This paper presents the optimal physical-layer security scheme of both primary user (PU) and secondary user (SU) in the underlay multiple-input multiple-output cognitive-radio network (MIMO-CRN) by using bi-directional zero-forcing beamforming technique. The proposed method enables the PU to communicate along with the SU without sacrificing their individual secrecy capacity, i.e., without causing interference to each other in the presence of eavesdropper(s). In this method, a bi-directional beamforming has been applied to eradicate the necessity of involving artificial noise for preventing the active eavesdropper(s). Both theoretical and numerical analyses of the secrecy outage probability are provided to demonstrate the effectiveness of our proposed method. The secrecy outage probability is also derived to evaluate the performance variations of our proposed scheme when the channel-estimation error occurs.
This paper presents the optimal physical-layer security scheme of both primary user (PU) and secondary user (SU) in the underlay multiple-input multiple-output cognitive-radio network (MIMO-CRN) by using bi-directional zero-forcing beamforming technique. The proposed method enables the PU to communicate along with the SU without sacrificing their individual secrecy capacity, i.e., without causing interference to each other in the presence of eavesdropper(s). In this method, a bi-directional beamforming has been applied to eradicate the necessity of involving artificial noise for preventing the active eavesdropper(s). Both theoretical and numerical analyses of the secrecy outage probability are provided to demonstrate the effectiveness of our proposed method. The secrecy outage probability is also derived to evaluate the performance variations of our proposed scheme when the channel-estimation error occurs.
This paper presents the optimal physical-layer security scheme of both primary user (PU) and secondary user (SU) in the underlay multiple-input multiple-output cognitive-radio network (MIMO-CRN) by use of a bi-directional zero-forcing beamformer. The proposed new method enables the PU to communicate along with the SUs through a relay node without sacrificing their individual secrecy capacity, i.e., without causing interference to each other even in the presence of eavesdropper(s). In the first phase, a transmitting beamformer at the PU/SU transmitters and a receiving beamformer at the relay have been adopted to separate PU and SU data. In the second phase, a bi-directional beamformer has been applied to eradicate the necessity of involving artificial noise for preventing the active eavesdropper(s). To maximize the total secrecy capacity, a generalized non-linear optimization problem has been formulated and converted to a simplified constrained optimization problem by utilizing the beamformer and the associated subspace restriction. Then, this problem is solved by the Lagrangian method. Both theoretical and numerical analyses of the total and individual ergodic secrecy rates are provided to demonstrate the effectiveness of our proposed method. The secrecy outage probability is also derived to evaluate the performance variations of our proposed scheme when the channel-estimation error occurs.
In this paper, we consider multiple-input single-output multi-eavesdropper cognitive radio networks (MISOME-CRNs), where a secondary user (SU) aims to transmit confidential information to a legitimate SU receiver in the presence of a primary user (PU) and a multi-antenna passive eavesdropper in fast fading environments. For this system setting, we study beamforming with artificial noise (AN) for the SU to achieve confidential communications. We consider designing an AN-assisted optimal beamforming scheme, denoted cognitive beamforming (CB), which maximizes the ergodic secrecy rate. Moreover, we propose two suboptimal beamforming schemes, namely, scaled beamforming (SB) and projected beamforming (PB). We develop an analytical framework to assess the performance of the proposed schemes in a unified manner. First, we analyze the achievable ergodic secrecy rate of the three schemes. Second, we derive the optimal power allocation for the information and AN signals that maximizes the achievable ergodic secrecy rate in the large-antenna regime. Third, we study the performance of the three schemes in terms of the secrecy outage probability. Using numerical simulations, we validate our analytical results and show that CB achieves the best performance among the three proposed schemes. In addition, we provide insights into the effect of various system parameters on the secrecy performance. In particular, we show that the interference threshold at the PU plays an important role in the beamforming design.
In this paper, we investigate the secrecy outage probability (SOP) for the cooperative decode-and-forward (DF) underlay cognitive radio networks (CRNs). Duo to the spectrum sharing approach in underlay CRNs, the secondary transmitters (secondary source (SUS) and secondary relay (SUR)) are subjected to interference power constraint at primary user (PU), and the SU receivers (SURand secondary destination (SUD)) suffer from the co-channel interferences (CCIs) from PU. We focus on the practical scenario where the SU transmitter has no channel state information (CSI) of the eavesdropper's channel. Interference-power-confined selection scheme is proposed for the cooperative DF CRNs in the presence of an eavesdropper. The proposed scheme selects the “best” terminal (SUSor SUR) to enhance the secure performance which must firstly satisfy the interference power constraint. What's more, the effect of feedback delay on the selection scheme is studied. We derive an exact closed-form expression for the SOP. Simulation results validate our theoretical analysis and show that the proposed selection scheme determinately enhance the performance, and feedback delay decreases the SOP seriously, specially, the interference power constraint hugely confine the SOP.
We have examined the physical layer security of an underlay cognitive radio network (CRN) consisting of L legitimate receivers ( STX), a secondary transmitter ( STX), an eavesdropper (Eve), and a primary user (PU). All SRX and the PU are equipped with a single antenna while the STX and Eve are implemented with multiple antennas. The optimal antenna selection scheme (OAS) is adopted at the STX, which maximizes the secrecy capacity while a generalized receiver selection scheme is adopted at the SRX. The STX sends information to the SRX with the lthbest signal to noise ratio (SNR). The concise expressions for exact and asymptotic secrecy outage probability (SOP) for an arbitrary number of SRX, number of transmit antenna NA, and number of eavesdropper antenna NE have derived.
In this paper, we address the physical-layer security issue of a secondary user (SU) in a spectrum-sharing cognitive radio network (CRN) from an information-theoretic perspective. Specially, we consider a secure multiple-input single-output (MISO) cognitive radio channel, where a multi-antenna SU transmitter (SU-Tx) sends confidential information to a legitimate SU receiver (SU-Rx) in the presence of an eavesdropper and on the licensed band of a primary user (PU). The secrecy capacity of the channel is characterized, which is a quasiconvex optimization problem of finding the capacity-achieving transmit covariance matrix under the joint transmit power and interference power constraints. Two numerical approaches are proposed to derive the optimal transmit covariance matrix. The first approach recasts the original quasiconvex problem into a single convex semidefinite program (SDP) by exploring its inherent convexity; while the second one explores the relationship between the secure CRN and the conventional CRN and transforms the original problem into a sequence of optimization problems associated with the conventional CRN, which helps to prove that beamforming is the optimal strategy for the secure MISO CR channel. In addition, to reduce the computational complexity, three suboptimal schemes are presented, namely, scaled secret beamforming (SSB), projected secret beamforming (PSB) and projected cognitive beamforming (PCB). Lastly, computer simulation results show that the three suboptimal schemes can approach the secrecy capacity well under certain conditions.
In this paper, the physical layer security in cognitive radio networks (CRNs) is investigated. We consider an underlay relay assisted CRN consisting of multiple secondary sources, multiple-antenna destination, a single relay, and multiple eavesdroppers. The destination node performs the maximal-ratio combining under uncorrelated Rayleigh fading channels. In more details, we consider, a secondary source is randomly selected to transmit its data, and a jammer is chosen from the remaining source nodes to send a jamming signal to the eavesdroppers. The closed-form expression of the secrecy outage probability is derived, based on the statistical characteristics of the communication channels, under the primary user's quality of service constraint. The derived analysis gives deep insights into the impact of network parameters on the performance of on the secrecy outage performance. Analytic results are corroborated through Monte Carlo simulation.