無線網路提供了使用者可隨時隨地存取網路服務的優點。然而，在傳統無線網路的低速傳輸環境下，無線系統只能提供使用者語音服務和低速的資料傳輸服務，並無法支援高頻寬需求的多媒體服務，為了提值高速的無線傳輸服務，3GPP(Third-Generation Partnership Project)組織提供了以分碼多工(CDMA, Code Division Multiple Access)技術為基礎的W-CDMA(Wideband CDMA)第三代無線通訊系統。
在無線網路系統中，無線電頻譜是相當珍貴的資源，因為無線電頻譜的使用效率將決定無線網路的系統容量。隨著第三代無線通訊系統的迅速發展，多樣化網際網路服務，勢必消耗大量的無線電資源。所以如何有效率運用無線電資源，將是個相當重要的議題。然而在第三俴無線通訊系統標準軟式換手方法，並無法有效率地使用下載鏈路無線電資源，因而降低整體系統容量。
因此在3GPP中，另一種換手方法基地台選擇(SSDT, Site Selection Diversity Transmission)被提出，以節省下載鏈路無線電資源使用。但基地台選擇方法，無法有效適用於不均衡的系統負載與多樣化的網際網路服務，造成服務品質(QoS, Quality of Service)低落。故本篇論文提出增進服務品質軟式換手演算法。增進服務品質軟式換手演算法是依使用者服務品質需求與系統負載狀況，從手機的活動集合(Active Set)中挑選出一個或多個適合的基地台作為下戴鏈路(down link)資料傳輸。以求在使用者服務品質保證前題下，減少不必要的無線電傳輸以增進無線電資源的使用效率。模擬結果顯示，增進服務品質軟式換手演算法在服務品質保證與無線電資源使用效率上，均獲得顯著成效。

[1] [Online]. Available: http://www.3gpp.org.

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