Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260

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Citation Count: Yıldırım, E.K., Güvenç. Z.B. (2009). A density functional study of small Li-B and Li-B-H clusters. International Journal of Hydrogen Energy , 34(11), 4797-4816. http://dx.doi.org/10.1016/j.ijhydene.2009.03.051
A density functional study of small Li-B and Li-B-H clusters
(Pergamon-Elsevier Science Ltd, 2009) Yıldırım, Erdem Kamil; Güvenç, Büşra; 1155
In this work we present the results of a detailed theoretical research for the small Li(n)B(m) clusters and their hydrogen storage properties by means of density functional theory. All calculations were performed by using Gaussian03 program. For the optimization of the clusters 6-311++G(d,p) basis set was employed. We have chosen global minimum of B(6) cluster as the starting point and replaced the boron atoms one at a time, in a stepwise manner, with Li atoms. For these new structures we have searched for the stable configurations, and calculated their energies, HOMO-LUMO energy gaps, Raman and infrared data, average boron, and lithium charge distribution, and vibrational frequencies. Our results show that as the number of Li atoms increases, stability of the clusters decreases and they become more reactive. In addition to that, there are significant charge transfers from boron atoms to lithium atoms on average. The hydrogen storage capabilities of the most stable isomers of Li(n)B(m) and B(6) clusters have also been investigated by the same methods, and the results are compared. The Li(3)B(3) has the highest hydrogen storage capacity among the clusters investigated in this study. Furthermore, formation of hydrogen molecules is observed in the vicinity of the clusters, some of which are attached to the Li atoms. In addition, as the number of hydrogen atoms increases, the boron atoms are separated from the other boron atoms, and they form satellite BH(x) (x = 3,4) clusters around the center. These are attached to the system by a bridging bond of a hydrogen or a Li atom
Citation Count: Umul, Y.Z. (2011). A hybrid Maliuzhinets/PO method for diffraction problems by impedance wedges. Optic Communications, 284(19), 4289-4294. http://dx.doi.org/10.1016/j.optcom.2011.06.045
A hybrid Maliuzhinets/PO method for diffraction problems by impedance wedges
(Elsevier Science Bv, 2011) Umul, Yusuf Ziya; 42699
The solution of Maliuzhinets of the diffraction problem of waves by an impedance wedge is transformed into a physical optics integral. The resultant expression is suitable for the investigation of various diffraction problems having impedance wedges. The method is applied to the scattering of waves by an impedance spherical reflector with wedge structure at its discontinuity. The results are examined numerically.
Citation Count: Şener, G. (2013). A new algorithm to locate the zero fields in antenna radiation pattern measurements. Journal Of Electromagnetic Waves And Applications, 27(10), 1238-1245. http://dx.doi.org/10.1080/09205071.2013.805169
A new algorithm to locate the zero fields in antenna radiation pattern measurements
(Taylor&Francis Ltd, 2013) Şener, Göker; 17740
This article describes a new method to determine the directions of the zero fields in antenna radiation measurements. Zero-field detection is important when there are null constraints in antenna analysis or synthesis. To identify the directions of the zero fields, the general practice is to measure the propagating field in a number of small incremental angles in 2D space. For an antenna with narrow beam characteristics, even more sampling is necessary for accuracy. As a result, the time efficiency is decreased. In order to speed up the process, an optimization algorithm may be employed such that the measurements may converge to the zero-field locations faster. However, the difficulty is that many optimization algorithms require the use of derivatives of the pattern function. The algorithm proposed in this paper is derivative free and utilizes only the amplitude data, hence it is suitable and applicable to antenna measurements providing time efficiency.
Citation Count: Gazi, Orhan. "A New Companding Technique for Papr Reduction in Ofdm Communication Systems", International Congress On Ultra Modern Telecommunications and Control Systems And Workshops, (2011).
