Quickest physical‐layer MGD anomaly detection for jamming attacks in centralized modulated wideband converter‐based ROC curve

In wireless communication systems, physical‐layer security menaces have evolved from jammers. Jammers, due to their furtive nature, make wireless communication systems vulnerable. The novelty in this work is to combine centralized modulated wideband converter, which is a networking system developed from the modulated wideband converter–based sub‐Nyquist sampling theory with a multivariate Gaussian distribution (MGD) anomaly detector‐based receiver operating characteristic curve that plot the detection rate (DR) versus false alarm rate (FAR) at various threshold values. We supposed the presence of a group of jammers in the spectrum corrupted with the primary source signal and noise. The received primary signal at each cognitive radio (CR) receiver is converted in to a digital signal using an analog‐to‐information converter. Each CR receiver give minimum number of samples denoted N₁. All these compressed samples from every CR receiver are collected in the form of matrix called compressed sampling matrix, which is considered directly as the input of the MGD detector. The intelligent MGD detector proposed in the level of fusion center is based on the characteristics of the MGD. The numerical results show that this new system of combination detects faster anomalies perfectly in the presence of jammers in the spectrum in real‐time scenarios. Performance evaluation is performed in terms of DR versus FAR at different detection threshold values, under the presence of attacks in the system. By employing well‐known machine learning algorithms called MGD, the performance of this new proposed system shows good.     

GPS空时抗干扰子空间投影方法

根据GPS接收机接收信号、噪声和干扰的特点，将子空间投影方法与空时信号处理相结合，利用基于数据域相关相减结构多级维纳滤波器（CSA-MWF）的前向递推多级分解特性构造出空时二维干扰子空间，进一步求出空时抗干扰最佳权。与传统的特征值分解方法相比，该方法避免了估计接收数据协方差矩阵及其特征分解运算，计算量大幅下降，同时抗干扰性能不受影响，适合多变环境和小数据样本情况。该方法结构简单，具有较高的可行性和实用性。仿真结果验证了该方法对窄带和宽带干扰均有效。     

Adaptive beamforming with the generalized sidelobe canceller in the presence of array imperfections

Antenna designers often employ linearly constrained adaptive beamforming as an antijamming measure. With minimal a priori knowledge of the signal environment, this technique nulls out jammers while simultaneously preserving the quality of the main lobe so that a friendly look-direction signal can be received with unity gain. Unfortunately, in the absence of special strategies, linearly constrained adaptive beamforming is hypersensitive to array imperfections when the input signal-to-noise ratio exceeds a certain threshold. This hypersensitivity manifests itself as a nailing of the friendly signal as if it were a jammer. Luckily, the signal nulling problem can be easily remedied by artificial receiver noise injection. A particularly simple and general structure for linearly constrained adaptive beamforming was proposed during the 1970's, and is known as the generalized sidelobe canceller. A detailed analysis of the generalized sidelobe canceller in the presence of array imperfections is discussed, and two new artificial receiver noise injection algorithms are proposed. Computer simulations are included to demonstrate that use of these new algorithms alleviates the signal nailing problem without seriously compromising jammer nulling. For the special case of the Capon maximum-likelihood beamformer, simple approximations are presented for: 1) the Wiener output signal-to-interference-plus-noise ratio (SINR_{0}astr), 2) the antenna element error variance that causes a 3 dB loss ofSINR_{0}astrfrom its value for an ideal array, and 3) the optimal artificial receiver noise that maximizesSINR_{0}astr.     

