Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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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 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 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.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: 5Queue-Aware Resource Allocation for Ofdma-Based Mobile Relay Enhanced Networks(VDE Publishing House, 2013) Baştürk, İlhan; Özbek, Berna; Le Ruyet, DidierMobile relay assisted OFDMA networks that are considered as a good candidate in future deployment scenarios for coverage extension and lower deployment costs are promising solutions for provision of ubiquitous high-data-rate services in wide coverage areas. However, it is required to design efficient resource allocation algorithms to exploit these opportunities. Thus, this paper designs an heuristic resource allocation algorithm based on the queue and channel state information of the users for mobile relay enhanced OFDMA networks. The proposed queue aware algorithm is appropriate for the realistic scenarios and use system resources efficiently. Numerical results revealed that the mobile-relay enhanced scheme improves coverage and assisting users having unfavorable channel conditions such as cell-edge users by increasing the data rate compared to existing fixed-relay enhanced and non-relaying schemes. © VDE Verlag GMBH.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.Conference Object Citation - Scopus: 2Fairness Aware Resource Allocation for Downlink Miso-Ofdma Systems(Institute of Electrical and Electronics Engineers Inc., 2012) Baştürk, İlhan; Özbek, BernaIn this paper, a resource allocation problem for downlink multiple input-single output orthogonal frequency division multiple access (MISO-OFDMA) systems is investigated. The problem is defined as maximizing the minimum user rate with the constraints of total power and bit error rate (BER). Since it is difficult to obtain the optimal solution to this problem, a suboptimal but efficient solution is proposed based on zero forcing beamforming (ZFBF) to reduce computational complexity. The proposed algorithm is a fairness aware radio resource allocation algorithm that shares the resources equally among the users who has different distances from the Base Station (BS). The simulation results show that the proposed algorithm satisfies the fairness criterion having higher data rates compared to the existing algorithms. © 2012 IEEE.Conference Object Citation - WoS: 1Citation - Scopus: 3Iterative Em-Based Channel Estimation for Stbc-Ofdm(Institute of Electrical and Electronics Engineers Inc., 2009) Baştürk, İlhan; Özbek, BernaIn this paper, an iterative EM based channel estimation algorithm is studied for STBC-OFDM systems. Compared to the time domain EM based channel estimation algorithm which needs matrix inversion, a frequency domain EM based channel estimation algorithm is proposed by estimating the channel coefficients for each subcarrier. The proposed channel estimation algorithm decreased the complexity without sacrificing the performance. The time domain and proposed frequency domain EM based channel estimation algorithms are compared in terms of bit error rate (BER), mean square error (MSE) and the number of iterations used in the EM algorithm.