Combining GPS + GLONASS observations to improve the fixing percentage and precision of long baselines with limited data

Although commercial GPS + GLONASS real-time kinematic systems are available for more than 15 years, GLONASS ambiguity resolution is limited to short baselines within a few tens of kilometers. Furthermore, until now, none of the IGS analysis center has reported ambiguity resolution for GLONASS long baselines in their routine GNSS data processing. The currently published double- or single-differencing techniques are all concentrated on short baselines and are not applicable for long baselines. In this study, we propose a new Single Differencing Between-Receiver (SDBR) method, which is especially suitable for GPS + GLONASS long baseline ambiguity resolution. The SDBR wide-lane ambiguity is directly fixed by rounding with SDBR Hatch–Melbourne–Wübbena combination; the SDBR narrow-lane ambiguity is directly fixed with LAMBDA method. To eliminate the receiver Inter Frequency Bias (IFB), we selected 63 stations with identical IFBs, so that IFBs can be eliminated by SDBR. The results shows, adding GLONASS can improve the fixing rate from 87.8% to 98.8% for half-hourly static solutions, and from 99.3% to 99.9% for hourly static solutions. The position accuracy is also improved significantly for each strategy respectively. Kinematic solutions with different session length are also performed and the fixing rate is improved even more significantly than static solutions.