防内外部窃听的多播物理层安全算法

针对无线多播系统同时存在内、外部窃听者的复杂情况,提出随机化干扰的物理层多播安全传输算法。该算法基于收发天线构成信道的代数空间进行设计:一方面在内部窃听者的信道代数空间方向上不发送信息,另一方面在合法用户信道的正交方向上引入随机干扰信号。这样直接使得内部窃听者接收的信号受到能量削减的同时,非合法用户受到随机化干扰,最终实现了物理层多播信息的安全传输。理论分析和仿真结果表明,算法可同时保证系统内、外部窃听者极高的误码率,从而无法获取信息。     

中继辅助的干扰信道中总体MSE最小化的安全波束成形

针对中继辅助的干扰信道中的通信安全问题，提出了一种基于均方误差的物理层安全编码，最大化窃听者与合法用户估计目标信号的均方误差之差。建立了中继辅助的干扰信道网络的窃听模型，并将物理层安全编码策略用最优化问题描述。将非凸的最优化问题变化为三个子凸优化问题，使其可以利用梯度下降法求解，并利用迭代算法，联合求解发射机、中继和收发机的最优编码矩阵。仿真实验表明，该算法能有效提高系统的安全性能。      

一种多天线信道特征投影物理层安全编码算法

针对现有安全编码设计方法对信道条件依赖性强、收发无法共享随机性等问题,该文提出了一种多天线信道特征投影物理层安全编码算法。在满足信道互易性的时分双工系统中,多天线发射机根据单天线接收机发送的训练符号估计信道得到授权信道特征,利用信道特征投影生成投影矢量对,发射每个符号时随机选择投影矢量作为发射权重矢量,窃听接收机由于还原码字的汉明距离发生随机置乱而无法正确译码,从而实现安全传输。仿真结果表明:该算法使窃听者的误比特率接近0.5,授权接收机的误比特率较已有多天线物理层安全传输方法低一个数量级。     

基于信道CSI的抗窃听信号安全保障方法研究

随着无线通信网络在全球范围内蓬勃发展,无线通信网络中的隐私和安全问题引起了广泛的研究。物理层安全技术方案已被证明是解决未来网络安全性能的重要方案,有望满足日益增长的用户安全通信需求。为了防止窃听者窃取保密信息,在合法信道和窃听信道的信道状态信息（Channel State Information,CSI）已知的情况下,文章提出一种抗窃听物理层安全预编码方案。该方案能够有效提升合法信道的信道容量,在合法用户（Bob）和窃听用户（Eve）之间产生容量差以保证信息的安全传输,同时使得合法用户的中断概率远低于窃听用户,从而保证信息传输的可靠性。仿真结果证明了所提方案的有效性。     

窃听多天线的多用户调度安全性能分析

物理层安全作为一种密钥缺省的安全方案,逐渐成为信息安全和无线通信两个领域的交叉热点,其主要利用物理层传输资源保证合法接收者正常通信,同时抑制窃听信道通信。针对这一特点,提出了基于无线通信网络中窃听用户多天线、发送端多用户调度,合法接收端选择最好用户的模型,这时窃听用户进行随机选择,分析这种情况下主信道信噪比、窃听信道信噪比、安全传输速率以及窃听用户天线数目对系统安全性能的影响。仿真结果表明,窃听信道多天线时中断概率增加,即降低了系统的安全性能,但增加发送端用户数目、降低窃听信道信噪比、增加主信道信噪比可以显著提高系统的安全速率。同时证明,这种方案同随机选择发送用户相比较,切实提高了系统的安全性能。     

面向物理层安全的广义随机空间调制技术

针对窃听信道质量优于合法信道质量时的物理层安全传输问题,提出了一种广义随机空间调制技术。该技术利用合法信道的瞬时状态信息随机扰乱比特到符号的映射关系,实现物理层安全传输。首先给出了广义随机空间调制系统的收发机结构。然后计算了合法接收用户的误码率上界和系统保密容量。从误码率上界的表达式得出,所提广义随机空间调制系统可靠性与传统广义空间调制相同,由此可在不损失系统可靠性的前提下实现安全传输。保密容量的计算表明,安全通信速率不随窃听方天线增多而下降,因此能抵抗具备海量天线的窃听者。最后用仿真验证理论分析的准确性和所提方案的有效性。     

