A Real-Time Kinematic (RTK) solution is provided to mobile devices having multi-constellation, multi-frequency (MCMF) functionality, in which a single base station may have a baseline much farther than traditional base station. To enable this, embodiments account for differences in atmospheric effects between the rover station and base station when determining a GNSS position fix for a mobile device (rover station), allowing for a separate tropospheric delay error for a base station to be determined. Embodiments may use additional satellite measurements for which no RTK correction is available, and may further use orbital clock correction for these additional satellite measurements.