Range walk and array rotation in space-time adaptive processing:effects and compensations

This paper proposes a unified clutter model incorporating the effects of range walk and array rotation for space-time adaptive processing（STAP） in airborne multi-channel early-warning radar.Based on this clutter model,STAP performance is then analyzed from the perspective of covariance matrix tapering（CMT）.For STAP performance degradation due to array rotation,a determinate compensation method is proposed based on the CMT method.Numerical examples are provided to verify the analysis and the proposed compensation method.

SPACE-TIME ADAPTIVE PROCESSING FOR AIRBORNE RADAR:A CONVENIENT IMPLEMENTATION APPROACH

A convenient implementation approach to space-time adaptive processing for airborne radar has been proposed, which is added by some auxiliary array elements in the area of main-lobe clutter on the basis of 2-D Capon approach . It is of practical use for its small computational load. This approach possesses the ideal performance in the area of main-lobe clutter . In addition, the approach which is added by some auxiliary beams in the area of main-lobe clutter has also been discussed.

Direct data domain approach to space-time adaptive processing

In non-homogeneous environment, traditional space-time adaptive processing doesn＇t effectively suppress interference and detect target, because the secondary data don＇ t exactly reflect the statistical characteristic of the range cell under test. A ravel methodology utilizing the direct data domain approach to space-time adaptive processing （ STAP ） in airbome radar non-homogeneous environments is presented. The deterministic least squares adaptive signal processing technique operates on a ＂snapshot-by-snapshot＂ basis to dethrone the adaptive adaptive weights for nulling interferences and estimating signal of interest （SOI）. Furthermore, this approach eliminates the requirement for estimating the covariance through the data of neighboring range cell, which eliminates calculating the inverse of covariance, and can be implemented to operate in real-time. Simulation results illustrate the efficiency of interference suppression in non-homogeneous environment.

STATISTICAL SPACE-TIME ADAPTIVE PROCESSING ALGORITHM

For the slowly changed environment-range-dependent non-homogeneity, a new statistical space-time adaptive processing algorithm is proposed, which uses the statistical methods, such as Bayes or likelihood criterion to estimate the approximative covariance matrix in the non-homogeneous condition. According to the statistical characteristics of the space-time snapshot data, via defining the aggregate snapshot data and corresponding events, the conditional probability of the space-time snapshot data which is the effective training data is given, then the weighting coefficients are obtained for the weighting method. The theory analysis indicates that the statistical methods of the Bayes and likelihood criterion for covariance matrix estimation are more reasonable than other methods that estimate the covariance matrix with the use of training data except the detected outliers. The last simulations attest that the proposed algorithms can estimate the covariance in the non-homogeneous condition exactly and have favorable characteristics.

A NON－INCREMENTAL TIME－SPACE ALGORITHM FOR NUMERICAL SIMULATION OF FORMING PROCESS

A non-incremental time-space algorithm is proposed for numerical. analysis of forming process with the inclusion of geometrical, material, contact-frictional nonlinearities. Unlike the widely used Newton-Raphson counterpart, the present scheme features an iterative solution procedure on entire time and space domain. Validity and feasibility of foe present scheme are further justiced by the numerical investigation herewith presented.

W ideband interference suppression based on space-time filter

Based upon the diagonal loading technique and the structure of the space-time adaptive processors, a novel anti-jamming method of satellite navigation is proposed. According to matrix in- verse theorem, the range of the diagonal loading values for space-time adaptive wideband signal pro- cessing structure is deduced, and the optimum equation of diagonal loading beam forming algorithm of space-time structure is obtained. Then, by the analysis of two-dimensional oriented vector in di- rection of the perturbation interference, the wideband interference covariance matrix obtained in the weights training period is modified. Finally, the optimum weight of multi-linear constrained space- time adaptive beam-forming alogrithm is derived for anti-interference filter processing. The new method effectively widens the null steering beams tion results prove the robustness of the proposed when discrepancy happens. The computer simula- method.

QUADRATIC PROGRAMMING NEURAL NETWORK BASED INTEGRATED SPACE-TIME INTERFERENCE SUPPRESSION IN CDMA SYSTEMS

Quadratic programming models for integrated space-time interference suppression in CDMA systems are proposed in this paper. The models integrate the advantages of smart antenna and RAKE receiver, mitigate multiuser access interference (MAI) and interchip interference (ICI),and combine multipath components. The zero-forcing conditions are derived. Neural network implementation of the models is also studied.

