Resolution of signal sources via spectral moment estimation

In different practical situations it is desired to estimate the number of signal sources and their positions in space or in frequency domain. The first problem is known as the detection or the order estimation and the second one as the resolution. For the resolution problem techniques such as nonlinear least squares (NLSM), high-order Yule-Walker method (HOYW), multiple signal classification (MUSIC), Pisarenko harmonic retrieval method, min-norm method, estimation of signal parameters by rotational invariance technique (ESPRIT), were proposed (Marple, 1987 and Stoica and Moses, 1997). All these high-resolution methods are based on the analysis of the signal covariance matrix. But the covariance matrix is not the only choice to represent the signal spectrum. In different applications (weather radars, synthetic aperture radar (SAR) signal processing, ultrasound imaging in medicine, atmospheric turbulence measurements) the signal spectrum can be modeled through its algebraic moments. Recently a number of efficient nonparametric methods have been proposed to estimate the algebraic spectral moments (Monakov, 1999). The presented paper is an attempt to solve the direction of arrival (DOA) problem via estimation of the algebraic spectral moments. A method proposed in the article is comparable in its accuracy with the MUSIC method. At the same time its computational burden is much lower. The method permits to estimate the signal power of sources easily to complete the full spectral line analysis. Additionally the method shows good robustness in situations when signal sources have noticeable spatial extend     

Aircraft flight parameter estimation using acoustic multipath delays

The signal emitted by an airborne acoustic source arrives at a stationary sensor located above a flat ground via a direct path and a ground-reflected path. The difference in the times of arrival of the direct path and ground-reflected path signal components, referred to as the multipath delay, provides an instantaneous estimate of the elevation angle of the source. A model is developed to predict the variation with time of the multipath delay for a jet aircraft or other broadband acoustic source in level flight with constant velocity over a hard ground. Based on this model, two methods are formulated to estimate the speed and altitude of the aircraft Both methods require the estimation of the multipath delay as a function of time. The methods differ only in the way the multipath delay is estimated; the first method uses the autocorrelation function, and the second uses the cepstrum, of the sensor output over a short time interval. The performances of both methods are evaluated and compared using real acoustic data. The second method provides the most precise aircraft speed and altitude estimates as compared with the first and two other existing methods.     

射手模型优化与辨识及其对图像制导的影响

基于数据链通信的人在回路制导模式额外引入了射手动力学而且存在图像信号延时,含有射手动力学的控制回路会对目标在视场（LOS）中的误差角进行跟踪补偿,从而提升图像制导弹药的制导控制性能。为探究射手动力学和图像信号延时对人在回路制导性能的影响,基于真实的图像导引头模型及参数,设计校正网络以满足导引头稳定回路的性能需求;引入两类射手模型,针对射手模型2,优化模型结构并通过贴近真实环境的辨识实验得到动力学参数,弥补了现有建模的不足。基于射手对不同图像信号延时的适应性,对比研究了两类射手模型与不同图像信号延时对导引头控制系统稳定性、快速性和人在回路比例导引制导精度的影响。仿真结果表明：图像信号延时越长,导引头跟踪速度越低、误差角越大,制导系统的收敛时间越长;优化后的射手模型2及其参数辨识更准确地描述了射手的操作行为,对制导系统的影响较低且满足系统性能要求。     

Acquisition of Pseudonoise Codes in FH Systems

Acquisition schemes for acquiring pseudonoise (PN) signals in a frequency hopping (FH), spread spectrum (SS) system are presented. For the purpose of acquiring the PN code the received signal is modeled by an autoregressive (AR) process. The parameters of the AR process are determined by identifying a related set of parameters called the partial correlation coefficients. The power spectrum of the received signal and hence the PN code is estimated from the identified AR parameters. The high accuracy of the estimated PN codes permits the use of a simple error correcting logic to accelerate the acquisition process.     

Prediction of Group Delay Distribution Around Receiving Point Using Modified IRI Model and IGRF Model

The international reference ionosphere (IRI) model is generally accepted standard ionosphere model. It describes the ionosphere environment in quiet state and predicts the ionosphere parameters within a certain precision. In this paper, we have made a breakthrough in the application of the IRI model by modifying the model for regions of China. The main objectives of this modification are to construct the ionosphere parameters foF2 and M (3000) F2 by using the Chinese reference ionosphere (CRI) coefficients, appropriately increase hmE and hmF2 height, reduce the thickness of F layer, validate the parameter by the measured values, and solve the electron concentration distribution with quasi-parabolic segment (QPS). In this paper, 3D ray tracing algorithm is constructed based on the modified IRI model and international geomagnetic reference field (IGRF) model. In short-wave propagation, it can be used to predict the electromagnetic parameters of the receiving point, such as the receiving area, maximum useable frequency (MUF) and the distribution of the group delay etc., which can help to determine the suitability of the communication. As an example, we estimate the group delay distributions around Changchun in the detection from Qingdao to Changchun using the modified IRI model and IGRF model, and provide technical support for the short-wave communication between the two cities.     

