Technique PPP-RTK combines the advantages of both the Precise Point Positioning(PPP)and the Real-Time Kinematic(RTK)positioning.With the emergence of multi-frequency Global Navigation Satellite System(GNSS)observation...Technique PPP-RTK combines the advantages of both the Precise Point Positioning(PPP)and the Real-Time Kinematic(RTK)positioning.With the emergence of multi-frequency Global Navigation Satellite System(GNSS)observations,it is preferable to formulate PPP-RTK functional models based on original(undiferenced and uncombined)observations.While there exist many variants of the undiferenced and uncombined PPP–RTK models,a unifed theoretical framework needs developing to link these variants.In this contribution,we formulate a class of undiferenced and uncombined PPP-RTK functional models in a systematic way and cast them in a unifed framework.This framework classifes the models into a code-plus-phase category and a phase-only category.Each category covers a variety of measurement scenarios on the network side,ranging from small-,medium-to large-scale networks.For each scenario,special care has been taken of the distinct ionospheric constraints and the diference between Code Division Multiple Access(CDMA)and Frequency Division Multiple Access(FDMA)signals.The key to systematically formulating these models lies in how to deal with the rank defciency problems encountered.We opt for the Singularity-basis(S-basis)theory,giving rise to the full-rank observation equations in which the estimable parameters turn out to be the functions of original parameters and those selected as the S-basis.In the sequel,it becomes straightforward to derive for each scenario the user model as it,more or less,amounts to the single-receiver network model.Benefting from the presented theoretical framework,the relationships and diferences between various undiferenced and uncombined PPP-RTK models become clear,which can lead to the better use of these models in a specifc situation.展开更多
The application scope of the forward scatter radar(FSR)based on the Global Navigation Satellite System(GNSS)can be expanded by improving the detection capability.Firstly,the forward-scatter signal model when the targe...The application scope of the forward scatter radar(FSR)based on the Global Navigation Satellite System(GNSS)can be expanded by improving the detection capability.Firstly,the forward-scatter signal model when the target crosses the baseline is constructed.Then,the detection method of the for-ward-scatter signal based on the Rényi entropy of time-fre-quency distribution is proposed and the detection performance with different time-frequency distributions is compared.Simula-tion results show that the method based on the smooth pseudo Wigner-Ville distribution(SPWVD)can achieve the best perfor-mance.Next,combined with the geometry of FSR,the influence on detection performance of the relative distance between the target and the baseline is analyzed.Finally,the proposed method is validated by the anechoic chamber measurements and the results show that the detection ability has a 10 dB improvement compared with the common constant false alarm rate(CFAR)detection.展开更多
When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling(PCC). This paper proposes a new fast global synchronous discontinuous pulse wi...When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling(PCC). This paper proposes a new fast global synchronous discontinuous pulse width modulation(GSDPWM) method of threephase inverters to effectively attenuate the high frequency current harmonics at PCC. Firstly, the basic principle and the realization method of GSDPWM for three-phase inverters are explained, which can be employed for different modulation types. Then a fast calculation method,which can equally derive the minimized total harmonic distortion(THD) of total current, is proposed to release the calculation burden. Finally, MATLAB simulations and experimental results are presented to verify the performance of GSDPWM.展开更多
In a global positioning system(GPS)passive radar,a high resolution requires a high sampling frequency,which increases the computational load.Balancing the computational load and the range resolution is challenging.Thi...In a global positioning system(GPS)passive radar,a high resolution requires a high sampling frequency,which increases the computational load.Balancing the computational load and the range resolution is challenging.This paper presents a method to trade off the range resolution and the computational load by experimentally determining the optimal sampling frequency through an analysis of multiple sets of GPS satellite data at different sampling frequencies.The test data are used to construct a range resolution-sampling frequency trade-off model using least-squares estimation.The theoretical analysis shows that the experimental data are the best fit using smoothing and nthorder derivative splines.Using field GPS C/A code signal-based GPS radar,the trade-off between the optimal sampling frequency is determined to be in the 20461.25–24553.5 kHz range,which supports a resolution of 43–48 m.Compared with the conventional method,the CPU time is reduced by approximately 50%.展开更多
