2-D spatial smoothing for multipath coherent signal separation

The use of two-dimensional spatial smoothing (SS) to increase channel capacity of wireless communications system is discussed, The necessary and sufficient conditions on array configuration for applying SS to multiple signal classification (MUSIC), and adaptive beamforming algorithms are defined and proved, This array must have an orientational invariance structure with an ambiguity free center array, and the number of subarrays must be larger than or equal to the size of the largest group of coherent signals. We also studied the cause of ambiguities in a multipath environment. We found the necessary and sufficient conditions for a three-sensor array manifold to be ambiguity free and identified several higher order ambiguity situations, If an array is also central symmetric, the forward/backward SS (FBSS) can be used to improve the resolution. Finally, we extended our results to the estimation of signal parameters via rotational invariance techniques (ESPRIT). All the predicted results are verified by simulations     

基于时空结构的双基MIMO雷达多维参数联合估计

为了充分利用目标的时域特性来改善双基多输入多输出(MIMO)雷达波达方向(DOA)和离波方向(DOD)的估计性能,探讨了双基MIMO雷达在时-空模型下的多维参数联合估计问题。针对慢动目标,基于多维旋转不变技术信号参数估计(ESPRIT)算法,同时利用时域相邻两级延迟包含的时间相位差、发射阵列相邻阵元包含的空间相位差以及接收阵列相邻阵元包含的空间相位差作为旋转因子,形成旋转不变子空间,再根据矩阵、矩阵的特征值及特征值对应的特征向量三者之间的关系解决了参数配对问题,实现了三维参数联合估计。该方法在信噪比低、积累脉冲数少时,目标的DOA与DOD估计性能比不利用时域特性时有明显改善。仿真结果验证了本方法的有效性。     

Direction-finding with sparse rectangular dual-size spatialinvariance array

A novel sparse array geometry embedding two sizes of spatial invariances is presented for use with a new ESPRIT-based (estimation of signal parameters via rotational invariance techniques) algorithm for aperture extension. The half-wavelength invariance yields unambiguous but high-variance direction cosine estimates to disambiguate low-variance but cyclically ambiguous estimates from the larger invariance. With larger invariance at 60 half-wavelengths, resolution threshold for two closely spaced emitters is reduced by 50 dB and estimation error by 100-fold. Array design formulas are also presented     

一种稀疏阵列下的二维DOA估计方法

研究了稀疏阵列下二维波达方向（DOA）的估计问题,提出一种基于不动点迭代的空间谱估计（FPC-MUSIC）算法。首先建立基于矩阵填充的DOA估计信号模型,并验证该信号模型满足零空间性质（NSP）,其次通过不动点迭代算法将稀疏阵列信号恢复为完整信号,最后利用恢复信号估计二维DOA。该算法可在稀疏阵列下大幅度降低谱估计平均副瓣,在大幅度降低阵元数的同时具有较高的估计精度。计算机仿真表明：FPC-MUSIC算法可在稀疏阵列下准确估计二维DOA,验证了该算法的有效性和优越性。     

DOA and steering vector estimation using a partially calibratedarray

We consider the problem of estimating directions of arrival (DOAs) using an array of sensors, where some of the sensors are perfectly calibrated, while others are uncalibrated. We identify a cost function whose minimizer is a statistically consistent and efficient estimator of the unknown parameters-the DOAs and the gains and phases of the uncalibrated sensors. Next we present an iterative algorithm for finding the minimum of that cost function The proposed algorithm is guaranteed to converge. The performance of the estimation algorithm is compared with the Cramer Rao bound (CRB). The derivation of the bound is also included. It is shown that DOA accuracy can be improved by adding uncalibrated sensors to a precisely calibrated array. Moreover, the number of sources that can be resolved may be larger than the number that can be resolved by the calibrated portion of the array     

Further study of the Pencil-MUSIC algorithm

For finding 2-D angles and polarizations of waves arriving at a rectangular array of crossed dipoles, the Pencil-MUSIC method can achieve the near optimum performance with much less computational burden than the MUSIC (multiple signal classification). Following an angle-only ESPRIT (estimation of signal parameters via rotational invariance techniques) method, an angle-only Pencil-MUSIC can be easily formulated which is far more accurate than the former especially in the coherent case. The angle-only Pencil-MUSIC is analyzed and compared with the original Pencil-MUSIC. The new version sacrifices the polarization estimation to achieve about 8 times more efficient computation The accuracy of the new version seems no more than 4 times worse in terms of estimation deviation     

