第三代夥伴合作計畫 (3rd Generation Partnership Project，3GPP) 在Release 12中制定出D2D (Device-to-Device) 技術；兩個行動裝置可以直接進行通訊，不須額外透過基地台傳輸資料，又因裝置間距離短，因此有較好的訊號品質。
現實環境中，使用者使用行動網路時，可能會隨時改變所在位置，並且遠離原本所連接之基地台，導致訊號變差，因此換手技術便是為了讓使用者具有一定的訊號品質，所以會將連線轉移至其它基地台。
本論文想法主要在於D2D裝置雖然能直接傳輸資料，但控制訊號仍必須連接至基地台，進而使基地台可調整裝置功率及分配資源等設置；此外目前換手機制中，由於遮蔽效應影響，可能導致不必要換手次數增加，使整體效能不升反降；並且標準皆為考量單一行動裝置之訊號狀況，但D2D pair中裝置可能因接收訊號不同而分別連至不同基地台，使基地台之間需額外透過X2介面進行訊息的溝通，導致控制訊號傳輸時間增長。因此我們會提出一個基於D2D pair中兩個行動裝置一起考量的換手決策機制，希望此兩個用戶設備盡量連接到同一基地台，藉此降低額外負擔；首先會根據兩個裝置連接到基地台之訊號狀況定義出訊號效能函式，並且考量使用者移動方向，以及與鄰近基地台之訊號關係，預測出目標基地台；接下來利用兩個裝置接收到原服務基地台與目標基地台之訊號關係，根據訊號情況或是連線穩定度，決定D2D裝置之換手時機，目的在於減少換手次數和降低負擔同時，也能滿足一定的訊號強度。最後於模擬結果中，可觀察出我們所提出之方法確實能夠減少不必要之換手次數，並且讓兩個裝置盡量連接到同一基地台，使整體的吞吐量以及控制訊號傳輸延遲都會有較佳的結果。

The 3rd Generation Partnership Project (3GPP) formulated a standard of “Proximity Services” (ProSe), also called “Device-to-Device” (D2D) communication, which is a promising technology to provide high throughput and low latency services between end-users.
Handover is an essential issue in wireless networks, especially for the mobility of a user equipment (UE). We need to transfer the connection from the source eNB to target eNB so that the UE can achieve the better quality.
The main idea of this paper is that the two D2D devices can communicate directly without additional transmissions through a base station, but their control signals must connect to the eNBs so that the base stations can adjust the power of devices and allocate the resources. And in the current standard of handover mechanism, the number of unnecessary handover could be increased by the effect of shadowing fading. Moreover, LTE-A only considers the handover procedure of single user; the handover mechanism for a D2D pair is not standardized. When a D2D pair moves around the cell boundary, the control signal of two UEs may connect to different base stations. The latency could be increased due to the exchange of D2D related information. Hence, we propose a mechanism of handover decision and timing based on D2D communication in order to minimize the signaling overhead. We hope that two D2D devices can connect to the same eNB as much as possible for a lower signaling overhead. First, we predict the target eNB based on the movement of the two devices and the relationship of signal with the neighboring eNBs. Second, we collaborate two D2D devices with eNBs to make a handover decision in the light of the received power or the stability of connection. Simulation results validate that the proposed scheme can reduce the number of handoffs and the signaling overhead to achieve a better performance.

[第一章 導論 + 01]
[1.1 前言 + 01]
[1.2 研究動機 + 03]
[1.3 論文架構 + 04]
[第二章 相關背景與研究 + 05]
[2.1 長期演進技術 (LTE) 架構介紹 + 05]
[2.2 D2D (Device-to-Device) + 09]
[2.2.1 裝置搜索 (Device Discovery) +11]
[2.2.2 模式選擇 (Mode Selection) + 13]
[2.2.3 干擾管理 (Interference Management) + 15]
[2.2.4群組通訊 (Group Communication) + 17]
[2.3 換手 (Handover) 技術 + 18]
[2.4 相關論文 + 25]
[第三章 研究方法 + 29]
[3.1 系統架構 + 29]
[3.2 問題定義 + 31]
[3.3 選擇目標基地台 + 34]
[3.4 換手決策機制 + 39]
[第四章 效能與分析 + 46]
[4.1 模擬環境與參數設定 + 46]
[4.2 模擬結果與效能分析 + 49]
[第五章 結論 + 65]

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