WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Conference Object User Selection for Secure Massive Mimo Based Mobile Edge Computing With Delay-Sensitive Applications(IEEE, 2025) Yilmaz, Saadet Simay; Ozbek, BernaMobile edge computing (MEC) has been a promising technology that leverages cloud computing capabilities at the network edge to address compute-intensive and delay-sensitive applications of mobile users with limited resources. Employing massive multiple-input multiple-output (mMIMO) and nonorthogonal multiple access (NOMA) in the MEC system facilitates simultaneous task offloading for multiple users, resulting in increased spectral efficiency and decreased offloading delay. Despite the great potential of the mMIMO-NOMA-based MEC system, offloading computation tasks to MEC servers can introduce inherent security concerns and vulnerabilities. We address a notable gap in the existing literature by investigating the effect of user selection to minimize the delay in MEC while enhancing the security of this framework. Specifically, this paper presents a user selection strategy for an uplink mMIMO-NOMA-based secure MEC system in the presence of a malicious eavesdropper (Eve) to minimize offloading and computing delays, subject to the transmit power, computing resource, and secrecy rate constraints with remote computing. We propose a two-step secure user selection algorithm and solve the optimization problem with the active-set algorithm. The simulation results demonstrate the effectiveness of the proposed user selection strategy on secure MEC with a malicious Eve by minimizing the task execution delay compared to the benchmark schemes.Article Citation - WoS: 2Citation - Scopus: 2Deep Learning Based Adaptive Bit Allocation for Heterogeneous Interference Channels(Elsevier, 2021) Aycan, Esra; Özbek, Berna; Le Ruyet, DidierThis 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: 4Citation - Scopus: 5Hybrid Beamforming Strategies for Secure Multicell Multiuser Mmwave Mimo Communications(Elsevier, 2021) Özbek, Berna; Erdoğan, Oğulcan; Busari, Sherif A.; Gonzalez, JonathanOver the last decade, many advancements have been made in the field of wireless communications. Among the major technology enablers being explored for the beyond fifth-generation (B5G) networks at the physical layer (PHY), a great deal of attention has been focused on millimeter-wave (mmWave) communications, massive multiple-input multiple-output (MIMO) antenna systems and beamforming techniques. These enablers bring to the forefront great opportunities for enhancing the performance of B5G networks, concerning spectral efficiency, energy efficiency, latency, and reliability. The wireless communication is prone to information leakage to the unintended nodes due to its open nature. Hence, the secure communication is becoming more critical in the wireless networks. To address this challenge, the concept of Physical Layer Security (PLS) is explored in the literature. In this paper, we examine the mmWave transmission through linear beamforming techniques for PLS based systems. We propose the secure multiuser (MU) MIMO mmWave communications by employing hybrid beamforming at the base stations (BSs), legitimate users and eavesdroppers. Using three Dimensional (3D) mmWave channel model for each node, we utilize the artificial noise (AN) beamforming to jam the transmission of eavesdropper and to enhance the secrecy rate. The secrecy performance on multicell mmWave MU-MIMO downlink communications is demonstrated to reveal the key points directly related to the system security for B5G wireless systems. (C) 2021 Elsevier B.V. All rights reserved.Article User-Relay Assisted Cellular Networks With Multiple Antennas(Taylor & Francis, 2019) Baştürk, İlhan; Özbek, BernaUser-relay assisted OFDMA-based cellular networks have gained great importance recently since these networks are indicated as one of the powerful technologies that will contribute the 5G standard. These networks can be used with novel three-phase frame structure unlike classical two-phase frame structure and can be enhanced with multiple antennas to utilise the advantages of them. The main advantage of the three-phase frame structure is taking care of the limitations of the current transceiver design in practical systems and not allowing users to be relay and user simultaneously. Diversity and capacity gains are also the advantages of extending the network with multiple antennas. In this paper, we will use the novel three-phase frame structure for downlink MISO-OFDMA cellular networks and develop resource management algorithms as relay selection and resource allocation to observe the benefits of this system.Article Traffic Aware Cell Selection Algorithm for Tetra Trunk Based Professional Mobile Radio(Springer Verlag, 2019) Özbek, Berna; Karataş, Azad; Bardak, Erinç Deniz; Sönmez, İlkerLoad balancing and traffic management are the critical needs in cell selection decision for a better and seamless communication demands in professional mobile radios. For the cases where cell selection algorithms do not consider the traffic load, there may be call drops due to the congestion in networks or longer call setup times for the users. These undesired consequences can cause dramatic quality degradation especially for the emergency cases or public safety services. In this paper, we propose two algorithms for Tetra Trunk based professional mobile radios by considering both traffic load and received signal strength indication (RSSI) in order to reduce the significant delays while establishing transmissions. The proposed full set cell selection algorithm is prioritized to reduce the call setup time for the mobile users and the proposed reduced set cell selection algorithm is focused on minimizing the number of RSSI measurements which causes significant delay in practical professional mobile radio. We illustrate the performance results in terms of delay for Tetra Trunk based professional mobile radio.Article Traffic Load-Based Cell Selection for Apco25 Conventional-Based Professional Mobile Radio(Springer Verlag, 2020) Yılmaz, Saadet Simay; Özbek, Berna; Taş, Murat; Bengür, SıdıkaWireless communication between public safety officers is very important to transmit voice or data during emergency crises. When the public communication networks cannot provide services during crises, disasters, and high traffic