第五代蜂巢式系統藉軟性換手改善SIR性能之研究

Abstract

在2020年，現有的通訊標準明顯已不符合未來所需。為了因應這個問題，我們研究第五代行動通訊系統的架構，並針對第五代行動通訊蜂巢式系統採用軟性換手方法來改善訊號干擾比值(SIR)性能進行研究。 在本論文中，我們研究當採用軟性換手方法時，上行以及下行訊號干擾比值(SIR)的改善，考慮主要細胞以及周圍4個層(tier)，由沒有進行軟性換手時的訊號干擾比值(SIR)開始討論，再接著將沒有達到SIR需求的使用者裝置(即沒有達到目標的E_b⁄I_0 的手機)進行兩個基地台參與的軟性換手，研究當進行了兩個基地台參與的軟性換手後能為訊號干擾比值(SIR)帶來多少改善。我們設定在軟性換手過程中，最多能夠有三個基地台參與軟性換手。因此我們接著將進行了兩個基地台參與軟性換手後還是沒有達到SIR需求的使用者裝置(即沒有達到目標的E_b⁄I_0 的手機)進行三個基地台參與的軟性換手，並研究當進行了三個基地台參與的軟性換手後能為訊號干擾比值(SIR)帶來多少改善。我們最後討論在第五代行動通訊系統的環境下，當採用軟性換手方法時，在符合系統SIR需求的情形下，能夠容許多少的通道數，並且討論當採用軟性換手方法時，在外加考慮功率控制的情形下，能夠帶來多少的總額外效益。模擬結果顯示，在第五代行動通訊系統下行傳輸的環境下，軟性換手方法能夠有效的提升系統容量。

In next ten years, existing mobile communication standards obviously cannot meet with users’ need. In reponse to this, we study on a fifth generation cellular system that uses the method of soft handoff. In this thesis, we research on the improvement of SIR in downlink and uplink system when soft handoff is executed. We consider the cellular system with home cell and four tiers. We start from a cellular system without soft handoff and calculate the SIR distribution. We will then do soft handoff with two base station for these users who cannot achieve the target E_b⁄I_0 and observe the improvement in SIR distribution. We assume in soft handoff, we allow at most three base station. As a result, we will do soft handoff with three base station for these users who cannot achieve the target E_b⁄I_0 and observe the improvement of SIR distribution. At the end, we will investigate for a cellular system with soft handoff for which the target E_b⁄I_0 is achieved, how many traffic channels it can serve at most. And when power control is used, how much additional system capacity it can bring in. From two simulation results, we observe that in the fifth generation downlink system, soft handoff can achieve very good system capacity improvement.