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    25 August 2011, Volume 31 Issue 4 Previous Issue    Next Issue
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    Modified Sliding Spectral Method for GPS Occultation
    XU Xian-Sheng, GUO Peng
    2011, 31 (4):  1-8.  doi: 10.3780/j.issn.1000-758X.2011.04.001
    Abstract ( 2252 )   PDF (469KB) ( 1880 )   Save
    The limitations of the sliding spectral (SS)method are the restriction of the resolution of bending angle profiles due to  the noise in the moist lower tropos phere. It has been  validated by simulations of atmospheric propagation using multiple phase screens technique under multipath conditions. A modified sliding spectral (MSS)method was developed to reduce these limitations. It demonstrates that MSS method can reasonably identify and decrease noise which may introduce retrieval errors in classical SS method, as well as further improve the resolution in the moist tropos pheric regions. About 4500 COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate)were analyzed using the SS method and MSS method respectively. Statistical comparisons of the retrieval refractivity profiles with that from ECMWF (European Centre for Medium range Weather Forecasts) analysis show that MSS method contains smaller systematic biases than SS method. Biases of the MSS method are close to that of  full spectrum inversion (FSI)method at all latitudes.
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    Research on COMPASS Navigation Signals of China
    TAN Shu-Sen, ZHOU Bing, GUO Sheng-Tao, LIU Zhi-Jian
    2011, 31 (4):  9-14.  doi: 10.3780/j.issn.1000-758X.2011.04.002
    Abstract ( 2300 )   PDF (353KB) ( 1723 )   Save
    The signals of global navigation satellite system of China must obey many constraints, and should  be coordinated with other navigation signals as well. The service type, carrier frequency, modulation scheme and spreading codes are essential for the coordination. The signal structure and parameters of COMPASS excerpted from the reference assumptions document(RAD)were presented. The correlation performances of the spreading codes of the COMPASS open signals were consistent with  that of GPS. Base on the signal structure and basic parameters of the RADs, COMPASS and GPS,   the L band frequency coordination  was completed in accordance with the frames established by ITU in September, 2010.
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    Design of New Signal System for Inter-satellite Links
    HE Shan-Bao, LIN Yi-Ming, WU Le-南, FENG Man, WANG Ping, CHEN Zhong-Gui, XIE Jun
    2011, 31 (4):  15-22.  doi: 10.3780/j.issn.1000-758X.2011.04.003
    Abstract ( 1880 )   PDF (548KB) ( 1809 )   Save
    A novel, special and highly efficient modulation system was proposed, which combined harmoniously EBPSK (Extended BPSK)modulation, digital impulsion filter, adaptive demodulation method and parametermatching technology. The signal system of GNSS ISLs with novel modulation and demodulation was simulated and analyzed. The results show that the integrated index (bit/s/Hz/SNR)of the new signal system outperforms other present systems. And many important parameters of the new signal system, such as rate, bandwidth and SNR, may change with space environment.
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    Equipment Delay Calibration Technique for Two-way Time Synchronization System
    LI Xing, GENG Shu-Min, LI Yuan-Ling
    2011, 31 (4):  23-29.  doi: 10.3780/j.issn.1000-758X.2011.04.004
    Abstract ( 2065 )   PDF (381KB) ( 1407 )   Save
    Equipment delay error is an important factor to implement two-way time synchronization in pseudo-noise code ranging system. And the accurate calibration is the key technology to reach a good time synchronization. Regarding to  the equipment time delay, a new  definition of equipment time delay with clear physical meaning was proposed. A scheme implementing delay calibration in two-way time synchronization was designed. The delay calibration technique was validated on the hardware platform of time synchronization station. And the experiment results show that the precision and accuracy of delay calibration reaches sub-nanosecond level.
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    Multi-correlators Techniques for GPS Signal Quality Monitoring
    GAN Xing-Li, YANG Yi, GUO Xiao-Feng
    2011, 31 (4):  30-37.  doi: 10.3780/j.issn.1000-758X.2011.04.005
    Abstract ( 1924 )   PDF (382KB) ( 1400 )   Save
    The signal quality of navigation satellites is the essential factor to the positioning performance. When the interferences occur  on the satellite′s hardware or on the space propagation signals, the corresponding waveforms will be  distorted, and the correlation peaks generated by the receivers become biased, hence degrade the positioning resolution, moreover, the positioning ability of users may also lost. Through  monitoring  the space signals, it may further assure the system′s service performance. The  causes of the distortion for GPS signals were concluded  based on current signal quality monitoring techniques.The modeling of distorted signals was completed based on digital fault model, analog fault model, digital/analog fault model.  The methods of multi-correlators GPS signal monitoring were presented and verified by applying the above three models.
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    Intelligent Tracking State Estimation Technology for New Generation GNSS Receivers
    JIN Li, LU Ming-Quan, FENG Zhen-Ming
    2011, 31 (4):  38-47.  doi: 10.3780/j.issn.1000-758X.2011.04.006
    Abstract ( 2190 )   PDF (610KB) ( 1635 )   Save
    New generation global navigation satellite system (GNSS)receivers should adjust internal parameters automatically according to the users′ locations to provide better navigation service. For this purpose, receivers should detect and analyze users′ situations by estimating the tracking state. Based on the analysis of traditional receiver control systems′ drawbacks, the conception, characteristic and framework of the intelligent receiver was introduced. Furthermore, the intelligent tracking state estimator was designed and analyzed. Finally, simulation results show the new methods can effectively identify the complex and changeable scenes.
