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Zhou S.,Chinese Academy of Sciences | Cao Y.,Chinese Academy of Sciences | Zhou J.,Beijing Global Information Application and Development Center | Hu X.,Chinese Academy of Sciences | And 6 more authors.
Science China: Physics, Mechanics and Astronomy | Year: 2012

Determined to become a new member of the well-established GNSS family, COMPASS (or BeiDou-2) is developing its capabilities to provide high accuracy positioning services. Two positioning modes are investigated in this study to assess the positioning accuracy of COMPASS' 4GEO/5IGSO/2MEO constellation. Precise Point Positioning (PPP) for geodetic users and real-time positioning for common navigation users are utilized. To evaluate PPP accuracy, coordinate time series repeatability and discrepancies with GPS' precise positioning are computed. Experiments show that COMPASS PPP repeatability for the east, north and up components of a receiver within mainland China is better than 2 cm, 2 cm and 5 cm, respectively. Apparent systematic offsets of several centimeters exist between COMPASS precise positioning and GPS precise positioning, indicating errors remaining in the treatments of COMPASS measurement and dynamic models and reference frame differences existing between two systems. For common positioning users, COMPASS provides both open and authorized services with rapid differential corrections and integrity information available to authorized users. Our assessment shows that in open service positioning accuracy of dual-frequency and single-frequency users is about 5 m and 6 m (RMS), respectively, which may be improved to about 3 m and 4 m (RMS) with the addition of differential corrections. Less accurate Signal In Space User Ranging Error (SIS URE) and Geometric Dilution of Precision (GDOP) contribute to the relatively inferior accuracy of COMPASS as compared to GPS. Since the deployment of the remaining 1 GEO and 2 MEO is not able to significantly improve GDOP, the performance gap could only be overcome either by the use of differential corrections or improvement of the SIS URE, or both. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.


Li C.,Beijing Global Information Application and Development Center | Chen J.,Beijing Global Information Application and Development Center | Chu H.,Beijing Global Information Application and Development Center
Lecture Notes in Electrical Engineering | Year: 2012

The pseudo-range measurement precision is an important index for evaluating the performance of a navigation receiver, and also one of the important factors for analyzing the receiver's positioning precision. In the real environment the pseudo-range is varying and it is difficult to measure its precision, so usually the pseudo-range precision is measured on a laboratory simulation condition. But this measuring method could not truly reflect the pseudo-range precision in the real environment. In this paper, a measuring method of pseudo-range precision using to the real environment, namely receiver and satellite double difference method, is presented. Its theory basis is given by deducing its mathematic model, and then experiment is made on pseudo-range precision measuring with this method. The results of the experiment show that when the receiver is stationary, this method can accurately measure the precision of its observation pseudo-range to a static satellite, and can accurately measure the precision of its observation pseudo-range to a motional satellite by controlling the observation time. Finally the obtained pseudo-range precisions are used to compare the precisions of two positioning modes, and the comparison relationship of the precisions of the two positioning modes observed in the real data is intuitively revealed. © 2012 Springer-Verlag.


Zhou S.,Chinese Academy of Sciences | Zhou S.,University of Chinese Academy of Sciences | Hu X.,Chinese Academy of Sciences | Wu B.,Chinese Academy of Sciences | And 9 more authors.
Science China: Physics, Mechanics and Astronomy | Year: 2011

Aiming at regional services, the space segment of COMPASS (Phase I) satellite navigation system is a constellation of Geostationary Earth Orbit (GEO), Inclined Geostationary Earth Orbit (IGSO) and Medium Earth Orbit (MEO) satellites. Precise orbit determination (POD) for the satellites is limited by the geographic distribution of regional tracking stations. Independent time synchronization (TS) system is developed to supplement the regional tracking network, and satellite clock errors and orbit data may be obtained by simultaneously processing both tracking data and TS data. Consequently, inconsistency between tracking system and TS system caused by remaining instrumental errors not calibrated may decrease navigation accuracy. On the other hand, POD for the mixed constellation of GEO/IGSO/MEO with the regional tracking network leads to parameter estimations that are highly correlated. Notorious example of correlation is found between GEO's orbital elements and its clock errors. We estimate orbital elements and clock errors for a 3GEO+2IGSO constellation in this study using a multi-satellite precise orbit determination (MPOD) strategy, with which clock error elimination algorithm is applied to separate orbital and clock estimates to improve numerical efficiency. Satellite Laser Ranging (SLR) data are used to evaluate User Ranging Error (URE), which is the orbital error projected on a receiver's line-of-sight direction. Two-way radio-wave time transfer measurements are used to evaluate clock errors. Experimenting with data from the regional tracking network, we conclude that the fitting of code data is better than 1 m in terms of Root-Mean-Square (RMS), and fitting of carrier phase is better than 1 cm. For orbital evaluation, difference between computed receiver-satellite ranging based on estimated orbits and SLR measurements is better than 1 m (RMS). For clock estimates evaluation, 2-hour linear-fitting shows that the satellite clock rates are about 1.E-10 s/s, while receiver clock rates are about 1×10-13-1×10 -12 s/s. For the 72-hour POD experiment, the average differences between POD satellite clock rates estimates and clock measurements based on TS system are about 1×10-13 s/s, and for receiver clock rates, the differences are about 1×10-15 s/s. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.


