Hybridation des méthodes de recherche taboue et du recuit simulé pour l’optimisation d’une antenne en réseau adaptative

The increasing pollution of the electromagnetic environment has prompted the study of array pattern nulling techniques. These techniques are very important in radar, sonar and communication systems for minimising degradation in signal-to-noise ratio performance due to undesired interferences. Adaptive array antennas backed by strong signal processing algorithms are able to automatically change the beam pattern in accordance with the changing signal environment. It not only directs maximum radiation in the direction of the desired mobile user but also introduces nulls for interfering directions while tracking the desired mobile user at the same time. The adaptation is achieved by multiplying the incoming signals with complex weights and then summing them together to obtain the desired radiation pattern. Adaptive array optimization is an NP-hardproblem. In this paper, a technique based on the coupling between tabu search and simulated annealing methods is presented to solve this problem. Several illustrative examples of patterns with imposed single and multiple null directions are given to show the versatility of the present method.     

相控阵部分自适应波束形成收发算法

为减少大型相控天线阵的优化唯相权值的计算量,本文提出一种新的相控阵部分自适应波束形成的收发算法.它采用自适应部分地选择控制零点的控制阵元(PA),按照最大信干噪比原则,用部分唯相共轭梯度法计算各个阵元的优化唯相权矢量来减轻干扰的影响.模拟结果表明,当干扰数目小于阵元半数时计算性能有很大提高,同时天线远场模式的主瓣损失、波形变化及干扰方向零点深度与全阵自适应相比几乎没有变化.     

自适应阵递归干扰置零

本文主要考虑自适应阵列的连续工作状态中的递归干扰置零问题,详细地介绍阵列在外部干扰增加,减少和平移等各种变化情况下自适应权的计算。系统的分析和模拟表明,这种新的方法与原SMI方法相比,优化权值的计算量降低了近似于阵列的阵元数倍,另外还可以降低对对角加载技术的要求。     

An adaptive beamforming technique based on cyclostationary signalproperties

A new approach to adaptive beamforming is presented. The method is based on the property of cyclostationary signals to generate spectral lines when they pass through certain nonlinear transformations. The beamformer coefficients are selected according to a new optimization objective, which consists on minimizing the mean square error between the array output after the nonlinearity and a complex exponential. This approach optimally extracts any signal that generates a spectral line at the same frequency as the reference complex exponential. A gradient-based algorithm is derived to compute the optimum weights. Since the proposed cost function is a nonconvex function of the array coefficients, minima are analyzed for the three most common types of perturbations found in communications: Gaussian noise, multiple interferences, and multipath propagation. It is demonstrated via analysis and simulations that minima correspond to points where output noise power is minimized, interferences are canceled, and intersymbol interference is removed, i.e., the beamformer eliminates the distortion introduced by the radiocommunication channel     

基于约束差分进化的阵列置零

阵列置零的同时,阵列的旁瓣电平升高、主瓣增益降低甚至阵列指向都会发生改变,导致阵列性能降低。针对阵列置零时阵列性能降低问题,提出一种约束优化模型。在约束优化模型中不仅设置了零陷深度约束和近旁瓣电平约束,还设置了阵列期望方向增益约束及阵列指向约束。在满足约束条件下,使得阵列旁瓣电平最低。并且针对标准约束差分进化算法收敛慢,采用自适应约束差分进化(e-SADE)算法,该算法采用多种变异方式相结合、自适应地调节交叉概率和缩放因子。运用自适应约束差分进化分别通过调节阵元相位和阵列功率一定时的阵元权值求解这个约束优化问题,仿真结果表明提出的方法实现了需求的目标方向图,利用自适应约束差分进化算法优化实现阵列置零是有效可行的。     

A new optimization technique for adaptive antenna arrays

An adaptive nulling algorithm for adjusting the array weights under the soft constraint of the weight norm being very much less than 1 or equal to 1, based on the measured correlations between the array and element outputs, is described. The algorithm can be regarded as an extension of the constrained least-mean-square algorithm. It is derived from the same concept of signal and noise subspaces defined in the multiple signal classification (MUSIC) algorithm. One of the unique features of the present algorithm is that the number of the iterations required to adapt the array weights to form nulls is exactly equal to the number of interferers     

