Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
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Conference Object Adaptive Limited Feedback Scheme for Stream Selection Based Interference Alignment in Heterogeneous Networks(IEEE, 2016) Beyazıt, Esra Aycan; Özbek, Berna; Le Ruyet,D.This paper presents a stream selection based interference alignment approach with imperfect channel state information for heterogeneous networks. The proposed algorithm performs the selection of a stream sequence among a predetermined set of sequences. Those selected sequences are the ones that mostly contribute to the sum rate when performing the exhaustive search. These stream sequences form a regular structure where the first stream is associated to a pico user. The effect of imperfect channel state information on the proposed algorithm is analyzed and a bit allocation scheme is proposed by deriving an upper bound on the rate loss due to quantization. © 2016 IEEE.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: 3Citation - Scopus: 3Space-Frequency Grouping Based Key Extraction for Mimo-Ofdm Systems(IEEE, 2017) Topal, Ozan Alp; Karabulut Kurt, Güneş; Özbek, BernaLatest developments in wireless communication networks push the limits of conventional security methods. Security can be improved with a secret key that is dynamically generated based on the surrounding physical environment. With this objective, physical layer security approaches can be implemented by means of simple signal processing methods. In this paper, we propose novel key extraction approaches based on spatial and frequency characteristics of the wireless environment. In a 2x2 MIMO-OFDM system, low key disagreement rates and key error rates are observed, proving the potential of physical layer key extraction techniques.Conference Object Citation - Scopus: 2Message-Passing Algorithm for Sum-Rate Maximization in Multi-Antenna Underlay D2d Communications(IEEE, 2018) Özbek, Berna; Pischella, Mylene; Le Ruyet, DidierIn this paper, we propose a resource allocation of device-to-device (D2D) communications underlaying multiantenna cellular systems by employing message-passing algorithm. It is possible to construct the factor graph of the D2D pairs by considering the interference power at the base station and among the D2D pairs. The goal is to avoid interfering the cellular transmission while increasing the sum data rate of D2D pairs. We show that the proposed resource allocation based on message passing algorithm allow us to almost reach the performance of the exhaustive search and outperforms the random allocation. Since the associated factor graph is not fully connected, the complexity of the algorithm is significantly reduced compared to the exhaustive search. © 2018 IEEE.Article Citation - WoS: 1Citation - Scopus: 1Spatial Signature for Secure Miso-Ofdm Systems(Institution of Engineering and Technology, 2018) Özbek, Berna; Karabulut Kurt, GüneşPhysical layer security is a promising approach to establish secure communications based on the characteristics of wireless channels. A spatial signature based secure multiple-input single-output (MISO) orthogonal frequency division multiplexing (OFDM) system is proposed to disrupt the reception of a passive eavesdropper by holding two practically relevant assumptions: a limited feedback link for legitimate node and the unavailability of channel state information of eavesdropper. The proposed algorithm achieves a higher average secrecy rate than the conventional secure MISO-OFDM systems in presence of a limited feedback link.Article Reduced Feedback Link Design for Devicerelaying Enhanced Multiple-Input Singleoutput Orthogonal Frequency-Division Multiple Access Wireless Systems(Institution of Engineering and Technology, 2016) Özbek, BernaDevice-relaying enhanced multiple-input single-output (MISO) orthogonal frequency-division multiple access (OFDMA) systems are one of the promising and cost-effective methods to satisfy data rate requirements of future wireless networks. To implement device relaying in MISO-OFDMA systems efficiently, the channel state information belonging to all links is required at the base station. However, the feedback load increases with the number of users, device-relay candidates, antennas and subcarriers. A novel scheduling and a joint feedback link design and relay selection algorithm in device-relaying enhanced downlink MISO-OFDMA systems are proposed, while reducing the feedback load significantly without sacrificing the system performance.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.Conference Object Citation - WoS: 3Citation - Scopus: 3Load Based Cell Selection Algorithm for Digital Mobile Radio(Institute of Electrical and Electronics Engineers Inc., 2016) Yılmaz, Simay; Özbek, Berna; Taş, Murat; Bardak, Erinç DenizDigital mobile radio is one of a digital radio standard for Professional Mobile Radio and it is commonly used for emergency services. The cell selection is very important for digital mobile radio based systems to improve system performance in terms of delay and bit error rate. In this work, we propose an efficient cell selection algorithm for Digital Mobile Radio. In the proposed algorithm, each user selects the base station according to the proposed utility value determined based on both cell load and signal-to-interference-noise ratio. The goal of the proposed algorithm is to balance the distribution of the users among the cells to reduce the waiting time for connection while establishing reliable transmission link. We illustrate the performance results for different scenarios and applications in terms of cell load, signal-to-interference-noise ratio and bit error rate. © 2016 IEEE.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: 3Reduced Feedback Designs for Sdma-Ofdma Systems(Institute of Electrical and Electronics Engineers Inc., 2009) Özbek, Berna; Le Ruyet, DidierIn SDMA-OFDMA wireless communication systems, the feedback load increases with the number of users, subcarriers and antennas in the cell. In this paper, we propose two efficient reduced feedback algorithms by selecting the clusters at the user side. For each cluster, we select the users according to their norm and their orthogonality. We evaluate the performance of the user selection algorithms considering the quantization effect. We also design a specific codebook design to quantize CSI for the proposed criterion.