隨著科技的蓬勃發展，從最早的必須透過電腦才能上網，到現在人手一台的智慧型手機，網路的速度更是不斷的增長，可支援更多樣的化的服務，然而高速成長的需求在資源有限的情況下，如何提升效能是一大挑戰。
3GPP在Release 12中探討了裝置對裝置(Device-to-Device, D2D)間的通訊，藉由兩裝置的直接傳輸，可提高頻譜的使用率、傳輸速率和減少電池的損耗等，更可進一步減輕核心網路的負擔。
現今環境中，有相同興趣的使用者通常樂意組成群集互相幫助，因此群集之間有時可以透過其他成員來下載資料，但在資訊如此多元的環境之下，不同的資料對於延遲的容忍程度也會不同。
因此本篇將探討使用者組成群集下載資料的情境，且使用者之間藉由D2D這樣的技術互相幫助，互相分享資料，並且經由分析得知這樣的情境會是一個多路徑的選擇問題，並且針對這多路徑選擇問題提出一效益函式，再同時考量延遲時間以及吞吐量對路徑選擇上的影響，然後考量過往多種A*演算法後，結合雙向搜尋以及終身規劃演算法提出自身的路徑決策演算法，更進一步地將效益函式應用於其中。
藉由模擬結果可得知本篇的方法，透過雙向搜尋可以有效較低演算所花時間，而擷取終身演算法的概念更可以適應動態的拓樸變化，加上效益函式中同時考量延遲與吞吐量，最終可讓使用者以較好的吞吐量與較少的延遲時間下載所需的資料。

Cisco predicted that mobile traffic will reach over 120 exabytes per month in 2018. Because of that, the Third Generation Partnership Project (3GPP) proposed a technology called “Device-to-Device (D2D)” communication. The first mention of this technology is in 3GPP release12.
D2D communications is a novel technology allowing user exchanges of their data over direct links instead of through base stations. D2D can improve system capacity, system throughput and data rate. It also can provide lower latency for user. Moreover, D2D communications play an important role in traffic offloading.
In recent years, there are serval research indicating that people will construct stable social structures when they are geographically close. People would like to help each other when they are in the same group. It means that they would help relay data and cache data for other group members.
In this paper, we designed an utility function, which consider delay and throughput at the same time, to evaluate the path. Because of the unit of delay and throughput are different, we defined how to standardize them. We also combine the advantages of Bidirectional search and Lifelong Planning A*, propose a new routing policy for group members, which can meet their demands with lower latency and better throughput. Furthermore, we device an utility function in our algorithm to select paths.
Our simulation results have shown that the proposed mechanism can choose the path which has better throughput and lower latency. In addition, the proposed mechanism can apply to dynamic topology efficiently.

[學位論文審定書+ii]
[論文公開授權書+iii]
[論文摘要+iv]
[Abstract+v]
[目錄+vi]
[圖目錄+viii]
[表目錄+x]
[第一章 導論+1]
[1.1 前言+1]
[1.2 研究動機+4]
[1.3 論文架構+6]
[第二章 相關背景與研究+7]
[2.1 長期演進技術(LTE)之基本架構+7]
[2.2 LTE通道存取相關簡介+10]
[2.2.1 LTE通道存取技術+10]
[2.2.2 傳輸基本單位+12]
[2.3 Device-to-Device (D2D)通訊技術+14]
[2.3.1 D2D基礎介紹+14]
[2.3.2 裝置搜索 (Device Discovery)+16]
[2.3.3 模式選擇 (Mode Selection)+17]
[2.3.4 資源配置 (Resource Allocation)+19]
[2.3.5 群組通訊 (Group Communication )+20]
[2.3.6 D2D 中繼 (Relay)+21]
[2.4相關論文+22]
[第三章 研究方法+27]
[3.1 系統架構+27]
[3.1.1 架構+27]
[3.2問題描述與定義+30]
[3.3 系統流程與演算法+37]
[3.3.1 延遲與吞吐量計算方式+37]
[3.3.2 主要機制流程+41]
[3.3.3 Header之決策流程+46]
[3.3.4 Relay決策演算法+47]
[第四章 效能與分析+56
[4.1 模擬環境與參數設定+56]
[4.2 模擬結果與效能分析+61]
[第五章 結論+74]
[參考文獻+75]

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