無線網路初期以固定式無線存取技術為主，隨著時代的進步，新規格不但支援可移動之通訊服務，更積極發展高速度下之行動通訊。然而行動台在移動時會受到基地台的干擾問題以及經由通道所接收到的各種衰落影響。除此之外，當行動台在系統中移動時，由於行動台與基地台距離發生變化，因此行動台所接收到的訊號會有所變動，當接收訊號越來越弱時，相對來說干擾也就越來越大。因此行動台想要維持好的服務品質就要使用換手技術，以確保資料能正常傳送，因此換手主要目的就是讓行動台不會因為移動而與基地台間之連線中斷。
本篇論文的通道模型適用於發展高速無線通訊系統。在此模型中，行動台所接收到的訊號強度包含二種主要的通道模型，包括大範圍訊號衰減所產生的遮蔽衰落模型，和瑞雷衰落(Rayleigh fading)所產生的快速衰落模型，並且討論四種由基地台和行動台間所產生的干擾問題進行分析與討論。
在換手的方式中，最主要的就是硬式換手與軟式換手二種方式。硬式換手藉由行動台與基地台間的訊號強弱來決策換手，並且使用遲滯值(Hysteresis)的方式來降低換手次數。在本篇論文中將討論行動台從時速六十公里上升至時速三百五十公里進行換手所發生的現象。藉由改變頻率重覆使用因子(reuse factor)、基地台間的覆蓋率(overlapping)和遲滯值的方式來降低換手次數並且提升系統效能。基於所設計的換手機制，我們藉由模擬許多的無線通道環境來描繪並發展出有效率的演算法。

In the past the access of wireless network was mainly emphasized on the fixed mode transmission. As time goes by, new standards and their associated wireless communication networks have been designed and developed lately to support high mobility users. When a mobile moves around and through a series of base stations the user will receive signals not only from its serving and neighboring base stations but also from its surrounding radio environment so that the user’s received signal strength will encounter various kinds of fading and interference effects. Furthermore as the user moves its received signal strength from its serving base station may be degraded time to time and it needs to be handover to other base station to maintain its quality of communication and to avoid it from dropping of service. 
In this thesis a channel model that is suitable for use in the high mobility wireless communication system is developed. In this model the mobile received signal strength is formulated it consists of two parts one is the long range signal attenuation with the accumulation of lognormal scattering factor and the other part is the fast fading attenuation that is mainly contributed from the Rayleigh fading effect. Four kinds of interferences from its neighboring base stations are discussed and analyzed, their effect on the quality of service are reviewed.
Hard and soft handoffs are considered in this thesis for mobile speed varying from low of 60 km/hr and up to 350 km/hr. The handoff phenomena and its effect on the system performance are widely discussed by varying the overlapping areas between base stations, the reuse factor, and the hysteresis value, i.e. the handoff threshold between the signal strengths of the serving and target base stations. Based on the handoff algorithm developed we have simulated many examples of the radio environments to depict the effectiveness of developed algorithm.

目錄
第一章	緒論 ……………………………….….…….…..1
1.1 研究動機與目的 ……………………………..…………...1
1.2 章節介紹 ……...………………..………..………………..2

第二章	無線通訊系統之分析……………………...……3
2.1 IEEE 802.16m 系統介紹…………………………...……...3
2.2 OFDMA系統之換手方式………………….…...................4
2.2.1 硬式換手 ……………………………….….....................8
2.2.2 軟式換手……………….………………………………...9
2.3 無線通訊系統之干擾………….…....................................12
2.3.1無線通訊系統之干擾介紹………….…..........................12
2.3.2 利用控制訊號降低IEEE 802.16m中UL/DL之干擾..15

第三章	通道及干擾模型……………………………….28
3.1	路徑損失模型 ..……….………………………………….28
3.2 遮蔽衰落模型………………….........................................35
3.3 快速衰落模型…………………..…...................................38
3.4 同頻道間干擾模型………….............................................42

第四章	模擬分析與研究……………………………….46
4.1行動台之系統路徑模擬…………………...........................47
4.2不同速度下之換手分析…………………………………...49
4.3使用Pilot降低同頻帶間之干擾….....................................57
4.3.1使用Pilot降低基地台間之干擾………………………..57
4.3.2使用Pilot降低Cluster間之干擾………………………..61