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    Carrier Phase Lock Loop Based on Four-way Signal Processing
    GAO Yuan, LI Jian, LIU Feng
    2011, 31 (4):  48-53.  doi: 10.3780/j.issn.1000-758X.2011.04.007
    Abstract ( 2060 )   PDF (298KB) ( 1556 )   Save
    Under a certain carrier noise ratio (CNR), the threshold of carrier tracking loop is mainly affected by the dynamic stress. Costas phase lock loop (PLL)is one of the most common carrier tracking loop, but it is too sensitive to the dynamic stress because of the limited frequency pull-in range. The frequency pull-in range of phase lock loop is determined by the maximum phase pull-in range. The phase pull-in range of classic Costas PLL based on two-way signal processing is just [-π/2, π/2], which is not good enough to track the carrier in dynamic environment. Therefore, a new four-way signal processing was proposed and applied into the Costas PLL, which can improve the phase pull-in range to [-3π/4, 3π/4]. In the proposed method, the π/4 and 3π/4 way signal processing were added to the classic Costas PLL to construct four-way signal processing. The simulation results show that the proposed four-way signal processing PLL can significantly improve the dynamic performance of the receiver.
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    Quantitative and Qualitative Model Based Fault Diagnosability Evaluation of Momentum Wheel
    LIU Wen-Jing, LIU Cheng-Rui, WANG Nan-Hua, WANG Da-Yi
    2011, 31 (4):  54-63.  doi: 10.3780/j.issn.1000-758X.2011.04.008
    Abstract ( 2083 )   PDF (477KB) ( 1219 )   Save
    The fault diagnosability evaluation method of the momentum wheel based on the quantitative and qualitative model was proposed to enhance its fault diagnosis performance. Considering the momentum wheel model and its controller model, the momentum wheel system model was obtained and it included the influence of three types of faults, namely measurement related, driven-related and the controller-related faults. By judging whether the transfer function from the fault to the output equals to 0 or whether different faults have different transfer functions, the fault detectability and isolability discriminant conditions were obtained and applied to the momentum wheel. Some problems related to the method based on the quantitative model were concluded. To the unisolable fault sets, the qualitative model based fault diagnosability evaluation method was addressed, including the fault symptom incidence matrix establishment by considering the relationship of the function modules, the FMEA and its data analysis. Finally, the quantitative indexes were proposed as well as the diagnosable degree of the momentum wheel which offered some important information to the fault diagnosability design.
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    Spacecraft Attitude Control under Control Constraint with Velocity-free
    WANG Yan, TANG Qiang, CHEN Xing-Lin
    2011, 31 (4):  64-69. 
    Abstract ( 1860 )   PDF (313KB) ( 1062 )   Save
    Attitude control of rigid spacecraft without the measurement of angular velocity was proposed in the case of physical limits of actuators. First a quaternion auxiliary dynamical system was defined, and then a nonlinear feedback control law of hyperbolic tangent function with real and estimated errors of unit-quaternion was presented. The stability of the tracking error system with bounded control effort was proved. The performance of the proposed control algorithm was verified through numerical simulations. It shows that both the satellite attitude accuracy and response speed can be improved greatly compared to other methods.
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    Effect Analysis of Measuring Time Error on Single Satellite Orbit Determination Error
    LIU Wen-Xiang, MOU Wei-Hua, WANG Fei-Xue
    2011, 31 (4):  70-76.  doi: 10.3780/j.issn.1000-758X.2011.04.010
    Abstract ( 2174 )   PDF (352KB) ( 1460 )   Save
    To evaluate the  effect of measuring time bias on single satellite orbit determination (SSOD)error, the theoretical model based on the SSOD strategy was analyzed. The measuring time bias of monitor station receiver was composed by clock error and measuring time uncertainty. The experiment data analysis results show that the clock residual error of monitor station after fitting by 1st order polynomial is approximately taken as noise with zero mean. The simulation results show that the equivalent ranging error for GEO, IGSO, MEO satellites, caused by 1ms error of the signal sending time, is 0.06cm, 40cm, 80cm respectively. 
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    Optimized Design of Structure Parameters for Large-aperture Mirrors
    YANG Jia-Wen, HUANG Qiao-Lin
    2011, 31 (4):  77-83.  doi: 10.3780/j.issn.1000-758X.2011.04.011
    Abstract ( 2223 )   PDF (456KB) ( 1482 )   Save
    With the development of the space optical remote sensor resolution and the primary mirror diameter, the lightweight design is becoming the key technology of the large aperture mirror. An optimized method was put forward for the mirror lightweight design. The parametric model of a mirror with honeycomb sandwich structure was established by MSC Patran software. The influence curve of different parameters to the mirror surface figure was obtained by the sensitivity analysis. According to the processing technology of the mirror, structure parameters optimized by orthogonal decomposition method were determined.
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