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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 {2. of Radar Signal Processing,xidian University,xi’an 710071,china national key {2. of Radar Signal Processing Xidian University

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 2. 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)

An eigenstructure-based 2. 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,{2. University,xi’an 710071,china national key Lab of Radar Signal Processing Xidian University

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 2. 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

A class of quasi-cyclic LDPC codes from B2.（mod m） sequences

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Science china(Information Sciences) 2011年第8期54卷 1645-1653页

作者： ZHANG GuoHua & WANG xinMei State key laboratory of Integrated Service Network,{2. University,xi’an 710071,china State key laboratory of Integrated Service Network Xidian University

A new class of binary low-density parity-check (LDPC) codes is proposed based on B 2.(mod m) sequences. The parity-check matrix of such a code has a column weight of three and a row weight of an arbitrary integer,and a quasi-cyclic *** parity-check matrix also has a girth at least 8,and corresponds to a code with minimal distance at least *** m is prime,an 8-cycles reduction method is presented to completely avoid the two types of 8-cycles within the total four types existed in the Tanner *** results show that,for a prime integer m,the new LDPC code outperforms the random (quasi-) regular counterpart generated by the PEG ***,a heuristic algorithm based on a strategy called neighboring extension search is presented to search for the B 2.(mod m) sequences whose lengths approach or meet the upper bound.

关键词： channel coding LDPC code B2.(mod m) sequencegirth

An approach to forward looking FMCW radar imaging based on two-dimensional Chirp-Z transform

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Science china(Information Sciences) 2010年第8期53卷 1653-1665页

作者： LIANG Yi 1 , WANG Hongxian 1 , ZHANG Long 1,2.& BAO Zheng 1 1 national key Lab of Radar Signal Processing, {2. University, xi’an 710071, china 2.xi’an Polytechnic University, xi’an 710048, china national key Lab of Radar Signal Processing Xidian University xi"an Polytechnic University

Airborne forward looking radar imaging, which is an important work mode of imaging radar system, has many advantages combined with frequency modulated continuous wave (FMCW) technology. This paper studies the configuration with one central antenna element for signal transmitting and other antenna elements for signal receiving. According to its imaging geometry, the analytical expression of the received signal for forward looking imaging radar based on FMCW is given. By performing the equivalent phase center principle, the received signal is equalized to the case of system configuration with antenna both for transmitting and receiving signals. The Doppler frequency shift effect, induced by the platform’s continuous motion while radar transmits and receives signals, is analyzed in detail and the approximate compensation method is shown. Based on this, a novel method for forward looking FMCW radar imaging is developed, which adopts two-dimensional Chirp-Z transform to implement scaling operation. Also the complete derivation process of the algorithm and the expression of each compensation factor are presented. The whole algorithm only includes FFT and complex multiplication, with interpolation free, and is easy to implement in reality. Simulation results verify the correctness of the analysis and the validity of the proposed algorithm.

关键词： forward looking radar imaging FMCW Chirp-Z transform

Response to“Discussion on the systematic position of the Early Cambrian priapulomorph worms”

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Science Bulletin 2006年第2期51卷 250-256页

作者： HAN Jian1 & HU Shixue2.1. Department of Geology and key laboratory for Continental Dynam- ics of the Education Ministry, Northwest University, xi’an 710069,{2. 2. Yunnan Geological Institute, Kunming 650011,{2. Department of Geology and key laboratory for Continental Dynamics of the Education Ministry Northwest University Xi’an China Yunnan Geological Institute Kunming China

A response by Han Jian & Hu Shixue to a letter to the editor about their article 'Systematic Position of the Early Cambrian priapulomorph worms' in the 2.04 issue is presented.