第五章	結論與未來展望……..……………………...…65

參考文獻……………………………………….…………66

圖目錄
圖2.1 行動台啟動換手流程圖…..…...…...…….………...…………………7
圖2.2 基地台啟動換手流程圖…..….……………..……...…………………7
圖2.3 硬式換手流程…..…………….…………..……...……………………9
圖2.4 宏分集切換…..….………………….……...………...………………11
圖2.5 快速基地台切換..…..……..….…………………...…………………12
圖2.6 行動台在基地台邊緣造成的干擾示意圖................………………..13
圖2.7 行動台在Sector邊緣造成的干擾示意圖............…......……………13
圖2.8 在TDD中資料傳輸時造成的干擾示意圖.….…………..…………14
圖2.9 在FDD中資料傳輸時造成的干擾示意圖……………....…..……...14
圖2.10 (a) TDD模式中控制訊號框架結構…..……………..………..……16
圖2.10 (b) FDD模式中控制訊號框架結構…..……………...……….……16
圖2.11 DL控制訊號中的基地台管理資訊…...……….…………...………17
圖2.12 UL控制訊號中的基地台管理資訊…....…………………...………18
圖2.13 分配不同的子訊框給不同干擾大小的行動台…..….….…………19
圖2.14 利用MAP定義在基地台邊緣或基地台中心的使用....…..………19
圖2.15 正方型Pilot型式…..………….………………………...……….…20
圖2.16 直線Pilot型式…..……..……..………………………….…………20
圖2.17 正方型Pilot型式之干擾權重…………..…………………………21
圖2.18 正方型Pilot型式之干擾權重……..………………………………22
圖2.19 在TDD模式中不同Sector的Pilot指定方式…………..…………23
圖2.20 指定Pilots於TDD模式的子訊框…………………………………23
圖2.21 在TDD模式中不同Cluster中Pilot的指定方式……….…………24
圖2.22 在FDD模式中的Pilot指定方式………………………..…………25
圖2.23 指定Pilots於FDD模式中DL 和UL的子訊框….………………25
圖2.24 基地台邊緣干擾示意圖………...………………….………………26
圖2.25 正交Pilot型式指定於基地台1和基地台2邊緣中的行動台….....26
圖3.1 不同環境下之路徑損失…………………….……….………………30
圖3.2 室外之路徑損失模型…………………….…………….……………34
圖3.3 室內之路徑損失模型…………….……….…………………………34
圖3.4 遮蔽效應示意圖……….………………….…………………………35
圖3.5 不同速度下遮蔽衰退之訊號強度…….….…………………………36
圖3.6 不同速度下遮蔽衰退之自相關函數…….…….……………………37
圖3.7 遮蔽衰退機率密度函數………………….…………………….……38
圖3.8 具有直射波之傳播路徑…………….…….…………………………39
圖3.9 不具有直射波之傳播路徑…………..….….………..………………39
圖3.10 Rayleigh Fading、Rician Fading訊號強度示意圖…..……..….……40
圖3.11 傑克斯模型…………………………………………..…..…………41
圖3.12(a) 同頻道間干擾模型示意圖(reuse factor 1~4)….…….…………42
圖3.12(b) 同頻道間干擾模型示意圖(reuse factor 5~7)……….….………43
圖3.13 不同頻率重複因子使用下之基地台邊緣SIR值...…...……..……44
圖3.14 不同頻率重複因子使用下基地台邊緣之頻寬………..………..…45
圖4.1 路徑一與訊號強度示意圖……...……..………………….…………47
圖4.2 路徑二與訊號強度示意圖………...……...……………....…………48
圖4.3 路徑三與訊號強度示意圖…………………..……...…….…………48
圖4.4 路徑四與訊號強度示意圖………...….…………………..…………49
圖4.5 換手系統流程圖…………………….……………..……...…………50
圖4.6 基地台之訊號強度及靈敏度示意圖……….…………….…………50
圖4.7 不同速度下之換手斷話率(reuse factor=1)……...……….…………52
圖4.8 不同速度下之換手斷話率(reuse factor=7)……...……....…….……52
圖4.9 基地台覆蓋率示意圖………………………………...…..….………53
圖4.10 不同速度下增加基地台間覆蓋率之系統斷話率…………………54
圖4.11 不同速度下增加基地台間覆蓋率之換手率………………………55
圖4.12 不同速度下增加系統遲滯值之斷話率…………………....………56
圖4.13 不同速度下增加系統遲滯值之換手率………………...….………57
圖4.14 行動台和基地台間之訊號及干擾路徑示意圖………….…..….…59
圖4.15 行動台和同頻率間之基地台訊號及干擾路徑示意…..……..……62

表目錄
表2.1 基地台和行動台中所有可能的干擾權重結果(型式一)…...………21
表2.2 基地台和行動台中所有可能的干擾權重結果(型式二)…....……...22
表2.3 干擾權重相對於三個Cluster中DL和UL 的Pilot 指定方式…….24
表3.1 不同環境下之路徑損失指數n ………………..…………………...30
表3.2 IEEE 802.16m 遮蔽衰退標準差………………….………….……...37
表4.1 系統模擬參數…...…………………………………...………….…...46
表4.2 頻率重複因子為1之模擬環境…………………….………………..58
表4.3 行動台與不同基地台之訊號強度和基地台Pilot型式…...………..59
表4.4 使用干擾降低Pilot與沒有使用的基地台干擾量模擬結果...……..60
表4.5 頻率重複因子為19之模擬環境……………………………....…….61
表4.6 行動台與同頻率之不同基地台訊號強度和基地台Pilot型式…….62
表4.7 使用干擾降低Pilot與沒有使用的基地台干擾量模擬結果……….64

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