第三代合作夥伴計劃(3GPP)建議5G地面網路可與低軌道(Low Earth Orbit, LEO)衛星網路互相合作，以達到真正的全球覆蓋。然而，低軌道衛星相對於地面高速移動，使得使用者裝置(User Equipment, UE)必須頻繁變更所連接的cell以確保網路服務的連續性。在連線狀態(connected state)的使用者裝置改變所連接cell的程序就稱為換手(Handover，HO)。在低軌道衛星網路中，分配有限的頻道資源以滿足不同類型的使用者的需求並減少大量裝置進行換手所帶來的訊號負擔是一個重大挑戰。在本文中，我們提出了一種動態的換手策略。根據cell的負載情況為5G的兩個場景，增強型行動寬頻(enhanced mobile broadband, eMBB)以及大規模低功耗聯網(Massive Machine Type Communications, mMTC)的使用者裝置動態的調整進行換手的時機。我們使用馬爾可夫過程建立頻道資源分配模型以分析所提出的動態換手策略的效能。分析結果證明我們的策略能有效減少換手並平衡cell的負載。;The 3rd Generation Partnership Project (3GPP) recommended that 5G terrestrial networks can cooperate with Low Earth Orbit (LEO) satellite networks to achieve global coverage. However, low-orbit satellites move at high speed relative to the surface of earth, user devices have to frequently change the cell which it connected. When User Equipment (UE) moves within the coverage area of the satellite network, it can connect to the other cells to ensure the continuity of services. If UE is in a connected state, the Handover (HO) procedure can change connected cell of the UE. In the LEO satellite networks, it is a challenge to allocate limited channel resources to meet the needs of different types of users and reduce the handover signalling overhead caused by large number of devices. In this paper, we proposed a dynamic handover scheme. According to the load of the cell, we dynamically adjust the handover timing for the UEs in the two scenarios: enhanced mobile broadband (eMBB) and Massive Machine Type Communications (mMTC). The Markov process is used to establish the channel resource allocation model, and the proposed scheme has been analyzed. The simulation have shown that we reduce the number of handover procedures and balancing the cell loading.
