Abstract

Research has demonstrated that receiver clock modeling can reduce the correlation coefficients among the parameters of receiver clock bias, station height and zenith tropospheric delay. This paper introduces the receiver clock modeling to GPS/GLONASS combined precise point positioning (PPP), aiming to better separate the receiver clock bias and station coordinates and therefore improve positioning accuracy. Firstly, the basic mathematic models including the GPS/GLONASS observation equations, stochastic model, and receiver clock model are briefly introduced. Then datasets from several IGS stations equipped with high-stability atomic clocks are used for kinematic PPP tests. To investigate the performance of PPP, including the positioning accuracy and convergence time, a week of (1–7 January 2014) GPS/GLONASS data retrieved from these IGS stations are processed with different schemes. The results indicate that the positioning accuracy as well as convergence time can benefit from the receiver clock modeling. This is particularly pronounced for the vertical component. Statistic RMSs show that the average improvement of three-dimensional positioning accuracy reaches up to 30%–40%. Sometimes, it even reaches over 60% for specific stations. Compared to the GPS-only PPP, solutions of the GPS/GLONASS combined PPP are much better no matter if the receiver clock offsets are modeled or not, indicating that the positioning accuracy and reliability are significantly improved with the additional GLONASS satellites in the case of insufficient number of GPS satellites or poor geometry conditions. In addition to the receiver clock modeling, the impacts of different inter-system timing bias (ISB) models are investigated. For the case of a sufficient number of satellites with fairly good geometry, the PPP performances are not seriously affected by the ISB model due to the low correlation between the ISB and the other parameters. However, the refinement of ISB model weakens the correlation between coordinates and ISB estimates and finally enhance the PPP performance in the case of poor observation conditions.

Highlights

  • GNSS has been demonstrated to be powerful in positioning, navigation, and timing (PNT)applications in the past decades

  • Compared to the GPS-only precise point positioning (PPP), solutions of the GPS/GLONASS combined PPP are much better no matter if the receiver clock offsets are modeled or not, indicating that the positioning accuracy and reliability are significantly improved with the additional GLONASS satellites in the case of insufficient number of GPS satellites or poor geometry conditions

  • Receiver clock modeling has been introduced into GPS/GLONASS combined PPP in this contribution

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Summary

Introduction

GNSS has been demonstrated to be powerful in positioning, navigation, and timing (PNT). Due to the presence of satellite and receiver clock offsets, GNSS observations are always biased. Processing of double difference observations between pairs of satellites and receivers that are free of clock offsets is a popular way in GNSS data processing. This approach only allows for the determination of baseline vectors rather than absolute positions. As to the receiver clock biases, they have to be determined at the user ends This is done by introducing an additional parameter for every observation epoch [9]. Additional GLONASS observations are applied to augment GPS PPP with receiver clock modeling.

Mathematical Models
Functional Model
Stochastic Model
Receiver Clock Model
Performance Evaluations
Accuracy and Reliability Analysis
Convergence Analysis
Impacts of Different Inter-System Bias Models
Findings
Conclusions
Full Text
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