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Liu X.-H.,National University of Defense Technology | Huang L.,National University of Defense Technology | Xie J.-S.,Beijing Global Information Application and Development Center
Guofang Keji Daxue Xuebao/Journal of National University of Defense Technology | Year: 2011

Quantization will be necessary in the digital signal processing because of the hardware's resource. It is important to improve the performance of the quantizer. An expression of quantization distortion to clip level was derived theoretical for N (μ, σ2) Gaussian pdf signal. Also the expression of the minimal quantization distortion and optimum clip level was deducted. The result of computer simulation is that the expression can be used to estimate the optimum clip level effectively and exactly in the related applications. Source


Wu X.,Beijing Global Information Application and Development Center | Han C.,Beijing Global Information Application and Development Center | Ping J.,CAS National Astronomical Observatories
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2013

Due to the geostationary feature of GEO satellites, the vertical total electron content (VTEC) at ionosphere piece point(IPP) obtained from GEO dual-frequency observations can fully reflect the temporal variety of ionosphere, and the VTEC spatial variety can be further obtained from the distribution of ground stations. The accuracy of measured VTEC from Compass observations is firstly analyzed, and theoretical analysis indicates the accuracy is better than 2 TECU. The daily and seasonal VTEC changes of different ionosphere piece points in different latitude regions are given by use of observations of Compass navigation system. Note that the VTEC changes during geomagnetic storm are also elaborated. In contrast, the interpolation results of the global ionosphere map (GIM) are given, which are provided by IGS. Analysis shows that there is considerable consistency between the trends of these two ionosphere results, but the peak discrepancy during geomagnetic storm in the low latitudes of China can be up to 29 TECU, and the standard deviation of VTEC of 2011 is 2~8 TECU. Measurement data ensure higher resolution and confidence on regional ionosphere monitoring. According to the observations of 2011, the ionosphere VTEC variety shows a significant semiannual anomaly phenomenon. Compass navigation system provides a new support for the monitoring of regional ionosphere, especially for the study of ionosphere response for space weather. Source


He F.,Beijing Global Information Application and Development Center | He F.,Chinese Academy of Sciences | Wang G.,Beijing Global Information Application and Development Center | Liu L.,Beijing Global Information Application and Development Center | And 5 more authors.
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2011

The phenomenon and regulation of parameter's exceeding limitation in the operation of system are introduced, and then the reasons are illustrated according to the ill-conditioned equation and the orbital characteristics, some fitting algorithms are designed on the condition of avoiding accuracy losing, and the experiments are carried out with the actual observation data. The results show that it is efficient to eliminate the parameter exceeding for the method of fixing one parameter while computing the others or the method of parameter ridge estimate. Source


Zhao B.,Beijing Global Information Application and Development Center | Zhou Q.-Y.,Xian Research Institute of Surveying and Mapping | Zhang W.,Beijing Global Information Application and Development Center | Fu J.-Y.,Beijing Global Information Application and Development Center
Guangdian Gongcheng/Opto-Electronic Engineering | Year: 2011

The Space-Based Space Surveillance (SBSS) system is an important way and the development tendency of accepting state information of space objects. However, only utilizing the measure information between the satellites would produce the deficient-rank phenomena in the process of orbit determination of space objects. The essence of deficient-rank problem in the autonomous orbit determination was discussed. The problem can be eliminated by the combined orbit determination strategy based on space/ground-based tracking telemetry and command technology. The tracking network was made up of 4 high-orbit surveillance platforms and 2 ground surveillance stations. The orbit determination function of the system for the space objects was simulated. Simulation experiment shows the orbit determination precision for three kinds of space objects based on the combined orbit determination strategy reaches kilometer level. Source


Zhou J.,Beijing Global Information Application and Development Center | Yang L.,Beijing Global Information Application and Development Center | Xu B.,Nanjing University of Aeronautics and Astronautics | Xie T.,Beijing Global Information Application and Development Center
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2011

A hybrid prediction model based on neural network is introduced for navigation satellite. The new model is based on dynamical model and the neural network model is adopted to modify it. During the training phase, neural network model tries to approach the difference of dynamical model prediction product, then compensate it in the prediction phase. The characteristics of DMM prediction error for GPS are explored, and then predition strategy for long term (longer than 15 d) is designed. At the last, a group of tests on GPS satellites are processed to prove and evaluate the performance of the new method, the test results show that the improvement for 15~40 d prediction is obvious. Source

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