# Performance Analysis of the Korean Positioning System Using Observation Simulation
## 4 Performance Analysis for KPS
### Standard Point Positioning (SPP)  
The SPP mode has been widely used for most navigation users. It is referred to as absolute positioning, which employs the L1 code measurements with the broadcast satellite orbit and clock error information to calculate a position for the user. Its positioning accuracy can be achieved at a level of a few meters [46]. In this study, the positioning performance for KPS single-frequency users was analyzed. Figure 8 shows the positioning accuracies for KPS-only, GPS-only, and KPS+GPS in the east (E), north (N), and up (U) components, respectively. We mainly considered SPP performance for KPS and GPS on a regional scale. For SPP, we also set the regular grids with the area that covers from 60\({}^{\circ}\)S to 60\({}^{\circ}\)N latitude and 60\({}^{\circ}\)E to 180\({}^{\circ}\)E longitude. The grid points are evenly spaced in latitude and longitude. As such, we process simulated observations for SPP at the grid points with a spatial resolution of 5\({}^{\circ}\) by 5\({}^{\circ}\) on a regional scale. The E component for KPS has the smallest RMS value at the central longitude of 128\({}^{\circ}\)E. The performance of SPP tends to drop sharply away from the central longitude of KPS IGSO satellites. It is directly related to the average number of visible satellites on the ground stations. When the number of visible satellites is less than 5, the KPS can result in large positioning errors of more than a few tens of meters. The N component has a small RMS value near the earth equator and has a large RMS value at higher latitude regions. An error of the U component is very similar to that of the E one. The KPS presents a good performance in the horizontal components. However, the RMS values of the vertical component are relatively large compared to those of the horizontal components. GPS has better SPP performance on a regional scale compared to KPS. GPS also provides consistent SPP performance at all grid points on a regional scale. In addition, the RMS value of U components is relatively large compared to the E and N components. The combined KPS and GPS SPP solutions are shown in the right Figure 8g-i. Obviously, combined KPS and GPS presents the highest positioning accuracy for all three components on a regional scale. It is noted that the combination of KPS and GPS can significantly improve the SPP performance. Figure 7: Signal-in-space ranging errors of GPS precise orbit. Orange solid line denotes the averaged RMS value of SISRE for GPS satellites. For each station, the RMS values for SPP errors are plotted in the E, N, and U components using a histogram. Furthermore, histograms are calculated by a 95% confidence level with the normal approximation. Figure 9 is related to the grids in Figure 8. It shows the probability distributions of the SPP position RMS errors in each component for KPS, GPS, and combined KPS+GPS, respectively. For statistical analysis, we investigated the averaged RMS values in each component. As shown in Figure 9, the averaged RMS values on a regional scale for KPS are about 4.7, 3.7, and 7.1 m for E, N, and U components, respectively. For GPS, the averaged value is about 1.2, 1.4, and 3.1 m for each component, respectively. It can be seen that the SPP performance of KPS is relatively poor compared to GPS. The positioning errors for KPS in each component are approximately twice those of GPS with respect to SPP on a regional scale. In particular, the error of the vertical component is relatively large compared to the horizontal components. While the position errors of the horizontal components are distributed less than about 1.2 cm, the vertical component is concentrated from about 1.5 to 3.0 cm. As shown in the right Figure 9g-i, the combination of KPS and GPS gives better positioning performance compared to KPS and GPS. The averaged RMS values for combined KPS+GPS are about 0.9, 0.9, and 2.0 m for E, N, and U components, respectively.