Reconfigurable Intelligent Surface Equipped UAV in Emergency Wireless Communications: A New Fading-Shadowing Model and Performance Analysis

TL;DR

This work tackles emergency wireless communications in post-disaster zones by introducing a novel modified Fisher-Snedecor F fading model to capture severe fading and shadowing in debris-affected environments. It develops a RIS-equipped UAV system model, derives exact and CLT-based channel statistics for small and large RIS element counts, and provides closed-form expressions for average capacity, energy efficiency, and outage probability. Two optimization problems are solved: maximizing energy efficiency by selecting the number of RIS elements and maximizing coverage by optimizing UAV altitude, both subject to realistic power and reliability constraints. Numerical results show that the modified fading model yields higher capacity, better energy efficiency, and larger coverage than conventional models, offering concrete design guidelines for EWC deployments.

Abstract

Communication infrastructure is often severely disrupted in post-disaster areas, which interrupts communications and impedes rescue. Recently, the technology of reconfigurable intelligent surface (RIS)-equipped-UAV has been investigated as a feasible approach to assist communication under such conditions. However, the channel characteristics in the post-disaster area rapidly change due to the topographical changes caused by secondary disasters and the high mobility of UAVs. In this paper we develop a new fading-shadowing model to fit the path loss caused by the debris. Following this, we derive the exact distribution of the new channel statistics for a small number of RIS elements and the approximate distribution for a large number of RIS elements, respectively. Then, we derive the closed-form expressions for performance analysis, including average capacity (AC), energy efficiency (EE), and outage probability (OP). Based on the above analytical derivations, we maximize the energy efficiency by optimizing the number of RIS elements and the coverage area by optimizing the altitude of the RIS-equipped UAV, respectively. Finally, simulation results validate the accuracy of derived expressions and show insights related to the optimal number of RIS elements and the optimal UAV altitude for emergency wireless communication (EWC).

Figures (13)

• Figure 1: UAV-RIS-based system model under emergency wireless communication scenario.
• Figure 2: The PDF of the conventional $\mathcal{F}$ fading channel versus the channel characteristics of envelope of the received signal $A$ and shadowing parameter $m_s$.
• Figure 3: The PDF of the modified-$\mathcal{F}$ fading channel versus the channel characteristics of envelope of the received signal $A$ and shadowing parameter $m_s$.
• Figure 4: The comparison of the theoretical and simulated results of the PDF of $A$ under CLT approximation
• Figure 5: The comparison of the theoretical and simulated results of the CDF of $A$ under CLT approximation