## 3 Precise Positioning Using Uncombined PPP (UPPP) Algorithm
### Analysis of GNSS Observations from Different Logging Apps
#### 4.1.1 Inconsistency between Pseudorange, Carrier-Phase and Doppler Observations
Therefore, we only present the GPS results in continue. Figure 5 represents the CMP and the carrier-phase predicted error for GPS PRNs 01 from the three RINEX files for the Xiaomi Mi8 on the L1 frequency. The main purpose of this plot is to evaluate how the possible anomalies/jumps or offsets affected the CMP and the carrier-phase predicted error. The top, middle and bottom panels of Figure 5 include the CMP plot computed by using the GnssLogger RINEX, the Geo++ RINEX logger output and the converted RINEX, respectively. There are two important points about this figure that needed to be expressed. (1) First, let us look at the plot of the CMP values obtained from the GnssLogger RINEX (the top panel). The CMP does not include the geometric part while it includes the carrier-phase ambiguity, twice the ionospheric error, pseudorange and carrier-phase noise and multipath. Therefore, such behavior is not expected from the CMP values for the GnssLogger RINEX file, as it must be a constant value with a reasonable noise level as long as there is no cycle-slip in the data. It shows that the pseudorange and carrier-phase observations are not consistent (i.e., they are divergent, see the smaller panel in Figure 5 (top-left) in which the pseudorange and carrier-phase observations shifted to zero to have a better view). This indicates that the CMP combination cannot be employed to detect the possible cycle-slips in this case. We should note that this slop is the same for all PRNs. Therefore, in the case of using single-difference between satellites or double-difference observations, this issue would not affect the positioning results as it is removed through the differencing procedure. (2) As can also be observed in this figure, the carrier-phase predicted error obtained from the Geo++ RINEX logger, depicted in the middle panel, does not have an expected behavior for any reason. This also indicates that the Doppler observations cannot be employed here to detect the possible cycle-slips in the data. It is not clear to us why these plots are like that, as these Apps have not disclosed their internal algorithms. Figure 2: First-order differentiation of GPS pseudorange and carrier-phase observations as well as Doppler observations on L1 frequency for PRN 01 (Xiaomi Mi8). Figure 3: First-order differentiation of GLONASS pseudorange and carrier-phase observations as well as Doppler observations on L1 frequency for PRN 17 (Xiaomi Mi8). Figure 4: First-order differentiation of Galileo pseudorange and carrier-phase observations as well as Doppler observations on L1 frequency for PRN 31 (Xiaomi Mi8). Finally, Table 4 provides a summary of consistency or inconsistency between different GNSS observations in the three RINEX files. The highlighted cells in this table indicate that the CMP combination cannot be implemented in the cycle-slip detection procedure while using the RINEX by GNSSLogger App. In addition, the Doppler observations cannot be employed for the cycle-slip detection while using Geo++ RINEX logger output. Finally, the same plots for the Samsung S20 and the Google Pixel 5 are given in Figures 6-9. Due to the page limitation, the plots are only provided for the GPS PRN 01. They support the similar conclusion as before. Figure 5: CMP (**left**) and carrier-phase predicted error (**right**) for GPS PRNs 01 (Xiaomi Mi8). \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Combination** & **GnssLogger** & **Geo++ RINEX Logger** & **UofC** \\  & & & **CSV2 RINEX** \\ \hline Code \& Phase & **No (Attention required)** & Yes & Yes \\ Code \& Doppler & No & No & Yes \\ Phase \& Doppler & Yes & **No (Attention required)** & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Consistency between different GNSS observations in three RINEX files. Figure 6: First-order differentiation of GPS pseudorange and carrier-phase observations as well as Doppler observations on L1 frequency for PRN 01 (Samsung S20). Figure 7: CMP carrier-phase predicted error for GPS PRNs 01 (Samsung S20).