In this work, we study the performance of an unmanned aerial vehicle (UAV)-aided mixed radio frequency (RF)/underwater acoustic communication (MRFUAC) transmission system, where the UAV transmits signals to an underwater node through the amplify-and-forward (AF) relay, such as a buoy located on the sea surface. In particular, the UAV-relay RF channel follows a Rician distribution, while κ-μ shadowed fading distribution is applied to model the UAC link. For this considered system with the fixed-gain AF relay, we obtain the statistical distributions of the end-to-end signal-to-noise ratio. To demonstrate the performance of the MRFUAC system, formulae for the outage probability and average bit-error rate are further obtained in closed form. Moreover, to obtain some interesting insights, we present the asymptotic analyses of these performance metrics. To show the validity of our analysis, the truncation error analysis is also provided and the results show that our proposed method has a smaller error than that in the previous literature. In addition, we present the analysis of the optimal height of the UAV at different horizontal distances. In addition to the fixed-gain analysis, we also provide few results for the variable-gain AF relaying MRFUAC system. Finally, the validity of the theoretical analysis is confirmed by Monte Carlo simulations.

In this paper, we study the performance of a cooperative underwater acoustic communication/free-space optical communication (UAC-FSO) transmission system supported by a fixed-gain amplify-and-forward (AF) relay, where an underwater source transmits signals to a satellite through the help of a buoy functioning as a relay located on the sea surface. In particular,Kand κ - μ shadowed fading distribution models are used to characterize the UAC link, while the FSO channel follows a unified Málaga distribution existing pointing errors. Based on the above considerations, we calculate the cumulative distribution function (CDF) and probability density function (PDF) of the end-to-end (e2e) signal-to-noise ratio (SNR). To assess the system performance, expressions for the outage probability (OP) and average bit-error rate (BER) are further obtained in closed-form. Furthermore, driven by a desire for more explicit insights, the high SNR analyses of the OP and average BER, and upper and lower bounds on the average capacity are presented. Finally, through Monte Carlo simulations, the correctness of the theoretical analysis is verified.