航天器DOR信号本地相关处理的建模与仿真

详述了DOR（差分单向测距）信号的本地相关处理方法。首先根据轨道预报确定先验时延模型值,利用高精度频率估算方法估计航天器DOR信号的星上发射频率,然后通过时延模型值与频率估计值构造DOR本地模型信号,再将此模型信号分别与测站接收的DOR实测信号进行互相关运算,提取相关相位,解算高精度时延观测量。推导了DOR信号本地相关处理的数学模型,通过信号仿真验证了该方法的有效性,在仅考虑系统噪声影响与轨道预报误差的条件下,仿真时延测量精度达到0.1 ns,为深空航天器精密轨道测量提供了一种可借鉴的技术方法。     

FrFT-CSWSF:Estimating cross-range velocities of ground moving targets using multistatic synthetic aperture radar

Estimating cross-range velocity is a challenging task for space-borne synthetic aperture radar（SAR）, which is important for ground moving target indication（GMTI）. Because the velocity of a target is very small compared with that of the satellite, it is difficult to correctly estimate it using a conventional monostatic platform algorithm. To overcome this problem, a novel method employing multistatic SAR is presented in this letter. The proposed hybrid method, which is based on an extended space-time model（ESTIM） of the azimuth signal, has two steps： first, a set of finite impulse response（FIR） filter banks based on a fractional Fourier transform（FrFT） is used to separate multiple targets within a range gate; second, a cross-correlation spectrum weighted subspace fitting（CSWSF） algorithm is applied to each of the separated signals in order to estimate their respective parameters. As verified through computer simulation with the constellations of Cartwheel, Pendulum and Helix, this proposed time-frequency-subspace method effectively improves the estimation precision of the cross-range velocities of multiple targets.     

A Recursive Method for Signal Resolution

A recursive method is given for resolving signals overlapping in time. Assume that the signal waveform is known and several signals are received. The signals (of unknown number) may overlap with one another and the amount of time delay of each individual signal is unknown. The signals are corrupted with additive white Gaussian noise. The problem is to estimate the number, the amplitudes, and the time delays of the overlapping signals. Assume that at a certain instant tk-1 estimates have been made on the number of signals arriving in the time interval (O, tk-1) and the amplitudes and time delays of these signals. Using these estimates, we test at tk the hypothesis H1 that a new signal arrives at tk against the null hypothesis Ho that no new signal arrives. The decision gives the number of signals arriving in the time interval (0, tk); the parameters are then re-estimated. The overlapping signals are detected and resolved, and the estimates are improved at each stage. The system is analyzed in detail, and computer-simulated results are presented.     

Multiple Signal Analysis for the Delay-Lock Discriminator

This correspondence deals with the effect of multiple signals on the control voltage of the delay-lock discriminator (tracker). Given n returned signals with known delay and power, a formula for the tracker estimate is derived. The analysis has specific application to low-altitude altimeters where the leak signal from the transmitter to the receiver may have delay comparable to the delay of the true signal.     

基于MISG算法的风力发电机液压变桨系统故障诊断

针对受状态延时影响的风机变桨系统故障诊断,提出了一种基于多新息随机梯度(MISG)的故障诊断方法。该方法将复杂系统转化为状态空间模型,并建立系统辨识模型。将新息标量扩展成新息向量改善算法精度,利用系统发生故障引起参数改变的特征,算法对风机状态延时变桨系统完成参数估计,将系统故障诊断问题转换为系统辨识问题。仿真所得结果验证该方法可以达到诊断风机状态延时变桨系统故障的目的。     

基于频率补偿的时延估计方法

无源时差定位中,当目标处于运动状态时,多普勒频率的存在将导致时延差估计精度变差。自相关法和互相关法相结合的多普勒频差估计方法可以获得可靠性较高、估计精度较好的频差估计结果。对该结果进行频差补偿后,采用基于相位谱的时延估计方法获得两信号间的时延差。经过仿真验证,这种基于频差补偿的时延估计方法可以有效降低多普勒频差对时延差估计精度的影响。     

鲁棒成形极化敏感阵列波束的方法及极化估计

基于极化敏感阵列,提出了一种鲁棒成形阵列波束的方法。该方法首先将阵列的数据模型进行了重新描述,从而获得了信号波达角(DOA)和极化解耦的模型。借助于该模型并对信号的两个极化方向分别进行鲁棒约束,设计出了一个新的鲁棒空域波束空间成形矩阵,利用该矩阵可以获得信号两个极化分量的鲁棒估计。基于特征值分解的方法,最后给出了估计信号极化参数的方法。分析和数值仿真实验均表明:提出的方法,在对DOA估计误差以及阵列位置误差等造成的阵列失配具有较强鲁棒性的同时,也能有效抑制干扰和噪声,进而提升了极化参数估计的性能。     

