This paper considers an amplify-and-forward (AF) cooperative system with multiple relays which may eavesdrop on the source signal without authorization. In conventional cooperative system where the relays are assumed trustworthy, the precoding design usually tends to optimize quality of the received signal at the relays. However, the considered system relies on the relays' assistance and requires to prevent source information eavesdropped by the relays. With this regard, we proposed that the destination transmits artificial noise to interfere the signal reception of wiretapping relays. The artificial noise can be fully eliminated at the destination with perfect channel information. We propose a precoder design for the cooperative system that aims to maximize the received SNR at the destination subject to constraining quality of received signal at the relays. It shows through simulation results that the proposed scheme is able to improve the secrecy capacity of the cooperative system with wiretapping relays effectively.
This paper considers an amplify-and-forward (AF) cooperative system with multiple relays which may eavesdrop on the source signal without authorization. In conventional cooperative system where the relays are assumed trustworthy, the precoding design usually tends to optimize quality of the received signal at the relays. However, the considered system relies on the relays' assistance and requires to prevent source information eavesdropped by the relays. With this regard, we proposed that the destination transmits artificial noise to interfere the signal reception of wiretapping relays. The artificial noise can be fully eliminated at the destination with perfect channel information. We propose a precoder design for the cooperative system that aims to maximize the received SNR at the destination subject to constraining quality of received signal at the relays. It shows through simulation results that the proposed scheme is able to improve the secrecy capacity of the cooperative system with wiretapping relays effectively.
In this paper, we consider a dual-hop amplify-and-forward (AF) multiple-input-multiple-output (MIMO) relay network, where the source, relay, and destination are each equipped with multiple antennas. The relay is untrusted if it is willing to forward the signal to the destination and, at the same time, acts as a potential eavesdropper to interpret the message from the source. Since there exists no direct link between the source and the destination, a positive secrecy rate cannot be obtained. Addressing this issue, we propose a joint destination-aided cooperative jamming and precoding at both the source and the relay scheme: joint source, relay, and destination precoding (JP). We target at maximizing the secrecy rate by jointly designing the source, relay, and destination precoding matrices and propose an alternating iterative optimization algorithm to tackle the nonconvex problem. Then, a comprehensive study on the asymptotic performance is conducted in a high signal-to-noise ratio (SNR) regime. In particular, we present simple closed-form expressions for the two key performance parameters in the asymptotic secrecy rate, i.e., the high-SNR slope and the high-SNR power offset. Finally, numerical results are conducted to demonstrate the validity of the proposed secure scheme and its performance analysis.
Robust artificial noise (AN) aided secure precoding for an amplify-and-forward multiple-input multiple-output untrusted relay system is studied, where the relay is untrusted and willing to help forwarding multiple data streams from the source to destination. We consider that the available channel state information is imperfect and modeled by the worst case model. Our objective is to maximize the worst case secrecy rate under the robust transmit power constraints at the source and relay, by jointly designing the signal and AN precoding matrices at the source and the precoding matrix at the relay. The robust secure precoding problem is nonconvex and hard to solve. To overcome this difficulty, we propose the weighted minimum mean square error based method, where the signdefiniteness lemma is used to eliminate the channel uncertainties and an effective iterative optimization algorithm is developed. Simulation results are provided to demonstrate the effectiveness of the proposed scheme.
The security of the multi-relay wiretap system with an eavesdropper is investigated in this paper, where the amplify-and-forward (AF) relaying protocol is used. Appropriate distributed precoding design at the relay nodes can be utilized to guarantee the secure communication, which means maximizing the ratio of received signal power at the destination node and the eavesdropper node. In decode-and-forward relaying systems, an iterative algorithm has been proposed to find sub-optimum distributed precoding angles at all the relay nodes [1]. In this paper, this algorithm is extended to be used in AF systems with some modifications. In the algorithm, after receiving the equivalent channel state information (CSI) from the last relay node, the current relay node derives the optimum distributed precoding angle, and updates the equivalent CSI for the next one, so that each relay node shares much less CSI information with each other, compared with the exhaustive search scheme. Numerical and simulation results demonstrate that in the AF protocol system, the iterative algorithm can help achieve considerable secrecy capacity with a little CSI sharing overhead.
We consider an amplify-and-forward (AF) relay network with multiple source-destination pairs in the presence of an eavesdropper. This paper studies the robust artificial noise (AN) assisted joint transceiver optimization for secure communication with imperfect channel state information (CSI) of legitimate users and no CSI regarding the eavesdropper. The goal is to design the linear precoding matrix of the relay and the linear equalizer of each destination, such that the transmit power for the information-bearing signals and forwarded background noises at the relay can be minimized subject to the quality of service (QoS) constraints at the destinations. The remainder of the constrained total power is used to generate the AN for jamming the eavesdropper. Although such a power minimization problem is nonconvex, we recast it into two semidefinite programming (SDP) subproblems which can be solved using interior-point methods. Then this problem can be solved with the alternating iterative optimization algorithm. Simulations demonstrate that the proposed algorithm can significantly reduce the sensitivity to imperfect CSI, while degrading the eavesdropper's capability of intercepting.
In this paper, secrecy communications with cooperative jamming in a two-hop one-way untrusted relay system is studied. Assuming that all nodes are equipped with multiple antennas, new precoding designs are proposed to increase the secrecy capacity. Two situations are considered, namely only designing precoding vector for jamming signal when user signal has been determined, and designing precoding vectors for both user and jamming signals by jointly considering the source node. For each situation, two alignment algorithms are proposed, namely zero-forcing-based (ZF) alignment algorithm and minimum-mean-squared-error-based (MMSE) alignment algorithm. Both algorithms are designed to ensure that the equivalent wiretap channel matrix forms two aligned vectors. The channel vector from the destination node is designed to be aligned with that from the source node, so that the eavesdropping node cannot decode user signals. Analytical and simulation results show that all proposed scheme can achieve secure communication, and the MMSE algorithm performs better than the ZF. In addition, the destination-relay link has greater impact on the secrecy performance than the relay-destination link.
We consider a secrecy dual-hop amplify-and-forward (AF) untrusted relay network, where the relay is willing to forward the signal to the destination while acting as a potential eavesdropper. Assuming that all these nodes are equipped with multiple antennas, we propose a joint destination aided cooperative jamming and precoding at both the source and the relay scheme, with the objective to maximize the worst case secrecy rate. The formulated problem is highly non-convex due to the maximization of the difference of several logarithmic determinant (log-det) functions in the CSI uncertainty region. To handle this challenge, we propose to linearize these log-det terms. After linearization, we tackle the CSI uncertainty based on epigraph reformulation and the sign-definiteness lemma. Finally, an alternating optimization (AO) algorithm is proposed to solve the reformulated problem. Numerical results are provided to demonstrate the performance of the proposed scheme.