We study the secure transmissions for channel-aware (CA) random access based on the notion of physical layer security in this paper, which might be suitable for machine type communications. Thanks to the availability of channel state information in CA random access, opportunistic jamming can be employed to improve the secrecy rate. As a result, a positive secrecy rate can be obtained even if the signal-to-noise ratio at an eavesdropper is higher than that at a legitimate receiver. Since a powerful eavesdropper equipped with multiple antennas can suppress the interference due to opportunistic jamming once jamming users are identified, it is important to know the number of received signals that allows Eve to identify them. Using the notion of unicity distance, we study this issue. Based on analysis, we find that it is necessary to keep the number of jamming users relatively small (compared with the number of ordinary active users) and use a fraction of the coherence time for secure transmissions when the coherence time is long.
We study the secure transmissions for channel-aware (CA) random access based on the notion of physical layer security in this paper, which might be suitable for machine type communications. Thanks to the availability of channel state information in CA random access, opportunistic jamming can be employed to improve the secrecy rate. As a result, a positive secrecy rate can be obtained even if the signal-to-noise ratio at an eavesdropper is higher than that at a legitimate receiver. Since a powerful eavesdropper equipped with multiple antennas can suppress the interference due to opportunistic jamming once jamming users are identified, it is important to know the number of received signals that allows Eve to identify them. Using the notion of unicity distance, we study this issue. Based on analysis, we find that it is necessary to keep the number of jamming users relatively small (compared with the number of ordinary active users) and use a fraction of the coherence time for secure transmissions when the coherence time is long.
As the technology and computing power advance day by day, physical layer security in wireless communications gains more importance. It allows the security of wireless communications based on information theoretical guarantees without the need for cryptography. One important practical challenge for physical layer security arises from the fact that no information about the passive eavesdroppers is available to the legitimate nodes. Without such information, optimizing the transmission parameters has always been a difficult task. In this study we aim to address various challenging aspects about this issue and propose a new perspective into the analysis of secrecy with a focus on jamming. We start from the case of eavesdropper's channel state information (CSI) known to users in a three-node single-antenna multi-subcarrier network and present an improved optimization algorithm compared to previous methods. Then we expand our horizon to the case of multiple-antenna nodes with eavesdropper's CSI unknown to users. We investigate a secure wireless communication scheme which combines two of the most effective strategies to combat eavesdropping, namely mixing information with artificial noise at the transmitter and jamming from a full-duplex receiver. While such setup has been investigated in related works, new and important insights are revealed in this study. We investigate the design of optimal jamming parameters to achieve higher secrecy.We then derive a closed-form expression for asymptotic normalized instantaneous secrecy rate of our model. Based on the results of the asymptotic analysis, we propose an alternative less complex tractable optimization problem for the design of optimal transmission parameters to achieve higher secrecy. We show that even with the optimal parameters, secrecy is compromised if Eve is able to increase her number of antennas. To address this issue, we provide a comprehensive analysis of a new scheme called anti-eavesdropping channel estimation (ANECE) which prevents Eve from acquiring accurate channel estimations. We show that the usage of such scheme, makes it extremely hard for Eve to drive secrecy to zero. Numerical analyses and simulations are presented to support the arguments made in this study.We then derive a closed-form expression for asymptotic normalized instantaneous secrecy rate of our model. Based on the results of the asymptotic analysis, we propose an alternative less complex tractable optimization problem for the design of optimal transmission parameters to achieve higher secrecy. We show that even with the optimal parameters, secrecy is compromised if Eve is able to increase her number of antennas. To address this issue, we provide a comprehensive analysis of a new scheme called anti-eavesdropping channel estimation (ANECE) which prevents Eve from acquiring accurate channel estimations. We show that the usage of such scheme, makes it extremely hard for Eve to drive secrecy to zero. Numerical analyses and simulations are presented to support the arguments made in this study.We then derive a closed-form expression for asymptotic normalized instantaneous secrecy rate of our model. Based on the results of the asymptotic analysis, we propose an alternative less complex tractable optimization problem for the design of optimal transmission parameters to achieve higher secrecy. We show that even with the optimal parameters, secrecy is compromised if Eve is able to increase her number of antennas. To address this issue, we provide a comprehensive analysis of a new scheme called anti-eavesdropping channel estimation (ANECE) which prevents Eve from acquiring accurate channel estimations. We show that the usage of such scheme makes it extremely hard for Eve to drive secrecy to zero. Numerical analyses and simulations are presented to support the arguments made in this study.
In this article, we investigate the physical layer security for a wireless communication system consisting of a base station (BS) and a user (U) in the face of an eavesdropper (E). A friendly jammer is opportunistically selected from multiple jammers to create intentional interference upon E. However, the legitimate user U is not aware of the information transmitted by the jammer and thus cannot remove the interfering signal. In this context, we propose interference-limited opportunistic jammer selection (IL-OJS) scheme and interference-canceled opportunistic jammer selection (IC-OJS) scheme to reduce the damage of interference to U for improving physical layer security. Specifically, in the IL-OJS scheme, the selected jammer sets an interference threshold. When the interference to U is less than the threshold value, the selected jammer will work (i.e., emit artificial noise), and vice versa, it will stop jamming. By contrast, IC-OJS scheme utilizes a specially designed signal to eliminate interference received by U from the selected jammer. For comparison, we also present the conventional non-jammer (NJ) scheme as a benchmark. Exact and asymptotic closed-form secrecy outage probability expressions for NJ, IL-OJS, and IC-OJS schemes are derived over Nakagami-mfading channels. Numerical results show that the secrecy performance of proposed IL-OJS and IC-OJS schemes is better than that of NJ scheme. Additionally, the secrecy outage probability performance of IL-OJS and IC-OJS schemes can be improved by increasing the number of jammers.
