Secrecy performance of a generalized partial relay selection protocol in underlay cognitive networks

This paper analyzes the unified performance of partial relay selection protocol for multiple relay assisted free space optical (FSO) network over exponentiated weibull (EW) links. The unification has been done for heterodyne and intensity modulation/direct (IM/DD) detection techniques. We have considered a decode and forward (DF) based network consisting of multiple finite sized two way relays (TWR) between two distant terminals. In partial relay selection protocol, two TWRs are chosen in order to create the bidirectional communication path between the two terminals. The considered protocol compresses the requirement of channel state information (CSI). More specifically, we derive the unified expressions for probability density function (PDF) and cumulative distribution function (CDF) of instantaneous signal to noise ratio (SNR) over EW turbulent FSO link along with pointing error and path loss. We then utilize the unified statistics in obtaining the outage probability expression for the considered network. It is shown by analytical and simulation results that the relay selection protocol based on partial CSI completely outperforms the single relay selection protocol for both detection techniques.

Energy and spectrum efficiency for energy management systems based on wireless sensor networks in intelligent structures and powered by ambient energy harvesting (EH) are the main problems in wireless sensor networks. Herein, we consider relay selection methods. To address this issue, we proposed the optimal multiantenna power beacon opportunistic relay selection (OMPB-ORS) protocol, which uses decoding and forward methods, in which the relay wireless sensor nodes and the second source are energy-restricted and can harvest energy from a power beacon (PB) multiantenna to transmit aggregated information data from source to destination. The proposed protocol based on specific s witching t ime r eceiver a rchitecture e nhances e nd-to-end p erformance f or m aximum h ardware impairments and interference for the transceiver. To evaluate the performance, we compared our proposed protocol with best ORS (B-ORS), conventional ORS (C-ORS), and hybrid partial relay selection (H-PRS) protocols. Using the Rayleigh-fading channel, the simulation is driven based on asymptotic and exact form expressions of throughput (TP) and outage probability (OP). Simulation results show that the OMPB-ORS protocol achieves a higher TP and OP than all compared protocols.

This paper investigates a time-switching energy-harvesting system in which a source communicates with a destination via energy-constrained amplify-and-forward relays. To exploit the benefit of using multiple relays, we propose a relay scheduling called consecutive relay selection (CRS), which allows all relays to assist the source-to-destination communication, to improve the transmission efficiency of the time-switching policy. The partial relay selection (PRS) is examined for performance comparison. The selected relay in the PRS protocol is considered in two cases: in one, it is selected based on the first-hop channel gains (PRS-1 protocol), and in the other, it is selected based on the second-hop channel gains (PRS-2 protocol). For performance evaluation, the analytical expressions of the outage probability and throughput for Nakagami-m fading channel are derived. Our results show that the CRS protocol outperforms the PRS protocol in terms of throughput, the PRS-1 protocol achieves better performance than the PRS-2 protocol. Moreover, we discuss the effects of various key system parameters on system performance, such as the energy-harvesting ratio, source transmission rate, and locations of relays, to provide insights into the various design choices.

In this paper, we focus on the half-duplex (HD) relaying with partial relay selection (PRS) scheme using destination-assisted jamming (DAJ). We consider one source (S), one destination (D), one passive eavesdropper and multiple amplify-and-forward (AF) relays. The relay node is selected based on the best instantaneous signal-to-noise ratio (SNR) of the first hop. Closed-form expressions for lower-bound of ergodic secrecy capacity (ESC) and secrecy outage probability (SOP) are derived over independent and identically distributed (i.i.d.) Rayleigh fading environment. Moreover, we present a comparison between the proposed system and the secure AF relaying system with reactive relay selection (RRS). In the RRS, the relay is chosen based on the best SNR of the second hop. Simulation results are presented to verify the exactness of our proposed mathematical analysis.

This paper studies the security performance of a multi-tag backscatter communication system, where a reader exchanges its information with multiple distributed tags in the presence of an eavesdropper. The system security performance is assessed using the secrecy outage probability (SOP), which quantifies the likelihood that the system secrecy capacity drops below a specified threshold. The paper provides a mathematical analysis on the communication links, considering Rayleigh fading, and investigates the effect of system monostatic and bistatic RFID configurations on the overall security. An optimal tag selection scheme is proposed to maximize the secrecy capacity by choosing the tag with the best link between the reader and the eavesdropper. Moreover, an analytical expression is derived for the system SOP, which incorporates the joint probability distributions of channel gains and the asymptotic SOP is provided as the signal-to-noise ratio increases. Simulation results are presented to verify the theoretical analysis, where the simulation results closely match the analytical predictions, confirming the accuracy of the proposed SOP analysis. Moreover, the asymptotic analysis offers an upper bound on the outage probability, consistent with theoretical analysis.

