近年來，行動裝置透過無線網路(Wireless Network)進行上網的使用已經非常普及，隨著無線區域網路(Wireless Local Area Network)的迅速發展，WLAN內的行動節點(Mobile Node)也越來越多，當MN隨著使用者移動時會因為AP(Access Point)服務範圍的限制，需要切換至不同的AP，以達到網路服務不中斷的目的，這樣的自動切換連線的機制稱為換手(Handoff)，每當MN當下連線的AP之接收訊號強度(Received Signal Strength)下降至一定的門檻時，將會啟動換手機制，尋找其他適合連線的 AP，並切換連線至適合的AP，當MN啟動換手機制時會造成換手延遲(Handoff Latency)，過長的換手延遲會影響即時性服務(例如：網路電話)的服務品質(Quality of Service)。此外，還需考慮換手的正確性，在無線網路的架構下，無線射頻訊號容易受環境因素干擾，例如：建築、鄰近頻道干擾(Adjacent Channel Interference, ACI)、藍芽等，會使MN的RSS不穩定，導致有不必要換手產生。
本論文提出具趨勢預測及自適應性預先掃描的換手(Trend-Forecasting and Adaptive Pre-scanning Handoff)，簡稱TFAPH，利用TFAPH換手機制改善換手延遲及正確性。

Recently, the mobile device surf the internet with Wi-Fi that is very common. Along with the rapid development of wireless local area network (WLAN), and therefore the increase of the mobile node (MN). When a MN moves from one basic service set(BSS) to another BSS, handoff mechanism will be performed. The execution of handoff depends on the Receive Signal Strength (RSS). When the RSS of MN decrease below a specific threshold value, handoff occurs. However, the handoff latency will affect the QoS (quality of service) of real-time application such as VoIP (voice over IP) service. Moreover, due to the RSS is unstable over the air, unnecessary handoff issue should be considered. Therefore, the error correction of handoff is very important. In order to keep the connection of internet service, the handoff mechanism is necessary.
To consider the unnecessary handoff and handoff latency issue, we proposed a Trend-Forecasting and Adaptive Pre-scanning Handoff mechanism to ensure the QoS of real-time application in 802.11 WLANs.

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