This paper investigates secure beamforming design for simultaneous proactive eavesdropping and communication in a multiuser multi-antenna system, where a full-duplex base station (FD-BS) serves multiple legitimate users, monitors a suspicious link, and suppresses multiple eavesdroppers. The proposed design is formulated as maximizing the weighted sum secrecy rate (WSSR) of legitimate users, subject to a total transmit-power requirement and a proactive eavesdropping constraint. The initial problem is hard to solve due to the high non-convexity of the objective function and the proactive eavesdropping constraint. By introducing three auxiliary variables, the original WSSR maximization problem is equivalently reformulated as a weighted minimum mean square error (WMMSE) minimization problem. The reformulated WMMSE minimization problem remains non-convex, where a block coordinate descent (BCD) algorithm based on first-order Taylor approximation is proposed to solve it iteratively. Aiming to reduce the computational complexity of the proposed method, a low complexity zero-forcing beamforming algorithm is designed. Simulation results demonstrate that the proposed algorithms can achieve superior trade-offs among communication efficiency, secrecy enhancement, and surveillance performance than conventional methods.
This paper investigates secure beamforming design for simultaneous proactive eavesdropping and communication in a multiuser multi-antenna system, where a full-duplex base station (FD-BS) serves multiple legitimate users, monitors a suspicious link, and suppresses multiple eavesdroppers. The proposed design is formulated as maximizing the weighted sum secrecy rate (WSSR) of legitimate users, subject to a total transmit-power requirement and a proactive eavesdropping constraint. The initial problem is hard to solve due to the high non-convexity of the objective function and the proactive eavesdropping constraint. By introducing three auxiliary variables, the original WSSR maximization problem is equivalently reformulated as a weighted minimum mean square error (WMMSE) minimization problem. The reformulated WMMSE minimization problem remains non-convex, where a block coordinate descent (BCD) algorithm based on first-order Taylor approximation is proposed to solve it iteratively. Aiming to reduce the computational complexity of the proposed method, a low complexity zero-forcing beamforming algorithm is designed. Simulation results demonstrate that the proposed algorithms can achieve superior trade-offs among communication efficiency, secrecy enhancement, and surveillance performance than conventional methods.
In this paper, we investigate the physical layer security of a full-duplex base station (BS)-aided system in the worst case, where an uplink transmitter (UT) and a downlink receiver (DR) are equipped with a single antenna, while a powerful eavesdropper is equipped with multiple antennas. For securing the confidentiality of signals transmitted from the BS and UT, an artificial noise (AN)-aided secrecy beamforming scheme is proposed, which is robust to the realistic imperfect state information of both the eavesdropping channel and the residual self-interference channel. Our objective function is that of maximizing the worst-case sum secrecy rate achieved by the BS and UT, through jointly optimizing the beamforming vector of the confidential signals and the transmit covariance matrix of the AN. However, the resulting optimization problem is non-convex and non-linear. In order to efficiently obtain the solution, we transform the non-convex problem into a sequence of convex problems by adopting the block coordinate descent algorithm. We invoke a linear matrix inequality for finding its Karush-Kuhn-Tucker (KKT) solution. In order to evaluate the achievable performance, the worst-case secrecy rate is analytically derived. Furthermore, we construct another secrecy transmission scheme using the projection matrix theory for performance comparison. Our simulation results show that the proposed robust secrecy transmission scheme achieves substantial secrecy performance gains, which verifies the efficiency of the proposed method.
To enhance secure communications, we deploy the dual-polarized antenna arrays at communication nodes of the multi-input multioutput (MIMO) system, where the base station communicates with multiple legitimate users in the presence of an eavesdropper. We also adopt the dual-structured precoding in which a preprocessing matrix based on the polarized array spatial correlation and a linear precoding based on the instantaneous channel state information (CSI) are concatenated. We design this dual-structured multiuser linear precoding under three cases. In the first case, given perfect global CSI, the secrecy rate optimization problem is formulated and transformed into the weighted minimum mean square error (MSE) problem, which can be effectively solved by the block coordinate decent method. In the second case, where the eavesdropper's CSI is unavailable, an artificial noise is generated to confuse the eavesdropper by minimizing the information transmit power subject to a preset MSE threshold for the recovered confidential signals, which can be solved by an efficient iterative algorithm. In the third case of imperfect global CSI, the robust optimization for secure communications is performed by minimizing the largest received MSE among the users subject to the total transmit power constraint, which can be reformulated into a biconvex semidefinite programming problem and solved by an efficient alternating convex optimization. Simulation results are included to demonstrate the excellent performance of our proposed designs over the conventional single-polarized array-based designs, in terms of achievable secrecy rate, minimum transmit power, and the MSE of recovered confidential signals.
