Secure Transmission for Cell-Free Symbiotic Radio Communications with Movable Antenna: Continuous and Discrete Positioning Designs

2025-08-09

AI Summary

This work addresses the vulnerability of the primary link to eavesdropping in reconfigurable intelligent surface (RIS)-assisted cell-free symbiotic radio systems. To enhance physical-layer security, we propose a secure transmission scheme leveraging a movable antenna (MA). The design jointly optimizes the MA’s continuous or discrete spatial positions, the RIS reflection coefficients, and radio resource allocation, formulated as a bi-level iterative and alternating optimization framework. A low-complexity algorithm is developed to efficiently solve the non-convex problem. Innovatively, differential evolution coupled with a mapping-based decision mechanism is introduced to overcome limitations of conventional fixed-antenna deployments. Simulation results demonstrate that the proposed scheme significantly improves the primary user’s secrecy rate while maintaining satisfactory communication performance for secondary users, outperforming existing benchmark schemes in overall security performance.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Mixed Discrete/Continuous Search
• Intelligent Robots: Multi-Robot Systems

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: Attacks and countermeasures in recommendation systems

Abstract

In this paper, we study a movable antenna (MA) empowered secure transmission scheme for reconfigurable intelligent surface (RIS) aided cell-free symbiotic radio (SR) system. Specifically, the MAs deployed at distributed access points (APs) work collaboratively with the RIS to establish high-quality propagation links for both primary and secondary transmissions, as well as suppressing the risk of eavesdropping on confidential primary information. We consider both continuous and discrete MA position cases and maximize the secrecy rate of primary transmission under the secondary transmission constraints, respectively. For the continuous position case, we propose a two-layer iterative optimization method based on differential evolution with one-in-one representation (DEO), to find a high-quality solution with relatively moderate computational complexity. For the discrete position case, we first extend the DEO based iterative framework by introducing the mapping and determination operations to handle the characteristic of discrete MA positions. To further reduce the computational complexity, we then design an alternating optimization (AO) iterative framework to solve all variables within a single layer. In particular, we develop an efficient strategy to derive the sub-optimal solution for the discrete MA positions, superseding the DEO-based method. Numerical results validate the effectiveness of the proposed MA empowered secure transmission scheme along with its optimization algorithms.

Problem

• Enhance secure transmission in RIS-aided cell-free SR systems
• Optimize MA positioning for primary secrecy rate maximization
• Develop efficient algorithms for continuous and discrete MA cases

Innovation

• Movable Antenna enhances secure transmission
• DEO optimizes continuous MA positioning
• AO framework reduces computational complexity