An adaptive array utilizing an adaptive spatial averaging technique for multipath environments

When the interference is coherent with the desired signal, the conventional adaptive arrays working under the guiding principle of output power minimization tend to cancel the desired signal by using the coherent interference. A technique is described which enables the adaptive array to function even under such an environment. The array is divided into subarrays, whose input correlation matrices are adaptively averaged so as to produce a Toeplitz matrix which would be obtained when the interference did not correlate with the desired signal. The averaged matrix is now free from correlation terms between the desired signal and interference, and therefore may be used to derive the optimum weight for the array element just as in the ordinary radio environment of incoherent interference. Numerical examples show that the new adaptive array is highly capable to suppress the coherent interferences as well as incoherent ones.     

空间平滑自适应阵列的优化

在多路径环境中，空间平滑是消除相干干扰对自适应阵列处理系统影响的有效方法。我们注意到空间平滑自适应阵列的权系数往往是在子阵列上得到的。这意味着存在一些剩余自由度可以用来改善自适应阵列的性能。本文提出了一种新方法，利用阵列自由度使得自适应阵列的响应具有期望的特性。我们指出如何优化空间平滑自适应阵列使得白噪声功率或者阵列的副瓣昼降低。数值结果说明了新方法的有效性。     

一种虚拟波束形成自适应加权空间平滑算法

该文提出了一种用于自适应阵列的自适应加权空间平滑算法。通过构造虚拟自适应波束形成问题求取用于子阵协方差矩阵加权的加权向量,然后进行加权空间平滑自适应波束形成。理论分析与仿真结果表明,新算法能更有效地降低期望信号和干扰之间的相关性,使得用于空间平滑的子阵数减少,以降低阵列孔径损失。     

基于二维虚拟空间平滑算法的跳频通信系统跟踪式干扰抑制研究

基于均匀矩形阵列,利用阵列接收信号及其共轭信息,推导出2维的虚拟空间平滑算法。通过构造2维虚拟子阵,消除干扰信号与期望信号之间的相关性,避免了有效阵列孔径的损失,提高了算法的空间谱分辨率。将该算法与相位补偿技术相结合,给出了一种抗跟踪式干扰的跳频通信系统。通过理论分析和模拟仿真,验证了该系统对跟踪式干扰具有较好抑制能力,在干扰方向的零陷抑制深度达50 dB以上,并且与普通跳频系统相比在-3 dB的强干扰环境下具有优良的误码率特性。     

Digital filters for attenuating interference arriving from a widerange of angles

Digital filters for the offline multichannel processing of the signals recorded by an array of sensors are derived with the objective of extracting a desired signal arriving from a known direction. Both the desired signal and coherent interference have arbitrary waveforms. Since the direction of arrival of the interference is unknown, the array response to it is treated as a random variable, and the expected value of its squared magnitude is taken as a minimization criterion in order to attenuate the coherent interference. The output power spectrum in response to the additive random sensor noise is taken as a second criterion. A convex combination of both criteria is minimized subject to an all-pass condition for the desired signal. Simulation results are presented showing the tradeoff between attenuating interference and random noise, the effect of the angular separation between the directions of arrival of the desired signal and interference and the effect of the number of sensors of the array on the output of the array filter     

On spatial smoothing for two-dimensional direction-of-arrivalestimation of coherent signals

We present an analysis of a spatial smoothing scheme extended for the estimation of two-dimensional (2-D) directions of arrival (DOAs) of coherent signals using a uniform rectangular array. The uniform rectangular array is divided into overlapping rectangular subarrays by the extended scheme, which is referred to as the 2-D spatial smoothing scheme. The analysis shows that when the extended preprocessing scheme is used in conjunction with the eigenstructure technique, the size of the subarrays should be at least (K+1)×(K+1), and the number of the subarrays must be no less than K×K in order to guarantee the “decorrelation” of κ coherent signals for all possible scenarios. The minimum size of the total uniform rectangular array is thus shown to be 2K×2K. Instead of using a uniform rectangular array, a minimal subarray structure incorporated with a minimal subarray grouping is also devised for resolving the 2-D DOAs of K coherent signals. The number of sensor elements of the minimal total array is then (K²+4K-2) instead of 4K²     

基于多级阻塞的稳健相干自适应波束形成

针对期望信号波达角(DOA)估计误差较大时相干波束形成性能下降的问题,该文提出一种基于多级阻塞的稳健相干自适应波束形成算法。该算法首先定义阻塞矩阵,推导多级阻塞原理,并利用其滤除阵列接收信号中的期望信号;然后给出空间中只存在期望信号时,子阵与全阵间阵列流型的映射关系,据此推导全阵扩展变换,并证明其在干扰信号存在条件下的有效性;最终利用扩展变换获取全阵最优权矢量,实现相干波束形成。该算法对期望信号波达角估计误差稳健,且无需干扰信号来向的先验信息,同时可以有效避免阵列孔径的损失。仿真分析验证了算法的优越性和理论分析的有效性。     

