Ill-Posedness Analysis of Ambiguity Resolution Using BDS-2 and Its Fusion with GPS
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Different from GPS or GLONASS, BDS (BeiDou Navigation Satellite System) consists of not only MEO satellites but GEO and IGSO satellites, both of which are high-orbit satellites. Now BDS has finished its second step of the all three steps, and can provide regional navigation and positioning service. BDS-2 now mainly consists of 5 GEO, 5 IGSO and 4 MEO satellites. For most places of China, the GEO satellites always gather in a south part of the visible satellites sky plot. The IGSO satellites are also often seen in the south part. These lead into poor satellite geometry. Besides this, the running angular velocities of GEO and IGSO satellites are much smaller compared with MEO satellites. This results in that the geometric relationship between the satellite and the station changes slowly, so that there exists strong correlation between the observation equations from adjacent epochs. The poor satellite geometry and the small velocities make the ambiguity resolution (AR) of BDS-2 be a more serious ill-posed problem. In this paper the ill-posedness of the AR of BDS-2 was analyzed. And on this basis, some different combinations of GEO, IGSO and MEO satellites of BDS-2 were used in the AR experiments to reveal the characteristic of ill-posedness. AR experiment of GPS was also carried out at the same time for comparison with BDS-2. At last, the fusion AR experiment of BDS and GPS was done. From these experiments we concluded that BDS-2 AR which mainly relied on high-orbit satellites is a serious ill-posedness problem, so it takes much more time than GPS. The fusion with GPS will make the problem change much better.
KeywordsBDS-2 Ambiguity resolution Ill-posed Fusion with GPS
This work is supported by the Key Projects in the National Science and Technology Pillar Program during the Twelfth Five-year Plan Period (No. 2012BAJ23B01). The authors are very grateful to the anonymous reviewers for their constructive comments and suggestions.
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