Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411

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Genişbant Erişim Telekomünikasyon Sistemlerinin Kullanım Kriterleri
(1) Küçükoğlu, Afşin; Baykal, Yahya; 7812
Hızla artan bilgisayar ağı ihtiyacını gidermek ve yüksek hızı son kullanıcı noktalarına ulaştırabilmek amacıyla geliştirilmiş olan genişbant erişim sistemlerinin (access systems) teknolojik son durumu incelendi. Herhangi bir erişim uygulamasında kullanılması gereken tercih nedenleri karşılaştırıldı. Bu karşılaştırmayı sistematik olarak yapan internet tabanlı bir yazılım geliştirildi. Yazılımda, sistem kullanıcısının ihtiyacı ve mevcut altyapı faktörleri doğrultusunda hangi erişim sisteminin kullanıcı tarafından tercih edilmesi gerektiği kararına optimum olarak varılabilmesi hedeflendi. Çalışmamız, xDSL (x Digital Subscriber Line) ile Fiber Optic erişimlerini kapsayan kablolu ve LMDS (Local Multipoint Distribution Services) ile FSO (Free Space Optics) erişimlerini kapsayan kablosuz sistemleri içermektedir. Yazılım tarafından istenilen sorular ihtiyaç doğrultusunda cevaplandırıldığında, tüm sistemler bir ana karşılaştırma tablosunda toplanmakta, sistem maliyetleri de göz önüne alınarak bir karşılaştırma yapılmakta, sonuçta ise teknik ve ekonomik olarak uygulanabilir çözümler ve optimum çözüm önerilmektedir.
Citation - WoS: 83
Citation - Scopus: 83
Correlation and structure functions of Hermite-sinusoidal-Gaussian laser beams in a turbulent atmosphere
(Optical Soc Amer, 2004) Baykal, Y
To study the performance of atmospheric optical links by using Hermite-sinusoidal-Gaussian laser beam sources, we derive the log-amplitude and the phase correlation and structure functions of such beams in a turbulent atmosphere. Our formulations correctly reduce to the known higher-order mode correlation and structure functions, which in turn reduce to the fundamental-mode (TEM00-mode) results. Several special cases of our formulation are presented, among which the case involving Hermite-cosh-Gaussian dependence is especially noted, since this case is of interest to us owing to the nature of cosh dependence exhibiting the concentration of the energy in the outer lobes of the beam. (C) 2004 Optical Society of America.
Citation - WoS: 1
Citation - Scopus: 1
Effects of laser multimode content on the angle-of-arrival fluctuations in free space optics access systems
(Spie-int Soc Optical Engineering, 2004) Eyyuboglu, HT; Baykal, Y; 7688; 7812
The effects of the multimode content in a laser beam on the angle-of-arrival fluctuations are examined for free space optics (FSO) access systems. Multimode excitation is represented by coherent addition of Hermite-Gaussian higher order modes. Root mean square angle-of-arrival fluctuations are formulated using the previously reported multimode phase structure function, which is valid in weak atmospheric turbulence. Results are found for practical FSO links operating at 1550 nm and 850 nm wavelengths and for link spans of up to 5 km. In choosing the mode content, various sequential grouping of all possible mode combinations are used up to a certain order (n,m) mode. We start with the single fundamental mode (TEM00) and span up to the highest order (n = 10, m = 10) mode. In this manner, different degrees of source coherence are also taken into account. Angle-of-arrival fluctuations are found to be in the range of several tens of muradians and almost insensitive to the mode content except for the cases when the mode group terminates with an odd mode. In such instances, the fluctuations rise to a few hundreds of murad. Comparing our results with the field of view of a practical FSO receiver, which is several mrad, we conclude that the-angle-of arrival fluctuations due to multimode excitation will not influence the FSO link performance to a major extent.
Citation - WoS: 38
Citation - Scopus: 44
Propagation of modified Bessel-Gaussian beams in turbulence
(Elsevier Sci Ltd, 2008) Eyyuboglu, Halil Tanyer; Hardalac, Firat; 7688
We investigate the propagation characteristics of modified Bessel-Gaussian beams traveling in a turbulent atmosphere. The source beam formulation comprises a Gaussian exponential and the summation of modified Bessel functions. Based on an extended Huygens-Fresnel principle, the receiver plane intensity is formulated and solved down to a double integral stage. Source beam illustrations show that modified Bessel-Gaussian beams, except the lowest order case, will have well-like shapes. Modified Bessel-Gaussian beams with summations will experience lobe slicing and will display more or less the same profile regardless of order content. After propagating in turbulent atmosphere, it is observed that a modified Bessel-Gaussian beam will transform into a Bessel-Gaussian beam. Furthermore it is seen that modified Bessel-Gaussian beams with different Bessel function combinations, but possessing nearly the same profile, will differentiate during propagation. Increasing turbulence strength is found to accelerate the beam transformation toward the eventual Gaussian shape. (c) 2007 Elsevier Ltd. All rights reserved.