关键词： Response to Discussion on the systematic position of the Early Cambrian priapulomorph worms

Statistical analysis and model of spread F occurrence in china

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Science china(Technological Sciences) 2010年第6期53卷 1725-1731页

作者： XU Tong1,WU ZhenSen2.HU YanLi1,WU Jian1,SUO YuCheng1 & FENG Jian1 1 national key {2. of Electromagnetic Environment,china Research Institute of Radiowave Propagation,Qingdao 2.6107,china 2.School of Science,xidian University,xi’an 710071,china national key {2. of Electromagnetic Environment China Research Institute of Radiowave Propagation School of Science Xidian University

The spread F data obtained over Lanzhou (36.1°N,103.9°E),Chongqing (2..5°N,106.4°E) and Haikou (2..0°N,110.3°E) of china during the period from 1978 to 1997 are used to analyze the occurrence *** statistical results show that the post midnight spread F occurrence is maximum during the summer solstice months of the lower solar activity period,while post sunset spread F is dominant in equinoxes of higher solar activity period over Haikou *** Chongqing and Lanzhou stations,spread F mostly occurs at post midnight and relates negatively with solar *** regression method and Fourier expansion,the preliminary single-station model of spread F occurrence is established and the accuracy of the model is evaluated.

关键词： spread F solar cycle variation seasonal variation empirical model

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A novel distortion elimination method of power amplifier in wideband OFDM system

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Science china(Information Sciences) 2012年第2期55卷 396-406页

作者： REN ZhiYuan & ZHANG HaiLin State key laboratory of integrated services network,{2. University,xi’an 710071,china State key laboratory of integrated services network Xidian University

The nonlinear,memory and saturate distortion caused by power amplifier lead to low BER per-formance and low power efficiency in wideband OFDM *** solve the related problems,a novel power amplifier based on combined amplification with multi power amplifiers is proposed in this *** addition,a novel simplified filter look-up table predistorter is *** novel predistorter connects to a memoryless predistorter subsystem with an adaptive filter subsystem in cascade,and can eliminate the nonlinear memory distortion *** simulation results indicate that the power efficiency and BER performance will be improved by using the novel amplifier structure together with the novel predistorter.

关键词： wideband OFDM dynamic range extended memory predistorter

Interfacial behaviors of PMMA-PEO block copolymers at the air/water interface

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Science china Chemistry 2005年第6期48卷 567-573页

作者： CHENG Caixia1, JIAO Tifeng2. TANG Rupei1, LIU Minghua2.& xi Fu1 1. State key laboratory of Polymer Physics and Chemistry, Joint laboratory of Polymer Science and Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, china 2. CAS key laboratory of Colloid and Interface Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, china State key laboratory of Polymer Physics and Chemistry Joint Laboratory of Polymer Science and Materials Institute of Chemistry Chinese Academy of Sciences Beijing China CAS key laboratory of Colloid and Interface Science Institute of Chemistry Chinese Academy of Sciences Beijing China

Diblock copolymer of PMMA2.1-b-PEO114 and triblock copolymer of PMMA12.-b- PEO2.7-b-PMMA12. were synthesized and their interfacial properties at the air-water interface were investigated, where both blocks of polyethylene oxide (PEO) and poly(methyl methacrylate) (PMMA) are surface active but the former is soluble in water while the latter is not. Both the block copolymers could form monolayers with two obvious transition regions. The first transition point is around 10 mN/m, which could be assigned to the pancake-brush change of the PEO chains. The other is around 18 mN/m, which could be ascribed to the condensed packing of PMMA. The surface morphological changes during the compression of the Langmuir monolayers are inves-tigated by using the AFM and SEM methods for the films deposited at different surface pressure or molecular areas. At a lower surface pressure, a typical morphology of PEO-con- taining lipopolymers is observed. Upon compression, sphere-dominant morphologies were observed. While the diblock copolymer is easy to folding, the triblock copolymer is in favor of formation of circular domains through vesiculation.

关键词： PMMA-PEO, block copolymers, monolayer, Langmuir-Blodgett films, AFM.

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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,{2. University,xi’an 710071,china national laboratory of Radar Signal Processing Xidian University

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