Multiple UAV-Based FSO Systems with Relay Selection over Málaga and IGGG Turbulence Channels

Abstract

Uncrewed aerial vehicle (UAV)-assisted free-space optics (FSO) communication provides an effective means to extend the capability and resilience of existing network infrastructures by offering flexible aerial relaying. In particular, the use of UAVs as relay nodes helps to mitigate the strict line-of-sight (LoS) requirements of conventional FSO links. In this work, a multi-UAV-based FSO communication system employing decode-and-forward (DF) relaying with energy harvesting (EH) at the relay is investigated, where both partial relay selection (PRS) and opportunistic relay selection (ORS) strategies are adopted to determine the optimal UAV for data forwarding. The optical wireless channel is modeled using two comprehensive turbulence distributions, namely the Málaga distribution and the doubly inverted Gamma-Gamma (IGGG) distribution, which jointly capture the effects of atmospheric turbulence, atmospheric attenuation, 2D and 3D pointing error misalignment, and angle-of-arrival (AoA) fluctuations. Closed-form expressions are derived for key performance metrics, including outage probability (OP), while the average symbol error rate (SER) and ergodic capacity (EC) are evaluated using Gauss-Laguerre (GL) quadrature under both relay selection schemes and channel models. Moreover, an asymptotic performance analysis is carried out in the high signal-to-noise ratio (SNR) regime, through which the diversity gain of the proposed system is explicitly characterized. The accuracy of the analytical results is validated through extensive Monte-Carlo simulations. Numerical results illustrate the influence of relay selection strategies, turbulence severity, and system parameters on the overall performance and provide clear insights into the achievable diversity gains and robustness of multi-UAV-assisted FSO systems under realistic atmospheric conditions. © 2020 IEEE.