Secrecy in Wireless Information and Power Transfer for One-Way and Two-Way Untrusted Relaying with Friendly Jamming

Hindawi Mobile Information Systems Volume 2017, Article ID 2192606, 10 pages https://doi.org/10.1155/2017/2192606 Research Article Secrecy in Wireless Information and Power Transfer for One-Way and Two-Way Untrusted Relaying with Friendly Jamming Lin Xiao,1 Tao Zhang,1 Xue Shen,1 Dingcheng Yang,1 and Laurie Cuthbert2 1 Information Engineering School, Nanchang University, Nanchang, China Information Systems Research Centre, Macao Polytechnic Institute, Rua de Luis Gonzaga Gomes, Macau 2 Correspondence should be addressed to Dingcheng Yang; Received 18 January 2017; Revised 12 May 2017; Accepted 2 July 2017; Published 10 August 2017 Academic Editor: Stefania Sardellitti Copyright © 2017 Lin Xiao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. An untrusted relay system combined with a simultaneous wireless information and power transfer (SWIPT) scheme is considered in one-way and two-way relaying transmission strategies. In the system, two source nodes can only communicate with each other via an untrusted energy harvesting relay node, which sends the message by using its harvested energy from the source nodes. Specifically, we classify the intermediate relay as an eavesdropper into two modes: active eavesdropper and nonactive eavesdropper, depending on whether it has sufficient energy of its own to transmit the message or not. Under a simplified three-node fading wiretap channel setup, the transmit power allocation and power splitting ratio are jointly optimized to minimize the outage probability in the delay-sensitive case and to maximize the average rate in the delay-insensitive case, subject to the average and peak total power constraints. Applying the dual-decomposition method, the optimization problem can be efficiently solved in the delay-sensitive scenario. Moreover, an iterative algorithm is proposed to derive the solution to maximize the average rate in the delay-insensitive scenario. Numerical results demonstrate the performance of system outage probability in the two modes versus different rates and how efficiently the secrecy rate is improved compared with traditional schemes. 1. Introduction Cooperative relaying is an effective approach for energy saving in wireless network, and two-way relay cooperation with network coding can enhance the capacity, coverage, and diversity. However, it does sacrifice the relay node’s energy to cooperate with the source node to achieve optimal system throughput. The relay node may lack the proper incentives to cooperate, since the energy consumption would severely degrade the donor’s experience, especially when the relay node is a battery constrained user. Recently, energy harvesting communication networks have emerged as alternative solutions with two different lines of research: the SWIPT scheme [1] and the wireless powered communication networks (WPCN) [2]. SWIPT has attracted many researchers’ interest since it is a promising technology to overcome the bottleneck of energy constrained wireless networks. Combining SWIPT with two-way relay communications, the relay node consumes the harvested energy instead of its own energy to cooperate with two source nodes to communicate with each other. From the perspective of the physical-layer security, the relay node can be friendly and protect the message from being eavesdropped by others. In heterogeneous networks, the relay node and source node are served by different network operators, so the message transmitted by the source node has different security levels. Moreover, the relay node should generally not be trusted in real life since the source nodes are likely to choose an untrusted relay to forward information. The untrusted relay can act as an essential relay that would strictly execute the forward behavior with specified power, as well as a malicious eavesdropper that has the incentive to eavesdrop on the information. When considering SWIPT with an untrusted relay, it is important to investigate the performance on the outage probability and the system secrecy rate. For the security communication, if the fading wiretap channel has a better channel gain than the main channel, 2 Mobile Information Systems the secrecy capacity of the system will be zero. Untrusted relay channels with confidential messages were first studied in [3], where the intermediate relay acted as both an eavesdropper and a helper. The papers [4–7] studied the security of the untrusted relay in different scenarios. The paper [4] considered the relay channel with a relay that was an eavesdropper and whether the untrusted relay may help the source and the destination. The work [5] investigated the problem of secure communication for amplify-and-forward (AF) systems with untrustworthy relay nodes and revealed the system performance worsened as the number of relays increased. In [6], a successive relaying scheme was proposed to secure the AF relaying network with multiple untrusted nodes and it was shown that the scheme could improve the security performance. In addition, secure beamforming with untrusted relay was considered in [7, 8]. The idea of the SWIPT scheme was first proposed in [9], and since then, it has been extended to wireless relay networks [10–18]. For the one-way single-antenna relay channel, time switching (TS) was proposed for AF relay networks in [10] and power splitting (PS) was proposed for DF relaying networks in [11]. More complex but efficient twoway relay systems were analyzed in [12–15]. The authors in [16–18] studied SWIPT in relay channels with the goal of minimizing the outage probability by jointly optimizing time assignment ratio and power splitting ratio. The papers [19, 20] considered the multirelay cooperative networks where the system throughput and SWIPT with rateless code were studied, respectively. These previous works presented the minimized outage probability in SWIPT-aware two-way relay systems. However, the authors did not consider that the relay could act as an eavesdropper with the SWIPT scheme. Besides, Liu et al. first analyzed the secrecy issue in multiple-input and singleoutput (MISO) systems combined with SWIPT in [21] where the joint information and energy beamforming design at the transmitter were investigated. In [22–24], the authors considered the application of the multiple-input multipleoutput (MIMO) technique with SWIPT, which improved the energy efficiency and also the spectral efficiency in the relay systems. Furthermore, for a fading wiretap channel, Xing et al. considered the optimal AN-aided secrecy design for SWIPT systems [25]. From the literature review above, it is noted that there have been limited studies of the untrusted relay combined with the SWIPT scheme. In this paper, we focus on the SWIPT scheme with the untrusted relay and the goal is to minimize the outa (...truncated)