長程演進網路中基於動態計時器設定之測量回報機制

Abstract

長程演進技術(LTE)為備受矚目的新一代行動無線寬頻技術，目前已被第三代行動通訊組織(3GPP)列為全新的無線標準技術。LTE提供一些優於其他cellular網路的競爭優勢，包括提升end-user吞吐量和減少封包傳送的延遲時間等。在LTE系統中，換手機制可以兩種方式進行，分別為網路控制和使用者裝置(UE)協助之換手流程。當使用者裝置處於connected模式時，即有資料傳輸動作時，使用者裝置可以定期傳送measurement report給基地台，回報量測到的資訊，例如Channel Quality Indicator (CQI)，並可根據移動性動態調整每個UE的換手相關參數，協助基地台進行換手程序。基地台基於收到的measurement report，為需要換手的UE決定適合之目標基地台，並事先與該目標基地台溝通，詢問是否有足夠資源可以容納該UE。目標基地台會為該UE準備所需資源，若成功完成準備程序，目標基地台會透過來源基地台將換手命令傳遞給該UE，使其開始進行換手程序。 本論文首先介紹LTE系統規格定義的測量回報機制，並探討在該機制下可能發生的問題，以及這些問題對於基地台換手決定之影響。基於觀察到的問題，我們提出改善的機制和規則，透過數學模型與最佳化分析，調整與換手機制相關的計時器參數設定，主要包括timeToTrigger和reportInterval。模擬結果顯示，本篇所提出的機制可以減少UE不正確換手的次數，並縮短端點間資料的傳輸時間。

Long Term Evolution (LTE) is expected to ensure 3GPP's competitive edge over other cellular technologies. The advantages of LTE include improving end-user throughputs, and reducing latency. LTE systems utilize a network-controlled and the user equipment (UE) assisted handover procedure for mobility in the connected mode. When a user equipment (UE) is in the connected mode, it sends measurement reports to its source eNB. The source eNB, based on these measurement reports, determines the suitable target eNB for that UE and queries the target eNB if it has enough resources to accommodate the UE. The target eNB prepares radio resources before the source eNB commands the UE to handover to the target eNB. In this thesis, we first introduce the measurement report mechanism defined in the specification of LTE systems. We further explore possible problems and the impact on handover decisions made by the source eNB. Followed, we propose rules for timer adjustment, including timeToTrigger and reportInterval. Our mechanism aims at reducing incorrect handover decisions and shortening the end-to-end data delivery time. By conducting simulation, we evaluate the designed mechanism. The simulation results show that our proposed mechanism does achieve our design goals.