Ubiquitous radar is a new radar system that provides continuous and uninterrupted multifunction capability within a coverage volume. Continuous coverage from close-in ＂pop-up＂ targets in clutter to long-range target...Ubiquitous radar is a new radar system that provides continuous and uninterrupted multifunction capability within a coverage volume. Continuous coverage from close-in ＂pop-up＂ targets in clutter to long-range targets impacts selection of waveform parameters. The coherent processing interval （CPI） must be long enough to achieve a certain signal-to-noise ratio （SNR） that ensures the efficiency of detection. The condition of detection in the case of low SNR is analyzed, and three different cases that would occur during integration are discussed and a method to determine the CPI is presented. The simulation results show that targets detection with SNR as low as -26 dB in the experimental system can possibly determine the CPI.展开更多
An adaptive approach to select analysis window param- eters for linear frequency modulated （LFM） signals is proposed to obtain the optimal 3 dB signal-to-noise ratio （SNR） in the short- time Fourier transform （S...An adaptive approach to select analysis window param- eters for linear frequency modulated （LFM） signals is proposed to obtain the optimal 3 dB signal-to-noise ratio （SNR） in the short- time Fourier transform （STFT） domain. After analyzing the instan- taneous frequency and instantaneous bandwidth to deduce the relation between the window length and deviation of the Gaus- sian window, high-order statistics is used to select the appropriate window length for STFT and get the optimal SNR with the right time-frequency resolution according to the signal characteristic under a fixed sampling rate. Computer simulations have verified the effectiveness of the new method.展开更多
The Radon-ambiguity transform （RAT）, although efficient for detecting the linear frequency modulated signals （LFMs）, is troubled by the energy accumulation of noise in low signal-to-noise ratio （SNR）. A secondor...The Radon-ambiguity transform （RAT）, although efficient for detecting the linear frequency modulated signals （LFMs）, is troubled by the energy accumulation of noise in low signal-to-noise ratio （SNR）. A secondorder difference （SOD） method is proposed to treat with this problem. In the SOD method, the optimal search step and difference step are derived from the LFM rate resolution formula. The sharpness of the peaks of RAT is measured by curvature, and the sharpness, but not the magnitude of the peaks, is used to detect the LFMs. The SOD method removes the noise energy accumulation and reserves the drastically changing components integrally; thus, it improves the detection probability of LFMs in low SNR. The expected performance of the new method is verified by 100 Monte Carlo simulations.展开更多
Introduces in brief the principle of three kinds pseudo-random code fuzes, viz. the pseudo-random code phase modulation fuze,the pseudo-random code phase modulation and pulse amplitude modulation(PAM) combined fuze,an...Introduces in brief the principle of three kinds pseudo-random code fuzes, viz. the pseudo-random code phase modulation fuze,the pseudo-random code phase modulation and pulse amplitude modulation(PAM) combined fuze,and the pseudo-random code phase modulation and random(pseudo-random) pulse position modulation(PPM) combined fuze. On this basis, their SNR gains in signal processing after band pass filter to the correlation detection, and the overall SNR gains of the whole procedure after correlation detection are deduced in detail. The results show that the latter two kinds of fuzes have the same performances concerning antinoise that are stronger than that of the pseudo-random code phase modulation fuze.展开更多
为实现星载数字时间延迟积分(Digital Time Integration Delay,DTDI)系统的有效设计与成像质量分析,文章提出星载DTDI系统全链路成像质量影响因素分析方法。首先,分析了技术的原理和影响因素,在此基础上构建了场景-大气-星载系统-处理...为实现星载数字时间延迟积分(Digital Time Integration Delay,DTDI)系统的有效设计与成像质量分析,文章提出星载DTDI系统全链路成像质量影响因素分析方法。首先,分析了技术的原理和影响因素,在此基础上构建了场景-大气-星载系统-处理的全链路DTDI成像系统仿真模型,开展了多要素影响下的DTDI成像仿真试验与分析评价。结果表明:0.9 m分辨率下,积分时间0.063 ms、量化位数12 bit、TDI级数6级可以获得较好的成像质量,利用DTDI技术可将平台稳定度要求降至0.1(°)/s。文章研究成果可为星载DTDI系统设计分析提供参考。展开更多