A New Companding Technique for Papr Reduction in Ofdm Communication Systems
(2011) Gazi, Orhan; 102896
One of the major disadvantages of OFDM communication systems is their high peak-to-average power ratio (PAPR) which degrades system performance when nonlinear power amplifiers are employed. Among the proposed PAPR techniques companding is favorable due to its simplicity and easy of implementation. In this article, using the arctangent function we propose a new compading technique for PAPR reduction. We compare the proposed technique to the previously suggested exponential companding, and μ-law companding methods. Via computer simulations it is verified that the proposed technique is better than exponential and μ-law companding methods for PAPR reduction.
Citation Count: Mezaal, Y.S.; Eyyuboglu, Halil T.; Ali, J.K., "A New Design of Dual Band Microstrip Bandpass Filter Based On Peano Fractal Geometry: Design and Simulation Results", Mediterranean Microwave Symposium, (2013).
A New Design of Dual Band Microstrip Bandpass Filter Based On Peano Fractal Geometry: Design and Simulation Results
(2013) Mezaal, Yaqeen S.; Eyyuboğlu, Halil T.; Ali, Jawad K.; 7688
The proposed filter design topology is based on dual coupled resonators constructed in the form of Peano fractal geometry. A dual-band microstrip bandpass filter with a quasi-elliptic response has been designed for first time based on 1st iteration Peano fractal geometry at resonant frequencies of 2.25 GHz and 4.825 GHz using a substrate of a relative dielectric constant of 10.8 and thickness of 1.27 mm. The performance of the bandpass filter structure has been analyzed using a method of moments (MoM) based software package, Microwave Office 2009, from Advanced Wave Research Inc. Results show that this filter possesses good frequency response characteristics in addition to dual bands gained which can be used for modern communication applications.
Citation Count: Umul, Y.Z. (2013). A new representation of the Kirchhoffs diffraction integral. Optic Communications, 291 48-51. http://dx.doi.org/10.1016/j.optcom.2012.11.038
A new representation of the Kirchhoffs diffraction integral
(Elsevier Science Bv, 2013) Umul, Yusuf Ziya; 42699
The diffraction integral of Kirchhoff is rearranged according to its integral boundaries. The new approach is based on the theory of the edge dislocation waves and provides a more correct field representation for the semi-infinite and infinite integrals in the direct numerical computation. The integral is studied on the diffraction problem of plane waves by a perfectly conducting half-plane. The correctness of the scattering diagrams is compared with the classical approach and the Fresnel integral representation of the scattered waves numerically
Citation Count: Mezaal, Yaqeen S.; Eyyuboglu, Halil T.; Ali, Jawad K. "A Novel Design of Two Loosely Coupled Bandpass Filter Based on Hilbert-zz Resonator with Higher Harmonic Suppression", 2013 Third International Conference On Advanced Computing & Communication Technologies (Acct 2013), pp. 343-347, (2013).
A Novel Design of Two Loosely Coupled Bandpass Filter Based On Hilbert-Zz Resonator With Higher Harmonic Suppression
(IEEE, 2013) Mezaal, Yaqeen S.; Eyyuboğlu, Halil T.; Ali, Jawad K.; 7688
New characteristics of fractal design scheme has been introduced to generate compact two poles capacitively coupled microstrip bandpass filter by using additional coupling stubs for different wireless applications. The presented fractal scheme is based on specific type of Hilbert space-filling curve which is called Hilbert-zz fractal geometry. The performance of generated bandpass filter structure has been analyzed using Sonnet software package with a relative dielectric constant of 9 and a substrate thickness of 1.27 mm. Results show that these filters possess good transmission and return loss characteristics, besides higher harmonics suppressions; meeting the specifications of most of wireless communication systems.