Constrained least squares in adaptive, imperfect arrays

Two new constrained deterministic least-squares algorithms are presented which are capable of enabling a narrow-band zero-order generalized sidelobe canceller (SLC), in the presence of array imperfections, to null out jammers while preserving the friendly look-direction signal with minimal a priori knowledge of the signal environment. The algorithms are capable of solving deterministic least-squares optimization problems subject to an equality constraint in an iterative, adaptive manner by imposing a `soft' constraint via the quadratic penalty function optimization method. The first algorithm is based on the matrix inversion lemma while the second is obtained by means of QR-decomposition using new three-dimensional Givens (1958) rotations and implemented with a systolic array architecture. These new constrained algorithms improve system performance when an artificial injection of a receiver noise vector is introduced     

单脉冲导引头对多干扰源的角分辨

当多个噪声调频干扰同时进入单脉信号引头主波束内时，导引头对干扰源的角度分辨是非常困难的。本文主要研究了导引头单脉冲接收机对宽带噪声调频干扰源的响应，分析了当单脉冲主波束内存在多个噪声调频干扰源时，导引头指向角的跟踪规律，并重点讨论了一种用聚类来提取角信息的方法，最后仿真证实了该方法的正确性和有效性。     

Demodulation with a Multichannel Estimation Method Using a Reduced Rank Constraint

This paper deals with the Maximum Likelihood Estimation of the multichannel impulse response in a mobile communication system whose base stations are equipped with antennas arrays. The following problem is solved: using the training sequence, find the maximum likelihood multichannel impulse response from one mobile to the base station under a reduced rank constraint in the presence of gaussian noise and jammers with unknown covariance matrix. This method finds applications in demodulation (the reduced rank channel estimate can be used in a Viterbi Algorithm), and experimental results using real signals demonstrate its high performance compared with the standard Minimum Mean Square Error (MMSE) multichannel estimate.     

Effect of worst case multiple partial-band noise and tone jammerson coded FH/SSMA systems

The author characterizes and evaluates the effect of simultaneous multiple partial-band noise or tone jammers and other user interference on a single communication link employing frequency-hopped spread-spectrum (FH/SS) signaling, M-ary frequency-shift keying (FSK) modulation with noncoherent demodulation, and Reed-Solomon coding. For the symbol error probability of these systems, the author derives exact expressions in the absence of multiple-access interference and tight upper bounds in the presence of other-user interference. Although the analytical methods are valid for any number of multiple jammers, the numerical study is restricted to the cases of two and three-partial-band noise and tone jammers. For fixed values of the spectral densities of noise jammers, or the energies per symbol of tone jammers, the worst-case fraction of the band that each jammer should use in order to maximize the error probability of the FH/SS or FH/SSMA system is evaluated. For the range of the signal-to-jammer power ratios examined, multiple-noise or multiple-tone jammers appear to have no advantage over single-tone jammers of equivalent spectral density or energy per symbol, but achieve approximately the same worst-case performance by jamming smaller fractions of the band     

Interference suppression via orthogonal projections: a performanceanalysis

Several recent studies indicate the promise of subspace separation principles when applied to adaptive jammer suppression in phased array antennas. This paper theoretically analyzes the performance of a subspace separation technique based on orthogonal projections (OP) for adaptively suppressing interference in phased arrays; the theoretical performance predictions are validated using computer simulations. This analysis holds for the case when it is possible to differentiate between the vector spaces spanned by jammers and additive noise. The performance parameters used are (a) the average residual interference (jammer plus noise) power at the output of the adapted array as a function of the number of jammer snapshots used for calculating the weight vector, and (b) the similarity of the adapted array pattern to the design pattern away from the jammer locations. The performance of the OP-based subspace separation technique is compared with the sample matrix inversion (SMI) algorithm. It is shown that the weight vector calculated using OP converges more quickly to the optimal solution (infinite number of interference snapshots) than the SMI weight vector. Further, in contrast to the SMI adapted pattern, which exhibits large sidelobe levels away from the jammer locations, the OP adapted pattern closely follows the design pattern both in the mainbeam and in the sidelobe region away from the jammer locations     

