IEEE 802.16無線都會網路標準，也可稱為WiMAX，已成為一項極具潛力之4G無線技術。在WiMAX中，基地台針對都會區提供高速進接以及透過點對點連線來服務用戶台。WiMAX支援五種流量UGS、rtPS、ertPS、nrtPS和BE。UGS、ertPS和rtPS屬於即時性流量且使用免競爭機制，然而nrtPS和BE屬於非即時性流量且使用競爭機制。明確的說，一個非即時流量的封包要傳送時，首先要先送出頻寬請求去做頻道競爭。一旦它在競爭中獲勝，用戶台就會尋求獲得來自基地台的允許以完成頻寬預留。在這篇研究中，我們著重在被nrtPS和BE使用的頻寬請求機制。因為一些以競爭為基礎的服務可能包含語音和影像的封包，這些封包需要較佳的處理，所以在以競爭為基礎的流量間提供優先權的差異化是必要的。首先，我們在頻寬請求進階競爭階段中提供群組機制去降低頻繁的碰撞。除此之外，每個群組中的站台可以有不同的競爭參數，像是初始視窗大小和最大視窗大小。第二，每個群組中的站台可獲得不同的允許機率。我們推導一個解析方法，並且就每一個群組的成功送達率、平均延遲、封包丟棄率和碰撞機率去研究提出之優先權化頻寬請求機制的效能。最後但並非最不重要的，我們使用C語言來撰寫電腦模擬程式，且以獲得的電腦模擬結果來驗證數學解析結果的正確性。對於我們所考慮的情形，解析結果皆接近模擬結果。

he IEEE 802.16 wireless metropolitan area network standard, which is also known as WiMAX, has become a promising 4G wireless technology. In WiMAX, the base station provides a high rate access for a metropolitan area, and the subscriber stations (SS) are served via point-to-point links. There are five types of traffics supported: UGS, rtPS, ertPS, nrtPS, and BE. Real-time traffics, e.g., UGS, ertPS and rtPS, are served using a contention-free mechanism, whereas non-real-time traffics, e.g., nrtPS, and BE, are served using a contention-based mechanism. Specifically, for a non-real-time traffic with packets to send, first, bandwidth requests are sent to contend for channel access. Once the bandwidth request wins the access contention, the SS seeks to obtain a grant from the base station to complete the bandwidth reservation. In this work, we focus on the bandwidth request mechanism used by BE and nrtPS. Since some contention-based applications may include voice and video packets and thus need better treatment, prioritization is necessary to provide service differentiation among contention-based traffics. First, we provide the grouping mechanism to alleviate the frequent collisions during bandwidth request access contention phase. Furthermore, each group of stations can have different contention parameters, e.g., initial window size and maximum window size. Second, each group of stations can be assigned a different request granting probability. We derive an analytical method to study the performance of the proposed prioritized bandwidth request mechanism in terms of throughput, mean delay, dropping probability, and collision probability for each group. Last but not least, analytical results are validated via simulation results, and the simulation program is written in C language. The analytical results are close to the simulation result for the cases studied.

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