Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
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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.Book Citation - Scopus: 17Feedback Strategies for Wireless Communication(Springer, 2014) Özbek, Berna; Le Ruyet, DidierThis book explores the different strategies regarding limited feedback information. The book analyzes the impact of quantization and the delay of CSI on the performance. The author shows the effect of the reduced feedback information and gives an overview about the feedback strategies in the standards. This volume presents theoretical analysis as well as practical algorithms for the required feedback information at the base stations to perform adaptive resource algorithms efficiently and mitigate interference coming from other cells. © 2014 Springer Science+Business Media New York. All rights are reserved.Conference Object Citation - Scopus: 1Interference Management for Multiuser Multiantenna Ofdma Underlaying Device-To Communications(IEEE, 2017) Özbek, Berna; Pischella, Mylene; Le Ruyet, DidierUnderlaying device-to-device (D2D) transmission in cellular wireless systems is one of the promising transmission techniques for fifth generation (5G) and beyond 5G applications. Nevertheless, the interference between the D2D pairs, the interference from cellular users to D2D receivers and the interference that affects the cellular communications should be mitigated to increase the overall system performance. In this paper, we propose interference management techniques for D2D underlaying communications in multiuser multiantenna orthogonal frequency division multiple access (OFDMA) systems. Our goal is to increase the data rate of both the cellular users and D2D pairs by performing interference management in frequency, power and spatial dimensions. The performance evaluations illustrate the effectiveness of the proposed algorithm in terms of average data rate and average transmitted power for both cellular users and D2D pairs.Conference Object Citation - WoS: 1Citation - Scopus: 1Interference-Based Clustering for Mimo D2d Underlay Communications(IEEE, 2018) Pischella, Mylene; Özbek, Berna; Le Ruyet, DidierClustering of Device-to-Device (D2D) pairs with cellular transmissions is particularly challenging to manage interference in future fifth generation networks. D2D pairs should coexist with cellular users in underlay scenario, taking advantage of frequency and spatial dimensions. We consider a Multiple Input Multiple Output (MIMO) channel where all users (whether cellular or devices) are equipped with N > 1 antennas, and the Base Station (BS) has M >= N antennas. Interference between D2D pairs, between D2D transmitters and the BS and between cellular users and D2D receivers is then managed by determining clusters of D2D pairs and cellular users with very low relative interference levels. Clusters are obtained after graph-coloring on a pairwise interference-leakage based matrix. Then, several Resource Blocks (RB) allocation algorithms are proposed, with various fairness levels. A final orthogonalization step using Minimum Mean Square Error (MMSE) may be added at the BS in order to further reduce interference. Simulation results show very large D2D data rates improvements, while cellular data rates degradation due to interference can be controlled.Conference Object Performance of Multicast Miso-Ofdm Systems(Ecole Nationale Superieure de Techniques Avancees, ENSTA, 2020) Le Ruyet, Didier; Özbek, Berna; Khanfir, HajerIn this paper, we evaluate the performance of multicast OFDM systems with single and multiple transmit antennas. We have shown that it is possible to increase the data rate of multicast OFDM systems by selecting the users with good channel for each subcarrier. For the single transmit antenna case, the resource allocation has been applied using the two-step algorithm where subcarrier allocation and bit loading are performed separately. For the multiple transmit antennas case, we have proposed a suboptimal algorithm using a set of precoding vectors. In this study, we present the simulation results of the complete transmission chain where we have associated the resource allocation algorithms with a powerful erasure code. The results show that the proposed algorithms outperform the classical worst case algorithm for both single and multiple transmit antennas. © EW 2007 - 13th European Wireless Conference: Enabling Technologies for Wireless Multimedia Communications. All rights reserved.Conference Object Heterojen Ağlarda Veri Katarı Seçimi Tabanlı Girişim Hizalama için Uyarlamalı Sınırlı Geri Besleme Yöntemi(Institute of Electrical and Electronics Engineers Inc., 2016) Aycan, Esra; Özbek, Berna; Le Ruyet, DidierBu bildiride, sınırlı geri beslemeli heterojen ağlar için veri katarı seçimi tabanlı bir girişim hizalama yöntemi sunulmuştur. Sunulan veri katarı seçimi yöntemi, veri katarlarını ilk olarak piko kullanıcılarından seçmeye başlar, daha sonra veri hızını artıran en güçlü veri katarı ile seçim işlemi devam eder ve tüm kullanıcıların en az bir veri katarının olması sağlanır. Seçim işleminden sonra, seçilen veri katarı ile diğerleri arasında oluşan girişimler ortogonal projeksiyonlarla