Novel space-time multiuser detection algorithm of WCDMA system

The structure and performance of space-time multiuser detection receiver at base stations of WCDMA system is analyzed, in which smart antenna is employed. WCDMA uplink signal model is established in this paper. Space-time multiuser receiver presented in this paper combines 2D-RAKE with parallel interference cancellation (PIC), and the improved parallel interference cancellation methods are given. A novel space-time multiuser detection scheme, 2DRAKE-GPPIC is proposed. This scheme employs smart antenna to suppress unexpected DOA (Direction Of Arrival) signal, uses RAKE receiver to combine different delays of expected signal, and utilizes grouped partial parallel interference cancellation (GPPIC) algorithm to suppress further the interference signal in the main lobe of array antennas. The simulation results reveal that the scheme of space-time multiuser detection presented in this paper has better performance for WCDMA system.

Variance minimization for continuous-time Markov decision processes: two approaches

This paper studies the limit average variance criterion for continuous-time Markov decision processes in Polish spaces. Based on two approaches, this paper proves not only the existence of solutions to the variance minimization optimality equation and the existence of a variance minimal policy that is canonical, but also the existence of solutions to the two variance minimization optimality inequalities and the existence of a variance minimal policy which may not be canonical. An example is given to illustrate all of our conditions.

Kravchenko atomic transforms in digital signal processing

The modified atomic transformations are constructed and proved. On their basis the new complex analytic wavelets are obtained. The proof of the Fourier transforms existence in L~ and L2 on the basis of the theory of atomic functions （AF） are presented. The numerical experiments of digital time series processing and physical analysis of the results confirm the efficiency of the proposed transforms.

Analysis of Moving Target Detection in Space-Surface BiSAR

Based on the geometric structure of multi-channel space-surface bistatic aperture radar（SS-BiSAR）,the time-frequency and spatial-frequency relationships of clutter and moving target are detailedly analyzed.It is found that the prepositive stationary receiver can improve the spatial separation between moving target and correspondingly competitive clutter,furthermore the processing scheme of space-time adaptive processing（STAP） in SS-BiSAR echo domain is given.Meanwhile,compared to the STAP in monostatic synthetic aperture radar（SAR）,it is firstly proved that the minimum detectable velocity in SS-BiSAR system can improve R0/R1（transmitter-to-target distance over receiver-to-target） times.Finally,the computer simulation verifies the effectiveness of the STAP processing scheme.

Collaborative Simulation Method with Spatiotemporal Synchronization Process Control

When designing a complex mechatronics system, such as high speed trains, it is relatively difficult to effectively simulate the entire system＇s dynamic behaviors because it involves multi-disciplinary subsystems. Currently, a most practical approach for multi-disciplinary simulation is interface based coupling simulation method, but it faces a twofold challenge： spatial and time unsynchronizations among multi-directional coupling simulation of subsystems. A new collaborative simulation method with spatiotemporal synchronization process control is proposed for coupling simulating a given complex mechatronics system across multiple subsystems on different platforms. The method consists of 1） a coupler-based coupling mechanisms to define the interfacing and interaction mechanisms among subsystems, and 2） a simulation process control algorithm to realize the coupling simulation in a spatiotemporal synchronized manner. The test results from a case study show that the proposed method 1） can certainly be used to simulate the sub-systems interactions under different simulation conditions in an engineering system, and 2） effectively supports multi-directional coupling simulation among multi-disciplinary subsystems. This method has been successfully applied in China high speed train design and development processes, demonstrating that it can be applied in a wide range of engineering systems design and simulation with improved efficiency and effectiveness.

