在5G行動通訊網路中，基地台(Next generation Node Base, gNB)的訊號涵蓋範圍較小，因為訊號涵蓋範圍較小，所以需要密集建置gNB，密集建置的gNB會導致跟其他gNB的重疊機率增加。當一個快速移動的使用者設備(User Equipment, UE)在多個gNB間移動時，快速移動的UE會發生頻繁的換手(Handover)，如果快速移動的UE無法被目標gNB分配到資源區塊(Resource Block, RB)，換手就會失敗，此UE就要花費大量時間與其他目標gNB重新連線，因此成功的換手對於移動中的UE非常重要，當一個gNB的RB數無法滿足所有UE (新連線與換手連線)的需求時，其結果會造成部分的UE斷線，另一方面，移動速度較快的換手UE會比較容易離開一個gNB的覆蓋範圍，其佔用的RB可以很快的被釋放，釋放的RB可以給速度較慢的UE與新連線UE使用。由於過去文獻都沒有將不同移動速度的UE分成不同的優先權來分配RB，為了有效分配RB給不同移動速度的UE，本論文在5G行動通訊網路(Mobile Communication Networks)中提出一個以移動速度(Mobile Speeds)作為優先權(Priority)的換手演算法(Handover Algorithm)。首先，本論文根據連線要求(Call Request, CR)將UE分為換手UE (Handoff Connection UE)與新連線UE (New Connection UE)兩種，再將換手UE根據移動速度的快慢分為三種RB使用的優先權，而新連線UE根據是否移動分為兩種RB使用的優先權，最後，我們在Linux撰寫C語言來模擬所提出的演算法，在模擬過程中，我們改變可分配的RB數與UE佔用RB的時間，從模擬的結果中，我們證明本論文所提出的機制能夠有效改善換手連線失敗率、減少高優先權UE的平均等待時間、降低高優先權UE的斷線率。

In a 5G mobile communication network, signal coverage of next generation node base (gNB) is relatively small. Because of the small coverage, gNBs need to be built intensively. Densely built gNBs will lead to the increased of overlap with other gNBs. When a fast-moving User Equipment (UE) moves among multiple gNBs, it will encounter frequent handover. If a fast-moving UE cannot be assigned to a resource block (RB) by the target gNB, the handover will fail and the UE will spend a lot of time in reconnecting to other target gNBs. Thus, a successful handover is very important for a moving UE. When the number of RBs in a gNB cannot meet the demand of all UEs (new or handoff connections), the result will cause some UEs to be disconnected. On the other hand, a fast-moving handoff UE will leave the coverage of a gNB more easily, and its occupied RBs can be released more quickly. The released RBs can be assigned to slow-moving or new-connection UEs. Since the past literatures have not considered how to divide different moving speeds of UEs into different priorities. To effectively allocate RBs to UE with different moving speeds, in this thesis we propose a handover algorithm with mobile speeds as the priority in a 5G mobile communication network. First, we classify UEs into handoff and new-connection UEs based on their call request. Then, we classify handoff UEs into three RB usage priorities, and new-connection UEs into two RB usage priorities. Finally, we write C language in Linux to simulate the proposed algorithm. During the simulation, we change the number of RBs that can be allocated and the time that a UE can occupy a RB. From the simulation results, we demonstrate that the proposed mechanism can effectively improve the dropping ratio of handoff connections, and reduce the average waiting time and the disconnection ratio of high-priority UEs.

論文審定書 i
致謝 ii
摘要 iii
Abstract iv
目錄 v
圖目錄 vii
表目錄 viii
第一章 導論 1
1.1研究動機 1
1.2研究方法 2
1.3章節介紹 3
第二章 5G行動通訊網路與換手 4
2.1 5GC 4
2.2 建立連線的程序 4
2.2.1 時序同步 5
2.2.2 註冊 6
2.2.3 認證 11
2.3路徑損失 12
2.4 5G換手 13
2.5 相關研究 16
第三章 移動速度優先換手演算法 20
3.1 5G的系統架構 20
3.2 UE的優先權 21
3.3 MPHA 22
3.3.1 新連線UE運作的流程 23
3.3.2 換手UE運作的流程 25
3.3.3 來源gNB運作的流程 27
3.3.4 目標gNB運作的流程 31
3.4 MPHA的虛擬碼 32
3.4.1 新連線UE的虛擬碼 32
3.4.2 換手UE的虛擬碼 35
3.4.3 來源gNB的虛擬碼 37
3.4.4 目標gNB的虛擬碼 40
第四章 模擬與結果分析 43
4.1 模擬拓樸 43
4.2 流量產生器的虛擬碼 44
4.3效能量測與模擬參數設定 48
4.4 模擬結果與討論 51
4.4.1 改變10個gNB的RB數 52
4.4.2 改變UE佔用一個RB的時間 56
第五章 結論與未來工作 59
5.1 結論 59
5.2 模擬遭遇的困難 60
5.3 未來工作 60
Reference 61
Acronyms 65
Index 68

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