Abstract

In wireless communication systems, for secure communication between a transmitter and receiver over the communication channel, the physical layer security is widely utilized. The paper presents a dual-hop wireless full-duplex relay (FDR) network with a source relay and destination relay between two nodes and listening devices. The relay and source use energy harvesting to gain energy from power beacon. Two cooperative techniques are utilized to investigate the amplify-forward (AF) and decode-forward (DF) secrecy capacity in the energy harvesting power splitting system. It is shown that the secrecy performance of an AF relay is better than the secrecy performance of a DF relay in the given form. At 40-meter distance between the relay and the eavesdropper in an energy harvesting system, the AF relay outperforms the DF relay. The simulation is performed using the Monte-Carlo method in MATLAB.

1. Introduction

Cooperative techniques (AF and DF) are significant techniques in wireless communication which play a vital role in wireless networks utilized widely in different branches and applications, including green monitoring systems, social networks, Internet of Things (IoT), and banking systems [1–4]. Thus, the physical layer security of cooperative relaying systems has recently become a major research scope of direction. Significant amount of work has been done in physical layer security to improve secure communication and reduce limitations in cooperative relay networks at both indoor and outdoor propagating environments [5–9].

In [5], a radio signal transmission was secured using an optimum design model from source node to destination through the DF network. In [6], a new two-phase protocol was presented for efficient energy transfer and information relaying, in which the relay operates in full-duplex mode with simultaneous energy harvesting. Ref [7] presents cooperative schemes in dual-hop relaying systems with EH over indoor communication channels categorized by log-normal fading. Similarly, in [8], the cooperative systems are considered with joint time allocation and power splitting schemes.

In addition to enhancing spectrum efficiency, wireless nodes also have major issues in cooperative wireless networks, particularly in energy considerations. In [10], the authors investigated EH to improve the system performance and secrecy rate in a jamming system but did not show the full power of the EH system. In [11], the performance and the secrecy rate for both TS and PS protocols were investigated, while [12] investigated the outage probability (OP) over the Rayleigh channel for DF and AF schemes in multiple antennas, respectively. Nevertheless, the EH from the interference node is not considered, and no interference is used, such that only EH from the source is analyzed [13, 14].

In [15], a secrecy performance is investigated comprising a single-hop relay system with improvement of EH of 8.89% for the AF relay and of 9.83% for the DF relay between the eavesdropper and the relay. Ref [16] investigated the secrecy performance of a single-hop relay network and observed a performance improvement of 30.47% for the DF cooperative scheme and of 23.63% for the AF cooperative scheme between the eavesdropper and the relay. A geometric programmed (GP) method in [17] was implemented on a full duplex relay network for physical secrecy in a dual-hop relay system. The GP program was applied to power allocation problem on the transmitter side. In [18], the secrecy rate performance of nonorthogonal multiple access and backscatter communication is considered. In [19], they investigated physical layer security ambient backscatter nonorthogonal multiple access in channel estimation errors and imperfect successive interference cancellation with emphasis on reliability and security. The authors in [20] investigated three hop relay cooperative communication networks to perform the two schemes AF and DF, improved by 50.55% (AF) and by 44.2% (DF).

In the current study, we have investigated a dual-hop relay cooperative network with a source, relay, eavesdropper, and EH scheme. The goal of this research is to increase the security performance of such a system, using cooperative scheme AF and DF techniques. We have examined the secrecy performance of our proposed model. The contribution of the present work is summarized as follows. (i)First, we have investigated a dual-hop wireless relay system containing a single source and a single destination relay, along with two nodes and one eavesdropper(ii)To propose AF and DF schemes and increase the system secrecy performance in the cooperative network(iii)Various parameters, like the time switching protocol, energy harvesting, power splitting ratio, interference relay, and eavesdropper distance, are investigated. The secrecy performance of designed schemes is discussed and compared to the secrecy performance in previous publications

1.1. Paper Organization

The layout of the paper is shown in Table 1.

Table 1 
Paper layout.

2. System Model

In this section, we consider a network that relies on a single hop and consists of a relay node (), source (), eavesdropper (), and destination node () as presented in Figure 1. It contains power from a beacon (). In Figure 1, , , , and define the complicated channel gain from to , while and define the complex channel gain from to . Additionally, we note that noise is complex. Additive white Gaussian noise (AWGN) at each node has zero mean and variance such that no interference is available. Additionally, the relay function is performed with mutual full-duplex relay and half-duplex relay mode techniques.


Figure 1 
Dual-hop relay network.
2.1. Energy Harvesting Technique

In the designed technique, the nodes relay () and source () harvest energy from the power beacon (). That energy is used to transmit the signals from source to and to . For high quantities, the time switching- (TS-) based protocol is used for energy harvesting as shown in Figure 2.


Figure 2 
Time switching-based protocol.

The energy harvesting by and is given by [17]

The competence coefficient of the proposed method is denoted by , and the power transmitted by is denoted by and . represents the time taken to transmit the specific block by and [17]. Thus, the power transferred by and is given by

2.1.1. Decode-Forward Relay Scheme

This scheme consists of two phases, the first of which is shown in Figure 3. During the initial transmission, the source sends a signal to the relay and the relay sends the jamming signal to the eavesdropper at the same time. In time slot , the established signal at the and is given by [17] where the strength of the interference signal from is given by . In the next time slot, as presented in Figure 4, the simply sends the already decoded signal to a valid junction and no longer receives the signal. The source at this point sends the jamming signal to the eavesdropper , and the signal established in time slots at and is expressed as [17]


Figure 3 
Illustration of the signal transmission for the time slot.

