許多新興的通信技術在近年來已經被發展為在無線都會區域網路(WMAN)裡提供高速和可靠的服務。IEEE 802.16e就是這樣的技術之一，並且已經被制訂來應用於固定和移動的寬頻無線存取系統。為了節省一個具移動性用戶端(MS)的可使用能源資源，IEEE 802.16e採用了睡眠模式。而在這篇論文中我們提出在壅塞情況下改進睡眠模式運作的能源效率的一個新的機制。因為框架間隔非常短，所以當網路發生壅塞時，基地台(BS)不能在一個框架間隔其間傳送它全部暫存的封包給處於睡眠模式的移動性的用戶端。這引起移動性的用戶端浪費額外的能源等待傳送給它們的封包。因此，在我們提出的方法中，名為Scheduled-TIM，基地台給定移動性的用戶端一個醒來的數值，表明移動性的用戶端只需要醒來的框架與流量指示訊息被傳送的框架之間的偏移量。以這種方法，移動性的用戶端 能更有效地使用他們的能源。我們的模擬結果顯示我們能夠有效地改善睡眠模式的能源效率。

Recently, many emerging communication technologies have been developed to provide high-speed and reliable services in Wireless Metropolitan Area Network (WMAN). The IEEE 802.16e is one of such technologies and has been standardized for fixed and mobile broadband wireless access systems. To conserve the available power resources of an Mobile Station (MS), the IEEE 802.16e adopt the sleep mode. In this thesis, we present a novel mechanism that improves the energy efficiency of the sleep mode in case of congestion. Since the frame interval is very short, the Base Station (BS) cannot transmit its whole buffered packet to the MSs in sleep mode during one frame interval when traffic congestion happens. This causes MSs to squander extra power to wait the pending packets. In our proposed scheme called Scheduled-TIM, BS assigns MSs the wakeup value which indicates the offset of frame where MS only needs to wake up with respect to the frame where the Traffic Indication Message (TIM) is transmitted. In this way, MSs can use their energy more efficiently. Our simulation result shows that we have better performance with respect to power efficiency.

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