This paper investigates an energy-constrained relay-assisted secure communication system in the presence of a legitimate source-destination pair and a passive eavesdropper with imperfect channel state information (CSI). The energy-constrained relay exploits a power splitting (PS) protocol to simultaneously harvest energy and decode information from the received signal from the source, and then forwards the confidential signal to the full-duplex (FD) destination while it simultaneously transmits artificial noise (AN) to confuse the passive eavesdropper. This robust beamforming design is developed by maximizing the secrecy rate under the constraints of energy harvesting (EH) requirement at the relay and AN transmit power at the destination. Specifically, we formulate the joint relay beamforming and PS ratio as well as the AN power optimization as a non-convex quadratically-constrained problem. In order to circumvent this non-convexity issue, we decompose the original problem into three subproblems which can be determined by the proposed semidefinite relaxation (SDR) and successive convex optimization methods. Furthermore, we derive closed-form expressions for the optimal solutions of each subproblem. Finally, the original non-convex problem can be solved through a convergence guaranteed iterative algorithm. Simulation results are provided to demonstrate the effectiveness and superior performance of the proposed robust design compared with the benchmark schemes.
This paper investigates an energy-constrained relay-assisted secure communication system in the presence of a legitimate source-destination pair and a passive eavesdropper with imperfect channel state information (CSI). The energy-constrained relay exploits a power splitting (PS) protocol to simultaneously harvest energy and decode information from the received signal from the source, and then forwards the confidential signal to the full-duplex (FD) destination while it simultaneously transmits artificial noise (AN) to confuse the passive eavesdropper. This robust beamforming design is developed by maximizing the secrecy rate under the constraints of energy harvesting (EH) requirement at the relay and AN transmit power at the destination. Specifically, we formulate the joint relay beamforming and PS ratio as well as the AN power optimization as a non-convex quadratically-constrained problem. In order to circumvent this non-convexity issue, we decompose the original problem into three subproblems which can be determined by the proposed semidefinite relaxation (SDR) and successive convex optimization methods. Furthermore, we derive closed-form expressions for the optimal solutions of each subproblem. Finally, the original non-convex problem can be solved through a convergence guaranteed iterative algorithm. Simulation results are provided to demonstrate the effectiveness and superior performance of the proposed robust design compared with the benchmark schemes.
This paper studies the secure beamforming design for simultaneous wireless information and power transfer in a multiple-input single-output broadcast channel with confidential messages and external eavesdroppers, where each receiver adopts the power splitting (PS) scheme to decode information and harvest energy concurrently, and it is also seen as a potential eavesdropper for messages not intended for it. Our objective is to minimize the total transmit power while guaranteeing the individual secrecy rate and energy harvesting constraints at each receiver by jointly optimizing transmit beamforming vectors, artificial noise covariance, and receive PS ratios. Both scenarios of perfect and imperfect channel state information (CSI) at the transmitter are considered. For the perfect CSI case, we propose a two-stage optimization approach to solve the original non-convex problem global optimality, and also provide a low-complexity suboptimal solution based on the particle swarm optimization algorithm. Furthermore, we also extend the above result to the colluding eavesdroppers scenario. For the imperfect CSI case, we propose a worst-case-based robust formulation, where the CSI errors are norm-bounded. With the aid of S-Procedure, we derive the equivalent forms for constraints and then transform the non-convex robust design into a convex optimization problem. Simulation results are finally presented to demonstrate the performance of our proposed schemes.
This paper focuses on information security in an energy harvesting relay system, in which confidential signals are transmitted from a source node to its desired destination with the assistance of one full-duplex (FD) relay. To empower simultaneous wireless information and power transfer, the time-switching (TS) protocol is embraced and the energy-limited FD relay node is powered by energy signals emitted by the source node. With the obtained statistical eavesdropper channel state information (CSI), the ergodic secrecy rate and its approximate expression are derived. As the objective is maximizing the ergodic secrecy rate performance, source beamformers, TS coefficient and the power control factor at FD relay are jointly optimized. To tackle the framed non-convex problem, an alternative method is hence proposed, and closed-form solutions for beamformers, TS coefficient and power control factor are derived iteratively. Besides, the convergence of our proposed algorithm can be guaranteed and is also theoretically proved. Simulation results demonstrate that our iterative algorithm is effective and improves the system secrecy rate considerably.
