WiMAX網路上傳具品質服務保證之公平排程機制

Abstract

在IEEE 802.16無線寬頻網路中，依據不同的品質服務保證需求定義出了各種不同的服務類型。然而，在最新的IEEE 802.16標準中，如何來排程不同的服務類型並沒有明確被定義，而在某些現有的研究當中，採用了一種嚴格優先權式排程，也就是當完成了高優先權的類型頻寬配置後，如果還有剩餘的頻寬時，才執行低優先權的服務類型之頻寬配置。如果用此方法來排序頻寬配置先後，將會造成低優先權的服務類型因為遲遲得不到頻寬配置，或者頻寬皆被高優先權的服務類型所佔據，而發生飢餓現象。為了改善這種不公平的現象發生，本篇論文提出了一個新的機制，”雙層式排程演算法”，來提升頻寬配置的公平性，也確保了品質服務保證的特性。在此改良的機制當中，第一層實作了服務串流的分類，分別依據各個串流的滿足程度來分類，可分成”未滿足”，”已滿足”，和”過度滿足”三種。而第二層的機制用來計算各個不同的串流在不同的類別當中所代表的權重，並且實作了頻寬配置。在模擬結果中，可證明不僅品質服務保證能夠確保，而且改善了頻寬配置的公平性。

IEEE 802.16 Broadband Wireless Access (BWA) Network supports classes of traffic with differentiated Quality of Service (QoS). However, the detailed of how to schedule traffic are left unspecified. While in some recent studies, traffic scheduling performs Strict Priority Scheduling (SPS). And the priority order is followed as UGS>rtPS>nrtPS>BE. While in this scheduling method, starvation of lower priority traffic will happen. The proposed scheduling algorithm is designed in purpose of fairness improvement. We propose a new scheduling algorithm called Two-Tier Scheduling Algorithm (2TSA). The first tier is category-based and the second tier is weight-based. Both tiers are implemented at BS. The first tier classifies all connections into three categories, Satisfied, Unsatisfied, and Over-satisfied. The second tier calculates weights of each connection differently in each category and performs bandwidth allocation. The simulation result shows that our proposed algorithm can achieve both QoS guarantee and fair bandwidth allocation.