title: The Impact of Satellite Time Group Delay and Inter-Frequency Differential Code Bias Corrections on Multi-GNSS Combined Positioning.
abstract: We present quad-constellation (namely, GPS, GLONASS, BeiDou and Galileo) time group delay (TGD) and differential code bias (DCB) correction models to fully exploit the code observations of all the four global navigation satellite systems (GNSSs) for navigation and positioning. The relationship between TGDs and DCBs for multi-GNSS is clearly figured out, and the equivalence of TGD and DCB correction models combining theory with practice is demonstrated. Meanwhile, the TGD/DCB correction models have been extended to various standard point positioning (SPP) and precise point positioning (PPP) scenarios in a multi-GNSS and multi-frequency context. To evaluate the effectiveness and practicability of broadcast TGDs in the navigation message and DCBs provided by the Multi-GNSS Experiment (MGEX), both single-frequency GNSS ionosphere-corrected SPP and dual-frequency GNSS ionosphere-free SPP/PPP tests are carried out with quad-constellation signals. Furthermore, the author investigates the influence of differential code biases on GNSS positioning estimates. The experiments show that multi-constellation combination SPP performs better after DCB/TGD correction, for example, for GPS-only b1-based SPP, the positioning accuracies can be improved by 25.0%, 30.6% and 26.7%, respectively, in the N, E, and U components, after the differential code biases correction, while GPS/GLONASS/BDS b1-based SPP can be improved by 16.1%, 26.1% and 9.9%. For GPS/BDS/Galileo the 3rd frequency based SPP, the positioning accuracies are improved by 2.0%, 2.0% and 0.4%, respectively, in the N, E, and U components, after Galileo satellites DCB correction. The accuracy of Galileo-only b1-based SPP are improved about 48.6%, 34.7% and 40.6% with DCB correction, respectively, in the N, E, and U components. The estimates of multi-constellation PPP are subject to different degrees of influence. For multi-constellation combination SPP, the accuracy of single-frequency is slightly better than that of dual-frequency combinations. Dual-frequency combinations are more sensitive to the differential code biases, especially for the 2nd and 3rd frequency combination, such as for GPS/BDS SPP, accuracy improvements of 60.9%, 26.5% and 58.8% in the three coordinate components is achieved after DCB parameters correction. For multi-constellation PPP, the convergence time can be reduced significantly with differential code biases correction. And the accuracy of positioning is slightly better with TGD/DCB correction.
authors.affiliation: National Time Service Center, Chinese Academy of Sciences, Xi'an 710600, China. geyulong15@mails.ucas.ac.cn.|Key Laboratory of Precise Navigation, Positioning and Timing Technology, Chinese Academy of Sciences, Xi'an 710600, China. geyulong15@mails.ucas.ac.cn.|University of Chinese Academy of Sciences, Beijing 100049, China. geyulong15@mails.ucas.ac.cn.
authors.forename: Yulong
authors.initials: Y
authors.lastname: Ge
authors.affiliation: School of Information Science Technology, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China. fzhou@gfz-potsdam.de.|German Research Centre for Geosciences GFZ, Telegrafenberg, Potsdam 14473, Germany. fzhou@gfz-potsdam.de.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhou
authors.affiliation: National Time Service Center, Chinese Academy of Sciences, Xi'an 710600, China. sunbaoqi@ntsc.ac.cn.|Key Laboratory of Precise Navigation, Positioning and Timing Technology, Chinese Academy of Sciences, Xi'an 710600, China. sunbaoqi@ntsc.ac.cn.|University of Chinese Academy of Sciences, Beijing 100049, China. sunbaoqi@ntsc.ac.cn.
authors.forename: Baoqi
authors.initials: B
authors.lastname: Sun
authors.affiliation: Institute of Ocean Engineering, Shandong University of Science and Technology, Qingdao 266590, China. shlwang@sdust.edu.cn.
authors.forename: Shengli
authors.initials: S
authors.lastname: Wang
authors.affiliation: College of Geomatics, Shandong University of Science and Technology, Qingdao 266590, China. shibo@sdust.edu.cn.
authors.forename: Bo
authors.initials: B
authors.lastname: Shi
keywords: GNSS; differential code bias (DCB); precise point positioning; quad-constellation; standard point positioning; time group delay (TGD)