In this paper, we consider a non-regenerative relay network supporting simultaneous wireless information and power transfer, in which the energy harvesting relay is powered by radio-frequency signals from the source node. Assuming imperfect channel state information from the source/relay to the destination/eavesdropper, we investigate the artificial noise-aided secure robust beamformer that minimize the transmission power at the relay, while guaranteeing the secrecy rate constraint and the transmit power constraint at the relay. In particular, two types of energy harvesting strategies are considered termed power splitting (PS) and time switching (TS), respectively. These constraints make the optimization problems formulated non-convex and challenging, which are efficiently solved by using the S-procedure and semidefinite relaxation techniques to formulate a tractable approximated version of the original problems. Numerical results show the effectiveness of the proposed robust beamforming schemes. Furthermore, the PS strategy performs better than the TS strategy.
This work studies a beamforming design for down-link transmission of a multi-user multiple-input single-output (MISO) system where each legitimate user employs a power splitting (PS) based simultaneous wireless information and power transfer (SWIPT) technique. The transmitter intends to send confidential information to its legitimate users in the presence of purely unknown eavesdroppers. Since the transmitter does not have any knowledge of the eavesdroppers' channel state information (CSI), we consider an artificial noise (AN) approach to establishing secure communication. This beamforming design is developed by maximizing the AN power to interfere with the eavesdropper as much as possible. Based on the assumption of imperfect CSI of legitimate users at the transmitter, two robust design approaches for the joint beamforming and PS ratio have been studied to maximize the AN power under both energy harvesting (EH) and signal-to-interference-plus-noise ratio (SINR) requirements at each legitimate user. In the first robust design, we consider the bounded channel uncertainties, and employ semidefinite relaxation (SDR) and a linear matrix inequality (LMI) representation to transform the original problem into a semidefinite program (SDP). In the second robust design, we consider the statistical channel uncertainties, and show that the proposed problem can be reformulated into another form of SDP through both SDR and Bernstein-type inequality. In addition, the non-linear energy harvesting (EH) model is incorporated in this work as it could reflect the characteristics of practical radio frequency(RF)-EH conversion circuit. Simulation results have been provided to demonstrate the performance of our proposed robust designs.
In this paper, we study secure beamforming for simultaneous wireless information and power transfer (SWIPT) in wireless-powered full-duplex (FD) relay networks. The relay assists transmission of confidential information, while simultaneously harvesting the energy with power switching scheme by the radio-frequency (RF) signals. We propose a joint amplify-and-forward beamforming (AB) and energy signal (AB-ES) with the receiver power splitting strategy (PS) scheme to maximize the secrecy rate under harvesting energy constraints. Since these constraints make the optimization problems become non-convex and hard to tackle. We propose a two-level optimization problem to solve this problem. The out part can be solved via the one-Dimensional search, and the inner part can be solved by semidefinite relaxation (SDR) technique. Simulation results show that the proposed scheme outperforms other schemes.
In this paper, we investigate the physical layer security for amplify-and-forward relay networks with simultaneous wireless information and power transfer. Specifically, by considering the dual-functional desired receiver, which is capable of decoding information and energy harvesting (EH), and assuming that only imperfect eavesdroppers' channel state information can be attained, we propose a joint robust cooperative beamforming, artificial noise, and power splitting scheme. We formulate the relay power minimization problem under both the secrecy rate constraint and the EH constraint, which is non-convex and hard to tackle. To tackle this problem, we propose a two-level optimization approach, which involves 1-D search and the semi-definite relaxation. In addition, we testify that the SDR can obtain the rank-one optimal solution. Simulation results show that the proposed robust scheme achieves better secrecy performance than other schemes.