Citation - Scopus: 2
Associativity Tick Averaged Associativity Based Routing (Ataabr) for Real Time Mobile Networks
(2009) Převeze, B.; Preveze, Barbaros; Şafak, A.; 17573; Elektrik-Elektronik Mühendisliği
This study proposes a long lived routing method which is also based on Associativity such as ABR (Associativity Based Routing) for real time applications. The main purpose of our work is improving the ABR algorithm in order to reduce the outage of the nodes and decreasing the number of reconstructions required to keep the nodes in communication. The performance of ABR is compared with other long-lived relay selection algorithms for real-time applications.
Citation - WoS: 1
Citation - Scopus: 3
Comparative Analysis of Novel Long Life Routing Methods In Mobile Networks
(Ieee, 2010) Preveze, Barbaros; Preveze, Barbaros; Safak, Aysel; 17573; Elektrik-Elektronik Mühendisliği
In this study we propose two novel ABR extended Long Life Routing Methods called Alternative enhancement for Enhanced Associativity Based Routing (AEABR) and Associativity Tick Averaged ABR (ATAABR) methods which are also modifications of Associativity Based Routing (ABR). Comparison of these associativity based long Life routing algorithms in Mobile Networks are done for route speeds, life times and outage times Since ABR at most focuses on power strength, it will be preferable in most systems to establish long life routes from source to destination considering the power constraints. It is shown in this paper that, the novel algorithms that we propose provide better life time, link speeds and outage time results than EABR (Enhanced Associativity Based Routing) method and other relay selection algorithms taken into consideration in this work. It's illustrated that the performance of EABR method, is really better than other relay selection algorithms for number of Route reconstructions (RRC) or relay changes and Connected Status Percentage (CSP). On the other hand it has also been illustrated that AEABR and ATAABR improve the connection stability of EABR by keeping the connection outage time at lower levels where ATAABR require less modification on algorithm and needs less computation time. AEABR improves either connection outage times or number of RRC. During this analysis message overhead and bandwidth wastage of each algorithm is also investigated. The proposed algorithms can be used in designing a unicast mobile network having power constraints to provide longer path life and lower number of route reconstructions.
Citation - Scopus: 3
Effects of ant colony and fastest path routing algorithms on performance improvement of novel cognitive methods
(2010) Preveze, B.; Preveze, Barbaros; Safak, A.; 17573; Elektrik-Elektronik Mühendisliği
This paper demonstrates the usage of novel cognitive methods that improve the throughput of a WIMAX network by minimizing packet loss. The effects of the ant colony and fastest path routing algorithms on the throughput are investigated. A combination of Time Division Multiple Access (TDMA) and Orthogonal Frequency Division Multiple Access (OFDMA) spectrum sharing techniques is used. Data packet loss rate is minimized for real-time voice and video packet transmissions. A unicast mobile multimedia network with improved system throughput is provided with both routing methods, even for a small node count. © 2010 IEEE.
Citation - Scopus: 1
Strong turbulence analysis of sinusoidal and hyperbolic Gaussian beams
(2010) Eyyuboǧlu, H.T.; 7688
We formulate the on-axis asymptotic scintillations of sinusoidal and hyperbolic Gaussian beams, namely cos and cosh Gaussian beam, under strong turbulence conditions. Our results are displayed in the form of plots of the scintillation index against propagation distance and wavelength at several source and propagation parameters. It is revealed that at small source sizes, cosh Gaussian beams will exhibit the lowest scintillations, but at large source sizes, this will reverse and cos Gaussian beams will attain such characteristics. It is further found that in strong turbulence, longer wavelengths will offer less scintillations, a behavior similar to the one, encountered in weak scintillation conditions. © 2010 IEEE.
Citation - Scopus: 2
Scintillation index of partially coherent asymmetrical multi Gaussian beams in extremely strong turbulence
(2010) Öztan, M.A.; Baykal, Y.; 7812
It is investigated whether partial coherent asymmetrical annular and flat-topped Gaussian beams provide advantage to decrease the scintillation noise effect when free space optics systems are used in long distance (longer than 5km) transmission links. Scintillation index of partially coherent asymmetrical multi Gaussian beam propagating in extremely strong turbulence is formulated and the scintillation indexes of asymmetrical annular and flat-topped Gaussian beams are calculated. Scintillation index variations are plotted against the source size and asymmetry ratio. It is determined that asymmetric beams have advantage over the symmetric beams in terms of the scintillation. It is found that the scintillation index decreases as the asymmetry ratio increases. It is also detected that by decreasing the coherence degree scintillation index of the propagating beam quickly goes to zero.
