We investigate the problem of physical layer security in a wireless cooperative network, where communication is assisted by the untrusted relay. It is impossible for the amplify-and-forward protocol to convey a confidential message from the source to the destination without the help of other nodes, where only an untrusted relay is available. Nonetheless, our results are quite optimistic when there are multiple untrusted relays, which amplify the received signal and forward it to the destination. We treat the untrusted relay nodes as eavesdroppers, despite the fact that they are the enablers of communication. First of all, we prove that a positive secrecy rate can always be ensured regardless of the transmit power and the channel condition of the untrusted relays, as long as there exists a sufficient number of untrusted relays. Furthermore, a closed-form solution to the upper bound of secrecy rate is obtained. Finally, a practical approach is proposed to acquire a positive secrecy rate, which brings nearly no extra communication cost. Simulations are conducted to demonstrate the validity of the proposed approach.
We investigate the problem of physical layer security in a wireless cooperative network, where communication is assisted by the untrusted relay. It is impossible for the amplify-and-forward protocol to convey a confidential message from the source to the destination without the help of other nodes, where only an untrusted relay is available. Nonetheless, our results are quite optimistic when there are multiple untrusted relays, which amplify the received signal and forward it to the destination. We treat the untrusted relay nodes as eavesdroppers, despite the fact that they are the enablers of communication. First of all, we prove that a positive secrecy rate can always be ensured regardless of the transmit power and the channel condition of the untrusted relays, as long as there exists a sufficient number of untrusted relays. Furthermore, a closed-form solution to the upper bound of secrecy rate is obtained. Finally, a practical approach is proposed to acquire a positive secrecy rate, which brings nearly no extra communication cost. Simulations are conducted to demonstrate the validity of the proposed approach.
Physical (PHY) layer security approaches for wireless communications can prevent eavesdropping without upper layer data encryption. However, they are hampered by wireless channel conditions: absent feedback, they are typically feasible only when the source-destination channel is better than the source-eavesdropper channel. Node cooperation is a means to overcome this challenge and improve the performance of secure wireless communications. This paper addresses secure communications of one source-destination pair with the help of multiple cooperating relays in the presence of one or more eavesdroppers. Three cooperative schemes are considered: decode-and-forward (DF), amplify-and-forward (AF), and cooperative jamming (CJ). For these schemes, the relays transmit a weighted version of a reencoded noise-free message signal (for DF), a received noisy source signal (for AF), or a common jamming signal (for CJ). Novel system designs are proposed, consisting of the determination of relay weights and the allocation of transmit power, that maximize the achievable secrecy rate subject to a transmit power constraint, or, minimize the transmit power subject to a secrecy rate constraint. For DF in the presence of one eavesdropper, closed-form optimal solutions are derived for the relay weights. For other problems, since the optimal relay weights are difficult to obtain, several criteria are considered leading to suboptimal but simple solutions, i.e., the complete nulling of the message signals at all eavesdroppers (for DF and AF), or the complete nulling of jamming signal at the destination (for CJ). Based on the designed relay weights, for DF in the presence of multiple eavesdroppers, and for CJ in the presence of one eavesdropper, the optimal power allocation is obtained in closed-form; in all other cases the optimal power allocation is obtained via iterative algorithms. Numerical evaluation of the obtained secrecy rate and transmit power results show that the proposed design can significantly improve the performance of secure wireless communications.
The Physical Layer Security (PLS) technology has been proved to be an effective way to reduce information leakage in wireless communication networks. This paper discusses the problem of secure transmission for Amplify-and-Forward (AF) cooperative network which contains both an external eavesdropper and some untrusted relays at the same time, where each relay acts as a helper of transmitting information and a potential eavesdropper. We adopt the technology of Cooperative Jamming (CJ), which yields a significant performance in terms of providing a better level of security against eavesdropping and improving the secure transmission performance of the system. First we discuss the security performance of this new system model, give the secrecy rate in theory and derive a tight lower bound of this secrecy rate. Then we propose a relay selection scheme, which avoids using the channel state information (CSI) of external eavesdropper, to transmit information. Afterward, we also discuss the problem of power allocation in order to maximize the secrecy rate.
This paper investigates the physical-layer security of an amplify-and-forward wireless cooperative network, where N source nodes communicate with their corresponding destination nodes under the help of an untrusted relay. In each slot, only one user-pair is scheduled to transmit the information, and the destination-aided cooperative jamming is adopted to protect information from being intercepted by the untrusted relay. Three user-pair selection schemes have been proposed for the considered system, namely opportunistic user-pair selection (OUS) scheme, greedy user-pair selection (GUS) scheme, and genie-aided user-pair selection scheme. Both the secrecy outage probability and the average secrecy rate have been studied to evaluate the performance of the OUS and GUS schemes, and the asymptotic analysis has also been obtained. It reveals that the proposed schemes can improve the secrecy performance for the cooperative multiuser networks as the number of user-pairs increases. We also prove that the achievable diversity order of both OUS and GUS schemes is N/2. Finally, numerical and simulation results are presented to validate the accuracy of the developed analytical results.
We consider a source-destination pair that can communicate only through an unauthenticated intermediate relay node. In this two-hop communication scenario, where the cooperation from the relay node is essential, we investigate whether achieving non-zero secrecy rate is possible. Specifically, we treat the relay node as an eavesdropper from whom the source information needs to be kept secret, despite the fact that its cooperation in relaying this information is needed. We find that a positive secrecy rate is indeed achievable, with the aid of the destination node or an external node that jams the relay, i.e., by cooperative jamming. We derive an upper bound on the secrecy rate by means of an eavesdropper-relay separation argument. We remark that this upper bound is the first of its kind in Gaussian channels with cooperative jamming. The upper bound is strictly smaller than the channel capacity without secrecy constraints. The achievable secrecy rates are found using stochastic encoding and compress-and-forward at the relay. Numerical results show that the gap between the bound and the achievable rate is small when the relay's power is larger than the power of the jammer and the source. In essence, this paper shows that a cooperative jammer enables secure communication to take place using an untrusted relay which would be otherwise impossible.
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.
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.