基于自适应字典校正的稀疏恢复STAP算法

空时自适应处理(Space-Time Adaptive Processing,STAP)技术在时间维(脉冲维)和空间维(阵元维)联合进行信号处理,以实现动目标检测功能。但是,传统STAP技术的计算复杂度非常高,而且在优化处理信号过程中需要大样本的支撑,在实际的工作场景中,杂波环境复杂易变,不易获取足够多的独立同分布样本,因此杂波抑制效果较差。稀疏恢复空时自适应处理(Sparse Recovery Space-Time Adaptive Processing,SR-STAP)算法可以利用很少的训练样本实现杂波抑制,但大多数SR-STAP算法的计算量巨大,运行速度慢,算法实时性不高。此外,SRSTAP算法需要对连续空时二维平面进行离散化处理,将空时二维平面划分为很多细小的网格,由于真实的杂波在空时平面上是连续分布的,同时考虑雷达接收信号中噪声、系统参数误差等因素的影响,真实杂波点与离散化网格点之间一定存在着偏差,会造成网格失配现象,导致SR-STAP算法杂波抑制性能下降。针对此问题,本文提出了基于自适应字典校正的稀疏恢复STAP算法。该算法首先通过子空间投影法筛选出与杂波最相关的原子;然后围绕选定原子由粗到细进行自适应局部网格划分,按照局部网格迭代选优准则,不断调整选择局域内的最优原子,直到满足迭代终止条件,以匹配真实的杂波点;最后利用选定的最优原子对应的空时导向矢量构造杂波子空间,更新噪声子空间上与杂波子空间正交的投影矩阵得到STAP权值。仿真实验表明,所提算法与传统SR-STAP算法相比,具有更高的稀疏恢复精度,更快的运行速度,改善了STAP性能。

High-Resolution Broadband Millimeter-Wave Astrophysical Spectrometer with Triple Product Acousto-Optical Processor

An advanced conceptual design of a high-bit-rate triple product acousto-optical processor is presented that can be applied in a number of astrophysical problems. We briefly describe the Large Millimeter Telescope as one of the potential observational infrastructures where the acousto-optical spectrometer can be successfully used. A summary on the study of molecular gas in relatively old (age > 10 Myr) disks around main sequence stars is provided. We have identified this as one of the science cases in which the proposed processor can have a big impact. Then we put forward triple product acousto-optical processor is able to realize algorithm of the space-and-time integrating, which is desirable for a wideband spectrum analysis of radio-wave signals with an improved resolution providing the resolution power of about 105 - 106. It includes 1D-acousto-optic cells as the input devices for a 2D-optical data processing. The importance of this algorithm is based on exploiting the chirp Z-transform technique providing a 2D-Fourier transform of the input signals. The system produces the folded spectrum, accumulating advantages of both space and time integrating. Its frequency bandwidth is practically equal to the bandwidth of transducers inherent in acousto-optical cells. Then, similar processor is able to provide really high frequency resolution, which is practically equal to the reciprocal of the CCD-matrix photo-detector integration time. Here, the current state of developing the triple product acousto-optical processor in frames of the astrophysical instrumentation is shortly discussed.

一种双天线GNSS接收机混合干扰抑制方法

相对于单天线GNSS接收机,阵列GNSS接收机具有空间分辨能力,当干扰信号与卫星信号在时域频域上产生混叠时,其能够从空域上对干扰信号进行抑制,具有更强的干扰抑制能力。但阵列GNSS接收机相对于单天线GNSS接收机需要更多的阵元,随着阵元数目的增加,系统成本也相应的增加,限制了阵列GNSS接收机的应用范围。双天线GNSS接收机既具有空域抗干扰能力,同时又具有价格低廉的特点,是一种较好的折中选择。对于单一的连续波干扰,其能够产生很好的抑制效果,但是当连续波干扰中混有脉冲干扰时,由于受到自由度的限制,双天线GNSS接收机无法对混合干扰进行有效抑制,进而影响接收机的正常工作。针对于上述问题,本文提出一种新的混合干扰抑制算法。首先利用脉冲的时域特征,对待处理信号进行分块处理,确保至少有一个数据块中不含有脉冲干扰,随后对不含脉冲干扰的数据块,使用空时最小功率(Space-Time Adaptive Processing Power Inversion,STAP-PI)算法得到最优权值,然后利用该权值抑制原信号中的连续波干扰。最后,对处理之后信号中残余的脉冲干扰进行时域置零处理,从而达到抑制混合干扰的目的。仿真实验和实采实验结果均证明了所提算法的有效性。

