Movable Antenna Empowered Secure Near-Field MIMO Communications

2025-08-31

AI Summary

Conventional physical-layer security mechanisms fail in near-field MIMO systems when eavesdroppers lie in the same direction as and closer to the base station than legitimate users, violating the far-field assumption and fixed-antenna constraints. Method: This paper proposes a mobile-antenna (MA)-enabled secure transmission framework that jointly optimizes hybrid beamforming at the base station and the physical positions of antennas. By integrating near-field beam focusing with dynamic antenna layout, it overcomes limitations imposed by far-field approximations and static antenna arrays. Beamforming is designed under a weighted minimum mean-square error (WMMSE) criterion, solved via manifold optimization and alternating optimization, while antenna positions are iteratively updated using a majorization-minimization (MM) algorithm. Contribution/Results: Simulation results demonstrate that the proposed scheme significantly improves secrecy rate in typical co-directional eavesdropping scenarios, outperforming conventional far-field and fixed-antenna approaches. It establishes a novel paradigm for secure communication in the near-field regime.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Multiagent Systems: Mechanism Design
• Machine Learning: Mixture of Experts (MoE)

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

This paper investigates movable antenna (MA) empowered secure transmission in near-field multiple-input multiple-output (MIMO) communication systems, where the base station (BS) equipped with an MA array transmits confidential information to a legitimate user under the threat of a potential eavesdropper. To enhance physical layer security (PLS) of the considered system, we aim to maximize the secrecy rate by jointly designing the hybrid digital and analog beamformers, as well as the positions of MAs at the BS. To solve the formulated non-convex problem with highly coupled variables, an alternating optimization (AO)-based algorithm is introduced by decoupling the original problem into two separate subproblems. Specifically, for the subproblem of designing hybrid beamformers, a semi-closed-form solution for the fully-digital beamformer is first derived by a weighted minimum mean-square error (WMMSE)-based algorithm. Subsequently, the digital and analog beamformers are determined by approximating the fully-digital beamformer through the manifold optimization (MO) technique. For the MA positions design subproblem, we utilize the majorization-minimization (MM) algorithm to iteratively optimize each MA's position while keeping others fixed. Extensive simulation results validate the considerable benefits of the proposed MA-aided near-field beam focusing approach in enhancing security performance compared to the traditional far-field and/or the fixed position antenna (FPA)-based systems. In addition, the proposed scheme can realize secure transmission even if the eavesdropper is located in the same direction as the user and closer to the BS.

Problem

• Enhancing physical layer security in near-field MIMO communication systems
• Maximizing secrecy rate through joint beamforming and antenna positioning
• Solving non-convex optimization with coupled variables using alternating optimization

Innovation

• Alternating optimization algorithm for joint beamforming
• Manifold optimization for hybrid beamformer approximation
• Majorization-minimization for movable antenna positioning