基于均匀圆阵的宽带相干LFM信号定位方法

本文提出一种基于均匀圆阵的宽带相干LFM信号定位方法。首先，算法根据LFM信号在分数阶傅里叶域的能量聚焦性，对接收信号做分数阶傅里叶变换，实现宽带信号的窄带化处理；其次，利用圆阵的虚拟轴向平移形成的相位差构造空间平滑矩阵，完成相干信号的解相干处理；最后，对空间平滑矩阵进行奇异值分解得到相邻阵元接收数据的相位差，结合相位差反演参数估计算法得到二维角度参数估计的闭式解。仿真实验验证了算法对宽带相干LFM信号定位的有效性。     

虚拟空间平滑算法

根据MASK、BPSK和AM等信号的实值特性,利用阵列接收数据及其共轭信息,构造了虚拟子阵,提出了虚拟空间平滑算法,较好地解决了信号高度相关问题.虚拟子阵具有M个阵元,避免了阵列孔径的损失,使该算法最大可分辨的相干信号数目为M-1.仿真实验证明,与前后空间平滑算法相比,该算法提高了空间分辨率,适应小样本,在一定程度上可以降低了计算量.     

On adaptive beamforming in correlated noise

This paper deals with the problem of adaptive beamforming in the presence of fully coherent (correlated) noise sources. Two different techniques are developed for minimizing the effects of coherent interference. The first method employs spatial interpolation of the array aperture, followed by spatial smoothing in order to decorrelate the desired signal and the interference. The second technique is based on a simple algebraic transformation for restoring the rank of the array signal correlation matrix, which is normally rank deficient in such situations. This technique is shown to work for nonuniform adaptive arrays as well. Extensive computer simulation results are presented to illustrate the effectiveness of the proposed techniques.This week was supported by the N.R.C., Resident Research Associateship Programme.     

Adaptive array utilising multimode antennas for correlated non-circular arrivals

A regularised Capon beamformer under multipath or smart jamming environments is designed wherein the desired signal and correlated interferences are decorrelated by a modal smoothing operation. Unlike conventional spatial smoothing, modal smoothing is not limited to the arrays of spatially-coupled subarrays, and does not decrease the array aperture. By incorporating a soft subspace projection, this beamformer is still robust to the look direction error even in the presence of unknown non-uniform noise.     

Adaptive beam forming using split-polarity transformation forcoherent signal and interference

Split-polarity transformation (SPT), which is incorporated into conventional linearly constrained minimum variance (LCMV) beamformers to decorrelate the desired signal from interference, is presented. The SPT processor does not distort the direction vectors associated with wave fronts impinging on the array, but it does reverse the phase of the signal coming from a specified direction. With the aid of SPT processing, the signal cancellation due to correlation between the desired signal and interference is almost eliminated. The design of a robust SPT processor for combating the effects of mismatch between idealized array model and actual scenario arising from causes such as sensor location, amplitude, and phase errors is discussed. A detailed performance study of the SPT-LCMV beamformer shows it to be robust against direction uncertainty in the assumed look direction. Numerical results are presented to demonstrate the effectiveness of the SPT-LCMV beamforming scheme is a coherent interference environment     

Computationally efficient subspace-based method for direction-of-arrival estimation without eigendecomposition

A computationally simple direction-of-arrival (DOA) estimation method with good statistical performance is attractive in many practical applications of array processing. In this paper, we propose a new computationally efficient subspace-based method without eigendecomposition (SUMWE) for the coherent narrowband signals impinging on a uniform linear array (ULA) by exploiting the array geometry and its shift invariance property. The coherency of incident signals is decorrelated through subarray averaging, and the space is obtained through a linear operation of a matrix formed from the cross-correlations between some sensor data, where the effect of additive noise is eliminated. Consequently, the DOAs can be estimated without performing eigendecomposition, and there is no need to evaluate all correlations of the array data. Furthermore, the SUMWE is also suitable for the case of partly coherent or incoherent signals, and it can be extended to the spatially correlated noise by choosing appropriate subarrays. The statistical analysis of the SUMWE is studied, and the asymptotic mean-squared-error (MSE) expression of the estimation error is derived. The performance of the SUMWE is demonstrated, and the theoretical analysis is substantiated through numerical examples. It is shown that the SUMWE is superior in resolving closely spaced coherent signals with a small number of snapshots and at low signal-to-noise ratio (SNR) and offers good estimation performance for both uncorrelated and correlated incident signals.     