Noncircularity restoral for multi-antenna blind beamforming

Blind beamforming for extracting noncircular signals without the prior knowledge about the objective steering vector is considered. Three second-order blind techniques via NonCircularity REstoral (NCRE) are proposed to recover a dominant noncircular signal from circular interferences plus sensor noise with arbitrary and unknown correlation structure. These schemes are labeled as NCRE1, NCRE2, and NCRE3, respectively. For the high-rank environments where a number of rectilinear/circular interfering signals are present a Mixed-Order BEamspace (MOBE) technique, using simultaneously the second- and fourth-order cumulants, is developed. The performance of these proposed methods is studied based on numerical simulations. NCRE1 is computationally simple but performs well only in the case of very weak interferences and moderate noise, NCRE3 can provide good performance in the presence of medium or weak interferences, while NCRE2 is very suitable for adverse signal environments. NCRE2 outperforms NCRE1 and NCRE3 in terms of convergence rate, over a wide range of signal to interference plus noise ratio values. It is demonstrated that all the three NCRE methods are better than the traditional sample matrix inversion technique in the presence of look direction mismatch. They are also more attractive than the high-order cumulant method when non-Gaussian circular interferences are encountered. The MOBE method is shown to be competent for handling rectilinear/circular interfering signals, with respect to the attainable output signal to interference plus noise ratio.     

Wideband LFM Interference Suppression Based on Fractional Fourier Transform and Projection Techniques

A novel wideband LFM interference suppression method is proposed based on fractional Fourier transform (FRFT) and projection techniques. By using the concentration property of LFM interferences in fractional Fourier domain, the initial frequency, frequency modulation rate and direction-of-arrival (DOA) of LFM interferences are first estimated. Afterwards, the space–time interferences subspace is constructed. In order to suppress wideband LFM interferences, the received signal is projected onto the subspace orthogonal to the interferences subspace when the signals are uncorrelated. Furthermore, considering the scenario when the signals are coherent, according to the properties of oblique projection, LFM interferences are suppressed by projecting the received signal onto the joint signal–noise subspace. Then, the desired signal is extracted by beamforming. Unlike the existing algorithms, the proposed method not only can exactly estimate parameters and directly solve the DOA of LFM interferences but also can construct the interferences subspace with the time-variant steering vector of interferences. Moreover, our method can effectively suppress LFM interferences without reducing the freedom, and significantly improve the performance, even at low signal-to-noise ratio (SNR) or small number of snapshots. Simulation results demonstrate the effectiveness of the proposed method.     

Broadband source tracking using adaptive directional filter withmaximally flat responses at null directions

A new algorithm for the tracking of broadband sources in linear arrays employing tapped delay line processing is presented and investigated. Using this technique, each broadband source is individually tracked in a time-multiplexed manner by steering a broadband null formed from the use of a tapped delay line filter whose weights are constrained to have a maximally flat frequency response at the nulling direction. To ensure that the other nulls are not changed while a particular null is being adjusted, a beamformer is employed to preprocess the element signals before adaptive processing. Since the new algorithm updates only one tapped delay line filter at any instant, the overall implementation complexity of the proposed algorithm is comparable with using the LMS algorithm directly on a broadband array. However, unlike the latter algorithm, the convergence behavior of the new algorithm is significantly faster and is almost independent of the external noise environment     

