IEEE 802.16標準是一種都會型無線網路的協定，並支援點對多點（point to multi-point）和網狀（mesh）兩種模式。而在IEEE 802.16標準網狀模式中，網路資源的分配可以用集中式（centralized）及分散式（distributed）兩種排程模式來做處理。在分散式排程模式中，每一節點利用EBTT（election-based transmission timing）的競爭機制與其二跳躍內的節點共同競爭控制子訊框傳輸排程資訊的機會。而資料子訊框內迷你時槽（minislot）的配置係採用三向交握（three-way handshaking）的機制，與相鄰節點間交換Request、Grant及Confirm等排程資訊，而迷你時槽的利用率對於媒體存取控制層的排程效能是相當重要的一項議題。
由於資源的不足及節點無法得知距離為二跳躍（2-hop）的節點之排程資訊，使得三向交握過程發生要求失效的問題，如主要衝突（primary conflict）及次要衝突（secondary conflict）等問題，而導致三向交握於Grant階段或Confirm階段發生失效，此三向交握失效問題將會導致傳輸產能的降低。
在本論文中，我們提出了二個強化分散式排程的方法，稱為部份回應機制（partial grant scheme；PGS）及預先配置機制（pre-allocation scheme；PAS）以降低三向交握的失效率，藉以改善網路資源的利用率。經由模擬結果顯示，部份回應機制可有效降低Grant階段所發生的失效率，而預先配置機制則可有效降低Confirm階段所發生的失效率。當同時採用部份回應及預先配置機制時，不論輕載或重載時，三向交握失效率均可獲得降低，進而提昇系統產能。

The IEEE 802.16 standard is a protocol for wireless metropolitan networks. IEEE 802.16 MAC protocol supports both of point-to-multipoint（PMP） and mesh mode. In the 802.16 mesh mode, network resource allocation can be handled in the centralized and distributed scheduling modes. In the distributed scheduling mode, every node competes for channel access using election-based transmission timing mechanism based on the MSH-DSCH Scheduling IE of the two hop neighbors. The minislots in data subframe are allocated based on a three-way handshaking mechanism by exchanging the Request , the Grant, and the Confirm information among the nodes. The minislot utilization is essential to achieving good performances of MAC-layer scheduling.
Because resource limited and local nodes do not know the exact scheduling information of 2-hop neighbors, the grant messages sent back by the receiver have the chance to conflict with other’s decision, known as primary and secondary conflict and cause three-way handshaking invalid in Grant step or Confirm step, and thus decreases throughput.
We propose two novel distributed scheduling schemes, known as partial grant scheme（PGS） and pre-allocation scheme（PAS） to decrease three-way handshaking invalid and improve network utilization. Our simulation results show that the PGS scheme can decrease Grant step fail and the PAS scheme can decrease Confirm step fail efficiency. The PGS+PAS scheme is better in throughput and three-way handshaking invalid ratio than others in light and heavy loading.

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