DOA and polarization estimation via signal reconstruction with linear polarization-sensitive arrays

This paper addresses the problem of direction-of-arrival(DOA) and polarization estimation with polarization sensitive arrays(PSA), which has been a hot topic in the area of array signal processing during the past two or three decades. The sparse Bayesian learning(SBL) technique is introduced to exploit the sparsity of the incident signals in space to solve this problem and a new method is proposed by reconstructing the signals from the array outputs first and then exploiting the reconstructed signals to realize parameter estimation. Only 1-D searching and numerical calculations are contained in the proposed method, which makes the proposed method computationally much efficient. Based on a linear array consisting of identically structured sensors, the proposed method can be used with slight modifications in PSA with different polarization structures. It also performs well in the presence of coherent signals or signals with different degrees of polarization. Simulation results are given to demonstrate the parameter estimation precision of the proposed method.     

Nonuniform array processing via the polynomial approach

A polynomial approach for maximum-likelihood (ML) estimation of superimposed signals in time-series problems and array processing was recently proposed. This technique was applied successfully to linear uniform arrays and to uniformly sampled complex exponential signals. However, uniformly spaced arrays are not optimal for minimum variance estimation of bearing, range or position, and uniform sampling of signals is not always possible in practice. The authors make use of the expectation-maximization algorithm to apply the polynomial approach to sublattice arrays and to missing samples in time-series problems     

Pulse Compression in Optical Radar

An analysis of the application of pulse-compression techniques in optical radar systems is presented. The particular case of pseudorandom on-off amplitude coding is chosen for ease of analysis. The roles of the siqnal and photodetector properties and the processing method are examined. The qualitative relationship between the concepts of coherent and incoherent integration in microwave radar and linear and nonlinear processing in optical radar is demonstrated, thus validating the application of pulse-compression techniques with optical signals. Finally, an experimental simulation of an optical rangefinder has been constructed to illustrate various findings of the analysis.     

一个新的实时光学图像识别系统

本文描述了一个新的实时光学图像识别系统。该系统主要是激光二极管、多换能器声光器件、电荷耦合器件以及光学透镜组成的。这个系统既不需要相干光输入图像,也不需要基准图像的付氏变换金息图。不同波段成像系统输出的实时视频图像信号和事先记录的或实时截获的基准图像均可施加给本系统。文中给出了理论分析以说明工作原理。实验结果证实这种非相干光相关器具有完成实时图像识别的能力。事实上,某些图像识别任务碰到的图像位移、尺寸、旋转不变性问题,本系统可容易地予以解决。     

一种平稳小波方向能量阈值滤波的SAR图像去噪方法

由于SAR图像相干斑噪声是非高斯分布的,无法直接采用光学成像系统的去噪技术处理,因此,目前还没有真正的理想算法广泛适用于SAR图像去噪.在分析目前流行的空频域去噪方法优缺点的基础上,提出了1种小波域SAR图像去噪方法.为了克服离散小波变换缺乏平移不变性及方向选择性受限的缺点,该方法利用平稳小波将图像分解为低频逼近信号和...     

Optical Processing Techniques for Simultaneous Pulse Compression and Beam Sharpening

A technique is described in which the separate techniques of beam sharpening (by synthetic antenna methods) and pulse compression are converted into a single two-dimensional operation, which is carried out with a coherent optical processor.     

Smart structures with nerves of glass

Aircraft and space platforms in the 21st century will probably be smart structures capable of sensing both their state and their environment. Networks of optical fibres will constitute an effective nervous system collecting sensory information from structurally integrated arrays of fibre optic sensors associated with each structural component. It is expected that the structural integrity of these smart structures would be monitored throughout their life. During manufacture and installation their built-in sensors would check for flaws or mishandling and therefore provide quality control. In operation their stress and thermal history would be constantly monitored to warn of impact damage, excessive loading or the onset of fatigue. These intelligent damage assessment systems could make obsolete the catastrophic failures that sometimes plague our aircraft, trains and cars today and lead to a revolution in engineering ethics. Structurally integrated optical fibre sensors could also provide the strain, displacement and deformation information required for many control situations. In some of these instances optical control signals might counterstream along these same optical paths to arrays of actuators. In the case of advanced aircraft real time monitoring of the aerodynamic load distribution combined with the extremely fast flight control made possible with distributed arrays of small actuators might permit the aircraft to respond instantly to turbulence. Another potential application is shape sensing and vibration monitoring for dynamic control of large space structures.     

