Adaptive Array Behavior with Sinusoidal Envelope Modulated Interference

The behavior of a LMS (least mean square) adaptive array with modulated interference is described. An interference signal with sinusoidal, double-sideband, suppressed-carrier modulation is assumed. It is shown that such interference causes the array to modulate the desired signal envelope but not its phase. The amount of the desired signal modulation is determined as a function of signal arrival angles and powers and the modulation frequency of the interference. Such interference also causes the array output signal-to-interference-plus-noise ratio (SINR) to vary with time. However, it is shown that when the desired signal is a digital communication signal, the averaged bit error probability is essentially the same as for continuous wave (CW) interference.     

Adaptive Array Behavior with Periodic Phase Modulated Interference

We consider a least mean square (LMS) adaptive array [1] receiving a phase modulated interference signal. The phase modulation is assumed to be periodic and to have finite bandwidth. Under these assumptions, we determine the time-varying array weights, the modulation on the array output desired signal, and the time-varying output interference-to-noise ratio (INR) and SINR (signal-to-interference-plus-noise ratio). We present numerical results describing the behavior of a 2-element adaptive array that receives an interference signal with sinusoidal phase modulation. We show how each signal parameter (arrival angle, power, modulation index, and modulation frequency) affects the performance of the array.     

The Effect of a Pulsed Interference Signal on an Adaptive Array

The performance of a least mean square (LMS) adaptive array in the presence of a pulsed interference signal is examined. It is shown that a pulsed interference signal has two effects. First, it causes the array to modulate the desired signal envelope (but not its phase). Second, it causes the array output signal-to-interferenceplus-noise ratio (SINR) to vary with time. The desired signal modulation is evaluated as a function of signal arrival angles, powers and interference pulse-repetition frequency (PRF) and pulsewidth. It is shown that the signal modulation is small except when the interference arrives close to the desired signal. To evaluate the effect of the time-varying SINR, it is assumed that the array is used in a differential phase-shift keyed (DPSK) communication system. It is shown that the SINR variation causes a noticeable but not disastrous increase in the bit error probability.     

The Performance of an LMS Adaptive Array with Frequency Hopped Signals

The performance of an LMS adaptive array with a frequency hopped, spread spectrum desired signal and a CW interference signal is examined. It is shown that frequency hopping has several effects on an adaptive array. It causes the array to modulate both the amplitude and the phase of the received signal. Also, it causes the array output SINR (signal-to-interference-plus-noise ratio) to vary with time and thus increases the bit error probability for the received signal. Typical curves of the desired signal modulation and the time-varying SINR at the array output are presented. It is shown how the array performance depends on hopping frequency, frequency jump size, interference frequency, signal arrival angles, and signal powers.     

An Adaptive Interference Canceling Array Utilizing Hybrid Techniques

The steady state properties of an adaptive array utilizing prior knowledge of both approximate signal arrival direction and signal characteristics are presented. The method combines the features of a directionally constrained array and an array with a self-generated reference signal. Explicit results are obtained for output signal, interference, and noise powers assuming a single interferer is present. The inclusion of a self-generated reference circuit is shown to reduce the sensitivity to pointing error typical of arrays utilizing a zero order directional constraint, the improvement being a consequence of the reduction of the desired signal component fed back to the sidelobe canceling circuit. A relationship between the degree of sensitivity reduction and the quality of the reference signal is developed. Results of computations of signal to interference plus noise ratios for a 7-element 10-wavelength nonuniformly spaced array as a function of pointing error are presented. These results show the behavior with one interferer inside and outside the beamwidth of the quiescent array and with multiple interferers for various degrees of perfection of the reference generating circuit. In all cases the computations confirm that the otherwise severe effects of small pointing errors are substantially reduced.     

Median cascaded canceller for robust adaptive array processing

A median cascaded canceller (MCC) is introduced as a robust multichannel adaptive array processor. Compared with sample matrix inversion (SMI) methods, it is shown to significantly reduce the deleterious effects of impulsive noise spikes (outliers) on convergence performance of metrics; such as (normalized) output residue power and signal to interference-plus-noise ratio (SINR). For the case of no outliers, the MCC convergence performance remains commensurate with SMI methods for several practical interference scenarios. It is shown that the MCC offers natural protection against desired signal (target) cancellation when weight training data contains strong target components. In addition, results are shown for a high-fidelity, simulated, barrage jamming and nonhomogenous clutter environment. Here the MCC is used in a space-time adaptive processing (STAP) configuration for airborne radar interference mitigation. Results indicate the MCC produces a marked SINR performance improvement over SMI methods.     

