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Double-characters detection of nonlinear frequency modulated signals based on FRFT

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Science china(Information Sciences) 2011年第1期54卷 136-145页

作者： XU ShuWen,SHUI PengLang & YANG xiaoChao national laboratory of radar signal processing,xidian university,xi’an 710071,china 1. national laboratory of radar signal processing Xidian University Xi’an 710071 China

In many practical applications,signals to be detected are unknown nonlinear frequency modulated (FM)and are corrupted by strong *** phase histories of the nonlinear FM signals are assumed to be unknown smooth functions of time,which are usually poorly modeled or cannot be modeled at all by a small number of *** of the lack of phase model,a nonparametric detection method is proposed based on successive fractional Fourier transform and double-characters *** detection process goes in three ***,an image is constructed by the fractional Fourier transforms of successive angles in one period. Then,the threshold procedure is utilized to transform the image into a binary *** the multiple median filtering,the binary image is refined where the isolated noise pixels are ***,two complementary features are extracted from the refined image,and a double-characters detector is proposed to decide whether the target is present or *** simulation experiments to three polynomial phase signals with different orders and a sinusoidal phase signal show that the proposed detection method is effective and robust.

关键词： fractional Fourier transform double-characters detector nonparametric detection multiple median filtering

An eigenstructure-based 2D DOA estimation method using dual-size spatial invariance array

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Science china(Information Sciences) 2011年第1期54卷 163-171页

作者： YANG XueYa,CHEN Baixiao & CHEN YunHai national key Lab of radar signal processing,xidian university,xi’an 710071,china 1. national key Lab of radar signal processing Xidian University Xi’an 710071 China

A sparse planar array vertically placed in y-z plane is proposed to improve the angle estimation accuracy of sources in low angle region with reflection *** two sizes of spatial invariances along both dimensions,the array estimates the azimuth and elevation angles using unitary ESPRIT(estimation of signal parameters via rotational invariance techniques).The first spatial invariance with a displacement of half-wavelength yields unambiguous coarse estimates of high-variance,while the second spatial invariance with much larger a displacement of subarrays obtains cyclically ambiguous fine estimates of *** final estimates are obtained by disambiguating fine estimates with coarse estimates.A novel pairing scheme is proposed to pair both the azimuth and elevation,coarse and fine angle estimates of the same *** addition, a new method is presented to calculate 2D angles,which substitutes the estimated elevation angle into the sin relative to the y-axis to get the azimuth *** real-valued processing and array aperture extension, the new DOA measuring method de-correlates the multipath signals and enhances angle resolution with no extra antennas and computational *** results show the effectiveness of the proposed technique and its advantages over the conventional methods.

关键词： DOA estimation sparse array correlated signals unitary ESPRIT dual-size spatial invariances

ISAR imaging via sparse frequency-stepped chirp signal

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Science china(Information Sciences) 2012年第4期55卷 877-888页

作者： WANG Hongxian,LIANG Yi,xiNG MengDao & ZHANG ShouHong national key laboratory of radar signal processing,xidian university,xi’an 710071,china 1. national key laboratory of radar signal processing Xidian University Xi’an 710071 China

Frequency-stepped chirp signal can simplify the designation of radar ***,it has a shortcoming of Doppler ambiguity for high-speed moving ***,it is of great significance to study how to increase its equivalent pulse repeat *** back scattering field of the ISAR target has strong sparsity;that is to say,most energy is contributed merely by a few scattering ***,based on the theory of the sparse signal representation,a novel method for ISAR imaging via sparse frequency-stepped chirp signals is proposed by analyzing the signal model of the *** the proposed method,part of sub-pulses of the frequency-stepped chirp signal is randomly selected to transmit,and then the 2D high-resolution image of the target can be constructed by sparse signal *** the cost of computational resources,the method can effectively resolve the problem of Doppler ambiguity,decrease the sidelobes and obtain a super-resolution ***,the validity of the proposed approach is confirmed by the results of numerical simulations and real data.

关键词： inverse synthetic aperture radar (ISAR) radar imaging sparse signal representation frequency-stepped (FS)

Correlation analysis of target echoes using distributed transmit array

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Science china(Information Sciences) 2010年第9期53卷 1860-1868页

作者： JIN Ming*,LIAO GuiSheng & LI Jun national laboratory of radar signal processing,xidian university,xi’an 710071,china 1. national laboratory of radar signal processing Xidian University Xi’an 710071 China

Transmit diversity multiple-input multiple-output(MIMO) radars decorrelate target echoes on distributed transmit array,and then through closely spaced receivers array estimate the angles of multiple targets using the received target echoes without separating transmitted *** this paper,the target echoes correlation is analyzed under Swerling I and Ⅱ target model *** results show that:(1) Target echoes are uncorrelated under Swerling II model;(2) under Swerling I model,in order to decrease the correlation of target echoes by increasing the number of transmitters,it is required that the normalized covariance matrices of the signals before and after the transmitter number increases should satisfy a relation given in this ***,the results are verified by computer simulations of the target echoes correlation and angles estimation performance.