In view of the scarcity of spectrum resources in wireless communication, it is studied in this paper over the two-hop cognitive secrecy transmission scheme of decoding and forwarding (DF) unmanned aerial vehicles (UAVs) assisted relay with energy harvesting under Nakagami-m channel. It is worth noting that the terminal node is equipped with multiple antennas and the optimal antenna selection can be adopted for signal reception. Meanwhile, the UAV assisted relay uses time switching (TS) and power splitting (PS) energy harvesting techniques and adopts optimal secrecy capacity selection scheme. It is successfully derived for the exact closed form expressions of non-zero secrecy capacity probability and optimal secrecy outage probability while the eavesdropper has no channel state information (CSI). Moreover, the system asymptotic secrecy outage probability demonstrates the secrecy diversity order and secrecy diversity gains of the UAV assisted relay cognitive network under Nakagami-m channel. Furthermore, joint optimization of power splitting factor and other parameters can effectively increase the system secrecy capacity and improve the system secrecy performance. Simulation results verify the correctness of the theoretical derivation and the effectiveness of the proposed scheme, which demonstrate that the proposed algorithm outperforms the other compared schemes.

In this paper, we propose a relay selection method in an amplify-and-forward (AF) scenario considering complete outdated channel state information (CSI) of all links. Differing from the methods in the literatures considering only outdated CSI over the link from the relay to the destination, another type of outdated CSI, i.e., the outdated CSI over the link from the source to the relay, is also considered in the relay selection. In order to overcome the effect of these outdated CSIs due to feedback delay, we use minimum mean square error (MMSE) estimation to predict the SNRs of the source-to-relay links and the relay-to-destination links at the forwarding instant. Along with the relay selection, an effective power allocation method is proposed to optimize the power allocation between the source and the relays. Moreover, the expression of the system outage probability is derived. The simulation results show that the proposed method, along with the power allocation, improves the outage performance of the system.

Unlike prior works assuming perfect attack detection, this paper investigates the physical layer security of a simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided network under a full-duplex active eavesdropper in the more realistic scenario where its jamming remains undetected by the legitimate transmitter. Assuming Nakagami-m fading channels, we first derive the probability density functions (PDFs) of the signal-to-interference ratios (SIRs) at both the legitimate user and the eavesdropper. Then, using the PDFs, we obtain novel closed-form expressions for key secrecy metrics, including the probability of nonzero secrecy capacity (PNSC), secrecy outage probability (SOP), and average secrecy capacity (ASC). Moreover, the asymptotic PNSC, SOP, and ASC at high signal-to noise ratio (SNR) are also derived. Based on those asymptotic expressions, we present compact expressions for several key performance indicators: 1) the secrecy diversity order and the secrecy array gain of the SOP, and 2) the high SNR slope and the high SNR power offset of the ASC. Results demonstrate that, compared to the passive eavesdropper scheme, the active jamming attack carried out by Eve will not cause any loss in secrecy diversity gain and high SNR slope, but only result in the loss of secrecy array gain and high SNR power offset. Finally, we verify our analytical results via simulations.

Physical layer security in SWIPT-based cooperative vehicular relaying networks

In this paper, we investigate the performance of asymmetric radio frequency (RF) and free space optical (FSO) dual-hop cooperative relay network along with a direct RF link between source and destination. The FSO link experiences double generalized Gamma turbulence in the presence of the generalized non-zero boresight pointing errors, and RF links experience non-identically distributed Nakagami-m fading. Moreover, considering both cognitive radio and non-cognitive scenarios, a partial relay selection (PRS) strategy has been employed. Furthermore, both relay selection and underlay power restriction are governed with the outdated channel state information (CSI). We also assume both heterodyne and intensity modulation/direct detection methods in the FSO receiver. Under the assumption of amplify-and-forward relaying and PRS, we derive closed-form expressions for outage probability (OP) of both scenarios, while bit-error probability and ergodic capacity of the non-cognitive scenario are also obtained. The asymptotic expressions of OP and diversity order of this network are derived for both perfect CSI and outdated CSI cases. It is demonstrated that the diversity order is a function of the fading severity of the RF links, turbulence parameters of the FSO link, and pointing error, regardless of interference channel parameter of the primary user.

