# National BDS Augmentation Service System (NBASS) of China: Progress and Assessment

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## Abstract

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## 1. Introduction

## 2. NBASS Tracking Network and Processing Strategy

#### 2.1. NBASS Tracking Network

#### 2.2. Processing Strategy

#### 2.2.1. Orbit and Clock Products

#### 2.2.2. Ionopshere Products

#### 2.2.3. Real-Time PPP

## 3. Accuracy Evaluation of Real-Time Orbit: Clock and Ionospheric Corrections

#### 3.1. BDS Orbit Results

#### 3.2. Real-Time BDS Clock Results

#### 3.3. Ionospheric Correction

## 4. Real-Time Kinematic PPP Results

#### 4.1. Simulated Kinematic Real-Time PPP

#### 4.1.1. Real-Time Dual-Frequency PPP

#### 4.1.2. Real-Time Single-Frequency PPP

#### 4.2. Shipboard Real-Time Dual-Frequency PPP

## 5. Discussion

## 6. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 2.**Distribution of stations which are used in the estimations of real-time orbits and clocks, the circles denote the stations for orbits estimation while the blue triangles denote stations for clock estimation.

Item | POD | Clock Estimation |
---|---|---|

Estimator | Least squares | Square root information filter |

Processing sampling | 300 s | 1 s |

Ambiguity | Fixed for GPS/BDS(IGSO, MEO) separately | Epoch-differenced method |

Earth rotation parameters | Estimated with tight constraint | Fixed |

Coordinates | Estimated with tight constraint | Fixed |

Observables | Un-differenced ionosphere-free combination of code and phase based on GPS L1/L2, BDS B1/B2 | |

Weighting | Elevation dependent weight ($p=1,e>{30}^{\xb0};\text{}p={\mathrm{sin}}^{2}e,\text{}e\le {30}^{\xb0}$ (p is the observation weight and e is satellite elevation angle) | |

Cutoff elevation | 7° | |

Satellite phase center | igs08.atx | |

Receiver phase center | igs08.atx for GPS, none for BDS | |

Phase wind-up | Corrected [31] | |

BDS pseudo-range bias | Corrected [32] | |

Tropospheric delay | Initial model (Saastamoinen [33] and GPT2 [34]) + random-walk process 10 cm, 5 mm/√(h) | |

Satellite clock | Estimated as white noise | |

Receiver clock | Estimated as white noise | |

Inter-system biases | Estimated as constant parameters with zero mean condition |

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## Share and Cite

**MDPI and ACS Style**

Shi, C.; Zheng, F.; Lou, Y.; Gu, S.; Zhang, W.; Dai, X.; Li, X.; Guo, H.; Gong, X.
National BDS Augmentation Service System (NBASS) of China: Progress and Assessment. *Remote Sens.* **2017**, *9*, 837.
https://doi.org/10.3390/rs9080837

**AMA Style**

Shi C, Zheng F, Lou Y, Gu S, Zhang W, Dai X, Li X, Guo H, Gong X.
National BDS Augmentation Service System (NBASS) of China: Progress and Assessment. *Remote Sensing*. 2017; 9(8):837.
https://doi.org/10.3390/rs9080837

**Chicago/Turabian Style**

Shi, Chuang, Fu Zheng, Yidong Lou, Shengfeng Gu, Weixing Zhang, Xiaolei Dai, Xianjie Li, Hailin Guo, and Xiaopeng Gong.
2017. "National BDS Augmentation Service System (NBASS) of China: Progress and Assessment" *Remote Sensing* 9, no. 8: 837.
https://doi.org/10.3390/rs9080837