## 5 Conclusions  
The purpose of providing communication services through satellites is to extend coverage to areas that cannot be reached by terrestrial networks. As a hyper-connected era is anticipated in the future, Non-Terrestrial Network (NTN) must ensure continuous and reliable communication in all regions above a certain altitude. While there are various challenges in applying NTN, the issue of mobility in connected mode is of utmost importance. Users may experience significant inconvenience if communication services are interrupted, emphasizing the critical need for uninterrupted connectivity. Satellites at high altitudes provide services to ground terminal nodes, but due to the long distance, there is a time delay for radio waves to reach the terminals. This temporal difference becomes more significant at higher altitudes. Moreover, Low Earth Orbit (LEO) satellites, operating at relatively low altitudes, move at high speeds compared to ground-based terminals, posing a challenge to maintaining communication continuity. Communication quality is bound to deteriorate even when satellites operate at higher altitudes. Our study conducted experiments in an environment closer to real-world communication situations by considering propagation delay, an actual environmental variable, rather than assuming only ideal conditions. In an actual NTN environment, Line-of-Sight (LOS) conditions may not always prevail, introducing more unpredictable variables. Obstacles between communication terminals, unexpected orbit deviations, and changes in channel quality over time are likely occurrences. To address this, this paper proposed a two-step XGBOOST model that compensates for propagation delay. The two-step XGBOOST model demonstrates superior performance across most altitude ranges compared to the existing handover triggering method based on New Radio (NR) that does not consider propagation delay, ensuring communication continuity with moving satellites. The handover triggering experiment considering propagation delay yielded favorable performance, especially from the 50 ms section. Although there is a slight difference in precision, the f1-score, which represents the overall model performance, shows better results. Thus, the proposed model exhibits enhanced handover triggering performance not only in LEO NTN and Medium Earth Orbit (MEO) NTN but also across the entire altitude range.  
Conceptualization, E.K.; Methodology, E.K.; Software, E.K.; Validation, E.K.; Investigation, E.K.; Data curation, E.K.; Writing--original draft, E.K.; Writing--review & editing, E.K.; Visualization, E.K.; Supervision, I.J.; Project administration, I.J.; Funding acquisition, I.J. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Institute of Information & Communications Technology Planning and Evaluation (IITP) grant funded by the Korean government (MSIT) (No. 2020-0-00107, Development of the technology to automate the recommendations for big data analytic models that define data characteristics and problems).  
**Data Availability Statement:** The data that support the findings of this study are available on request from the corresponding author, I.J. The data are not publicly available due to their containing information that could compromise the privacy of research participants.  
**Conflicts of Interest:** The authors declare no conflict of interest.