Citation Count: Abdulkhaleq, Nadhir Ibrahim; Gazi, Orhan (2017). "A Sequential Coding Approach for Short Length LT Codes over A WGN Channel",
A Sequential Coding Approach for Short Length LT Codes over A WGN Channel
(2017) Abdulkhaleq, Nadhir Ibrahim; Gazi, Orhan
Luby Transform (LT) codes which can be considered as one of the first type of rate less codes are introduced to be an efficient erasure code. In such codes a fountain of encoded symbols is continuously transmitted until the successfully delivery of all the data packets. Whenever the receiver collects N noisy encoded symbols the decoding operation starts. Usually belief propagation (BP) algorithm is used to decipher the code and extract the k data symbols. In this paper, short length LT codes are generated using efficient sequential encoding approach (SEA) and performance measurements have been done over additive white Gaussian (A WGN) channel. This coding technique generates its degree in a repeated sequential manner which yields a mutual relation between adjacent codes that will be used in the decoding part. The decoding complexity of the proposed structure is similar to that of the Raptor codes. The simulation results show that the proposed approach has better performance in terms of error floor and successful decoding ratio when compared to LT codes using robust soliton distribution (RSD) and memorybased-RSD (MBRSD) even when supported by belief propagation-pattern recognition (BP-PR) technique.
Citation Count: Dursun, H.D., Güvenç, Z.B., Kasap, E. (2010). A simple analytical EAM model for some bcc metals. Communications In Nonlinear Science And Numerical Simulation, 15(5), 1259-1266. http://dx.doi.org/10.1016/j.cnsns.2009.05.034
A simple analytical EAM model for some bcc metals
(Elsevier Science Bv, 2010) Dursun, İbrahim H.; Güvenç, Ziya B.; Kasap, E.; 47800
An analytical embedded atom method which can treat bcc transition metal iron has been developed. In this model, a new potential was presented and a modified term has been introduced to fit the negative Cauchy pressure P-C = (C-12 - C-44)/2 for Fe element. The new model was applied to calculate thermodynamic properties of binary alloys of the bcc transition metals: Fe, V and Cr. The calculated dilute-solution enthalpies and formation enthalpies of random alloys are in good agreement with the results of first principles calculations and that of the thermodynamic calculations.
Citation Count: Eyyuboğlu, H.T. (2008). A study of source plane Mathieu beams. Applied Physisc B-Lasers And Optics, 91(3-4), 629-637. http://dx.doi.org/10.1007/s00340-008-3046-y
A study of source plane Mathieu beams
(Springer, 2008) Eyyuboğlu, Halil T.; 7688
We derive the source field expressions of different Mathieu beams. In particular, Mathieu beams consisting of the infinite summations of J-type Bessel functions and their Gaussian counterparts are studied. Mathieu beams based on the summation of I-type Bessel functions are introduced as well. By plotting the source intensities of such beams, the variations of the related profiles are examined against the changes in the source parameters. It is found that, via the adjustment of these parameters, it is possible to obtain completely new beam configurations and also those similar to the existing beams of the present literature
Citation Count: Arlı, Ahmet Çağrı; Gazi, Orhan (2021). "A survey on belief propagation decoding of polar codes", China Communications, Vol. 18, No. 8, pp. 133-168.
A survey on belief propagation decoding of polar codes
(2021) Arlı, Ahmet Cağrı; Gazi, Orhan
The increasing data traffic rate of wireless communication systems forces the development of new technologies mandatory. Providing high data rate, extremely low latency and improvement on quality of service are the main subjects of next generation 5G wireless communication systems which will be in the people's life in the years of 2020. As the newest and first mathematically proven forward error correction code, polar code is one of the best candidates among error correction methods that can be employed for 5G wireless networks. The aim of this tutorial is to show that belief propagation decoding of polar codes can be a promising forward error correction technique in upcoming 5G frameworks. First, we survey the novel approaches to the belief propagation based decoding of polar codes and continue with the studies about the simplification of these decoders. Moreover, early detection and termination methods and concept of scheduling are going to be presented throughout themanuscript. Finally, polar construction algorithms, error types in belief propagation based decoders and hardware implementations are going to be mentioned. Overall, this tutorial proves that the BP based decoding of polar codes has a great potential to be a part of communication standards.
