Time delay and Doppler shift between the echo signal and the reference signal are two most commonly used measurements in target localization for the passive radar. Doppler rate, which can be obtained from the extended...Time delay and Doppler shift between the echo signal and the reference signal are two most commonly used measurements in target localization for the passive radar. Doppler rate, which can be obtained from the extended cross ambiguity function, offers an opportunity to further enhance the localization accuracy. This paper considers using the measurement Doppler rate in addition to measurements of time delay and Doppler shift to locate a moving target. A closed-form solution is developed to accurately and efficiently estimate the target position and velocity.The proposed solution establishes a pseudolinear set of equations by introducing some additional variables, imposes weighted least squares formulation to yield a rough estimate, and utilizes the function relation among the target location parameters and additional variables to improve the estimation accuracy. Theoretical covariance and Cramer-Rao lower bound(CRLB) are derived and compared, analytically indicating that the proposed solution attains the CRLB. Numerical simulations corroborate this analysis and demonstrate that the proposed solution outperforms existing methods.展开更多
Considering the estimation accuracy reduction of Frequency Difference of Arrival (FDOA) caused by relative Doppler companding, a joint Time Difference of Arrival (TDOA), FDOA and differential Doppler rate estimati...Considering the estimation accuracy reduction of Frequency Difference of Arrival (FDOA) caused by relative Doppler companding, a joint Time Difference of Arrival (TDOA), FDOA and differential Doppler rate estimation method is proposed and its Cramer-Rao low bound is derived in this paper. Firstly, second-order ambiguity function is utilized to reduce the dimensionality and estimate initial TDOA and differential Doppler rate. Secondly, the TDOA estimation is updated and FDOA is obtained using cross ambiguity function, in which relative Doppler com- panding is compensated by the existing differential Doppler rate. Thirdly, differential Doppler rate estimation is updated using cross estimator. Theoretical analysis on estimation variance and Cramer-Rao low bound shows that the final estimation of TDOA, FDOA and differential Doppler rate performs well at both low and high signal-noise ratio, although the initial estimation accuracy of TDOA and differential Doppler rate is relatively poor under low signal-noise ratio conditions. Simulation results finally verify the theoretical analysis and show that the proposed method can overcome relative Doppler companding problem and performs well for all TDOA, FDOA and differential Doppler rate estimation.展开更多
In writings on relativity time, the various relations are only changed by the transverse shift. This paper proves that the axial Doppler shift does that as well and gives some impacts of that on common differential re...In writings on relativity time, the various relations are only changed by the transverse shift. This paper proves that the axial Doppler shift does that as well and gives some impacts of that on common differential relations in physics. When a modulated signal lasting a time = T is subjected to an optical Doppler shift K (either axial or transverse or both), where K is shifted frequency/original frequency, the Doppler shifted signal will last T/K. This because all shifted harmonics of its Fourier series (with a fundamental period of T) will last 1/K times the period of the original harmonic. The reader can graph any Fourier series and then graph its shifted series. The reader will see the shifted period is T/K. The Fourier series of the original repeats when time is greater than T and the shifted one when time is greater than T/K, which means the original series only represents the signal from time = 0 to T and the shifted series represents the shifted signal from time = 0 to T/K. Hence, the shifted one has all of the information in T/K as the original has in T. Therefore everything in the series including information is T/K long in the shifted series. Therefore, both the axial and the transverse Doppler shift change time periods in a vacuum, independent of material involved. That has not been obvious for over 100 years the axial shift changes time from the definition of frequency = 1/time.展开更多
A method is presented for near-Earth spacecraft or aviation vehicle's attitude rate estimation by using relative Doppler frequency shift of the Global Positioning System (GPS)carrier. It comprises two GPS receivin...A method is presented for near-Earth spacecraft or aviation vehicle's attitude rate estimation by using relative Doppler frequency shift of the Global Positioning System (GPS)carrier. It comprises two GPS receiving antennas, a signal processing circuit and an algorithm.The whole system is relatively simple, the cost and wcight, as well as power consumption, are very low.展开更多