A fully integrated hybrid integer/fractional frequency synthesizer is presented.With a single multiband voltage-controlled-oscillator（VCO）,the frequency synthesizer can support GPS,Galileo,Compass and TDSCDMA standa...A fully integrated hybrid integer/fractional frequency synthesizer is presented.With a single multiband voltage-controlled-oscillator（VCO）,the frequency synthesizer can support GPS,Galileo,Compass and TDSCDMA standards.Design is carefully performed to trade off power,die area and phase noise performance.By reconfiguring between the integer mode and fractional mode,different frequency resolution requirements and a constant loop bandwidth for each standard can be achieved simultaneously.Moreover,a long sequence length,reduced hardware complexity multi-stage-noise-shaping（MASH）.-.modulator is employed to reduce fractional spur in the fractional mode.Fabricated in a 0.18 m CMOS technology,the frequency synthesizer occupies an active area of 1.48 mm2 and draws a current of 13.4-16.2 mA from a 1.8 V power supply.The measured phase noise is lower than-80 dBc/Hz at 100 kHz offset and-113 to-124 dBc/Hz at 1 MHz offset respectively,while the measured reference spur is-71 dBc in integer mode and the fractional spur is-65 dBc in fractional mode.展开更多
An optimization design technique to obtain global solution for a two-stage operational amplifier(op-amp) with frequency compensation is presented.This frequency compensation technique can adjust the equivalent resista...An optimization design technique to obtain global solution for a two-stage operational amplifier(op-amp) with frequency compensation is presented.This frequency compensation technique can adjust the equivalent resistance to guarantee that the phase margin is stable even though circumstance temperature varies.Geometric programming is used to optimize the component values and transistor dimensions.It is used in this analog integrated circuit design to calculate these parameters automatically.This globally optimal amplifier obtains minimum power while other specifications are fulfilled.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 receiv...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 weight, as well as power consumption, are very low.展开更多
Through the research into the characteristics of 7-DoF high dimensional nonlinear dynamics of a vehicle on bumpy road, the periodic movement and chaotic behavior of the vehicle were found.The methods of nonlinear freq...Through the research into the characteristics of 7-DoF high dimensional nonlinear dynamics of a vehicle on bumpy road, the periodic movement and chaotic behavior of the vehicle were found.The methods of nonlinear frequency response analysis, global bifurcation, frequency chart and Poincaré maps were used simultaneously to derive strange super chaotic attractor.According to Lyapunov exponents calculated by Gram-Schmidt method, the unstable region was compartmentalized and the super chaotic characteristic of ...展开更多
We investigate the Cauchy problem for the 3D magneto-hydrodynamics equations with only horizontal dissipation for the small initial data. With the help of the dissipation in the horizontal direction and the structure ...We investigate the Cauchy problem for the 3D magneto-hydrodynamics equations with only horizontal dissipation for the small initial data. With the help of the dissipation in the horizontal direction and the structure of the system, we analyze the properties of the decay of the solution and apply these decay properties to get the global regularity of the solution. In the process, we mainly use the frequency decomposition in Green's function method and energy method.展开更多
基金This work was partially funded by the National Natural Science Foundation of China(Grant Nos.41774042,42174034)the Key Research and Development Plan of Hubei Province(Grant No.2020BHB014)+1 种基金the Scientifc Instrument Developing Project of the Chinese Academy of Sciences(Grant No.YJKYYQ20190063)The frst author is supported by the CAS Pioneer Hundred Talents Program。
文摘Technique PPP-RTK combines the advantages of both the Precise Point Positioning(PPP)and the Real-Time Kinematic(RTK)positioning.With the emergence of multi-frequency Global Navigation Satellite System(GNSS)observations,it is preferable to formulate PPP-RTK functional models based on original(undiferenced and uncombined)observations.While there exist many variants of the undiferenced and uncombined PPP–RTK models,a unifed theoretical framework needs developing to link these variants.In this contribution,we formulate a class of undiferenced and uncombined PPP-RTK functional models in a systematic way and cast them in a unifed framework.This framework classifes the models into a code-plus-phase category and a phase-only category.Each category covers a variety of measurement scenarios on the network side,ranging from small-,medium-to large-scale networks.For each scenario,special care has been taken of the distinct ionospheric constraints and the diference between Code Division Multiple Access(CDMA)and Frequency Division Multiple Access(FDMA)signals.The key to systematically formulating these models lies in how to deal with the rank defciency problems encountered.We opt for the Singularity-basis(S-basis)theory,giving rise to the full-rank observation equations in which the estimable parameters turn out to be the functions of original parameters and those selected as the S-basis.In the sequel,it becomes straightforward to derive for each scenario the user model as it,more or less,amounts to the single-receiver network model.Benefting from the presented theoretical framework,the relationships and diferences between various undiferenced and uncombined PPP-RTK models become clear,which can lead to the better use of these models in a specifc situation.
基金This work was supported by the National Natural Science Foundation of China(62071475,61890541,62171447).
