Abstract
The abnormal effect in the GPS broadcast ephemeris could cause significant influence on the real-time navigation and positioning solution by using orbit and clock error data provided by GPS broadcast ephemeris. In this paper, three types of non-integer-hour navigation data in GPS broadcast ephemeris were described, firstly. Compared with GPST integer hour data, we find that there are two kinds of data block of non-integer-hour navigation containing gross error with different levels of precision, which can reflect from User Range Accuracy (URA) in the broadcast ephemeris. This gross error would cause a large deviation when using GPS broadcast ephemeris for orbit calculation, and leads to a decrease in kinematic positioning accuracy. Secondly, an improved weighted method which according to the consistency relationship between the URA value and the orbital precision is proposed to improve the positioning accuracy by controlling the influence of gross errors in broadcast ephemeris. Finally, the correction algorithm proposed in this paper is applied to real-time kinematic positioning with shipborne GPS data over the South China Sea. The results show that the proposed positioning algorithm can efficiently reduce the influence of the gross error in the broadcast ephemeris, and improve the accuracy of the navigation and positioning greatly.
Highlights
Real-time kinematic positioning is one of the main modes employed by most navigation users, especially for marine navigation, and it has long been a key research field in the area of global navigation satellite systems (GNSS) [Yi (2011)]
The orbit accuracy calculated from the broadcast ephemeris correlates well with the user range accuracy (URA); this means that the presence of different types of broadcast ephemeris data blocks can be confirmed from the URA
An improved weighting method based on the consistency relationship between the URA value and the orbital precision is proposed to improve the accuracy of kinematic positioning when there are abnormal errors in the broadcast ephemeris
Summary
Real-time kinematic positioning is one of the main modes employed by most navigation users, especially for marine navigation, and it has long been a key research field in the area of global navigation satellite systems (GNSS) [Yi (2011)]. The accuracy of the prediction of the satellite orbit is 5 cm in IGU products when the clock is 3 ns; this represents a range of 0.9 m, and the predicted clock errors will increase with time [Nie, Gao, Wang et al (2018)] To make it easier to access real-time navigation and positioning, the international GNSS service (IGS) has been providing an open-access real-time service (RTS) since 2013, with an accuracy of about 5 cm in the RTS orbit, and of about 0.1-0.15 ns for the clock (http://www.igs.org/rts/monitor), which allows RT-PPP users to achieve a high positioning performance. It is difficult to obtain real-time service products for areas without network coverage, and the receiver must resolve location information with no outside information In this situation, the accuracy of the broadcast ephemeris data received in real time has a direct impact on the positioning result. Some recommendations are provided on how to use GPS non-integerhour data blocks
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