Abstract In this paper, the selective cooperation with untrusted relays is studied for wireless multipair two‐way relay networks. We first investigate the feasibility of secure transmission in the presence of cooperative but untrusted relays and then formulate a general optimization problem of secrecy sum‐rate maximization under the constraints of relay selection. By decomposing the original problem into solvable subproblems, we develop a low‐complexity greedy algorithm for selective cooperation, in which the untrusted relays are selected as cooperators or the potential eavesdroppers according to the overall contributions to the secrecy sum rate. Simulation results reveal that the proposed greedy algorithm for selective cooperation with untrusted relays achieves performance gain both in instantaneous and average secrecy sum rate and that the algorithm can converge quickly with the iterations.
Abstract In this paper, the selective cooperation with untrusted relays is studied for wireless multipair two‐way relay networks. We first investigate the feasibility of secure transmission in the presence of cooperative but untrusted relays and then formulate a general optimization problem of secrecy sum‐rate maximization under the constraints of relay selection. By decomposing the original problem into solvable subproblems, we develop a low‐complexity greedy algorithm for selective cooperation, in which the untrusted relays are selected as cooperators or the potential eavesdroppers according to the overall contributions to the secrecy sum rate. Simulation results reveal that the proposed greedy algorithm for selective cooperation with untrusted relays achieves performance gain both in instantaneous and average secrecy sum rate and that the algorithm can converge quickly with the iterations.
Physical‐layer security is usually ensured by the injection of artificial noise (AN) at the legitimate source or destination when relays are cooperative but untrusted. In this work, in order to avoid the power‐consuming AN at the legitimate user pairs, the authors investigate multi‐pair two‐way relaying as a solution for secure transmission in wireless relay networks with untrusted relays. They formulate a generalised problem for the joint design of cooperative beamforming (CB) and AN at relays to maximise the secrecy sum‐rate in wireless networks with multi‐pair legal users, multiple untrusted relays as well as multiple non‐colluding eavesdroppers. Further, they reformulate, approximate and relax the original non‐convex problem into a sequence of convex sub‐problems based on semi‐definite relaxation (SDR) and Taylor series approximation. Particularly, for the reformulated problem they prove that the SDR is in fact tight, and hence propose an iterative algorithm for CB and AN design at the relays. In the simulations, they demonstrate the fast convergence and high achievable secrecy sum‐rate of the proposed algorithm. Also, they simulate and discuss the impact of the number of user pairs on the secrecy sum‐rate, and reveal the change of performance gain with the number of multiple user pairs.
Abstract A half‐duplex relaying network provides 2 opportunities for passive eavesdroppers (Eves) and 1 opportunity for untrusted relays to intercept the information. In this paper, we aim to enhance the physical layer security of a cooperative network where a single‐antenna source intends to communicate with a single‐antenna destination in the presence of a group of untrusted relays and a passive eavesdropper. The objective is to protect the data confidentially while concurrently relying on the untrusted relays as potential Eves to improve both the security and reliability of the network. To realize this objective, we design a joint cooperative beamforming and cooperative jamming strategy. With the aim of maximizing the instantaneous secrecy rate, an optimal power allocation (OPA) scheme is proposed where the transmission powers of both jammer and source are optimized simultaneously under the total power budget constraint. To further improve the secrecy rate, a jammer selection strategy is also proposed where cooperative jamming is performed by the destination or one of the idle relays. For the proposed scheme, a closed‐form expression of beamformer vector is derived by solving a generalized eigenvalue problem. Finally, for the OPA problem, it is possible to be neither convex nor concave. In this regard, all possible cases are investigated to determine the OPA factor accurately. Numerical results illustrate that the proposed joint OPA–cooperative beamforming scheme, together with the most appropriate jammer selection strategy, significantly increases the secrecy rate.
In this paper, we investigate physical-layer transmission security problem of a two-way relay wireless network consisting of two legitimate terminal nodes who wants to communicate with each other in presence of one eavesdropper, with help of N intermediate nodes. We propose a cooperative relaying and jamming strategy, which selecting one intermediate node to create intentional interference upon the eavesdropper, while other K = N -1 intermediate nodes operating in relay mode and assisting the source nodes to deliver data to their corresponding destinations using an amplify-and-forward (AF) protocol. All N intermediate nodes in this system are under a per-node power constraint. When K ≥ 3, we propose two different system design criteria based on null-space beamforming, to maximize secrecy sum rate by rate-splitting method with a bisection numerical algorithm iteratively getting the maximal secrecy sum rate, or to maximize the minimum rate between the two terminals. And we also propose the modified security schemes when the number of intermediate nodes is not enough for the previously mentioned schemes (K <; 3).
We investigate the problem of physical layer security in a wireless cooperative network, where communication is assisted by the untrusted relay. It is impossible for the amplify-and-forward protocol to convey a confidential message from the source to the destination without the help of other nodes, where only an untrusted relay is available. Nonetheless, our results are quite optimistic when there are multiple untrusted relays, which amplify the received signal and forward it to the destination. We treat the untrusted relay nodes as eavesdroppers, despite the fact that they are the enablers of communication. First of all, we prove that a positive secrecy rate can always be ensured regardless of the transmit power and the channel condition of the untrusted relays, as long as there exists a sufficient number of untrusted relays. Furthermore, a closed-form solution to the upper bound of secrecy rate is obtained. Finally, a practical approach is proposed to acquire a positive secrecy rate, which brings nearly no extra communication cost. Simulations are conducted to demonstrate the validity of the proposed approach.