Fluid Antenna-Aided Robust Secure Transmission for RSMA-ISAC Systems

2025-03-07

AI Summary

This paper addresses physical-layer security in multi-user multiple-input single-output (MISO) integrated sensing and communication (ISAC) systems. To tackle this, we propose a joint secure transmission framework integrating fluid antennas (FAs) and rate-splitting multiple access (RSMA). Leveraging the FA’s position-tunable capability and RSMA’s dual-functional common stream—which simultaneously conveys information to legitimate users and actively jams eavesdroppers—we formulate an alternating optimization framework adaptable to both perfect and imperfect channel state information (CSI). By combining semidefinite programming (SDP), successive convex approximation (SCA), the S-procedure, and joint beamforming and rate allocation design, we effectively handle the infinite constraints arising from continuous channel uncertainty. Compared with conventional fixed-antenna and SDMA-based schemes, the proposed approach significantly improves the secrecy sum rate and demonstrates superior robustness under imperfect CSI. To the best of our knowledge, this is the first work achieving deep synergy between FA dynamic reconfiguration and RSMA-enabled security enhancement.

Technology Category

• Multiagent Systems: Agent Communication
• Intelligent Robots: Multi-Robot Systems
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications

Abstract

This paper leverages fluid antenna (FA) and rate-splitting multiple access (RSMA) to enhance the physical layer security (PLS) of an integrated sensing and communication (ISAC) system. We consider a practical multi-user multi-input single-output (MU-MISO) system, where a base station (BS) equipped with fixed position antennas (FPAs) employs RSMA to communicate with multiple single-FA users, while an eavesdropping target may potentially wiretap the signals. The system adopts a novel rate splitting (RS) scheme, where the common layer stream serves a dual purpose: it conveys valid data to legitimate users (LUs) while simultaneously generating jamming signals to confuse potential eavesdroppers. We establish the problem and propose the optimization algorithm under two conditions: perfect and imperfect channel state information (CSI) conditions. Specifically, under perfect the CSI condition, we address the non-convex optimization problem by proposing an alternating optimization (AO) algorithm, which decomposes the problem into two subproblems: beamforming matrix optimization and the adjustment of FA positions. For beamforming optimization, we utilize semidefinite programming (SDP) and successive convex approximation (SCA) to convert the problem into a more tractable convex form. Given a fixed beamforming matrix, SCA is applied to handle the surrogate upper bound of the constraints. In the case of imperfect CSI, the continuous nature of CSI errors leads to an infinite number of constraints. To overcome this challenge, we propose an AO-based algorithm that incorporates the S-Procedure and SCA to obtain a high-quality beamforming matrix and effective FA positions. Extensive simulation results demonstrate that the proposed FA-aided RSMA-ISAC system significantly enhances security compared to traditional FPA-based and SDMA-based systems.

Problem

• Enhance physical layer security in ISAC systems using FA and RSMA.
• Optimize beamforming and FA positions under perfect and imperfect CSI.
• Propose AO algorithm to solve non-convex optimization for secure transmission.

Innovation

• Fluid antenna enhances ISAC system security.
• RSMA with dual-purpose common layer stream.
• AO algorithm optimizes beamforming and FA positions.