基于均匀圆阵的信号二维方向角高精度估计

基于均匀圆阵(UCA),提出一种信号二维方向角的高精度估计方法。首先,充分利用了信号的空、时域信息,构造时空旋转矩阵,从而达到多个信源分离的目的。其次,直接利用UCA的阵列流形,采用最小二乘法估计信号二维方向角。最后,给出解相位整周期性模糊的方法。计算机仿真表明了此方法具有估计精度高,对阵元的幅相误差鲁棒性强等特点。     

一种结合角距特征的改进栅格星图识别算法

针对栅格算法易受邻域星点影响导致误匹配的问题,提出了一种结合角距特征的改进栅格星图识别算法。首先介绍了改进栅格算法的原理,其次设计了融合栅格识别模式和星角距识别模式的算法实现流程,最后开展了基于不同视角下的大视场仿真星图的算法试验验证和性能分析。结果表明,由于角距特征具有旋转不变性和不易受观测星邻域星点分布影响等特点,结合角距特征对失效观测星进行再匹配的改进栅格算法,在兼顾存储量需求小、运行速度快等优势的同时,识别率和鲁棒性也得到了提升,最高识别率可达98.88%,在位置噪声干扰以及缺失星干扰下,改进算法的识别率仍可保持在95%,说明算法鲁棒性强,具有较好的应用前景。     

一种基于协方差矩阵重构的相干信源DOA估计算法

针对空间相干信源的波达方向估计问题,提出了一种基于协方差矩阵重构的TSVD-ESPRIT算法。它利用包含所有信源信息的特征向量构造Toeplitz协方差矩阵,避免了阵列有效孔径的损失,分辨率高且稳定性好;并且利用ESPRIT算法代替MUSIC算法进行DOA估计,避免了谱峰搜索,大大降低了计算量。数据仿真和分析证明了该算法的正确性和有效性。     

低频标准角振动台

低频标准角振动台产生标准角位移、角速度和角加速度,用正弦信号对角位移传感器、角速度传感器(陀螺、转速表等)和角加速度计进行幅频和相频特性校准。简要介绍了低频标准角振动台的工作原理,并应用其对角运动传感器进行校准。校准范围为0.1~100H z;幅值灵敏度不确定度优于1%;相移不确定度小于1°。     

Direction of arrival tracking below the ambiguity threshold

We present an algorithm for direction-of-arrival (DOA) tracking that allows operation below the ambiguity threshold of the direction-finding (DF) system. Using multiple target tracking techniques, the algorithm turns the most likely DOAs of each measurement into multiple potential tracks and then selects the true track as that with the maximum cumulative likelihood. The improvement offered by the algorithm, namely the extension of the ambiguity-free signal-to-noise ratio (SNR) domain, is demonstrated in several simulated experiments using several array structures, including a sparse array and a uniform linear array     

Performance of diversely polarized antenna arrays for correlatedsignals

The performance of direction finding systems in a correlated signal environment utilizing diversely polarized antenna arrays is investigated. The Cramer-Rao bound (CRB) is used to evaluate the accuracy of the estimated directions of arrival (DOAs). Compact closed form formulas are presented for the CRB corresponding to the joint estimation of the DOAs, signal covariance matrix, signal polarization parameters, and noise variance. The CRB is evaluated numerically for selected examples, to provide insights into the potential improvement in direction-finding accuracy due to polarization diversity     

A Superlimiting Phased-Array Receiving System in a Two-Source Environment

The performance of a uniformly spaced phased-steered line array with element channel superlimiting is studied for far-field sources consisting of 1) two sinusoidal signals with different frequencies and angular locations, and 2) a sinusoid and a noise signal at different angular locations. Attention is focused on the nonlinear case where internal noise is negligible compared to both input signals. The analysis for the two-sinusoid case gives the precise frequencies, positions, and amplitudes of all apparent sources. In addition to the two active sources, the array output has an array of images arranged symmetrically in sine space about the larger input, at intervals equal to the spacing between the two active sources. For the case of a separated sinusoid and a noise source, the analysis shows that the angular positions and average powers of the array outputs duplicate the double-sinusoid results, but the images have noise-like spectra. The analyses are confirmed by experimental results obtained with a 60-element superlimiting X-band array.     

