## 4 Test Results
### Static Test
If \(\delta_{u},\delta_{r}\) are the measurement errors of the user and RS, respectively, and \(\delta_{r}\) is equal to the correction from the DGPS RS, the residual error of the user after applying the correction from the DGPS RS can be positive, implying that the positioning error lies in the west direction. Figure 12a shows the case wherein the GPS satellite is on the east side of the user and RS. Figure 11: (a) DGPS horizontal error (WULJ); (b) FKP-DGPS horizontal error (WULJ); and (c) FKP-DGPS and DGPS vertical errors (WULJ). Figure 12: _Cont._  
Tables 4 and 5 present the detailed numerical results including the results of other stations. The results show that the FKP-DGPS has more accurate positioning accuracy than the DGPS. With the increase in the baseline length, the effect of the FKP correction on the errors due to the spatial decorrelation increases with respect to the positioning accuracy. Thus, in cases of the FKP-DGPS, the improvements of the 95% horizontal accuracy of all stations are 3%, 18%, 26%, and 40% for the corresponding baseline lengths of the RSs compared to the accuracy of the DGPS. In particular, the error components of the east direction are visibly reduced when the FKP-DGPS is applied, which were large when the corrections were used from an RS far apart from the user in the east direction of DGPS. Based on the statistics in Tables 4 and 5, Figure 13a shows the 95% horizontal and vertical results corresponding to the baseline lengths. In addition, Figure 13b shows the RMS errors in the north, east, and downward directions. In Figure 13, the dashed line indicates the FKP-DGPS and the solid line indicates the DGPS. The results show that the accuracies of the FKP-DGPS remain largely constant even if the baseline lengths increase. The valid baseline length of the FKP correction for the pseudorange measurements is clearly above 200 km. An additional test was conducted to compare the performance of the user-oriented FKP-DGPS with those of other alternatives, such as SBAS or VRS-DGPS. The configuration of the additional test is largely similar to that of the static test; the u-blox LEA-6T evaluation kit is used, and the user is located at Bldg. 312 in Seoul National University. Figure 14a shows the visible satellites in the sky during the test. Figure 14b shows the PDOP. The test was conducted for approximately 3 h from 1 July 2017 13:30 in local time (UTC+09). For the SBAS test, PRN 137 satellite of MSAS was used, which is observed at the elevation of 43\({}^{\circ}\) and the azimuth of 151\({}^{\circ}\) in Korea. For the VRS-DGPS test, we need an assumption on the dynamic user and its situation to compare the performance with VRS-DGPS, because there is no infrastructure for VRS-DGPS in Korea. The SBAS mode of the U-blox receiver had been set to be enabled via the u-center program. Once the configuration was set to the SBAS mode, the rover can apply the augmentation message to generate the range correction appropriate to the rover's real-time position, because the same SBAS message is broadcast to all the users in the service area regardless their location. On the other hand, a generic VRS system provides the rover's proper correction only after it got the rover's approximate position. Moreover, a VRS user without multi-channel datalinks to nearby VRSs might experience performance degradation or discontinuity due to the absence of the correction during the handover from the previous VRS to a new one. Assuming a user who left  
Figure 14: (a) Skylplot in additional test; and (b) PDOP during additional test. Figure 13: (a) 95% position accuracies corresponding to baseline lengths; and (b) RMS errors in north, east, downward directions corresponding to baseline lengths. from WULJ and arrived at Seoul without updating its real-time position because of privacy problem or RS handover issue, the static DGPS accuracy using WULJ correction is equivalent to the VRS-DGPS accuracy of the rover at Seoul, because its VRS was not changed from the initial VRS, WULJ, through the entire journey.