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In this letter, we investigate covert communication in relay networks with relay selection. We consider the scenario that while forwarding the source's message, the selected relay opportunistically transmits its own message to the destination covertly. We derive the probability of detection error (PDE) and the average covert rate (ACR) in a closed form, based on which we analyse the effects of system parameters on the performance of the covert communication. Our analysis indicates that applying relay selection causes a decrease in the PDE, however, it can provide an ACR gain when the transmission rate of the source increases.

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Wireless sensor network (WSN) has been one of the most important network technologies nowadays. However, the communication of wireless sensor nodes is often constrained by computation capability and energy efficiency, and direct transmission is hard to adapt to all communication environments. Cooperative transmission can achieve the low energy consumption requirements effectively. But most researches considered multirelay and singular-hop scheme, and their energy efficiencies were not satisfactory in a longer transmission distance. To address this problem, we investigate the effect of the relay links and the relay node hops on the energy consumption in this paper. By deriving the outage probability of the multirelay and multihop transmission scheme, the minimum transmitting power of the source node is obtained. Then the existence of the minimum energy consumption is proved with respect to the number of relay links. Simultaneously, to reduce the computational complexity to ensure the effective implementation of the communication, the optimal number of relay links is calculated based on the minimum energy consumption. The simulation results show that the proposed multirelay and multihop transmission scheme has better transmission efficiency and can achieve satisfactory performance of communication and computation cooperation. KEYWORDScooperative transmission, energy consumption, multirelay and multihop, the optimal number of relay links, wireless sensor networks (WSNs)

In this paper, a new security and green communication scheme is proposed to the Interference-Alignment (IA) based networks. To achieve a secured communication, full-duplex receivers are utilized to transmit artificial noise (AN). Both the signals and the ANs are used to harvest energy to realize green communication. For these reasons, the feasible conditions of this scheme are analyzed first. Secondly, the average transmission rate, the secrecy performance and the harvested energy are investigated. Thirdly, an optimization scheme of simultaneous wireless information and power transfer (SWIPT) is given to optimize the information transmission and the energy harvesting efficiency. Meanwhile, an improved IA iteration algorithm is designed to eliminate both the AN and the interference. Furthermore, relay cooperation is considered and its system performance is analyzed. The simulations show that the target average transmission rate is not affected by AN, while the secrecy performance can be greatly improved. The energy harvesting efficiency is also better than the traditional schemes. As expected, the average transmission rate further is improved with the relay cooperation. Index Terms-Artificial noise (AN), eavesdropping, interference alignment (IA), relay, secrecy, simultaneous wireless information and power transfer (SWIPT) I. INTRODUCTION HE broadcast characteristics of the wireless communication networks (WCNs) determine that it is an open communication environment. The sharing of its information medium leads to intricate electromagnetic radiation problems. Of these, multiuser interference, wireless transmission secrecy and radio signal enabled wireless power transfer are intensively discussed in these WCNs [1]-[3].  Interference exists widely in multiuser WCNs, and this affects multiplexing rate of time slots, frequencies, and code space, which severely limits the reusability of channel resources and reduces the spectrum of networks. It has become  Manuscript received April 06, 2019.

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