This paper considers a two-way relay network, in which two sources exchange data through a relay and a cooperative jammer transmits an artificial noise (AN) while a number of nearby eavesdroppers overhear to recover data from both sources. The relay harvests energy from the two source signals and the AN, and then, uses this harvested energy to forward the received signals to the two sources. Each source eliminates its own signal from the relaying signal by self-cancellation and then decodes the data signal received from the other source. For this wireless-powered two-way relay system, we propose two secure relay protocols based on power splitting and time switching techniques. The two protocols are power splitting-based two-way relaying (PS-TWR) and time switching-based two-way relaying (TS-TWR), in which the relay, respectively, controls the power splitting ratio (p) and time switching ratio (α), in order to achieve a balance between the data receiving and the energy harvesting. The optimal values of p and α for each protocol are found analytically to maximize the minimum guaranteed secrecy capacity (CSmin) considering multiple eavesdroppers in high signal-to-noise ratio environments. Numerical results show that both the PS-TWR and TS-TWR protocols using the optimized values of p and α achieve the near-optimal CSminno matter how many eavesdroppers exist anywhere. Comparisons of the two protocols in various scenarios also show that PS-TWR achieves better CSminthan TS-TWR because PS-TWR inherently has a shorter vulnerable time for eavesdropping than TS-TWR.
This paper considers a two-way relay network, in which two sources exchange data through a relay and a cooperative jammer transmits an artificial noise (AN) while a number of nearby eavesdroppers overhear to recover data from both sources. The relay harvests energy from the two source signals and the AN, and then, uses this harvested energy to forward the received signals to the two sources. Each source eliminates its own signal from the relaying signal by self-cancellation and then decodes the data signal received from the other source. For this wireless-powered two-way relay system, we propose two secure relay protocols based on power splitting and time switching techniques. The two protocols are power splitting-based two-way relaying (PS-TWR) and time switching-based two-way relaying (TS-TWR), in which the relay, respectively, controls the power splitting ratio (p) and time switching ratio (α), in order to achieve a balance between the data receiving and the energy harvesting. The optimal values of p and α for each protocol are found analytically to maximize the minimum guaranteed secrecy capacity (CSmin) considering multiple eavesdroppers in high signal-to-noise ratio environments. Numerical results show that both the PS-TWR and TS-TWR protocols using the optimized values of p and α achieve the near-optimal CSminno matter how many eavesdroppers exist anywhere. Comparisons of the two protocols in various scenarios also show that PS-TWR achieves better CSminthan TS-TWR because PS-TWR inherently has a shorter vulnerable time for eavesdropping than TS-TWR.
A two-hop relay network is considered, in which an eavesdropper can overhear the relaying signal. To prevent the eavesdropper from decoding this signal, a destination transmits a jamming noise while a source transmits the data signal to the relay. At the same time, the relay can harvest energy from both the source signal and the jamming noise, and use this harvested energy to forward the received signal to the destination. In such a wireless-powered relay system with cooperative jamming, we propose two adaptive relaying schemes based on power splitting and time switching techniques. In the proposed power splitting-based relaying (PSR) and time switching-based relaying (TSR) schemes, the relay controls the power splitting ratio (p) and time switching ratio (α), respectively, in order to achieve a balance between signal processing and energy harvesting. We find analytically the optimal values of p and α in each scheme to maximize the secrecy capacity under the assumption of high signal-to-noise ratio (SNR). Interestingly, although the eavesdropper's channel state information (CSI) is used in the derivation of the optimal control parameters (p and α), they are shown not to be affected by the eavesdropper's CSI in a high SNR regime. This implies that the proposed schemes can be effective even for practical environments where there is no eavesdropper's CSI. Furthermore, simulation results show that they well coincide with the exact solutions in practical environments even though the closed-form solutions are obtained with a high SNR assumption. Moreover, the comparisons of PSR and TSR in various scenarios show that the two relaying schemes have complementary performances depending on the network conditions. Specifically, PSR achieves greater secrecy capacity than TSR when the channel condition is unfavorable to the eavesdropper for wiretapping.
In this paper, we consider a two-way relay system in which two users exchange data via a relay based on analog network coding (ANC) when multiple eavesdroppers exist. The relay replenishes energy from the two users’ signal and utilizes it to forward the ANC signal to each user. Each user removes its own signal from the received signal through self-interference cancellation and decodes the desired data signal. On the other hand, the eavesdroppers overhear the relaying signal and attempt to recover the data of two users. For this ANC-based two-way relay network with multiple eavesdroppers, we propose two secure ANC protocols: power splitting-ANC (PS-ANC) and time switching-ANC (TS-ANC), in which the relay determines the power splitting ratio ($\alpha )andtimeswitchingratio(\beta ),respectively,tobalancebetweentheenergyharvestingandthedatareception.Theoptimal\alpha and\beta foreachprotocolareobtainedanalyticallytomaximizetheminimumachievablesecrecyrate(S_{\text {min}})inconsiderationofmultipleeavesdroppers.AnalyticalresultsshowthatboththePS−ANCandTS−ANCprotocolswiththeoptimal\alpha and\beta accomplishthenear−optimalS_{\text {min}}$irrespective of the locations and number of eavesdroppers. The comparison of these two protocols in various network environments exhibits that PS-ANC has a better performance than TS-ANC when the network conditions are unfavorable for wiretapping by the eavesdroppers.