This paper considers a movable antenna (MA)-aided secure multiple-input multiple-output (MIMO) communication system consisting of a base station (BS), a legitimate information receiver (IR) and an eavesdropper (Eve), where the BS is equipped with MAs to enhance the system’s physical layer security (PLS). Specifically, we aim to maximize the secrecy rate (SR) by jointly optimizing the transmit precoding (TPC) matrix, the artificial noise (AN) covariance matrix and the MAs’ positions under the constraints of the maximum transmit power and the minimum spacing between MAs. To solve this non-convex problem with highly coupled optimization variables, the block coordinate descent (BCD) method is applied to alternately update the variables. Specifically, we first reformulate the SR into a tractable form, and derive the optimal TPC matrix and the AN covariance matrix with fixed MAs’ positions by applying the Lagrangian multiplier method in semi-closed forms. Then, the majorization-minimization (MM) algorithm is employed to iteratively optimize each MA’s position while keeping others fixed. We also extend this work to the more general multicast scenario. Finally, simulation results are provided to demonstrate the effectiveness of the proposed algorithms and the significant advantages of the MAs over conventional fixed position antennas (FPAs) in enhancing system’s security.
This paper studies the beamforming design problem of a multi-user downlink network, assuming perfect channel state information (CSI) known to the base station (BS). In this scenario, the BS is equipped with multiple antennas, and each user is wiretapped by a specific eavesdropper where each user or eavesdropper is equipped with one antenna. It is supposed that the BS employs transmit beamforming with a given requirement on sum transmitting power. The object is to maximize the sum secrecy rate (SSR) of the network, which leads to a nonconvex complicated structure, and makes he considered beamforming design problem difficult to handle. To solve this problem, a beamforming design scheme is proposed to transform the original problem into a convex approximation problem, by employing semidefinite relaxation (SDR) and first-order approximation technique based on Taylor expansion. Besides, with the advantage of low complexity, a zero-forcing (ZF) based beamforming method is presented in the case that BS is able to nullify he eavesdroppers' rate. Numerical results show that the former strategy achieves better performance than the later one, which is mainly due to the ability of optimizing beamforming direction, and both outperform the traditional signal-to-leakage-and-noise ratio (SLNR) based algorithm.
Physical layer security (PLS) is a promising paradigm for safeguarding 6G wireless networks by exploiting the inherent characteristics of wireless channels. However, the efficiency of conventional PLS is often limited by fixed orientation antennas. This paper investigates a rotatable antenna (RA)-aided secure multiple-input multiple-output (MIMO) communication system, where both the transmitter and the receiver are equipped with RAs in the presence of an eavesdropper. By dynamically optimizing the orientations of RAs, we can proactively reshape the effective MIMO channels to enhance legitimate transmission while simultaneously suppressing information leakage to the eavesdropper. We formulate a secrecy rate maximization problem by jointly optimizing the transmit beamforming, artificial noise (AN) covariance matrix, and the transmit/receive RA orientations, subject to the transmit power budget and antenna orientation constraints. To tackle the resulting highly coupled and non-convex problem, we first study a simplified single-input single-output (SISO) case to reveal the structure of the optimal RA orientation. For the general MIMO case, we develop an alternating optimization algorithm by reformulating the original problem through the minimum mean-square error framework. In particular, the transmit beamforming and AN covariance matrix are derived in semi-closed forms, while the RA orientations are updated via the Riemannian Frank-Wolfe method. The proposed design is further extended to the multi-receiver secure transmission scenario. Simulation results show that the proposed scheme converges rapidly and achieves significant secrecy rate gains over the conventional fixed-orientation scheme.
From the perspective of national security, legitimate government agencies have long been committed to enforcing powerful surveillance measures on suspicious individuals or communications. This paper investigates a wireless legitimate surveillance system, where a full-duplex multi-antenna legitimate monitor aims to eavesdrop on a dubious communication link between a suspicious pair via proactive jamming. It is assumed that the legitimate monitor can successfully eavesdrop the suspicious information only when its achievable data rate is no smaller than that of the suspicious receiver. To maximize the eavesdropping non-outage probability, optimal joint design of the jamming power, receive and transmit beamformers at the legitimate monitor is presented. Moreover, two low-complexity suboptimal beamforming schemes are proposed and the corresponding analytical results are obtained. Our outcomes demonstrate that by exploiting multiple antennas at the legitimate monitor, the eavesdropping non-outage probability exhibits a significant improvement compared to the single antenna case. In addition, the proposed suboptimal transmit zero-forcing scheme yields similar performance as the optimal scheme.