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The broadcast nature of wireless communications makes transmission susceptible to eavesdropping. Recently, physical-layer security has been extensively studied to secure the wireless transmissions, but the security is severely compromised when the eavesdropper has the superiority in the channel quality. Toward this issue, we in this paper propose a joint ARQ and network coding method exploiting the characteristics of both the physical layer and the link layer. Specifically, we relate the message to be transmitted in the current slot with the successfully decoded messages in previous slots, where the ARQ is employed at the legitimate side to guarantee the successful transmission and decoding. Once one or more received messages fail to be decoded at the eavesdropper, it further prevents the eavesdropper from decoding the transmissions in later slots and thus the message transmitted currently and later is secured at the legitimate side. Moreover, for the more disadvantageous case that the eavesdropper is geographically closer to the transmitter, we further propose a destination-aided network coding scheme, which secures private information no matter where the eavesdropper is. The closed-form expressions of intercept probability and loss probability of the private information are analytically presented. The simulation results are provided to confirm our theoretical findings. [ABSTRACT FROM AUTHOR]

Among the plenty of studies on physical layer security, multi-antenna signal processing and nodes cooperation are two widely adopted techniques. However, in practical systems there are many single-antenna devices that do not support cooperative transmission either. To guarantee the information security in this scenario, we propose a novel transmission strategy that exploits the temporal characteristics of a multipath fading channel. Specifically, we apply this strategy to a time-reversal-based communication system. We consider a joint design of signal waveform and artificial noise. Based on this approach, specific transmission schemes are designed for the cases with and without eavesdropper's channel state information (CSI), respectively. The numerical results show the superiority of our proposed schemes in terms of security enhancement even when the eavesdropper's CSI is unavailable. [ABSTRACT FROM AUTHOR]

In power-domain nonorthogonal multiple access, passive eavesdropping may appear among the users by successive interference cancellation. Furthermore, the external eavesdropper may do active eavesdropping (i.e., passive eavesdropping plus jamming) by a full-duplex technique. To combat this hybrid eavesdropping, we propose a novel physical layer security scheme. The main contributions in this scheme are as follows: 1) A time constellation is set up by the concept of timing channel, where each point contains several symbols and the intervals between them, exploits these intervals to carry privacy information, and can represent different values (i.e., multiple mapping rules are introduced). Based on this time constellation, different mapping rules are allocated to different users. 2) The beginning symbols of time constellation points are devised to take the information of mapping rule allocation. Moreover, an extra symbol transformation method for each beginning symbol is designed. According to these contributions, the advantages of our scheme are evident: 1) Each user only needs to judge the intervals and extract privacy information from them. It is predicted that the impact of jamming on this operation should be lower than that on directly using the modulated symbols to carry and transfer privacy information. In other words, the mistakes of privacy information acquisition with the time constellation should be less than that with the modulated symbols. 2) The mapping rule allocation and symbol transformation methods generate multiple possible values for one time constellation point. These possibilities bring the difficulty of determining the actual value represented by each point. Therefore, passive eavesdropping can be effectively suppressed. [ABSTRACT FROM AUTHOR]

In this paper, we consider the physical layer security issue for the multi-channel full-duplex (FD) communications in the presence of eavesdroppers. There co-exist multiple FD pairs, where the two users in each pair perform bi-directional transmissions. The secure communication is then challenged by the users’ self-interference, external interference from other pairs, and threats from the eavesdroppers. We investigate the problem from a distributed perspective and formulate the problem as a non-cooperative game, where each user optimizes their power allocation over the channels to maximize their own secrecy rate. Confirming the existence of the Nash equilibrium, we introduce an equivalent variational inequality (VI) formulation to derive the sufficient condition for the equilibrium to be unique. We then develop the iterative security-aware water-filling (ISWF) algorithm that can be implemented at each individual user in a distributed manner and prove that the condition for the unique equilibrium also claims the convergence of ISWF algorithm. Furthermore, we extend our formulation to the heterogeneous cases that there co-exist FD and half-duplex users with different security requirements in the networks, and demonstrate that they can all be covered as special cases under our formulated VI framework. Finally, we present simulation results to validate our theoretical findings. [ABSTRACT FROM AUTHOR]

Security is an issue of paramount importance, yet is it a significant challenge for wireless communications, which becomes more intricate when facing a full duplex (FD) active eavesdropper capable of performing eavesdropping and jamming simultaneously. In this paper, we investigate the physical layer security issue in the presence of an FD active eavesdropper, who launches jamming attacks to further improve the eavesdropping. The jamming, however, also results in self-interference at the eavesdropper itself. This security problem is formulated within a hierarchical game framework where the eavesdropper acts as the leader and the legitimate user is the follower. In particular, we first investigate the follower’s secrecy rate maximization problem and derive the optimal legitimate transmission strategy. Then, the leader’s wiretap rate maximization is expressed as a mathematical program with equilibrium constraints (MPEC). Leveraging the concavity of the follower’s problem, we transform the MPEC problem into a single-level optimization and obtain the jamming power allocation strategy by applying the primal-dual interior-point method. Moreover, we analyze the situations where only partial channel state information is available at the legitimate user and the corresponding impacts on the game. Finally, we present extensive simulation results to validate our theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper studies the cooperative device-to-device (D2D) transmissions in cellular networks, where two D2D users communicate bidirectionally with each other and simultaneously serve as relays to assist the two-way transmissions between two cellular users. For this scenario, both cellular and D2D links share the same spectrum, thus creating mutual interference. In addition to that, a security problem also exists since the cellular users want to keep their messages secret from the D2D users and vice versa. To address these two issues, a security-embedded interference avoidance scheme is proposed in this paper. By exploiting the constellation rotation technique, the proposed scheme can create interference-free links for both D2D and cellular communications, thereby significantly improving the system error performance. Moreover, our scheme also provides an inherent secrecy protection at the physical layer, which makes the information exchange between cellular users and that between D2D users confidential from each other. [ABSTRACT FROM PUBLISHER]