This paper presents a Doppler passive location method for moving targets with fixed single station using the Doppler frequency shift and time difference information.First,based on the relationship between frequency sh...This paper presents a Doppler passive location method for moving targets with fixed single station using the Doppler frequency shift and time difference information.First,based on the relationship between frequency shift and path difference,the virtual path difference is calculated from the measured value of Doppler frequency shift by means of mean value correction.Then,under the assumption that the target is moving at a constant speed along a straight line,two coaxial virtual double base arrays are constructed by using the moving track of the moving target based on the method of fixed period time difference.On this basis,the moving distance of the moving target can be calculated by using the ratio relationship between the frequency difference and the radial distance between the two adjacent detection points in the middle of the array,and the linear solution of the two double base path difference positioning equations.At this point,the relative coordinate position of the moving target can be obtained by directly using the linear solution of the double base path difference positioning equation again.展开更多
Objectives: The aim of this work was to compare the effectiveness and safety of endometrial scratching at different times of the menstrual cycle on cumulative pregnancy rate and also to assess and clarify its relation...Objectives: The aim of this work was to compare the effectiveness and safety of endometrial scratching at different times of the menstrual cycle on cumulative pregnancy rate and also to assess and clarify its relationship and effect on sub-endometrial vasculature blood flow by Doppler ultrasound, in cases of unexplained infertility attempting to conceive spontaneously (without ovulation induction). Study Design: A prospective randomized clinical control study. Patients and Methods: A total of 252 eligible participants were included in the study and randomly allocated using block randomization into three groups: Group A (n = 84): endometrial scratching was performed during the pre-ovulatory days and Group B (n = 84): endometrial scratching has been done at day 7 of the cycle. Group C (control group): includes 84 cases without endometrial scratching. The Doppler ultrasound will be done. The pulsatility index (PI) and resistance index (RI) of endometrial and sub endometrial arteries were calculated. All women were followed up to 3 months. Results: Cumulative pregnancy rate is 21.42% and 28.57% in the study groups A and B respectively which is higher than group C (control group) (4.76%) but with statistically insignificant P-value = 0.254. There is statistically significant difference in RI & PI between the studied groups and the control group on day 13 (P value < 0.001). There is statistically significant difference in PI between day 13 and day 6 for the same group in both groups (A&B) (P value < 0.003), while there is no statistically significant difference in Group C (P value = 0.156). Conclusion: Endometrial scratching is a cost-effective and easy technique which may improve clinical pregnancy rates and endometrial blood flow in women with unexplained infertility.展开更多
AIM:To evaluate the effects of eicosapentaenoic acid(EPA) on regional arterial stiffness assessed by strain rate using tissue Doppler imaging.METHODS:Nineteen eligible patients were prospectively studied(mean age 62 &...AIM:To evaluate the effects of eicosapentaenoic acid(EPA) on regional arterial stiffness assessed by strain rate using tissue Doppler imaging.METHODS:Nineteen eligible patients were prospectively studied(mean age 62 ± 8 years,68% men).Subjects with large vessel complications and/or diabetes mellitus were excluded.The strain rate of the ascending aorta was measured by tissue Doppler imaging as an index of regional arterial stiffness,and brachialankle pulse wave velocity(baPWV) was measured as an index of degree of systemic arteriosclerosis.These indices were compared before and after administration of EPA at 1800 mg/d for one year.RESULTS:The plasma concentration of EPA increased significantly after EPA administration(3.0% ± 1.1% to 8.5% ± 2.9%,P 【 0.001).There were no significant changes in baPWV(1765 ± 335 cm/s to 1745 ± 374 cm/s),low-density lipoprotein cholesterol levels(114 ± 29 mg/dL to 108 ± 28 mg/dL),or systolic blood pressure(131 ± 16 mmHg to 130 ± 13 mmHg) before and after EPA administration.In contrast,the strain rate was significantly increased by administration of EPA(19.2 ± 5.6 s-1,23.0 ± 6.6 s-1,P 【 0.05).CONCLUSION:One year of administration of EPA resulted in an improvement in regional arterial stiffness which was independent of blood pressure or serum cholesterol levels.展开更多
