Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
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Conference Object Ofdm Sistemleri için Pilot Tabanlı Em Kanal Kestirim Başarımı(Institute of Electrical and Electronics Engineers Inc., 2007) Baştürk, İlhan; Özbek, BernaIn this work, pilot-based Expectation-Maximization (EM) channel estimation for OFDM systems are studied by considering different pilot placements. In the first method, the pilot symbols are distributed at certain locations in the OFDM time-frequency lattices to find appropriate initial values. In the second method, the pilot symbols are placed in the first OFDM symbol and then a sequential channel estimation is applied. These two methods are compared and the performances are studied in terns of mean square error and bit error rate. Moreover, the number of iterations used in the algorithm are given to compare the complexity of the methods.Conference Object Citation - Scopus: 2Genetik Algoritma ile Çok Kullanıcı Dfbç Sistemleri için Toplam Veri Hızı Enbüyüklemeli Uyarlanır Alttaşıyıcı ve Bit Yerleşimi(Institute of Electrical and Electronics Engineers Inc., 2008) Özbek, Berna; Le Ruyet, DidierIn this work, we perform the adaptive subcarrier and bit allocation to maximize the sum data rate for multiuser OFDM systems using genetic algorithm. Since the convergence time of the genetic algorithm could be slow, we propose to use a different initial condition to accelerate it without increasing the complexity of genetic algorithm and sacrificing the performance of the system. We obtain the simulation results and compare them with the classical methods. We show that the genetic algorithm with proposed initial condition gives better performances than the classical ones for sum data rate maximized allocation.Conference Object Citation - WoS: 2Citation - Scopus: 2Gezgin Rölelerin Dfbçe Tabanlı Hücresel Ağ Performansına Etkisi(Institute of Electrical and Electronics Engineers Inc., 2014) Baştürk, İlhan; Özbek, BernaOFDMA-based mobile relay enhanced cellular networks which have lower infrastructure cost and larger coverage areas are important technologies for the next generation communication systems since they allow to communicate at higher data rates. However, it is required to develop efficient radio resource management algorithms in order to reveal these advantages. Thus, in this study, relay selection and resource allocation algorithms are proposed for the mobile relay enhanced cellular networks. It is revealed that the number of satisfied users and the data rate of the cell-edge users that are far from the base station and have lower channel gains are increased by using mobile relays with the proposed algorithms.Conference Object Citation - WoS: 2Citation - Scopus: 3Heterojen ağlarda iyileştirilmiş veri katarı seçimi ile girişim hizalama(IEEE, 2015) Le Ruyet, Didier; Aycan, Esra; Özbek, BernaIn this article, interference that occurs in heterogeneous networks is studied and a new stream selection approach with an interference alignment solution is presented. In the proposed algorithm, stream selection starts with the streams that belongs to the pico cell users and continues to select the strongest streams that increase the total sum rate. The power of each stream with the precoding and the postcoding vectors are calculated by performing singular value decomposition (SVD). Virtual channels that belong to the selected stream are calculated by using precoding and postcoding vectors. After the selection procedure, the interferences between the selected stream and the remaining streams are mitigated by orthogonally projecting the channel matrices of the remaining streams to the virtual channels of the selected stream.Conference Object Citation - Scopus: 1Kablosuz Ağlarda Hücre Seçim Algoritmalarının Başarımı(IEEE, 2012) Aycan, Esra; Özbek, BernaIn this paper, the performance of signal to interference and noise ratio (SINR) and distance based cell selection algorithms for wireless systems are examined considering different cells. The performance results are obtained by assuming the users are not moving within a setup includes macrocell, picocell and femtocells. The comparisons of the obtained results are shown in