In order to deal with the power leakage of side lobes in physical layer security, this paper investigates a secure transmission system aided by Orbital Angular Momentum (OAM) jamming. The receiver, located at the center of the beam, remains unaffected due to the power null of OAM radio wave. Based on its distinctive power null, a secure transmission system with imperfect Channel State Information (CSI) and random eavesdroppers is proposed in this paper. To be specific, the artificial noise and the desired information signal are transmitted by the radio wave with OAM and without OAM respectively. Meanwhile, a power allocation optimization algorithm is designed to acquire the target secrecy capacity. Simulations are implemented to evaluate the effectiveness of the proposed algorithm compared with other methods. Furthermore, we find that there is a secrecy capacity upper bound in the presence of imperfect angle measurement and random eavesdroppers. Moreover, the proposed power allocation algorithm leads to a higher secrecy capacity upper bound.
In order to deal with the power leakage of side lobes in physical layer security, this paper investigates a secure transmission system aided by Orbital Angular Momentum (OAM) jamming. The receiver, located at the center of the beam, remains unaffected due to the power null of OAM radio wave. Based on its distinctive power null, a secure transmission system with imperfect Channel State Information (CSI) and random eavesdroppers is proposed in this paper. To be specific, the artificial noise and the desired information signal are transmitted by the radio wave with OAM and without OAM respectively. Meanwhile, a power allocation optimization algorithm is designed to acquire the target secrecy capacity. Simulations are implemented to evaluate the effectiveness of the proposed algorithm compared with other methods. Furthermore, we find that there is a secrecy capacity upper bound in the presence of imperfect angle measurement and random eavesdroppers. Moreover, the proposed power allocation algorithm leads to a higher secrecy capacity upper bound.
Orbital angular momentum (OAM) provides an additional degree of freedom for information transmission. However, wireless transmissions with OAM are challenged by secrecy issues since the OAM modes can be observed over a wide range along the beam axis, and it allows that the eavesdroppers intercept the information bits encoded on the OAM modes. In this letter, targeting against unintended receivers, we propose a secure range-dependent transmission scheme with OAM radio beams generated by the frequency diverse array (FDA). Specifically, we consider a line-of-sight communication link overheard by an unknown eavesdropper. The transmitter employs FDA of antennas to generate range-dependent OAM radio beams and target at the legitimate receiver, in which the confidential information is encoded on the OAM modes. The eavesdropper outside the target region observes distorted OAM modes and thus is unable to recover the secret messages. The proposed scheme enhances the security of OAM mode modulation and achieves higher energy efficiency compared to the conventional secure transmission schemes with artificial noise.
In this paper, we study a secure cooperative transmission system in which a transmitter (Alice) intends to send a secret message to an authorized receiver (Bob), with the aid of a friendly private cooperative jammer (Oscar), in the presence of a malicious eavesdropper (Eve). Specifically, artificial noise (AN) assisted secrecy beamforming is utilized for secure transmission. Under the imperfect channel state information (CSI) of legitimate channels and the statistic CSI of illegitimate channels, the optimal power allocation ratio between the information-bearing signal and the AN signal for maximizing secrecy rate is derived. Through mathematical analysis, we notice that the high channel estimation error is greatly detrimental to the realization of the positive secrecy rate in secure system. For overcoming this drawback, back propagation neural network (BPNN) is employed for a high accuracy channel estimation to simulate a realistic security communication scenario. The numerical results show that the channel estimation errors result in a decrease in secrecy rate, but the BPNN channel estimator still can guarantee secure transmission that verifies the feasibility of the application of physical layer security. Analytical derivations and numerical simulations are presented to validate the correctness of obtained expressions and our analysis.
In this paper, we study the secure multiantenna transmission with artificial noise (AN) under imperfect channel state information (CSI) in the presence of spatially randomly distributed eavesdroppers. We derive the optimal solutions of the power allocation between the information signal and the AN for minimizing the secrecy outage probability (SOP) under a target secrecy rate and for maximizing the secrecy rate under an SOP constraint, respectively. Moreover, we provide an interesting insight that channel estimation error affects the optimal power allocation strategy in opposite ways for the two given objectives. When the estimation error increases, more power should be allocated to the information signal if we aim to decrease the rate-constrained SOP, whereas more power should be allocated to the AN if we aim to increase the SOP-constrained secrecy rate.
In recent years, physical layer security has been regarded as a promising technique to facilitate secure communications in next generation mobile systems, where theoretically massive MIMO can significantly enhance the system secrecy performance under its advantage in shaping the transmitted signals to null the interference or leakage. However, in practical systems, the achievable secrecy performance under imperfect channel state information (CSI) deserves further investigation. In this paper, we give a detailed analysis about the physical layer security problem in a multi-user massive MIMO system with imperfect CSI. The considered imperfect CSI includes both the outdated CSI due to the transmission and processing delay, and the channel estimation error. We first derive a tight asymptotic lower bound of the ergodic system secrecy capacity under imperfect CSI, and then analyze how imperfect CSI affects the system secrecy performance. Moreover, we propose a channel prediction scheme that can result in more accurate CSI, in order to alleviate the negative effect on the achievable system secrecy capacity caused by imperfect CSI. Simulation results reveal that the imperfect CSI greatly reduces the system secrecy capacity, while our designed channel prediction scheme can effectively mitigate the harmful impact of imperfect CSI and thus improve the system secrecy performance.
This paper investigates cooperative security in wireless networks, where a source (Alice) intends to transmit a confidential message to a legitimate destination (Bob), with the help of a cooperative jammer (Charlie), coexisting with multiple passive eavesdroppers (Eves). In particular, by assuming knowledge of Bob's perfect channel state information (CSI) but only Eves’ statistical CSIs, secrecy beamforming with artificial noise (AN) is utilized for secure transmission, and cooperative jamming (CJ) is explored to further enhance secrecy. We first derive an accurate closed-form expression for the secrecy outage probability (SOP), and establish the condition under which positive secrecy rate is achievable. Then, we provide a secure transmit design for maximizing the SOP constrained secrecy rate. Moreover, based on a strict mathematical analysis, we characterize the impact of the main channel quality and the number of Eves on transmit design and secrecy performance. Specifically, optimal power allocation ratio between the information-bearing signal and the AN signal increases as the main channel quality improves, and decreases with the number of Eves. Numerical results confirm that our design achieves performance improvement in terms of both secrecy rate and secure energy efficiency, as compared to the approach without CJ.
At present, there has been a large amount of research on secrecy rate optimization. However, the reliability analysis of secure transmission is equally important although relatively less attention has been dedicated to. Therefore, this paper proposes a secure transmission method with artificial noise for the physical layer security issues in the transmission process of Multiple Input Multiple Output (MIMO) wireless communication systems. Firstly, we establish an artificial noise assisted MIMO systems model. Then, the channel state information (CSI) matrix is subjected to singular value decomposition to obtain the reasonable precoding and artificial noise matrices. Finally, the impact of artificial noise on the bit error rate performance of potential eavesdropper is analyzed, and based on the analysis, the problem of maximizing the system secrecy rate is established. The concave-convex procedure (CCCP) method is used to obtain the optimal power allocation, which significantly improves the security of MIMO systems. The simulation results show that using the null space of CSI matrix and artificial noise for signal encryption effectively improves the bit error rate of potential eavesdropping nodes. In addition, the secrecy rate obtained by the CCCP algorithm is consistent with the performance obtained by the particle swarm optimization algorithm, which verifies the effectiveness of the proposed algorithm.