In this paper, we consider secure communications between a source and a destination helped by a relay, in the presence of an eavesdropper. We consider both path-loss and fading in our channel models. We investigate such a question that whether the relay operates as a tradition relay or a jammer. A one time slot cooperative jamming and two time slots cooperative relaying transmission scheme are proposed. For fairness, we consider the total power constraint and assume that the two proposed schemes are with the same power budget. Optimal power allocation among the information signal and jamming signal are derived. For the proposed schemes, we give the performance comparison in the high and low transmitted power regimes, which gives some insight into the choice of transmission schemes to achieve a better performance. Furthermore, We analyze the impact of eavesdropper's position on security in our simulation.
In this paper, we consider secure communications between a source and a destination helped by a relay, in the presence of an eavesdropper. We consider both path-loss and fading in our channel models. We investigate such a question that whether the relay operates as a tradition relay or a jammer. A one time slot cooperative jamming and two time slots cooperative relaying transmission scheme are proposed. For fairness, we consider the total power constraint and assume that the two proposed schemes are with the same power budget. Optimal power allocation among the information signal and jamming signal are derived. For the proposed schemes, we give the performance comparison in the high and low transmitted power regimes, which gives some insight into the choice of transmission schemes to achieve a better performance. Furthermore, We analyze the impact of eavesdropper's position on security in our simulation.
In this paper, we consider the problem of secure communications for a four-node system consisting of one source, one destination, one eavesdropper, and one helper. We investigate the question of which role should the helper act to improve the secrecy, to jam, or to relay. Two transmission schemes are investigated: (1) direct transmission scheme (DTS) with jamming and (2) relay transmission scheme (RTS). We consider both the path-loss and fading-in channel models and define a notion of distance normalized signal-to-noise-ratio (DN-SNR) to account for propagation. The ergodic secrecy rate (ESR) is adopted as the performance metric and semi-closed-form expressions of ESR for the two schemes are derived. Additionally, optimal power allocations in both low and high DN-SNR regimes are characterized analytically. We give the performance comparison of the two schemes from the perspective of energy efficiency in the low DN-SNR regime, and characterize the secrecy degree of freedom in the high DN-SNR regime. In the high DN-SNR regime, DTS provides higher secrecy rate compared with RTS, while in the low DN-SNR regime, RTS outperforms DTS. Furthermore, we show that eavesdropper's position impacts greatly on security.
In this paper, we study the problem of secure dual-hop transmission in the presence of an eavesdropper, where a secrecy-enhanced relay selection as well as a destination cooperation are presented to prevent the source information from being eavesdropped. Taking into account the total power budget, a power allocation scheme is investigated to optimize the destination contribution. We present the system performance in terms of secrecy capacity where we derive a closed form expression for its lower bound. Simulation results reveal that a higher power allocation to the jamming signal should be balanced by a closer placement of the relay to the source to get better system performance, and vice versa.
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.
To improve physical (PHY) layer security of a wireless relay system in the presence of an eavesdropper, a two-phase cooperative relaying scheme is investigated in this paper. In phase I, the source transmits confidential message, simultaneously, it cooperates with the friendly jammers and destination to create jamming signal at the eavesdropper without affecting the forwarding relay which is preselected. In phase II, the forwarding relay retransmits the decoded signal, meanwhile, the particular relay cooperates with the friendly jammers to create jamming signal at the eavesdropper without affecting the destination. We focus on the investigation of optimal power allocation for maximizing achievable secrecy rate subject to a total power constraint. Optimal relay selection and suboptimal relay selection schemes are also proposed. It is shown that as the number of relays increases, both secrecy rate and the performance of suboptimal relay selection scheme improve significantly. Numerical results are presented to validate the derived analytical results and compare them to existing work.
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.
We consider wireless secure communications between a source and a destination aided by a multi-antenna relay, in the presence of an eavesdropper. In particular, two cooperation schemes of the relay are explored: cooperative relaying (CR) and cooperative jamming (CJ). We first investigate the transmit weight optimization of CR and CJ, for both cases with and without the eavesdropper's channel state information (ECSI). Then, for the case with ECSI, we derive the conditions under which CR achieves a higher secrecy rate than CJ; for the case without ECSI, we compare the secrecy rates of CR and CJ in high transmit power regimes. Building on this, we propose a novel hybrid scheme in which the relay utilizes both CR and CJ, and study the power allocation of the relay between CR and CJ for maximizing the secrecy rate under individual power constraints. Further, we study the case with imperfect channel state information (CSI) for both CR and CJ. At last, extensive numerical results are provided.