Beam wander of J (0)- and I (0)-Bessel Gaussian beams propagating in turbulent atmosphere
(2010) Çil, Celal Zaim; Baykal, Yahya Kemal; Baykal, Yahya Kemal; Korotkova, O.; Cai, Y.; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
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.
Beam wander of J 0- and i 0-Bessel Gaussian beams propagating in turbulent atmosphere
(2010) Çil, C.Z.; Eyyuboğlu, H.T.; Baykal, Y.; Korotkova, O.; Cai, Y.; 7812
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.
Alternative Enhancement of Associativity Based Routing (Aeabr) for Mobile Networks
(Springer, 2010) Preveze, Barbaros; Safak, Aysel; 17573; Elektrik-Elektronik Mühendisliği
This study proposes an alternative enhancement for the Enhanced Associativity Based Routing (EABR) method which is a derivation of ABR (Associativity Based Routing) by relative speed and relative distance estimation using the received power strength (RPS) of the nodes. In this study, it is shown that EABR outperforms some other well known protocols. The performance of EABR is improved in terms of number of route reconstructions (RRC) and connected status percentage (CSP). Message overhead and bandwidth utilization is also investigated.
Citation - WoS: 0
Citation - Scopus: 1
Intensity Fluctuations of Incoherently Superposed Gaussian Beams In Atmospheric Turbulence
(Spie-int Soc Optical Engineering, 2010) Baykal, Yahya; 7812
Intensity fluctuations of incoherently superposed Gaussian beams are formulated in weak turbulence by employing the extended Huygens-Fresnel principle. Each individual beam superposed is taken to be fully incoherent. The scintillation index evaluated for different number of beams indicates that as the number of beams increase, scintillations decrease. Incoherent superposition of smaller sized Gaussian sources exhibits smaller fluctuations. Comparing the scintillation index arising from incoherently superposed Gaussian beams to the scintillation index of coherently superposed Gaussian beams of the same structure shows that incoherent superposition yields lower intensity fluctuations, thus can be advantageous in atmospheric optical communication links.
Citation - Scopus: 0
Effects of type of incidence on the second and fourth order moment parameters evaluated in turbulent atmosphere
(2010) Baykal, Y.; Baykal, Yahya Kemal; 7812; Elektrik-Elektronik Mühendisliği
Using a general type incidence, the second and fourth order moments are formulated in atmospheric turbulence. Received field and intensity correlations are evaluated and the behaviour of these correlations are compared for different beam types. © 2010 OSA/FiO/LS.
Citation - WoS: 2
Citation - Scopus: 3
Method of Evaluation of the Mutual Coherence Function of Laser Beams and Its Application for Symmetric Dark Hollow Beams
(Spie-int Soc Optical Engineering, 2011) Banakh, V. A.; Marakasov, D. A.; Rytchkov, D. S.; Baykal, Y. K.; Eyyuboglu, T.; 7812
In our report, a method of evaluation of the mutual coherence function (MCF) of optical wave propagating in turbulent atmosphere is proposed. The method is based on using inverse Fresnel transform and 2-D Fast Fourier Transformation procedure (FFT) and provides a high accuracy in various propagation conditions from weak up to strong optical turbulence regime. This technique allows significantly reducing the evaluation time of MCF. The proposed method is suitable for optical waves with arbitrary initial distribution of amplitude and phase. Results of investigations on the degradation of coherence of symmetric dark hollow beams (DHB) propagating in turbulent atmosphere are presented. Analysis of evolution of MCF is brought up, and some characteristics of DHB, such as mean intensity distribution, and moments of Wigner distribution are calculated for various kinds of profiles of structural characteristic of refractive index. All of the evaluations for DHB are fulfilled for Kolmogorov spectrum of correlation function of refractive index fluctuations. The comparison between mean intensity calculations within the proposed method and method based on semi-analytical approach using of quadratic approximation of spherical wave structure function, is presented.
