This paper investigates the problem of almanac affecting the signal acquisition time with two constraints: different age of data and multi-sets of almanac. The contributions made in this paper include: 1) the exploiti...This paper investigates the problem of almanac affecting the signal acquisition time with two constraints: different age of data and multi-sets of almanac. The contributions made in this paper include: 1) the exploiting of signal acquisition concept to extend well-known almanac function of predicting visible satellite and initializing signal acquisition to minimizing the signal acquisition time; 2) a model based on code phase and Doppler frequency to reflect the impact of multi-sets of almanac on the signal acquisition time; 3) the evaluation of the existing GPS almanac with different broadcast strategy. The theoretical analyses and simulations conducted on three sets of almanac show that the model proposed in this paper is general and efficient for almanac design and application.展开更多
Acquisition time of global position system （GPS） receiver, which is the main factor contributes to time to first fix （TTFF）, can be shortened by estimating the Doppler frequency shift through external inertial nav...Acquisition time of global position system （GPS） receiver, which is the main factor contributes to time to first fix （TTFF）, can be shortened by estimating the Doppler frequency shift through external inertial navigation system （INS） information and almanac data and reducing the searching area. The traditional fast acquisition is analyzed, the fast acquisition of the GPS receiver aided is presented by INS information, and the signal is fine captured by spectrum zooming. Then the algorithm is simulated by sampled GPS intermediate frequency （IF） signal and the result verifies that this acquisition can dramatically improve the capability of GPS receiver and reduce its acquisition time.展开更多
A stable and accurate pointing,acquisition system is an important part of initially building intersatellite optical communication links.Satellite platform vibration can cause the system instability and reduce the syst...A stable and accurate pointing,acquisition system is an important part of initially building intersatellite optical communication links.Satellite platform vibration can cause the system instability and reduce the system precision in building and maintenance of a satellite optical communication system.In this paper,vibration influence is consciously discussed by acquisition time for intersatellite optical communications.Analytical expression of acquisition possibility is derived,taking the scan parameters and platform vibration into account,and vibration influence on the multi-scan acquisition time is also presented.The theoretical result calculated by the proposed analytical expression is approximate to the result by the Monte Carlo simulation.展开更多
For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform ...For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform （FRFT） is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the received signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.展开更多
BACKGROUND A key cardiac magnetic resonance(CMR)challenge is breath-holding duration,difficult for cardiac patients.AIM To evaluate whether artificial intelligence-assisted compressed sensing CINE(AICS-CINE)reduces im...BACKGROUND A key cardiac magnetic resonance(CMR)challenge is breath-holding duration,difficult for cardiac patients.AIM To evaluate whether artificial intelligence-assisted compressed sensing CINE(AICS-CINE)reduces image acquisition time of CMR compared to conventional CINE(C-CINE).METHODS Cardio-oncology patients(n=60)and healthy volunteers(n=29)underwent sequential C-CINE and AI-CS-CINE with a 1.5-T scanner.Acquisition time,visual image quality assessment,and biventricular metrics(end-diastolic volume,endsystolic volume,stroke volume,ejection fraction,left ventricular mass,and wall thickness)were analyzed and compared between C-CINE and AI-CS-CINE with Bland–Altman analysis,and calculation of intraclass coefficient(ICC).RESULTS In 89 participants(58.5±16.8 years,42 males,47 females),total AI-CS-CINE acquisition and reconstruction time(37 seconds)was 84%faster than C-CINE(238 seconds).C-CINE required repeats in 23%(20/89)of cases(approximately 8 minutes lost),while AI-CS-CINE only needed one repeat(1%;2 seconds lost).AICS-CINE had slightly lower contrast but preserved structural clarity.Bland-Altman plots and ICC(0.73≤r≤0.98)showed strong agreement for left ventricle(LV)and right ventricle(RV)metrics,including those in the cardiac amyloidosis subgroup(n=31).AI-CS-CINE enabled faster,easier imaging in patients with claustrophobia,dyspnea,arrhythmias,or restlessness.Motion-artifacted C-CINE images were reliably interpreted from AI-CS-CINE.CONCLUSION AI-CS-CINE accelerated CMR image acquisition and reconstruction,preserved anatomical detail,and diminished impact of patient-related motion.Quantitative AI-CS-CINE metrics agreed closely with C-CINE in cardio-oncology patients,including the cardiac amyloidosis cohort,as well as healthy volunteers regardless of left and right ventricular size and function.AI-CS-CINE significantly enhanced CMR workflow,particularly in challenging cases.The strong analytical concordance underscores reliability and robustness of AI-CS-CINE as a valuable tool.展开更多
