臺灣博碩士論文加值系統

我們提出一分配通話頻道的機制，應用在無線通訊網路雙層架構下，所有可使用頻道由高層微細胞基地台及低層微細胞基地台共享。此機制主要運用動態分配頻道的方式，整合其他機制包括:通話中使用者的優先權、區域性最密堆積法(local-packing)、被保留頻道可與被相互干擾鄰近基地台(interference cell)共用、從低層微細胞基地台溢出(overflow)至高層微細胞基地台。
在基地台分散的網路環境裡，這些機制透過各基地台所維護的資料庫表(ACOR table)，獲得頻道使用狀況而運作。此資料庫表儲存基地台本身頻道使用狀況及相互干擾的基地台頻道使用狀況，並由基地台彼此交換訊息而更新。
我們從模擬的結果可看出，在雙層網路架構下，此整合機制對於降低通話中使用者被中斷的機率有較好的成效，但不造成嘗試通話的使用者增加過多失敗的機率。影響此結果的因素有二：通話中使用者在不同方向非等機率移動的模式，以及通話中使用者在高層微細胞基地台與低層微細胞基地台所待時間的不同。
此外，我們設計從低層微細胞基地台溢出至高層微細胞基地台的機制已包含在被保留頻道可與相互干擾鄰近基地台共用的機制中，因此不需要額外增加流程即達到此效果。

We propose a channel assignment strategy, called Hierarchical cellular system - Prioritized Handoff Dynamic Channel Allocation strategy (HPHDCA), for use in hierarchical cellular networks, in which channel resources are shared by both tiers of cells. The HPHDCA is essentially a DCA scheme with additional operational features including prioritized-handoff, local-packing, reservation-sharing and overflow. In distributed operation environment, these features are achieved through looking up channel status maintained in an ACOR table. The ACOR table is developed to support enough information of channel usage patterns of interference cells sufficient for each cell to determine channel allocation by itself. By the mobility of nonuniform transition probability between cells and different dwell time distribution in microcells and macrocell-only areas, simulations show that the HPHDCA in macrocell/microcell overlay is able to yield favorable performance on handoff call blocking over new call blocking, at the cost of new call blocking probability. One additional feature is found that HPHDCA takes the conventional overflow technique completely into the reservation-sharing scheme, with no need to crank up a new overflow mechanism.

Abstract (in Chinese)i
Abstract (in English)ii
Acknowledgmentiii
Table of Contentsiv
List of Figuresvi
List of Tablesix
Chapter 1 Introduction 1
1.1 Introduction1
1.2 Background2
1.2.1 Hierarchical Networks2
1.2.2 Prioritized Handoff3
1.2.3 Distributed DCA Schemes4
1.2.4 Local Packing and ACO Table4
1.3 Objective5
1.4 Thesis organization6
Chapter 2 System Model7
2.1 System model7
2.1.1 Hierarchical cellular system7
2.1.2 Traffic model9
2.1.2.1 Traffic pattern9
2.1.2.2 Nonuniform transition probability10
2.2 Channel allocation11
2.2.1 Channel assignment strategy11
2.2.1.1 ACOR table pattern11
2.2.1.2 Reserve channel for handoff attempts13
2.2.1.3 LP algorithm15
2.2.1.4 The algorithm of sharing reserved channels16
2.2.1.5 Overflow to macrocell17
2.2.2 System operation and channel allocation algorithm17
Chapter 3 Simulation models22
3.1 Network topology22
3.2 Table ACOR and Interference cells24
3.3 Traffic model26
3.3.1 Nonuniform transition probability26
3.3.2 Traffic pattern27
Chapter 4 Simulation Results29
4.1 Simulation parameters29
4.1.1 Offered load in HPHDCA30
4.2 Simulation results31
4.2.1 Results from using 105 available channels31
4.2.1.1 New-call blocking probability31
4.2.1.2 Handoff blocking probability37
4.2.2 Results from using 210 available channels43
4.2.2.1 New-call blocking probability43
4.2.2.2 Handoff blocking probability48
4.2.3 The effect of channel reservation R on blocking probability54
Chapter 5 Conclusion and Future Work57
Appendix A59
References68

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