臺灣博碩士論文加值系統

頻道分配方法是用來解決無線網路系統頻譜資源不足，交通量變化迅速且各細胞基地台的交通量不均勻的問題。在頻道分配之前，有兩個主要的參數需要參考:新服務要求的拒絕率與交遞服務要求的中斷率。從服務品質的角度來說，中斷一個交遞服務要求對服務品質的傷害遠大於拒絕一個新服務要求，所以在分配頻道時，應給予交遞服務要求較高的優先等級。為了保持交遞服務要求的優先等級，保衛頻道策略(Guard Channel, GC)保留了一些固定數量的頻道專門供交遞服務要求使用。分配固定數量的保衛頻道，這種策略實施簡單但是無法適應交通量的變動，容易造成頻道的浪費或效率不彰。本研究的方法擬利用馬可夫模型(Markov model)計算在維持一個水平下，不同交通量之交遞服務要求需要的頻道數，並根據新服務要求與交遞服務要求的到達率比例來設立一個門檻值。這個門檻值會依照交通流量動態調整，當使用量超過門檻值時，利用模糊邏輯技術讓新服務要求能夠使用保衛頻道或是向周圍交通量輕的細胞基地台借用頻道。如果基地台內已無可使用的頻道，則新服務要求與交遞服務要求皆可向周圍交通量輕的細胞基地台借用頻道。研究結果顯示出此方法在交通量變化的狀態下，能夠將交遞服務要求的中斷率控制在一定的水平下，而新服務要求也有較高的彈性，並透過借用頻道的方法使得各細胞基地台的負載量能夠較為均衡。

In this paper, an adaptive channel assignment scheme is proposed to ensure the quality of services for the wireless networks. The proposed scheme based on the FCA (fixed channel assignment) strategy divides the channels into two categories, the guard channels and the shared channels. The number of guard channels is estimated by the Markov Model. The shared channels can be used by both new calls and handoff calls. This new scheme based on the fuzzy process can allocate most guard channels to the handoff calls and few to the new calls. In addition, the proposed scheme provides a load balance method for balancing the channel utilization between adjacent cells. From the simulation, the proposed scheme significantly improves the drop rate and the block rate in comparison with the existing methods.

Chapter 1 Introduction...................................1
Chapter 2 Previous Works.................................4
2.1 Channel Assignment Methods.........................4
2.2 Guard Channel Method...............................5
2.3 Channel Balance Methods............................6
Chapter 3 Dynamic Channel Assignment and Balance.........9
3.1 Markov Model.......................................9
3.2 Fuzzy Assignment Method of New Calls..............12
3.3 Borrowing Scheme..................................14
Chapter 4 Simulation Result.............................18
Chapter 5 Conclusions...................................31
Reference...............................................32
Appendix................................................34

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