In this paper, we study the secrecy performance of a wirelessly powered relay-aided system, where a pair of legal users (source-destination) communicate in the presence of multiple untrusted relays. All of the nodes mentioned above are energy constrained and powered by a dedicated power beacon (PB). To prevent the untrusted relays from intercepting the source message and to achieve positive secrecy rate, the destination-based cooperative jamming technique is employed. Besides, the optimal time allocation coefficient to maximize the secrecy throughput and the optimal transmit power of PB to maximize the secrecy energy efficiency are addressed. Specifically, three relay selection schemes with various requirements for channel state information (CSI), i.e., random relay selection, partial relay selection and optimal relay selection are also proposed to enhance the system security further. Finally, simulation results indicate the cooperative jamming technique indeed achieve positive secrecy rate and the proposed optimization strategies can improve the system performance.

This paper studies on the relaying selective matter in amplify-and-forward (AF) cooperation communication with full-duplex (FD) activity. Various relay choice models supposing the present of different instant information are investigated. We examine a maximal relaying choice that optimizes the instant FD channel capacity and asks for global channel state information (CSI) as well as partial CSI learning. To make comparison easy, accurate outage probability clauses and asymptote form of these strategies that give a diversity rank are extracted. From that, we can see clearly that the number of relays, noise factor, the transmittance coefficient as well as the information transfer power had impacted on their performance. Besides, the optimal relay selection (ORS) model can promote than that of the partial relay selection (PRS) model.

Cooperative communication in wireless relay systems can improve the physical layer security, and the relay selection has great impacts on the security performances. In this paper the relay selection in Amplify-and-Forward (AF) cooperative networks is investigated. The system model constitutes of a source, an eavesdropper, a destination, and a number of intermediate nodes with secrecy constraints. The proposed optimal selection (OS) algorithm is based on the instantaneous channel state information (CSI) of two hops, jointly protects the target destination against eavesdropping and interference. To simplify the complexity of OS, the suboptimal selection (SS) algorithm is also presented, which is based on the instantaneous of the first hop and the statistical CSI of the second hop respectively. The secrecy capacity and secrecy outage probability of these two relay selection algorithms are analyzed. Simulation results of OS and SS validate our theoretical analysis and show enhancement in the secrecy rate over the direct transmission.

We study a dual-hop relaying system, composed of mixed radio frequency (RF)/free-space optical (FSO) links. Partial amplify-and-forward relay selection is assumed, which is based on outdated channel state information (CSI). The RF link is subject to Rayleigh fading, while the FSO link is affected by atmospheric turbulence, modeled by Gamma–Gamma distribution. Novel analytical expressions for the outage probability and average bit error rate (BER) are derived. Numerical results are presented and validated by Monte–Carlo simulations. The outage probability and average BER dependence on turbulence strength, average signal-to-noise ratio (SNR) over RF hop, average electrical SNR over FSO hop, number of relays, and rank of selected relay, are also investigated, while the effect of time correlation between current source-relay channel and its outdated CSI, is considered. The results illustrate that the outdated CSI used for the relay selection has a strong effect on the system performance, especially in weak turbulence conditions of the FSO hop. Furthermore, the improvement of the system performance with an increase of the number of the relays is highly dependent on the FSO channel state.

In this paper, we study outage probability (OP) and diversity order of a M-source and N-relay wireless network that combines network coding (NC) and relay selection (RS). More specifically, a decode-and-forward (DF) relaying protocol is considered and the network-encoding vectors at the relays are assumed to constitute a maximum distance separable (MDS) code. Single relay selection (SRS) and multiple relay selection (MRS) protocols are investigated, where the best relay and the L best relays forward the network-coded packets to the destination, respectively. An accurate mathematical framework for computing the OP is provided and from its direct inspection the following conclusions on the achievable diversity are drawn: 1) the SRS protocol achieves diversity order equal to two regardless of M and N and 2) the MRS protocol achieves diversity order equal to L + 1 if L <; MandequaltoN + 1 if L ≥ M.These analytical findings are substantiated with the aid of Monte Carlo simulations, which also show that RS provides a better OP than NC based on repetition coding if L ≥ M.