关键词： multiple-input multiple-output(MIMO) radar transmit diversity target echoes decorrelation

Generalized adaptive subspace detector for range-Doppler spread target with high resolution radar

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Science china(Information Sciences) 2011年第1期54卷 172-181页

作者： DAI FengZhou,LIU HongWei & WU ShunJun national Lab of radar signal processing,xidian university,xi’an 710068,china 1. national Lab of radar signal processing Xidian University Xi’an 710068 China

A generalized adaptive subspace detector for range-Doppler spread target(RDST-GASD)in the non-Gaussian clutter is derived in this *** subspace model of multi-pulse wideband radar target returns is established in the frequency-slow time *** clutters are modeled as nonhomogeneous spherically invariant random vectors(SIRVs);that is,the power of the clutter is different from one range cell to *** clutter covariance matrix is estimated with the secondary *** constant false alarm rate(CFAR)property of RDST-GASD with respect to both the power and the covariance matrix of the clutter is demonstrated *** that there is target range walking across range cells during a coherent processing interval(CPI)for wideband radar,the RDST-GASD does range alignment to the multiple returns of the target in a *** a result,the coherent integration is implemented and the detection performance is improved.

关键词： high resolution radar range-Doppler spread target range walking SIRV adaptive subspace de- tector

Target classification with low-resolution radar based on dispersion situations of eigenvalue spectra

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Science china(Information Sciences) 2010年第7期53卷 1446-1460页

作者： CHEN Feng, LIU HongWei, DU Lan & BAO Zheng national laboratory of radar signal processing, xidian university, xi’an 710071, china 1. national laboratory of radar signal processing Xidian University Xi’an 710071 China

Most low-resolution radar systems, especially ground surveillance radar systems, work at relatively low pulse repeat frequency (PRF) and with short time-on-target (TOT) (duration in scanning). Low PRF leads to Doppler ambiguity and short TOT results in low Doppler resolution, which poses a problem to target classification with low-resolution radar based on the jet engine modulation (JEM) characteristic of radar echo. From the pattern classification viewpoint, we propose a method of using dispersion situations of JEM eigenvalue spectra to categorize aeroplanes into three kinds, namely turbojet aircraft, prop aircraft and helicopter. We analyze the mathematical model of JEM echoes consisting of a series of line spectra and regard them as a sum of several series of harmonious waves. Classification features can be extracted based on the harmonious wave sum model. Some schemes for extracting features from echoes within or between pulses are proposed. Low-dimensional features are extracted to reduce computation burden. Our methods do not compensate for the fuselage echoes and are insensitive to the variation of fuselage Doppler. The feasibility of our methods is demonstrated by simulation experiment.

关键词： jet engine modulation (JEM) low-resolution radar low pulse repeat frequency (PRF) short time-on-target (TOT) target classification

Coherent processing for ISAR imaging with sparse apertures

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Science china(Information Sciences) 2012年第8期55卷 1898-1909页

作者： SHENG JiaLian,ZHANG Lei,XU Gang,xiNG MengDao&BAO Zheng national key laboratory of radar signal processing,xidian university,xi’an 710071,china 1. national key laboratory of radar signal processing Xidian University Xi’an 710071 China

To implement target detection,tracking and imaging in a multifunctional radar system,the wideband measurements for inverse synthetic aperture radar(ISAR)imaging are usually sparsely *** the incoherence problem in such sparse-aperture ISAR(SA-ISAR)systems,we concentrate on the study of a coherent processing method in this *** on an all-pole model,the incoherence parameters between abutting sub-apertures can be effectively *** coherence compensation,an optimization-based SAISAR imaging approach is provided from the view of *** and real data experiments validate the feasibility and effectiveness of the proposals.

关键词： sparse aperture ISAR all-pole model coherent processing

Super-orthogonal space-time code design based on the trellis diagram integrated operation

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Science china(Information Sciences) 2011年第7期54卷 1481-1490页

作者： AO Jun 1,2,MA ChunBo 1,AO FaLiang 1 & LIAO GuiSheng 3 1 College of Information and Communication,Guilin university of Electronic and Technology,Guilin 541004,china 2 national key laboratory of Electromagnetic Environment,QingDao,266107,china 3 national Lab of radar signal processing,xidian university,xi’an 710071,china 1. College of Information and Communication Guilin University of Electronic and Technology Guilin 541004 China2. National Key Laboratory of Electromagnetic Environment QingDao 266107 China3. National Lab of Radar Signal Processing Xidian University Xi’an 710071 China

By studying the super-orthogonal space-time coding designs for 2 transmit antennas and superquasi orthogonal space-time coding designs for 4 transmit antennas,a novel super-orthogonal space-time coding design for 4 transmit antennas is *** exploiting the inherent structure association between OSTBC and QOSTBC,the proposed schemes can obtain the full-rate and good performance while keeping the coding complexity as super-orthogonal space-time coding schemes for 2 transmit *** results demonstrate that the proposed schemes outperforms the existing super-quasi orthogonal space-time coding schemes by almost 2 dB.

关键词： STBC TCM SOSTTC SQOSTTC

Narrow-band radar imaging of spinning targets

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Science china(Information Sciences) 2011年第4期54卷 873-883页

作者： BAI XueRu,SUN GuangCai,WU QiSong,xiNG MengDao & BAO Zheng key laboratory for radar signal processing,xidian university,xi’an 710071,china 1. key laboratory for radar signal processing Xidian University Xi’an 710071 China

According to the characteristics of narrow-band radar echoes from spinning targets,this paper applies the complex-valued back-projection method to image *** it accumulates the sinusoidal phase of spinning scatterers effectively,this method can obtain high resolution *** resolution and required radar pulse repetition frequency (PRF) of this method are *** imaging of fast spinning targets,however,spurious peaks appear due to azimuth down sampling with a low ***,a signal model of azimuth down-sampled echoes is created according to the compressed sensing (CS) *** an imaging method based on orthogonal matching pursuit (OMP) is proposed according to the sparsity nature of ISAR ***,the effectiveness of the proposed methods is demonstrated using simulated data.

关键词： radar imaging spinning targets complex-valued back-projection compressed sensing orthogonal matching pursuit