一种基于时空编码的物理层安全算法

针对多天线窃听系统的物理层安全问题,提出一种基于时空编码的预编码算法。首先,合法接收者发送训练序列用于发送者估计主信道状态信息,而窃听信道的状态信息合法用户均未知;其次,发送者利用均匀信道分解的方法提取主信道状态信息的特征参数,生成发射端预编码矩阵和合法接收端均衡矩阵,收发联合加密处理提高物理层安全;最后,利用 Monte Carlo方法进行仿真实验,数值分析表明,该算法在窃听者天线数目增多时能够实现非负的保密容量,即使窃听信道质量较好时,窃听者的接收性能仍维持在很差的水平,误码率高达0.5。     

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%。     

Preventing Eavesdropper by Artificial Noise in MIMO-OFDM Systems

The PHY security has been the focus of the researchers since the day it was proposed. The researchers have mentioned many kinds of methods to prevent the eavesdropper from overhearing the confidential signal in different types of networks and environments. However, none of them have proposed a method which can be used in MIMO-OFDM. In this paper, we propose a new method to protect the confidential signal from the eavesdropper. We present a new antennas allocation scheme to make a full use of the CSI of the transmitter and helpers, and propose a double check scheme to distinguish the eavesdropper from helpers. At last, we use GA solve the optimization equation and gain the maximum of the secrecy capacity within limited power consumption. To the best of our knowledge, this is the first method of dealing with the eavesdropper in MIMO-OFDM, and both the schemes, including the antennas allocation scheme and the double check scheme, are the first of its kinds in this type of network environment.     

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.      

Secrecy outage analysis in a hybrid cognitive relay network with energy harvesting

In this paper, we investigate the physical layer security of a hybrid cognitive relay network using an energy harvesting relay in presence of an eavesdropper. In the hybrid scheme, a secondary user (SU) as well as a cognitive relay works either in underlay or in overlay mode. In underlay, the transmit power of the SU as well as the relay is limited by the maximum acceptable interference at primary user (PU) receiver as required by an outage constraint of PU, a quality of service for PU. The secondary network consists of a decode and forward relay that harvests energy from radio frequency signal of secondary transmitter as well as PU transmitter to assist the SU in forwarding the information signal to the destination. A time switching relaying protocol is used at the relay. We evaluate the secrecy outage probability of secondary relay network assuming that channel state information of the interfering links from both the SU and relay transmitter to PU receiver is imperfect. Our results reveal the impact of imperfect channel state information, energy harvesting time, tolerable interference threshold, and PU outage constraint on the secrecy outage probability of SU.     

Joint transmitter-receiver optimization in synchronous multiusercommunications over multipath channels

Transmitter optimization, in addition to receiver optimization, contributes significantly to efficient interference suppression in multiple access and multipath channels. The system design is based on the joint optimization of the transmitter and the receiver in a synchronous multiuser channel characterized by multipath propagation. Joint optimization is represented by a linear transformation of the transmitted signals at the transmitter and a linear transformation of received signals at each receiving site that minimize the effect of multiple access and multipath interference. The minimum mean squared error between the true bit value and its estimate at the output of the receiver is taken as the cost function, subject to average and peak transmit power constraints. It is shown that joint transmitter-receiver optimization outperforms significantly either transmitter optimization or receiver-based techniques. The crucial assumption, in the case of multipath channels, is that the transmitter knows the multipath characteristics of all channels and that the channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over a block of preceded bits. The practical applications can be found in indoor and cellular communications, satellite communications, or military communications where nonorthogonal signature waveforms are employed     

Underlay协同频谱共享系统中基于SDF-DZFB的物理层安全传输

协同中继传输不仅能改善认知用户的传输可靠性,而且也能增强认知用户物理层安全性。针对Underlay模式下多中继协同频谱共享认知无线网络,本文设计了基于选择译码转发和分布式迫零波束成形（SDF-DZFB）的物理层安全传输方案,其中,假设存在单个被动窃听节点窃听中继节点的发送信号,在认知用户发送端同时考虑峰值干扰温度约束和最大发射功率约束,中继和认知用户目的端都受到主用户干扰。在此情况下,分析了认知用户发送端分别到目的端（称为主链路）和到窃听节点（称为窃听链路）的等效信干噪比的统计特性,进而推导出系统安全中断概率性能的闭式表达式。为了揭示所提物理层安全传输方案的安全分集度性能,本文进一步分析了高信噪比条件下安全中断概率的渐近表达式。计算机仿真验证了本文的理论分析结果。      

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.     

