This paper investigates secure communication from a wireless-powered transmitter to a desired receiver with multiple eavesdroppers in the wireless powered communication networks (WPCNs). Considering the non-linear energy harvesting (EH) model, we propose a secure two-phase communication protocol with the help of a hybrid base station (HBS). First, in the power transfer (PT) phase, the HBS transfers wireless power to the transmitter. Then in the subsequent secure information transmission (SIT) phase, the transmitter sends the secret information using the energy harvested in the PT, under the protection of artificial noise (AN) generated by the HBS. First, based on this communication protocol, we maximize the secrecy throughput with perfect channel information state (CSI) under the transmit power constraint at the HBS. The secrecy throughput maximization (STM) problem is non-convex, and hence we reformulate it by exploiting the primal decomposition method (PDM) to obtain tractable forms. The PDM-based transmit scheme (PDM-TS) is proposed for the STM. In addition, considering the imperfect CSI of wiretap channel, we further design the robust transmit scheme for the worst-case secrecy throughput maximization (wSTM) problem. Since the wSTM shows high non-convexity, we extend the PDM by combining it with the Sprocedure, and the PDM-based robust transmit scheme (PDM-RTS) is proposed for the wSTM. Finally, the numerical simulations are provided to show the effectiveness of the proposed transmit schemes.INDEX TERMS Wireless powered communication networks (WPCNs), non-linear energy harvesting (EH) model, physical layer security (PLS), secrecy throughput, robust beamforming.

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The faster-than-Nyquist (FTN) signalling is a bandwidth-efficient technology which has drawn attention in the bandwidth-starved world. However, inter-symbol interference is introduced by transmitting signals at a higher signalling rate than allowed by the Nyquist criterion. Decision feedback equalisation (DFE) cancellation is an efficient signal detection scheme for FTN-based communication system. However, since the DFE interference cancellation is executed by overall matrix computation, the required memory size is very large. In order to reduce the complexity of the interference cancellation process, a novel simple interference cancellation is proposed. Simulation results show that the scheme can perform better than DFE, and its complexity is very low because of the absence of QR decomposition.Introduction: Faster-than-Nyquist (FTN) signalling is a method that could potentially achieve higher capacity by introducing controlled inter-symbol interference (ISI). It was first studied by Mazo as early as 1975 [1] he showed that one can transmit the signal pulses faster than the Nyquist frequency without decreasing the Euclidian distance between any two signals, thus it can pack more data in the same bandwidth at the same energy without loss in performance compared with traditional methods. The main reason of Mazo's result did not attract much attention at that time is that the huge receiver complexity of FTN signalling.Recently, it has attracted interest in this bandwidth-starved world. In 2003, Liveris and Georghiades [2] investigated the structure of error events for binary FTN signalling when using root raised cosine (RRC) pulses, and showed that the same phenomenon occurred with RRC pulses. In 2006, Rusek and Anderson [3] investigated the lower and upper bounds of the information rates using RRC pulses for FTN schemes. In 2008, non-binary FTN was investigated in detail [4] describing a method to compute the minimum distance. Rusek and Anderson also investigated the constrained capacities for FTN [5] and compared their capacity computations with signal using orthogonal modulation. In [6], Rusek and Anderson introduced the 2D Mazo limit by packing signals in time and stacking signals in frequency together. Kim and Bajcsy in [7] analysed the information rates and their upper bounds for cyclostationary FTN signalling using additive white Gaussian noise (AWGN) and continuous time ISI channels. The pulse design is presented in [8], and showed that arbitrary modulation pulses were used which not only reduce the detection complexity but also achieve the channel capacity.However, due to the inevitable ISI is introduced with the FTN signalling, and much faster symbol rate is used, the number of interference is highly increased, thus the computational complexity of removal of ISI is the main challenge for FTN signalling. So far, a number of demodulating methods have been proposed for the FTN signalling receiver. For example, maximum likelihood sequence estimation (MLSE) technique [9] and Viterbi algorithm (VA) [10], as the ...

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In this paper, we investigate an energy-harvesting cooperative communication network, which comprises of a source, a destination, and multiple decode-and-forward (DF) relays in the presence of multiple passive eavesdropper (Es). Es attempt to intercept confidential information transmissions from the source to destination via DF relays. In this network, all the DF relays harvest energy from radio-frequency (RF) signals of a source through time-switching receivers. In order to improve the physical layer security of energyharvesting cooperative communication networks, we propose a best relay selection (BRS) scheme, where the ''best'' relay is chosen to assist the source-destination transmission. For the purpose of comparison, we consider the classic direct transmission (DT) and equal relay selection (ERS) as benchmark schemes. We derive the exact closed-form expressions of outage probability (OP) and intercept probability (IP) for the ERS and BRS schemes over Rayleigh fading channels. Besides, the security-reliability tradeoff (SRT) is analyzed as a metric to evaluate the tradeoff performance of the proposed BRS scheme. Numerical results show that the SRT of the BRS scheme consistently outperforms that of the ERS scheme, which demonstrates the advantage of our proposed scheme against eavesdroppers. Besides, it is verified that total error rate (TER) defined as the sum of OP and IP can be minimized for both the ERS and BRS schemes through changing the time allocation factor between information transmission and energy harvesting phases. Moreover, there is a best energy conversation efficiency to obtain a maximal SRT value of the ERS and BRS schemes. In addition, as the number of DF relays increases, the SRT of BRS scheme improves notably, while that of ERS scheme remains unchanged. And as the number of Es increases, the SRT of both the ERS and BRS schemes become worse. INDEX TERMS Cooperative communication, physical layer security, best relay selection (BRS), outage probability (OP), intercept probability (IP), security-reliability tradeoff (SRT).