Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/11

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Institution Author: search.filters.institutionAuthor.Özbek, BernaLanguage: search.filters.language.en

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Now showing 1 - 10 of 73
  • Conference Object
    Carrier Frequency Offset Based Shared Randomness for Secure Transmission in M-Psk Noma
    (IEEE, 2023) Göztepe, Caner; Karabulut Kurt, Güneş; Özbek, Berna
    Power domain non-orthogonal multiple access (NOMA) enhances spectral efficiency by superposing multiple users in the same time-frequency resource block at the expense of exposing the users' data. However, current approaches to improve the secrecy levels of users are limited to rate reduction. This paper proposes a secure NOMA system based on the shared randomness extracted from the reciprocal carrier frequency offsets (CFOs) between the transmitter-receiver pairs for M-ary phase-shift keying. As multiple users will have physically separated oscillators, it will result in independent CFOs among users. This randomness is used to introduce a constellation rotation in the transmitted symbols. We show that under ideal CFO estimates, the proposed approach achieves perfect secrecy among all NOMA users without introducing any rate reduction. We also demonstrate the practical applicability of the proposed approach by using a software-defined radio-based test bed. © 2023 IEEE.
  • Conference Object
    Detection Scheme for Pnc-Based Cell-Free Mimo Systems
    (IEEE, 2023) Cumali, Irem; Ozbek, Berna; Kurt, Gunes Karabulut
    Cell-free multiple-input multiple-output (cell-free MIMO) is a promising concept to overcome inter-cell interference and avoid non-uniform data rates among users by combining the best features of ultra-dense networks and MIMO. Hence, cell-free MIMO can fulfill the increasing demand on data rate with uniformly good coverage for the sixth-generation (6G) wireless communications. In addition to that, physical-layer network coding (PNC) reduces the transmission delay since it requires only two time slots instead of four time slots to exchange information between two users. In this paper, we propose a novel scheme called PNC-based cell-free MIMO to improve reliability further while reducing the transmission delay. We demonstrate the effectiveness of the proposed scheme regarding the bit error rate in different system configurations. The proposed PNC-based cell-free MIMO achieves significantly lower error probability than the conventional cell-free MIMO.
  • Conference Object
    Testbed Sdr Implementation Approach for Millimetre Wave Iot Applications
    (IEEE, 2022) Glazkov, Roman; Özbek, Berna; Pyattaev, Alexander; Musavian, Leila; Koucheryavy, Yevgeni
    Millimetre wave (mmWave) communication is a promising technology which can fulfil the growing demands for spectrum for future wireless networks. One of the key areas for the development of the mmWave networks is the Internet of Things (IoT) communications within fifth generation (5G) and beyond 5G networks. For significant analysis and development of the compliant IoT systems through testbed implementation, current mmWave spectrum transceivers are too expensive when substantial number of the nodes is required by the IoT applications. Considering all the above, it is suggested to use Software Defined Radio (SDR) transceivers with a lower frequency band and with an increased distance between the nodes. The idea is to scale observation time and distance to emulate mmWave radio without actual mmWave hardware. Using scaling factors for the certain system parameters to keep the signal characteristics in accordance with the mmWave band makes it possible. This approach allows to develop mmWave IoT testbeds with significant improvement in the system scalability and cost-effectiveness without the need to transmit and receive the signal in the mmWave band. In this paper, the concept of SDR-based Hardware-in-the-loop (HIL) system combined with the observation time and distance scaling approach is proposed. As an example, a testbed with a simple Wireless Physical Network Coding scheme is implemented and demonstrated. © 2022 IEEE.
  • Conference Object
    Citation - WoS: 2
    Citation - Scopus: 2
    Physical Layer Network Coding Enabled Noma With Multiple Antennas
    (IEEE, 2022) İlgüy, Mert; Özbek, Berna; Okyere, Bismark; Musavian, Leila; Pereira, Aathur
    In this work, a combination of non-orthogonal multiple access (NOMA) with multiple antennas and physical layer network coding (PNC) scheme is proposed to increase the overall data rate. In the proposed scheme, we employ higher-order modulations for the users with relatively high signal-to-noise ratio (SNR) in the PNC-NOMA pair to increase the data rate. Meanwhile, lower-order modulations are chosen for the users with relatively lower SNR values in the PNC-NOMA pair. We showed the results in terms of bit error rate (BER) for different number of antennas and users in the proposed PNC-NOMA scheme. © 2022 IEEE.
