This paper investigates the physical layer secrecy performance for an underlay wiretap spectrum sharing network with optimal relay and antenna selection (ORAS). It jointly selects a transmit antenna at a secondary source, a receive antenna at its destination, and a relay between them to maximize the secrecy rate at the destination under a passive eavesdropping scenario. We derive novel, exact expressions for secrecy outage probability (SOP) and secrecy throughput (ST) in a single integral-form. We also provide their accurate approximations in closed-form. Considering three distinct scenarios depending on whether the main link is stronger than the wiretap link and the nature of the primary interference constraint, we obtain different useful system design insights. Under a proportional interference constraint, secrecy diversity gain is achieved only when the main link is stronger than the wiretap link, otherwise the diversity gain is lost and leads to an SOP floor. Under a fixed interference constraint, the SOP floor is further increased. Through numerical results, we show the impact of different signal combining strategies by the eavesdropper on the SOP and ST. We also illustrate the efficacy of the ORAS scheme as compared to other relay and antenna selection schemes.
This paper investigates the physical layer secrecy performance for an underlay wiretap spectrum sharing network with optimal relay and antenna selection (ORAS). It jointly selects a transmit antenna at a secondary source, a receive antenna at its destination, and a relay between them to maximize the secrecy rate at the destination under a passive eavesdropping scenario. We derive novel, exact expressions for secrecy outage probability (SOP) and secrecy throughput (ST) in a single integral-form. We also provide their accurate approximations in closed-form. Considering three distinct scenarios depending on whether the main link is stronger than the wiretap link and the nature of the primary interference constraint, we obtain different useful system design insights. Under a proportional interference constraint, secrecy diversity gain is achieved only when the main link is stronger than the wiretap link, otherwise the diversity gain is lost and leads to an SOP floor. Under a fixed interference constraint, the SOP floor is further increased. Through numerical results, we show the impact of different signal combining strategies by the eavesdropper on the SOP and ST. We also illustrate the efficacy of the ORAS scheme as compared to other relay and antenna selection schemes.
To address secrecy performance in a multi-relay underlay wiretap spectrum sharing network, we present a secrecy rate-optimal relay and antenna selection scheme, which serves as a fundamental benchmark. It jointly selects a transmit antenna at a secondary source, a receive antenna at its destination, and a relay between them to maximize the secrecy rate at the destination under the malicious attempt of an eavesdropper. We derive exact and asymptotic expressions for the secrecy outage probability, which accurately reveal the secrecy diversity order and the coding gain. Under a proportional interference constraint, full secrecy diversity order is achieved only when the main link is stronger than the wiretap link, otherwise the diversity gain is lost. We then consider a practical scenario where the secondary users have only the mean channel power gains of the wiretap links. Under such channel state information (CSI), we propose a statistical CSI-based relay and antenna selection scheme and numerically show that this can be used as a better performance/complexity tradeoff. Both the schemes substantially outperform the conventional relay and antenna selection scheme, which requires no CSI about the wiretap links.
This paper investigates the secrecy performance of a single-input multiple-output (SIMO) based underlay cognitive radio networks. In particular, a single-antenna secondary transmitter transmits its secret message to a multi-antenna equipped secondary node in the presence of a multi-antenna equipped passive eavesdropper under a peak interference constraint at the single-antenna primary receiver. We proficiently derive the expressions for secrecy outage probability (SOP), intercept probability, and ergodic secrecy capacity (ESC) for the considered system over$\alpha -\mu fadingchannels.Further,wecarryouttheasymptoticanalysisofSOPandinterceptprobabilityundertwocasesofinterest;1)whentheaveragesignal−to−noiseratio(SNR)ofthemainlink,i.e.,betweenthesecondarysourceandsecondarydestination,goestoinfinitywithafixedaverageSNRofwiretaplinkbetweenthesecondarysourceandsecondaryeavesdropper,and2)whentheSNRsofboththemainandwiretaplinkstendtoinfinity.Wecaninferthatasecrecydiversityorderof\frac {\alpha _{D}N_{D}\mu _{D}}{2}canbeachievedundercase1,where\alpha _{D}and\mu _{D}arethemainlinkfadingparameters,andN_{D}$denotes the number of antennas at the destination. Whereas, under case 2, the system’s secrecy diversity order becomes zero. Moreover, we also present some interesting findings for the ESC when the interference constrained secondary transmitter power is considerably high. Further, we validate our analytical framework through extensive simulation and numerical results, and demonstrate the effects of system/channel parameters on the secrecy performance of the considered system. Our results reveal that the higher number of eavesdropper antennas can have a more deleterious impact on the system’s secrecy performance.
