Wireless UV scattering communication is a technology that leverages the scattering of atmospheric particles to enable wireless communication. Its strong scattering characteristics make it suitable for specialized applications, such as non-line-of-sight (NLOS) communication. However, these same characteristics limit it to short-range transmissions and cause significant path loss. Moreover, atmospheric temperature and pressure variations can lead to fluctuations in the air’s refractive index, causing turbulence and random signal fluctuations at the receiver. To mitigate high path loss and signal scintillation from turbulence, relay-assisted UV optical communication has emerged as an effective solution. Most existing UV relay systems are designed for terrestrial applications, while ground-to-air communications remain underexplored. Unmanned aerial vehicles (UAVs) offer a promising option for mobile air relays due to their high maneuverability, compact design, and low cost. As UAV technology continues to advance, UAV-based communication systems are expected to play a vital role in next-generation wireless networks. UAV-assisted UV communication dynamically optimizes relay positions and establishes flexible NLOS links, which traditional ground relays lack.

In this paper, we propose a novel framework for analyzing and optimizing a decode-and-forward (DF) relay in UAV-assisted NLOS UV communication systems. The analysis accounts for attenuation losses and atmospheric turbulence. Specifically, the effects of log-normally distributed turbulence on both the source-to-UAV and UAV-to-destination links are evaluated. The probability density function (PDF) of the ground-to-air link is derived to establish closed-form expressions for the end-to-end outage probability and the average bit error rate (ABER) under the DF relay protocol. In addition, we explore the optimal system and channel parameters to enhance the UAV-assisted UV relay system’s performance. We evaluate the performance of UAV-assisted NLOS UVC systems, analyze the influence of various system and channel parameters, and provide valuable engineering insights for optimizing UAV-assisted NLOS UVC systems.

The system’s performance is analyzed based on two key metrics: outage probability and ABER. At a power margin of 6 dB, an increase in turbulence intensity from Cn2=5×10-15m-2/3 to Cn2=1×10-14m-2/3 leads to approximately a fourfold rise in the outage probability for M=1. However, an outage probability of 1.6×10-6 remains within acceptable performance limits. Interestingly, when atmospheric turbulence intensity rises from Cn2=5×10-15m-2/3 to Cn2=1×10-14m-2/3, the UAV-assisted system demonstrates improved performance rather than degradation. This is attributed to the UAV’s ability to reduce the effects of turbulence through its flexible positioning (Fig. 11). In addition, the optimal distance between the UAV and the source transmitting node remains nearly constant regardless of changes in turbulence intensity (Fig. 13), indicating that the optimal relay position is unaffected by atmospheric variations.

Using UAVs as relay nodes in UV optical communication systems not only extends communication coverage but also mitigates atmospheric impairments affecting UV signal quality. In this paper, we propose and evaluate a UAV-assisted UV optical communication system using a DF relay under low-altitude turbulence. A log-normal fading model, accounting for both path loss and turbulence-induced fading, is developed. Closed-form expressions for the source-to-destination outage probability and ABER are derived from the PDF of the channel power fading factor. Using these analytical expressions, we investigate the effects of various atmospheric turbulence intensities, system parameters, and channel parameters on the performance of the airborne UV relay system. Simulation results show that the proposed system achieves a performance improvement of about 10 dB with an outage probability of 10-6. The relay position significantly influences system performance, although the optimal relay position remains unaffected by changes in atmospheric turbulence.