This paper proposes using cooperative relays to improve the ergodic secrecy capacity (ESC) of a multi-hop decode-and-forward (DF) relaying system where communication takes place in the presence of multiple non-colluding eavesdroppers. The proposed scheme is based on a recent approach to generate artificial noise in which transmitter of each hop allocates a portion of its power for generating an intentional interference at the eavesdroppers. Under the assumption that the transmitters can only use limited transmit power, a power allocation strategy has been developed which maximizes the secrecy capacity by optimally distributing the power between the original signal and the artificial noise. Since the optimal solution depends on the channel state information (CSI) of the eavesdroppers, which is difficult to obtain in practice, a sub-optimal solution is also presented in which the CSI of the eavesdroppers is not needed.
This paper proposes using cooperative relays to improve the ergodic secrecy capacity (ESC) of a multi-hop decode-and-forward (DF) relaying system where communication takes place in the presence of multiple non-colluding eavesdroppers. The proposed scheme is based on a recent approach to generate artificial noise in which transmitter of each hop allocates a portion of its power for generating an intentional interference at the eavesdroppers. Under the assumption that the transmitters can only use limited transmit power, a power allocation strategy has been developed which maximizes the secrecy capacity by optimally distributing the power between the original signal and the artificial noise. Since the optimal solution depends on the channel state information (CSI) of the eavesdroppers, which is difficult to obtain in practice, a sub-optimal solution is also presented in which the CSI of the eavesdroppers is not needed.
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.
This paper studies cooperative transmission for securing a decode-and-forward (DF) two-hop network where massive cooperative nodes coexist with a potential single eavesdropper. With only the statistical channel state information (CSIs) of the eavesdroppers, we propose an opportunistic relaying with artificial jamming secrecy scheme, where a “best” cooperative node is chosen to forward the confidential signal and the others act as jammers to send the jamming signals to confuse the eavesdropper. Utilizing the limiting distribution technique of extreme order statistics, we optimize the power allocation between the confidential information and jamming signal based on the statistical CSIs of the legitimate nodes for ergodic secrecy rate (ESR) maximization. Although the optimization problems are non-convex, we propose a sequential parametric convex approximation (SPCA) algorithm to locate the KKT solutions. Then, we derive an analytical closed-form expression of the achievable ESR, which reduces the complexity of the system analysis and design.
This paper studies the cooperative transmission for securing a decode-and-forward (DF) two-hop network where multiple cooperative nodes coexist with a potential eavesdropper. Under the more practical assumption that only the channel distribution information (CDI) of the eavesdropper is known, we propose an opportunistic relaying with artificial jamming secrecy scheme, where a “best” cooperative node is chosen among a collection of N possible candidates to forward the confidential signal and the others send jamming signals to confuse the eavesdroppers. We first investigate the ergodic secrecy rate (ESR) maximization problem by optimizing the power allocation between the confidential signal and jamming signals. In particular, we exploit the limiting distribution technique of extreme order statistics to build an asymptotic closed-form expression of the achievable ESR and the power allocation is optimized to maximize the ESR lower bound. Although the optimization problems are non-convex, we propose a sequential parametric convex approximation (SPCA) algorithm to locate the Karush-Kuhn-Tucker (KKT) solutions. Furthermore, taking the time variance of the legitimate links' CSIs into consideration, we address the impacts of the outdated CSIs to the proposed secrecy scheme, and derive an asymptotic ESR. Finally, we generalize the analysis to the scenario with multiple eavesdroppers, and give the asymptotic analytical results of the achievable ESR. Simulation results confirm our analytical results.
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.
The feasibility of physical-layer-based security approaches for wireless communications in the presence of one or more eavesdroppers is hampered by channel conditions. In this paper, cooperation is investigated as an approach to overcome this problem and improve the performance of secure communications. In particular, a decode-and-forward (DF) based cooperative protocol is considered, and the objective is to design the system for secrecy capacity maximization or transmit power minimization. System design for the DF-based cooperative protocol is first studied by assuming the availability of global channel state information (CSI). For the case of one eavesdropper, an iterative scheme is proposed to obtain the optimal solution for the problem of transmit power minimization. For the case of multiple eavesdroppers, the problem of secrecy capacity maximization or transmit power minimization is in general intractable. Suboptimal system design is proposed by adding an additional constraint, i.e., the complete nulling of signals at all eavesdroppers, which yields simple closed-form solutions for the aforementioned two problems. Then, the impact of imperfect CSI of eavesdroppers on system design is studied, in which the ergodic secrecy capacity is of interest.
In this paper, we propose a random phase shifting scheme applied to modulated data symbols of a dual-hop decode-and-forward (DF) relaying system to enhance its secrecy capacity in the presence of an eavesdropper, which can wiretap the communication signals of both hops. The random phase shift used in the proposed scheme is generated using a shared secret between transmitter and receiver of each hop, such as the reciprocal channel between the communicating devices, which is not accessible to the eavesdropper. Through theoretical analysis of the secrecy capacity, we have proven that the proposed scheme improves the ergodic secrecy capacity of the system. Notably, the proposed scheme is energy efficient so it can be applied to the systems with limited power resources at source and relay nodes.