ON TWO-DIRECTION SPATIAL SMOOTHING FOR ESTIMATION ANGLE-OF-DIRECTION OF COHERENT SIGNALS

Based on Evans'spatial smoothing preprocessing scheme,a new approach calledtwo-direction spatial smoothing preprocessing method is presented.It is proved that the decorre-lation,the effective aperture and the maximum number of distinguishable coherent signals(whenarray size is given)of the new method are better than those of the Evans'method.Simulationresults give a comparison between the eigenvector spectrums produced by the two methods.     

Direction finding of coherent signals via spatial smoothing foruniform circular arrays

We present a preprocessing technique that in conjunction with spatial smoothing circumvents the difficulty of direction-of-arrival estimation of coherent signals in the case of uniform circular arrays. Special consideration is given to problems arising in practice, such as mutual coupling and array geometry imperfections. Simulation results illustrating the performance of this scheme in conjunction with the MUSIC method are included     

Improved spatial smoothing techniques for DOA estimation ofcoherent signals

In the context of coherent signal classification, spatial smoothing is necessary for the application of the eigen-based direction of arrival (DOA) estimation methods. However, the currently known spatial smoothing algorithms not only reduce the effective aperture of the array, but also do not consider the cross correlations of the subarray outputs. An improved spatial smoothing algorithm which can fully utilize the correlations of the array outputs and produce a more stable estimate of the covariance matrix is presented. Simulation results are provided to verify the theoretical prediction. The superiority of this method over the conventional methods is obvious, especially when the SOSR (subarray to overall size ratio) is small     

Improved adaptive ing of coherent interference without spatial smoothing

A new scheme for adaptive ing in the presence of coherent interference is proposed that finds the weight vector using a nonsquare correlation matrix without spatial smoothing. Conventional schemes, which use square matrices, correspond to specific cases of the new method. It allows us to increase the dimension of the weight vector such that the ing capability is enhanced. Theoretic performance analysis is made, showing that the output signal-to-interference ratio (SINR) of such a beamformer is proportional to the weight dimension for sidelobe interference. Simulation results confirm this.     

相干信源波达方向估计的加权空间平滑算法

提出了一种用于空间相干源DOA估计的加权空间平滑算法(WSS，weighted spatial smoothing)。常规的空间平滑算法没有利用子阵输出的互相关信息，而且对相干信源的分辨力较差。WSS算法充分利用了子阵输出的自相关信息和互相关信息，将主阵协方差矩阵的所有子阵阵元数阶的子矩阵进行加权平均，以期提高常规空间平滑算法的分辨性能。文中以加权平滑后等效的信源协方差矩阵的对角化为约束条件，推导了加权矩阵的理论表达式。计算机仿真结果表明，WSS算法与常规空间平滑算法相比具有更高的分辨性能和更低的信噪比门限。特别是在于阵划分较多时其优越性更加明显。     

On maximum-likelihood localization of coherent signals

We consider the problem of localizing multiple signal sources in the special case where all the signals are known a priori to be coherent. A maximum-likelihood estimator (MLE) is constructed for this special case, and its asymptotical performance is analyzed via the Cramer-Rao bound (CRB). It is proved that the CRB for this case is identical to the CRB for the case that no prior knowledge on coherency is exploited, thus establishing a quite surprising result that, asymptotically, the localization errors are not reduced by exploiting this prior knowledge. Also, we prove that in the coherent case the deterministic signals model and the stochastic signals model yield MLE's that are asymptotically identical. Simulation results confirming these theoretical results are included     

MODE SPACE SMOOTHING ALGORITHM TO ESTIMATE DOA OF COHERENT SIGNALS IMPINGING ON UNIFORM CIRCULAR ARRAY

A novel method to estimate DOA of coherent signals impinging on a uniform circular array( UCA) is presented in this paper. A virtual uniform linear array (VULA) is first derived by using spatial DFT technique, transforming the UCA from element space to phase mode space to obtain the properties of ordinary ULA, and then the well known spatial smoothing technique is applied to the VULA so that the lost rank of covariance matrix due to signal coherence can be retrieved. This method makes it feasible to use the simple MUSIC algorithm to estimate DOA of coherent signals impinging on a UCA without heavy computation burden. Simulation results strongly verify the effectiveness of the algorithm.     

相干多径环境下信号空间特征及波达方向估计

以均匀直线阵和四阶累积量为基础,提出了一种新的空间特征盲估计算法.该算法首先利用阵列输出四阶累积量构造了一种空间特征矩阵,对其作特征分解可以得到各用户的空间特征估计.然后,在空间特征估计基础上,结合前向/共轭后向空间平滑技术进行了多径波达方向(Direction of Arrival,DOA)估计.该方法突破了传统MUSIC、ESPRIT等算法的局限,可以利用M阵元估计2M2/3个DOA,且各DOA与信源自动配对.该算法不依赖于信号具体特征,适用于任意加性高斯噪声(如有色噪声)环境.理论分析和仿真结果说明了算法的有效性和鲁棒性.     

