Movable-Element Simultaneously Transmitting And Reflecting Reconfigurable Intelligent Surface-Assisted Integrated Sensing And Covert Communication System: Joint Active and Flexible Passive Beamforming Design

ZHOU Tao; XU Kui; XIA Xiaochen; HU Guojie; LI Chunguo; XIE Wei

doi:10.11999/JEIT240601

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ZHOU Tao, XU Kui, XIA Xiaochen, HU Guojie, LI Chunguo, XIE Wei. Movable-Element Simultaneously Transmitting And Reflecting Reconfigurable Intelligent Surface-Assisted Integrated Sensing And Covert Communication System: Joint Active and Flexible Passive Beamforming Design[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT240601

Citation:

ZHOU Tao, XU Kui, XIA Xiaochen, HU Guojie, LI Chunguo, XIE Wei. Movable-Element Simultaneously Transmitting And Reflecting Reconfigurable Intelligent Surface-Assisted Integrated Sensing And Covert Communication System: Joint Active and Flexible Passive Beamforming Design[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT240601

Citation:

ZHOU Tao, XU Kui, XIA Xiaochen, HU Guojie, LI Chunguo, XIE Wei. Movable-Element Simultaneously Transmitting And Reflecting Reconfigurable Intelligent Surface-Assisted Integrated Sensing And Covert Communication System: Joint Active and Flexible Passive Beamforming Design[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT240601

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Movable-Element Simultaneously Transmitting And Reflecting Reconfigurable Intelligent Surface-Assisted Integrated Sensing And Covert Communication System: Joint Active and Flexible Passive Beamforming Design

doi: 10.11999/JEIT240601

1.
College of Communication Engineering, Army Engineering University of PLA, Nanjing, 210007, China
2.
College of Communication Engineering, Rocket Force University of Engineering, Xi’an, 710025, China
3.
School of Information Science and Engineering, Southeast University, Nanjing, 210096, China

Funds: The National Natural Science Foundation of China (62471488, 62471486, 62271503, 62071485), The Natural Science Foundation of Jiangsu Province of China (BK20231485)

Received Date: 2024-07-15
Rev Recd Date: 2024-11-26

Available Online: 2024-11-29

Abstract

Abstract

Objective: Next-generation communication networks will enhance converged “endogenous sensing” and communication service capabilities by improving information transmission. Integrated Sensing and Communication (ISAC) is a key technology for achieving the 6G vision and has attracted significant attention from both academia and industry. The integration of ISAC with emerging technologies, such as Reconfigurable Intelligent Surface (RIS) and Movable Antenna (MA), is currently a hot research topic. Because the same waveforms are used for both communication and target sensing, ISAC systems are more vulnerable to information leakage. Unlike Physical Layer Security (PLS)-based designs, it is necessary not only to prevent the signals of legitimate users from being eavesdropped but also to hide the existence of communication behavior activities from malicious targets. This paper examines a generic Integrated Sensing and Covert Communication (ISCC) system involving multiple sensing targets (wardens) and multiple covert users. To facilitate communication between the Base Station (BS) and legitimate users, a simultaneously transmitting and reflecting RIS with movable elements (ME-STAR-RIS) is deployed. Inspired by the MA concept, the ME-STAR-RIS features movable elements that allow for Flexible And Passive Beamforming (FAPB). A key challenge is to design a rational architecture that minimizes the control cost of the ME-STAR-RIS. Our goal is to create an effective beamforming and element deployment strategy for this system and to investigate the benefits of element-level movement at the STAR-RIS. Methods: First, a Discrete Element Position (DEP)-based coupled phase-shift model for STAR-RIS is proposed. This model aims to reduce control costs associated with the movability and phase shifts of STAR-RIS elements. Then, a joint beamforming optimization problem is formulated based on this model. The goal is to jointly optimize active beamforming at the ISAC BS and flexible passive beamforming (including element positions, phase shifts, and amplitude coefficients) at the ME-STAR-RIS. This is intended to maximize the probing beam gain at the sensing target while adhering to covert communication quality constraints. The problem formulated is non-convex and presents strong coupling, making it challenging to solve. To address this, we develop an effective algorithm leveraging Semi-Definite Program (SDP), Block Coordinate Descent (BCD), Successive Convex Approximation (SCA), and Penalty Convex-Concave Procedure (PCCP) techniques. By introducing auxiliary variables and employing the SDP method, the original problem can be transformed into a more manageable Augmented Lagrangian form. Our approach features a two-layer iterative algorithm. In the inner loop, the element placement problem is modeled as a binary integer programming problem, using a penalty-based SCA method to solve it. In the outer layer, a penalty-based BCD method is proposed to maintain constraints on the coupled STAR-RIS phase shift upon convergence. Results and Discussions: The simulation results validate the effectiveness of the proposed algorithm and provide significant insights. The performance evaluation indicates that the STAR-RIS with 15 movable elements achieves 80% of the performance of a fixed full-array STAR-RIS with 30 elements while halving the required elements. This highlights the potential for a limited number of movable elements to approximate the performance of a fully fixed array. Furthermore, the proposed algorithm consistently converges to a high-performance smooth point, meeting constraints on array element positions and phase shift differences. The results also show that moving the elements leads to a narrower and stronger detection beam, enhancing the system's performance. Additionally, the findings reveal a trade-off between communication, sensing, and covert presence. Specifically, as the communication Signal-to-Interference-Noise Ratio (SINR) threshold increases, the sensing performance decreases. Due to covert communication constraints, beamforming design freedom is limited, requiring additional system resources for covertness, which ultimately reduces overall sensing performance. Conclusions: This paper examines the ME-STAR-RIS-assisted pass-sense integrated system through the lens of covert communication. The BS senses target nodes and communicates with legitimate users via a ME-STAR-RIS. To ensure data security, it is essential to conceal communication activities from potential targets. A joint active-passive covert beamforming scheme designed for the ME-STAR-RIS-assisted ISAC system is designed. This scheme aims to maximize probing power while maintaining covert communication quality. This paper serves as an initial exploration of the STAR-RIS with movable elements. Simulation results indicate that element-level mobility offers advantages for the STAR-RIS-assisted ISAC system. Several issues warrant further investigation, including channel estimation, non-ideal Channel State Information (CSI), and optimization of array element positions in practical settings.

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References(26)

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