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.

翻译：本文利用流体天线（FA）与速率分割多址接入（RSMA）技术，增强集成感知与通信（ISAC）系统的物理层安全（PLS）。我们考虑一个实际的多用户多输入单输出（MU-MISO）系统，其中配备固定位置天线（FPA）的基站（BS）采用RSMA与多个单FA用户通信，而一个窃听目标可能试图窃听信号。该系统采用一种新颖的速率分割（RS）方案，其中公共层流具有双重作用：既向合法用户（LU）传递有效数据，同时生成干扰信号以迷惑潜在窃听者。我们建立了该问题，并在两种条件下提出了优化算法：完美与不完美信道状态信息（CSI）条件。具体而言，在完美CSI条件下，我们通过提出一种交替优化（AO）算法来处理非凸优化问题，该算法将问题分解为两个子问题：波束成形矩阵优化与FA位置调整。对于波束成形优化，我们利用半定规划（SDP）和逐次凸逼近（SCA）将问题转化为更易处理的凸形式。在给定固定波束成形矩阵的情况下，应用SCA处理约束的代理上界。在不完美CSI情况下，CSI误差的连续性导致约束数量无限。为克服这一挑战，我们提出了一种基于AO的算法，结合S-过程与SCA，以获得高质量的波束成形矩阵和有效的FA位置。大量仿真结果表明，与传统基于FPA和基于SDMA的系统相比，所提出的FA辅助RSMA-ISAC系统显著增强了安全性。