WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7150

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Institution Author: search.filters.institutionAuthor.Özbek, BernaPublisher: search.filters.publisher.Institute of Electrical and Electronics Engineers Inc.

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Now showing 1 - 10 of 46
  • Article
    Citation - WoS: 7
    Citation - Scopus: 8
    The Resilience of Massive Mimo Pnc To Jamming Attacks in Vehicular Networks
    (Institute of Electrical and Electronics Engineers Inc., 2021) Okyere, Bismark; Musavian, Leila; Özbek, Berna; Busari, Sherif A.; Gonzalez, Jonathan
    In this article, we investigate the resilience of Massive MIMO Physical Layer Network Coding (PNC) to jamming attack in both sub-6 GHz and millimeter-Wave (mmWave) systems in vehicular networks. Massive MIMO generally is resilient to jamming attacks, and we investigate the impact that PNC has on this resilience, if combined with Massive MIMO. The combination of Massive MIMO and PNC has shown a significant improvement in the bit error rate (BER) in our previous investigation. The corresponding framework is analysed against a barraging attack from a jammer, where the jamming channel is not known to the base station (BS), and the jammer can use any number of transmit antennas. Over Rayleigh channel, our simulation results reveal that Massive MIMO PNC performs better in the lower signal-to-noise ratio (SNR) regions to jamming attacks and this is achieved at twice the spectral efficiency. A similar performance is observed over mmWave channel.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 5
    Design and Implementation of Spatial Correlation-Based Clustering for Multiuser Miso-Noma Systems
    (Institute of Electrical and Electronics Engineers Inc., 2021) Göztepe, Caner; Özbek, Berna; Karabulut Kurt, Güneş
    In this letter, we propose a novel user clustering algorithm for downlink multiuser multiple-input single-output (MISO) non-orthogonal multiple access (NOMA) systems along with its implementation in a real-time testing environment. The proposed method selects the clusters by considering users' spatial channel properties against the generated orthogonal directions. This is then followed by power allocation and zero-forcing precoding steps to mitigate the interference between the selected clusters. Performance comparisons are provided in terms of both real-time tests and simulations. It is demonstrated that a notable improvement in capacity and reliability can be obtained through the proposed approach in multiuser MISO-NOMA systems with reduced complexity.
  • Article
    Citation - WoS: 5
    Citation - Scopus: 8
    Coverage Analysis of Physical Layer Network Coding in Massive Mimo Systems
    (Institute of Electrical and Electronics Engineers Inc., 2021) İlgüy, Mert; Özbek, Berna; Mumtaz, Rao; Busari, Sherif A.; Gonzalez, Jonathan
    Wireless networks are prone to interference due to their broadcast nature. In the design of most of the traditional networks, this broadcast nature is perceived as a performance-degrading factor. However, Physical Layer Network Coding (PNC) exploits this broadcast nature by enabling simultaneous transmissions from different sources and thereby enhances the performance of the wireless networks with respect to improvement in spectral efficiency, coverage, latency and security of the system. For fifth generation (5G) networks and beyond, massive multiple input multiple output (MIMO) is considered as a key physical layer technology. Thus, its combination with PNC can significantly enhance the performance of the network, facilitating capacity-coverage improvement, among other benefits. While the bit error rate performance of multiuser massive MIMO-PNC systems through linear detection has been investigated extensively, their coverage probability for a given target signal-to-noise ratio has not been explored yet. In this paper, we derive a closed form expression for coverage probability in PNC based multiuser massive MIMO systems employing zero-forcing equalization. Both theoretical and simulation results are provided for different number of users and antennas in the multiuser massive MIMO-PNC communications systems.
  • Conference Object
    Citation - Scopus: 1
    Yüksek İrtifa Platform İstasyonları için Korelasyon Matrisinin Yaklaşımı
    (Institute of Electrical and Electronics Engineers Inc., 2021) Cengiz, Aybüke; Tedik Başaran, Semiha; Karabulut Kurt, Güneş; Özbek, Berna; Yanıkömeroğlu, Halim
    A High Altitude Platform Station (HAPS) is a new and promising technology with different uses like wireless communication services, traffic monitoring, navigation applications and Internet of Things (IoT) applications. Since it is positioned much higher than ground-level users, line-of-sight (LOS) is more common in HAPS systems. Especially in HAPS systems that include multiple antennas, the effect of correlation between antennas is an important factor limiting the performance. The effect of correlation is strongly influenced by the spacing between the antenna elements and environmental factors. This effect can be reduced by the effect of rich scattering environment in terrestrial Multi-Input/Multi-Output (MIMO) systems, yet this observation is not applicable to HAPS systems. In this study, a tight bound expression for the correlation matrix which does not have an expression in closed form and has a significant place in the performance of HAPS systems has been obtained. Comprehensive numerical values have been obtained under different system parameters to demonstrate the convergence performance of the approximate expression to the real value, and the results have been compared. © 2021 IEEE.
  • Conference Object
    Ofdm Sistemleri için Pilot Tabanlı Em Kanal Kestirim Başarımı
    (Institute of Electrical and Electronics Engineers Inc., 2007) Baştürk, İlhan; Özbek, Berna
    In 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: 2
    Genetik 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, Didier
    In 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
    Transmit Beamforming Techniques for Multicast Wireless Communication Systems
    (Institute of Electrical and Electronics Engineers Inc., 2009) Özbek, Berna; Le Ruyet, Didier
    In this paperg transmit beamforming algorithm is designed for multicast wireless communication providing only one beam and multiple beams. The reduced complexity algorithms are imyproved the system performance with multiple transmit beamy forming techniques.
  • Conference Object
    Citation - WoS: 2
    Citation - Scopus: 2
    Gezgin Rölelerin Dfbçe Tabanlı Hücresel Ağ Performansına Etkisi
    (Institute of Electrical and Electronics Engineers Inc., 2014) Baştürk, İlhan; Özbek, Berna
    OFDMA-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
    Energy-Efficient Resource Allocation for Multiuser Ofdm Wireless Networks
    (Institute of Electrical and Electronics Engineers Inc., 2015) Durbaş, Şükrü; Özbek, Berna
    In the last decades, the energy consumption in wireless communication systems is increasing and becoming a major problem for cellular operators. As a result of that, solutions to increase energy-efficiency (EE) in wireless networks are becoming more popular. Therefore, the resource allocation algorithms that provides EE for multiuser OFDM based wireless networks is presented in this paper. Then, the conventional spectrum-efficient (SE) designs are compared with EE based schemes and EE characteristics of the system has been analyzed. The simulation results show the advantages of EE scheme especially on high channel-gain-to-noise ratio and low number of users cases.
  • Conference Object
    Stbc-ofdm Sistemler için Em Tabanlı Kanal Kestirim Başarımı
    (Institute of Electrical and Electronics Engineers Inc., 2009) Baştürk, İlhan; Özbek, Berna
    Bu 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.