  • Conference Object
    Citation - Scopus: 1
    Interference Mitigation for Device-To Based Cellular Communications
    (IEEE, 2022) Acar, Süleyman Onur; Özbek, Berna
    Device-to-device (D2D) communication underlaying cellular networks can improve the performance of cellular systems and it provides an effective way to meet growing mobile traffic and capacity demand. When user equipments are located in close proximity, they can communicate through direct links. In this case, D2D links can increase both energy and spectrum efficiency by reusing uplink (UL) cellular resources while satisfying the users' quality-of-service requirements. However, integrating D2D links into the cellular infrastructure causes an interference since D2D communication can increase co-channel interference and degrade cellular users' transmission link quality. In this paper, the interference mitigation techniques including power control, multiple antenna and resource allocation based on graph coloring are proposed for D2D communications underlaying cellular systems to increase the data rate of both the cellular users and D2D pairs. Compared to the prior works, in the proposed algorithm, D2D and cellular users have same priority for resource allocation. Finally, the proposed algorithm improves the overall system capacity significantly.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 13
    User Selection and Codebook Design for Noma-Based High Altitude Platform Station (haps) Communications
    (IEEE, 2022) Cumalı, İrem; Özbek, Berna; Karabulut Kurt, Güneş; Yanıkömeroğlu, Halim
    High altitude platform station (HAPS) communications have made a tremendous impact on recent research into sixth-generation (6G) and beyond wireless networks. The large coverage area and significant computational capability of HAPS systems enable many areas of utilization in 6G and beyond applications, including Internet of Things (IoT) services, augmented reality, and connected autonomous vehicles. In addition, non-orthogonal multiple access (NOMA) is a cutting-edge technology that can be utilized to enhance spectral efficiency in HAPS systems. In this paper, we exploit NOMA-based HAPS communications and multiple antennas to meet the connectivity, reliability, and high-data-rate requirements of 6G and beyond applications. We propose a user selection and correlation-based user pairing algorithm for a NOMA-based multi-user HAPS system. Moreover, we investigate the codebook design for HAPS communication and adapt the polar-cap codebook (PCC) to the HAPS channel which shows Rician fading propagation characteristics dominated by the line-of-sight (LOS) component. Performance evaluations show that the proposed user selection algorithm is perfectly suited to the HAPS channel and that the PCC provides a remarkable spectral efficiency.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 11
    Delay Minimization for Massive Mimo Based Cooperative Mobile Edge Computing System With Secure Offloading
    (IEEE, 2022) Mümtaz, Rao; Yılmaz, Simay; Özbek, Berna
    Mobile edge computing (MEC) has been envisioned as a promising technology for enhancing the computational capacities of mobile devices by enabling task offloading. In this paper, we present a novel framework for a cooperative MEC system by employing Massive Multiple-Input Multiple-Output (MIMO) and non-orthogonal multiple access (NOMA) technologies, including security aspects. Specifically, in the proposed cooperative MEC system, there is no strong direct transmission link between the cell-edge user and the MEC server; consequently, the user sends their tasks to the MEC server through the helpers at the cell-centers. In the proposed framework, we minimize the overall delay, including secure offloading under the constraints of computing capability and transmit power. The proposed algorithm minimizes the overall delay in downlink and uplink transmission while satisfying security constraints to solve the formulated problem. The simulation results show that Massive MIMO based NOMA improves the performance of the secure MEC system by employing more than one helper.
  • Conference Object
    Citation - WoS: 2
    Citation - Scopus: 2
    Limited Feedback Design for Massive Full Dimension Mimo Systems
    (IEEE, 2022) Özbek, Berna; Arslan, Caner; Demirtaş, Mahmut; Şahan, Hüsne; Kadı, Furkan Kerim; Elçi, Erdem
    Massive Multiple-input Multiple-output (MIMO) systems serve simultaneously multiple users to increase spectral efficiency in wireless communication systems. Using two dimension antenna design for massive MIMO systems namely massive FD-MIMO, the overall system performance is further improved. For the massive FD-MIMO systems, the availability of channel state information (CSI) at the base station is essential to achieve overall performance gain. In this paper, we design limited feedback link for massive FD-MIMO by designing two separate codebooks for horizontal and elevation domains to reduce the feedback load. The simulation results are provided for the proposed scheme by considering 3-dimension wireless channel models.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Deep Learning Based Adaptive Bit Allocation for Heterogeneous Interference Channels
    (Elsevier, 2021) Aycan, Esra; Özbek, Berna; Le Ruyet, Didier
    This paper proposes an adaptive bit allocation scheme by using a fully connected (FC) deep neural network (DNN) considering imperfect channel state information (CSI) for heterogeneous networks. Achieving an accurate CSI has a crucial role on the system performance of the heterogeneous networks. Different quantization techniques have been employed to reduce the feedback overhead. However, the system performance cannot increase linearly with the number of bits increasing exponentially. Since optimizing the total number of bits is too complex for the entire network, an initial step is performed to distribute the bits to each cell in the conventional method. Then, the distributed bits are further allocated to each channel optimally. In order to enable direct allocation for the entire network, a FC-DNN based method is presented in this study. The optimized number of bits can be directly obtained for a different number of bits and scenarios by the proposed approach. The simulations are performed by using various scenarios with different allocation schemes. The performance results show that the DNN based method achieves a closer performance to the conventional approach. (C) 2021 Elsevier B.V. All rights reserved.
  • 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.