导航辅助下基于LAS码的天基多目标测控

中继卫星的天基测控是解决中低轨道航天器大范围、长时间、多目标测控的有效途径,但用户星到中继卫星的时延误差、多普勒频移校正误差等参数会对多目标测控带来干扰。针对该问题,首先分析了定位误差引起的时延误差、多普勒频移校正误差等因素,设计了天基多目标前向链路遥控SMA(S-band Multiple Access,S频段多址)信号形式和反向遥测链路SMA信号形式,选择与时延校正误差相匹配的LAS(Large Area Synchronous,大区域同步)码作为反向遥测信息的扩频码,建立了导航辅助的终端时延和频率预校正方案模型,可以有效消除多用户干扰。仿真表明,当Eb/N0≥10.5dB时,前向遥控信息误码率pe≤1×10~(-6),反向遥测信息误码率pe≤1×10~(-6),使用LAS码比Gold序列约有2dB性能改善,为基于我国天链卫星的中低轨道卫星稳定运行、载人航天交会对接以及后续空间站建设等任务的测控提供重要参考。     

Some Matched Filter Configurations for Infrared Systems

An analysis of the output of three alternative matched filter configurations in an infrared scanning system model is presented. The sensor is corrupted by thermal noise, generation-recombination noise, photon noise, and modulation noise, the latter providing an extreme discoloration in the signal passband. Expressions for the signal voltage density spectrum, signal pulse shape, noise power spectrum, and average noise power at the matched filter output are derived where the integral evaluations attendant to these derivations do not appear elsewhere in the literature. The paper also provides graphical displays of the signal-to-noise power ratio at the filter output versus various system parameters, noise power spectrum out of the matched filter versus ?, and the signal pulse shape out of the filter versus time. Also included are discussions of practically realizable approximations to the matched filters and curve fitting techniques for the signal pulse shape function.     

一种基于数据跳变检测的高动态环境GPS信号参数估计方法

鉴于高动态环境中 Ｇ Ｐ Ｓ信号参数估计和调制数据跳变检测所遇到的问题,采用扩展卡尔曼滤波方法（ Ｅ Ｋ Ｆ）对信号参数进行了估计,分析了通过载波辅助技术实现伪码延时估计的原理,重点研究了一种简单的数据跳变检测和估计参数修正方法。模拟结果表明这种方法在信号参数估计精度和动态跟踪性能等方面都能够满足高动态环境的要求。     

航空发动机闭环辨识研究

 本文介绍了在航空发动机闭环控制系统的反馈通路上施加伪随机试验信号时,对发动机模型参数进行辨识的方法。同时还介绍了对辨识试验所录取信号的相关分析与谱分析,以此来证明所录取信号的正确性。在用Hsia法进行辨识处理后得到了发动机的数学模型。最后通过对模型的验证表明辫识结果是满意的。     

运动单阵元被动合成阵列波达方向估计

 提出了一种运动单阵元被动合成阵列波达方向(DOA)估计算法。该算法基于被动合成阵列(PSA)的概念,结合空间谱估计的思想构建了运动单阵元被动合成阵列模型,通过多次不同速度合成阵列过程实现对信号DOA的无模糊估计。通过对单次匀速合成阵列过程进行分析得到,在假设信号频率已知条件下,合成阵列算法能够达到与同孔径实阵列多重信号分类（MUSIC）算法相当的DOA估计性能。仿真验证了被动合成阵列与同孔径实阵列的渐近等效性及算法的有效性。     

Optimum time delay detection and tracking

An optimum solution to the time delay tracking problems has been previously achieved by recursively computing the time-delay posterior probability density function (PDF), or time-delay PDF conditioned on knowing all observed data, by numerical means. Any optimum estimate is determined from the posterior PDF. The same approach is extended to an optimum solution for the time delay detection problem with a randomly appearing and disappearing signal. The detector-tracker is suitable for a stand-alone detection and tracking system     

Multipath-adaptive GPS/INS receiver

Multipath interference is one of the contributing sources of errors in precise global positioning system (GPS) position determination. This paper identifies key parameters of a multipath signal, focusing on estimating them accurately in order to mitigate multipath effects. Multiple model adaptive estimation (MMAE) techniques are applied to an inertial navigation system (INS)-coupled GPS receiver, based on a federated (distributed) Kalman filter design, to estimate the desired multipath parameters. The system configuration is one in which a GPS receiver and an INS are integrated together at the level of the in-phase and quadrature phase (I and Q) signals, rather than at the level of pseudo-range signals or navigation solutions. The system model of the MMAE is presented and the elemental Kalman filter design is examined. Different parameter search spaces are examined for accurate multipath parameter identification. The resulting GPS/INS receiver designs are validated through computer simulation of a user receiving signals from GPS satellites with multipath signal interference present The designed adaptive receiver provides pseudo-range estimates that are corrected for the effects of multipath interference, resulting in an integrated system that performs well with or without multipath interference present.     

测量参数时间延迟对气动导数辨识结果的影响

主要讨论了测量参数间的时间延迟对飞机气动导数辨识结果的影响。通过对飞机仿真数据的计算表明,为了保证气动导数辨识的准确性,必须对测量参数间的延迟时间作一定的限制。结果表明,飞机的主要导数对时间延迟不敏感,而一些小值导数则较敏感。文中还根据实际计算经验对测量参数间的延迟时间给出了适当的限制。这些结果可为工程应用提供理论参考。