第五代通訊之毫米波異質性網路中波束導向之換手策略

Abstract

本論文的目標是提出一個針對密集基站佈建之毫米波異質性網路，提出一個換手機制以解決換手率問題。為了克服高頻段在傳輸過程中所遇到的高傳播損益，毫米波的傳輸非常依賴高指向性天線。然而，由於指向性的傳輸對於位置的改變很敏感，導致現有只考量瞬間訊號強度的換手機制無法提供穩定的連線給移動中的使用者。在本論文中，我們提出了一個以連線穩定度為考量的換手機制，而穩定度則是以有效波束覆蓋機率(EBCP)來進行評估，其被定義為一個使用者在一段時間間隔內仍然待在同一個波束覆蓋範圍的機率。我們也將所提出的換手機制應用於以隨機幾何模型建立與Wireless InSite軟體建立之有遮蔽物的環境中。從模擬的結果顯示，我們所提出的換手機制能降低換手的失敗率，並對於無遮蔽物及有遮蔽物的環境，分別以更低的換手率增加10.9%及10.5%的傳輸量。

The goal of this thesis is to propose a handover strategy to deal with the handover frequency problem in mmWave HetNets with dense base station (BS) deployment. To overcome the high propagation loss experienced at high frequencies, mmWave transmission heavily relies on highly directional antennas. However, because directional transmission is sensitive to position changes, the existing handover strategies which only consider the instantaneous received signal strength fails to provide robust connections for moving users. In this thesis, we propose an improved handover strategy taking the connection robustness issue into account. The connection robustness is evaluated in terms of the effective beam coverage probability (EBCP), which is defined as the probability that a user stays in the coverage area of the same beam coverage area after a certain time interval. We examine the proposed handover strategy with stochastic geometric blockage and campus building environment. Simulation results show that the proposed handover strategy can reduce handover failure probability and improve throughput up to 10.9% and 10.5% with much lower handover frequency in the environment with and without blockages, respectively.