基于子阵近场零陷权的联合波达方向估计方法

针对海底长线阵在近场辐射声干扰及空间水平非均匀噪声下的远距离估计目标波达方向 (DoA)问题,该文提出一种基于长线阵分子阵近场零陷权的联合目标方位估计方法。该方法将长线阵分解为多个高重叠子阵,对各个子阵利用零陷抑制技术去除近场强干扰对目标探测的影响,再利用各子阵对远距离目标方位估计结果差异性小、非目标所在频率即噪声对应空间谱最大值随机的特点,空间频率方差加权综合各子阵的目标方位估计结果,从而抑制空间非均匀噪声,实现对远距离目标的探测。仿真结果表明,与长线阵常规波束形成、长线阵近场零陷常规波束形成、长线阵近场零陷传统多重信号分类方法相比,该文方法能够有效降低空间谱背景级60 dB以上,输出信噪比提高15 dB以上,具有较强的提高信噪比能力及较高的空间分辨力,因此具有较好的工程应用价值。     

零陷优化的稳健波束形成算法

传统的自适应波束形成算法在干扰方向出现扰动且期望信号导向矢量失配时,不仅无法持续有效地抑制干扰,而且会在期望信号方向产生零陷致使期望信号相消,算法性能严重下降。针对该问题,本文提出了一种零陷优化的稳健波束形成算法。该算法首先通过干扰导向矢量的左右旋转来展宽零陷,接着将采样数据向干扰子空间投影,并对干扰分量进行加权处理以增强采样数据中的干扰强度,加深干扰零陷,最后采用导向矢量不确定集约束算法保证期望信号的接收增益。计算机仿真结果表明:该算法能够有效展宽干扰零陷,并能够保证期望信号增益,具有较好的稳健性。      

智能天线中新的波束形成方法

提出了智能天线中三种利用估计得到的信号导向向量直接形成波束的新方法.根据CDMA信号模型和多径信道模型,用码滤波法估计得到用户最强信号(主径)的导向向量,利用这些导向向量形成恢复期望信号,抑制干扰的制约条件.根据制约条件可直接得到最小二乘(LS)波束形成方法;按照制约条件使输出能量最小得到广义最小方差无失真响应(GMVDR)波束形成方法;在GMVDR方法的基础上引入虚拟信号来进一步抑制旁瓣得到扩展最小方差无失真响应(EMVDR)波束形成方法.模拟表明这三种方法都能很好的恢复期望信号、抑制干扰和噪声,但通过比较看出EMVDR方法形成的波束最好.     

A robust adaptive array based on signal subspace approach

In this note, we propose a signal subspace approach that improves the performance of a beam steered adaptive array in the presence of steering errors due to look-direction error (LDE) and/or random steering error (RSE). In the method, the degrees of freedom (DOF) are reduced so as not to cancel the desired signal while preserving the optimal characteristic of the array, and thus the weights of the array are determined by a linear combination of the eigenvectors of the signal subspace. The proposed method works as far as the eigen decomposition of the input covariance matrix into signal and noise subspaces is possible. The proposed method improves noticeably the array performance of the beam steered array in the presence of steering errors and provides the optimum array performance in the absence of steering errors     

基于混合遗传算法的唯相位直接数据域算法

提出一种基于混合遗传算法的唯相位直接数据域最小二乘算法.通过采用标准遗传算法与Neider-Mead单纯形法相结合的混合遗传算法,提高了优化效率和运算速度.首先根据标准直接数据域算法推导得出目标函数,继而将目标函数作为适应度函数,将所有自适应权值的未知相位作为决策变量,通过混合遗传算法进行非线性优化,从而求得各个自适应权值的优化解.作为一种唯相位自适应算法,它在硬件实现上比传统算法更具简单性.同时,它只对单快拍数据进行处理,避免了样本协方差矩阵的构造以及矩阵求逆运算,更适合于实时处理.仿真结果表明,算法具有良好的信号恢复和干扰置零性能,比基于非线性其轭梯度法的唯相位直接数据域算法性能更优.     

