Impact of UAV-assisted jamming on IRS-enhanced FSO systems: a Gamma-Gamma turbulence and pointing error perspective

This paper investigates the performance of optical intelligent reflecting surface (IRS)-enhanced free-space optical (FSO) communication systems over a Gamma-Gamma turbulence-induced fading channel with pointing errors, considering dynamic unmanned aerial vehicle (UAV)-assisted jamming scenarios. We propose a comprehensive channel model that integrates the cascaded impairments from atmospheric turbulence (AT), pointing errors (PE), and path loss for both legitimate IRS-reflected signals and UAV-induced jamming channels. What we believe to be a novel angle-of-arrival (AoA) fluctuation model is developed to characterize the spatial dynamics of a mobile jammer. The expressions for probability density functions (PDFs) of the end-to-end legitimate FSO channel and jamming FSO channel are provided. Furthermore, the closed-form expressions for outage probability (OP), average bit error rate (ABER), and ergodic capacity are derived, accommodating both heterodyne detection (HD) and intensity modulation/direct detection (IM/DD) techniques. The asymptotic expressions of the aforementioned performance metrics are also derived to obtain the diversity order of the considered system. Finally, a comprehensive analysis is conducted to investigate the impacts of key parameters such as the number of IRS reflecting elements (N), detection modes (IM/DD versus HD), and environmental conditions on the system performance. Theoretical models are validated through Monte Carlo (MC) simulations. Results indicate that multi-element IRS configurations can significantly enhance anti-jamming and anti-fading capabilities through spatial diversity gains. Increasing the number of IRS elements can achieve performance gain, with the ABER reduced by up to six orders of magnitude and ergodic capacity enhanced by a factor of 13. HD significantly outperforms IM/DD under jamming scenarios due to its coherent detection mechanism. Environmental impairments, such as fog attenuation, and geometric constraints, including receiver aperture size, can be effectively mitigated through IRS optimization.