AIM： To compare the clinical performance of 4 spectraldomain（SD） optical coherence tomography angiography（OCTA） systems： AngioVueTM, AngioPlexTM, Spectralis？ OCTA, AngioScan, and 1 swept-source（SS） OCTA SS OC...AIM： To compare the clinical performance of 4 spectraldomain（SD） optical coherence tomography angiography（OCTA） systems： AngioVueTM, AngioPlexTM, Spectralis？ OCTA, AngioScan, and 1 swept-source（SS） OCTA SS OCT AngioTM. METHODS： Twenty-seven undilated right eyes of 27 participants underwent OCTA examination using five different systems respectively for both 3×3 and 6×6 mm^2 scan pattern（Spectralis OCTA for 3×3 mm^2 scan only）. Image quality, including vessel valid visibility and the number of motion artifacts, and acquisition time were evaluated. Repeated measures analysis of variance（ANOVA） with Bonferroni＇s post-test and Friedman test with Dunn＇s posttest were used to compare measurements.RESULTS： The age of the subjects was 28.19±5.55 y（range, 23-49 y）. The spherical equivalent refraction was-2.55±1.84 D（range, 0.00 to-5.25 D）. Significant difference was observed in the evaluation of vessel valid visibility（Angio Vue the highest： 0.111±0.031 for 3×3 mm^2 scan and 0.128±0.020 for 6×6 mm^2 scan）, number of motion artifacts（AngioVue the fewest： 0.778±1.086 for 3×3 mm^2 scan and 0.333±0.620 for 6×6 mm^2 scan） and acquisition time（AngioPlex the shortest： 8.537±1.921 s for 3×3 mm^2 scan and 8.298±1.741 s for 6×6 mm^2 scan; all P〈0.001）. CONCLUSION： There is poor agreement of measurements among systems. AngioVue provides images with the highest vessel valid visibility and the fewest motion artifacts. AngioPlex achieves the shortest acquisition.展开更多
A modiΡed pseudo-noise(PN)code regeneration method is proposed to improve the clock tracking accuracy without impairing the code acquisition time performance.Thus,the method can meet the requirement of high accuracy ...A modiΡed pseudo-noise(PN)code regeneration method is proposed to improve the clock tracking accuracy without impairing the code acquisition time performance.Thus,the method can meet the requirement of high accuracy ranging measurements in short time periods demanded by radio-science missions.The tracking error variance is derived by linear analysis.For some existing PN codes,which can be acquired rapidly,the tracking error variance performance of the proposed method is about 2.6 dB better than that of the JPL scheme(originally proposed by Jet Propulsion Laboratory),and about 1.5 dB better than that of the traditional double loop scheme.展开更多
In this paper a closed-form approximated expression is proposed for the Intersymbol Interference (ISI) as a function of time valid during the entire stages of the non-blind adaptive deconvolution process and is suitab...In this paper a closed-form approximated expression is proposed for the Intersymbol Interference (ISI) as a function of time valid during the entire stages of the non-blind adaptive deconvolution process and is suitable for the noisy, real and two independent quadrature carrier input case. The obtained expression is applicable for type of channels where the resulting ISI as a function of time can be described with an exponential model having a single time constant. Based on this new expression for the ISI as a function of time, the convergence time (or number of iteration number required for convergence) of the non-blind adaptive equalizer can be calculated. Up to now, the equalizer’s performance (convergence time and ISI as a function of time) could be obtained only via simulation when the channel coefficients were known. The new proposed expression for the ISI as a function of time is based on the knowledge of the initial ISI and channel power (which is measurable) and eliminates the need to carry out any more the above mentioned simulation. Simulation results indicate a high correlation between the simulated and calculated ISI (based on our proposed expression for the ISI as a function of time) during the whole deconvolution process for the high as well as for the low signal to noise ratio (SNR) condition.展开更多
As a frontier technology,holography has important research values in fields such as bio-micrographic imaging,light feld modulation and data storage.However,the real-time acquisition of 3D scenes and high-fidelity reco...As a frontier technology,holography has important research values in fields such as bio-micrographic imaging,light feld modulation and data storage.However,the real-time acquisition of 3D scenes and high-fidelity reconstruction technology has not yet made a breakthrough,which has seriously hindered the development of holography.Here,a novel holographic camera is proposed to solve the above inherent problems completely.The proposed holographic camera consists of the acquisition end and the calculation end.At the acquisition end of the holographic camera,specially configured liquid materials and liquid lens structure based on voice-coil motor-driving are used to produce the liquid camera,so that the liquid camera can quickly capture the focus stack of the real 3D scene within 15 ms.At the calculation end,a new structured focus stack network(FS-Net)is designed for hologram calculation.After training the FS-Net with the focus stack renderer and learnable Zernike phase,it enables hologram calculation within 13 ms.As the first device to achieve real-time incoherent acquisition and high-fidelity holographic reconstruction of a real 3D scene,our proposed holographic camera breaks technical bottlenecks of difficulty in acquiring the real 3D scene,low quality of the holographic reconstructed image,and incorrect defocus blur.The experimental results demonstrate the effectiveness of our holographic camera in the acquisition of focal plane information and hologram calculation of the real 3D scene.The proposed holographic camera opens up a new way for the application of holography in fields such as 3D display,light field modulation,and 3D measurement.展开更多
基金Sponsored by the National Basic Research Program of China(Grant No.2010CB731800)the National Natural Science Foundation of China(GrantNo.60879012/F01)
文摘This paper investigates the problem of almanac affecting the signal acquisition time with two constraints: different age of data and multi-sets of almanac. The contributions made in this paper include: 1) the exploiting of signal acquisition concept to extend well-known almanac function of predicting visible satellite and initializing signal acquisition to minimizing the signal acquisition time; 2) a model based on code phase and Doppler frequency to reflect the impact of multi-sets of almanac on the signal acquisition time; 3) the evaluation of the existing GPS almanac with different broadcast strategy. The theoretical analyses and simulations conducted on three sets of almanac show that the model proposed in this paper is general and efficient for almanac design and application.
