Accurate knowledge of seawater optical properties is essential for underwater imaging, sensing, and optical communication, particularly in coastal and shallow-water environments where geometric light propagation effects can influence measurement accuracy. While empirical formulations describing the refractive index of seawater are well established and widely used in the visible spectral range, their applicability in the near-ultraviolet region has received limited experimental validation. In this work, the applicability of an established empirical seawater refractive-index formulation in the near-ultraviolet band is investigated through a combined numerical and experimental approach. First, the empirical model is evaluated numerically to examine its spectral behavior across the visible-near-ultraviolet transition. The results indicate smooth and physically consistent refractive-index variation near the ultraviolet boundary. Second, a controlled laboratory experiment is conducted in which near-ultraviolet beam refraction through stratified seawater is measured using a multi-compartment tank designed to emulate discrete ocean depth intervals. Beam displacement measurements at two near-ultraviolet wavelength bands are compared directly with predictions obtained from a multi-layer ray-tracing simulation based on the empirical formulation. The close agreement between simulated and experimentally measured beam displacement across multiple depth configurations provides physical validation of the empirical refractive-index model in the near-ultraviolet region under the investigated conditions. These findings support the use of established refractive-index formulations for near-ultraviolet underwater optical modeling and contribute to a more reliable foundation for near-UV marine optical sensing and measurement applications.

We study underwater optical communication under photon-counting (Poisson) detection with realistic attenuation, background radiance, directionality, and pointing uncertainty. Information is embedded in (i) a temporal dictionary of pseudo-random noise (PRN) intensity sequences and (ii) an optional spatio-temporal extension, denoted SIM-TS (spatial-index modulation with temporal signaling), that combines temporal coding with spatial indexing across multiple transmit/receive apertures. For a fixed optical energy-per-symbol (photon budget), these structured waveforms increase observation dimensionality and improve maximum-likelihood separability under Poisson statistics. We present a layered modeling framework, derive the corresponding Poisson detection metrics, and use Monte Carlo evaluation to extract maximum range at a target symbol error rate. The results show that dimensional signaling provides a modest but repeatable gain in clear-water photon-limited regimes: at 100 kbps, SIM-TS increases the clear-water range from 593.8 m to 617.2 m at 450 nm (3.95%) and from 457.8 m to 473.4 m at 420 nm (3.41%) under fixed total power. In coastal water the gain falls below 1%, while in the 1 Gbps benchmark SIM-TS under fixed total power remains within about 2% of on-off keying (OOK) and the larger improvement under power combining is attributable primarily to increased photon budget. These rate-range trade-offs clarify when dimensional signaling yields practical gains and when attenuation, background, and misalignment dominate the link budget.

Given the nature of broadcasting systems having limited feedback to the transmitter, impairments induced during transmission need to be coped with at the receiver. In this paper, we focus on digital multimedia broadcasting (DMB) which is deployed in South Korea. An extensive measurement campaign conducted in a live DMB system resulted in a set of videos containing a wide range of syntax, freeze, and texture impairments. Subjective tests were conducted with participants from East Asia which rated the quality of DMB video clips with syntax, freeze, and texture impairments and the related repaired clips. The analysis of the obtained quality ratings has revealed the potential of quality of experience (QoE) improvement of each of the three impairment types. The results support the conjecture that syntax repair offers the largest QoE improvement followed by freeze repair and texture repair. This finding can assist system developers of digital broadcasting systems in deciding about the range of repair techniques to be engaged subject to, e.g., QoE, complexity, and latency constraints. 

The advancements of high resolution display technologies support applications ranging from mobile multimedia streaming to automotive cockpits and infotainment systems. Given the limited transmission and processing resources in a mobile communication context, a large number of upscaling methods for restoring high-resolution visual content from low-resolution representations have been proposed and assessed from a theoretical point of view. This paper, therefore, deals with the practical implementation of state-of-the-art upscaling methods on development boards. The proposed tool chain and solutions may be applied as a general framework for the implementation of current and future upscaling methods on resource limited devices.