Research On Key Issues And Service Performance Analysis Of BDS/GNSS Global Augmentation System

The Bei Dou/GNSS global real-time augmentation service is an effective means that can provide wide-area high-precision positioning services currently.With the incremental development of the number of navigation constellation satellites and the continuous deepening of the demand for higher precision positions,it has brought great challenges to multi-GNSS fusion high-precision data processing.It is urgent to develop multi-GNSS real-time high-efficiency global augmentation information estimation technology for different GNSS characteristics,and solve the signal difference of different GNSS at the receiver terminal in order to improve the high-precision application performance.This paper aims at the key technologies of Bei Dou/GNSS global real-time augmentation services,and focuses on the receiver-dependent Inter-Satellite Code Bias(ISCB)caused by the individual chip shape distortions in the ranging signals and the inter-satellite zero-value bias of the precise GNSS clock products.The multi-GNSS ISCB estimation algorithm and multi-GNSS global real-time high-efficiency augmentation information estimation technology are developed and proposed in this paper.The performance of Bei Dou-2 satellites fusing with Bei Dou-3 satellites to provide global high-precision augmentation service is analyzed and verified.The main work and research results of this article are as the following:i.The development history of GNSS global real-time augmentation system and technology is reviewed and summarized.The basic theories and methods of GNSS global real-time augmentation are studied systematically.The impact on precise positioning of satellite-dependent and receiver-dependent ISCB caused by the individual chip shape distortions in the ranging signals and the inter-satellite bias of precise clock products are analyzed.The existing issues and difficulties currently are pointed out at the same time.ii.Aiming at the problem of existing receiver-dependent ISCB degrading the accuracy of pseudo-range observations and then affecting positioning performance,a multi-GNSS ISCB real-time estimation algorithm is proposed to implement ISCB real-time self-calibration by single-station.The algorithm weakens the receiver-dependent ISCB and the inter-satellite zero-value bias of precise clock products,and significantly improves the correction accuracy of pseudorange observations,thereby significantly improving the PPP convergence time and accuracy.The testing results show the accuracy of GLONASS SPP is improved by about 54%,the convergence performance of GLONASS PPP is improved by about 73%,the accuracy of the convergence-phase and post-convergence-phase are increased by about 64% and 19%,respectively;for GPS+GLONASS fusion PPP,the convergence performance is improved by about 23%,and The improvement of the accuracy at the convergence-phase is about 13% and the accuracy after convergence is equivalent.iii.Aiming at the common inter-satellite zero-value bias problem in real-time precise clock products,the multi-GNSS real-time precise clock estimation model considering ISCB is proposed.The model could obtain the zero-bias absolute precise real-time clock products,which can obviously resolve the system bias problems of GLONASS and Bei Dou clock products.The real-time clock RMS of GPS/GLONASS/Galileo/Bei Dou is 0.13 ns,0.12 ns,0.17 ns and 0.25 ns improved by 63% comparing to MD,separately;the STD is 0.10 ns,0.09 ns,0.15 ns and 0.17 ns with the same level as the Epoch-Differenced model,which is better than the Un-Differenced model and Mixed-Differenced model.The clock STD of GLONASS and Bei Dou is improved by 45% comparing to MD.On the base of Mixed-Differenced model eliminating ambiguity parameters,the model designed in this paper further removes a large number of system-bias parameters in multi-GNSS fusion solution and can realize the updating of real-time clock in 1Hz with just 5% parameters in normal equation.Selecting appropriate hardware environment and global stations network,the model can fully meet the incremental development needs of multi-GNSS satellites.iv.Aiming at the inconsistency of the receiver-dependent ISCB between Beidou-2 and-3 satellites,a joint positioning model of Bei Dou-2/-3 considering ISCB parameters is proposed in this paper.The data processing strategy of Bei Dou/GNSS global real-time augmentation is studied,Based on making full use of Bei Dou-2 satellite global signal(B1I+B3I)resources,Bei Dou global real-time augmentation is realized,which further improve the high-precision positioning performance of Bei Dou global signal.Post-simulation tests show that the accuracy of SLR calibrating Bei Dou orbit in one month is about 3-4cm;the real-time overlap accuracy of radial-direction is better than 5cm;the RMS of real-time clock is about 0.25 ns and the STD is about 0.21ns;the convergence performance of Bei Dou PPP is improved by about 35% by the Bei Dou joint positioning model considering ISCB,the accuracy of the convergence-phase and post-convergence-phase is improved by about 30% and 10%,separately.The joint of Bei Dou global signal satellites improves the GPS PPP convergence performance by about 35%,and accuracy of the convergence-phase and post-convergence-phase is improved by about 20% and 20%,respectively,and 4-5cm high-precision positioning can be achieved.v.Based on about 100 GNSS stations real-time data stream around the world,we design and construct Bei Dou/GNSS global real-time augmentation prototype software and broadcast the global augmentation products of the four global navigation systems including Bei Dou-3 with SISRE 3-10 cm,which has reached the same level as the relevant international research institutions.It can achieve fast convergence within 15-20 minutes worldwide,with a high-precision positioning of 4.44 cm horizontally and 5.55 cm high.