In the past few years, there has been a rapid increase in demand on transmitting data over the open wireless medium. Severe issues of information security and privacy thus arise, as the wireless transmissions may be intercepted by any unintended receiver in the network. There is a need to design the transmission system in an efficacious way, such that the available space and time can be used adequately. This becomes a challenging job as there are random variations in the channel quality due to deleterious effects of the multi-path fading. Hence, to improve the transmission reliability, coverage probability and throughput, relay aided communication draw in great attention from both academia and industry. Relays provide the advantage of cooperative diversity, where the directly transmitted signal and the relayed signal can be combined at the receiver using various diversity combining schemes to mitigate the fading effect. In this paper, we review the secrecy performance of dual-hop cooperative relay system with diversity reception and relay selection. The significance and secrecy effect of channel knowledge at the transmitter is also studied. We have corroborated that CSI knowledge at the transmitter can improve secrecy.
In the past few years, there has been a rapid increase in demand on transmitting data over the open wireless medium. Severe issues of information security and privacy thus arise, as the wireless transmissions may be intercepted by any unintended receiver in the network. There is a need to design the transmission system in an efficacious way, such that the available space and time can be used adequately. This becomes a challenging job as there are random variations in the channel quality due to deleterious effects of the multi-path fading. Hence, to improve the transmission reliability, coverage probability and throughput, relay aided communication draw in great attention from both academia and industry. Relays provide the advantage of cooperative diversity, where the directly transmitted signal and the relayed signal can be combined at the receiver using various diversity combining schemes to mitigate the fading effect. In this paper, we review the secrecy performance of dual-hop cooperative relay system with diversity reception and relay selection. The significance and secrecy effect of channel knowledge at the transmitter is also studied. We have corroborated that CSI knowledge at the transmitter can improve secrecy.
In this paper, a source communicates to the destination with the cooperation of a relay, in the presence of an eavesdropper. All the links undergo Rayleigh fading and perfect decoding at the relays is not considered. The secrecy outage probability expression is evaluated for a decode-and-forward (DF) dual-hop cooperative relay network, both with and without the presence of direct source to eavesdropper transmission link. The performance of the maximal ratio combining (MRC) and selection combining (SC) diversity at the eavesdropper is investigated. Asymptotic and diversity gain analysis for both the single relay and multi-relay system is obtained, when average SNRs of source-relay and relay-destination links are balanced or unbalanced. We have shown that the increase in target secrecy rate and eavesdropper channel quality significantly affects the outage performance of the system. We have investigated the outage probability of optimal relay selection scheme, when either full instantaneous channel state information (ICSI) or statistical channel state information (SCSI) of all the links is available and have shown that there is improvement in the secrecy performance with the increase in the number of relays.
In this paper, the secrecy of a cooperative system consisting of a single source, relay, destination and eavesdropper is analyzed. The threshold-selection decode-and-forward relay is considered, where the relay can correctly decode and forward only if it satisfies a threshold signal-to-noise ratio (SNR). Both destination and eavesdropper take advantage of the direct and relayed transmissions through maximal ratio diversity combining. The secrecy outage probability (SOP) and ergodic secrecy rate are derived in closed-form for different channel state information (CSI) availability. It was observed that when the required rate is low, having CSI knowledge is more advantageous than in the case of higher rate. An increase in the required threshold SNR at the relay can increase the SOP if the relayed link SNR is relatively higher than the direct link SNR. It was also shown that SOP cannot be improved beyond a certain value when keeping either dual-hop link average SNR fixed and increasing the other link SNR, whereas the ergodic secrecy rate can be increased by keeping the source to destination average SNR fixed.
Security is one of the most important issues in wireless communication.Because using wireless channels entails broadcasting data transmissions, malicious nodes can eavesdrop on wireless transmission, which leads to insecure data transmission.Traditional security methods are based on cryptography.Recently, physical-layer security (PLS) has gained much attention as an efficient method of obtaining secure information without using cryptography.PLS protocols employ the physical characteristics of wireless channels such as channel state information (CSI) and the distances between connection links in order to enhance secrecy performances in wireless systems.To enhance secrecy performances, the dual-hop/multi-hop relay protocols can be used efficiently.However, according to my best knowledge, there are few published works considering the impact of hardware impairments on secrecy performances for the wireless relaying networks.Hence, this dissertation examines the diversity-based relay protocols for wireless communication networks in order to improve secrecy performances in presence of hardware imperfections.First, new dual-hop and multi-hop cooperative relaying schemes with various relay selection methods are proposed in order to obtain improved secrecy performance compared with the existing schemes.Second, new joint relay and jammer selection protocols are also considered in order to improve the channel capacity for data links while reducing the channel capacity of eavesdropping links.Finally, this dissertation proposes harvest-to-transmit and harvest-to-jam protocols, where the relay and jammer nodes harvest energy from the radio frequency signal for use in the data transmission and the jamming process, respectively.To evaluate the performance of the proposed protocols over fading channels, this dissertation focuses on deriving the closed-form expressions for secrecy performances.Then, the derived expressions are verified by Monte Carlo simulations, which also present the advantages of the proposed protocols.
