Liu, Haizhe; (2025) Intelligent Surface Wave Communications: From Fundamental Physics to System Modeling Optimization. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis explores the transformative potential of surface wave-assisted wireless communications, addressing critical limitations of conventional millimeter wave (mmWave) and terahertz (THz) systems in dense urban environments. By leveraging engineered metasurfaces to guide electromagnetic waves along building surfaces, the research proposes an alternative propagation paradigm that significantly enhances coverage, energy efficiency, and robustness in the presence of obstacles. The theoretical contribution commences with an electromagnetic characterization of surface wave propagation in three-layer media systems. This characterization is followed by the derivation of field solutions with interface-normal attenuation coefficients. A novel patch sandwich metasurface model is introduced, demonstrating tunable impedance properties and superior angular tuning capability (0°–90° Brewster angle adjustment) through variations in dielectric material and dimensions, validated by extensive numerical simulations at 20–30 GHz frequencies. Additionally, a five-stage hybrid propagation framework has been developed to capture the entire transmission path from base station (BS) to user equipment (UE), incorporating both space wave and surface wave phenomena. This model quantifies key system parameters, such as boundary conversion efficiency and practical losses due to edge transitions and window obstructions. In order to optimize system performance, a joint design framework is proposed that combines second-order cone programming (SOCP) for BS beamforming and the difference of convex functions algorithm (DCA) for relay configuration. The channel model utilizes uniform and non-uniform spherical wave components in both uniform linear array (ULA) and uniform planar array (UPA) antenna arrays to capture near-field effects. The simulation results indicate a substantial power reduction in 40-meter buildings in comparison to 10-meter baselines. Notable enhancements in signal strength and reduced power consumption are observed, particularly in high-rise scenarios and blocked-user environments, when employing dual-surface configurations. This research redefines the role of urban infrastructure in wireless communications by transforming passive building surfaces into active propagation media. The demonstrated capability to mitigate penetration losses while achieving power reduction in high-rise deployments addresses critical limitations of current wireless networks. The metasurface design principles and optimization frameworks provide practical tools for implementing smart radio environments in future cities, bridging the theoretical electromagnetics and practical wireless system design for sustainable sixth-generation (6G) deployment in dense urban landscapes.

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