Multichannel post-filtering in nonstationary noise environments

In this paper, we present a multichannel post-filtering approach for minimizing the log-spectral amplitude distortion in nonstationary noise environments. The beamformer is realistically assumed to have a steering error, a blocking matrix that is unable to block all of the desired signal components, and a noise canceller that is adapted to the pseudo-stationary noise but not modified during transient interferences. A mild assumption is made that a desired signal component is stronger at the beamformer output than at any reference noise signal, and a noise component is strongest at one of the reference signals. The ratio between the transient power at the beamformer output and the transient power at the reference noise signals is used to indicate whether such a transient is desired or interfering. Based on a Gaussian statistical model and combined with an appropriate spectral enhancement technique, we derive estimators for the signal presence probability, the noise power spectral density, and the clean signal. The proposed method is tested in various nonstationary noise environments. Compared with single-channel post-filtering, a significantly reduced level of nonstationary noise is achieved without further distorting the desired signal components.     

唯相相控阵自适应赋形收发波束形成

在大型窄带自适应相控阵列中,由于实际阵列的非理想化及处理随机分布的干扰时的各种误差,导致控制方向错误,包括控制方向角度错误和载频波动引起的错误,急剧地降低了阵列的性能。本文为减小控制方向错误,考虑在主瓣幅度波形在主瓣方向的导数为零的约束下,按最大信干噪比原则自适应地波束形成,获得优化的唯相权值,采用优化方法中的罚函数法,并结合共轭梯度和拟牛顿法来计算优化的唯相数值权向量。模拟结果表明,在相控阵列的有效自由度下,这种方法能够有效的对抗干扰,同时保持阵列的主瓣波束的幅度波形。     

A robust phase-only Direct Data Domain algorithm based on generalized rayleigh quotient optimization using hybrid Genetic Algorithm

A robust phase-only Direct Data Domain Least Squares （D3LS） algorithm based on generalized Rayleigh quotient optimization using hybrid Genetic Algorithm （GA） is presented in this letter. The optimization efficiency and computational speed are improved via the hybrid GA composed of standard GA and Nelder-Mead simplex algorithms. First, the objective function, with a form of generalized Rayleigh quotient, is derived via the standard D3LS algorithm. It is then taken as a fitness function and the unknown phases of all adaptive weights are taken as decision variables Then, the nonlinear optimization is performed via the hybrid GA to obtain the optimized solution of phase-only adaptive weights. As a phase-only adaptive algorithm, the proposed algorithm is simpler than conventional algorithms when it comes to hardware implementation. Moreover, it proc- esses only a single snapshot data as opposed to forming sample covariance matrix and operating matrix inversion. Simulation results show that the proposed algorithm has a good signal recovery and interferences nulling performance, which are superior to that of the phase-only D3LS algorithm based on standard GA.     

Pattern nulling in difference pattern by amplitude control

A method of placing nulls in directions of any unwanted radio frequency interference (RFI) sources in the difference pattern of a phased array by controlling the current amplitudes is discussed. Thus one can now achieve pattern nulling in both the sum and difference patterns by amplitude control and can therefore carry out the minimization of RFI noise independently of the maximization of the desired signal. The method therefore provides an efficient alternative approach to the design of adaptive phased arrays.     

A subspace-tracking approach to interference nulling for phasedarray-based radio telescopes

Several next-generation radio telescopes, now in the planning stages, are based on phased-array technology. One reason for this is to make use of adaptive nulling techniques to combat radio frequency interference, which is a growing problem for radio astronomy. This paper presents a low-complexity approach to interference nulling which is suitable for use in such systems. The approach uses subspace-tracking to identify interference, followed by spatial projections to place deep nulls in the directions of interferers. This technique overcomes two limitations of power-minimization algorithms (e.g., "minimum variance"), namely power inversion and pattern rumble, which create serious problems for radio astronomy. Furthermore, this technique imposes a lower computational burden and provides side information which is useful in later stages of data processing. Performance results from a phased array demonstrator system and a simulation are presented     

一种快速唯相位方向图置零方法

在相控阵雷达中,为了降低雷达信号被敌方侦收设备截获的概率,需要在阵列发射方向图某一角度形成零点。对此,提出一种快速相位加权方向图置零方法。该方法依据零点位置设置虚拟干扰,并构建干扰协方差矩阵;根据最小输出功率准则,建立零点生成数学模型;最后通过单坐标迭代算法求解相位权值。计算机仿真结果验证了该方法的正确性和有效性。