Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
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Conference Object Carrier Frequency Offset Based Shared Randomness for Secure Transmission in M-Psk Noma(IEEE, 2023) Göztepe, Caner; Karabulut Kurt, Güneş; Özbek, BernaPower 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 KarabulutCell-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, YevgeniMillimetre 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: 2Citation - Scopus: 2Physical Layer Network Coding Enabled Noma With Multiple Antennas(IEEE, 2022) İlgüy, Mert; Özbek, Berna; Okyere, Bismark; Musavian, Leila; Pereira, AathurIn 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: 1Interference Mitigation for Device-To Based Cellular Communications(IEEE, 2022) Acar, Süleyman Onur; Özbek, BernaDevice-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: 10Citation - Scopus: 13User Selection and Codebook Design for Noma-Based High Altitude Platform Station (haps) Communications(IEEE, 2022) Cumalı, İrem; Özbek, Berna; Karabulut Kurt, Güneş; Yanıkömeroğlu, HalimHigh 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: 8Citation - Scopus: 11Delay Minimization for Massive Mimo Based Cooperative Mobile Edge Computing System With Secure Offloading(IEEE, 2022) Mümtaz, Rao; Yılmaz, Simay; Özbek, BernaMobile 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: 2Citation - Scopus: 2Limited Feedback Design for Massive Full Dimension Mimo Systems(IEEE, 2022) Özbek, Berna; Arslan, Caner; Demirtaş, Mahmut; Şahan, Hüsne; Kadı, Furkan Kerim; Elçi, ErdemMassive 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: 6Citation - Scopus: 6User Selection for Millimeter Wave Non-Uniform Full Dimensional Mimo(IEEE, 2020) Mumtaz, Rao; Gonzalez, Jonathan; Cumalı, İrem; Özbek, BernaThe millimeter wave (mmWave) based full-dimensional (FD) MIMO communication is one of the promising technology to fulfill the demand of high data rate for the sixth generation (6G) services including 6D hologram, haptic and multi-sensory communications. In order to satisfy the requirements of 6G applications, we investigate a non-uniform rectangular array (NURA) structure with FD-MIMO antenna systems for the multiuser mmWave communications. For the dense scenarios where the number of users to be served is high, we propose user selection algorithms for both digital and hybrid transceiver designs in FD-MIMO with NURA for the multiuser mmWave communications. For the digital transceivers, the users are selected based on their channel correlation considering FD-MIMO with NURA structures. For the hybrid transceivers, sequential user and beam selection is performed using the correlation between the beamspace channels in FD-MIMO with NURA case. The superiority of the NURA compared to uniform antenna structure is shown through the performance evaluations in the multiuser mmWave communications. Besides, the sum data rate results and complexity analysis denote the feasibility of the proposed algorithms compared to the joint user and beam selection schemes.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.