WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection

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

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Author: search.filters.author.Özbek, BernaScopus Q: search.filters.scopusQuartile.Q3

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Now showing 1 - 10 of 11
  • Conference Object
    Citation - Scopus: 1
    Interference Management for Multiuser Multiantenna Ofdma Underlaying Device-To Communications
    (IEEE, 2017) Özbek, Berna; Pischella, Mylene; Le Ruyet, Didier
    Underlaying 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: 3
    Citation - Scopus: 3
    Space-Frequency Grouping Based Key Extraction for Mimo-Ofdm Systems
    (IEEE, 2017) Topal, Ozan Alp; Karabulut Kurt, Güneş; Özbek, Berna
    Latest 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.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Spatial Signature for Secure Miso-Ofdm Systems
    (Institution of Engineering and Technology, 2018) Özbek, Berna; Karabulut Kurt, Güneş
    Physical 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, Berna
    Device-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: 2
    Citation - Scopus: 2
    Iterative Channel Estimation for Higher Order Modulated Stbc-Ofdm Systems With Reduced Complexity
    (Korean Society of Internet Information, 2016) Baştürk, İlhan; Özbek, Berna
    In 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: 3
    Citation - Scopus: 3
    Load Based Cell Selection Algorithm for Digital Mobile Radio
    (Institute of Electrical and Electronics Engineers Inc., 2016) Yılmaz, Simay; Özbek, Berna; Taş, Murat; Bardak, Erinç Deniz
    Digital 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: 3
    Reduced Feedback Designs for Sdma-Ofdma Systems
    (Institute of Electrical and Electronics Engineers Inc., 2009) Özbek, Berna; Le Ruyet, Didier
    In 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.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 3
    Low Complexity Zf Receiver for Orthogonal Sfbc-Ofdm in Broadband Wireless Channels
    (Institution of Engineering and Technology, 2006) Özbek, Berna; Le Ruyet, Didier
    Orthogonal space-frequency block coded (SFBC) orthogonal frequency division multiplexing (OFDM) systems are analysed in broadband wireless channels where adjacent subcarriers do not have the same channel coefficients and the matched filter receiver causes an error floor in bit error rate performance. To avoid this, a low complexity zero forcing (ZF) receiver for the orthogonal schemes with two and three transmit and one receive antennas are proposed.
  • Conference Object
    Citation - WoS: 6
    Citation - Scopus: 11
    Adaptive Resource Allocation for Multicast Ofdm Systems With Multiple Transmit Antennas
    (Institute of Electrical and Electronics Engineers Inc., 2006) Özbek, Berna; Le Ruyet, Didier; Khiari, Hajer
    We evaluate the impact of multiple transmit antennas on the performance of multicast OFDM systems by proposing a suboptimal low complexity algorithm. Associated with a powerful erasure code, it is possible to increase the data rate of multicast OFDM systems by selecting for each subcarrier to the users with a good channel condition. We show that the resource allocation which includes the precoding vector selection, subcarrier allocation and bit loading is a difficult optimization problem. We propose a suboptimal algorithm to solve this problem by avoiding the optimization to reduce complexity. When the users are not symmetrically distributed around the base station, we add a fair scheduler to guarantee that each user receives the same amount of data. We present simulation results where we compare the proposed multicast systems with the classical multicast OFDM systems. When the users are symmetrically distributed around the base station, the gain is rather small, whereas when the users are non-symmetrically distributed, the proposed algorithm outperforms OFDM systems with subcarrier allocation.
  • Conference Object
    Citation - Scopus: 5
    Partial and Analog Feedback for Miso Precoding Systems
    (Institute of Electrical and Electronics Engineers Inc., 2007) Le Ruyet, Didier; Özbek, Berna
    We consider a multiple input single output antenna system with a feedback link. While most of the previous works have considered perfect feedback channels, in this paper, we evaluate the impact of a noisy feedback channel on the quality and the performance of the transmission. We compare the finite rate feedback scheme with the analog feedback schemes where the channel parameters are transmitted without quantization over the uplink channel. Two analog feedback schemes are considered : the feedback of the channel vector and the feedback of the normalized channel vector. We provide bounds on the performance and give numerical results. We have shown that at low to medium uplink SNR the analog feedback of the normalized channel vector outperforms the analog feedback of the channel vector. Depending on the range of uplink SNR, quantized feedback can perform poorlz y compared to analog feedback.