大动态范围抗干扰导航接收机AGC 电路性能分析与优化设计

导航接收机的特点是信号比较微弱,通常淹没于噪声以下,其入口电平的波动几乎都由干扰引起。针对这一特点,存在干扰情况下,要求接收机的噪声系数不能显著恶化。射频通道的噪声系数是制约接收机噪声系数的因素之一,本文在给定射频通道噪声系数恶化容限的条件下,以射频通道能实现最大动态范围为优化目标,分析了动态范围及各级电路增益的求解方法;进一步,针对特殊的纯电阻网络AGC 电路,得到了更为简洁的求解方法;最后,本文给出了该类AGC 电路动态范围的设计实例并进行了测试,设计预期与测试结果得到较好的吻合。本文虽然针对导航接收机设计,但可推广应用于指导各类接收机的设计。     

Optimization Schemes for Protective Jamming

In this paper, we study strategies for allocating and managing friendly jammers, so as to create virtual barriers that would prevent hostile eavesdroppers from tapping sensitive wireless communication. Our scheme precludes the use of any encryption technique. Applications include domains such as (i) protecting the privacy of storage locations where RFID tags are used for item identification, (ii) secure reading of RFID tags embedded in credit cards, (iii) protecting data transmitted through wireless networks, sensor networks, etc. By carefully managing jammers to produce noise, we show how to reduce the SINR of eavesdroppers to below a threshold for successful reception, without jeopardizing network performance. In this paper, we present algorithms targeted towards optimizing power consumption and number of jammers needed in several settings. Experimental simulations back up our results.     

无源单脉冲雷达多干扰源目标分辨方法

对同时进入单脉冲雷达主波束内的多个宽带噪声调频干扰源进行角度分辨是非常困难的,该文分析了单脉冲雷达接收机对宽带噪声调频干扰信号的响应,通过适当选择接收机带宽,使接收机输出的干扰脉冲分离,并通过测量瞬时角信息,用统计分析法分辨多个干扰源目标角度,计算机仿真证实了该方法的正确性和有效性。     

Simultaneous nulling in sum and difference patterns by amplitude control

A method is discussed of suppressing jammers simultaneously in the sum and the difference patterns of a linear antenna array by either using complex weights or controlling the current amplitudes only, with special emphasis on the latter method. For a given array size, the total number of jammers that can be nulled is doubled if complex weights are used instead of real weights. However, the amplitude-only technique has many attractions. It is shown that because the resulting current amplitude distribution has a double symmetry, the number of attenuators required for simultaneous nulling can be as low as a quarter of the total number of elements in the array. This means a much faster computing speed as well as a considerable saving in hardware. The method also allows the main beam of the antenna to be scanned by using phase-shifters while nulls are placed in directions of known jammers in both the sum and difference patterns by using attenuators. As a result, the maximization of the signal-to-jammer ratio can be achieved with relative ease, because the stronger a jammer is, the easier it is to locate it and hence to suppress it.     

一种冲击噪声环境中的二维DOA估计新方法

该文提出了一种新的在冲击噪声环境中基于阵列输出信号分数低阶矩的二维测向方法稳健的协变异波达方向矩阵法。该方法利用冲击噪声和SS过程的特点,扩展了原波达方向矩阵法的信号模型和应用环境,对冲击噪声有较好的抑制作用,增强了算法的通用性和稳健性,弥补了传统的基于二阶或高阶统计量的子空间测向算法不能应用于冲击噪声环境的不足,计算机仿真验证了该算法的可行性和有效性。     

Maximum number of independent paths and radio connectivity

Methods for determining the network reliability of a multihop packet radio network in the presence of hostile jammers are discussed. A new connectivity parameter called radio connectivity is defined as the maximum number of disjoint communication paths that are still usable between given nodes s and d after the jammer is on or, more generally, the minimum number of jammers needed to disconnect s and d. A lower bound on the radio connectivity is computed by studying the number of jamming independent paths. The time complexity of obtaining the radio connectivity is analyzed and shown to be NP-hard except for some special cases. Greedy heuristics for developing approximate answers for general networks are described. Euclidean networks, in which the nodes and links correspond to points and line segments in the Euclidean geometry and satisfy Euclid's four fundamental axioms, are also discussed. It is found that the maximum number of independent paths between a pair of source and destination nodes that can possibly exist is five. An extension in which there is a protected zone of known size around the sender and receiver is studied     

