The Impact of Satellite Time Group Delay and Inter-Frequency Differential Code Bias Corrections on Multi-GNSS Combined Positioning.

Yulong Ge,Feng Zhou,Shengli Wang,Baoqi Sun,Bo Shi

doi:10.3390/s17030602

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.

Highlights

With more and more satellites joining the family of navigation systems, multiple global navigation satellite systems standard point positioning (SPP) [1], precise point positioning (PPP) [2], precise orbit determination (POD) [3] and meteorology are becoming increasingly popular
For all precise global navigation satellite systems (GNSSs) applications that are supported by code and carrier-phase observations, existing code biases represent a non-negligible error source
Even though the broadcast orbits of GPS (WGS84), GLONASS (PZ90.11), Beidou (CGCS2000), and Galileo (GTRF) are formally referred to different reference frames, current realizations of these frames are very closely aligned with the International Terrestrial Reference Frame (ITRF), and they are commonly considered to agree at a few centimeter level [23], the difference in reference frames can be ignored in multi-GNSS SPP processing

Summary

Introduction

With more and more satellites joining the family of navigation systems, multiple global navigation satellite systems (multi-GNSS) standard point positioning (SPP) [1], precise point positioning (PPP) [2], precise orbit determination (POD) [3] and meteorology are becoming increasingly popular.GNSS pseudorange observations are well known to exhibit systematic biases related to delays caused by internal electronic/hardware components of the overall signal generation, transmission and processing chain [4]. In the new multi-GNSS and multi-frequency context, observations from different constellations, signals, frequencies and channels need to be processed along with each other and a proper consideration of biases becomes mandatory for a consistent modeling of all observations. For all precise GNSS applications that are supported by code and carrier-phase observations, existing code biases represent a non-negligible error source. This includes ”time-oriented” applications such as high-precision GNSS satellite clock estimation [5] as well as time transfer among GNSS observing stations [6], and code- and phase-based carrier phase ambiguities resolution. Code biases should be considered [7]

Methods

Results

Conclusion