Relying on physical layer security is an attractive alternative of utilizing cryptographic algorithms at upper layers of protocol stack for secure communications. In this paper, we consider a two-hop wireless relay network in the presence of an eavesdropper. Our scenario of interest spans over a four-node network model including a source, a destination, a trusted relay, and an untrusted eavesdropper in which the relay forwards the source message in a decode-and-forward (DF) fashion. The source and relay are allowed to use some of their available power to transmit jamming signals in order to create interference at the eavesdropper. The relay and destination are assumed to have the knowledge of the jamming signals. An important question is how to allocate the transmission power of the message signal and that of the jamming signal. First, we propose an optimal power allocation solution in which the knowledge of global channel state information (CSI) is required. To facilitate practical system design, two simple yet sub-optimal power allocation solutions are proposed which do not rely on eavesdropper's channels. For the purpose of performance comparisons, power allocation problems for two benchmark schemes without jamming are also analyzed.
Relying on physical layer security is an attractive alternative of utilizing cryptographic algorithms at upper layers of protocol stack for secure communications. In this paper, we consider a two-hop wireless relay network in the presence of an eavesdropper. Our scenario of interest spans over a four-node network model including a source, a destination, a trusted relay, and an untrusted eavesdropper in which the relay forwards the source message in a decode-and-forward (DF) fashion. The source and relay are allowed to use some of their available power to transmit jamming signals in order to create interference at the eavesdropper. The relay and destination are assumed to have the knowledge of the jamming signals. An important question is how to allocate the transmission power of the message signal and that of the jamming signal. First, we propose an optimal power allocation solution in which the knowledge of global channel state information (CSI) is required. To facilitate practical system design, two simple yet sub-optimal power allocation solutions are proposed which do not rely on eavesdropper's channels. For the purpose of performance comparisons, power allocation problems for two benchmark schemes without jamming are also analyzed.
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.
A wireless network with one source, one destination, one eavesdropper, and multiple decode-and-forward relays is considered. A two-slot cooperative relaying scheme is proposed that targets at maximizing the secrecy rate. In the first slot, the source transmits the information bearing signal, and at the same time, it cooperates with the destination in jamming the eavesdropper without creating interference at the relay. In the second slot, one optimally selected relay retransmits the decoded source signal, and at the same time, that particular relay cooperates with the source to jam the eavesdropper without creating interference at the destination. Optimal relay selection and also optimal power allocation among the first/second slot data signal and jamming noise are proposed. It is shown that the secrecy rate of the proposed scheme scales with the total system powerP0and the number of available relaysKaccording to 1/2log2(1 +P0/8logK) - 1.6 bits/channel use . Although the proposed power allocation and relay selection assume global CSI available, the performance under imperfect relay CSI is also investigated. Also, the performance under distributed relay selection with limited feedback is demonstrated.
In this paper, we consider secure communications of one source-destination pair in wireless multi-hop decode-and-forward (DF) relay networks. In the presence of an eavesdropper, we derive an optimal power allocation strategy to maximize achievable secrecy rates under an overall transmit power constraint assuming that a single relay is located at each individual hop. We demonstrate that the optimal power allocation is obtained when the overall power constraint and the DF-relaying constraints necessary to guarantee that each DF relay correctly decodes the information signals hold with equality, which rely on channel conditions between the source, relays, and destination. The channel conditions for the eavesdropper are shown to only influence relays that may be inactive for secrecy rate maximization. We also consider multiple cooperative relays at each hop to perform cooperative beamforming in the presence of multiple eavesdroppers. To improve the secrecy rate in multi-hop relay networks, which include more than two hops, we propose an iterative cooperative beamformer design and transmit power allocation scheme with relay selection. Numerical results are presented to investigate the secrecy capacity obtained by the optimal power allocation in multi-hop DF relay networks and to confirm the secrecy rate enhancement of the proposed cooperative beamforming scheme.
A wireless network with one source, one destination, one eavesdropper and multiple decode-and-forward (DF) relays is considered. A two-slot cooperative relaying scheme is proposed that targets at maximizing the secrecy rate. In the first slot, the source transmits the information bearing signal, and at the same time, it cooperates with the destination in jamming the eavesdropper without creating interference at the relay. In the second slot, one optimally selected relay retransmits the decoded source signal, and at the same time, it cooperates with the source to jam the eavesdropper without creating interference at the destination. For the beamforming, no eavesdropper channel information is required. Optimal relay selection and also optimal power allocation among the first/second slot data signal and jamming noise are proposed. It is shown that the system secrecy rate of the proposed scheme scales with the total system power, P0and the number of available relays, K, according to log2(1 + P0/8 log K) - 1.6252bps.
A two-hop relay network is considered, in which an eavesdropper can overhear the relaying signal. To prevent the eavesdropper from decoding this signal, a destination transmits a jamming noise while a source transmits the data signal to the relay. At the same time, the relay can harvest energy from both the source signal and the jamming noise, and use this harvested energy to forward the received signal to the destination. In such a wireless-powered relay system with cooperative jamming, we propose two adaptive relaying schemes based on power splitting and time switching techniques. In the proposed power splitting-based relaying (PSR) and time switching-based relaying (TSR) schemes, the relay controls the power splitting ratio (p) and time switching ratio (α), respectively, in order to achieve a balance between signal processing and energy harvesting. We find analytically the optimal values of p and α in each scheme to maximize the secrecy capacity under the assumption of high signal-to-noise ratio (SNR). Interestingly, although the eavesdropper's channel state information (CSI) is used in the derivation of the optimal control parameters (p and α), they are shown not to be affected by the eavesdropper's CSI in a high SNR regime. This implies that the proposed schemes can be effective even for practical environments where there is no eavesdropper's CSI. Furthermore, simulation results show that they well coincide with the exact solutions in practical environments even though the closed-form solutions are obtained with a high SNR assumption. Moreover, the comparisons of PSR and TSR in various scenarios show that the two relaying schemes have complementary performances depending on the network conditions. Specifically, PSR achieves greater secrecy capacity than TSR when the channel condition is unfavorable to the eavesdropper for wiretapping.
In this paper, we consider a multi-node-assisted two-hop cooperative network, where an energy constrained source (S) aims to establish secure communications with a legitimate user in the presence of an eavesdropper. The cooperative nodes simultaneously assist the transmission from base station to legitimate user. Each cooperative node applies power splitting protocol to coordinate the received signal energy for information decoding and energy harvesting. The power splitting ratios at multi-node are formulated based on decode-and-forward (DF) relaying protocols. Depending on the available channel state information (CSI) at the source, we propose two different jamming schemes for secrecy performance enhancement. An optimal node is selected as a jammer to interfere the eavesdropper or a relay to forward the information to legitimate user. we evaluate the network performance based on secrecy outage probability (SOP). In addition, simple and accurate approximations are obtained at different transmission speed thresholds. Furthermore, numerical results reveal that there exist unique splitting ratios and harvesting efficiency that minimize the SOP.