This paper presents a comparative investigation of analog and digital optical wireless
communication (OWC) through a water-filled polyvinyl chloride (PVC) pipe sealed at both ends with optically
transparent PMMA windows using visible-light light-emitting diodes (LEDs) operating at four wavelengths: blue
(475 nm), green (528 nm), yellow (583 nm), and red (625 nm). A unified experimental and simulation framework
is developed to evaluate continuous (analog) and modulated (digital) transmission under varying water-filling
conditions of 0%, 25%, 50%, 75%, and 100%. In the analog analysis, the received optical power is measured to
quantify absorption, refraction, and scattering effects based on the Beer–Lambert model. For digital transmission,
pseudo-random binary sequence (PRBS7) on–off keying (OOK) modulation is employed to assess signal-to-noise
ratio (SNR), analytically estimated bit-error rate (BER), eye diagrams, and information-theoretic channel capacity
upper bounds. The presented digital performance metrics are intended for relative trend analysis and physical
interpretation, rather than demonstrating a fully optimized or practically deployable communication system. The
results show that the 50% water-filled condition introduces the most severe impairment due to repeated air–water
interface interactions, which cause additional Fresnel losses, angular redistribution, and enhanced multipath
scattering. In contrast, fully submerged operation provides a more homogeneous propagation medium, leading to
improved transmission behavior. Among the tested wavelengths, the red LED exhibits the highest relative
robustness under the present baseline implementation. The reported digital metrics should be interpreted as
comparative indicators for trend analysis and physical interpretation of channel-dependent degradation, rather than
as evidence of reliable or optimized communication performance.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)