# RTK with the Assistance of an IMU-Based Pedestrian Navigation Algorithm for Smartphones
## 3 Results
### RTK Performances Based on the Xiaomi Mi 8
#### 3.1.2 RTK Performances in Dynamic Mode  
This section shows RTK performances in dynamic mode. We chose an M300 receiver as the base station (Figure 5a). The M300 receiver was capable of tracking all the signals of all the constellations. The M300 receiver was connected with an antenna located on the roof of our laboratory (Figure 5b). This antenna was also able to receive all the signals of all the constellations. We put the Xiaomi Mi 8 on a small handcart as the rover. We also located a receiver equipped with an DEM617-CDS-R0G-550 card close to the Xiaomi Mi 8 for comparison. This card that could track the L1/L2 signal of GPS was manufactured by NovAtel. The NovAtel receiver was connected to a mini-survey antenna GPS500, which was capable of receiving GPS L1/L2 (Figure 5c,d). The GPS500 was much more resistant to the influence of multipath and noise than the antenna in smartphones. We treated the dual-frequency RTK results provided by the NovAtel receiver as the reference. Figure 4: RTK performances in static mode. (**a**) The visible signals; (**b**) vertical positioning errors; (**c**) horizontal positioning errors (single frequency); (**d**) horizontal positioning errors (dual frequency). We tested the RTK performance in dynamic mode on the sports ground of Peking University on 31 May 2019. We started from the north of the sports ground and walked counterclockwise. A tall building was located to the southeast of the sports ground, which could block signals. We compared the performance between single-frequency RTK and dual-frequency RTK with the NovAtel receiver. Signals tracked by the NovAtel receiver are shown in Figure 6a,b. All the signals shown in Figure 6a,b were tracked by both the rover and base station. The receiver could track the signals of at least four satellites thanks to the high quality of GPS500, which helped to keep providing positioning results during the test. Figure 5: View of the base station and the rover. (**a**) View of the M300 receiver; (**b**) view of the antenna on the roof; (**c**) view of the rover; (**d**) brief description of the rover. The performances of single-frequency RTK and dual-frequency RTK with the NovAtel receiver are presented in Figure 6c,d. The fixed rate of ambiguity resolution for single-frequency RTK was less than 9%, while that for dual-frequency RTK exceeded 82%. The differences between the results verified the conclusion that dual-frequency RTK was much more likely to get fixed ambiguity resolution than single-frequency RTK. We chose the dual-frequency RTK results as the reference to compare the performance of RTK in different modes based on the Xiaomi Mi 8. We divided RTK into four modes: RTK with L1 signals of GPS; RTK with L1 signals and L5 signals of GPS; RTK with L1 signals of GPS and E1 signals of Galileo; RTK with L1/L5 signals of GPS and E1/E5a signals of Galileo. Signals tracked by the Xiaomi Mi 8 are shown in Figure 7. Comparison of Figure 7 and Figure 6 explains that the Xiaomi Mi 8 had a little lower capacity of tracking GPS L1 signals than the NovAtel receiver because of the antenna with poor performance. As mentioned in the Introduction, the GPS constellation has more operational satellites than the Galileo constellation does. As a result, there are more GPS visible satellites at the same time. Figure 7 reflects that the number of Galileo satellites tracked by the Xiaomi Mi 8 was less than the number of GPS satellites tracked by the Xiaomi Mi 8. Figure 7 also reflects that the number of visible GPS satellites with both L1 and L5 signals was fewer than that of visible GPS satellites with only L1 signals. We can refer to the Trimble GNSS Planning to  
Figure 6: RTK performances based on the NovAtel receiver. (**a**) Visible signals and satellites; (**b**) number of different signals); (**c**) single-frequency RTK; (**d**) dual-frequency RTK. find the moments when there were enough visible GPS satellites that were broadcasting L5 signals and visible Galileo satellites. The performances of RTK in different modes are presented in Figures 8 and 9.