基于数据云处理的物理特征安全验证系统

与传统加密技术相比，物理层安全技术利用信道噪声实现与明文等长的密钥加密效果，窃听者即使拥有强大的破解计算能力，在没有主信道信息的前提下依然无法破译保密数据，在未来的通信系统中极有可能实现“一次一密”，为无线通信系统提供了强有力的安全保障。提出了基于数据云处理的物理特征安全验证系统，基站和合法用户可以高效获取信道信息，窃听者可凭借云服务器强大的存储及计算资源不限时地进行保密信号破译。基于此系统，设计并验证了联合预编码及人工噪声的物理层安全方案，填补了该方案原型机验证平台的空白，为验证物理层安全技术的无条件安全特性提供了有力支撑。     

高斯窃听信道中删余Polar码的设计方法研究

本文针对高斯窃听信道模型下的物理层安全问题,提出一种基于删余Polar码的、拥有编码比特的可信度计算的物理层安全编码方案。方案考虑到信道噪声对译码结果的影响,通过Bhattacharyya参数评估各信息比特的恢复差错概率,并将这恢复差错概率应用于编码比特的可信度计算。理论证明所提出的方案可使窃听者保持较高误码率,同时合法用户在高于自身信噪比门限时保证较低误码率。数值仿真结果表明所提出的安全编码方案能够有效地减小安全间隙。当窃听信道质量比合法信道质量稍差时窃听者误码率能迅速逼近0.5,而合法信道的误码率能够降到10-5以下,大大地降低了Bob和Eve间的安全间隙。      

人工噪声辅助MIMO系统下数据信号功率占比的误码率研究

针对多输入多输出（Multiple-Input Multiple-Output,MIMO）无线通信系统传输过程中的安全问题,提出了一种基于人工噪声辅助的安全传输方法。首先,建立人工噪声辅助MIMO系统的信道状态矩阵;其次,将信道状态矩阵进行奇异值分解,设计合理的预编码和人工噪声矩阵,从而显著提升MIMO系统的安全性。对于窃听节点的译码采用最大似然检测译码。仿真结果表明,利用MIMO系统信道信息的零空间矩阵,采用人工噪声进行信号加密,有效提高了潜在窃听节点的误码率,当合法信道质量降低时,通过降低分配数据信号功率系数来提高MIMO无线系统的窃听误码率。     

一种改进型的多天线加权跳空保密通信技术

多天线阵列随机加权方法和人工噪声方法可以在物理层保障无线通信的安全。但是,当窃听者天线数大于等于发送者时,窃听者就有可能通过Music-like窃取信号。针对此问题,提出了一种改进的多天线阵列加权方法。该方法是通过阵列加权方法和跳空技术相结合,接收者根据生成的跳空图案选择相应信道接收解调,而窃听者没有跳空图案所以不能解调出信号,即使窃听者知道跳空图案,但他不能消除零空间内的人工噪声,窃听者仍然没有办法得到正确的发送信息。仿真结果显示,该方法是一种有效的物理层保密通信方法。     

On the Secrecy Capacity of Fading Channels

We consider the secure transmission of information over an ergodic fading channel in the presence of an eavesdropper. Our eavesdropper can be viewed as the wireless counterpart of Wyner's wiretapper. The secrecy capacity of such a system is characterized under the assumption of asymptotically long coherence intervals. We first consider the full channel state information (CSI) case, where the transmitter has access to the channel gains of the legitimate receiver and the eavesdropper. The secrecy capacity under this full CSI assumption serves as an upper bound for the secrecy capacity when only the CSI of the legitimate receiver is known at the transmitter, which is characterized next. In each scenario, the perfect secrecy capacity is obtained along with the optimal power and rate allocation strategies. We then propose a low-complexity on/off power allocation strategy that achieves near-optimal performance with only the main channel CSI. More specifically, this scheme is shown to be asymptotically optimal as the average signal-to-noise ratio (SNR) goes to infinity, and interestingly, is shown to attain the secrecy capacity under the full CSI assumption. Overall, channel fading has a positive impact on the secrecy capacity and rate adaptation, based on the main channel CSI, is critical in facilitating secure communications over slow fading channels.      

