## 4 Results and Discussion
Because of the challenging environment, the DOP (Dilution of Precision) values of GLONASS only constellation was always over three during the kinematic test. When the combination of the GPS+GLONASS+BDS were considered (Scenario 3), the mean values reached 4 cm in the 2D position and 1 cm in height components. The triple-constellation GNSS PPP results have the best RMSE values among them with \(\pm\)5 cm for 2D position and \(\pm\)7 cm for height components (Table 4). It is clearly seen that BDS constellation, in addition to GPS and GLONASS constellations, improves the 2D positioning accuracy by 28 % and 50% in 2D position and height with respect to RMSE values, respectively. When compared to the GPS-only solution, improvements of about 17% and 42% in 2D position and height, respectively, are seen. For the other triple-constellation kinematic PPP, GPS+GLONASS+Galileo (Scenario 4), the solution provided mean values of 5 cm with \(\pm\)6 cm RMSE for 2D position while 12 cm mean with \(\pm\)14 cm RMSE with for height component. When the RMSE values were investigated, the 2D positional accuracy was found to be almost the same level for this solution in comparison with the both GPS-only and GPS+GLONASS combination solutions. This result indicates that the contribution of the Galileo satellites to the GPS-only and GPS+GLONASS combinations did not provide significant improvement. However, when the results obtained from GPS+GLONASS+Galileo solution were compared to GPS+GLONASS+BDS, the RMSE value was found at almost the same level for 2D position, whereas it was worse than by a factor of about two for the height component. Due to the harsh environmental conditions, the number of tracked Galileo satellites was below four in 12% of the kinematic tests (Figure 3), and the calculated DOP values were above six in 40% of the test times (Figure 10). \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Scenarios**} & \multicolumn{2}{c}{**2D Position (cm)**} & \multicolumn{2}{c}{**Height (cm)**} \\ \cline{2-5}  & _Mean_ & _RMSE_ & _Mean_ & _RMSE_ \\ \hline
**Scenario 5 (G+R+E+C)** & 4 & \(\pm\)5 & 2 & \(\pm\)8 \\
**using CODE’s COM 1D precise products** & 3 & \(\pm\)4 & 0 & \(\pm\)5 \\
**Scenario 9 (G+R+E+C)** & 7 & \(\pm\)8 & 8 & \(\pm\)11 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Statistical analysis of the differences in 2D position and height components for different precise products (for quad-constellation Solutions). \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Scenarios**} & \multicolumn{2}{c}{**2D Position (cm)**} & \multicolumn{2}{c}{**Height (cm)**} \\ \cline{2-5}  & _Mean_ & _RMSE_ & _Mean_ & _RMSE_ \\ \hline
**Scenario 1 (G)** & 6 & \(\pm\)6 & 9 & \(\pm\)12 \\
**Scenario 6 (G)** & 2 & \(\pm\)3 & 5 & \(\pm\)6 \\
**using IGS’s precise products** & 2 & \(\pm\)3 & 4 & \(\pm\)6 \\
**Scenario 7 (G)** & 2 & \(\pm\)3 & 4 & \(\pm\)6 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Statistical analysis of the differences in 2D position and height components for different precise products (for GPS-only Solutions). Finally, the quad-system, GPS+GLONASS+Galileo+BDS (Scenario 5), revealed differences between PPP to reference solution with 4 cm mean and \(\pm\)5 cm RMSE for 2D position and 2 cm mean and \(\pm\)8 cm RMSE for height component. This combination has almost the same mean and RMSE values with the combination of GPS+GLONASS+BDS. Looking at the RMSE values for the GPS+GLONASS+Galileo+BDS solution given in Table 4, it was seen improvements of 17%, 29%, and 17%, in the 2D position, respectively, in comparison with GPS-only, GPS+GLONASS, and GPS+GLONASS+Galileo combinations, respectively. For height component, improvements of 33%, 43%, and 43% in comparison with GPS-only, GPS+GLONASS, and GPS+GLONASS+Galileo combinations, respectively. When the differences given in Figure 7 and Table 5 were analyzed, the mean values 2 cm for 2D position and 5 cm for height were obtained from the GPS-only solution using IGS products (Scenario 6).