暂态信号形成的参量阵声场特性

暂态参量阵技术容易获得低频宽带信号,是诸多声呐系统广泛使用的信号模式。在众多描述非线性声波 传播的理论模型中,KZK方程能够准确地描述有限振幅声波传播的衍射、吸收及非线性效应,是描述参量阵非线性 声场最为精确的方程之一。文章从KZK方程的时域求解出发,对常见暂态信号自解调形成的参量阵进行分析。 理论研究表明,暂态信号参量阵的声场特性主要与信号包络的载波、上升沿有直接关系。高斯包络脉冲的上升沿 越陡峭,相同轴向位置的低频分量幅值越大,相同峰值功率前提下的能量转换效率越高；当被调制载波的中心频率 一致时,正线性调频信号调制得到的参量阵声压幅值要略高于负线性调频信号。文章可为暂态信号参量阵的辐射 波形选择提供初步的理论指导。     

基于Kalman滤波的GPS/INS接收机自适应干扰抑制方法

 考虑到惯导信息辅助GPS(GPS/INS)接收机对干扰抑制实时性的要求,提出一种基于Kalman滤波的GPS/INS接收机自适应干扰抑制方法。自适应广义旁瓣相消(GSC)多采用低复杂度最小均方(LMS)算法更新权矢量,收敛速率较低,严重时会导致接收机定位中断。首先利用Householder变换构建GSC下支路的阻塞矩阵,用于阻塞任意二维阵型阵列接收的期望信号;再用Kalman滤波自适应更新下支路权矢量,从而有效提高阵列输出信干噪比(SINR)。理论分析和仿真结果说明本文方法可有效抑制干扰对接收机的影响,且具有实时性高的特点。     

调频引信中噪声调幅干扰的自适应抑制

噪声调幅干扰是一种有效的压制性干扰,可压制近炸无线电引信对目标信息的获取。为提高线性调频无线电引信抗噪声调幅干扰的能力,将单频率自适应陷波器应用到线性调频引信中,对噪声调幅干扰进行抑制。分析了噪声调幅干扰抑制原理,并对噪声调幅干扰抑制效果进行了仿真。仿真结果表明:SJB=-10 d B时,仍然能达到很好的噪声调幅干扰抑制效果。     

数模转换器毛刺对光纤陀螺相关检测的影响分析

数模转换器(DAC)是全数字闭环光纤陀螺反馈通道的重要部件,DAC的毛刺特性会对光纤陀螺的调制解调结果产生影响.基于DAC中值毛刺特性建立了光纤陀螺反馈回路的非理想调制方波模型,分析了调制频率与本征频率不同时DAC毛刺在干涉信号中产生的各类周期干扰信号.利用周期干扰信号的Fourier级数推导出了DAC毛刺造成调制解调误差的数学模型,仿真分析了数模转换器毛刺的宽度、高度,光纤陀螺调制频率、本征频率及放大电路的增益带宽对陀螺解调误差的影响.最后,通过开环实验验证了DAC毛刺对光纤陀螺调制解调的影响.     

The Effects of Gaussian Interference on Communication Systemswith Adaptive Arrays

The performance of a bandlimited binary phase-shift-keyed (BPSK) communication system is examined when the received BPSK signal is corrupted by both thermal noise and a directional Gaussian noise interfering signal. The system uses an LMS adaptive array to suppress this interference. The effects of signal power levels, arrival angles, bandwidths, and the array bandwidth are examined. The performance of a system that uses tapped delay lines for the array weights is also examined. It is shown that the performance of a system with tapped delay lines is not affected by the interference bandwidth for a single interferer.     

阵列宽带Lamb波在结构损伤检测中的应用

阵列信号处理中的空间谱估计可以对信号源进行辨别和定位,于是通过采集在结构上布置的阵列传感器Lamb波信号用来检测损伤发生的位置。通常,大多数空间谱估计方法均以窄带信号为假定,在很多基于Lamb波的结构损伤检测中,为了减小频散特性的影响,大多数研究以Lamb波为窄带信号进行分析,但无限窄的激励信号是物理不可实现的。因此,其在多数情况下Lamb波信号并不符合窄带信号假定,更应被认为是一种宽带信号来进行处理。进而利用空间谱估计中宽带信号非相干子空间处理方法（Incoherent Signal Subspace Method,ISM）中阵列接收的宽带Lamb波信号进行处理,检测出结构发生单一损伤时的损伤位置。随后,当结构损伤与边界反射波有叠加时会引起损伤信号相干,采用宽带信号相干子空间方法（Coherent Signal Subspace Method,CSM）对损伤位置进行检测,得到了较好的结果。     

The Effect of Random Steering Vector Errors in the Applebaum Adaptive Array

The effect of random errors in the steering vector of an Applebaum adaptive array is examined. Each component of the steering vector is assumed to have a random error component uncorrelated between elements. The array output signal-to-interferenceplus-noise ratio (SINR) is computed as a function of the error variance. It is shown that the array output SINR becomes more sensitive to steering vector errors as more elements are added to the array and as the received desired signal power becomes larger. The variance of the steering vector error that may be tolerated depends on the required desired signal dynamic range. The larger the dynamic range that must be accommodated, the smaller the error variance must be.     

