In this work, information security of a cooperative wireless communication system over three-phase amplify-and-forward (AF) two-way relaying channels is investigated. A relay power allocation scheme is proposed to improve secrecy capacity of the system. We first derive the secrecy rate expression for the basic scenario which consists of one source, one destination, one single relay, and an eavesdropper. A relay power allocation scheme which maximizes the overall secrecy rate of the single-relay system is studied accordingly. Then the power allocation coefficients are calculated under the assumption of perfect channel state information (CSI). This design framework is then extended to a cooperative wireless system having multiple relays. In the numerical example, secrecy rate performance of the proposed scheme is compared with the classic three-phase two-way AF scheme and it is concluded that conducting power allocation at the relay can achieve the goal of improving the secrecy capacity. It is also observed that the best performing scenario of the relay power allocation scheme is when the relay locates right in the middle of the two legitimate communicants.
In this work, information security of a cooperative wireless communication system over three-phase amplify-and-forward (AF) two-way relaying channels is investigated. A relay power allocation scheme is proposed to improve secrecy capacity of the system. We first derive the secrecy rate expression for the basic scenario which consists of one source, one destination, one single relay, and an eavesdropper. A relay power allocation scheme which maximizes the overall secrecy rate of the single-relay system is studied accordingly. Then the power allocation coefficients are calculated under the assumption of perfect channel state information (CSI). This design framework is then extended to a cooperative wireless system having multiple relays. In the numerical example, secrecy rate performance of the proposed scheme is compared with the classic three-phase two-way AF scheme and it is concluded that conducting power allocation at the relay can achieve the goal of improving the secrecy capacity. It is also observed that the best performing scenario of the relay power allocation scheme is when the relay locates right in the middle of the two legitimate communicants.
In this paper, we investigate secrecy communications in two-hop wireless relaying networks which consist of one source, one amplify-and-forward (AF) relay, one legitimate destination, and one eavesdropper. To prevent the eavesdropper from intercepting the source message, we make the destination send the intended noise to the AF relay during the first phase. This is referred to as cooperative jamming. According to the channel information at the destination, we address two types of jamming power allocation; (i) rate-optimal power allocation and (ii) outage-optimal power allocation. More specifically, without the instantaneous channel knowledge for the eavesdropper side, the outage probability of the secrecy rate is minimized with respect to the intended noise power level. We show that the outage-optimal allocation gives almost the same outage probability as the rateoptimal one. In addition, the jamming power consumption can be significantly reduced compared to the fixed and rate-optimal power allocation methods.
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.
In this work, physical layer secure transmission of a cooperative wireless communication system over a three-phase amplify-and-forward (AF) two-way relaying channels is studied. A cooperative jamming and multi-antenna relay beamforming scheme that improves physical layer security of the system is proposed. Specifically, it is suggested that in the first and second timeslots when the legitimate users transmit alternatively, a jamming signal can be transmitted by the legitimate party that is not transmitting information-bearing signals This scheme, compared with the approach using a dedicated jammer, achieves a similar jamming effect with reduced complexity. In the third time slot of the protocol, the relay uses two beamforming matrices to process the bidirectional information signals. The jamming signal components at the relay are projected onto the null space of the legitimate relay-destination channels such that they do not affect legitimate communications. Through joint optimization, the sum throughput of the legitimate communication is maximized. In the numerical examples, the proposed scheme is shown to improve the system's secrecy transmission performance.
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.
In this paper the cooperation of beam-forming and artificial noise (AN) in two-hop amplify-and- forward (AF) relaying system is proposed to enhance the security. we consider a half duplex AF relaying network with a multi-antenna source node and a destination in the presence of a passive eavesdropper.Since channel state information (CSI) of the eavesdropper is unknown, the AN transmitted by the source in the first phase and by the relays in the second phase is in all directions except the legitimate node one. As such two scenarios are considered here,: i) when all the relays amplify and forward the information source signal ii) when only the best relay is selected to amplify and forward the information source signal. The beam-former weights and the power allocation are obtained by solving an optimization problem. Results reveal that the proposed system can provide considerable improvements in terms of secrecy rate. It is also found that increasing the AN power, relative to the information signal power, will further improve the secrecy rate.