## 2 Test Study Scope  
The scope of the study is to investigate the variation in kinematic PPP's accuracy based on the used system (GPS, GLONASS, and mixed GPS/GLONASS). Also, the study investigates the effect of using single- and dual-frequency observations from those three system configurations on kinematic PPP's accuracy (Figure 2). Commonly, the use of a single-frequency receiver is more cost-effective than a dual-frequency receiver. A kinematic track of 10.4 km was observed on the campus of King Saud University [54], Riyadh, KSA (Figures 3 and 4) using dual-frequency mixed (GPS/GLONASS) observations using the Sokkia-GRX1 instrument [55]. Observations were gathered using a 15-degree mask elevation angle and a one-second observation interval in clear sky conditions to prevent multipath errors. The rover receiver was mounted on a moving vehicle with an average speed of 15 km/h, and its antenna was positioned vertically above the vehicle's roof for an unobstructed sky view. The total observation time was 54 min and 29 s. The Sokkia-GRX1 instrument processed multiple signal types, including GPS (L1, L2, C/A) and GLONASS (L1, L2, C/A) signals. Observation timing was carefully planned to maximize the number of visible satellites and achieve the best position dilution of precision (PDOP) values. Table 1 presents the no. of visible satellites and PDOP values for used systems on observation day (22,306 GPS day). Figure 3: The study’s observed kinematic track (KSU campus), Riyadh, KSA (8 October 2022). Figure 2: Study scope. The reference solution was acquired through differential positioning, utilizing a reference station with a maximum baseline of 3 km. This differential solution was generated by processing two observation files (Figure 2), one from the reference control station and the other from the kinematic rover receiver. Differential corrections from the reference station are used to correct errors in the observations of the kinematic rover receiver. Six PPP solutions were investigated using NET_DIFF online Processing service [56], namely GPS (single and dual frequency), GLONASS (single and dual frequency), and mixed GPS/GLONASS (single and dual frequency). TEQC software (2019 Feb 25 final release) was used during this study for translation, editing, and quality checks of the originally collected observation file [57]. The translation process aims at converting the format of the originally collected observation file from binary to Rinex format (required by the online processing service). The editing process aims to generate six observation files from the originally collected observation file. Each generated file provides a unique PPP solution (GPS dual frequency, GPS single frequency, GLONASS dual frequency, GLONASS single frequency, mixed GPS/GLONASS dual frequency, and mixed GPS/GLONASS single frequency). The observation data were processed using Net_Diff 1.16 software for GNSS download, positioning, and analysis [56]. The Net_Diff service allowed us to carrying out SPP/PPP/PPP-AR/DSPP/DPPP/RTK/PPP-RTK [1; 58]. From single frequency to triple frequency, all the current GPS, GLONASS, BeiDou, Galileo, QZSS, and IRNSS signals are enabled. Table 2 presents PPP processing parameters used in Net_Diff. software. The advantages of Net_Diff. service over other PPP services is its ability to process observations from all available systems (GPS/GLONASS/BeiDou/Galileo/QZSS/IRNSS) with different combinations between those systems as well as its ability to process different-frequency observations (single/dual/triple). Those two advantages are ideal for research purposes. \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**System**} & **Average No. Visible** & \multirow{2}{*}{**Average PDOP**} \\  & **Satellites** & \\ \hline GPS & 9 & 1.85 \\ GLONASS & 6 & 3.41 \\ Mixed GPS/GLONASS & 15 & 1.39 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Average (no. visible satellites and PDOP) for observed track during GPS day (22,306).