önlenir. Sınırlı geri beslemeli kanalda toplam kapasite, uyarlanır bit paylaşımıyla iyileştirilmektedir.Conference Object Citation - Scopus: 3Improved Successive Stream Selection With Quantized Channel in Heterogeneous Networks(Institute of Electrical and Electronics Engineers Inc., 2015) Aycan, Esra; Özbek, Berna; Le Ruyet, DidierThis paper focuses on different distortion metrics in order to analyze the influence of the imperfect channel state information (CSI) on the improved successive stream selection algorithm that manages the interference in a heterogeneous network. The presented approach initially selects the streams from the user of the pico cell, continuing with the strongest streams among the remaining streams that increase the sum rate and satisfy the constraint that at least one stream is selected from each user. In order to reduce the interference, the channel matrices of the remaining streams are projected orthogonally to the virtual transmit and receive channels of the selected stream. The impact of the quantization distortion on the precoding and postcoding design is examined. The performance of two distortion metrics which are the Chordal distance and the Euclidean distance are compared for different number of quantization bits. The performance evaluations are obtained by considering different locations of small cells with respect to the macro cell.Conference Object Citation - Scopus: 2Sum Capacity Maximization in Distributed Multicell Miso-Ofdma Systems With Reduced Feedback Links(Institute of Electrical and Electronics Engineers Inc., 2014) Özbek, Berna; Le Ruyet, Didier; Pischella, MyleneIn this paper, we examine distributed and fair resource allocation for weighted sum multicell capacity maximization in multi-input single-output (MISO)-Orthogonal Frequency-Division Multiple Access (OFDMA) multicell systems with reduced feedback links. We apply zero forcing (ZF) precoding to reduce interference between the users in the same cell and then propose iterative distributed power allocation algorithm for the users with high signal-to-interference-plus-noise ratio (SINR) to reduce the interference between BSs. In order to perform distributed RA for MISO-OFDMA multicell systems, the channel state information (CSI) of all required links are fed back to all base stations. However, the feedback load increases with the number of users, base stations, subcarriers and antennas. Therefore, we propose a user selection algorithm at the receiver side to reduce the feedback load while providing CSI of the users with high SINR at the BSs. The performance results of the proposed algorithms are illustrated for multicell MISO-OFDMA systems in wireless channels. © 2014 IEEE.Conference Object Citation - WoS: 5Citation - Scopus: 3Hierarchical Successive Stream Selection for Heterogeneous Network Interference(Institute of Electrical and Electronics Engineers Inc., 2014) Aycan, Esra; Özbek, Berna; Le Ruyet, DidierThis paper presents a hierarchical stream selection approach to deal with the interference in a heterogeneous network where different cell types are coexisting with each other to increase the sum capacity. Due to the variety of the transmit powers between the macro and small cells, interference levels are different. The proposed solution hierarchically selects the strongest streams of each cell with a contribution to the sum rate, while constructing the streams via singular value decomposition (SVD). In order to reduce the interference, the channel matrices of the remaining streams are projected orthogonally to the virtual transmit channel and virtual receive channel of the selected stream. The performance evaluations are obtained by considering different locations of small cells with respect to the macro cell. It is shown that the proposed method can dynamically select more streams in heterogeneous networks and achieve higher data rates compared to the existing algorithms. © 2014 IEEE.Conference Object Citation - WoS: 5Citation - Scopus: 5On Precoding Mimo-Fbmc With Imperfect Channel State Information at the Transmitter(Institute of Electrical and Electronics Engineers Inc., 2014) Le Ruyet, Didier; Zakaria, Rostom; Özbek, BernaThis paper studies the impact of imperfect channel state information (CSI) due to limited feedback link on the performance of multi-user MIMO system using filter bank based multicarrier (FBMC) modulation. The system is composed of a transmitter performing Zero Forcing (ZF) precoding and single antenna receivers applying decoding techniques. Simulation-based results show that except when the number of users is less than the number of transmit antennas, the BER performance and capacity of FBMC and OFDM modulation are the same. These results are theoretically justified due to the distribution of the interfering terms. As in OFDM, depending on the number of interferers, for a given BER performance target, the required number of feedback bits per channel vector can be rather high. FBMC becomes attractive not only because it relaxes the synchronization with respect to OFDM, but also because it achieves the same performance results as OFDM for multiuser MIMO precoding even in the case of imperfect CSI at the transmitter. © 2014 IEEE.