Communication and positioning in ultraviolet non-line-of-sight secure transmission

Ultraviolet (UV) non-line-of-sight (NLOS) communication has emerged as a promising candidate for locally secure, point-to-area broadcast communication due to its minimal ambient noise, robust weather and terrain adaptability, and inherent local confidentiality. However, most existing research on UV NLOS transmission remains confined to point-to-point systems, lacking efficient methods for coverage estimation, standoff boundary quantification, and source localization in point-to-area scenarios. This dissertation aims to investigate a comprehensive framework that supports both positioning and communication within UV NLOS point-to-area links, thereby addressing the key challenges of coverage prediction, security analysis, and positioning under scattering-based transmission conditions. We begin by developing a Monte Carlo integration model for coverage estimation in UV NLOS point-to-area links, demonstrating a significant reduction in simulation time compared to classical methods. This model is then extended to quantify the covert communication performance using newly introduced metrics, enabling the derivation of standoff boundaries for UV secure transmissions. Next, we explore how weather conditions impact NLOS coverage. Using Mie theory and classical atmospheric models, we characterize the scattering and absorption coefficients in various meteorological scenarios, revealing that certain conditions can enhance UV coverage ranges. Subsequently, we focus on positioning in point-to-area transmission scenarios, namely, NLOS source localization. To facilitate NLOS source localization, we propose using a spatially resolved photon-level (SRPL) receiver and assess its performance through validation by an industrial solar-blind photon-level (SBPL) camera. Outdoor experiments confirm that when integrated with kernel density estimation-based direction finding and received signal strength indicator-based ranging, the SBPL camera localizes NLOS sources with a root-mean-square deviation of only a few meters in a 6900-square-meter test field. Finally, we address inter-symbol interference (ISI) mitigation in NLOS UV communications using an SRPL receiver. Our discrete-time finite-state model reveals that ISI photon-counting channels behave like multipath channels, where the path of the strongest signal is not necessarily the shortest. We demonstrate that time-aligned equal gain selective combining, in combination with a counting instant that maximizes photon counts within a single window, concentrates the majority of signal photons into one counting interval and significantly enhances link reliability.