Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Özbek, BernaSubject: search.filters.subject.Physical layer security

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  • Master Thesis
    Secure Beamforming for Millimeter Wave Communications
    (Izmir Institute of Technology, 2020) Erdoğan, Oğulcan; Özbek, Berna
    Over the last decade, many advancements have been made in the field of wireless communications. Among the major technology enablers being explored for the fifth-generation (5G) networks at the physical layer (PHY), a great deal of attention has been focused on millimeter-wave (mmWave) communications, massive multipleinput multiple-output (MIMO) antenna systems and beamforming techniques. These enablers bring to the forefront great opportunities for enhancing the performance of 5G and beyond-5G networks, concerning throughput, spectral efficiency, energy efficiency, latency, and reliability. At the meantime, 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 this thesis, we examine the statistical 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 (BS), legitimate users and eavesdroppers. Using a 3 Dimensional mmWave channel model for each node, we employ the artificial noise (AN) beamforming to jam the channels of eavesdroppers and to enhance the secrecy capacity of the overall communication system. We investigate the secrecy performance on different scenarios including the single cell and multicell mmWave MU-MIMO downlink communications and reveal the key points directly related to the system security.
  • Master Thesis
    Multiple Antenna Based Phyical Layer Security Wireless Systems
    (Izmir Institute of Technology, 2017) Özdoğan Şenol, Özgecan; Özbek, Berna
    In the last decade, the demand for wireless services increases at unprecedented rates. Due to the inherent open nature of radio propagation, wireless transmission is vulnerable to various attacks despite its popularity. Therefore, communication security in wireless networks is becoming more critical than ever. Conventionally, cryptographic techniques are deployed on upper layers of network protocols as a solution. As a complement to the traditional cryptographic techniques, physical layer (PHY) security exploits the characteristics of wireless channels to enable secure wireless communications. The aim is to limit the amount of information that can be extracted by any unauthorized users via utilizing inherent randomness of noise and communication channels. The design of PHY security schemes is not based on the premise that eavesdropper has limited computational power contrary to upper layer secrecy techniques. In fact, the eavesdropper may have infinite computational power. Nevertheless, secure communication can be achieved by the combination of appropriate coding and transmit precoding design with the usage of available channel state information. PHY security methods can work independently from upper layer encryption techniques. Thus, PHY security techniques can be used to leverage the secrecy of already existing communication systems. In this thesis, PHY security enhancement mechanisms, especially in multiuser multiple antenna systems with a limited feedback link are investigated. Four different system models under secrecy consideration with different channel conditions including quasi-static fading channels, temporally correlated fading channels are presented. In order to disrupt the reception of any potential eavesdropper, artificial noise (AN) beamforming scheme is employed. The effects of lack of perfect channel state information (CSI) at the transmitter and the AN leakage that is caused by limited CSIT are analyzed. The thesis proposes a reduction in feedback load using receiver side selection criterion with special codebook design and appropriate beamforming. Our approach is capable of enhancing the security of wireless communications by selecting the users with favorable channel conditions and quantizing channel direction information (CDI) by a special codebook. Also, inter-user interference is utilized as a jamming method when eavesdropper’s CSI unknown by the transmitter. Simulation results demonstrate the feasibility of the proposed PHY security mechanisms by examining the achievable secrecy rates.