In this paper, we investigate the performance of a mixed radio-frequency-underwater wireless optical communication (RF-UWOC) system where an unmanned aerial vehicle (UAV), as a low-altitude mobile aerial base station, transmits information to an autonomous underwater vehicle (AUV) through a fixed-gain amplify-and-forward (AF) or decode-and-forward (DF) relay. The analysis accounts for the main factors that affect the system performance, such as the UAV height, air bubbles, temperature gradient, water salinity variations, detection techniques, and pointing errors. Employing the fixed-gain AF and DF relays, expressions for some key performance metrics are derived, e.g., outage probability (OP), average bit error rate (ABER), and average channel capacity. Moreover, in order to get further insights, asymptotic analyses for the OP and ABER are also carried out. Additionally, for the two relaying systems, we derive analytical expressions for the optimal UAV altitude that minimizes the OP. Simulation results show that the UAV altitude influences the system performance and there is an optimal altitude which ensures a minimum OP. Furthermore, it is demonstrated that the diversity order of the fixed-gain AF relaying depends on the RF link and pointing errors, while the diversity order of the DF relaying depends on the detection techniques and pointing errors.

In this work, we study the performance of a reconfigurable intelligent surface (RIS)-aided unmanned aerial vehicle (UAV) system where an RIS is installed on a UAV to reflect the signal to the ground user from the sky. More specifically, we present two different methods to denote the probability density functions (PDFs) of the instantaneous signal-to-noise ratio (SNR). With these two distributions, closed-form expressions for the outage probability, average bit error rate (BER), and average sum-rate are derived, respectively. Additionally, we develop the analysis on the optimal UAV altitude and location. Finally, numerical results are given to verify our analysis.

In this letter, a performance study of a mixed dual-hop communication system consisting of free-space optical/underwater wireless optical communication (FSO-UWOC) links is presented. In particular, considering both heterodyne detection and intensity modulation with direct detection (IM/DD), we assume that the FSO channel suffers a Gamma-Gamma fading in the presence of pointing error impairments, while the UWOC channel experiences a mixture Exponential-Generalized Gamma (EGG) fading with pointing errors. Assuming a fixed-gain amplify-and-forward (AF) protocol, closed-form expressions for the outage probability, average bit-error-rate, and average capacity in terms of the bivariate Fox’s H-function are derived. To verify the derived analytical expressions, numerical results are provided to verify the accuracy of our results.

Radiative cooling presents a promising passive cooling strategy, though its widespread adoption is often constrained by elevated costs and manufacturing complexities. This study introduces a cost-effective, scalable fabrication method for a composite membrane utilizing a spraying technique, and it was fabricated by spraying a mixture of modified nano-zirconia and ethylene-octene copolymer (POE), dissolved in petroleum ether, onto a polyethylene (PE) bubble film substrate. This composite membrane demonstrates a hydrophobic property, with a water contact angle of 100.6°. A cooling structure was formed by covering the composite membrane onto a polytetrafluoroethylene (PTFE) plate which served as an emitter, and the cooling power of this structure reaches 66.2 ± 4.3 W/m². Field tests reveal a temperature reduction of 3 ± 0.3 °C at noon and an average cooling effect of 4.7 ± 0.3 °C throughout the day, relative to ambient temperatures. This work advances the development of cost-effective, scalable radiative cooling technologies, holding promise for applications in building cooling and energy efficiency.