文摘Acquisition time of global position system （GPS） receiver, which is the main factor contributes to time to first fix （TTFF）, can be shortened by estimating the Doppler frequency shift through external inertial navigation system （INS） information and almanac data and reducing the searching area. The traditional fast acquisition is analyzed, the fast acquisition of the GPS receiver aided is presented by INS information, and the signal is fine captured by spectrum zooming. Then the algorithm is simulated by sampled GPS intermediate frequency （IF） signal and the result verifies that this acquisition can dramatically improve the capability of GPS receiver and reduce its acquisition time.
基金Project supported by the Program of Excellent Team in Harbin Institute of Technology,China
文摘A stable and accurate pointing,acquisition system is an important part of initially building intersatellite optical communication links.Satellite platform vibration can cause the system instability and reduce the system precision in building and maintenance of a satellite optical communication system.In this paper,vibration influence is consciously discussed by acquisition time for intersatellite optical communications.Analytical expression of acquisition possibility is derived,taking the scan parameters and platform vibration into account,and vibration influence on the multi-scan acquisition time is also presented.The theoretical result calculated by the proposed analytical expression is approximate to the result by the Monte Carlo simulation.
基金supported by the National Natural Science Foundation of China(60672047).
文摘For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform （FRFT） is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the received signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.
基金Supported by James Russell Hornsby and Jun Xiong Fund and United Imaging Healthcare.
文摘BACKGROUND A key cardiac magnetic resonance(CMR)challenge is breath-holding duration,difficult for cardiac patients.AIM To evaluate whether artificial intelligence-assisted compressed sensing CINE(AICS-CINE)reduces image acquisition time of CMR compared to conventional CINE(C-CINE).METHODS Cardio-oncology patients(n=60)and healthy volunteers(n=29)underwent sequential C-CINE and AI-CS-CINE with a 1.5-T scanner.Acquisition time,visual image quality assessment,and biventricular metrics(end-diastolic volume,endsystolic volume,stroke volume,ejection fraction,left ventricular mass,and wall thickness)were analyzed and compared between C-CINE and AI-CS-CINE with Bland–Altman analysis,and calculation of intraclass coefficient(ICC).RESULTS In 89 participants(58.5±16.8 years,42 males,47 females),total AI-CS-CINE acquisition and reconstruction time(37 seconds)was 84%faster than C-CINE(238 seconds).C-CINE required repeats in 23%(20/89)of cases(approximately 8 minutes lost),while AI-CS-CINE only needed one repeat(1%;2 seconds lost).AICS-CINE had slightly lower contrast but preserved structural clarity.Bland-Altman plots and ICC(0.73≤r≤0.98)showed strong agreement for left ventricle(LV)and right ventricle(RV)metrics,including those in the cardiac amyloidosis subgroup(n=31).AI-CS-CINE enabled faster,easier imaging in patients with claustrophobia,dyspnea,arrhythmias,or restlessness.Motion-artifacted C-CINE images were reliably interpreted from AI-CS-CINE.CONCLUSION AI-CS-CINE accelerated CMR image acquisition and reconstruction,preserved anatomical detail,and diminished impact of patient-related motion.Quantitative AI-CS-CINE metrics agreed closely with C-CINE in cardio-oncology patients,including the cardiac amyloidosis cohort,as well as healthy volunteers regardless of left and right ventricular size and function.AI-CS-CINE significantly enhanced CMR workflow,particularly in challenging cases.The strong analytical concordance underscores reliability and robustness of AI-CS-CINE as a valuable tool.
