# Real-time Precise Point Positioning with a Xiaomi MI 8 Android Smartphone
## 3 Preliminary Analysis  
We conducted a preliminary analysis on the obtained GNSS raw observations and determined the specific positioning methodology accordingly. Figure 3 shows the GNSS raw observations (BDS 02 satellite) of a geodetic receiver and a Huawei P10 smartphone in the same time. Figure 1: Mobile phones and geodetic receivers at the site of first and third dataset. There is a plastic board on the top of the middle tripod, and smartphones are placed on the board. Figure 3: The pseudorange and carrier phase observations (BDS 02 satellite) of a geodetic receiver and a Huawei P10 smartphone. (**a**) The observations of a geodetic receiver; (**b**) The observations of a Huawei P10 smartphone. The actual acquired carrier phase of smartphones is a set of data that is cumulatively incremented from 0 m at the beginning of observation, thus the values are small. In this figure, the mobile phone carrier phase values are added a constant. Figure 2: The control point named GE01 at Southeast University Jiulonghu Campus. The precise coordinates of this control point are obtained by a geodesic receiver through the network RTK positioning method. (**a**) Distant view of the control point; (**b**) Close-up of the control point; (**c**) A Xiaomi MI 8 smartphone placed on the control point. In panel (a) of Figure 3, the blue and red lines are coincident (so only the red line is visible), which indicates that the pseudorange and carrier phase observations (in meters) of the geodetic receiver are consistent. In fact, the difference between the two values is equal to the carrier phase integer ambiguity in meters. However, in panel (b), the orange and purple lines are not consistent and have different slopes, which indicates that the differences between the pseudorange and the carrier phase observations of Huawei P10 are not fixed. At the same time, we found that this phenomenon also exists in Huawei Honor 9 and Xiaomi MI 8. This property is different from the geodetic receivers, which affects the use of carrier phase measurements of smartphone. By the way, the raw measurements of the geodetic receiver have a large jump after a period of time, which is caused by receiver's clock jump and does not affect the positioning solutions [15]. Particularly for the Xiaomi MI 8 smartphone, the dual-frequency raw observations (Galileo 03 satellite) and its change rate are shown in Figure 4. In panel (a), P1 and P5 denote pseudorange observations of two frequencies E1 and E5, L1 and L5 denote corresponding carrier phase observations. In panel (b), P1, P5, L1, and L5 denote a corresponding change rate. Obviously, the pseudorange observations of two frequencies are coincident (the corresponding two lines are coincident), and the carrier phase observations of two frequencies are also coincident. However, it is evidently that the differences between pseudorange observations and carrier phase observations are not fixed, which is same with Huawei P10 and Huawei Honor 9. Panel (b) shows that the change rate of observations also exists the same phenomenon. At the same time, P5 is more stable than P1 according panel (b), which means the data quality of P5 is better obviously. As shown in Figure 4, the differences between the smartphone pseudorange and carrier phase observations are gradually increased, and the difference values are large. At the same time, the differences between pseudorange change rate and carrier phase change rate are relatively stable. Therefore, in order to better evaluate this phenomenon in different satellites' observations, we calculated the differences between pseudorange change rate and carrier phase (in meters) change rate of all GNSS satellites of a Huawei P10 smartphone and a Xiaomi MI 8 smartphone (L1/E1 frequency), as shown in Figure 5. The RMS of smartphone pseudorange observations exceeds a few meters, thus the difference value between the change rate of pseudorange and the change rate of carrier phase observations should have an amplitude of several meters too.