基于权值平滑的自适应调零算法研究与实现

在卫星导航定位系统中,由于导航信号的功率较低,在到达地面时极易受到干扰,导致定位失败。自适应零陷技术可以有效地提高卫星导航接收机的抗干扰能力,然而由于常规的空时联合最小功率响应会时常出现零陷抖动,不能有效的对准干扰来向,从而导致接收机的抗干扰性能下降。对于该情况,本文提出对抗干扰算法中的权值进行平滑滤波处理的方法,并且通过仿真验证、FPGA实现、现场实测等手段验证了该算法的可行性。该方法可有效抑制系统权值以及零陷位置的抖动,从而提高抗干扰算法的稳定性和可靠性,对相关工程领域具有一定的参考价值。

基于波束对消的车辆运动地物杂波抑制方法

针对在快速运动车辆载体上雷达目标检测中强地物杂波的抑制问题,借鉴机载雷达空时处理原理,分析了车辆运动地物杂波分布特性,探讨了运动车辆雷达差波束地物杂波对消和波束地物杂波的适用性。实测数据表明该方法可有效抑制主副瓣地物杂波,提高车辆运动中对慢速飞行目标的检测能力。

基于KA-SRCN-pSTAP的低空风切变风速估计方法

针对由于独立同分布(IID)样本严重不足,导致极化空时自适应(pSTAP)处理性能下降,进而导致低空风切变风速估计不准确的问题,本文提出了一种基于知识辅助的稀疏表示杂波零陷极化空时自适应(KA-SRCN-pSTAP)的低空风切变风速估计方法。该方法首先利用杂波脊的先验知识辅助构造极化空时稀疏字典,然后利用极化空时稀疏字典,通过SRCN算法挑选原子并对到杂波线性子空间补空间上的投影矩阵进行估计,从而得到pSTAP权矢量,最后构造pSTAP滤波器对地杂波进行抑制,准确估计低空风切变风速。该方法仅使用少量IID样本,将SRCN算法与极化-空时域相结合,完成对风切变风速的有效估计。仿真实验结果证明该方法可以有效实现少样本情况下的风速准确估计。

多模式对四川盆地强降水过程的预报性能检验

为进一步认识当前数值预报模式的预报能力,选取2018—2020年发生在四川盆地的47次强降水过程进行分型,再基于多源降水融合产品和地面观测资料,通过TS评分、时空滑动等方法对欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)数值预报模式、国家气象中心区域中尺度数值预报模式(China Meteorological Administration Mesoscale Model,CMA_MESO)和西南区域数值预报系统(Southwest Center WRF ADAS Real-time Modeling System,SWC_WARMS)在强降水过程范围、强度、极值、时间和位移偏差等方面的预报能力进行检验评估。结果表明,各模式08:00(北京时,下同)预报优于20:00预报,ECMWF对中雨和大雨预报更优,SWC_WARMS的暴雨量级评分更高。各模式对中雨的预报范围普遍较实况偏大,随着降水量级增大,逐渐转为低估,其中SWC_WARMS更接近实况。对于降水强度,ECMWF和CMA_MESO的平均降水量和极值普遍较实况偏小,SWC_WARMS更接近实况。3种模式时间偏差不明显,仅个别起报时次有-6~3 h的时间偏差;ECMWF的位移偏差最小,纬向上ECMWF和SWC_WARMS以偏北为主,经向上ECMWF以偏西为主,CMA_MESO和SWC_WARMS以偏东为主。

机载多载频频控阵非均匀距离模糊杂波抑制方法

机载雷达下视工作面临严重的地海杂波,雷达平台运动造成杂波多普勒频率严重扩散,将微弱目标完全淹没。空时自适应处理(space time adaptive processing,STAP)技术通过联合多天线脉冲的接收信号,能够有效地抑制杂波,实现运动目标检测。对于非正侧视阵列高速平台雷达,杂波距离依赖和距离模糊严重制约着目标检测性能。基于多载频频控阵,通过发射一组载频不同的正交信号,在杂波回波中,获得新的发射维自由度,并根据不同模糊在发射维的差异分离各模糊区域。此外,通过进一步对分离后的近程进行杂波补偿,利用降维STAP实现杂波抑制。仿真结果验证了所提方法的有效性。