To improve the secrecy performance of the untrusted relay system with a multiple-antenna destination, a novel full-duplex destination jamming scheme with optimal antenna selection (FDJ-OAS) is proposed in this paper. The exact closed-form expressions of the ergodic achievable secrecy rate are derived for the proposed scheme. To attain more insightful results, the approximated closed-form expressions for the ergodic achievable secrecy rate and the optimal power allocation factor for FDJ-OAS are derived in the case with a large-scale antenna array, and simple power allocation solutions are also provided in the high and low SNR regimes, respectively. Furthermore, we derive the asymptotic expressions for the secrecy outage probability (SOP) under different asymptotic conditions for the proposed scheme, and the analysis results indicate that, the secrecy diversity order of FDJ-OAS is significantly superior to that of the comparable schemes. Simulation results show that, the analytical curves match well with the simulation results, and the advantage of FDJ-OAS is also clearly demonstrated through performance comparison.

This paper investigates full-duplex (FD) secure transmissions with simultaneous wireless information and power transfer (SWIPT) on downlink (DL), where an FD base station, with multiple transmit antennas and multiple receive antennas, serves a group of single-antenna users on both DL and uplink (UL). An optimization problem with non-convex form is formulated for minimizing the system power under constraints on energy harvesting (EH) and security rates. In order to efficiently solve it, the original non-convex problem is first approximated to a convex one and then casted into a form of second-order cone programming (SOCP). Iterative solving algorithms are presented with the computational complexity analysis. Simulation results show that the proposed FD secure scheme is more power-efficient than conventional one, and the SOCP formulation is more computationally efficient than its semi-definite programming alternative. Compared with half-duplex (HD) schemes, the FD scheme is also advantageous in power performance especially under high DL and low UL security rate requirements.

This paper addresses robust designs of secure simultaneous wireless information and power transfer for multiple-input single-output (MISO) multiuser systems. By using a bounded uncertainty model for the channel state information (CSI) from transmitters to legitimate receivers and under the assumption of only available statistic knowledge of the CSI to eavesdroppers, we consider the robust designs with both worst-case and chance-constrained optimizations. To jointly optimize transmit beamforming vectors and power splitting factors, we formulate three problems aiming at minimizing the system power, maximizing the sum secrecy rate, and maximizing the minimal secrecy rate, respectively, subject to both energy harvesting and secrecy outage constraints. These problems are intractable in their original forms due to the CSI models and their non-convexity. To reach computationally efficient solutions, we first rewrite the original problems by semi-definite relaxation, then transform the CSI uncertainty related constraints by S-procedure, and finally approximate the non-convex constraints by the first-order Taylor expansion. By the reformulations, we present iterative successive convex approximation algorithm for approaching the optimized solutions. Simulation results under various setups of system parameters are provided to examine the system performance and validate the effectiveness of the proposed schemes.

This article investigates the secure transmissions for a wireless powered full-duplex (FD) device-to-device (D2D) overlay system. To coordinate the cellular downlink transmissions and the D2D transmissions, we propose a two-phase transmission protocol, where the first phase is dedicated to the transmissions of information and energy from the base station (BS) to its users and the devices, respectively, and the second phase is dedicated to information exchanging between the two devices over an FD link overheard by either active or passive eavesdroppers. In the case of active eavesdroppers, perfect channel state information (CSI) is assumed to be available, whereas for passive eavesdroppers, only statistic CSI is available. Both self-interference (SI) mitigation and BS-aided cooperative jamming are considered for the D2D secure transmissions. For system design, nonconvex power minimization problems under transmission rate constraints are formulated and convex approximated for efficiently obtaining numerical solutions. Simulation results show that the proposed scheme can well coordinate the cellular transmissions and the FD-D2D secure transmissions, while the cooperative jamming strategy can enhance the D2D transmission security, especially in the case of passive eavesdroppers.

In case the dual-functional base station (BS) is only equipped with half-duplex (HD) transceivers, integrated sensing and communications (ISAC) becomes a challenge task especially when the bidirectional communications for each HD user are involved. To address this situation, under the framework of a wireless network with two adjacent cells and with the aid of BSs cooperation, this paper presents two integrated cooperative sensing and bidirectional communication schemes that involve two and four transmission phases, respectively. Power minimization problems under the constrains of bidirectional communication rates and sensing signal to interference plus noise ratios (SINRs) are formulated for optimizing the downlink transmit beamforming vectors, uplink transmit power, and transmission time of each phase. Due to variables coupling, the problems are shown to be non-linear and non-convex. Relying on the successive convex approximation, iterative algorithms that are guaranteed to be convergent are derived to obtain these design variables. Simulations show that both of the proposed schemes well accomplish the bidirectional communications and cooperative target sensing in the considered situation. By contrast, the scheme with two transmission phases possesses lower implementation complexity while the scheme with four transmission phases owns the performance advantage. When uplink non-orthogonal multiple access is further used, the performance difference between the two schemes is reduced substantially.