The limited overcrowded radio frequency spectrum compelled researchers to ex plore higher frequency ranges for wireless transmission. In recent decades, visible light communications (VLC) have gained lots of research attention thanks to the abundant bandwidth and the existing lighting infrastructure they offer. Throughout this dissertation, we study the downlink of multi-user VLC systems with the aim of operation and architecture enhancement. In this context, we accommodate the chal lenges imposed by the visible light nature such as illumination requirements and mod ulation constraints. On the operation optimization front, we investigate three VLC setups: indoor single cell, outdoor energy harvesting enabled single cell, and indoor energy harvesting enabled multi-cell VLC systems. We formulate, and provide low complexity solutions to, resource allocation problems for each setup while accounting for scenario-tailored system objectives and quality of service requirements. For the first setup, the temporal average illumination is maintained fixed while maximizing the system SE and dynamic time-division-multiple-access is employed to serve users in an interference free setup. As for the second setup, owing to the favored joint lighting and SE maximization, we solve a multi-objective optimization problem accounting for both objectives. We found that the severity of the illumination - communications tradeoff increases as the available system power budget decreases or the minimum rate requirements get tighter. In the third setup, transmitters average currents and receivers fields of view tuning strategies are developed to maximize both spectral ef ficiency and energy harvesting objectives in an interference limited scenario, where spatial illumination uniformity is required. It is found that receivers fields of view tuning is substantial to performance enhancement in dense deployments. On the architecture optimization front, we propose two intelligent reflecting surfaces-aided VLC systems and derive their power density distribution in the receiver plane. In addition, we prove their power concentration capability and quantify their relative gain with respect to one another and with respect to the reflector-free VLC systems enjoying direct line of sight. Finally, we study the channel impulse response of the proposed reflecting systems and quantify the incurred delay spread through exact ex pression, simplified bounds and asymptotic expressions when the number of reflecting elements grows unboundedly.
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|KAUST Research Repository