To solve security vulnerability and energy scarcity problems in relay, we propose two secure relaying protocols, power splitting-based relaying (PSR) and time switching-based relaying (TSR), in a wireless-powered relay network with destination-assisted cooperative jamming. In these protocols, the relay adaptively controls the amount of energy harvested from the received signals using PS or TS policy, considering information leakage to the eavesdropper. We first prove the convexity of the secrecy outage probability with respect to the PS ratio ($\rho )andTSratio(\alpha ),andthenderivetheclosed−formexpressionsoftheoptimal\rho and\alpha forminimizingsecrecyoutageunderthesignal−to−noiseratio(SNR)assumption.NumericalresultsrevealthattheproposedPSRandTSRprotocolsusingthederived\rho and\alpha canachievenear−optimalperformanceintermsofsecrecyoutage.Itisobservedthattheoptimal\rho and\alpha $do not depend on the eavesdropping channels in a high SNR regime such that the near-optimal secrecy outage can be achieved practically without knowledge of the eavesdropper location. Furthermore, intensive simulations reveal that it is advantageous to allocate more power to energy harvesting for PSR, whereas more time to signal processing for TSR to minimize secrecy outage.
In this paper, we propose a self-dependent two-way secure communication where two sources exchange confidential messages via a wireless powered untrusted amplify-and-forward (AF) relay and friendly jammer (FJ). By adopting the time switching (TS) architecture at the relay, the data transmission is accomplished in three phases: Phase I) Energy harvesting by the untrusted relay and the FJ through non-information transmissions from the sources, Phase II) Information transmission by the sources and jamming transmissions from the FJ to reduce information leakage to the untrusted relay; and Phase III) Forwarding the scaled version of the received signal from the untrusted relay to the sources. For the proposed system, we derive a new closed-form lower bound expression for the ergodic secrecy sum rate (ESSR). Numerical examples are provided to demonstrate the impacts of different system parameters such as energy harvesting time, transmit signal-to-noise ratio (SNR) and the relay/FJ location on the secrecy performance. The numerical results illustrate that the proposed network with friendly jamming (WFJ) outperforms traditional one-way communication and the two-way without friendly jamming (WoFJ) policy.
The broadcast nature of the wireless medium allows unintended users to eavesdrop on confidential information transmission. In this regard, we investigate the problem of secure communication between a source and a destination via a wireless energy harvesting untrusted node that acts as a helper to relay the information; however, the source and destination nodes wish to keep the information confidential from the relay node. To realize the positive secrecy rate, we use destination-assisted jamming. Being an energy-starved node, the untrusted relay harvests energy from the received radio-frequency (RF) signals, which include the source's information signal and the destination's jamming signal. Thus, we utilize the jamming signal efficiently by leveraging it as a useful energy source. At the relay, to enable energy harvesting and information processing, we adopt power splitting (PS) and time switching (TS) policies. To evaluate the secrecy performance of this proposed scenario, we derive analytical expressions for two important metrics, viz., the secrecy outage probability and the ergodic secrecy rate. The numerical analysis reveals design insights into the effects of different system parameters such as PS ratio, energy harvesting time, target secrecy rate, transmit signal-to-noise ratio (SNR), relay location, and energy conversion efficiency factor, on secrecy performance. Specifically, the PS policy achieves better optimal secrecy outage probability and optimal ergodic secrecy rate than that of the TS policy at higher target secrecy rate and transmit SNR, respectively.
In this paper, we investigate the physical layer security (PLS) of cooperative wireless-powered networks where a source transmits confidential information to a destination with the aid of wireless-powered intermediate nodes equipped with multiple antennas in the presence of a passive eavesdropper. We consider two generalized joint relay and jammer selection (GJRJS) frameworks based on the power splitting (PS) and time switching (TS) techniques, respectively. Specifically, the intermediate nodes which cannot decode the source signal successfully are selected to act as friendly jammers to transmit artificial noise, and the remaining nodes are exploited as relays to simultaneously forward the source signal through cooperative beamforming. We further propose two cooperative secure beamforming (CSB) schemes for the PS-based GJRJS (PS-GJRJS) and TS-based GJRJS (TS-GJRJS) frameworks, respectively. To be specific, we investigate the optimization of the beamforming vector of our selected relays for maximizing the secrecy rate of the source–destination transmission. A closed-form solution is derived under the assumption of available instantaneous channel state information (CSI) of the main link and statistical CSI of the wiretap link. In addition, we also illustrate that the pure relay selection (PRS) scheme is a special case of our GJRJS framework at high signal-to-noise ratios (SNRs). The numerical results show that the proposed CSB scheme achieves a higher secrecy rate than the traditional maximal ratio transmission (MRT) method for both the PS-GJRJS and TS-GJRJS frameworks. Additionally, the GJRJS framework outperforms the PRS as well as the joint best relay and jammer selection (JBRJS) methods in terms of secrecy rate.