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IEEE Communications Letters

Near-Field Assisted Secure ISAC System: Synergistic Enhancement Between Sensing and Secure Transmission

Zhuochen Chen, Shengqi Zhu, Ximin Li

Published Jul 25, 2025• 1 citation
Publisher

Abstract

In this letter, we propose a near-field secure integrated sensing and communication (ISAC) system architecture, where the ISAC system simultaneously performs target detection and tracking while transmitting communication information to downlink users. However, in the presence of malicious eavesdropping devices, the security of communication transmission in ISAC systems cannot be guaranteed. Near-field effects introduce an additional advantage in the distance dimension, which improves the accuracy of target distance and angle estimation. Simultaneously, beamforming can be spatially focused at specific points to prevent information leakage. Motivated by these benefits, We construct a weighted optimization framework aimed at jointly maximizing the overall secrecy rate and reducing the Cramér-Rao Bound (CRB) for target estimation in near-field scenarios, while adhering to communication demands and total power limitations of the system. By integrating fractional programming (FP) and semidefinite relaxation (SDR) techniques, we jointly optimize the transmit waveform covariance matrix and the beamforming vectors to enhance both sensing accuracy and secure transmission performance simultaneously. Numerical results reveal that the secure near-field ISAC scheme can effectively achieve a synergy enhancement between sensing and secure communication while maintaining reliable system performance.

