Intelligent Sky Mirrors: SAC-Driven MF-RIS Optimization for Secure NOMA in Low-Altitude Economy

TL;DR

This paper proposes an innovative approach using UAV-mounted intelligent sky mirrors to enhance secure energy efficiency in NOMA systems within low-altitude economies, combining trajectory, power, and phase optimization.

Contribution

It introduces a novel SAC-driven two-layer optimization scheme for joint UAV trajectory, power, and RIS phase shift design in secure NOMA communications.

Findings

Significant improvement in secure energy efficiency over benchmarks.

Effective UAV trajectory and power management for security enhancement.

Optimized RIS phase shifts improve signal quality and security.

Abstract

Low-altitude economy (LAE) has become a key driving force for smart cities and economic growth. To address spectral efficiency and communication security challenges in LAE, this paper investigates secure energy efficiency (SEE) maximization using intelligent sky mirrors, UAV-mounted multifunctional reconfigurable intelligent surfaces (MF-RIS) assisting nonorthogonal multiple access (NOMA) systems. These aerial mirrors intelligently amplify legitimate signals while simultaneously generating jamming against eavesdroppers. We formulate a joint optimization problem encompassing UAV trajectory, base station power allocation, RIS phase shifts, amplification factors, and scheduling matrices. Given the fractional SEE objective and dynamic UAV scenarios, we propose a two-layer optimization scheme: SAC-driven first layer for trajectory and power management, and channel alignment-based second layer for phase optimization. Simulations demonstrate that our proposed scheme significantly outperforms benchmark approaches.