Estimation of 3D angular motion using gyroscopes and linear accelerometers

The authors present a novel, real-time angular motion estimation technique using a linear Gaussian estimator, and the outputs of linear accelerometers and gyroscopes, to assess the actual angular velocity of a rigid body in three-dimensional (3D) space. The method obtains the covariances of the random actual 3D angular velocity, the angular velocity measurement, and the measurement noise from the time averages of the outputs of an array of nine linear accelerometers and the outputs of three orthogonal gyroscopes. These statistics are used by the estimator to calculate the angular velocity of the rigid body in 3D space. The multisensor technique performance is evaluated through a computer simulation. Results indicate that the method leads to more accurate angular velocity values than are obtained conventionally.<>     

弹性体上惯性测量系统的传递对准

 给出了一套弹性体上惯性测量系统的传递对准方案。该方法只采用角速度陀螺作为测量元件,能够对传感器误差进行补偿,并且可给出两套测量坐标系失配角的可靠估计。本文应用弹性力学的模态法建立机翼的运动方程;应用自适应Kalman滤波器在线估计由空气动力诱导的广义外力。     

An experimental investigation of three eigen DF techniques

The comparative direction-finding (DF) performance of multiple signal classification (MUSIC), ROOT-MUSIC, and estimation of signal parameters via rotational invariance techniques (ESPRIT) is considered. Data were collected from two target transmitters operating simultaneously. The objective of the experiment was to evaluate multipath resolution capability using measurement precision equivalent to that found in modern radio direction-finding systems     

Conceptual design,modeling and compliance characterization of a novel 2-DOF rotational pointing mechanism for fast steering mirror

In this paper, a novel 2-DOF rotational pointing mechanism (RPM) is designed inspired by the guidelines of the graphical approach. The mechanism integrates with a fast steering mirror (FSM) for compensating pointing errors of a laser beam. The design intends to achieve an angular travel of ±10 mrad and steers a 25 mm mirror aperture. A planar flexure with beam flexures accompanied in parallel with an axial flexure build-up mechanism configuration. Compliant mechanism-based RPM ensures high precision and compactness. Compliance characteristics are established based on the stiffness matrix method for four different planar flexure layouts. One layout with best in-plane rotational compliance is then assessed for performance sensitivity to mechanism dimension parameters and parasitic error, thus informing the design space. Rotational stiffness in both the in-plane rotational axes and stress is determined based on finite element analysis (FEA). The wire electrical discharge machining (EDM) is employed for developing the proof of concept for the RPM and is then assembled in FSM. Experiments are conducted to determine the rotational stiffness and angular travel about both in-plane rotational axes. Comparison among theoretical, numerical and experiments reveal excellent linearity of rotational stiffness along the rotational travel range. The maximum theoretical error is less than 5.5% compared with FEA while, the experimental error has a mean of 5% and 3% for both rotational axes thus satisfying the intended design requirement.     

反向旋转盘腔内部流动特性

对反向旋转盘腔系统内部流动特性进行了数值模拟,计算结果与已有文献中的实验结果对比表明,采用的数学模型和计算方法是准确的.数值模拟结果表明:反向旋转盘腔内流动结构较为复杂,转速比对流动结构有重要影响.根据流动结构特点研究了旋转雷诺数和转速比对盘腔内压力分布以及转盘壁面摩擦力矩的影响,旋转雷诺数越大,盘腔内的压力越低,转盘壁面的摩擦力矩越大.反向同速旋转有助于增大盘腔内的压力,但与其他转速比相比其摩擦力矩最大.      

Interlaced Kalman filtering of 3D angular motion based on Euler'snonlinear equations

A novel Kalman filtering technique is presented that reduces the mean-square-error (MSE) between three-dimensional (3D) actual angular velocity values and estimated ones by an order of magnitude (when compared with the MSE resulting from direct measurements) even under extremely low signal-to-noise ratio conditions. The filtering problem is nonlinear in nature because the dynamics of 3D angular motion are described by Euler's equations. This nonlinear set of differential equations state that the angular acceleration in one axis is proportional to the torque applied to that axis, and to the products of angular velocity components in the other two axes of rotation. Instead of using extended Kalman filtering techniques to solve this complex problem, the authors developed a new approach where the nonlinear Euler's model is decomposed into two pseudolinear models (primary and secondary). The first model describes the time progression of the state vector containing the linear terms, while the other characterizes the propagation of the state vector containing the nonlinearities. This makes it possible to run two interlaced discrete-linear Kalman filters simultaneously. One filter estimates the values of the state vector containing the linear terms, while the other estimates the values of the state vector containing the nonlinear terms in the system. These estimates are then recombined, solving the nonlinear estimation process without linearizing the system. Thus, the new approach takes advantage of the simplicity, computational efficiency and higher convergence speed of the linear Kalman filter form and it overcomes many of the drawbacks typical of conventional extended Kalman filtering techniques. The high performance and effectiveness of this method is demonstrated through a computer simulation case study     

Tracking with distributed sets of proximity sensors using geometric invariants

We propose a new approach to forming an estimate of a target track in a distributed sensor system using very limited sensor information. This approach uses a central fusion system that collects only the peak energy information from each sensor and assumes that the energy attenuates as a power law in range from the source. A geometrical invariance property of the proximity of the distributed sensors relative to a target track is used to generate potential target track paths. Numerical simulation examples are presented to illustrate the practicality of the technique.