文摘The application scope of the forward scatter radar(FSR)based on the Global Navigation Satellite System(GNSS)can be expanded by improving the detection capability.Firstly,the forward-scatter signal model when the target crosses the baseline is constructed.Then,the detection method of the for-ward-scatter signal based on the Rényi entropy of time-fre-quency distribution is proposed and the detection performance with different time-frequency distributions is compared.Simula-tion results show that the method based on the smooth pseudo Wigner-Ville distribution(SPWVD)can achieve the best perfor-mance.Next,combined with the geometry of FSR,the influence on detection performance of the relative distance between the target and the baseline is analyzed.Finally,the proposed method is validated by the anechoic chamber measurements and the results show that the detection ability has a 10 dB improvement compared with the common constant false alarm rate(CFAR)detection.
文摘When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling(PCC). This paper proposes a new fast global synchronous discontinuous pulse width modulation(GSDPWM) method of threephase inverters to effectively attenuate the high frequency current harmonics at PCC. Firstly, the basic principle and the realization method of GSDPWM for three-phase inverters are explained, which can be employed for different modulation types. Then a fast calculation method,which can equally derive the minimized total harmonic distortion(THD) of total current, is proposed to release the calculation burden. Finally, MATLAB simulations and experimental results are presented to verify the performance of GSDPWM.
基金supported by the National Natural Science Foundation of China(42001297)the Research Foundation of Education Department of Hunan Province(19B061)the National Natural Science Foundation of Hunan Province(2021JJ40631)。
文摘In a global positioning system(GPS)passive radar,a high resolution requires a high sampling frequency,which increases the computational load.Balancing the computational load and the range resolution is challenging.This paper presents a method to trade off the range resolution and the computational load by experimentally determining the optimal sampling frequency through an analysis of multiple sets of GPS satellite data at different sampling frequencies.The test data are used to construct a range resolution-sampling frequency trade-off model using least-squares estimation.The theoretical analysis shows that the experimental data are the best fit using smoothing and nthorder derivative splines.Using field GPS C/A code signal-based GPS radar,the trade-off between the optimal sampling frequency is determined to be in the 20461.25–24553.5 kHz range,which supports a resolution of 43–48 m.Compared with the conventional method,the CPU time is reduced by approximately 50%.
基金Project supported by the National Science and Technology Major Project,China (No.2010ZX03007-002-01)the State Key Development Program for Basic Research of China (No.2010CB327404)
文摘A fully integrated hybrid integer/fractional frequency synthesizer is presented.With a single multiband voltage-controlled-oscillator（VCO）,the frequency synthesizer can support GPS,Galileo,Compass and TDSCDMA standards.Design is carefully performed to trade off power,die area and phase noise performance.By reconfiguring between the integer mode and fractional mode,different frequency resolution requirements and a constant loop bandwidth for each standard can be achieved simultaneously.Moreover,a long sequence length,reduced hardware complexity multi-stage-noise-shaping（MASH）.-.modulator is employed to reduce fractional spur in the fractional mode.Fabricated in a 0.18 m CMOS technology,the frequency synthesizer occupies an active area of 1.48 mm2 and draws a current of 13.4-16.2 mA from a 1.8 V power supply.The measured phase noise is lower than-80 dBc/Hz at 100 kHz offset and-113 to-124 dBc/Hz at 1 MHz offset respectively,while the measured reference spur is-71 dBc in integer mode and the fractional spur is-65 dBc in fractional mode.
基金the Shanghai Application Material(AM) Research Foundation (No.08700740700)
文摘An optimization design technique to obtain global solution for a two-stage operational amplifier(op-amp) with frequency compensation is presented.This frequency compensation technique can adjust the equivalent resistance to guarantee that the phase margin is stable even though circumstance temperature varies.Geometric programming is used to optimize the component values and transistor dimensions.It is used in this analog integrated circuit design to calculate these parameters automatically.This globally optimal amplifier obtains minimum power while other specifications are fulfilled.
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 weight, as well as power consumption, are very low.
文摘Through the research into the characteristics of 7-DoF high dimensional nonlinear dynamics of a vehicle on bumpy road, the periodic movement and chaotic behavior of the vehicle were found.The methods of nonlinear frequency response analysis, global bifurcation, frequency chart and Poincaré maps were used simultaneously to derive strange super chaotic attractor.According to Lyapunov exponents calculated by Gram-Schmidt method, the unstable region was compartmentalized and the super chaotic characteristic of ...
基金National Natural Science Foundation of China (Grant No. 11771284).
文摘We investigate the Cauchy problem for the 3D magneto-hydrodynamics equations with only horizontal dissipation for the small initial data. With the help of the dissipation in the horizontal direction and the structure of the system, we analyze the properties of the decay of the solution and apply these decay properties to get the global regularity of the solution. In the process, we mainly use the frequency decomposition in Green's function method and energy method.
