A tailored alternating optimization framework is developed that decomposes the original joint design into tractable subproblems, where each admits an efficient solution while preserving the system constraints, enabling an effective joint optimization of beamforming and FARIS reconfiguration.
Abstract
This paper investigates secure downlink transmission assisted by a fluid active reconfigurable intelligent surface (FARIS), which enables both active reflection and dynamic port selection, offering enhanced flexibility for physical-layer security. We formulate a secrecy rate maximization problem that jointly optimizes the transmit beamformer, active reflection coefficients, and fluid port configuration under practical power constraints. To efficiently handle the resulting highly nonconvex problem, we develop a tailored alternating optimization (AO) framework that decomposes the original joint design into tractable subproblems, where each admits an efficient solution while preserving the system constraints, enabling an effective joint optimization of beamforming and FARIS reconfiguration. Numerical results demonstrate that the proposed FARIS-assisted design consistently outperforms the benchmarks. The results further highlight the robustness of FARIS against unfavorable eavesdropping geometries, confirming its potential as a powerful enabler for secure communications in challenging environments.
This work investigates physical-layer security design for near-field integrated sensing and communication systems assisted by a hybrid reconfigurable intelligent surface (H-RIS). The H-RIS supports both signal reflection and sensing-echo reception, enabling secure cascaded transmission and local echo measurement. A worst-case secrecy rate maximization problem is formulated by jointly optimizing BS beamforming, artificial noise covariance, and H-RIS reflection phases under transmit-power, sensing, and hardware constraints. An alternating optimization algorithm combining fractional programming, successive convex approximation, and penalty-based relaxation is developed. Simulation results show that the proposed scheme achieves higher WCSR than benchmark schemes and improves security performance under different system configurations.
Liu-Yu Li, Jian-Long Zhang, Ze Li et al.· International Conference on...· 0 citations
In an integrated sensing and communications (ISAC) system, targets may intercept information. We address this specific security issue in a full-duplex ISAC system with malicious eavesdroppers aiming to intercept uplink (UL) and downlink (DL) communication exchanges between the dual-functional radar and communication base station and legitimate communication users. We formulate an optimization framework to maximize the sum secrecy rate for both DL and UL, considering power budget constraints for sensing and communications. The optimization problem is non-convex, so we introduce an iterative joint Taylor-block cyclic coordinate descent (IJTB) method to approximate it as a convex problem. The IJTB method alternates between sub-problems: one for UL beamformers and another for UL power allocation, artificial noise covariance, and DL beamforming, using Taylor approximations to simplify optimization. Simulations demonstrate the effectiveness of our approach compared to standard benchmarks.
Aleksandar Boljevi'c, Mingjun Ying, Ahmad Bazzi et al.· 0 citations
In this paper, we propose a robust transmission design for multi-user systems assisted by a fluid active reconfigurable intelligent surface (FARIS), which enables both active reflection and dynamic port selection and thereby offers enhanced flexibility, under imperfect channel state information (CSI). We formulate a robust minimum sum-rate maximization problem by jointly optimizing the base station beamformer, the utilized FARIS coefficients, and the active element selection, while explicitly accounting for CSI errors and practical power constraints. The resulting problem is inherently nonconvex due to the coupled optimization variables and discrete port-selection structure. To tackle this challenge, we first reformulate the original problem via a weighted minimum mean square error (WMMSE) approach and then devise an alternating optimization (AO) framework, where each resulting subproblem admits efficient solutions and the overall algorithm converges to a stationary point. Simulation results demonstrate that the proposed robust FARIS scheme consistently outperforms conventional designs, highlighting the effectiveness of jointly leveraging degree-of-freedom (DoF) enhancement and active signal amplification under CSI uncertainty.
Hong-Bae Jeon, Yonghwi Kim, Hyung-Joo Moon et al.· 0 citations
This paper investigates a reconfigurable intelligent surface (RIS)-assisted movable antenna (MA) secure integrated sensing and communication (ISAC) system. In this architecture, the RIS establishes indirect transmission links to provide communication services for multiple legitimate users, while the high spatial diversity gain of MA is leveraged to enhance system security. Then, we formulate an optimization problem to maximize the system total secrecy rate by jointly optimizing the MA position selection, active beamforming design for base station and passive beamforming design for RIS. The problem also accounts for practical constraints including transmit power budget, sensing beampattern mean square error (MSE), RIS unit-modulus constraint. However, it is challenging to solve this problem due to its non-convexity and strong coupling of the optimization variables. Consequently, we propose an alternating optimization (AO) framework, employing techniques including discrete binary particle swarm optimization (BPSO), successive convex approximation (SCA) and difference-of-convex (DC) programming to transform the optimization problem into convex subproblems. Based on the solution above, the convex sub-problems are solved iteratively until convergence is achieved. Numerical results demonstrate that the proposed algorithm outperforms other baseline algorithms in terms of secure communication performance.
This paper investigates a reconfigurable intelligent surface (RIS)-enabled secure integrated sensing and communication (ISAC) system, where the direct links between the base station (BS) and users are blocked and a mobile eavesdropper is treated as both a potential wiretapper and a sensing target. The time-varying eavesdropper state leads to dynamically changing wiretap channels, which may degrade the effectiveness of conventional transmission designs based on outdated eavesdropper information. To address this issue, the BS tracks the eavesdropper over consecutive time slots and exploits the predicted state information to adapt secure transmission. An optimization problem is formulated to maximize the sum secrecy rate by jointly designing the BS beamforming, artificial noise, and the RIS reflection coefficients for secure transmission and echo sensing. Meanwhile, an error-covariance constraint is imposed to guarantee the required tracking accuracy. To solve the nonconvex and temporally coupled problem, we propose an optimization algorithm integrating the extended Kalman filter (EKF) and block coordinate optimization framework, in which the eavesdropper state is recursively predicted and updated, while the joint design problem is decomposed into four tractable subproblems. Simulation results demonstrate that compared with benchmark schemes, the proposed algorithm can better guarantee the secrecy rate and effectively track the moving trajectory of the eavesdropper.
Zhendong Li, Wei-Chun Zhao, Zhou Su et al.· 0 citations
Satellite-terrestrial integrated networks with simultaneous wireless information and power transfer (SWIPT) provide wide-area connectivity and sustainable service support, but they also face serious security challenges due to the broadcast nature of satellite links and the possibility that an energy receiver may act as potential eavesdropper. To address this issue, this paper proposes a secure precoding design for a high-altitude platform (HAP)-assisted rate-splitting multiple access (RSMA) architecture under a quasi-static transmission model. Specifically, a cooperative direct and relay transmission (CDRT) framework is developed, in which the HAP assists the satellite transmission to improve the physical layer security for multi-user SWIPT services. By assuming the energy receiver near the target user as potential eavesdropper, we formulate a sum secrecy rate maximization problem subject to energy harvesting and transmit power constraints. To transform the original nonconvex optimization problem into a tractable convex problem, we employ techniques such as first-order Taylor expansion approximation, rank-one constraint relaxation, successive convex approximation, and semidefinite relaxation. Numerical results demonstrate that the proposed CDRT-RSMA scheme significantly outperforms conventional non-orthogonal and time-division multiple access schemes in terms of security performance.
Mengyan Huang, Xing-Wang Li, Chengjun Jiang et al.· IEEE Journal on Selected Are...· 0 citations
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