In this paper, we investigate the secure transmission in the single-input multiple-output (SIMO) wireless systems. Motivated by the existing destination-feedback schemes, and the utilization of artificial noise, a novel destination-feedback based two-phase transmission strategy is proposed to secure the SIMO communications. In the first phase, the multiple-antenna destination transmits both artificial interference and artificial noise on the backhaul links. In the second phase, the source utilizes the received interference signals to mask the confidential messages and emits the mixed signals to the destination. In the high signal-to-noise ratio (SNR) region, the lower bound of the worst-case ergodic secrecy rate is derived. Then we obtain the closed-form optimal power allocations that maximize the above lower bound. Moreover, we derive an analytical high-SNR approximation of the worst-case secrecy outage probability. Simulations are demonstrated to verify the secrecy performance analysis and corroborate the effectiveness of our scheme.
In this paper, we investigate the secure transmission in the single-input multiple-output (SIMO) wireless systems. Motivated by the existing destination-feedback schemes, and the utilization of artificial noise, a novel destination-feedback based two-phase transmission strategy is proposed to secure the SIMO communications. In the first phase, the multiple-antenna destination transmits both artificial interference and artificial noise on the backhaul links. In the second phase, the source utilizes the received interference signals to mask the confidential messages and emits the mixed signals to the destination. In the high signal-to-noise ratio (SNR) region, the lower bound of the worst-case ergodic secrecy rate is derived. Then we obtain the closed-form optimal power allocations that maximize the above lower bound. Moreover, we derive an analytical high-SNR approximation of the worst-case secrecy outage probability. Simulations are demonstrated to verify the secrecy performance analysis and corroborate the effectiveness of our scheme.
The issue of physical layer security of the wireless single-input multiple-output (SIMO) system is addressed in this paper. We proposed a two-step transmission approach to improve the secrecy rate with perfect knowledge of channel state information. In the first step, the destination which has multiple antennas generates a random message and transmits it to the source which has a single antenna. The message is transmitted in a system of multiple-input single-output (MISO) in this step, and it is encoded under the secrecy capacity of the MISO system and thus can be securely transmitted to the source without leaking to the eavesdropper. In the second step, the message of the source is encrypted to a new message by using the received random message in the first step. The new message is then transmitted to the destination under the capacity of the SIMO system without considering the security. The secrecy of the source's message is guaranteed by the first random message, thus it is unknown for the eavesdropper. The information-theoretic security of the two-step transmission approach is proven in this paper, and the optimal power allocation is also proposed by solving an equation. The performance of the two-step transmission approach is analyzed in theory and evaluated by numerical simulations, and the results show that the proposed approach outperforms the traditional approach when the transmit power is great.
In this paper, we consider secure communications in a multi-cell downlink multi-antenna system, where each multi-antenna base station (BS) sends confidential messages to one intended legitimate user (LU) with a passive multi-antenna eavesdropper trying to intercept the messages in this cell. To enhance the secure communications of the cell-edge users, the multiple BSs employ coordinated beamforming with the aid of artificial-noise (AN) beamforming. We conduct a mathematically rigorous secrecy performance analysis of the considered system and obtain new accurate closed-form expressions of a lower bound on the ergodic rate of each LU and an upper bound of the ergodic rate of each eavesdropper without assuming asymptotes for any system parameter (except for the “worst-case” scenario with zero noise power). Then, a lower bound on the ergodic secrecy rate (ESR) of each LU follows. Based on the derived analytical results, we propose a low-complexity algorithm to optimize the channel sate information (CSI) feedback bits allocation for the channels of target signal link and inter-cell interference links. Furthermore, we develop explicit sufficient conditions on the set of system parameters under which there are at least two BSs to coordinated secure transmission. Through both theoretical analysis and numerical results, we can verify that the obtained analytical lower bound on ESR of each LU as a function of the set of power allocation coefficients is generallyneither convex nor concave. Thus, we propose to employ some numerical method to find a sub-optimal power allocation solution. Finally, numerical results are also provided to validate our theoretical results and the proposed feedback bits and power allocation methods.
We consider the problem of secure communication in wireless fading channels in the presence of quantized version of the receivers channel sate information at transmit side. The transmitter has multiple antennas and is able to simultaneously transmits an information bearing signal and artificial noise. For general values of signal to noise ratio (SNR), we obtain the exact closed-form expression for the distribution function of output signal to interference plus noise ratio at the legitimate receiver and a lower bound of the ergodic secrecy capacity can be obtain by using simple numerical integration. For the interference-limited case, we obtained a closed-form expression for a lower bound of secrecy capacity. Our results apply to arbitrary number of antennas and number of feedback bits. The analytical and numerical results show that the ergodic secrecy capacity lower bound approaches to a constant as the SNR of system grows large. In addition, we find that, for system with reasonable number of feedback bits, the optimal power allocation strategy should allocate most of the available power to the information signal.
