## 5 Conclusions  
In this study, we suggested a real-time user-oriented FKP-DGPS algorithm as a new augmentation method to improve the positioning accuracy of the DGPS. While the DGPS is the most popular augmentation system for a low-cost L1 single-frequency GPS receiver, the FKP is originally used for carrier-phase-based positioning to reduce the spatial decorrelation. To use the FKP method to improve the current DGPS accuracy without implementing a unique infrastructure for the service, we modified the FKP correction for the low-cost GPS receiver. To implement the user-oriented method to real-world applications, we combined the DGPS correction from the current DGPS server and the FKP correction from the current network RTK server operated by the NGII, and then provided the modified correction in the format of the message type 1 in the RTCM version 2.3. To verify its effect, mathematical and preliminary test-based analyses have been conducted before developing the real-time FKP-DGPS software. The preliminary-test results show that the DD residual errors with the FKP correction are less compared to those without the FKP correction. After identifying its positive effect through the analyses, the FKP-DGPS software was developed in visual C++ and several static and dynamic tests were conducted to improve the accuracy of the DGPS using the modified FKP correction. From the test results, we can confirm the improvement in the positioning accuracy of the DGPS and the positive effect of the modified FKP corrections. In the static test, compared to the accuracy of the DGPS, the improvements of the 95% horizontal accuracy of all the stations are found to be 3%, 18%, 26%, and 40% for baseline lengths of 50, 90, 140, and 225 km, respectively, which are located along the south-east direction with respect to the static user. Furthermore, the improvements in the vertical accuracy have been identified. From the dynamic test, it is difficult to identify the improvements in the vertical accuracy because the test was conducted for a short period. Nevertheless, compared to the accuracy of the DGPS, the improvements of the 95% horizontal accuracy of all the stations are 18%, 32%, 46%, and 62% for the corresponding baseline lengths. The results of the additional test show the FKP-DGPS has better performance rather than the SBAS. Hence, the new real-time FKP-DGPS algorithm is expected to exploit many applications used in our daily lives such as smartphone, car navigation, and Internet of things (IoT) devices.  
This research was supported by a grant (17 CTAP-C129724-01) from Technology Advancement Research Program funded by the Ministry of Land, Infrastructure, and Transport of Korean government, contracted through SNU-IAMD at the Seoul National University.  
Figure 18: **(a)** 95% position accuracies corresponding to baseline lengths; and **(b)** RMS errors in north, east, and downward directions corresponding to baseline lengths.  
**Author Contributions:** All the authors have contributed to the presented work. Jungbeom Kim suggested the original algorithm of the FKP-DGPS and validated it through data processing and analysis. Changdon Kee and Byungwoon Park provided valuable comments and critical feedback regarding the algorithm. Byungwoon Park supervised its development and the direction of the research. Junesol Song and Heekwon No provided intuitive insights regarding the basic principle of the algorithm. Deokhwa Han and Donguk Kim helped in conducting the test program. All authors participated in formulating the idea and in discussing the proposed approach and results. All authors read and approved the final manuscript.  
**Conflicts of Interest:** The authors declare no conflict of interest.