## 4 Discussion  
Table 3 presents the RMSE and 3D position RMSE for different kinematic PPP solutions resulting from this study compared with the differential solution.  
On the date of the study (22,306 GPS day), GPS has 31 healthy satellites, while GLONASS has 22 healthy satellites. This constellation status explains the GPS no. of visible satellites (nine), while the GLONASS no. of visible satellites was only six. The mixed system offers 15 visible satellites with 1.68 position (3D) dilution of precision (PDOP). Mixed PDOP improved by 25% over GPS-PDOP and by 100% over GLONASS-PDOP. As GPS is better than GLONASS in satellite geometry for the study geographic region (Riyadh, KSA), it can be concluded that GPS will provide better performance for kinematic PPP positioning accuracy over GLONASS. However, the GLONASS system serves as a viable alternative to GPS, and also, it can augment GPS in different environments to ensure better behavior using a mixed system (GPS/GLONASS).  
From the resulting kinematic PPP coordinate differences shown in Figure 5a,b,d,e, it can be concluded that GPS offers stable performance for kinematic PPP positioning accuracy. As GLONASS's performance is variable due to the effect of satellite geometry variation, PDOP gets higher, which indicates worse positioning accuracy. GPS single frequency performance is twice as great as GLONASS single frequency. The GPS dual frequency performance is twice as good as the GPS single frequency. The accuracy difference can be justified due to the excellent performance of dual frequency observations in mitigating the ionospheric delay which considers the largest source of error that affects GNSS observations. GPS and GLONASS provide better positioning accuracy for latitude than longitude coordinates using either type of observation (single or dual). This behavior is due to the increased number of satellite tracks in the latitude direction (north-south) compared with the least number of satellite tracks in the longitude direction (east-west).  
From Figure 5c,f and Table 3, it can be concluded that a mixed system (GPS/GLONASS) is providing the best performance in positioning accuracy compared with individual  
Figure 6: Kinematic PPP RMSE from GPS, GLONASS, and mixed GPS/GLONASS using (**a**) single-frequency observations, and (**b**) dual-frequency observations.  
\begin{table}
\begin{tabular}{l l c c c c} \hline \hline \multicolumn{1}{c}{**Obs. Type**} & \multicolumn{1}{c}{**System**} & \multicolumn{3}{c}{**RMSE (m)**} & \multicolumn{1}{c}{**3D Position RMSE (m)**} \\  & & **Lat.** & **Long.** & **Height** & **3D Position RMSE (m)** \\ \hline \multirow{2}{*}{
\begin{tabular}{l} Single \\ Frequency \\ \end{tabular} } & GPS & 0.056 & 0.125 & 0.157 & 0.208 \\  & GLONASS & 0.129 & 0.314 & 0.258 & 0.426 \\  & GPS/GLONASS & 0.039 & 0.071 & 0.104 & 0.132 \\  & GPS & 0.031 & 0.074 & 0.078 & 0.112 \\  & GLONASS & 0.044 & 0.141 & 0.122 & 0.192 \\  & GPS/GLONASS & 0.021 & 0.069 & 0.057 & 0.092 \\ \hline \hline \end{tabular}
\end{table}
Table 3: RMSE from different kinematic PPP solutions compared with the differential solution.  
systems (GPS or GLONASS). Using mixed single-frequency observations improves the acquired accuracy by 100% over GLONASS and by 38% over GPS.  
Using mixed-dual frequency observations improves the acquired accuracy by 100% over GLONASS and by 18% over GPS. Using mixed-dual frequency observations improves the acquired accuracy by 30% over mixed single-frequency observations. The results of Table 3 are in agreement with recent studies [33, 35, 53, 59]. The paper's findings on accuracy and cost percentages provide valuable design guidelines for mobile robot designers, expediting the sustainable integration of outdoor robot-based CPS systems in Industry 4.0.