The emergence of non-terrestrial networks (NTN) as a new access network has led to a change in the communication paradigm, prompting the 3rd generation partnership project (3GPP) to start new radio (NR)-based NTN standardization. The wide coverage capabilities of NTN enhance the next-generation mobile communication network system, particularly with low earth orbit (LEO) satellites showing considerable commercial potential, thanks to reduced costs resulting from reusable rockets. Although most studies have focused on using NTN with LEO satellites to provide fully covered scenarios, it is also important to consider handover and link stability. LEO satellites have fast mobility, so they face challenges such as frequent handover and link instability. To address these challenges, this thesis proposes a random access channel (RACH)-less conditional handover (CHO) method in LEO-based NTN. To reduce the handover processing time and handover failure, the proposed algorithm reduced the random access (RA) procedure. In conclusion, the performance results demonstrate that the proposed RACH-less CHO outperforms conventional CHO, achieving better performance.
