Novel Theoretical Contributions to Physical Layer Security in Millimeter Wave 5G Networks Deployed in High-Density Nigerian Commercial Districts

Physical layer security exploits the information-theoretic properties of wireless channels to achieve provably secure communications without reliance on computationally hard cryptographic assumptions, with millimeter wave propagation offering distinctive physical layer security characteristics due to high path loss, directivity, and atmospheric absorption. The theoretical characterization of physical layer security in millimeter wave 5G networks deployed in high-density commercial district environments representative of Onitsha, Lagos Island, and Kano City Center represents a novel doctoral contribution. This doctoral study develops novel theoretical contributions to physical layer security in millimeter wave 5G networks in high-density commercial district environments, deriving original secrecy capacity bounds and optimal beamforming designs under the statistical channel models characterizing these environments. An original statistical model for the eavesdropper spatial distribution in commercial district environments, incorporating the distinctive building density, pedestrian mobility, and commercial activity patterns of Nigerian commercial districts, is developed from crowd-sourced mobility and occupancy data. Ergodic secrecy capacity lower bounds are derived analytically for single-user and multi-user scenarios under the proposed commercial district eavesdropper model, with bounds expressed in closed form as functions of transmit beamforming parameters, building blockage probability, and eavesdropper density. An original secrecy-aware hybrid beamforming design algorithm that simultaneously maximizes desired user throughput and minimizes information leakage to the modeled eavesdropper distribution is derived and its optimality conditions characterized. Simulation calibrated to channel measurement data from Onitsha's commercial district demonstrates secrecy rate improvements of 41% over conventional beamforming designs. Keywords: physical layer security, millimeter wave, 5G, secrecy capacity, beamforming.