This paper investigates the secure transmission in multiple access wiretap channels, where multiple legitimate users transmit private information to an intended receiver in the presence of multiple eavesdroppers. In order to improve security, we propose a novel cooperative jamming scheme, in which users do not share channel state information (CSI) but the legitimate channels will not be degraded by the artificial noise. The basic idea is to make each user exploit its own CSI in two slots to design artificial noise, so that the intended receiver can eliminate all the artificial noise but the eavesdroppers cannot. In this process, the interference between users plays a key role to achieve security, because it guarantees that the artificial noise from different users helps each other. We consider the non-collusion and collusion of eavesdroppers and analyze the secrecy performance for both scenarios. We adopt the secrecy sum-rate as the main metric, and show that positive secrecy sum-rate can be achieved by using the proposed scheme. Especially, we observe that when eavesdroppers collude and their additive white Gaussian noise (AWGN) close to zero, the number of users must not be less than twice the number of eavesdroppers to ensure positive secrecy sum-rate. Finally, simulation results are provided to corroborate our theoretical findings.
In this paper, we examine the physical-layer security for a spectrum sharing system consisting of multiple source-destination pairs, which dynamically access their shared spectrum for data transmissions in the presence of an eavesdropper. We propose a source cooperation (SC) aided opportunistic jamming framework for protecting the transmission confidentiality of the spectrum sharing system against eavesdropping. Specifically, when a source node is allowed to access the shared spectrum for data transmissions, another source is opportunistically selected in the spectrum sharing system to transmit an artificial noise for disrupting the eavesdropper without affecting the legitimate transmissions. We present two specific SC aided opportunistic jamming schemes, namely the SC aided random jammer selection (RJS) and optimal jammer selection (OJS), which are referred to as the SC-RJS and SC-OJS, respectively. We also consider the conventional non-cooperation as a baseline. We derive closed-form intercept probability expressions for the non-cooperation, SC-RJS and SC-OJS schemes, based on which their secrecy diversity gains are determined through an asymptotic intercept probability analysis in the high signal-to-noise ratio (SNR) region. It is proved that the conventional non-cooperation exhibits a secrecy diversity of zero, whereas the proposed SC-RJS and SC-OJS achieve a higher secrecy diversity of one. This also surprisingly means that no additional secrecy diversity gain is achieved by the optimal jammer selection compared to the random selection strategy. In addition, numerical results show that the intercept probability performance of the SC-OJS is always better than that of the SC-RJS and non-cooperation, even when the legitimate channel is worse than the eavesdropping channel.
This paper investigates the physical layer security for a distributed antenna system, where a base station (BS) equipped with multiple distributed antennas transmits signals to a legitimate user (U) through an opportunistic antenna. Meanwhile, multiple non-colluding eavesdroppers (Es) attempt to tap the information transmission between the BS and U. To enhance the physical layer security, a friendly jammer (J) is employed to create a potential interference to Es by emitting artificial noise. However, since U is not aware of the information sent by J, it can be affected by the interference. In this context, this paper proposes adaptive jamming (AJ) scheme and interference cancellation (IC) scheme to mitigate the interference’s impact on U and consequently improve secrecy performance. Specifically, the AJ scheme avoids interference from having a negative effect on the system security by setting an interference threshold, activating the jammer only when the interference to U is below the threshold value. By contrast, the IC scheme designs an advanced special signal to eliminate the interference from J to U. For comparison, we present conventional non-jammer (NJ) scheme as a benchmark. Exact and asymptotic secrecy outage probability expressions for NJ, AJ, and IC schemes are derived over Nakagami-mfading channels. Numerical results show that the proposed AJ and IC schemes perform better than NJ scheme in terms of secrecy outage probability. Additionally, the physical layer security of all schemes can be improved by increasing the number of distributed antennas.
Physical layer security is a promising technique for information security. In multi-antenna systems, secure transmission designs are of crucial importance for physical layer security. In this thesis, our research focuses on the secure transmission designs for jamming signal aided multi-antenna systems. We first investigate robust secure transmission designs for a cooperative jamming aided multiple-input-single-output (MISO) system. Two scenarios are considered: (a) eavesdroppers' channel state information (ECSI) is available and (b) ECSI is unavailable. In scenario (a), a quality-of-service (QoS)-based design is considered to minimize the worst case signal-to-interference-and-noise ratio at the eavesdroppers. A secrecy rate based design is also studied. In scenario (b), a QoS-based design is considered to maximize the power of jamming signals, and the secrecy rate based design is not applicable. We propose an algorithm for each design problem through semidefinite relaxation. Our analysis shows that, even though the beamforming scheme in our designs is fixed as single stream beamforming, this does not cause any loss of optimality. We further consider secure transmission designs for a simultaneous wireless information and power transfer enabled MISO heterogeneous cellular network. In the considered system, all base stations (BSs) send confidential messages to information receivers and energy signals to energy receivers (ERs). BSs collaboratively utilize the energy signals as jamming signals to cripple ERs' interceptions. We propose a sum logarithmic secrecy rate maximization design problem. To tackle the design problem, we propose a semidefinite relaxation and successive convex approximation based centralized secure transmission design algorithm. Moreover, an alternating direction method of multipliers based distributed secure transmission design is also proposed. Simulation results demonstrate the effectiveness of the proposed algorithms. Secure transmission is designed for a cooperative jamming aided MISO non-orthogonal multiple access system. We consider an outage constrained secure transmission design problem under the assumption that only statistical ECSI is available. In the design problem, the minimum probabilistic secrecy rate is maximized. Based on 0-norm and the path-following approach, we develop an algorithm to find a solution to the design problem. Simulation results demonstrate that the secrecy outage probability can be guaranteed through the proposed secure transmission design algorithm.