Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu

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

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Analog and Digital Filter Design
(Springer Science and Business Media B.V., 2018) Gazi, O.
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. © Springer Nature Singapore Pte Ltd. 2018.
Concept of Information, Discrete Entropy and Mutual Information
(Springer Science and Business Media Deutschland GmbH, 2018) Gazi, O.
In this chapter, we will try to explain the concept of information, discrete entropy and mutual information in details. To master on the information theory subjects, the reader should have a knowledge of probability and random variables. For this reason, we suggest to the reader to review the probability and random variables topics before studying the information theory subjects. Continuous entropy and continuous mutual information are very closely related to discrete entropy and discrete mutual information. For this reason, the reader should try to understand very well the fundamental concepts explained in this chapter, then proceed with the other chapters of the book. © 2018, Springer Nature Singapore Pte Ltd.
Citation - WoS: 31
Density Functional Study of Physical and Chemical Properties of Nano Size Boron Clusters: Bn (n=13-20)
(Chinese Physical Soc, 2009) Ozdogan, Cem; Guvenc, Ziya B.; Atis, Murat
Boron is an element that has ability to build strong and highly directional bonds with boron itself. As a result, boron atoms form diverse structural motifs, ultimately can yield distinct nano structures, such as planar, quasi-planar, convex, cage, open-cage, tubular, spherical., ring, dome-like, shell, capsule, and so on, i.e., it can take almost any shape. Therefore, a deep understanding of the physical and chemical properties becomes important in boron cluster chemistry. Electronic and geometric structures, total and binding energies, harmonic frequencies, point symmetries, charge distributions, dipole moments, chemical bondings and the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps of neutral B-n (n=13-20) clusters have been investigated by, density functional theory (DFT), B3LYP with 6-311++G(d,p) basis set. Furthermore, the first and the second energy differences are used to obtain the most stable sizes. We have observed that almost all physical properties are size dependent, and double-ring tubular form of B-20 has the highest binding energy per atom. The icosahedral structure with an inside atom is found as impossible as a stable structure for the size thirteen. This structure transforms to an open-cage form. The structural transition from two-dimensional to three-dimensional is found at the size of 20 and consistent with the literature. The calculated charges by the Mulliken analysis show that there is a symmetry pattern with respect to the x-z and y-z planes for the charge distributions. The unusual planar stability of the boron clusters may be explained by the delocalized pi and sigma bonding characteristic together with the existence of the multicentered bonding. The results have been compared to available studies in the literature.
Citation - WoS: 20
Citation - Scopus: 33
Effect of Beam Types on the Scintillations: a Review
(Spie-int Soc Optical Engineering, 2009) Eyyuboglu, Halil T.; Cai, Yangjian; Baykal, Yahya
When different incidences are launched in atmospheric turbulence, it is known that the intensity fluctuations exhibit different characteristics. In this paper we review our work done in the evaluations of the scintillation index of general beam types when such optical beams propagate in horizontal atmospheric links in the weak fluctuations regime. Variation of scintillation indices versus the source and medium parameters are examined for flat-topped-Gaussian, cosh-Gaussian, cos-Gaussian, annular, elliptical Gaussian, circular (i.e., stigmatic) and elliptical (i.e., astigmatic) dark hollow, lowest order Bessel-Gaussian and laser array beams. For flat-topped-Gaussian beam, scintillation is larger than the single Gaussian beam scintillation, when the source sizes are much less than the Fresnel zone but becomes smaller for source sizes much larger than the Fresnel zone. Cosh-Gaussian beam has lower on-axis scintillations at smaller source sizes and longer propagation distances as compared to Gaussian beams where focusing imposes more reduction on the cosh-Gaussian beam scintillations than that of the Gaussian beam. Intensity fluctuations of a cos-Gaussian beam show favorable behaviour against a Gaussian beam at lower propagation lengths. At longer propagation lengths, annular beam becomes advantageous. In focused cases, the scintillation index of annular beam is lower than the scintillation index of Gaussian and cos-Gaussian beams starting at earlier propagation distances. Cos-Gaussian beams are advantages at relatively large source sizes while the reverse is valid for annular beams. Scintillations of a stigmatic or astigmatic dark hollow beam can be smaller when compared to stigmatic or astigmatic Gaussian, annular and flat-topped beams under conditions that are closely related to the beam parameters. Intensity fluctuation of an elliptical Gaussian beam can also be smaller than a circular Gaussian beam depending on the propagation length and the ratio of the beam waist size along the long axis to that along the short axis (i.e., astigmatism). Comparing against the fundamental Gaussian beam on equal source size and equal power basis, it is observed that the scintillation index of the lowest order Bessel-Gaussian beam is lower at large source sizes and large width parameters. However, for excessively large width parameters and beyond certain propagation lengths, the advantage of the lowest order Bessel-Gaussian beam seems to be lost. Compared to Gaussian beam, laser array beam exhibits less scintillations at long propagation ranges and at some midrange radial displacement parameters. When compared among themselves, laser array beams tend to have reduced scintillations for larger number of beamlets, longer wavelengths, midrange radial displacement parameters, intermediate Gaussian source sizes, larger inner scales and smaller outer scales of turbulence. The number of beamlets used does not seem to be so effective in this improvement of the scintillations.