Citation Count: Umul, Y.Z. (2017). A uniform function for the diffraction of spherical waves. Optik, 130, 963-975. http://dx.doi.org/10.1016/j.ijleo.2016.11.032
A uniform function for the diffraction of spherical waves
(Elsevier GMBH, 2017) Umul, Yusuf Ziya; 42699
A function which occurs in the scattering problem of the spherical waves by a perfectly conducting half-plane is introduced for constructing the transition functions of the uniform theory of diffraction and uniform asymptotic theory of diffraction. The important properties of the function, related with the geometrical optics and diffracted field components, are derived mathematically. A uniform asymptotic theory of wedge diffraction is introduced based on the new function. The resultant field expressions-are investigated numerically.
Citation Count: Moor, T.; Schmidt, K.; Wittmann, T., "Abstraction-Based Control for Not Necessarily Closed Behaviours", Ifac Proceedings Volumes (Ifac-Papersonline), Vol. 44, No. 1-1, pp. 6988-6993, (2011).
Abstraction-Based Control for Not Necessarily Closed Behaviours
(IFAC Secretariat, 2011) Moor, Thomas; Schmidt, Klaus Werner; Wittmann, Thomas
This paper addresses abstraction-based supervisory control for plant and specification behaviours that are not necessarily ω-closed, i.e. plant behaviours that exhibit eventuality properties and specifications that impose eventuality properties on the closed loop. Technically, the core idea is to combine results from previous work on abstraction-based supervision of input-output behaviours with results on supervisory control of ω-languages. As our main result, we identify a controllability condition for the plant, that ensures a nonblocking closed-loop behaviour with a controller that has been obtained for a plant abstraction.
Citation Count: Khalid, Harith M.; Schmidt, Klaus. "Abstraction-Based Modeling and Control For Reconfigurable Machine Tools (RMT)", Engineering and Technology Symposium, 2014.
Abstraction-Based Modeling and Control For Reconfigurable Machine Tools (RMT)
(2014) Khalid, Harith M.; Schmidt, Klaus
Citation Count: Schmidt, K. (2010). Abstraction-based verification of codiagnosability for discrete event systems. Automatica, 46(9), 1489-1494. http://dx.doi.org/10.1016/j.automatica.2010.06.010
Abstraction-based verification of codiagnosability for discrete event systems
(Pergamon-Elsevier Science LTD, 2010) Schmidt, Klaus Werner
In this paper, we investigate the verification of codiagnosability for discrete event systems (DES). That is, it is desired to ascertain if the occurrence of system faults can be detected based on the information of multiple local sites that partially observe the overall DES. As an improvement of existing codiagnosability tests that resort to the original DES with a potentially computationally infeasible state space, we propose a method that employs an abstracted system model on a smaller state space for the codiagnosability verification. Furthermore, we show that this abstraction can be computed without explicitly evaluating the state space of the original model in the practical case where the DES is composed of multiple subsystems. (c) 2010 Elsevier Ltd. All rights reserved
Citation Count: Cai, Y., Korotkova, O., Eyyuboğlu,H.T., Baykal, Y. (2008). Active laser radar systems with stochastic electromagnetic beams in turbulent atmosphere. Optics Express, 16(20), 15834-15846. http://dx.doi.org/10.1364/OE.16.015834
Active laser radar systems with stochastic electromagnetic beams in turbulent atmosphere
(Optical Soc Amer, 2008) Cai, Yangjian; Korotkova, Olga; Eyyuboğlu, Halil T.; Baykal, Yahya; 7688; 7812
Propagation of stochastic electromagnetic beams through paraxial ABCD optical systems operating through turbulent atmosphere is investigated with the help of the ABCD matrices and the generalized Huygens-Fresnel integral. In particular, the analytic formula is derived for the cross-spectral density matrix of an electromagnetic Gaussian Schell-model (EGSM) beam. We applied our analysis for the ABCD system with a single lens located on the propagation path, representing, in a particular case, the unfolded double-pass propagation scenario of active laser radar. Through a number of numerical examples we investigated the effect of local turbulence strength and lens' parameters on spectral, coherence and polarization properties of the EGSM beam
Citation Count: Umul, Y.Z. (2008). Alternative interpretation of the edge-diffraction phenomenon. Journal of the Optical Society of America A-Optics Image Science and Vision, 25(3), 582-587. http://dx.doi.org/10.1364/JOSAA.25.000582
