臺灣博碩士論文加值系統

近年來，隨著手機用戶的日益遽增，系統業者紛紛將單一基地台所涵蓋的範圍縮小，以增加所能容納的負載量。然而，基地台所涵蓋的範圍也因此縮小。很明顯的，交接次數將比以往更加頻繁，交接技術亦將日益重要。不間斷的通訊連接一直都是行動通訊的重要課題。為了提供移動中的手機用戶能持續埠斷地與基地台維持連線，『交接』程序必須夠快。而且，必須能夠適時的觸發交接程序，甚至是以預測手機的行為來觸發交接。另一方面，過多的交接程序將使得系統負荷量過重，且會浪費不必要的信令資源。因此，如何同時改善強迫中斷率和系統負荷量將是一大議題。
在本論文中，我們採用一種新的可適性交接演算法。這種演算法使得交接程序更適時被觸發，而且，也同時改善了系統負荷平衡的問題。正如模擬結果所示，這種交接演算法切確地改善了整體效能與服務品質。

With the mobile subscriber increasing, the cellular system will increase the amount of cells in the same geographic area. That is, the coverage of a cell will be smaller, and the handoff occurs more frequently. If handoff occurs slowly or happens frequently, the quality of service may degenerate below an acceptable level. Furthermore, the voice call may be dropout or the packet data will be lost. In order to reduce the network load due to switching cell, handover algorithms have to be
designed to minimize the number of handoffs. Conventional handoff algorithms use the threshold values and/or hyteresis margin to improve the performance.
However, the issues of handover in cellular communications have several components including handover initiation and traffic load balance (availability of channel resources). Often researchers consider these issues separately, but overall
performance should be determined by all. In this thesis, therefore, we adapted a new adaptive handover algorithm. Dwell time factor, cell load factor and a control timer are broached to the decision of handover. This algorithm based on these factors adjust hysteresis margin of each mobile station to make handover decisions more accurately and share the traffic loads of cells. By these factors, we reduce unnecessary handoff
rate and forced terminated probability successfully .

1. Introduction ……………………………………………………….………………1
2. Overview of Handover Techniques ………………………………………………4
2.1 Handover Types …………………………..………………………………...4
2.1.1 Depending on the gradations ……………………………………..4
2.1.2 Depending on channel usages ………………...……………….....6
2.1.3 Depending on the decisions ………………..…………………….6
2.1.4 MEHO inter-cell hard handoff …………………………………...7
2.1.5 Depending on the purposes …………...………………………….9
2.2 Handoff process and related issues ……………………………....................9
2.2.1 Handoff process ……..…………………………………………...9
2.2.2 Handover Issues …………..…………………………………….10
2.2.3 Other problems in cellular system ………………………………14
3. Conventional Handover Algorithm ……………………………………………..16
3.1 Conventional handover initiation algorithms ………………...……………16
3.2 Performance Criteria ……………………...………………………………19
4. Adaptive Handover Algorithm ………………………………………………….21
4.1 Introduction to our algorithm ……………………………………………..21
4.2 Design dwell time factor …………………..………………………………22
4.3 Design cell load factor ………………..…………………………………...24
4.4 Design control timer ……………………………..………………………..26
4.5 Adaptive Hysteresis function ………..……………………………………28
5. Simulation Methodology and Environment …………………………………...30
5.1 Simulation Methodology ……………..….…..……………………………30
5.1.1 New Call Blockings …….………………………………………31
5.1.2 Handover Call drops …………..………………………………..32
5.2 Simulation Environment ……………………………………………...…33
5.2.1 System model ….…………………………………………….…33
5.2.2 User Mobility Model ……..………………………………….….34
6. Simulation Results and discussion
6.1 Conventional algorithm with different Hysteresis ………………………...38
6.2 Proposed algorithm with adaptive Hysteresis ……………………………..41
7. Conclusions ……………………………………………………………………….45
Reference …………………………………………………………………………….46

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