Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
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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 - 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 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.Article User-Relay Assisted Cellular Networks With Multiple Antennas(Taylor & Francis, 2019) Baştürk, İlhan; Özbek, BernaUser-relay assisted OFDMA-based cellular networks have gained great importance recently since these networks are indicated as one of the powerful technologies that will contribute the 5G standard. These networks can be used with novel three-phase frame structure unlike classical two-phase frame structure and can be enhanced with multiple antennas to utilise the advantages of them. The main advantage of the three-phase frame structure is taking care of the limitations of the current transceiver design in practical systems and not allowing users to be relay and user simultaneously. Diversity and capacity gains are also the advantages of extending the network with multiple antennas. In this paper, we will use the novel three-phase frame structure for downlink MISO-OFDMA cellular networks and develop resource management algorithms as relay selection and resource allocation to observe the benefits of this system.Article Citation - WoS: 3Citation - Scopus: 3Channel and Queue Aware Joint Relay Selection and Resource Allocation for Miso-Ofdma Based User-Relay Assisted Cellular Networks(Springer Verlag, 2018) Baştürk, İlhan; Özbek, BernaUser-relay assisted orthogonal frequency division multiple access (OFDMA) networks are cost-effective solutions to meet the growing capacity and coverage demands of the next generation cellular networks. These networks can be used with multiple antennas technology in order to obtain a diversity gain to combat signal fading and to obtain more capacity gain without increasing the bandwidth or transmit power. Efficient relay selection and resource allocation are crucial in such a multi-user, multi-relay and multi-antenna environment to fully exploit the benefits of the combination of user-relaying and multiple antennas technology. Thus, we propose a channel and queue aware joint relay selection and resource allocation algorithm for multiple-input single-output (MISO)-OFDMA based user-relay assisted downlink cellular networks. Since, the proposed algorithm is not only channel but also queue-aware, the system resources are allocated efficiently among the users. The proposed algorithm for the MISO-OFDMA based user-relay assisted scheme is compared to existing MISO-OFDMA based non-relaying and fixed relay assisted schemes and it is also compared with the existing single-input single-output (SISO)-OFDMA based user-relay assisted scheme. Simulation results revealed that the proposed scheme outperforms the existing schemes in terms of cell-edge users’ total data rate, average backlog and average delay.Conference Object Citation - WoS: 1Citation - Scopus: 1Dfbçe Tabanlı Kablosuz Ağlarda Kullanıcı Röleler için Uzaklık Bazlı Seçim(Institute of Electrical and Electronics Engineers Inc., 2016) Baştürk, İlhan; Özbek, BernaDüşük kurulum maliyetine ve geniş kapsama alanına sahip kullanıcı-rölelerle geliştirilmiş dikgen frekans bölmeli çoklu erişim (DFBÇE) tabanlı kablosuz ağlar, yüksek veri hızlarına iletişime olanak sağlamaları açısından gelecek nesil iletişim sistemlerinde önemli bir yer tutmaktadır. Kullanıcı-röleli sistemlerde kullanıcı sayısına paralel olarak artan röle sayısı performansı arttırmaktadır. Tüm kullanıcıların röle olma durumu performans açısından olumlu bir durum olmasına rağmen sinyalleşme yükünü ve dolayısıyla karmaşıklığı çok arttırdığı için pratik sistemlere uygun olmayabilir. Bu nedenle, bu çalışmada performans ve sinyalleşme yükü arasındaki ödünleşimi dengelemek için kullanıcı-röle adayları belirli bir alanda uzaklığa dayalı olarak seçilmiş ve sonuçlar benzetimler yapılarak değerlendirilmiştir.Conference Object Citation - Scopus: 2Resource Allocation for User-Relay Assisted Miso-Ofdma Networks(Institute of Electrical and Electronics Engineers Inc., 2015) Baştürk, İlhan; Özbek, BernaThe next generation cellular networks request higher capacity and coverage that user-relay assisted Orthogonal Frequency Division Multiple Access (OFDMA) networks are costeffective solutions to meet these demands. These networks can be enriched with multiple antennas in order to obtain a diversity gain to combat signal fading and to achieve more capacity gain without increasing the bandwidth or transmit power. However, radio resource management (RRM) such as relay selection and resource allocation (RA) is important in such a multi-user, multirelay and multi-antenna environment to fully take advantage of multiple-input single-output (MISO)-OFDMA based user-relay assisted cellular networks. Thus, we propose a RA algorithm for these networks to reveal the benefits of the combination of userrelaying and multiple antennas technologies and compare the proposed scheme with existing schemes in terms of percentage of satisfied users and cell-edge users' data rate.Article Citation - WoS: 2Citation - Scopus: 2Iterative Channel Estimation for Higher Order Modulated Stbc-Ofdm Systems With Reduced Complexity(Korean Society of Internet Information, 2016) Baştürk, İlhan; Özbek, BernaIn this paper, a frequency domain Expectation-Maximization (EM)-based channel estimation algorithm for Space Time Block Coded-Orthogonal Frequency Division Multiplexing (STBC-OFDM) systems is investigated to support higher data rate applications in wireless communications. The computational complexity of the frequency domain EM-based channel estimation is increased when higher order constellations are used because of the ascending size of the search set space. Thus, a search set reduction algorithm is proposed to decrease the complexity without sacrificing the system performance. The performance results of the proposed algorithm is obtained in terms of Bit Error Rate (BER) and Mean Square Error (MSE) for 16QAM and 64QAM modulation schemes.Article Citation - WoS: 9Citation - Scopus: 10Radio Resource Management for User-Relay Assisted Ofdma-Based Wireless Networks(Urban und Fischer Verlag GmbH und Co. KG, 2016) Baştürk, İlhan; Özbek, BernaOrthogonal frequency division multiple access (OFDMA) based relay assisted networks are important for current and next-generation wireless networks since they have great potential to provide high data rate to users at anywhere, anytime. Towards that end, fixed relay assisted OFDMA networks are commonly utilized by the operators. However, they require supplementary costly infrastructure. User-relay assisted OFDMA-based networks are promising candidates to fulfill the demanding coverage and capacity requirements of future wireless networks in a cost efficient way. Thus, they have become popular as a complementary solution to fixed relay networks. Generic frame structure that divides the resource allocation frame into two subframes is mostly used in the literature for fixed and user-relay assisted networks in which it is assumed that a user can act as a destination and a relay simultaneously. However, it may be difficult to apply this assumption to practical systems because of the limitations of the current transceiver design. Thus, we propose a novel frame structure for user-relay assisted OFDMA-based wireless networks in order to cope with these drawbacks. The efficient radio resource management algorithms including relay selection and resource allocation are developed in order to exploit the opportunities of the proposed frame structure.Conference Object Citation - Scopus: 9Radio Resource Management for Ofdma-Based Mobile Relay Enhanced Heterogenous Cellular Networks(Institute of Electrical and Electronics Engineers Inc., 2013) Baştürk, İlhan; Özbek, Berna; Edemen, Çağatay; Tan, Ahmet Serdar; Zeydan, Engin; Ergüt, SalihIn this paper, we focus on the radio resource management problem for the Orthogonal Frequency Division Multiple Access (OFDMA)-based mobile relay-enhanced het erogenous cellular networks. We combine mobile relaying and data offloading scenarios to increase the capacity of the system and cope with the mobile data traffic volume that is increased by the number of wireless subscribers accessing mobile data services. We propose network interface selection, relay selection and resource allocation solutions for this scenario and show effect of relaying and data offloading on the system capacity and on the ratio of satisfied users. © 2013 IEEE.