文摘背景与目的:在乳腺X线摄影质量控制中,信噪比(signal-to-noise ratio,SNR)是指图像中有用的信号强度与背景噪声的比值,是衡量图像质量好坏的重要指标之一。变异系数是描述SNR一致性和可重复性的常用指标。本研究通过分析不同厂家的3台乳腺X线摄影设备在不同曝光模式下的二维图像和X线断层摄影(tomography,Tomo)图像(简称断层图像)中SNR变异系数的变化情况,旨在评估乳腺X线摄影设备性能的稳定性和可重复性。方法:选用乳腺X线摄影质量控制专用的聚甲基丙烯酸甲酯模体(polymethylmethacrylate phantom,PMMA),分别在全数字化乳腺X线摄影(full-field digital mammography,FFDM)、低剂量乳腺X线摄影和数字乳腺断层摄影(digital breast tomosynthesis,DBT)3种曝光模式下行PMMA厚度从20~80 mm,实际压迫厚度等效于乳腺平均密度的压迫厚度21~103 mm的自动曝光检测。计算不同乳腺X线摄影设备在不同曝光模式、不同压迫厚度时二维图像和断层图像中SNR的变异系数变化情况。结果:在FFDM、低剂量乳腺X线摄影、DBT曝光模式下,等效于乳腺平均密度的压迫厚度21~103 mm时,分析乳腺X线摄影设备1、2、3在不同曝光模式下二维图像的SNR变异系数间的差异,仅DBT曝光模式下不同设备间的二维图像差异有统计学意义(P=0.003),设备1、2、3中二维图像的SNR变异系数分别为0.188%~0.720%、0.368%~1.073%和0.402%~1.662%。FFDM和低剂量曝光模式下设备1、2、3中二维图像的SNR变异系数差异均无统计学意义(P=0.060)。在DBT曝光模式时不同乳腺X线摄影设备的断层第一张投影图和0°投影图的SNR变异系数变化范围在设备1(2种角度)、2、3中差异均无统计学意义(P=0.373,P=0.742,P=0.225,P=0.693)。结论:不同乳腺X线摄影设备、不同曝光模式时二维图像和断层图像的SNR变异系数变化范围各不相同,没有固定和标准的数值,但都在乳腺X线摄影设备质量控制要求范围内。在FFDM和低剂量曝光模式时乳腺X线摄影设备二维图像的稳定性、可重复性更好;在DBT曝光模式时断层第一张投影图和0°投影图的变异系数值差异无统计学意义,均显示设备的稳定性良好。
文摘Ubiquitous radar is a new radar system that provides continuous and uninterrupted multifunction capability within a coverage volume. Continuous coverage from close-in ＂pop-up＂ targets in clutter to long-range targets impacts selection of waveform parameters. The coherent processing interval （CPI） must be long enough to achieve a certain signal-to-noise ratio （SNR） that ensures the efficiency of detection. The condition of detection in the case of low SNR is analyzed, and three different cases that would occur during integration are discussed and a method to determine the CPI is presented. The simulation results show that targets detection with SNR as low as -26 dB in the experimental system can possibly determine the CPI.
基金supported by the National Natural Science Foundation of China(6107313361175053+8 种基金6127236960975019)the Heilongjiang Postdoctoral Grant(LRB08362)the Fundamental Research Funds for the Central Universities of China(2011QN0272011QN1262012QN0302011ZD010)the Science and Technology Planning Project of Dalian City(2011A17GX0732010E15SF153)
文摘An adaptive approach to select analysis window param- eters for linear frequency modulated （LFM） signals is proposed to obtain the optimal 3 dB signal-to-noise ratio （SNR） in the short- time Fourier transform （STFT） domain. After analyzing the instan- taneous frequency and instantaneous bandwidth to deduce the relation between the window length and deviation of the Gaus- sian window, high-order statistics is used to select the appropriate window length for STFT and get the optimal SNR with the right time-frequency resolution according to the signal characteristic under a fixed sampling rate. Computer simulations have verified the effectiveness of the new method.
基金supported by the Program for New Century Excellent Talents in University, Ministry of Education (NCET-05-0803)
文摘The Radon-ambiguity transform （RAT）, although efficient for detecting the linear frequency modulated signals （LFMs）, is troubled by the energy accumulation of noise in low signal-to-noise ratio （SNR）. A secondorder difference （SOD） method is proposed to treat with this problem. In the SOD method, the optimal search step and difference step are derived from the LFM rate resolution formula. The sharpness of the peaks of RAT is measured by curvature, and the sharpness, but not the magnitude of the peaks, is used to detect the LFMs. The SOD method removes the noise energy accumulation and reserves the drastically changing components integrally; thus, it improves the detection probability of LFMs in low SNR. The expected performance of the new method is verified by 100 Monte Carlo simulations.
基金Sponsored by National Defence Key Technology Pre-research Program During the Tenth Five-Year Plan Period
文摘Introduces in brief the principle of three kinds pseudo-random code fuzes, viz. the pseudo-random code phase modulation fuze,the pseudo-random code phase modulation and pulse amplitude modulation(PAM) combined fuze,and the pseudo-random code phase modulation and random(pseudo-random) pulse position modulation(PPM) combined fuze. On this basis, their SNR gains in signal processing after band pass filter to the correlation detection, and the overall SNR gains of the whole procedure after correlation detection are deduced in detail. The results show that the latter two kinds of fuzes have the same performances concerning antinoise that are stronger than that of the pseudo-random code phase modulation fuze.