On Processing Optical Images Propagated Through the Atmosphere

The problem of how to process optical images that have propagated through a turbulent atmosphere is considered. It is assumed that either the object or its (free-space) scattered field at the receiving aperture is known, except for unknown parameters that are to be estimated. Isotropic and homogeneous turbulence as discussed by Tatarski and Chernov is assumed. It is assumed that a very short (in time) reception is made, that the turbulence-induced complex phase errors are either small or have a correlation distance short relative to the receiving aperture extent, and that the object is within an isoplanatic region. The method of maximum likelihood (ML) is used as a criterion; its applicability is discussed. The ML image-processing structure is found and is nonlinear. Asymptotic cases are examined; among other conclusions, it is shown that the ML processing of independent receptions is more complex than an ML processing of the sum of the receptions. A coherent optical system that realizes the ML image processor is described; it includes the capability to generate the scattered field. Simplifications are pointed out.     

Phase Compensation for Widely-Spaced Antenna Systems Employing Coherent Signal Combinations

This paper describes a technique for providing phase compensation to signals received at widely-spaced antennas and processed at a central location. Self-compensation is provided for pathlength variations in reference-signal distribution systems. The technique may be adapted to include the measurement and compensation of signal-channel phase variations. Practical systems which require this type of compensation include interferometric systems used for position and position-rate measurements of missiles and spacecraft, interferometers and arrays of antennas used for radio and radar astronomy, and arrays of large-aperture antennas used for deep-space communications.     

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。     

An intelligent algorithm for coherent sound source localization based on a strong tracking filter

Background noise is inevitable when sensor arrays are used for aeroacoustic measurements in wind tunnels. The direct removal of background noise, however, would affect the measurement accuracy. In particular, the existing array signal processing algorithms are either invalid or inefficient for removing the noise that is coherent with the signal of interest. In this paper, an intelligent algorithm is developed to localize the coherent sound sources and background noise in real time by iteratively checking the collected data from the array. The proposed method can automatically adjust the suboptimal fading factor to extract useful information as much as possible in residual sequence. This algorithm is tested in simulations and then demonstrated in an experiment.Compared to the two existing methods, the results indicate that the new method has a good phase-shift tracking ability and rapid estimation-error convergence speed, and can achieve an acceptable performance even for low-cost acoustic sensors. Overall, the proposed method should assist array beamforming and hence benefit aeroacoustic measurement.     

基于协方差矩阵高阶幂的二维DOA估计新算法

 针对稀疏分解方法进行均匀圆阵(UCA)的二维波达方向(DOA)估计运算复杂度大的问题,提出了一种基于协方差矩阵高阶幂稀疏分解的二维DOA估计新算法。该算法首先利用协方差矩阵高阶幂无需进行特征值分解和信源数估计的特性,构建了协方差矩阵高阶幂的稀疏分解向量;然后运用粒度分层思想,构造了粗区域估计和细方位估计的分层多粒度的快速分解模型,分层字典的长度大大减少,在保持估计精度的前提下,算法运算时间远小于现有的恒定冗余字典的稀疏分解方法,从而解决了基于稀疏分解的圆阵二维DOA估计问题。论文提出的算法与二维MUSIC算法相比,估计精度高,且能满足对相干信号的估计。仿真结果验证了算法的有效性和可行性。     

基于高速串行总线的电路交换开关模块的设计与实现

电路交换开关模块是新一代航空电子系统中实现数字信号并行处理的关键模块,为数字信号并行处理系统中的各个数据处理模块、信号处理模块提供高速数据传输与交换。从新一代航空电子系统并行处理的发展趋势及需求的角度出发,介绍了电路交换开关模块的设计和实现。电路交换开关模块采用M21131交叉开关构成交换结构,能够快速交换高速信号,支持重配置和重构,能够满足新一代航空电子系统中数字信号并行处理高速率、高可靠性和低延迟等需求。     

ETS-II Experiments Part II: Earth Station Facilities

A part of the Earth station at the Kashima Branch of the Radio Research Laboratories has a highly sensitive receiving system newly designed for receiving 3 coherent and weak beacon signals transmitted from the Engineering Test Satellite Type-II (ETS-II) of Japan and obtaining propagation data on quasimillimeter and millimeter wavelengths. The ground system includes a main receiving station which has a 10-m diameter antenna for multifrequencies, highly sensitive receivers, a rain radar, which has many unique functions, a radiometer, meteorological instruments, and data processing computers. The facilities of the main receiving station for ETS-II propagation experiments, except for the rain radar, are described.     

