## 4 Results and Validation
### Assessment of Homogeneous Receivers
Outliers correspond to there being no IFCB estimate for this satellite on this day. Figure 6: Fixing percentage of daily static precise point positioning (PPP) with different strategies for each rover station. Receivers with homogeneous type are used as rover sites. We first calculated the IFCB corrections using data of 3 days, and compared improvement in fixing percentage with respect to the one-day IFCB corrections. Results are shown in Figure 7. The figure shows that for an observation time shorter than 10 min, the fixing percentage improves almost equally using either one-day IFCB or three-day IFCB corrections. For an observation time longer than 25 min, improvement in the one-day IFCB is within \(-0.007\) to \(-0.004\%\) while that in the three-day IFCB within \(-0.002\) to \(0.001\%\). The improvement in fixing percentage achieved using three-day IFCB corrections is thus very little, less than 0.005%. Therefore, we propose that one-day IFCB estimates may be adequate for GLONASS PPP-IAR, although multi-day data would allow more reliable IFCB estimates. We performed simulated kinematic PPP-IAR for all the hourly datasets of the 40 rover stations, and got the fixing percentage as a function of observation duration, which is shown in Figure 8; while Table 2 gives typical values for observation durations 5, 10 and 15 min. It is seen that upon adding GLONASS, the fixing percentage for the GPS-only solution can be improved for different observation durations. By further applying IFCB calibration, the fixing percentage barely improves, i.e., the improvement is only 0.28% and 0.01% for observation durations 5 and 10 min, respectively. The small improvements mean that the IFCBs are slightly different even in the receivers with the same type. For observation duration of 15 min, the fixing percentage even degrades, by 0.04%. This might be because IFCB estimates obtained using only one day of data are not perfect, but the effect on the fixing percentage is so small that it may be neglected. Figure 8: Fixing percentage with various observation durations for kinematic PPP with different strategies. Receivers with homogeneous type are used as rover sites. Figure 7: Improvement in fixing percentage for various observation durations using one-day and three-day IFCB estimates. Figure 9 shows the fixing percentage for GPS + GLONASS kinematic PPP, with and without IFCB calibration, for observation duration of 15 min for each station. Among the 40 rover stations, 13 show little degradation upon applying the IFCB corrections. The degraded fixing percentages are within 0.39% except for the 38 th station, for which it was 4.3%. For all remaining 27 stations, the improvements in fixing percentages by IFCB corrections are below 0.59%. The over-station average fixing percentage improves from 98.15 to 98.27%. We also calculated the fixing percentage for GPS + GLONASS kinematic PPP, with and without IFCB calibration, for observation duration of 15 min on each day (Figure 10). The figure shows that among the 21 days, the fixing percentages are degraded on 5 days but the maximum degradation was within 0.31%. For the remaining 16 days, the fixing percentages improve but by less than 0.43%. The over-day-averaged fixing percentage improves from 98.58 to 98.60%. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Time (min)**} & \multirow{2}{*}{**GPS Only (\%)**} & \multicolumn{2}{c}{**GPS + GLONASS**} \\ \cline{3-4}  & & **No IFCB (\%)** & **With IFCB (\%)** \\ \hline
05 & 13.23 & 69.94 & 70.22 \\
10 & 48.98 & 94.80 & 94.81 \\
15 & 70.03 & 98.27 & 98.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fixing percentage with various observation durations for kinematic PPP with different strategies. Figure 10: Fixing percentage for kinematic PPP with different strategies for an observation duration of 15 min on each day. Receivers with homogeneous type are used as rover sites. Figure 9: Fixing percentage of kinematic PPP with different strategies for an observation duration of 15 min for each station.