Cooperative communications is obviously an evolution in wireless networks due to its noticeable advantages such as increasing the coverage as well as combating fading and shadowing effects. However, the broadcast characteristic of a wireless medium which is exploited in cooperative communications leads to a variety of security vulnerabilities. As cooperative communication networks are globally expanded, they expose to security attacks and threats more than ever. Primarily, researchers have focused on upper layers of network architectures to meet the requirements for secure cooperative transmission while the upper-layer security solutions are incapable of combating a number of security threats, e.g., jamming attacks. To address this issue, physical-layer security has been recommended as a complementary solution in the literature. In this thesis, physical layer attacks of the cooperative communication systems are studied, and corresponding security techniques including cooperative jamming, beamforming and diversity approaches are investigated. In addition, a novel security solution for a two-hop decode-and-forward relaying system is presented where the transmitters insert a random phase shift to the modulated data of each hop. The random phase shift is created based on a shared secret among communicating entities. Thus, the injected phase shift confuses the eavesdropper and secrecy capacity improves. Furthermore, a cooperative jamming strategy for multi-hop decode-and-forward relaying systems is presented where multiple non-colluding illegitimate nodes can overhear the communication. The jamming signal is created by the transmitter of each hop while being sent with the primary signal. The jamming signal is known at the intended receiver as it is according to a secret common knowledge between the communicating entities. Hence, artificial noise misleads the eavesdroppers, and decreases their signal-to-noise-ratio. As a result, secrecy capacity of the system is improved. Finally, power allocation among friendly jamming and main signal is proposed to ensure that suggested scheme enhances secrecy.
In the last decade, multi-hop cooperation has evolved bringing several advantages including coverage improvement, more reliability of wireless links, and power consumption reduction. Still, its application has raised several challenges, such as the need for secure transmission at each hop, algorithms to perform relay selection and the accurate models to facilitate performance analysis. This paper addresses the problem of physical layer (PHY) security in a multi-hop wireless cooperative network, where communication at each hop is assisted by multiple relays forming a cluster, each cluster being surrounded by multiple eavesdroppers which together may tap transmissions from both the source and the relays. The main focus of the study is on analyzing the benefits of various relay selection schemes for protecting the source-destination transmission against the eavesdroppers, which can collude and combine information via diversity combining techniques. To be specific, four relay selection schemes, which differ in the way they employ available measures link quality, are considered to deliver the source information to the destination via a decode-and-forward (DF) strategy. To evaluate the security performance of the multi-hop cooperative link in the presence of colluding eavesdroppers, we derive novel closed-form analytical expressions for the secrecy outage probability (SOP) with consideration of special cases of practical interest.
In the last decade, multi-hop cooperation has evolved bringing several advantages including coverage improvement, more reliability of wireless links, and power consumption reduction. Still, its application has raised several challenges, such as the need for secure transmission at each hop, algorithms to perform relay selection and the accurate models to facilitate performance analysis. This paper addresses the problem of physical layer (PHY) security in a multi-hop wireless cooperative network, where communication at each hop is assisted by multiple relays forming a cluster, each cluster being surrounded by multiple eavesdroppers which together may tap transmissions from both the source and the relays. The main focus of the study is on analyzing the benefits of various relay selection schemes for protecting the source-destination transmission against the eavesdroppers, which can collude and combine information via diversity combining techniques. To be specific, four relay selection schemes, which differ in the way they employ available measures link quality, are considered to deliver the source information to the destination via a decode-and-forward (DF) strategy. To evaluate the security performance of the multi-hop cooperative link in the presence of colluding eavesdroppers, we derive novel closed-form analytical expressions for the secrecy outage probability (SOP) with consideration of special cases of practical interest.