Instantaneous Doppler frequency for squint SAR imaging has been found with ChirpScaling Algorithm (CSA). Because the azimuth sample is not perpendicular to the range sample,the range signal must impact on the azimuth ...Instantaneous Doppler frequency for squint SAR imaging has been found with ChirpScaling Algorithm (CSA). Because the azimuth sample is not perpendicular to the range sample,the range signal must impact on the azimuth signal in the squint SAR data processing, andthe different slant range targets have different Doppler frequencies. From the mathematicalmodel of SAR echo signal, this paper carefully analyzes the instantaneous azimuth frequency, theinstantaneous Doppler frequency component of the azimuth frequency and the impact of rangechirp on azimuth frequency, which explains that Doppler frequency should be properly selected forcorrect SAR imaging in the squint SAR. The results of point target simulation experiments showthat the way is reasonable for the squint SAR and can effectively complete range compressionand azimuth focusing, and improve images' quality.展开更多
基金supported by the National Natural Science Foundation of China (61703433)。
文摘Time delay and Doppler shift between the echo signal and the reference signal are two most commonly used measurements in target localization for the passive radar. Doppler rate, which can be obtained from the extended cross ambiguity function, offers an opportunity to further enhance the localization accuracy. This paper considers using the measurement Doppler rate in addition to measurements of time delay and Doppler shift to locate a moving target. A closed-form solution is developed to accurately and efficiently estimate the target position and velocity.The proposed solution establishes a pseudolinear set of equations by introducing some additional variables, imposes weighted least squares formulation to yield a rough estimate, and utilizes the function relation among the target location parameters and additional variables to improve the estimation accuracy. Theoretical covariance and Cramer-Rao lower bound(CRLB) are derived and compared, analytically indicating that the proposed solution attains the CRLB. Numerical simulations corroborate this analysis and demonstrate that the proposed solution outperforms existing methods.
基金supported by the National Natural Science Foundation of China(No.61671273)
文摘Considering the estimation accuracy reduction of Frequency Difference of Arrival (FDOA) caused by relative Doppler companding, a joint Time Difference of Arrival (TDOA), FDOA and differential Doppler rate estimation method is proposed and its Cramer-Rao low bound is derived in this paper. Firstly, second-order ambiguity function is utilized to reduce the dimensionality and estimate initial TDOA and differential Doppler rate. Secondly, the TDOA estimation is updated and FDOA is obtained using cross ambiguity function, in which relative Doppler com- panding is compensated by the existing differential Doppler rate. Thirdly, differential Doppler rate estimation is updated using cross estimator. Theoretical analysis on estimation variance and Cramer-Rao low bound shows that the final estimation of TDOA, FDOA and differential Doppler rate performs well at both low and high signal-noise ratio, although the initial estimation accuracy of TDOA and differential Doppler rate is relatively poor under low signal-noise ratio conditions. Simulation results finally verify the theoretical analysis and show that the proposed method can overcome relative Doppler companding problem and performs well for all TDOA, FDOA and differential Doppler rate estimation.
文摘In writings on relativity time, the various relations are only changed by the transverse shift. This paper proves that the axial Doppler shift does that as well and gives some impacts of that on common differential relations in physics. When a modulated signal lasting a time = T is subjected to an optical Doppler shift K (either axial or transverse or both), where K is shifted frequency/original frequency, the Doppler shifted signal will last T/K. This because all shifted harmonics of its Fourier series (with a fundamental period of T) will last 1/K times the period of the original harmonic. The reader can graph any Fourier series and then graph its shifted series. The reader will see the shifted period is T/K. The Fourier series of the original repeats when time is greater than T and the shifted one when time is greater than T/K, which means the original series only represents the signal from time = 0 to T and the shifted series represents the shifted signal from time = 0 to T/K. Hence, the shifted one has all of the information in T/K as the original has in T. Therefore everything in the series including information is T/K long in the shifted series. Therefore, both the axial and the transverse Doppler shift change time periods in a vacuum, independent of material involved. That has not been obvious for over 100 years the axial shift changes time from the definition of frequency = 1/time.
基金Supported by the National Aeronautics and Space Administration(NASA),Goddard Space Flight Center,USA,under Contract AN13709
文摘A method is presented for near-Earth spacecraft or aviation vehicle's attitude rate estimation by using relative Doppler frequency shift of the Global Positioning System (GPS)carrier. It comprises two GPS receiving antennas, a signal processing circuit and an algorithm.The whole system is relatively simple, the cost and wcight, as well as power consumption, are very low.
