Electronic Theses and Dissertations (PhDs)

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Author: search.filters.author.Osman, Amani Alged Fetaha

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    Physical layer of Security with NOMA in mixed RF/FSO systems
    (University of the Witwatersrand, Johannesburg, 2024) Osman, Amani Alged Fetaha; Takawira, Fambirai; Moualeu, Jules
    The ever-increasing demand for spectrum resources, driven by the surge in high data tra c poses a signi cant challenge to the e ciency of wireless communication systems. In response, non-orthogonal multiple access (NOMA) has been proposed as a pivotal technique designed to address the spectral challenges inherent to tra- ditional multiple access schemes. NOMA, through its ability to allow multiple users to share the same time-frequency resources non-orthogonally, represents a promising avenue for improving spectral e ciency (SE). To further improve connectivity and enhance e ciency, NOMA can seamlessly be integrated with multiple-input-multiple-output (MIMO) systems. MIMO, a cor- nerstone technology in modern wireless communication, utilizes multiple antennas at both the transmitter and receiver to exploit spatial diversity, thereby achieving substantial gains in terms of capacity and reliability. The integration of MIMO with NOMA not only addresses the escalating demand for connectivity but also unlocks the potential for massive connectivity and enhanced spectral e ciency in wireless networks. However, the distribution of radio resources within the MIMO- NOMA framework brings forth security challenges owing to the intrinsic charac- teristics of wireless transmissions. In this regards, this thesis tackles the security aspect of MIMO-NOMA systems from an information theoretic viewpoint. The information theoretic security or physical layer security (PLS) e ectively mitigates vulnerabilities stemming from eavesdropping and interception, thereby fortifying the overall security of wireless communication in the present case of MIMO-NOMA systems. Another challenge that requires some attention is ensuring reliability over long distances. Although the radio frequency (RF) spectrum band is recognized for its reliability in diverse weather conditions, its inherent nature renders it sus- ceptible to security concerns. To address the imperative for secure long-distance communications, it is essential to explore innovative solutions that harness the inherent reliability of the RF spectrum while concurrently mitigating its vulner- abilities through enhanced security measures. Integrating technologies such as free-space optical (FSO) communication, acknowledged for its secure transmission capabilities, along with the implementation of advanced security protocols stands as a promising solution to achieving reliability and security in long-distance com- munications. In this work, PLS of a MIMO-NOMA based system in a mixed RF-FSO com- munications is investigated. Additionally, this thesis delves into the injection of vi arti cial noise (AN) in an e ort to explore other features of the proposed sys- tem from a PLS perspective. The last part of the work investigates the secrecy performance of the proposed system in the presence of multiple colluding and non- colluding eavesdroppers. To this end, the statistical properties are examined by deriving the statistical characteristics of the underlying system model, which will subsequently be used to establish both the analytical and asymptotic frameworks for evaluating secrecy performance measures. Finally, Monte Carlo simulations are adopted to validate the accuracy of our proposed mathematical derivations.