In this study, we deal with a cooperative wireless communications system of security constraints in which there is no knowledge about channel state information (CSI) of the eavesdropper. In order to improve the tradeoff between security and reliability, we opportunistically employ relays via an incremental and selective cooperation with respect to the CSI of the main link. In this cooperation, named as opportunistic cooperative transmission (OCT), the first priority is communication through the direct link as far as possible. However, a relay that has the best link to the main destination is employed for retransmitting the source information when the direct link is so weak which cannot provide a specific quality. In fact, since improving the reliability of the favorable communications by use of the relays increases the risk of successful interception by the eavesdropper at the same time, the OCT scheme tries to avoid excess of rebroadcasting the secret information by the relays whenever the direct link is strong enough; otherwise it employs an opportunistically selected relayed link. Hence, it can improve the security for a specific level of reliability and vice versa. We derive closed-form expressions for the security-reliability tradeoff (SRT) and secrecy outage probability (SOP) of the OCT scheme. Moreover, we provide asymptotic analyses which are illustrative on the security behavior of the proposed scheme. Finally, simulation results are presented which confirm validity of the analysis and reveal the desired performance of OCT in terms of both SRT and SOP.
In this study, we deal with a cooperative wireless communications system of security constraints in which there is no knowledge about channel state information (CSI) of the eavesdropper. In order to improve the tradeoff between security and reliability, we opportunistically employ relays via an incremental and selective cooperation with respect to the CSI of the main link. In this cooperation, named as opportunistic cooperative transmission (OCT), the first priority is communication through the direct link as far as possible. However, a relay that has the best link to the main destination is employed for retransmitting the source information when the direct link is so weak which cannot provide a specific quality. In fact, since improving the reliability of the favorable communications by use of the relays increases the risk of successful interception by the eavesdropper at the same time, the OCT scheme tries to avoid excess of rebroadcasting the secret information by the relays whenever the direct link is strong enough; otherwise it employs an opportunistically selected relayed link. Hence, it can improve the security for a specific level of reliability and vice versa. We derive closed-form expressions for the security-reliability tradeoff (SRT) and secrecy outage probability (SOP) of the OCT scheme. Moreover, we provide asymptotic analyses which are illustrative on the security behavior of the proposed scheme. Finally, simulation results are presented which confirm validity of the analysis and reveal the desired performance of OCT in terms of both SRT and SOP.
Physical layer security offers an efficient means to decrease the risk of confidential information leakage through wiretap links. In this paper, we address the physical-layer security in a cooperative wireless subnetwork that includes a source-destination pair and multiple relays, exchanging information in the presence of a malevolent eavesdropper. Specifically, the eavesdropper is active in the network and transmits artificial noise (AN) with a multiple-antenna transmitter to confound both the relays and the destination. We first analyse the secrecy capacity of the direct source-to-destination transmission in terms of intercept probability (IP) and secrecy outage probability (SOP). A decode-and-forward incremental relaying (IR) protocol is then introduced to improve security of communications in the presence of the active eavesdropper. Within this context, and depending on the availability of channel state information, three different schemes (one optimal and two sub-optimal) are proposed to select a trusted relay and improve the achievable secrecy rate. For each one of these schemes, and for both selection and maximum ratio combining at the destination and eavesdropper, we derive new and exact closed-form expressions for the IP and SOP. Our analysis and simulation results demonstrate the superior performance of the proposed IR-based selection schemes for secure communication. They also confirm the existence of a floor phenomenon for the SOP in the absence of AN.
In this paper, we investigate the physical-layer security of cooperative communications relying on multiple two-way relays using the decode-and-forward (DF) protocol in the presence of an eavesdropper, where the eavesdropper appears to tap the transmissions of both the source and of the relay. The design tradeoff to be resolved is that the throughput is improved by invoking two-way relaying, but the secrecy of wireless transmissions may be degraded, since the eavesdropper may overhear the signals transmitted by both the source and relay nodes. We conceive an artificial noise aided two-way opportunistic relay selection (ANaTWORS) scheme for enhancing the security of the pair of source nodes communicating with the assistance of multiple two-way relays. Furthermore, we analyze both the outage probability and intercept probability of the proposed ANaTWORS scheme, where the security and reliability are characterized in terms of the intercept probability and the security outage probability. For comparison, we also provide the security-reliability tradeoff (SRT) analysis of both the traditional direct transmission and of the one-way relaying schemes. It is shown that the proposed ANaTWORS scheme outperforms both the conventional direct transmission, as well as the one-way relay methods in terms of its SRT. More specifically, in the low main-user-to-eavesdropper ratio (MUER) region, the proposed ANaTWORS scheme is capable of guaranteeing secure transmissions, whereas no SRT gain is achieved by conventional one-way relaying. In fact, the one-way relaying scheme may even be inferior to the traditional direct transmission scheme in terms of its SRT.
