在感知無線網路（Cognitive Radio，CR）領域中,次要使用者(Secondary User)如何選擇空閒的頻譜來傳輸是一項重要的議題。
然而，次要使用者在順利取得頻譜資源並開始傳輸之後,
遇到有主要使用者(Primary User)要傳輸資料時,為了不侵害到主要使用者的傳輸權利,
次要使用者必須中斷傳輸讓出頻譜。

有鑒於IEEE 802.11 標準中,主要使用者要傳輸需先等待一段DIFS頻譜空閒時間,
並且於競爭成功後才能開始傳輸資料。而在各種感知無線網路文獻中,
並未具體描述次要使用者是如何偵測到主要使用者的傳輸需求,也鮮少詳細提出次要使用者被中斷後，
未傳完的資料該如何處理。

因此,本論文針對此不足,在考量 IEEE 802.11 網路特性下,
提出一個兼顧主要使用者與次要使用者的碰撞避免機制與續傳機制。
透過模擬結果,本論文所提出的機制於吞吐量(Throughput)、平均跳頻次數(Hopping Times)、
及主要使用者的平均延時(Primary User's Average Delay)上均可優於文獻上相近之機制。

In a wireless Cognitive radio network, how do Secondary Users select an idle channel to transmit is an important issue.
However, if there are Primary Users need to transmit data after Secondary Users get resource and start to transmit ,
in order not to infringe upon the rights of Primary Users of the transmission, Secondary Users must be interruptted .

In view of the IEEE 802.11 standard, Primary Users need to wait for an idle period called DIFS ,
and success in the competition to begin transmitting data. The perception of wireless networks in a variety of literature,
not specifically describe how Secondary Users detect the Primary User's transmission needs,
but also rarely provided details on the secondary users's data transmission interruptted by Primary Users.

Therefore, this paper for this lack of features in IEEE 802.11 networks under consideration,
proposed a collision avoidance mechanism and resume mechanism of both the Primary Users and Secondary Users
Through simulation results,
we show that our mechanism proposed in this paper can outperform the closely related mechanisms on throughput,
average hopping times, and Primary Users' average delay time .

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