Efficient eigenspace-based array signal processing using multipleshift-invariant subarrays

This paper deals with the construction of eigensubspaces for adaptive array signal processing. An efficient technique for extracting the eigensubspaces spanned by the data vector received by an N-element adaptive array is presented. We first decompose the original array into several subarrays with multiple shift invariances and find the eigensubspaces corresponding to each of the subarrays. By solving a least-squares (LS) or total least-squares (TLS) problem, the signal and noise subspaces corresponding to the original array can be found from the eigensubspaces spanned by the subarray data vectors. Hence, there is no need to perform the eigenvalue decomposition of the N×N correlation matrix of the received data vector. The proposed technique significantly reduces the required computational complexity as compared to the conventional eigenspace-based (ESB) methods. In conjunction with the spatial smoothing scheme or a proposed cross-correlation method, this technique can also deal with the case of coherent signals. The effectiveness of the proposed technique is demonstrated by several computer simulations     

极化域-空域联合的APES波束形成

为了进一步提高极化敏感阵列的滤波性能、得到更为稳定的波束图,将常规的幅度相位估计算法扩展到极化域-空域联合的自适应波束形成中,提出了一种新的波束形成算法SPAPES(Spatial-Polarization Amplitude and Phase Estimation)。首先,给出了算法的信号模型。然后,对所提出算法的滤波原理作了理论推导,得到了最优权向量的表达式。最后,通过仿真实验验证了算法的有效性。计算机仿真结果表明,在强期望信号功率、低采样快拍数的情况下,所提算法都可以很好地在空间-极化联合域中抑制干扰,同时该算法还具有对相干信号的解相干能力。     

Finite data performance analysis of MVDR beamformer with andwithout spatial smoothing

The finite-data performance of a minimum-variance distortionless response (MVDR) beamformer is analyzed with and without spatial smoothing, using first-order perturbation theory. In particular, expressions are developed for the mean values of the power gain in any direction of interest, the output power, and the norm of the weight-error vector, as a function of the number of snapshots and the number of smoothing steps. It is shown that, in general, the smoothing, in addition to decorrelating the sources, can alleviate the effects of finite-data perturbations. The above expressions are reduced to the case in which no spatial smoothing is used. These expressions are valid for an arbitrary array and for arbitrarily correlated signals. For this case, an expression for the variance of the power gain is also developed. For a single interference case it is shown explicitly how the SNR, spacing of the interference from the desired signal and the correlation between them influence the beamformer performance. Simulations verify the usefulness of the theoretical expressions     

基于极化敏感阵列均匀线阵的二维DOA估计

针对残缺电磁矢量传感器的极化敏感阵列多参数联合估计问题,该文提出一种基于正交偶极子的均匀线阵的2维波达方向(Direction-Of-Arrival, DOA)估计算法。首先,对极化敏感阵列的接收数据矢量的协方差矩阵进行特征分解,然后将信号子空间划分成4个子阵,根据旋转不变子空间(ESPRIT)算法分别求出其中1个子阵与其它3个子阵的相位差,再对不同子阵间的相位差进行配对,最后根据相位差求出信号的DOA估计和极化参数。由正交偶极子组成的均匀线阵使用极化MUSIC算法和传统ESPRIT算法无法进行2维DOA估计,该文提出的算法解决了这个问题,并且相较于极化MUISC算法降低了算法的复杂度。仿真结果验证了该文算法的有效性。     

Low sidelobe design considerations of large linear array antennas with contiguous subarrays

Design of large array antennas with contiguous subarrays and having very low sidelobe levels of the order of - 40 dB is discussed. The effects of the amplitude quantization, phase quantization and the number of subarrays on the radiation patterns of contiguous arrays are studied, and results are presented for both sum and difference patterns. A linear array of length200 lambdawith different number of contiguous subarrays and having true time delay steering at the subarray level and phase steering at the element level is analyzed. It is shown that peak sidelobe/quantization lobe levels better than - 39 dB for the sum patterns and better than - 35 dB for the difference patterns can be realized withinpm 60degscan and 0.3 percent bandwidth.     

Rejection of Direct Blast Interference Based on Signal Phase-Matching Array Processing

In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been studied, through which the object scattering signal is accurately extracted. Characteristics of bistatic acoustic testing and signal phase matching processing principle are fully integrated in this algorithm. Firstly, the direct blast interference is calculated from the receiving signal based on three subarrays signal phase matching processing. Secondly, the direct blast is rejected by subtraction from the receiving signal. In this way the limitations of the high signal to noise ratio that signal phase matching processing required for direct calculating the object scattering signal can be avoided. Simulation and sea trial results show that, when the ratio of signal to interference is greater than -20 dB, this algorithm of direct blast interference rejection based phase matching signal processing can accurately extract the object scattering signal.     

Performance analysis of the minimum variance beamformer

We present an analysis of the signal-to-interference-plus-noise ratio (SINR) at the output of the minimum variance beamformer. The analysis is based on the assumption that the signals and noise are Gaussian and that the number of samples is large compared to the array size, and it yields an explicit expression for the SINR in terms of the different parameters affecting the performance, including signal-to-noise ratio (SNR), interference-to-noise ratio (INR), signal-to-interference ratio (SIR), angular separation between the desired signal and the interference, array size and shape, correlation between the desired signal and the interference, and finite sample size