This paper investigates the security at the physical layer in cooperative wireless networks (CWNs) where the data transmission between nodes can be realised via either direct transmission (DT) or relaying transmission (RT) schemes. Inspired by the concept of physical-layer network coding (PNC), a secure PNC-based modify-and-forward (SPMF) is developed to cope with the imperfect shared knowledge of the message modification between relay and destination in the conventional modify-and-forward (MF). In this paper, we first derive the secrecy outage probability (SOP) of the SPMF scheme, which is shown to be a general expression for deriving the SOP of any MF schemes. By comparing the SOPs of various schemes, the usage of the relay is shown to be not always necessary and even causes a poorer performance depending on target secrecy rate and quality of channel links. To this extent, we then propose an opportunistic secure transmission protocol to minimise the SOP of the CWNs. In particular, an optimisation problem is developed in which secrecy rate thresholds (SRTs) are determined to find an optimal scheme among various DT and RT schemes for achieving the lowest SOP. Furthermore, the conditions for the existence of SRTs are derived with respect to various channel conditions to determine if the relay could be relied on in practice.
This paper investigates the secure communication in a two-hop cooperative wireless network, where a buffer-aided relay is utilized to forward data from the source to destination, and a passive eavesdropper attempts to intercept data transmission from both the source and relay. Depending on the availability of instantaneous channel state information of the source, two cases of transmission mechanisms, i.e., adaptive-rate transmission and fixed-rate transmission are considered. To enhance the security of the system, novel link selection policies are proposed for both cases to select source-to-relay, relay-to-destination, or no link transmission based on the channels qualities. Closed-form expressions are derived for the end-to-end secrecy outage probability (SOP), secrecy outage capacity (SOC), and exact secrecy throughput (EST), respectively. Furthermore, we prove the condition that EST reaches its maximum, and explore how to minimize the SOP and maximize the SOC by optimizing the link selection parameters. Finally, simulations are conducted to demonstrate the validity of our theoretical performance evaluation, and extensive numerical results are provided to illustrate the efficiency of the proposed link selection polices for the secure communication in two-hop cooperative networks.
This article examines secrecy coding aided wireless communications from a source to a destination in the presence of an eavesdropper from an SRT perspective. Explicitly, security is quantified in terms of the intercept probability experienced at the eavesdropper, while the outage probability encountered at the destination is used to measure transmission reliability. We characterize the SRT of conventional direct transmission from the source to the destination and show that if the outage probability is increased, the intercept probability decreases, and vice versa. We first demonstrate that the employment of relay nodes for assisting source-destination transmission is capable of defending against eavesdropping, followed by quantifying the benefits of SRS as well as MRS schemes. More specifically, in the SRS scheme, only the single "best" relay is selected for forwarding the source signal to the destination, whereas the MRS scheme allows multiple relays to participate in this process. It is illustrated that both the SRS and MRS schemes achieve a better SRT than conventional direct transmission, especially upon increasing the number of relays. Numerical results also show that, as expected, MRS outperforms SRS in terms of its SRT. Additionally, we present some open challenges and future directions for wireless relay aided physical-layer security.
We study opportunistic decode-and-forward relaying transmission in cooperative cluster-based wireless sensor networks (WSNs) with secrecy constraints, where a passive eavesdropper may overhear the source message. To deal with this problem, we consider the novel opportunistic relay section cooperative transmission for the cluster configuration of WSNs. The system performance in terms of the secrecy outage probability and the probability of nonzero secrecy capacity are analyzed and the exact closed-form expressions are derived over Rayleigh fading channels. Furthermore, we derive the asymptotic secrecy outage probability which accurately reveals the secrecy diversity order. Finally, numerical results are presented to verify the theoretical analysis and depict that node cooperation has a great potential to enhance physical layer security against eavesdropping.