隨著無線通訊的技術的成長，未來的行動通訊網路應包含多種不同的網路技術，也因此行動裝置應要有能力接受多模式之通訊技術，其中移動管理演算法之設計可確保使用者在移動過程中能夠保持通訊狀態更甚者提高其傳輸能力；在行動通訊技術，例如：3G提供較高速的移動速度但較低的傳輸速率，相對的，IEEE 802.11 WLAN提供高傳輸速率但較低的移動速度；這些不同的網路系統共同存在於我們的週遭以提供計算與通訊的環境，也因此行動裝置應配置多網路介面以利在任何時間與地點與各類型網路相連結．而整合這些異質之網路便形成了一種階層式網路系統。 換手對行動通訊系統而言是相當重要的一種功能，它是用來將一行動裝置之通訊由舊基地台轉移到新基地台的程序，在異質整合網路中被命名為垂直式換手；一般而言，垂直式換手被分成三個步驟：換手初始化，決定換手，執行換手，其中決定換手扮演了決定通訊品質的重要角色；由於無線存取網路之傳輸速率增加，令使用者可於行動中使用大傳輸量的即時性通訊服務，因此對於服務品質較高之即時性通訊服務，應於換手決策時考量其服務品質之保證。 本論文主要目標為提出一個異質整合網路架構之垂直式換手決策機制，利用一個函式判斷目前候選網路之能力，並依照使用者之通訊類型分別考量換手的可行性及必要性，以有效降低換手之頻率並提高整體網路效能的表現，提供給使用者一個更好的通訊品質。 According to the development of the wireless communication technologies. The wireless communication network should consist of several wireless network technologies in the future. And the mobile devices should be able to communicate with multiple network technologies. There are several wireless network technologies coexist to provide computing and communicating capability. The mobility management could assure of the connection when user is roaming in the heterogeneous wireless networks. Handoff is a very important function for the mobile communication network. It is a procedure of transferring the connection from old base station to new base station. It is called vertical handoff in heterogeneous networks. Generally speaking, vertical handoff was formed by: handoff initialization, handoff decision, handoff execution. Because of the increasing of transmission rate of mobile communication technologies. Users could utilize real-time service with large transmission rate. We hope to reduce the frequency of vertical handoff and enhance the performance of the efficiency. Therefore, in this paper, we bring up a handoff decision scheme for heterogeneous networks. We make the decision according to the user’s communicating type and the performance of the networks. The results of simulations show that the scheme reduces the frequency of vertical handoff and enhance the performance of the efficiency.