基于LMD的包络谱特征值在滚动轴承 故障诊断中的应用

滚动轴承故障振动信号往往是多分量的调幅-调频信号,而传统包络分析方法需要根据经验设置滤波器的中心频率与带宽,因而会带来解调误差.基于此,提出了一种基于局域均值分解(local mean decomposition,简称LMD)的包络谱特征值的滚动轴承故障诊断方法.该方法可以将一个多分量的调幅-调频信号分解成若干瞬时频率具有物理意义的PF (product function,简称PF )分量之和,由于每一个PF分量是分量包络信号和纯调频信号的积,因此可以直接对包络信号进行频谱分析得到包络谱.然后定义信号在包络谱中不同故障特征频率处的幅值比为包络谱特征值,并以此作为特征向量输入到支持向量机分类器中,用以区分滚动轴承的工作状态和故障类型.对滚动轴承正常状态、内圈故障和外圈故障振动信号的分析结果表明了该方法的有效性.      

An Lms Adaptive Array Using a Pilot Signal

A least mean square (LMS) adaptive array requires a reference signal. When the desired signal contains a pilot signal, it may be used as the reference signal. In this paper the steady-state performance of an LMS adaptive array in which the pilot signal is used as the reference signal is examined. It is shown that the LMS adaptive array occasionally suppresses the desired signal. The loop gain, which is an important parameter, is also considered.     

Cumulant-based blind optimum beamforming

Sensor response, location uncertainty, and use of sample statistics can severely degrade the performance of optimum beamformers. We propose blind estimation of the source steering vector in the presence of multiple, directional, correlated or coherent Gaussian interferers via higher order statistics. In this way, we employ the statistical characteristics of the desired signal to make the necessary discrimination, without any a-priori knowledge of array manifold and direction-of-arrival (DOA) information about the desired signal. We then improve our method to utilize the data in a more efficient manner. In any application, only sample statistics are available, so we propose a robust beamforming approach that employs the steering vector estimate obtained by cumulant-based signal processing. We further propose a method that employs both covariance and cumulant information to combat finite sample effects. We analyze the effects of multipath propagation on the reception of the desired signal. We show that even in the presence of coherence, cumulant-based beamformer still behaves as the optimum beamformer that maximizes the signal-to-interference-plus-noise ratio (SINR). Finally, we propose an adaptive version of our algorithm simulations demonstrate the excellent performance of our approach in a wide variety of situations     

一种盲多波束形成GNSS天线阵抗干扰算法

天线阵抗干扰是现代卫星导航接收机抗干扰的重要手段。传统的天线阵波束形成类算法能够在抑制干扰的同时提升抗干扰后输出信噪比,但是在信号捕获阶段,由于缺少先验信息的支持,该类算法无法在信号方向形成增益。因此,提出了一种盲多波束形成的天线阵抗干扰算法,通过形成多个波束覆盖天线阵上半球面,可在无先验信息的条件下对卫星信号形成增益,从而提升信号捕获阶段信噪比,使得接收机在干扰环境中具备更强的信号捕获能力。仿真结果表明:与传统的天线阵抗干扰算法相比,提出的算法能够在有效抑制干扰的同时显著提升接收机信号捕获成功率。     

基于相减式信号抵消的带内隐藏干扰检测

为实现对通信信号的实时监测,提出一种带内隐藏干扰检测方法。该方法先利用解调结果重构期望信号,然后通过时延估计及自适应滤波使其与接收信号中的有用信号在时间、幅度和相位上尽量保持一致,最后利用相减式信号抵消技术将其从接收信号中消除,能够在不中断通信业务的前提下检测出信号带宽内隐藏的干扰。仿真结果表明,当信干比不低于6 dB、信噪比不低于3 dB时,期望信号、干扰信号与各自原信号的相似系数均能达到0.9以上,提取的干扰信号非常准确。将利用文中方法估计出的干扰抵消后,信号的星座图也得到了显著的收敛。     

非圆特征恢复特征空间投影鲁棒波束形成

提出了一种利用非圆特征恢复思想的鲁棒波束形成方法。该方法在特征空间投影技术的基础上,进一步利用波束形成器输出的非圆特征参数构造代价函数,通过角度搜索使代价函数最大化来修正主瓣中心指向,在保证鲁棒性的同时尽可能提升波束形成器的输出性能。同时,该方法不需要设置用户参数,且适用于任意阶非圆信号,对于旁瓣干扰信号的非圆特性不敏感,具有广泛的应用背景。最后分别针对二阶非圆信号情形和高阶非圆信号情形进行了仿真,仿真结果验证了该方法的有效性和优越性。     

Comparison of Bit Synchronization Schemes Using AM and Summed Clocks

This paper considers bit synchronization through the use of a separate clock signal which is either amplitude modulated onto or summed with the data signal. For continuous data transmission, such schemes are known to be inferior, in the sense of efficient use of power, to schemes which derive synchronization directly from the data signal. However, these techniques have application in burst systems such as spacecraft command systems, and in systems where receiver simplicity is more important than power conservation. For systems in which the composite data-clock signal subsequently modulates an RF carrier, it is shown that the summed clock signal performs slightly better than the AM clock signal, and that for both signal types, the optimum allocation of power between data and clock is approximately 9:1.