Secure data transmission in future high-capacity high-coverage multi-tier hierarchical networks, for which cognitive radio(CR) has emerged as an essential recipe, is of utmost importance. This paper investigates the secrecy outage performance of selection combining(SC) in CR networks(CRNs) over Rayleigh fading channels. In a single-input multiple-output(SIMO) wiretap channel, a secondary user transmits confidential messages to another secondary user, which is equipped with( 1)B Bn n ≥ antennas. Meanwhile, a passive eavesdropper, which is equipped with( 1)E En n ≥ antennas, intends to overhear the messages. Both the legal receiver and the eavesdropper adopt SC scheme to process the received multiple signals. The secondary transmitter uses the underlay strategy to guarantee the quality of service of the primary user without spectrum sensing. Compared to the work proposed by Maged Elkashlan et al. in Ref. [1], we present an alternative method to derive the closed-form expression for the secrecy outage probability(SOP) and develop a simplified SOP when the maximal transmit power at the secondary user is sufficiently high. Our results reveal the impact of the primary network on the secondary network with a multi-antenna wiretap channel and simulations are conducted to validate the accuracy of our proposed analytical models.
We propose and analyze transmit antenna selection (TAS) to enhance physical layer security in a wiretap channel with multiple antennas at the transmitter, the receiver, and the eavesdropper. We consider the practical scenario of passive eavesdropping, where the transmitter does not have any channel state information (CSI) of the eavesdropper's channel. In the main channel between the transmitter and the receiver, we select a single antenna at the transmitter that maximizes the instantaneous signal-to-noise ratio (SNR) at the receiver. At the receiver and the eavesdropper, we consider two combining techniques: 1) maximal-ratio combining (MRC) and 2) selection combining (SC). For non-identical Rayleigh fading between the main channel and the eavesdropper's channel, we first derive new closed-form expressions for the exact and asymptotic secrecy outage probabilities. The asymptotic results accurately reveal the secrecy diversity order and the secrecy array gain. Next, we derive new closed-form expressions for the probability of positive secrecy and characterize the ε-outage secrecy capacity. We show that, under TAS/MRC and TAS/SC protocols, the secrecy outage probability approaches zero and the ε-outage secrecy capacity increases with increasing number of transmitter antennas.
In this paper, the physical layer security in cognitive radio networks (CRNs) is investigated. We consider an underlay relay assisted CRN consisting of multiple secondary sources, multiple-antenna destination, a single relay, and multiple eavesdroppers. The destination node performs the maximal-ratio combining under uncorrelated Rayleigh fading channels. In more details, we consider, a secondary source is randomly selected to transmit its data, and a jammer is chosen from the remaining source nodes to send a jamming signal to the eavesdroppers. The closed-form expression of the secrecy outage probability is derived, based on the statistical characteristics of the communication channels, under the primary user's quality of service constraint. The derived analysis gives deep insights into the impact of network parameters on the performance of on the secrecy outage performance. Analytic results are corroborated through Monte Carlo simulation.
Abstract Secure transmission is essential for future non-orthogonal multiple access (NOMA) system. This paper investigates relay–antenna selection to enhance physical-layer security of cooperative NOMA system in the presence of an eavesdropper, where multiple antennas are deployed at the relays, the users, and the eavesdropper. In order to reduce expense on radio frequency chains, selection combining (SC) is employed at both the relays and the users, whilst the eavesdropper employs either maximal-ratio combining or SC to process the received signals. Under the condition that the channel state information of the eavesdropping channel is available or unavailable, two effective relay–antenna selection schemes are proposed. Additionally, the closed-form expressions of secrecy outage probability (SOP) are derived for the proposed relay–antenna selection schemes. In order to gain more deep insights on the derived results, the asymptotic performance of the derived SOP is analyzed. In simulations, it is demonstrated that the theoretical results match well with the simulation results and the SOP of the proposed schemes is less than that of the conventional orthogonal multiple access scheme obviously.