## 4 Results and Validation
### Assessment of Heterogeneous Receivers
The difference is within 3%, 1.3% and 1% for observation durations 5, 10 and 15 min, respectively. It is thus confirmed that the smaller fixing percentage in Figure 14 is from the poorer data quality of the network and not a problem with the method. To present the improvement achieved upon applying IFCB corrections for each receiver type, Figure 16 shows the fixing percentage of kinematic PPP for different processing strategies for observation duration of 15 min for each station. The over-manufacturer-average fixing percentage is summarized in Table 5. The figure shows that the fixing percentage for GPS-only is below 71% for each station. For GPS + GLONASS without IFCB corrections, the fixing percentage is 30% for the 12 Leica receivers and below 55% for the five TPS receivers; all values are smaller than the corresponding GPS-only solutions. Upon applying the IFCB corrections, the fixing percentage for GPS + GLONASS improves to over 88% for these 17 stations. For the 12 Trimble stations, because they have an IFCB similar to that of the base stations, the improvement was not appreciable upon applying the IFCB corrections; all improvements are below 1.2% and there is even small degradation for two stations (0.2% and 0.6%). \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 & 7.43 & 20.41 & 49.14 \\
10 & 33.52 & 47.14 & 84.88 \\
15 & 52.92 & 56.92 & 92.86 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Fixing percentage for various observation durations for kinematic PPP with different strategies. Figure 15: Fixing percentage for various observation durations for kinematic PPP with different strategies for base station. The fixing percentage for kinematic PPP using different processing strategies for observation duration of 15 min on each day is shown in Figure 17. The fixing percentage is between 47% and 63% on each day for GPS-only and between 70.2% and 78.5% for GPS + GLONASS without IFCB corrections. Upon applying IFCB corrections, the fixing percentages exceed 86.9% for all days and average 93.3%. We calculated the position RMS of each fixed epoch, and the results are shown in Table 6. For GPS + GLONASS PPP, because the ambiguity fixing percentage is very small without IFCB correction, we only calculated the RMS with IFCB calibration. On average, the position RMS is 0.80,  
Figure 16: Fixing percentage for kinematic PPP with various strategies for observation duration 15 min for each station; rover stations are grouped according to the manufacturer. Figure 17: Fixing percentage for kinematic PPP with different strategies for observation duration 15 min on each day. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Manufacture**} & \multirow{2}{*}{**GPS Only (\%)**} & \multicolumn{2}{c}{**GPS + GLONASS**} \\ \cline{3-4}  & & **No IFCB (\%)** & **With IFCB (\%)** \\ \hline LEICA & 53.19 & 26.51 & 93.44 \\ TPS & 61.83 & 43.90 & 92.34 \\ TRIMBLE & 49.18 & 92.15 & 92.58 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Over-manufacturer-average fixing percentage with different strategies for observation duration 15 min. 0.68 and 2.79 cm for GPS-only in the north, east and up directions, respectively, whereas it degrades to 0.66, 0.60 and 2.45 cm for GPS + GLONASS, with improvements of 17.5%, 11.8% and 12.1%. The above results confirm that the proposed IFCB calibration method is efficient for GPS + GLONASS PPP-IAR with heterogeneous receivers.