Eigenstructure-based algorithms for direction finding withtime-varying arrays

This paper considers the problem of finding the directions of narrowband signals using a time-varying array whose elements move during the observation interval in an arbitrary but known way. We derive two eigenstructure-based algorithms for this problem, which are modifications of techniques developed originally for time-invariant arrays. The first uses array interpolation, and the second uses focusing matrices. Like other eigenstructure-based methods, these algorithms require a modest amount of computations in comparison with the maximum likelihood (ML) estimator. The performance of the algorithms is evaluated by Monte-Carlo simulations, and is compared with the Cramer Rao Bound (CRB). Although both techniques were successful for wideband array processing with time-invariant arrays, we found that only the interpolated array algorithm is useful for direction finding (DF) with time-varying arrays     

Reference Loop Phase Shift in an N-Element Adaptive Array

Adaptive arrays based on the LMS algorithm require the generation of a reference signal which is usually derived from the array output. A particular problem associated with this technique is that of a phase shift in the reference signal loop. The effects of this phase shift on the performance of an N-element adaptive array are discussed. It is shown that a reference loop phase shift causes the array weights to cycle, thereby frequency translating the signals at the output. The weight-cycling frequency is related to various system parameters of an N-element array. In particular, it is observed that the cycling frequency increases as the number of antennas (N) increases.     

Cross-correlation properties of algebraically constructed Costasarrays

The problem of determining the cross-correlation properties of signals based on algebraically constructed Costas arrays is addressed by examining the discrete cross-correlation of the algebraically constructed Costas arrays for a given construction and dimension. Finding two arrays that minimally correlate implies that the signals based on these arrays also minimally correlate. The properties of finite fields are reviewed, and the major algebraic constructions for Costas arrays are presented, i.e. the Welch construction and the Golomb construction. The discrete cross-correlation properties of the Costas arrays are derived for arrays of the same dimension derived from the same construction. The use of Costas arrays in the signal design problem is discussed, and examples are given to show the cross-correlation of the signals based on the algebraically constructed arrays     

Performance Analysis of Monopulse Receivers for Secondary Surveillance Radar

In modern secondary surveillance radar (SSR) the monopulse technique is currently introduced for the measurement of the azimuth of the targets. The monopulse technique is based on a suitable processing of signals received by a multiple antenna. In SSR the signals are generated by a transponder on the aircraft as replies to interrogations from ground equipment, and consist of trains of pulses. The monopulse measurements can be carried out on the basis of a single pulse from each train, so that it provides a great number of azimuth estimates. Many monopulse measurement devices exist, corresponding to different processing techniques. From the point of view of accuracy and precision, their behaviors differ with respect to the sources of errors, both internal (noise and imperfect calibrations) and external (interference and propagation effects). The four main types of monopulse receivers are analyzed here with respect to the effects of the internal error sources on the resulting measurement accuracy. After an introductory discussion of the performances of the receivers, a detailed analysis is carried out on the basis of a general mathematical model. The results are given in an analytical form and in some comprehensive diagrams.     

Proposed airborne optical fiber asynchronous CDMA systems usingfully optical orthogonal codes for real-time avionic data distributionsand computer interconnects

We report the design of optical fiber asynchronous code-division multiple-access (CDMA) systems using fully optical orthogonal codes (FOOCs), which can be employed to support future airborne real-time communication services. The use of incoherent optical CDMA (IO-CDMA) can result in lower complexity and more reliable implementation than that of the coherent version, so this makes IO-CDMA more adequate for operation in the severe aircraft environment. When FOOCs are used in the IO-CDMA systems, the peaks of all the cross-correlation functions and all the sidelobes of any auto-correlation function are then limited to “1” (i.e., the minimum correlation constraint for incoherent optical processing) in fully asynchronous transmissions. Moreover, proposed systems can effectively support multi-rate and variable-rate data communications with no violation of the minimum correlation constraint and no change of IO-CDMA encoders/decoders. This characteristic can be used to improve the system flexibility and availability. A basic experiment is also demonstrated to verify the characteristics of FOOCs