An RIS-Empowered THz-UWO Relay System for Air-to-Underwater Mixed Network: Performance Analysis With Pointing Errors

In the realm of the Internet of Things, reconfigurable intelligent surfaces (RISs) have emerged as a pivotal technology, offering unprecedented opportunities to enhance signal quality, coverage, and energy efficiency as part of the ongoing pursuit to overcome the limitations of conventional wireless communication systems. In this context, this article focuses on the analysis of performance in an integrated air-to-underwater network under the amplified-and-forward relay with variable gain, specifically examining the impact of RISs on a mixed terahertz (THz)-underwater optical communication system. This study utilizes the alpha - mu distribution to characterize the fading effects and pointing error on the THz signal. On the other hand, the underwater turbulence on the optical signal is modeled using the mixture of the Exponential Generalized Gamma distribution with pointing error impairments. To provide a basis for comparison, the heterodyne detection technique and the intensity modulation with the direct detection technique are also incorporated. Therefore, analytical expressions of outage probability, average bit error rate, and average channel capacity are demonstrated in terms of the Meijer- G function. To provide more insights, high signal-to-noise approximations of these metrics are also presented. Furthermore, the impact of various modulation schemes, fading severity, pointing errors, atmospheric turbulence conditions, and receiver detection techniques are inspected on the system performance. Finally, the analytical findings are validated through Monte Carlo simulations, ensuring the robustness of the results.