多径传播条件下宽带线性调频信号波达方向估计方法

针对信号出现多径传播情况时现有宽带信号波达方向（direction of arrival, DOA）估计方法性能下降的问题,提出了一种多径传播条件下宽带线性调频（chirp）信号波达方向估计方法,该方法将导向有效投影（steered effective projection, STEP）技术与宽带线性调频信号的时频特性相结合,对具有不同时频特性的信号分量进行分离,逐个处理,并以时频分布矩阵代替传统的协方差矩阵,从而构造有效噪声子空间,实现时域角度估计。本方法无需进行信号聚焦操作,因此理论上不受聚焦误差的影响。仿真结果验证了所提方法的有效性。      

基于广义协方差矩阵的乘性和加性噪声中的谐波恢复

针对非零均值乘性噪声中的谐波恢复问题,本文提出一种基于广义协方差矩阵的乘性噪声中谐波个数和频率的估计方法。首先定义一类广义协方差并构造广义协方差矩阵,通过对广义协方差矩阵进行特征值理论分析,得到了非零均值乘性噪声中谐波分量个数与协方差矩阵特征值之间的内在联系,这个性质可以用来估计谐波分量个数。而且利用子空间旋转不变性技术,可以从协方差矩阵中估计出谐波的频率。本文所提方法对于乘性和加性噪声的颜色和分布均无任何假设,可以应用于任意分布和任意颜色的乘性和加性噪声中的谐波恢复。仿真实验表明,本文所提谐波恢复方法具有很高的频率分辨率。      

有源干扰机组网技术分析

研究有源干扰机在空中与地面相结合的情况下 ,可能实现的两种有源干扰机组网技术 ,讨论原理方案 ,分析组网的限制条件和特有的干扰技术 ,指出了应用组网形成的干扰技术 ,不仅增加了雷达或组网雷达抗干扰的难度 ,在某种条件下 ,反辐射武器也无能为力 ,能大大提高干扰机的生存概率 ,甚至能获得噪声相参干扰信号。     

一种基于正交加权约束的GPS抗干扰盲算法

针对GPS信号C/A码的周期重复特性,联合CAB算法和子空间技术提出了一种盲自适应波束形成方法。该算法通过将CAB算法的权矢量和控制矢量约束到干扰导向矢量的正交补空间内,使之在期望信号方向上产生高的增益,并在干扰方向上形成零陷。该方法具有盲处理、收敛速度快和低计算复杂度等优点。仿真结果证明了算法的有效性。     

噪声分布式干扰最佳分布方式研究

分布式干扰是现代战争中一种重要的雷达对抗方式。在总干扰资源有限的情况下,通过对多部干扰机的空间分布进行优化布置,可以实现最佳干扰效果。为了使噪声分布式干扰的有效干扰扇面最大,从多干扰机最佳相对干扰角度出发,提出多干扰机实施主瓣叠加干扰时的最佳分布方式。理论分析和计算机仿真表明,该分布方式可以实现最大有效干扰扇面。     

An adaptive nulling system for a narrow-band signal with alook-direction constraint utilizing the conjugate gradient method

The problem of iterative adjustments of the weights of a phased array with a look-direction constraint in the presence of jammers is presented. The technique described uses the adaptive conjugate method instead of the popularly used method of steepest descent to eliminate the jammer components, thus minimizing the error between the received signal and the actual one. This iterative method minimized the L₂ norm (the mean square error) and is guaranteed to converge in a finite number of steps which is not available for the present techniques utilized to solve this problem. Improvement in rate of convergence is thus achieved at the expense of algorithmic complexity