臺灣博碩士論文加值系統

下一代無線網路之關鍵性目標包含稀少無線頻譜之高效率運用、服務品質之改良與各種多媒體服務之提供。分碼多重進接(code division multiple access, CDMA)的細胞式行動通訊系統可運用分集(diversity)技術來進行軟性交遞(soft handoff)。相較於中斷再連接之硬式交遞，連接再中斷之軟式交遞可在交遞期間提供更高的通訊品質。另一方面，行動用戶可具有不同之移動性，例如車輛與步行速度。如果細胞很小，則快速移動的行動用戶會造成交遞之頻繁出現；但如果細胞過大，則會造成頻率重用之降低，進而導致系統容量之減少。在階層式細胞網路中，一個上層的巨細胞覆蓋了 個下層相鄰的微細胞，其中微細胞可用來承載慢速移動用戶而巨細胞可用來承載快速移動用戶。微細胞層有較高的頻率重用，故可提供更高的系統容量，而巨細胞層則可降低快速移動用戶之交遞次數。因為正在進行之通話之中斷遠較一通新電話之無法接通更令人無法接受，所以我們通常給與交遞連結高於新連結之優先權。我們將提供交遞佇列給無法立即取得所需通道之交遞連結，以降低交遞連結之中斷機率。在本篇論文中，我們考慮支援軟式交遞之階層式細胞CDMA網路，其中將具有不同移動性的行動用戶指配到不同層，且提供交遞佇列給無法立即取得所需通道之交遞連結。根據是否提供交遞佇列於微細胞及/或巨細胞層，我們提出四種不同之佇列方法。我們運用多維馬可夫鏈(multi-dimensional Markov chain)來建立所考慮之系統之數學模型，並運用高斯-賽都(Gauss-Seidel)疊代方法來求得相關之穩態機率與因此感興趣之效能量度：新連結阻塞機率、交遞失敗機率及連結中斷機率。分析結果顯示同時在微細胞及巨細胞提供交遞佇列之模型可以獲得最大之系統效能改善。

The key goals of the next generation wireless networks include high utilization of frequency spectrum, improvement of quality of service and provision of various multimedia services. Code division multiple access (CDMA) cellular communication systems utilize diversity technology to perform soft handoff. Compared to break-before-make hard handoff, make-before-break soft handoff can provide higher quality of service during handoff. On the other hand, mobile users can possess different mobility, e.g., move at vehicular or pedestrian speed. If the cell size is too small, fast-moving users may cause frequent handoffs, whereas if the cell size is too large, frequency reuse will decrease and thus reduce system capacity. In hierarchical cellular systems, a macrocell in the upper layer covers N microcells in the lower layer, where microcells are used to carry slow-moving users, whereas macrocells are for fast-moving users. Microcell layer has higher frequency reuse and thus can provide higher system capacity, whereas nacrocell layer can reduce the number of handoffs of fast-moving users. As forced termination of an ongoing call is less tolerable than blocking of a new call, handoff calls are usually given priority over new calls. Handoff queues are provided for handoff calls that can not obtain the required channel immediately, so that forced termination probability is reduced. In the thesis, we consider hierarchical cellular networks supporting soft handoff, where users with different mobility are assigned to different layers, and handoff queues are provided for handoff calls that can not obtain the required channel immediately. According to whether handoff queues are provided in microcells and/or macrocells, four different handoff queueing strategies are proposed and studied. We derive the mathematical model of the considered system with multi-dimensional Markov chain, and utilizes Gauss-Seidel iterative method to find the steady state probability distribution and thus the performance measures of interest: new call blocking probability, handoff failure probability, and forced termination probability. Analytical results show that providing handoff queues in both microcells and macrocells can achieve largest performance improvement.

目 錄
中文摘要 I
英文摘要 II
目錄 III
圖目錄 V
表目錄 X
第一章 緒論 1
第二章 系統模型 7
2.1基本假設 7
2.2不同連結之指配方式 8
2.3流量模型 9
2.3.1新連結及交遞連結抵達速率 10
2.3.2連結服務時間 10
2.3.3停留時間 11
2.3.4通道服務時間 11
2.4 連結允入控制 12
2.4.1無佇列之允入控制 12
2.4.2有佇列之允入控制 13
2.5 四種佇列模型 15
第三章 數學分析 18
3.1 狀態轉移 18
3.1.1新連結抵達 18
3.1.2連結完成 19
3.1.3交遞連結離開 19
3.1.4交遞連結抵達 19
3.1.5區域轉換 20
3.2 微細胞流量之分析 20
3.2.1狀態特性 20
3.2.2狀態轉移速率 21
3.2.3流量平衡方程式及穩態機率 27
3.2.4效能量度 28
3.2.4.1佇列方式 28
3.2.4.2無佇列方式 30
3.3 溢流流量模型 32
3.4 巨細胞流量之分析 33
3.4.1狀態特性 33
3.4.2狀態轉移速率 34
3.4.3流量平衡方程式及穩態機率 49
3.4.4效能量度 50
3.4.4.1佇列方式 50
3.4.4.2無佇列方式 53
3.5整體之效能量度 55
3.5.1疊代演算法 58
第四章 數值結果及分析 59
4.1相關參數 59
4.2流量參數變化之評估 60
4.2.1不同模型之比較 60
4.2.2通道容量之影響 63
4.2.3佇列大小之影響 64
4.2.4移動性之影響 64
4.3分析結果的評估 66
第五章 結論 91
參考文獻 94

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