The Effect of BDS-3 Time Group Delay and Differential Code Bias Corrections on Positioning

Peipei Dai,Yanchen Dong,Jianping Xing,Yulong Ge,Weijin Qin,Xuhai Yang,Zhe Zhang

doi:10.3390/app11010104

Abstract

The timing group delay parameter (TGD) or differential code bias parameter (DCB) is an important factor that affects the performance of GNSS basic services; therefore, TGD and DCB must be taken seriously. Moreover, the TGD parameter is modulated in the navigation message, taking into account the impact of TGD on the performance of the basic service. International GNSS Monitoring and Assessment System (iGMAS) provides the broadcast ephemeris with TGD parameter and the Chinese Academy of Science (CAS) provides DCB products. In this paper, the current available BDS-3 TGD and DCB parameters are firstly described in detail, and the relationship of TGD and DCB for BDS-3 is figured out. Then, correction models of BDS-3 TGD and DCB in standard point positioning (SPP) or precise point positioning (PPP) are given, which can be applied in various situations. For the effects of TGD and DCB in the SPP and PPP solution processes, all the signals from BDS-3 were researched, and the validity of TGD and DCB has been further verified. The experimental results show that the accuracy of B1I, B1C and B2a single-frequency SPP with TGD or DCB correction was improved by approximately 12–60%. TGD will not be considered for B3I single-frequency, because the broadcast satellite clock offset is based on the B3I as the reference signal. The positioning accuracy of B1I/B3I and B1C/B2a dual-frequency SPP showed that the improvement range for horizontal components is 60.2% to 74.4%, and the vertical components improved by about 50% after the modification of TGD and DCB. In addition, most of the uncorrected code biases are mostly absorbed into the receiver clock bias and other parameters for PPP, resulting in longer convergence time. The convergence time can be max increased by up to 50% when the DCB parameters are corrected. Consequently, the positioning accuracy can reach the centimeter level after convergence, but it is critical for PPP convergence time and receiver clock bias that the TGD and DCB correction be considered seriously.

Highlights

Key Laboratory of Precise Positioning and Timing Technology, Chinese Academy of Sciences, China National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China
The effects of differential code biases can be mitigated as time goes by, and similar positioning accuracy can be obtained after convergence, the bias will be absorbed and affected by other parameters
The impact of timing group delay parameter (TGD) or differential code bias parameter (DCB) parameters on BDS-3 single-frequencies and dual-frequency combinations of standard point positioning (SPP) and precise point positioning (PPP) positioning were evaluated by three different scenarios schemes (“dcb-corr”, “tgd-corr” and “non-corr”)

Summary

Introduction

Key Laboratory of Precise Positioning and Timing Technology, Chinese Academy of Sciences, China National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China. Correction models of BDS-3 TGD and DCB in standard point positioning (SPP) or precise point positioning (PPP) are given, which can be applied in various situations. The experimental results show that the accuracy of B1I, B1C and B2a single-frequency SPP with TGD or DCB correction was improved by approximately 12–60%. Most of the uncorrected code biases are mostly absorbed into the receiver clock bias and other parameters for PPP, resulting in longer convergence time. The positioning accuracy can reach the centimeter level after convergence, but it is critical for PPP convergence time and receiver clock bias that the TGD and DCB correction be considered seriously. The current BDS-3 offers all-weather, all-time, high-accuracy positioning and navigation and timing (PNT) services to users worldwide. There are five frequencies capable of transmitting in BDS-3 satellites, which include B1C, B2a, B2b, B1I and B3I [4]

Methods

Findings

Discussion

Conclusion