A Comparative Study of Mathematical Modelling for GPS/GLONASS Real-Time Kinematic (RTK)

The benefit of combining GLONASS and GPS measurements is obvious when a limited number of satellites are available due to the sky view being partially blocked. However, adding GLONASS observations to those of GPS is not a straightforward process. Due to the differences in signal structure between GPS and GLONASS, the techniques to eliminate relative receiver clock errors from GLONASS carrier phase observations are different from the GPS data processing algorithms. Several approaches have been suggested to address this challenge when processing combined GPS and GLONASS observations. These can be grouped into two main classes: receiver clock error estimation or receiver clock elimination. This paper reports on the issues related to the mathematical modelling of a combined GPS/GLONASS real-time kinematic (RTK) system. Two experiments, static RTK and kinematic RTK, were carried out to compare the two strategies for combining GPS and GLONASS observations. In the static positioning experiment, three short baselines of 24hour data set among five CORS stations in a network located in the Sydney region, Australia, were processed on an epoch-by-epoch basis. Several data quality measures were used to compare different processing strategies. The influence of system selection on ambiguity resolution was assessed using some of the commonly used measures for ambiguity validation such as the F-ratio (Frei and Beutler, 1990), R-ratio (Euler and Schaffrin, 1991) and W-ratio (Wang et al., 1998). The precision of baseline vector estimation was also analysed. The investigation found insignificance difference between both modelling strategies considering both baseline precision and ambiguity resolution.