Distributed QoS Based Robust Transmission Design for MISO Wiretap Channel with Cooperative Jamming

A communication network that consists of a transmitter, a legitimate receiver, an eavesdropper and several friendly helpers is considered. Both the transmitter and the helpers are equipped with multiple antennas while the legitimate receiver or the eavesdropper has one antenna. The transmitter and the helpers have the channel state information to the legitimate receiver. The channels to the eavesdropper are partially known and modeled with uncertainty ellipsoids. The transmitter applies maximum ratio transmission to the legitimate receiver. The helpers generate interference to degrade the receiving performance of the eavesdropper. The transmit power of the helpers is optimized with the worst-case secrecy rate requirement as the Quality of Service constraint. Based on robust convex optimization, a centralized optimization problem is developed for the helpers to generate interference efficiently with minimum total transmit power. A distributed algorithm is developed which scales well with a large number of helpers.     

Performance analysis of secure communications over correlated slow‐fading additive white Gaussian noise channels

The broadcast nature of communications in wireless communication networks makes it vulnerable to some attacks, particularly eavesdrop attack. Hence, information security can have a key role to protect privacy and avoid identity theft in these networks, especially in distributed networks. In the wireless systems, the signal propagation is affected by path loss, slow fading (shadowing), and fast fading (multi‐path fading). As we know, there is a correlation between communication channels in the real radio environments. This correlation is defined by the correlation between their shadowing and/or multipath fading factors. So when there are several channels in the wireless systems, there is certainly a correlation between the channels. In this paper, we assume that the transmitter knows the full channel state information (CSI), it means the transmitter knows both the channel gains of the illegitimate (ie, eavesdropper) and the legitimate receivers and study the performance of secure communications of single‐input single‐output (SISO) systems consisting of single antenna devices, in the presence of a single antenna passive eavesdropper over correlated slow fading channels, where the main (transmitter to legitimate receiver) and eavesdropper (transmitter to illegitimate receiver) channels are correlated. Finally, we present numerical results and verify the accuracy of our analysis by Monte‐Carlo simulations.     

Secrecy outage performance analysis of MIMO underlay cognitive radio networks with delayed CSI and transmitter antenna selection

Cognitive radio network is an emerging solution to deal with spectrum scarcity and to utilize the radio spectrum in opportunistic and efficient manner. Secure data transmission is one of the important issues in these kind of networks. This work studies the secrecy outage performance of a multiple-input multiple-output underlay cognitive wiretap radio network system over Rayleigh fading channel with delayed channel state information. This work considers that the secondary transmitter is equipped with multiple antennas and confidential information is transmitted from to multiantenna receiver in the presence of multiantenna eavesdropper. Further, the transmit antenna selection scheme is considered at secondary transmitter to reduce the complexity of antenna selection and to make it more practicable. To improve the quality of signal, this work considers maximal ratio combining (MRC) at secondary receiver, while selection combining and MRC techniques are utilized at the eavesdropper. The closed form expression for exact, asymptotic, and intercept secrecy outage probability has been derived, and the simulation is done for the validation of analytical results. The derived results reveal deterioration of channel secrecy performance with outdated channel state information, and the eavesdropper with outdated channel state information has also an adverse effect. Moreover, the diversity order that can be achieved in underlay cognitive radio network with outdated channel state information is unity.     

智能反射表面辅助无线能量传输的保密率最大化算法

为了减少窃听者对合法接收者的信息接收影响和窃听者的有用信息接收量,该文研究利用智能反射表面(IRS)来实现无线供电通信网络(WPCN)中窃听端处的波束抵消。首先在传输能量的同时进行窃听检测,IRS根据合法用户的能量状态选择是否采取防窃听模式,然后在存在窃听的情况下,研究了窃听信道完美和不完美状态下系统的保密率最大化问题。分析表明,这一最大化问题是相移、功率分配、时间分配的多变量耦合非凸问题,可以采用分步优化、变量替换和S-Lemma等方法进行求解。仿真结果表明,与基准算法相比,所提算法提升了保密率,当智能反射表面元件数为80时保密率提升了44%,发射功率为40 dBm时保密率提升了34%。     