cases, Professional or private mobile radio (PMR) such as Association of Public Safety Communications Officials (APCO25) conventional systems are needed to improve the service quality and to provide uninterrupted service to the users. In this paper, we propose traffic-based cell selection algorithms for the APCO25 conventional systems to attach users to base stations in a balanced manner to reduce waiting time while establishing a connection. The simulation results of the proposed traffic load-based cell selection algorithms are illustrated in terms of the RSSI measurements counter, the number of connection requests, the average waiting time, and the number of re-selections for the APCO25 conventional systems.Article Citation - WoS: 3Citation - Scopus: 3Secure Multiuser Mimo Communication Systems With Imperfect Channel State Information(Elsevier Ltd., 2019) Özbek, Berna; Özdoğan Şenol, Özgecan; Karabulut Kurt, GüneşIn this paper, we propose a secure wireless communications system through a multiple input multiple output (MIMO) channel which includes a multiple antenna base station and multiple single antenna legitimate users that are overheard by a multiple antenna eavesdropper. By assuming that the eavesdropper's channel is unknown by the base station, an artificial noise beamforming is used to prevent this eavesdropper to decode legitimate users' message in the downlink. Additionally, the base station has only imperfect channel state information (CSI) of legitimate users which is the practically relevant case. Under the condition of imperfect CSI, a noise leakage on legitimate users' signal is occurred and it degrades the achievable average secrecy sum rate. In order to reduce this noise leakage, the semi-orthogonal selection having a rotated codebook is proposed to establish a secure communications link. We demonstrate the average secrecy sum rate results of the proposed algorithm for secure multiuser MIMO systems under imperfect CSI through extensive simulation results. (c) 2019 Elsevier B.V. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 2Secure Multiuser Miso Communication Systems With Limited Feedback Link(Springer Verlag, 2018) Özbek, Berna; Özdoğan Şenol, Özgecan; Karabulut Kurt, GüneşPhysical layer security is one of the promising techniques for the security of next-generation wireless systems. In this paper, we analyze the impact of the limited feedback link on the secrecy capacity for a system which includes a base station with multiple antennas, a single legitimate user selected from multiple active ones and multiple eavesdroppers. We propose to design a limited feedback link by reducing the feedback load and quantizing the channel state information (CSI) of legitimate users to establish a secure communication system. The feedback load is decreased with a self discrimination criterion at the legitimate users’ side while keeping the secrecy capacity constant. The best legitimate user is selected based on the quantized CSI through a limited feedback link. We also analyze the impact of CSI of eavesdroppers, which information may or may not be available at transmitter. In practical cases where eavesdroppers are passive and their location is not known by the transmitter, an artificial noise is used to disrupt their reception. When the CSI of eavesdroppers is known, the generalized singular value decomposition is applied. We illustrate the performance results of the proposed limited feedback link through the availability of CSI of eavesdroppers at the transmitter.Article Citation - WoS: 3Citation - Scopus: 3Channel and Queue Aware Joint Relay Selection and Resource Allocation for Miso-Ofdma Based User-Relay Assisted Cellular Networks(Springer Verlag, 2018) Baştürk, İlhan; Özbek, BernaUser-relay assisted orthogonal frequency division multiple access (OFDMA) networks are cost-effective solutions to meet the growing capacity and coverage demands of the next generation cellular networks. These networks can be used with multiple antennas technology in order to obtain a diversity gain to combat signal fading and to obtain more capacity gain without increasing the bandwidth or transmit power. Efficient relay selection and resource allocation are crucial in such a multi-user, multi-relay and multi-antenna environment to fully exploit the benefits of the combination of user-relaying and multiple antennas technology. Thus, we propose a channel and queue aware joint relay selection and resource allocation algorithm for multiple-input single-output (MISO)-OFDMA based user-relay assisted downlink cellular networks. Since, the proposed algorithm is not only channel but also queue-aware, the system resources are allocated efficiently among the users. The proposed algorithm for the MISO-OFDMA based user-relay assisted scheme is compared to existing MISO-OFDMA based non-relaying and fixed relay assisted schemes and it is also compared with the existing single-input single-output (SISO)-OFDMA based user-relay assisted scheme. Simulation results revealed that the proposed scheme outperforms the existing schemes in terms of cell-edge users’ total data rate, average backlog and average delay.Article Citation - WoS: 2Citation - Scopus: 3Joint Beamforming and Power Control Technique for Femtocell Networks(Springer Verlag, 2017) Özbek, Berna; Bayrak, UğurThe need for high data rate increases with the growing demand for wireless communication. In order to meet this demand, one of the most effective ways is deployment of small cells which are considered as a promising technique for future wireless networks. However, the deployment of these low-power base stations brings many challenges. Interference management will be one of the major drawbacks for the deployment of small cells in coverage of the macro base stations. In order to cope with interference problem, we propose a joint beamforming and power allocation technique for a two-tier network system involving femtocell and macrocell layers to design power efficient networks. The beamforming technique is applied by using partial zero-forcing method to remove the highest cross-tier interference while satisfying the macro and femtocell users’ data rate requirements. Then, we perform power allocation to further reduce interference and design power efficient femtocell networks. The performance results of the proposed technique are illustrated in terms of power consumption in femtocell networks.