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.     

Security enhancement with joint transmit antenna selection and transmit beamforming under energy harvesting constraints

This paper considers a multiuser multiple‐input single‐output (MISO) broadcasting system with simultaneous wireless information and power transfer (SWIPT), which consists of one information receiver (IR) and several energy harvesting receivers (ERs) which are capable of eavesdropping the legitimate signals. For reducing cost and hardware complexity, transmit antenna selection (TAS) is applied in the transmitter. We aim to maximize the achievable secrecy rate under the individual energy harvesting constraint at the ERs and the transmit power constraint at the transmitter by jointly optimizing TAS, transmit beamforming, and artificial noise (AN). The joint optimization problem is a non‐convex mixed integer programming problem. We apply variable replacements to decouple the variable couplings and relax and approach the binary constraint by the difference of two convex constraints. Afterwards, penalty method and constrained concave convex procedure (CCCP) are applied to transform the relaxed problem into a sequence of semi‐definiteness programming (SDP) problems. Simulation results shows that our proposed joint optimization scheme is superior over existing non‐joint optimization schemes. This paper studies the joint transmit antenna selection (TAS), transmit beamforming, and artificial noise (AN) optimization in a multiple‐input multiple‐output (MISO) wiretap system with simultaneous wireless information and power transfer (SWIPT). The joint optimization problem is nonconvex and we propose a penalty method based scheme to solve it. The simulation results show that our joint optimization scheme is superior to other non‐joint optimization schemes.     

Antenna combining for the MIMO downlink channel

A multiple antenna downlink channel where limited channel feedback is available to the transmitter is considered. In a vector downlink channel (single antenna at each receiver), the transmit antenna array can be used to transmit separate data streams to multiple receivers only if the transmitter has very accurate channel knowledge, i.e., if there is high-rate channel feedback from each receiver. In this work it is shown that channel feedback requirements can be significantly reduced if each receiver has a small number of antennas and appropriately combines its antenna outputs. A combining method that minimizes channel quantization error at each receiver, and thereby minimizes multi-user interference, is proposed and analyzed. This technique is shown to outperform traditional techniques such as maximum-ratio combining because minimization of interference power is more critical than maximization of signal power in the multiple antenna downlink. Analysis is provided to quantify the feedback savings, and the technique is seen to work well with user selection and is also robust to receiver estimation error.     

Impact of the secondary service transmit power constraint on the achievable capacity of spectrum sharing in rayleigh fading environment

The two main constraints on the transmit power allocation of the secondary service in a spectrum sharing scheme are the received interference threshold at the primary receiver, and the maximum transmit power of the secondary user. We obtain a critical system parameter which relates these two constraints and enables the system designer to eliminate the interference threshold constraint by adjusting the maximum transmit power of the secondary users. Eliminating the interference threshold constraint significantly reduces the system complexity by making the power allocation of the secondary service independent from the channel state information between the secondary transmitter and the primary receiver; thus removes the need for signaling between primary and secondary systems.     

Approaching MIMO-OFDM Capacity with Per-Antenna Power and Rate Feedback

This paper presents power-efficient transmission schemes for the multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) block-fading channel under the assumption that the channel during each fading block is known perfectly at the receiver, but is unavailable at the transmitter. Based on the well-known vertical Bell Labs layered space-time (V-BLAST) architecture that employs independent encoding for each transmit antenna and successive decoding at the receiver, this paper presents a per-antenna-based power and rate feedback scheme, termed the "closed-loop" V- BLAST, for which the receiver jointly optimizes the power and rate assignments for all transmit antennas, and then returns them to the transmitter via a low-rate feedback channel. The power and rate optimization minimizes the total transmit power for support of an aggregate transmission rate during each fading block. Convex optimization techniques are used to design efficient algorithms for optimal power and rate allocation. The proposed algorithms are also modified to incorporate practical system constraints on feedback complexity and on modulation and coding. Furthermore, this paper shows that the per-antenna-based power and rate control can be readily modified to combine with the conventional linear MIMO transmit preceding technique as an efficient and capacity-approaching partial-channel-feedback scheme. Simulation results show that the closed-loop V-BLAST is able to approach closely the MIMO-OFDM channel capacity assuming availability of perfect channel knowledge at both the transmitter and the receiver.     

