Research On Key Issues Of BDS/GNSS Real-time Precise Orbit Determination Service

Since the GPS began to provide the service,many countries and regions have built their own satellites navigation systems,such as GLONASS,Galileo,BDS and QZSS,IRNSS,SBAS,which all belong to Global Navigation Satellite System(GNSS).GNSS provides Positioning,Navigation and Timing services for global users,but limited to the precision of pseudorange,the Positioning precision is about 1meter.With the development of 5G communication technology,real-time high precision positioning becomes the requirement of more and more users.In general,multi-GNSS real-time precise orbit products are the prerequisite of worldwide real-time high precision positioning.At the moment,there are two ways to generate real-time orbit products,including: 1)Least square batch method and dynamic orbit determination.The method makes full use of post observation data and can achieve relatively high orbit precision by stricted data quality control.But this method provides real-time orbit products by orbit prediction and long-time prediction can reduce the orbit precision.2)Filtering algorithms and short-time prediction.Due to the constraint of orbit force models,orbit products by short-time prediction can keep high precision.But this method needs real-time stream data and contaminated by gross error data easily.How to select these two orbit determination methods is a considerable issue.With more and more GNSS satellites providing services,redundant observation can achieve for the receivers,which is a challenge for data-processing efficiency.It is noted that fast data-processing efficiency has much significance for framework maintain,geocenter estimation,the precision and reliability of multi-GNSS precise orbit determination.In addition,there are eighteen BDS3 FOC(Fully Operational Capability)satellites operated in orbit.It is necessary to analyse the signal performance,geometry and attitude models for BDS3 FOC satellites.The thesis aims at fast updating of multi-GNSS real-time orbits and solving the above issues.Efficient solutions is proposed for multi-GNSS real-time precise orbit determination with high-timeliness requirement in observation model and stochastic model.The thesis also explores antenna phase center offset(PCO),yaw attitude control model,signal quality estimation for BDS3.The characteristics of high-resolution ERP prediction error is also analyzed.The details can be listed as follows:1)The thesis proposes a real-time precise orbit solution based on recursive least square collocation.It can ensure the precision and reduce the computation and updating time obviously.On the basis of real-time orbit theory,recursive least square collocation is developed for normal equation accumulation in terms of observation range,which can retain the stricted consistency between real-time and post estimated parameters.The issues that new observation data accumulation,the constraint transfer and relaxation of the initial orbit parameters and ambiguity parameters operation are derived in detail.The unified model for real-time precise orbit determination based on recursive least square collocation is achieved and proved to be equal to the filtering method.Owing to the post-processing mode for data,the proposed method performs better than the filtering method in both data quality control and precision of estimated parameters.Moreover,it can realize every-hour update and thirty-minute-delay publication for GPS,GLONASS,Galileo and BDS,which improves the timeliness and precision of orbit products for real-time users.2)For the time-consuming issue of resolving large-scale GNSS undifference data,an improved parameter calculating method is presented.On the basis of analyzing bottleneck problems in resolving undifference data,a blocked normal equation algorithm is proposed to optimize the elimination and recovery of “outdated”parameters.This method can achieve the same precision as the traditional method and improve the computational efficiency significantly.According to the test results,this method can provide a unified and rigorous parameter calculating method for large-scale multi-GNSS precise orbit determination and precise positioning.3)A refined geometry observation model for BDS3 satellites is presented to improve the precision of orbit determination in special situations.The issues,including antenna phase center variation(PCV),attitude control model,navigation signal quality and performance of the satellite borne atomic clock,are studied in detail.About more than two hundred data during initial stage of BDS3 is adopted to estimate PCV,which improves the consistency between precise orbit and clock bias.A yaw attitude control model for BD3 is constructed to enhance the precision of geometry observation model during “noon” and “midnoon” maneuvering period.The precision of BDS3 satellite signal and stability of atomic clock are verified to be superior to GPS BLOCK IIF but worse than Galileo FOC satellites.4)An ultra-short-term prediction model for ERP is built to improve the prediction precision of real-time orbit.A LS+AR prediction model for EOP combined with high-frequency periodic term is proposed to enhance the ultra-short-term prediction precision,which provides guideline for real-time orbit resolving and other real-time space application.5)Based on PANDA software,a multi-GNSS real-time precise orbit determination system is developed to provide the real-time precise orbit products of GPS,GLONASS,Galileo,BDS and QZSS.The new adopted strategy is every-hour update and thirty-minute-delay publication.The related products have been published in IGS data center.The proposed algorithm has been applied in operation system of iGMAS analysis center.It is noted that the published post products using the presented method rank the top in iGMAS analysis center.In addition,multi-GNSS real-time positioning service obtained by the proposed method has been also published,which can provide the SSR of orbit,clock bias,ionosphere and UPD by Ntrip protocol for users and achieve centimeter-level worldwide positioning.