文摘This paper presents a Doppler passive location method for moving targets with fixed single station using the Doppler frequency shift and time difference information.First,based on the relationship between frequency shift and path difference,the virtual path difference is calculated from the measured value of Doppler frequency shift by means of mean value correction.Then,under the assumption that the target is moving at a constant speed along a straight line,two coaxial virtual double base arrays are constructed by using the moving track of the moving target based on the method of fixed period time difference.On this basis,the moving distance of the moving target can be calculated by using the ratio relationship between the frequency difference and the radial distance between the two adjacent detection points in the middle of the array,and the linear solution of the two double base path difference positioning equations.At this point,the relative coordinate position of the moving target can be obtained by directly using the linear solution of the double base path difference positioning equation again.
文摘Objectives: The aim of this work was to compare the effectiveness and safety of endometrial scratching at different times of the menstrual cycle on cumulative pregnancy rate and also to assess and clarify its relationship and effect on sub-endometrial vasculature blood flow by Doppler ultrasound, in cases of unexplained infertility attempting to conceive spontaneously (without ovulation induction). Study Design: A prospective randomized clinical control study. Patients and Methods: A total of 252 eligible participants were included in the study and randomly allocated using block randomization into three groups: Group A (n = 84): endometrial scratching was performed during the pre-ovulatory days and Group B (n = 84): endometrial scratching has been done at day 7 of the cycle. Group C (control group): includes 84 cases without endometrial scratching. The Doppler ultrasound will be done. The pulsatility index (PI) and resistance index (RI) of endometrial and sub endometrial arteries were calculated. All women were followed up to 3 months. Results: Cumulative pregnancy rate is 21.42% and 28.57% in the study groups A and B respectively which is higher than group C (control group) (4.76%) but with statistically insignificant P-value = 0.254. There is statistically significant difference in RI & PI between the studied groups and the control group on day 13 (P value < 0.001). There is statistically significant difference in PI between day 13 and day 6 for the same group in both groups (A&B) (P value < 0.003), while there is no statistically significant difference in Group C (P value = 0.156). Conclusion: Endometrial scratching is a cost-effective and easy technique which may improve clinical pregnancy rates and endometrial blood flow in women with unexplained infertility.
文摘AIM:To evaluate the effects of eicosapentaenoic acid(EPA) on regional arterial stiffness assessed by strain rate using tissue Doppler imaging.METHODS:Nineteen eligible patients were prospectively studied(mean age 62 ± 8 years,68% men).Subjects with large vessel complications and/or diabetes mellitus were excluded.The strain rate of the ascending aorta was measured by tissue Doppler imaging as an index of regional arterial stiffness,and brachialankle pulse wave velocity(baPWV) was measured as an index of degree of systemic arteriosclerosis.These indices were compared before and after administration of EPA at 1800 mg/d for one year.RESULTS:The plasma concentration of EPA increased significantly after EPA administration(3.0% ± 1.1% to 8.5% ± 2.9%,P 【 0.001).There were no significant changes in baPWV(1765 ± 335 cm/s to 1745 ± 374 cm/s),low-density lipoprotein cholesterol levels(114 ± 29 mg/dL to 108 ± 28 mg/dL),or systolic blood pressure(131 ± 16 mmHg to 130 ± 13 mmHg) before and after EPA administration.In contrast,the strain rate was significantly increased by administration of EPA(19.2 ± 5.6 s-1,23.0 ± 6.6 s-1,P 【 0.05).CONCLUSION:One year of administration of EPA resulted in an improvement in regional arterial stiffness which was independent of blood pressure or serum cholesterol levels.
文摘Instantaneous Doppler frequency for squint SAR imaging has been found with ChirpScaling Algorithm (CSA). Because the azimuth sample is not perpendicular to the range sample,the range signal must impact on the azimuth signal in the squint SAR data processing, andthe different slant range targets have different Doppler frequencies. From the mathematicalmodel of SAR echo signal, this paper carefully analyzes the instantaneous azimuth frequency, theinstantaneous Doppler frequency component of the azimuth frequency and the impact of rangechirp on azimuth frequency, which explains that Doppler frequency should be properly selected forcorrect SAR imaging in the squint SAR. The results of point target simulation experiments showthat the way is reasonable for the squint SAR and can effectively complete range compressionand azimuth focusing, and improve images' quality.