terms of SINR and load in the cells. © 2012 IEEE.Conference Object Çoklu Kullacılı Çgtç-dfbçe Sistemleri için Adil Kaynak Paylaşımı(IEEE, 2011) Baştürk, İlhan; Özbek, BernaIn this study, the user selection at the base station and resource allocation algorithms are presented for multiuser multipleinput single-output orthogonal frequency division multiple access (MU-MISO OFDMA) systems when the number of users in a cell is much more than the number of transmitter antennas. A fair resource allocation algorithm is proposed in order not to victimize the users far from the base stations. In general, Shannon capacity has been shown as the performance measure for MU-MISO-OFDMA systems. In this paper, the bit error rate (BER) is used as an performance metric instead of the Shannon capacity since, increasing the system capacity does not automatically yield the best performance in terms of error rates. It is also shown that the proposed algorithm provides fairness by calculating the fairness index. © 2011 IEEE.Conference Object Çoklu Antenli Ev Baz İstasyonlarının İç Mekan Kapasite Başarımı(IEEE, 2011) Aycan, Esra; Özbek, BernaIn this paper, indoor channel models for femtocells are examined and capacity performances are obtained. In order to evaluate the indoor channel models, the performance results are obtained employing the ray tracing based Wireless Insite model, the well known i.i.d model and the IEEE802.11n model. All the comparisons are shown for the single input single output (SISO) and the multiple input multiple output (MIMO) systems.1 © 2011 IEEE.Conference Object Citation - Scopus: 9Çoklu Antenli̇ Bili̇şsel Radyo Si̇stemleri̇nde Dönemli̇-duraǧan Özelli̇k Algılama Yöntemi̇ne Dayanan Spektrum Sezi̇mi̇(Institute of Electrical and Electronics Engineers, 2011) Üstok, Refik Fatih; Özbek, BernaCognitive radios aim to implement dynamic frequency usage which is proposed to increase the efficiency of the spectrum and can sense their environment, detect the idle bands and then allocate the secondary users into the detected idle bands without any interference to primary users' communications. Cyclostationary Feature Detection is one of the commonly used methods in the literature for spectrum sensing. This paper focuses on sensing the idle bands using cyclostationary feature detection method in Cognitive Radio based systems. The performance is improved by using the proposed multiple antenna technique and the simulation results are analyzed. © 2011 IEEE.Conference Object Ofdm Sistemler için Pilot Tabanlı Yinelemeli Kanal Kestirimi(IEEE, 2008) Baştürk, İlhan; Özbek, BernaIn this study, pilot-based iterative channel estimation, which use virtual pilots, is proposed for OFDM systems In order to find final channel estimates, instead of averaging the group estimates, which are found by virtual pilots, it is proposed to combine them by taking into account their reliabilities that are calculated by using probability density function. Then the proposed method is compared to Expectation-Maximization (EM) algorithm with respect to performance and computational complexity. The performance results are given in terms of Bit Error Rate (BER) and Mean Squared Error (MSE). ©2008 IEEE.Conference Object Stbc-ofdm Sistemler için Em Tabanlı Kanal Kestirim Başarımı(Institute of Electrical and Electronics Engineers Inc., 2009) Baştürk, İlhan; Özbek, BernaBu çalışmada Uzay-zaman blok kodlu dikgen frekans bölmeli çoğullama sistemleri için Beklenti- Enbüyükleme algoritması yardımıyla frekans alanında her bir alttaşıyıcı için ayrı ayrı kanal katsayılarının kestirildiği bir algoritma önerilmiştir. Başlangıç kanal kestirimi olarak pilot sembollerden yararlanılmış ve bant genişliğinin verimli kullanılması için az sayda pilotla ardışıl kanal kestirimi yapılmıştır. Önerilen algoritma zaman alanında kanal katsayılarını Beklenti-Enbüyükleme algoritmasıyla kestiren ve hesaplama sırasında matris tersi işlemine ihtiyaç duyan algoritma ile karşılaştırılmış ve herhangi bir performans kaybı olmadan karmaşıklığı azalttığı gözlenmiştir. Her iki algoritma için bilgisayar benzetimleri yapılarak, başarımları bit hata oranı, en küçük karesel hata ve Beklenti-Enbüyükleme algoritmasında kullandıkları döngü sayıları ile incelenmiştir.