Several noteworthy breakthroughs have been made with the BeiDou Navigation Satellite System (BDS) and other global navigation satellite systems as well as the associated augmentation systems, such as the commissioning of the BDS-3 preliminary system and the successful launch of the first BDS-3 GEO satellite which carries the satellitebased augmentation payload. Presently, BDS can provide basic services globally, and its augmentation system is also being tested. This paper gives an overview of BDS and satellite navigation augmentation technologies. This overview is divided into four parts, which include the system segment technologies, satellite segment technologies, propagation segment technologies, and user segment technologies. In each part, these technologies are described from the perspectives of preliminary information, research progress, and summary. Moreover, the significance and progress of the BeiDou Satellite-based Augmentation System (BDSBAS), low earth orbit augmentation, and the national BeiDou ground-based augmentation system are presented, along with the airborne-based augmentation system. Furthermore, the conclusions and discussions covering popular topics for research, frontiers in research and development, achievements, and suggestions are listed for future research.

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First, in the first paragraph of this article, the sentence “In recent years, China has been actively promoting the construction and development of the BeiDou Navigation Satellite System (BDS), and by the end of the year 2000 the construction of BDS-1 was complete and BDS-1 began to provide GPS services for China.” should be changed into “In recent years, China has been actively promoting the construction and development of the BeiDou Navigation Satellite System (BDS), and by the end of the year 2000 the construction of BDS-1 was completed and BDS-1 began to provide services for China.” The word “GPS” should be removed.

Fast corrections are the vital parameters of satellite-based augmentation system, mitigating the rapidly changing errors of satellite clock. It is necessary to develop a feasible method to determine fast corrections because the rapidly changing errors of satellite clock badly affect the service performance. For such a purpose, a user equivalent range error-based method is proposed to determine fast corrections in this paper. Firstly, a generation process of satellite corrections is given for the control segment of satellite-based augmentation system. In this process, long-term corrections are generated first. Once the slowly varying errors of satellite ephemeris and clock are eliminated by long-term corrections, a user equivalent range errorbased method is developed to solve fast corrections. Finally, the performance of the proposed method is analyzed in signal-in-space domain and position domain. Results demonstrate that compared with WAAS method, the accuracy of signal-in-space is improved by over 25.74% and the integrity bounding rate in pseudorange domain is improved by 4.23%. INDEX TERMS Satellite-based augmentation system, long-term corrections, fast corrections, Markov process, Kalman filter.

Satellite integrity monitoring is vital to satellite-based augmentation systems, and can provide the confidence of the differential corrections for each monitored satellite satisfying the stringent safety-of-life requirements. Satellite integrity information includes the user differential range error and the clock-ephemeris covariance which are used to deduce integrity probability. However, the existing direct statistic methods suffer from a low integrity bounding percentage. To address this problem, we develop an improved covariance-based method to determine satellite integrity information and evaluate its performance in the range domain and position domain. Compared with the direct statistic method, the integrity bounding percentage is improved by 24.91% and the availability by 5.63%. Compared with the covariance-based method, the convergence rate for the user differential range error is improved by 8.04%. The proposed method is useful for the satellite integrity monitoring of a satellite-based augmentation system.