DOI
10.1109/lcomm.2025.3592736

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In this letter, we propose a near-field secure integrated sensing and communication (ISAC) system architecture, where the ISAC system simultaneously performs target detection and tracking while transmitting communication information to downlink users. However, in the presence of malicious eavesdropping devices, the security of communication transmission in ISAC systems cannot be guaranteed. Near-field effects introduce an additional advantage in the distance dimension, which improves the accuracy of target distance and angle estimation. Simultaneously, beamforming can be spatially focused at specific points to prevent information leakage. Motivated by these benefits, We construct a weighted optimization framework aimed at jointly maximizing the overall secrecy rate and reducing the Cramér-Rao Bound (CRB) for target estimation in near-field scenarios, while adhering to communication demands and total power limitations of the system. By integrating fractional programming (FP) and semidefinite relaxation (SDR) techniques, we jointly optimize the transmit waveform covariance matrix and the beamforming vectors to enhance both sensing accuracy and secure transmission performance simultaneously. Numerical results reveal that the secure near-field ISAC scheme can effectively achieve a synergy enhancement between sensing and secure communication while maintaining reliable system performance.
In this paper, we consider the joint beamforming design in secure integrated sensing and communication (ISAC) systems, where the active eavesdropper intercepts the transmitted confidential information with an external passive eavesdropper. To improve the sensing performance while preventing the potential eavesdropping, the base station transmits a signal consisting of information symbols and sensing waveform, in which the sensing waveform is also used as artificial noise to interfere with eavesdroppers. Under this setup, we formulate the communication and sensing beamforming design problem, which aims to enhance the transmit beampattern performance, while ensuring the quality of service (QoS) of communication transmission and the secure communication constraint. Furthermore, we propose the semi-definite relaxation (SDR) algorithm to solve the non-convex problem. Numerical results demonstrate the effectiveness of the proposed scheme in both sensing and secure communication.
The channel state information (CSI) of malicious users in the field of physical layer security is usually difficult to obtain due to the users’ passive listening. However, as sensing is integrating into the cellular network, it becomes feasible to acquire the CSI of passive eavesdroppers. Motivated by this, we propose a novel sensing-aided secure communication (SASC) scheme in this paper, which is implemented by a two-stage transmission protocol including beam sensing of the eavesdropper’s CSI and secure communication to the legitimate user against the eavesdropper. In the first stage, the base station (BS) needs to decide the number of sensing beamsLLL, and we derive the closed-form Cramer-Rao bound (CRB) to establish the relationship between the estimated angle range for the eavesdropper’s location andLLL, where a largerLLLfor beam sensing returns a tighter CRB to locate the eavesdropper. In the second stage, the BS designs the beamforming vector to transmit confidential data to the legitimate user and avoid leakage to the eavesdropper in the estimated range. As sensing affects the subsequent secure communication, we decouple the non-convex two-stage joint optimization problem into two subproblems and solve it by backward induction. In particular, in the secrecy beamforming subproblem givenLLL, we investigate the worst-case information leakage by constructing a convex hull to approximate the angle range from sensing. Then we develop a semi-closed-form solution of robust secrecy beamforming vector, and use it for the other subproblem to decide initialLLL. To achieve this goal, we also obtain a semi-closed-form solution ofLLLby considering all potential estimated results in the worst case. Finally, we present simulation results to show the effectiveness and robustness of the proposed SASC scheme as compared to various benchmarks.
Emerging wireless applications pursue a paradigm shift towards the integrated system that is capable of secure data transmission and high-resolution sensing in near-field environments. Conventional far-field use-cases suffer from the fundamental limitations in security, spatial precision, and spectral coexistence. Against this backdrop, this paper investigates an integrated covert communications and sensing (ICCS) system operating in the near-field environment. Specifically, the transmitter (Alice) aims to covertly convey messages to legitimate receivers (Bobs), while circumventing the detection by the eavesdropper (Willie) as well as improving the sensing performance at the target. To elevate communication performance, we aim to maximize the achievable sum rate to jointly optimize the communication and sensing beamforming matrices at Alice. The optimization problem is subject to multiple constraints with coupled variables: the transmit power budget at Alice, the minimum communication rate requirements for Bob, the Crameˊ\acute {e}eˊr-Rao bound (CRB) constraint to ensure accurate parameter estimation in sensing, and the covertness constraint against Willie’s detection. Given the non-convex nature of the formulated problem, an efficient successive convex approximation and semidefinite relaxation algorithms are proposed. In addition, we provide a theoretical analysis to confirm the convergence behaviour of the proposed algorithm, which can achieve the near-optimal solution. Finally, the numerical results are presented to highlight the superiority of the proposed ICCS system over existing counterparts. These results numerically verify the effectiveness of the proposed approach in enhancing communication rates while maintaining sensing performance and covertness in the near-field regime.
This paper studies the joint secure transceiver design for the full-duplex integrated sensing and communication (ISAC) system, in which the base station performs the target tracking and communicates with the downlink and the uplink users by reusing the resources. Here, the target, referred to as Eve, is a potential eavesdropper with the intention of intercepting both the downlink and the uplink information. The security problem of the full-duplex ISAC system has not been studied well, where the sensing and communication signals suffer from the serious interference. In this paper, we jointly design the information beamformer, the radar waveform, the uplink communication receive filter, and the radar receive filter to achieve the downlink and uplink communication security and the target tracking. Specifically, both the Eve’s signal-to-interference-plus-noise ratio minimization and the secrecy rate maximization problems, subject to the sensing and the communication constraints, are formulated for the ISAC system from the perspectives of the quality of service and the secrecy rate. An iterative algorithm is proposed for solving the formulated problems. We prove that, under appropriate conditions, the proposed iterative algorithm converges to the Karush-Kuhn-Tucker optimal point of the original problem without the rank 1 constraint. We further extend the joint design to the case of the imperfect wiretap channel and the angle uncertainty. Numerical results show that our scheme remarkably outperforms the benchmark approaches. The performance is close to that of designing the secure communication and the sensing separately.
Empowered by the integrated sensing and communication capability, this paper proposes a new two-stage artificial noise (AN)-assisted secure beamforming design towards physical layer security enhancement. Specifically, in the first stage a nearly omni-directional AN is used for sensing the eavesdropper, where the AN is radiated istropically except in the direction of the communication user. With the known channel knowledge of the eavesdropper, a spatially AN is transmitted in the second stage to deliberately degrade the eavesdropper. To balance the sensing and secure communication performance, we aim to maximize the effective secrecy rate by jointly optimize the time allocation and the transmit beamforming in both stages. A efficient optimization algorithm based on weighted minimum mean square error is then developed to solve the formulated non-convex problem. Simulation results are provided to demonstrate the performance advantage of our proposed design over the existing benchmark schemes in terms of achieving a larger effective secrecy rate.
This paper proposes a near-field integrated sensing and covert communication (ISCC) system, where Alice transmits covertly to Bob against Willie’s detection. We jointly optimize hybrid digital and analog beamforming and radar waveforms via the weighted minimum mean square error and manifold optimization algorithm to maximize covert rate while ensuring security, and use the extended Kalman filter to track the adversarial target in real-time for adaptive parameter adjustment. By addressing covertness constraints including leakage power, the proposed system ensures a low probability of detection while enabling superior system performance. The simulation results demonstrate that the proposed method provides secure communication and reliable target tracking under various conditions, achieving effective communication with Bob even in the presence of detection threats. The results validate the effectiveness of the proposed ISCC system in near-field scenario.