Alternative interpretation of the edge-diffraction phenomenon
(Optical Soc Amer, 2008) Umul, Yusuf Ziya; 42699
An alternative interpretation of the phenomenon of edge diffraction is proposed according to a new separation of the Fresnel function. The subfields are investigated in the problem of diffraction of a plane wave by a perfectly conducting half-plane, and the results are compared numerically with other interpretations
Citation Count: Eyyuboğlu, H.T., Ji, X. (2010). An analysis on radius of curvature aspects of hyperbolic and sinusoidal Gaussian beams. Applied Physisc B-Lasers And Optics, 101(1-2), 353-359. http://dx.doi.org/10.1007/s00340-010-4039-1
An analysis on radius of curvature aspects of hyperbolic and sinusoidal Gaussian beams
(Springer, 2010) Eyyuboğlu, Halil T.; Ji, Xiaoling; 7688
The effective radius of curvature of hyperbolic and sinusoidal Gaussian beams in free space and turbulent atmosphere is studied analytically and numerically. It is shown that the radius of curvature rises with growing source size, and changes slowly with wavelength. In general, given the same source and propagation settings, the beams can be listed in descending order of radius of curvature magnitudes as sinh Gaussian, cosh Gaussian, sine Gaussian, pure Gaussian and cos Gaussian beams. However, the radius of curvature and the difference of the radius of curvature between the different beams reduce with growing strength of turbulence because the beam's spatial phase distribution is destroyed by turbulence
Citation Count: Yarkan, S...et al. (2012). An online adaptive cooperation scheme for spectrum sensing based on a second-order statistical method. IEEE Transactions On Vehicular Technology, 61(2), 675-686. http://dx.doi.org/10.1109/TVT.2011.2179325
An online adaptive cooperation scheme for spectrum sensing based on a second-order statistical method
(IEEE-Inst Electrical Electronics Engineers Inc, 2012) Yarkan, Serhan; Töreyin, Behçet Uğur; Qaraqe, Khalid A.; Çetin, A. Enis; 19325
Spectrum sensing is one of the most important features of cognitive radio (CR) systems. Although spectrum sensing can be performed by a single CR, it is shown in the literature that cooperative techniques, including multiple CRs/sensors, improve the performance and reliability of spectrum sensing. Existing cooperation techniques usually assume a static communication scenario between the unknown source and sensors along with a fixed propagation environment class. In this paper, an online adaptive cooperation scheme is proposed for spectrum sensing to maintain the level of sensing reliability and performance under changing channel and environmental conditions. Each cooperating sensor analyzes second-order statistics of the received signal, which undergoes both correlated fast and slow fading. Autocorrelation estimation data from sensors are fused together by an adaptive weighted linear combination at the fusion center. Weight update operation is performed online through the use of orthogonal projection onto convex sets. Numerical results show that the performance of the proposed scheme is maintained for dynamically changing characteristics of the channel between an unknown source and sensors, even under different physical propagation environments. In addition, it is shown that the proposed cooperative scheme, which is based on second-order detectors, yields better results compared with the same fusion mechanism that is based on conventional energy detectors.
Citation Count: Gazi, Orhan (2018). "Analog and digital filter design", Springer Topics in Signal Processing, Vol. 13, pp. 233-298.
Analog and digital filter design
(2018) Gazi, Orhan
In this chapter, we will study analog and digital filter design techniques. A filter is nothing but a linear time invariant (LTI) system. Any LTI system can be described using its impulse response. If the impulse response of a LTI system is known, then for any arbitrary input the system output can be calculated by taking the convolution of the impulse response and arbitrary input. This also means that filtering operation is nothing but a convolution operation. And filter design is nothing but finding the impulse response of a linear time invariant system. For this purpose, we can work either in time domain or frequency domain.

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Browsing Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu by Department "Çankaya Üniversitesi, Mühendislik Fakültesi, Elektronik ve Haberleşme Mühendisliği"