基金Supported by National Key Research and Development Program for Precision Medicine of China (No.2016YFC0904800)
文摘AIM： To compare the clinical performance of 4 spectraldomain（SD） optical coherence tomography angiography（OCTA） systems： AngioVueTM, AngioPlexTM, Spectralis？ OCTA, AngioScan, and 1 swept-source（SS） OCTA SS OCT AngioTM. METHODS： Twenty-seven undilated right eyes of 27 participants underwent OCTA examination using five different systems respectively for both 3×3 and 6×6 mm^2 scan pattern（Spectralis OCTA for 3×3 mm^2 scan only）. Image quality, including vessel valid visibility and the number of motion artifacts, and acquisition time were evaluated. Repeated measures analysis of variance（ANOVA） with Bonferroni＇s post-test and Friedman test with Dunn＇s posttest were used to compare measurements.RESULTS： The age of the subjects was 28.19±5.55 y（range, 23-49 y）. The spherical equivalent refraction was-2.55±1.84 D（range, 0.00 to-5.25 D）. Significant difference was observed in the evaluation of vessel valid visibility（Angio Vue the highest： 0.111±0.031 for 3×3 mm^2 scan and 0.128±0.020 for 6×6 mm^2 scan）, number of motion artifacts（AngioVue the fewest： 0.778±1.086 for 3×3 mm^2 scan and 0.333±0.620 for 6×6 mm^2 scan） and acquisition time（AngioPlex the shortest： 8.537±1.921 s for 3×3 mm^2 scan and 8.298±1.741 s for 6×6 mm^2 scan; all P〈0.001）. CONCLUSION： There is poor agreement of measurements among systems. AngioVue provides images with the highest vessel valid visibility and the fewest motion artifacts. AngioPlex achieves the shortest acquisition.
基金supported by the National Natural Science Foundation of China(60904090)the Postdoctoral Science Foundation of China(20080431306)the Special Postdoctoral Science Foundation of China(20081458)
文摘A modiΡed pseudo-noise(PN)code regeneration method is proposed to improve the clock tracking accuracy without impairing the code acquisition time performance.Thus,the method can meet the requirement of high accuracy ranging measurements in short time periods demanded by radio-science missions.The tracking error variance is derived by linear analysis.For some existing PN codes,which can be acquired rapidly,the tracking error variance performance of the proposed method is about 2.6 dB better than that of the JPL scheme(originally proposed by Jet Propulsion Laboratory),and about 1.5 dB better than that of the traditional double loop scheme.
文摘In this paper a closed-form approximated expression is proposed for the Intersymbol Interference (ISI) as a function of time valid during the entire stages of the non-blind adaptive deconvolution process and is suitable for the noisy, real and two independent quadrature carrier input case. The obtained expression is applicable for type of channels where the resulting ISI as a function of time can be described with an exponential model having a single time constant. Based on this new expression for the ISI as a function of time, the convergence time (or number of iteration number required for convergence) of the non-blind adaptive equalizer can be calculated. Up to now, the equalizer’s performance (convergence time and ISI as a function of time) could be obtained only via simulation when the channel coefficients were known. The new proposed expression for the ISI as a function of time is based on the knowledge of the initial ISI and channel power (which is measurable) and eliminates the need to carry out any more the above mentioned simulation. Simulation results indicate a high correlation between the simulated and calculated ISI (based on our proposed expression for the ISI as a function of time) during the whole deconvolution process for the high as well as for the low signal to noise ratio (SNR) condition.
基金supported by National Natural Science Foundation of China(U22A2079,62275009,62175006,and U21B2034).
文摘As a frontier technology,holography has important research values in fields such as bio-micrographic imaging,light feld modulation and data storage.However,the real-time acquisition of 3D scenes and high-fidelity reconstruction technology has not yet made a breakthrough,which has seriously hindered the development of holography.Here,a novel holographic camera is proposed to solve the above inherent problems completely.The proposed holographic camera consists of the acquisition end and the calculation end.At the acquisition end of the holographic camera,specially configured liquid materials and liquid lens structure based on voice-coil motor-driving are used to produce the liquid camera,so that the liquid camera can quickly capture the focus stack of the real 3D scene within 15 ms.At the calculation end,a new structured focus stack network(FS-Net)is designed for hologram calculation.After training the FS-Net with the focus stack renderer and learnable Zernike phase,it enables hologram calculation within 13 ms.As the first device to achieve real-time incoherent acquisition and high-fidelity holographic reconstruction of a real 3D scene,our proposed holographic camera breaks technical bottlenecks of difficulty in acquiring the real 3D scene,low quality of the holographic reconstructed image,and incorrect defocus blur.The experimental results demonstrate the effectiveness of our holographic camera in the acquisition of focal plane information and hologram calculation of the real 3D scene.The proposed holographic camera opens up a new way for the application of holography in fields such as 3D display,light field modulation,and 3D measurement.