Citation - Scopus: 0
Fair spectrum sharing in wireless networks
(2011) Preveze, B.; Preveze, Barbaros; Şafak, A.; 17573; Elektrik-Elektronik Mühendisliği
Efficient utilization of available resources and the avoidance of overload conditions have high importance for any communication network. For a CSMA based VANET the wireless bandwidth must be shared fairly among all nodes. In VANET the network and available bandwidth are in dynamical structures. Thus, if the congestion control is not provided for the VANET based broadcast communication; the lower priority applications may use the entire spectrum and may cause starvation of some important applications. In this work it is shown that our proposed MCAF (Most Congested Access First) throughput improvement method also provides fair data rate per node in vehicular communication. The data rate per node with fair spectrum allocation is determined using the MCAF simulation and calculation results. Finally, the evaluated results are confirmed by comparing them with the results of other works evaluated in the literature. © 2011 IEEE.
Yeni Rotalama Algoritmalarının 802.16j AĞI Etkin Çıktı Oranı Artırımına Düşük Araç Hızları Altındaki Etkileri
(2011) Preveze, Barbaros; 17573; Elektrik-Elektronik Mühendisliği
Çoklu ortam verileri içeren kablosuz gezgin ağlarda, yeni bilişsel yöntemler ve rotalama algoritmaları kullanılarak, sistemdeki rota ömrü, bağlantı kesinti miktarı, ortalama sekme sayısı ve paket kaybı gibi performans parametrelerinin iyileştirilmesiyle, IEEE 802.16j ağ yapısının etkin çıktı oranının arttırılması sağlanmıştır. Bu amaçla, mevcut IEEE 802.16j ağında kullanılmakta olan OFDMA ve TDMA erişim tekniklerine ek olarak kullanılmak üzere önerilen, En Çok Sıkışan İlk Erişir (MCAF), Spektrumsal Yardımlaşma (SA) ve Arabellek Yönetimi (BM) metotları ile 802.16j ağında etkin çıktı oranı artırımı için elde edilen simülasyon sonuçları, elde edilen teorik sonuçlarla ve literatürde elde edilmiş olan diğer çalışmaların sonuçlarıyla kıyaslanarak doğrulanmıştır. Bu çalışmada ayrıca, önerilen AEABR (Erişebilirlik Tabanlı Rotalama Alternatif Geliştirimi) ve ATAABR (Erişilebilirlik Tik Ortalamalı Erişebilirlik Tabanlı Rotalama) isimli yeni uzun ömürlü rotalama algoritmalarının, geliştirilen etkin çıktı oranı yükseltimi metotlarıyla birlikte uygulanmasıyla, diğer rotalama algoritmalarına göre, daha da yüksek etkin çıktı oranları elde ettikleri gösterilmiştir. Önerilen yeni metotlar, dağınık ağ yapılarının, gezgin düğümler tarafından, anlık plansız sinyalleşme ile yönetimine dayanarak çalışmaktadır.
Citation - WoS: 2
Citation - Scopus: 0
Flat-Topped Field Correlations In Extremely Strong Turbulence
(Electromagnetics Acad, 2011) Baykal, Yahya; 7812
In extremely strong turbulent horizontal atmospheric optical links, field correlations of flat-topped Gaussian incidence are evaluated. Field correlations are represented versus the diagonal distance at the receiver plane, for variations in the number of beams forming the flat-topped structure, receiver points, source sizes, link lengths, structure constants and the wave-lengths. Our results in extremely strong turbulence are compared to their free space counterparts which only reflect the diffraction patterns at the receiver plane. The effects of the inner scale of turbulence on the field correlations in extremely strong turbulence are examined in detail and it is observed that the size of the inner scale in extremely strong turbulence can considerably influence the field correlations of flat-topped beams.
Işık hüzmesi profili ölçme sistemi
(2011) Çil, Celal Zaim; Baykal, Yahya Kemal; Çil, Celal Zaim; Cambaz, Göknur; Baykal, Yahya Kemal; Erseven, S.; Karabulut, S.; Ertuğ, A. Mithat; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
Citation - Scopus: 6
Wavelet based flame detection using differential PIR sensors
(2012) Erden, F.; Töreyin, Behçet Uğur; Töreyin, B.U.; Soyer, E.B.; Inaç, I.; Günay, O.; Köse, K.; Çetin, A.E.; 19325; Elektrik-Elektronik Mühendisliği
In this paper, a flame detection system using a differential Pyro-electric Infrared (PIR) sensor is proposed. A differential PIR sensor is only sensitive to sudden temperature variations within its viewing range and it produces a time-varying signal. The wavelet transform of the differential PIR sensor signal is used for feature extraction and feature vectors are fed to Markov models trained with uncontrolled fire flames and walking person. The model yielding the highest probability is chosen. Results suggest that the system can be used in spacious rooms for uncontrolled fire flame detection. © 2012 IEEE.

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