Design and Performance Analysis of Hybrid FSO/THz Relay with Aerial RIS for Future NTN-Integrated 6G Wireless Communications

TL;DR

The paper addresses the reliability and data-rate limitations of traditional backhaul by proposing a dual-hop hybrid FSO/THz first hop coupled with an aerial RIS-enabled RF second hop. It develops a unified analytical framework that derives closed-form outage and BER expressions for hard and soft switching across Málaga, α-μ, and Rician channels, and validates these with Monte Carlo simulations. The work demonstrates significant performance gains—e.g., a 52.54% improvement in outage probability and a 41.39% gain from aerial RIS integration—while providing practical design guidelines on UAV placement, RIS size, and switching strategies. This provides a rigorous, generalizable foundation for designing NTN-6G backhaul networks with hybrid optical/RF links and UAV-mounted RIS.

Abstract

In the context of emerging sixth-generation (6G) wireless networks, reconfigurable intelligent surfaces (RISs) are gaining prominence for their ability to intelligently control electromagnetic wave propagation and enhance backhaul communication performance. In this paper, we propose a novel dual-hop wireless network, where the first hop consists of a hybrid free-space optics (FSO) / terahertz (THz) link, and the second hop incorporates an aerial RIS-based radio frequency (RF) link. To provide a comprehensive performance evaluation, a comparative analysis of two switching strategies is conducted: (1) hard switching and (2) soft switching. Novel closed-form expressions are derived for key performance metrics, including outage probability and bit error rate. These expressions are then utilized to investigate the impact of various system parameters. Our proposed hybrid model demonstrates a 52.54% performance improvement over the traditional RF-FSO framework. Moreover, the integration of an aerial RIS in the second hop enhances system performance by 41.39%. Numerical findings suggest that strategically placing the aerial RIS at a lower altitude and maintaining an equal, shorter distance from both communication endpoints significantly improves overall system performance. To analyze the response under high signal-to-noise ratio (SNR) conditions, asymptotic analysis is performed, and the diversity order of the system is determined. Finally, the analytical results are validated through a Monte Carlo simulation.

Figures (12)

• Figure 1: Proposed system model incorporating a source, a switching center, an aerial RIS, and a receiver.
• Figure 2: ABER versus $\overline{\gamma }_o$ for different turbulence conditions and receiver detection techniques.
• Figure 3: ABER versus $\overline{\gamma }_o$ under different turbulence and pointing errors.
• Figure 4: ABER vs $\overline{\gamma }_t$ under different numbers of antenna and pointing error.
• Figure 5: OP versus $\overline{\gamma }_o$ for various fading parameters.