窃听信道相关条件下最大比传输技术安全分析

在无线通信系统的实际传输中,当窃听用户距离合法接受者足够近,或者位于合法接收机信号的无线电波路径上时,就会出现主信道与窃听信道相关的场景。为此我们考虑一个多输入单输出,并且存在单天线被动窃听者的无线通信系统,研究了当基站采用最大比技术发射技术发送信号时,相关对系统性能的影响。推导了安全中断概率与平均安全容量的闭合表达式。数值仿真结果表明:（1）当主信道的信道质量高于窃听信道时,较低的相关对系统安全中断概率性能影响不大,然而强相关却能够带来更低的安全中断概率;（2）该相关对系统平均安全容量始终是有害的,且随着相关程度的增强,最大比发射技术相对于天线选择的优势逐渐变小。      

Enhancing secrecy rates in a wiretap channel

Reliable communication imposes an upper limit on the achievable rate, namely the Shannon capacity. Wyner's wiretap coding ensures a security constraint and reliability, but results in a decrease of achievable rate. To mitigate the loss in secrecy rate, we propose a coding scheme in which we use sufficiently old messages as key and prove that multiple messages are secure with respect to all the information possessed by the eavesdropper. We also show that we can achieve security in the strong sense. Next, we study a fading wiretap channel with full channel state information of the eavesdropper's channel and use our coding/decoding scheme to achieve a secrecy capacity close to the Shannon capacity of the main channel (in the ergodic sense). Finally, we study a case where the transmitter does not have instantaneous information of the channel state of the eavesdropper, but only its distribution.     

Proactive Eavesdropping via Pilot Contamination and Jamming

Proactive eavesdropping is a new paradigm shift in wireless physical layer security from preventing conventional eavesdropping attacks to legitimate intercepting suspicious communications, which has attracted a lot of attention recently. Pilot contamination is one effective technique in proactive eavesdropping, which spoofs the suspicious transmitter on channel estimation by sending the same pilot signal as the suspicious receiver, and lets it leak information in the direction of the legitimate eavesdropper during its transmission. However, this technique may fail when an anti-pilot-contamination mechanism called “energy ratio detector (ERD)” is applied at the suspicious receiver. To deal with the case that the suspicious receiver is a smart device using ERD, in this paper, we study using pilot contamination along with jamming to improve the legitimate eavesdropping performance. We first derive a closed-form expression for the probability of pilot contamination being detected by the suspicious receiver, and use it to obtain a closed-form expression for the eavesdropping rate. Using this theoretical analysis result, we propose an algorithm to maximize the eavesdropping rate by jointly optimizing the pilot contamination power and jamming power via two-dimensional search. Simulation results show that the proposed eavesdropping rate maximization algorithm can significantly improve eavesdropping rate, as compared to other benchmark schemes.     

Secure MIMO Communications in a System with Equal Numbers of Transmit and Receive Antennas

Secure communications in a multiple input multiple output (MIMO) system in which the eavesdropper's channel is inherently superior to that of the legitimate receiver is described. Both the legitimate receiver and the eavesdropper are assumed to have equal knowledge and comparable computational capabilities and there is no "secret key" known only to the legitimate receiver. The combination of artificial noise added at the transmitter, parallelization of the legitimate channel using the singular value decomposition, and low density parity check (LDPC) codes can overcome the superiority of the eavesdropper's channel and enable secure communications. The effectiveness of the method is greater for larger numbers of antennas and larger modulation constellations.     

Resource optimization of secure energy efficiency based on mmWave massive MIMO-NOMA system with SWIPT

The secure energy efficiency (SEE) problem was investigated for the millimeter wave (mmWave) multiple input multiple output (MIMO) non-orthogonal multiplex access (NOMA) systems with simultaneous wireless information and power transfer (SWIPT) in the presence of multiple legitimate receiver (LR) and an eavesdropper.LR was first grouped according to the channel state information and the cluster heads of each group were selected,then the LR of each cluster was served by each beam with NOMA and hybrid precoding technology.Based on this,a SEE maximization problem was formulated by optimizing power allocation and power splitting factors.The Dinkelbach algorithm and first order Taylor approximation were proposed to transform the original non-convex problem into a convex one,and an iterative algorithm was developed to solve it.Finally,numerical results show that the proposed scheme can effectively improve the SEE.