This paper proposes a framework for the artificial noise assisted secure transmission in multiple-input, multiple-output, multiple antenna eavesdropper (MIMOME) wiretap channels in frequency-division duplexed (FDD) systems. We focus on a practical scenario that only the eavesdroppers' channel distribution information (CDI) is available and the imperfect channel state information (CSI) of the legitimate receiver is acquired through training and analog feedback. By taking explicitly into account the signaling overhead and training power overhead incurred by channel estimation and feedback, we define the achievable effective ergodic secrecy rate (ESR), and investigate a joint power allocation and training overhead optimization problem for the maximization of effective ESR. We first derive a deterministic approximation for the achievable effective ESR which facilitates the joint optimization. Then, efficient iterative algorithms are proposed to solve the considered nonconvex optimization problem. In particular, in the high-SNR regime, a block coordinate descent method (BCDM) is proposed to handle the joint optimization. In the low-SNR regime, we transform the problem into a sequence of geometric programmings (GPs) and locate its Karush-Kuhn-Tucker (KKT) solution using the successive convex approximation (SCA) method. For the general case of SNR, we maximize the lower bound of the achievable effective ESR. Simulation results corroborate the theoretical analysis and illustrate the secrecy performance of the proposed secure transmission scheme.
Utilizing artificial noise (AN) is a good means to guarantee security against eavesdropping in a multi-input multi-output system, where the AN is designed to lie in the null space of the legitimate receiver's channel direction information (CDI). However, imperfect CDI will lead to noise leakage at the legitimate receiver and cause significant loss in the achievable secrecy rate. In this paper, we consider a delayed feedback system, and investigate the impact of delayed CDI on security by using a transmit beamforming and AN scheme. By exploiting the Gauss-Markov fading spectrum to model the feedback delay, we derive a closed-form expression of the upper bound on the secrecy rate loss, where Nt= 2. For a moderate number of antennas where Nt>; 2, two special cases, based on the first-order statistics of the noise leakage and large number theory, are explored to approximate the respective upper bounds. In addition, to maintain a constant signal-to-interference-plus-noise ratio degradation, we analyze the corresponding delay constraint. Furthermore, based on the obtained closed-form expression of the lower bound on the achievable secrecy rate, we investigate an optimal power allocation strategy between the information signal and the AN. The analytical and numerical results obtained based on first-order statistics can be regarded as a good approximation of the capacity that can be achieved at the legitimate receiver with a certain number of antennas, Nt. In addition, for a given delay, we show that optimal power allocation is not sensitive to the number of antennas in a high signal-to-noise ratio regime. The simulation results further indicate that the achievable secrecy rate with optimal power allocation can be improved significantly as compared to that with fixed power allocation. In addition, as the delay increases, the ratio of power allocated to the AN should be decreased to reduce the secrecy rate degradation.
This paper investigates the secrecy performance of a single-input multiple-output (SIMO) based underlay cognitive radio networks. In particular, a single-antenna secondary transmitter transmits its secret message to a multi-antenna equipped secondary node in the presence of a multi-antenna equipped passive eavesdropper under a peak interference constraint at the single-antenna primary receiver. We proficiently derive the expressions for secrecy outage probability (SOP), intercept probability, and ergodic secrecy capacity (ESC) for the considered system over$\alpha -\mu fadingchannels.Further,wecarryouttheasymptoticanalysisofSOPandinterceptprobabilityundertwocasesofinterest;1)whentheaveragesignal−to−noiseratio(SNR)ofthemainlink,i.e.,betweenthesecondarysourceandsecondarydestination,goestoinfinitywithafixedaverageSNRofwiretaplinkbetweenthesecondarysourceandsecondaryeavesdropper,and2)whentheSNRsofboththemainandwiretaplinkstendtoinfinity.Wecaninferthatasecrecydiversityorderof\frac {\alpha _{D}N_{D}\mu _{D}}{2}canbeachievedundercase1,where\alpha _{D}and\mu _{D}arethemainlinkfadingparameters,andN_{D}$denotes the number of antennas at the destination. Whereas, under case 2, the system’s secrecy diversity order becomes zero. Moreover, we also present some interesting findings for the ESC when the interference constrained secondary transmitter power is considerably high. Further, we validate our analytical framework through extensive simulation and numerical results, and demonstrate the effects of system/channel parameters on the secrecy performance of the considered system. Our results reveal that the higher number of eavesdropper antennas can have a more deleterious impact on the system’s secrecy performance.