cil, C. Z.; Eyyuboglu, H. T.Benefiting from the earlier derivations for the Gaussian beam, we formulate beam wander for dark hollow (DH) and flat-topped (FT) beams, also covering the annular Gaussian (AG) beam as a special case. Via graphical illustrations, beam wander variations of these beams are analyzed and compared among themselves and to the fundamental Gaussian beam against changes in propagation length, amplitude factor, source size, wavelength of operation, inner and outer scales of turbulence. These comparisons show that in relation to the fundamental Gaussian beam, DH and FT beams will exhibit less beam wander, particularly at small primary beam source sizes, lower amplitude factors of the secondary beam and higher beam orders. Furthermore, DH and FT beams will continue to preserve this advantageous position all throughout the considered range of wavelengths, inner and outer scales of turbulence. FT beams, in particular, are observed to have the smallest beam wander values among all, up to certain source sizes.