基於長程演進系統之使用者協助式動態無線資源狀態轉換機制的設計

Abstract

隨著行動裝置效能的提升，使用者可以在同時間運行多個應用程式，其中有些應用程式即使使用者沒有與之互動仍然會有一些自發性的封包在使用者與網路之間傳輸，我們稱之為背景訊務。當使用者在背景訊務期間保持無限資源連線狀態，此期間所發生的換手事件將付出信令負載而降低無線資源的效能，在長程演進系統中，為了降低換手所造成的信令負載，基地台會釋放無線資源連結讓使用者進入無線資源閒置狀態，當有資料封包產生時再重新回到無線資源連線狀態，然而無線資源狀態轉換仍會有信令負擔。在這篇論文中，我們討論如何決定一個適當的無線資源釋放計時器以降低整體的信令負擔。我們發現當換手和無線資源狀態轉換所造成的信令負擔相當時的無線資源釋放計時器會很接近有最低整體信令負擔的最佳無線資源釋放計時器。根據以上的觀察，我們設計了一個透過使用者回報換手以及連線次數就可以讓基地台隨著使用者行為的改變而動態地調整到良好無線資源釋放計時器的方法，比起目前無線資源狀態轉換機制中基地台使用固定無線資源釋放計時器更能降低整體的信令負擔。

Since capabilities of mobile devices have been raised tremendously, user can perform multiple applications in the device simultaneously. There are some packets autonomously transfer between the user equipment (UE) and network, which are also referred as background traffic. If UE keeps in radio resource control connected (RRC_Connected) state during the background period, the handover event within this period will generate signaling overhead and reduce efficiency of radio resources. In long term evolution (LTE) system, evolved node B (eNB) will release the connection with the UE to let UE enter radio resource control idle (RRC_Idle) state in order to save network resources and reduce the signaling overhead from handover. When interactive data packet occurs, UE reenters RRC_Connected state. However RRC state transition also costs signaling overhead. In this thesis, we discuss how to determine an appropriate RRC release timer to reduce the overall signaling overhead. We found that the RRC release timer which causes the same amount of handover overhead to RRC state transition overhead is very close to optimal RRC release timer which has minimum total signaling overhead. From above observation, based on the number of handover and connection reported, we design a scheme that eNB adjusts RRC release timer dynamically to a suitable value according to the change of UE behavior. Proposed scheme can reduce the overall signaling overhead comparing to the current mechanism that a fixed RRC release timer is used by eNB.