臺灣博碩士論文加值系統

長程演進網路是由3GPP所定義的高速無線網路的標準，以提供高傳輸速率以及低封包延遲的無線網路。在支援高速移動性的無線通訊系統下，換手決策是相當重要的一個議題。尤其是在大型蜂巢式基地台與毫微微蜂巢式基地台共存的系統下，使用者設備處於高速移動時，很容易產生非必要換手。於是，可以避免非必要換手的換手決策顯得更加重要。
傳統換手決策的換手參數為信號強度；而有的文獻提出之換手決策乃基於信號強度再加上使用者設備的移動速度、即時性服務類型以及使用者設備的存取模式之考量，來減少非必要換手。還有部分文獻提出的換手決策為考量信號對干擾及雜訊比來取代信號強度，用於提高毫微微蜂巢式基地台的使用率。本論文將分析這些換手決策，並提出一套新的換手決策。我們的模擬結果顯示：我們提出新的換手決策，相較於傳統的換手決策，可以減少非必要換手率達百分之八十四。
另外，我們觀察到：使用者設備在道路上移動的時候，並不會考慮到基地台的分布情形，然而，不一樣的基地台分布卻會導致不一樣的換手發生。假如我們能夠選擇行進在換手次數較少之路徑，則可減少無線電資源的浪費，也可以提供使用者較佳的服務品質。我們的模擬結果顯示，選擇路徑的策略比隨機移動路徑的策略，可以減少非必要換手次數達百分之八十。

3GPP Long Term Evolution (LTE) defines a high speed wireless communication standard for mobile phones and data terminals. Handover strategy is considered as one of the crucial topics in high-speed mobility-supported wireless communication systems. In the macrocell and femtocell coexisting system, the high speed movement of user equipment may often cause unnecessary handovers. Therefore, an efficient handover strategy is necessary to avoid unnecessary handovers.
The parameter used in conventional handover strategy is signal strength. Some proposed handover strategy considered not only signal strength, but also mobility of user equipment, real time service, and access mode of user equipment to reduce unnecessary handovers. In addition, some study proposed SINR (Signal to Interference and Noise Ratio) instead of signal strength to improve femtocell utilization. In this thesis, we analyze these handover strategies and propose a new one. Our simulation result shows that our proposed handover strategy, in comparison with conventional strategy, can reduce the ratio of unnecessary handover by 84%.
In addition, we observe that the movement of user equipment does not dependent on the distribution of the base station. However, different distribution of base stations will result in different occurrence of handovers. Suppose we are able to choose the path with less number of handovers, the radio resource can be well conserved and better quality of service can be provided to users. Our simulation result shows that the path selection strategy can reduce the number of unnecessary handovers by 80% in comparison with random walk strategy.

摘要I
ABSTRACTII
誌謝IV
目錄V
表目錄VII
圖目錄VIII
第一章　緒論1
1.1　前言 1
1.2　研究背景1
1.2.1　LTE 標準簡介1
1.2.2　Macrocell 與 Femtocell 簡介3
1.2.3　換手簡介6
1.3　研究動機6
1.4　研究目的7
1.5　論文架構7
第二章　背景知識與相關研究8
2.1　Femtocell 存取模式8
2.2　換手情境9
2.3　Femtocell於 LTE 的基本架構10
2.4　LTE換手流程12
2.5　相關研究16
第三章　適用於毫微微蜂巢式網路之換手決策20
3.1　前言 20
3.2　換手決策之研究20
3.2.1　相關研究之分析20
3.2.2　提出的換手決策22
3.3　模擬實驗與效能分析23
3.3.1　模擬環境23
3.3.2　模擬參數設定23
3.3.3　模擬結果及效能分析25
第四章　基於換手決策之路徑選擇27
4.1　前言 27
4.2　系統假設27
4.3　路徑選擇之研究30
4.3.1　路徑選擇之流程30
4.3.2　Cost計算方法31
4.4　模擬實驗與效能分析34
4.4.1　模擬環境34
4.4.2　模擬參數設定35
4.4.3　模擬結果及效能分析36
第五章 結論與未來工作40
參考文獻41

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