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。      

单用户MIMO系统的可信通信技术

针对由一个发射者、一个合法接收者和一个非法接收者组成的单用户多输入多输出（MIMO,Multiple Input Multiple Output）窃听信道,研究了未知非法接收者任何信息的前提下,实现可信通信的人为干扰机制,给出了设计人为干扰的两种方式和高效的预编码算法。该算法增强了信号传播的方向性,同时最大化了人为干扰对非法接收者的影响。仿真结果表明,采用该算法的人为干扰在满足合法接收者所要求的最低信干噪声比（SINR,Signal to Interference Plus Noise Ratio）的同时,极大地降低了非法接收者的SINR。     

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.     

Outage Probability Analysis of MIMO Cognitive Radios with Single Transmit and Receive Antenna Selection

For multiple-input multiple-output cognitive radio systems, we propose an optimal single transmit and receive antenna selection scheme which maximizes the signal-to-interference-and-noise ratio. Considering peak interference power constraint, peak transmit power constraint, and interference from primary transmitter to cognitive receiver, we theoretically derive the exact system outage probability. It is shown that the theoretical results match simulation results.     

Adaptive transmitter optimization for blind and group-blind multiuser detection

The linear subspace-based blind and group-blind multiuser detectors recently developed represent a robust and efficient adaptive multiuser detection technique for code-division multiple-access (CDMA) systems. In this paper, we consider adaptive transmitter optimization strategies for CDMA systems operating in fading multipath environments in which these detectors are employed. We make use of more recent results on the analytical performance of these blind and group-blind receivers in the design and analysis of the transmitter optimization techniques. In particular, we develop a maximum-eigenvector-based method of optimizing spreading codes for given channel conditions and a utility-based power control algorithm for CDMA systems with blind or group-blind multiuser detection. We also design a receiver incorporating joint optimization of spreading codes and transmitter power by combining these algorithms in an iterative configuration. We will see that the utility-based power control algorithm allows us to efficiently set performance goals through utility functions for users in heterogeneous traffic environments and that spreading code optimization allows us to achieve these goals with lower transmit power. The signal processing algorithms presented here maintain the blind (or group-blind) nature of the receiver and are distributed, i.e., all power and spreading code adjustments can be made using only locally available information.     

MISO窃听信道下有限反馈波束成形算法的保密速率分析(英文)

The secrecy rate of limited feedback beamforming is studied for a Multiple-Input Single-Output(MISO) wiretap channel with a multi-antenna eavesdropper.We first obtain the secrecy rate of limited feedback beamforming achieved at the legitimate receiver.We then derive a lower bound for the asymptotic secrecy rate in the large system limit.From this bound,we observe a threshold for the ratio of eavesdrop antennas to transmit antennas to obtain a positive secrecy rate.We further show that the secrecy rate loss due to limited feedback decays with the number of feedback bits per transmit antenna.     

Joint interference alignment precoding based on the optimization algorithm on the Grassmannian manifold

To solve the interference problem between users of the multiuser MIMO system, we first transform the system sum rate maximization problem into joint optimization of interference signal power and useful signal power. On this basis, we propose a weighted interference alignment objective function, causing the system to obtain a higher sum rate by adjusting the weight with different signal-to-noise ratios. Then, we model the transmit subspace and the interference subspace on the Grassmannian manifold and propose joint interference alignment precoding based on the Grassmannian conjugacy gradient algorithm (GCGA-JIAP algorithm). In contrast to conventional interference alignment algorithms, our proposed algorithm can reduce the computational cost by transforming the constrained optimization of the complex Euclidean space into unconstrained optimization with the degenerate dimension on the Grassmannian manifold. Computer simulation shows that the proposed algorithm improves the convergence of the iterative optimization of the transmitter precoding matrix and the receiver postprocessing matrix and also improves the sum rate performance of the multiuser MIMO interference system.