Figure 4 
Illustration of the signal transmission in the time slot.
2.1.2. Amplify-Forward Relay Scheme

This scenario part has two phases; further, in the first phase, it is the DF scheme. During the initial stages, the signal acquired at and the eavesdropper is applied; relay transmits enhanced performance of signals received at the destination in the second phase. The source sends jamming signals to and , in the time slot , which are received at the same time, given

Here, we defined the scaling factor . The fluctuation of the channel coefficient is where is the AWGN noise variance.

3. Secrecy Capacity Performance

Further, we present a performance secrecy model in terms of secrecy rate. The signal information that may be transferred over a wireless channel to an eavesdropper is defined as the secrecy rate. The next two sections investigate the secrecy rate in AF and DF cooperative networks.

3.1. DF Scheme

The secrecy capacity at and is defined by equations (3)–(6) for a full-duplex relay in [17]. Thus, we obtain

Here, we define

Using equations (6) and (7), the achievable secrecy rate is given by , where it is given in

3.2. AF Scheme

Using further equations (7) and (8) at and , the secrecy capacity rate can be obtained from

The secrecy rate is here obtained as given as , whereas

4. Numerical Results and Performance

This section presents the numerical results for the investigation of the secrecy performance of the proposed system model, in dual-hop EH and AF and DF cooperative scenarios in terms of relay distance. The numerical results based on the simulation model are shown in Figure 5; the , , and are assumed to be the presence of a line of sight (LOS); moreover, , , , and indicate the distances between and nodes, between and , between and , between and , between and , and between and . The distance between and nodes can be, respectively, given as


Figure 5 
Numerical model.

Source, relay, and destination are located in the line of sight (LOS). The channel model configuration describes the channel between any two nodes, which is uniformly distributed within , with path loss exponent [17].

We assume that the transmission power of the beacon is and the noise power is .

Furthermore, it is assumed that . Moreover, , , and .

The parameters used for the simulation of this research are shown in Table 2.

Table 2 
Parameter used for the simulation.

In Figures 6 and 7, we give the plot of the security performance AF and DF dual-hop scheme and distance between relay () and destination (), when , , and in the proposed EH system and PS EH system. The plot of secrecy capacity shows that the secrecy capacity decreases with increasing distance between destination and relay, but at the same time due to the power splitting receiver in the EH system, the secrecy rate is quite high which is good. Also, this figure clearly shows that the AF single-relay scheme gives a better secrecy rate than the DF single-relay scheme.


Figure 6 
Secrecy rate vs. for the EH system.

Figure 7 
Secrecy rate vs. for the proposed EH and PS system.

In Figures 8 and 9, we compare the secrecy rate distance between relay and eavesdropper between the AF and DF schemes, when and . The graph shows the secrecy rate in the energy harvesting (EH) system depending on the distance between and . In the proposed EH PS system, the secrecy rate is very high for the power splitting receiver. Also, in the AF scheme, the secrecy rate is better than that in the DF Scheme. Therefore, to increase the secrecy rate, it is important to use a share of useful power to relay jamming signals in both AF and DF.


Figure 8 
Secrecy rate vs. for the energy harvesting system.

Figure 9 
Secrecy rate vs. for the energy harvesting power splitting system.

In Figures 10 and 11, we plot the average secrecy rate as a function of the path loss exponent factor in the single-relay AF and DF schemes, when , , and . Path loss plays a vital role in the calculation of the secrecy rate. The graph shows that as we increase the path loss exponent, the secrecy rate decreases gradually in both the existing EH systems and the proposed EH PS system. It is shown that the increment in the path loss exponent degraded the system secrecy capacity in both AF and DF schemes. This implies that self-interference should be minimized.


Figure 10 
Secrecy capacity rate vs. PLE for the EH system.

Figure 11 
Secrecy capacity rate vs. PLE for the EH PS system.

The comparison of the cooperative proposed techniques with the published literature is shown in Table 3.

Table 3 
Performance comparison of the cooperative scheme concerning their secrecy rate.

5. Conclusions

In this study, we have proposed the energy harvesting single-relay cooperative system, to enhance the performance of secure wireless communications in the existence of one eavesdropper and relay . Under a total transmitted power constraint of 30 dBm and noise power of -40 dBm, the secrecy performance of a single-relay wireless cooperative system is investigated, and an innovative single-relay technique has been applied. In the proposed technique, each transmits a signal to the and gets a transmission signal at the same time. Two cooperative schemes have been examined: amplify-forward (AF) and decode-forward (DF) in energy harvesting. The results show that secrecy rate performance is improved by AF FDR for single relay to 65.5% and DF FDR for single relay to 52.5% in the energy harvesting power splitting system. Furthermore, we show that an increase in the path loss exponent degrades the performance of the system.

Notations

FDR:Full duplex relay
HADF:Hybrid decode forward
LOS:Line of sight
EPA:Equal power allocation
:Transmission period of energy harvesting
:Energy conversion efficiency of an eavesdropper
:Power relay jamming
:Signal of power relay
:The energy efficiency of the destination
:Noise variance
:The fluctuation of the channel coefficient
:Channel gain source to relay
:Time switching factor
PE:Power signal eavesdropper
PB:Power Beacon
dBR:Distance beacon relay
:Relay eavesdropper.

Data Availability

All the data have been included in the study.

Conflicts of Interest

The authors declare that they have no conflicts of interest.