存在相干信号时的最优波束形成

本文提出一种新的存在相干信号时的最优波束形成方法。该方法首先利用估计得到的期望信号和相干信号 的方向形成变换矩阵,去掉数据中的期望信号和相干信号成分，求得不相关干扰信号的子空间以及其正交子空间，然后得到期望信号和相干信号的合成导向矢量在该正交子空间中的投影矢量，并把该投影矢量作为自适应权矢量。经理论分析表明，这种方法基本上和理论上的最优方法相同。另外，该方法可以适用于任意的阵列结构，并且对期望信号和相干信号方向估计误差具有很强的稳健性。计算机仿真结果证实了本文方法的有效性。     

宽频段空间信号频率、二维到达角和极化联合估计

在空间欠采样的条件下,通过巧妙定义稀疏L型阵列的四阶累积量输出矩阵,利用高阶累计量的盲高斯及阵列扩展特性,实现了宽频段空间非高斯信号频率、到达角和极化估计的分离,给出了一个基于四阶累积量 ESPRIT和整数搜索解模糊的任意高斯噪声环境下多个独立空间信号频率、二维到达角和极化的联合估计算法,L型阵列由和坐标轴方向一致的偶极子对组成,数值模拟结果证实了该文方法的有效性。     

Microwave coherent demodulator for phase-shift-keyed signals

A coherent demodulator for p.s.k. signals at microwave-carrier frequencies using an open-squaring phase-locked loop is described and evaluated experimentally. The circuit has been operated at a 50 Mbit data rate, and should operate at much higher data rates. Error measurements in the presence of Gaussian noise confirm that the circuit performs as an ideal coherent detector until the phase-locked-loop threshold is reached.     

Two-dimensional DFT projection for wideband direction-of-arrivalestimation

A statistical analysis of the spatial-temporal DFT projection technique for estimation of the direction-of-arrivals (DOAs) of wideband signals is presented. One of the advantages of this technique is its simple implementation as it does not require the construction of focusing matrices. Simulation results and comparisons with existing techniques show satisfactory performance, especially at low signal-to-noise (SNR) ratios and a relatively low SNR threshold     

Improved spatial smoothing technique

The authors present a spatial smoothing technique which can be considered as being an improvement on two spatial smoothing techniques developed previously. To verify its usefulness, our improved technique and those previously developed are applied to decorrelate coherent multipath signals in the context of indoor radio channels. The multipath arrival times are then super-resolved using forward-backward (FB) MUSIC and the results are compared to determine the improvement     

Improved angular resolution for spatial smoothing techniques

Spatial smoothing techniques are used to estimate the directions of coherent arrivals. The performance of these techniques deteriorates rapidly as the coherent arrivals become closely spaced. The author examines the resolution performance of the existing forward-only and forward/backward spatial smoothing techniques. It is shown that the resolution for coherent signals can be improved by squaring array covariance matrices before forming smoothed array covariance matrices     

Performance of spatial smoothing algorithms for radar signaturemodelling

In the area of radar signature modelling, subspace-based methods have recently become very popular. To model radar signals using subspace-based methods, spatial-smoothing preprocessing (SSP) is essential to estimate the covariance matrix of the received signals. Here, the performances of two typical SSP techniques are compared in the context of radar signature modelling     

Recursive linear smoothing of two-dimensional random fields

In an earlier paper, recursive formulas for the causal filtering of two-dimensional random fields were developed. "Causality" in two dimensions is not a physical constraint but rather an artifact introduced to generate recursion, which in turn is motivated by computational efficiency. The earlier results are extended here in order to derive some recursive formulas for "smoothing" estimators which use all the data rather than just the data in the "past".     

Feedback beamforming technique for receiving multipath coherent signals

A novel feedback beamformer is proposed for receiving multipath coherent signals. First, a subtraction-based minimum variance distortionless response beamformer is utilized to obtain an estimation of the desired signal. Then its output is fed back to the original full aperture array where a minimum mean square error (MMSE) beamformer is applied. Due to multipath-matched feature of the MMSE beamformer, the novel feedback beamformer can combine multipath signals without aperture loss. Two feedback schemes are proposed and their effectiveness is verified via simulation.     

HIGH-RESOLUTION 35GHz COHERENT LFM-CW RADAR FOR TWO-DIMENSIONAL IMAGING

This paper presents the system design and experimental results of a 35GHz coherent LFM-CW radar for use in near range two-dimensional imaging. Special techniques, including FM sweep linearization, range-segment processing, system background voltage suppression and dynamic range compression are also presented.     

相干宽带线性调频信号的波达方向估计新方法

提出了一种相干宽带线性调频(LFM)信号的波达方向(DOA)估计新方法。该方法利用LFM信号在分数阶Fourier域上的解线调特性,构造出新的解线调域阵列数据模型,然后结合传统的矩阵重构解相干以及MUSIC算法实现相干LFM信号的DOA估计。若同时存在多组相干LFM信号入射,则首先在不同的能量聚集域上将各信号组分离,然后逐一进行各组内相干信号的DOA估计。该方法充分地挖掘了观测信号所包含的时频信息,增加了可检测的DOA数目,提高了分辨性能和抗噪声性能。此外,该方法无冗余阵元与孔径损失,且适用于任意流型阵列。仿真结果显示,在DOA估计的均方根误差(RMSE)相同时,与传统方法相比,本方法可获得8dB左右的信噪比增益。