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.


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.


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.


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.


Guo R.,Beijing Global Information Application and Development Center | Zhou J.,Beijing Global Information Application and Development Center | Hu X.,Chinese Academy of Sciences | Liu L.,Beijing Global Information Application and Development Center | And 2 more authors.
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2011

Real time, continuous and high precision orbit is needed for the geostationary satellite orbit (GEO) maneuver. How to recover orbit rapidly for GEO based on short-arc tracking is the key factor. A new kinematic orbit determination approach is introduced in order to solve this problem, which is based on 9-parameter ephemeris parameter fitting. The mathematical model and partial derivative model are deduced in detail. And the coordinate rotation method is introduced to solve the singular problem in the ephemeris parameter fitting for the GEO satellite. In order to check the precision and availability of this method, the short-arc orbit determination tests are carried out using real COMPASS GEO C-band transfer ranging data. The results indicate that: (1) with a 10 minutes tracking arc the position accuracy is better than 19 m, the velocity accuracy is 4 mm/s, which is better than the MEO satellite; (2) the 5-minute orbit prediction accuracy is 17.760 m, and the 10-minute orbit prediction accuracy is 18.168 m; (3) several problems in the dynamics orbit determination and single point position determination are solved, the rapid orbit recovery for GEO is achieved, which satisfied the requirement of RDSS.


Cao Y.L.,Chinese Academy of Sciences | Cao Y.L.,University of Chinese Academy of Sciences | Hu X.G.,Chinese Academy of Sciences | Wu B.,Chinese Academy of Sciences | And 6 more authors.
Science China: Physics, Mechanics and Astronomy | Year: 2012

The regional satellite navigation system of COMPASS (Phase I) provides both open services and authorized services. Authorized services offer differential corrections and integrity information to users to support higher positioning, navigation and timing precision. Experimenting with real data, positioning accuracy is estimated with a 3GEO/4IGSO COMPASS constellation. The results show that with dual-frequency and single-frequency pseudo-range measurements, the positioning errors are respectively 8 and 10 m (RMS) for open service users, while for authorized users, the errors are 4 and 5 m (RMS), respectively. The COMPASS constellation geometry may cause large error to occur in the height component by 7-9 m for dual- or single-frequency users, which can be effectively reduced with the differential corrections supplied by the authorized services. Multipath errors are identified and corrected for COMPASS, resulting in 25% positioning accuracy improvement for dual-frequency users and 10% improvement for single-frequency users. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.


Wu X.L.,Chinese Academy of Sciences | Zhou J.H.,Beijing Global Information Application and Development Center | Wang G.,Beijing Global Information Application and Development Center | Hu X.G.,Chinese Academy of Sciences | Cao Y.L.,Chinese Academy of Sciences
Science China: Physics, Mechanics and Astronomy | Year: 2012

Constellations of regional satellite navigation systems are usually constituted of geostationary satellites (GEO) and inclined geostationary satellites (IGSO) for better service availability. Analysis of real data shows that the pseudorange measurements of these two types of satellites contain significant multipath errors and code noise, and the multipath for GEO is extremely serious, which is harmful to system services. In contrast, multipath error of carrier phase measurements is less than 3 cm, which is smaller than the multipath of pseudorange measurements by two orders of magnitude. Using a particular combination of pseudorange and dual-frequency carrier phase measurements, the pseudorange multipath errors are detected, and their time varying features are analyzed. A real-time multipath correction algorithm is proposed in this paper, which is called CNMC (Code Noise and Multipath Correction). The algorithm decreases the influence of the multipath error and therefore ensures the performance of the system. Data processing experiments show that the multipath error level may be reduced from 0.5 m to 0.15 m by using this algorithm, and 60% of GEO multipath errors and 42% of IGSO multipath errors are successfully corrected with CNMC. Positioning experiments are performed with a constellation of 3 GEO plus 3 IGSO satellites. For dual-frequency users the East-West position accuracy is improved from 1.31 m to 0.94 m by using the CNMC algorithm, the South-North position accuracy is improved from 2.62 m to 2.29 m, and the vertical position accuracy is improved from 4.25 m to 3.05 m. After correcting multipath errors, the three-dimensional position accuracy is improved from 5.16 m to 3.94 m. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

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