隨網際網路的普及與相關技術日新月異，IEEE 802.16無線寬頻都會網路(WMAN)是一種優異的無線通訊技術以提供使用者能自由且快速的進行無線資料通訊服務，其主要運用在固定用戶端與移動用戶端之無線寬頻網路存取。由於使用者(MS)在不穩定的無線環境下進行資料傳送與接收，可能發生資料接收錯誤，因此透過自動重傳請求(Automatic Repeat Request; ARQ)機制回報接收狀態並要求重送來確保接收端正確接收到資料。IEEE 802.16規格中定義四種不同的ARQ回報種類，而每一種回報種類擁有自己相對應之格式。不同的回報格式會產生不同的訊務長度與回報能力。 接收端使用規格中所定義之ARQ Feedback IE回報所接收區塊正確與否，傳送端視回報訊息重送錯誤區塊，確保資料能夠正確傳送。因為規格中沒有定義如何使用回報種類，若使用單一回報方式可能於特殊情況下無法獲得最佳的效能與最少的回報封包數量，導致自動重傳請求機制無法能夠快速地重送錯誤之資料。因此，為了提升自動重傳請求機制之效率與減少回報的封包數量，在此論文中，我們提出了一個具調適能力之回報機制讓接收端能動態評估目前所接收的資料區塊以及歷史訊息，快速求得目前最佳的回報種類，使傳送端能更快速的接收回報訊息並重傳錯誤區塊。本文會先解釋並圖例IEEE 802.16自動重傳請求機制，並提出改良方案。論文模擬並比較各種回報機制對系統的使用率的影響。模擬結果顯示，所提出之機制可於不同的環境下動態選擇回報的方式並獲得最佳的效能。 The IEEE 802.16 wireless metropolitan area network (WMAN) standard is an advanced wireless communication technology, which is designed to provide ubiquitously and fast communication services for mobile station (MS). In an error-prone wireless environment, receiver is likely to fail to receive data sent from transmitter. To curb this problem, automatic repeat request (ARQ) mechanism is usually adopted to synchronize the reception status between transmitter and receiver. That is, receiver is responsible to report acknowledge information of received data blocks to the transmitter and the transmitter retransmits those erroneous data blocks received by receiver in order to achieve reliable data delivery. Four different ARQ report types have been defined in IEEE 802.16e-2005 standard, and each report type has its specific format, overhead and report capability. The receiver is free to use any ARQ type to indicate which blocks are correct and incorrect. However, from our observations, using improper type to report statuses of blocks may cause extra signal overhead and response time. Unfortunately, the 802.16e-2005 standard does not specify the policy of choosing ARQ report type. As a solution, this thesis proposes a simple policy for optimizing the ARQ report scheme. In order to enhance the efficiency of ARQ mechanism and decrease the number of required report frames, this study focuses on the adaptive and hybrid reporting scheme, which still complies with standard. The concept of adaptive reporting scheme is to dynamically evaluate the most proper method for reporting according to the present statuses of received blocks. Simulation results demonstrate that, with this adaptive reporting scheme, the transmitter could quickly receive the report frame and retransmits data blocks if any. This thesis will first elaborate and illustrate the operations of ARQ mechanism defined in IEEE 802.16 standard. After then, the proposed scheme is introduced and the performance of proposed scheme will be evaluated by simulations. Simulation results will show that the dynamic choice of report types will obtain the best performance in all cases.
