Combined GPS and BDS for single-frequency continuous RTK positioning through real-time estimation of differential inter-system biases

• Published in: GPS solutions 2018, Vol.22 (1), p.1-13, Article 20
• Main Authors: Gao, Wang, Meng, Xiaolin, Gao, Chengfa, Pan, Shuguo, Wang, Denghui
• Format: Article
• Language: English
• Subjects: Ambiguity; Ambiguity resolution (mathematics); Atmospheric Sciences; Automotive Engineering; Computer simulation; Earth and Environmental Science; Earth Sciences; Electrical Engineering; Geophysics/Geodesy; Global navigation satellite system; Global positioning systems; GPS; Integers; Model accuracy; Original Article; Parameterization; Performance evaluation; Real time; Satellite navigation systems; Satellite observation; Satellites; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Stability analysis
• ISSN: 1080-5370; 1521-1886
• DOI: 10.1007/s10291-017-0687-5

Double-differenced (DD) ambiguities between overlapping frequencies from different GNSS constellations can be fixed to integers if the associated differential inter-system biases (DISBs) are well known. In this case, only one common pivot satellite is sufficient for inter-system ambiguity resolution. This will be beneficial to ambiguity resolution (AR) and real-time kinematic (RTK) positioning especially when only a few satellites are observed. However, for GPS and current operational BDS-2, there are no overlapping frequencies. Due to the influence of different frequencies, the inter-system DD ambiguities still cannot be fixed to integers even if the DISBs are precisely known. In this contribution, we present an inter-system differencing model for combined GPS and BDS single-frequency RTK positioning through real-time estimation of DISBs. The stability of GPS L1 and BDS B1 DISBs is analyzed with different receiver types. Along with parameterization and using the short-term stability of DISBs, the DD ambiguities between GPS and BDS pivot satellites and the between-receiver single-difference ambiguity of the GPS pivot satellite can be estimable jointly with the differential phase DISB term from epoch to epoch. Then the inter-system differencing model can benefit from the near time-constant DISB parameters and thus has better multi-epoch positioning performance than the classical intra-system differencing model. The combined GPS and BDS single-frequency RTK positioning performance is evaluated with various simulated satellite visibilities. It will be shown that compared with the classical intra-system differencing model, the proposed model can effectively improve the positioning accuracy and reliability, especially for severely obstructed situations with only a few satellites observed.