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International Conference on Communications and Networking in China (ChinaCom)

Distributed precoding in multi-relay wiretap systems with amplify-and-forward

Jing Wang, Xiaoting Wang, Qianghua Guo, Hang Long, Yixian Shen

Published Aug 1, 2013• 1 citation
Publisher

Abstract

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.

DOI
10.1109/chinacom.2013.6694635

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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.
The secrecy capacity of relay communications is investigated in this paper, where an eavesdropper is present. Distributed precoding through multiple relay nodes can be used to enhance the received signal power at the destination node and to mitigate the signal leakage to the eavesdropper, simultaneously. Due to individual power constraints at relay nodes, the distributed precoding scalar at each relay node is equivalent to a distributed precoding angle. An iterative algorithm is proposed to find the suboptimum distributed precoding angles at all the relay nodes, where the channel state information (CSI) sharing overhead among the relay nodes can also be substantially reduced. Each relay node receives the equivalent CSI from its preceding relay node, computes its distributed precoding angle, and updates the equivalent CSI for the next relay node. Compared with the simple decode-and-forward relaying protocol with random distributed precoding, the proposed iterative distributed precoding algorithm is able to further improve on the secrecy capacity of the multirelay wiretap system with an acceptable CSI sharing overhead.
Summary Distributed precoding has provento be capable of enhancing the secrecy capacity of the multi‐relay wiretap system. An iterative distributed precoding and channel state information (CSI) sharing scheme can be used to reduce the CSI overhead at each relay node. However, in practical applications, the CSI of each relay node cannot be perfectly known to themselves, especially that of the relay‐eavesdropper channels. Thus, partial CSI for the relay‐eavesdropper links is assumed, and the corresponding distributed precoding and CSI sharing schemes are investigated. Under the assumption that the average value of the relay‐eavesdropper channel is known at each relay node, an extended iterative distributed precoding and CSI sharing scheme is proposed. Simulation results demonstrate that with the increase of the power ratio of the constant part to the random part of the relay‐eavesdropper channels, the proposed scheme with partial CSI performs increasingly close to the one with perfect CSI in secrecy capacity. Copyright © 2014 John Wiley & Sons, Ltd.
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 investigate the security issue of a two-hop amplify-and-forward multiple-input multiple-output wireless relay network in the existence of a multiantenna eavesdropper. The optimal scheme to achieve the secrecy capacity involves a nonconvex optimization and is still an open problem. Aiming to find an efficient way to enhance the secrecy rate with a tractable complexity, we propose a suboptimal joint source and relay linear precoding and power allocation scheme. In the scheme, the source node adopts a generalized singular value decomposition (SVD)-based precoding to transmit the signal in the first phase, and the relay node forwards the received signal based on the SVD precoding in the null-space of the wiretap channel in the second phase. Power allocations in both phases are optimized to maximize the secrecy rate by an alternating iterative optimization algorithm. Each iteration involves two subproblems. One has a water-filling solution and the other has a closed-form solution or a water-filling-like solution as well, both of which are computationally very efficient. The iteration converges fast and we prove that it guarantees to find a stationary optimum. Furthermore, we show that when the eavesdropper has equal or more antennas than the source does, the secrecy rate is a quasi-concave function of the source power so that allocating all the source power is generally not optimal. Numerical evaluation results are provided to show the effectiveness of the iterative algorithm and the proposed secrecy scheme.
In this paper, we investigate the security issue of a two-hop amplify-and-forward MIMO wireless relay networks in the existence of a multi-antenna eavesdropper. The optimal scheme to achieve the secrecy capacity involves a non-convex optimization and is still an open problem. Aiming to find an efficient way to enhance the secrecy rate, we propose a suboptimal joint source and relay linear precoding scheme. In the scheme, the source node adopt a generalized singular value decomposition (GSVD) based precoding to transmit the signal in the first phase, and the relay node forwards the received signal based on SVD in the null-space of the wiretap channel in the second phase. Power allocations in both phases are optimized to maximize the secrecy rate. An alternating iterative optimization algorithm is proposed to solve the problem. The algorithm is computationally efficient and guarantees to converge to a local optimum. Numerical evaluation results are provided to show the effectiveness of the iterative algorithm and the proposed secrecy scheme.
The problem of secure unicast communication over multihop wireless relay networks with directed links in the presence of an eavesdropper is considered. In the existing literature this problem has been considered in one or both of the following two scenarios: (A) relay nodes employ relaying schemes, such as Decode-and-Forward (DF), (B) the source communicates with the destination over a two-hop relay network. We argue that computationally complex relaying schemes such as DF render end-to-end performance characterization intractable, without providing any performance guarantee in general channel and network scenarios. Therefore, we consider one of the simplest relaying scheme: Amplify-and-Forward (AF) that allows us to provide guarantees on the optimal performance over a wide range of channel conditions. A node performing AF-relaying scales and forwards the signal received at its input. Further, with AF-relaying the end-to-end performance characterization problem remains tractable for much larger class of networks than those that can be considered with other relaying schemes. The key contribution of this work is twofold. We first provide the optimal vector of scaling factors that maximizes the achievable AF secrecy rate, no matter which relay the eavesdropper listens to. Further, we prove that in high-SNR regime, the optimal AF secrecy rate thus achieved is within a constant gap from the cutset upper bound on the secrecy capacity.