Citation - Scopus: 1
Information theory perspective of polar codes and polar encoding
(Springer Science and Business Media B.V., 2019) Gazi, Orhan
Polar codes are one of the recently discovered capacity achieving channel codes. What makes the polar codes different from other channel codes is that polar codes are designed mathematically and their performance are mathematically proven. © Springer Nature Singapore Pte Ltd. 2019.
Citation - WoS: 6
Citation - Scopus: 4
Propagation of Cross Beams Through Atmospheric Turbulence
(Spie-int Soc Optical Engineering, 2005) Yenice, YE; Eyyuboglu, HT; Baykal, Y; Venice, Yusuf E.
Propagation properties of cross beam in turbulent medium are studied. A cross beam is constructed by the sum of two highly asymmetric Gaussian beams placed along transverse axes. It is known that such beams, when propagating in free space, will exhibit contrasting diffraction behaviours; they expand widely in one axis, while they are almost nondiffracting in the other axis within useful link lengths. This behaviour allows detecting the two components and a sum component if desired separately with a practical multiaperture receiver. Bearing in mind that this property can be exploited for a diversity scheme, our present work focuses on the propagation of such beams in turbulent atmosphere. To this end, starting with a source field expression of the cross beam, the second order mutual coherence function is formulated at the receiver plane. Intensity plots describing the dependence on the source and propagation parameters on the receiver plane are provided. The results tend to confirm the applicability of the concept provided the design parameters are appropriately chosen. For a decisive assessment, however, turbulence-induced beam wander must also be examined.
Rate Averaging in Free Space Optics Systems Using Incoherent Sources
(Spie-int Soc Optical Engineering, 2004) Baykal, Y
Effect of the information rate on the scintillation index is examined for free space optical (FSO) broadband access applications that use spatially incoherent sources. For this purpose, intensity fluctuations are formulated indicating the effect of the rate on the scintillation index in the presence of the atmospheric turbulence. The bandwidth of modulation of the incoherent source is taken to be much smaller than the carrier frequency, i.e., narrowband approximation is employed. Rate averaging factor for spatially incoherent source is derived as to represent the averaging in weak atmospheric turbulence due to rate of modulation of the intensity. It is found that the scintillations decrease as the rate of transmission through atmospheric turbulence increases. This decrease is independent of the carrier wavelength of the FSO system but depends on the outer scale of turbulence. Up to 10 Gbps, the decrease is negligible for realistic outer scale values. When extremely large eddies are present in the formation of turbulence, rate can be effective in the reduction of the scintillations even at rates up to 10 Gbps. In the limit when the information rate is taken as zero, our results correctly reduce to the known scintillations for spatially incoherent monochromatic excitation.
Citation - WoS: 4
Citation - Scopus: 5
The Theory of the Boundary Diffraction Wave
(Elsevier Academic Press inc, 2011) Umul, Yusuf Ziya
Throughput maximisation of different signal shapes working on 802.16e mobile multihop network using novel cognitive methods
(Springer-Verlag Berlin, 2010) Preveze, Barbaros; Şafak, Aysel
This study proposes cognitive methods for managing the multimedia packet traffic of 802.16e system providing the dynamic spectrum sharing by TDM & OFDMA under heavy traffic conditions. The cognitive techniques are used in order to maximize the throughput of a system having different signal shapes such as video, voice or data packets. All real time voice and video packets transmissions have been provided with full success where the loss rate of data packets has been minimized using the cognitive methods. By these methods buffers are managed successfully for the given parameters, optimum buffer sizes have been formulized and it's shown that we brought the throughput up to its calculated theoretical limits for multi-hop mobile wimax (802.16e).
Typical Sequences and Data Compression
(Springer Science and Business Media Deutschland GmbH, 2018) Gazi, O.
In this chapter, we will first provide information about typical sequences the introduce the data compression subject. In fact, the data compression subject is a direct consequence of the typical sequences. For this reason, it is very important to comprehend the concept of typical sequences to understand the data compression phenomenon. © 2018, Springer Nature Singapore Pte Ltd.
Citation - Scopus: 12
Understanding digital signal processing
(Springer Science and Business Media B.V., 2018) Gazi, O.

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