以IP為基礎之OFDMA系統在FFR架構下適用於即時性服務之快速基地台切換技術

Abstract

以網際網路協定(Internet Protocol, IP) 為基礎的正交分頻多重接取(Orthogonal Frequency Division Multiple Access, OFDMA)系統憑藉著與網際網路良好的互連能力以及在多路徑(Multi-path)傳播環境下可提供更高的資料傳輸率而被視為下一世代重要的無線通訊傳輸技術。 本篇論文研究在以IP為基礎的OFDMA系統下實際的換手方法。 部份頻率重複使用(Fractional Frequency Reuse, FFR)細胞架構藉由規劃一個細胞的內外區域使用不同的頻率重複係數(Frequency Reuse Factor)來提高頻譜的使用效率(Spectrum Efficiency)。 在OFDMA系統中，快速基地台切換技術已是目前受歡迎的換手方法，此技術可以減少換手所造成的服務中段時間，也被IEEE 802.16e-2005標準所採用。 然而在換手的過程中，訊號品質不佳以及乒乓效應(Ping-pong Effect)的問題依然存在。 本篇論文提出一套換手方法，利用FFR細胞架構的優點與快速調距(Fast Ranging)的方式來改善訊號品質不佳的問題，也降低乒乓效應的發生率。模擬結果顯示本方法可大幅減少換手的過程中封包遺漏率同時減低乒乓效應。

IP (Internet Protocol)-based OFDMA (Orthogonal Frequency Division Multiple Access) is regarded as one of the key technologies for the next generation wireless communication due to its capability to inter-work with Internet and to achieve high transmission rate in a multi-path environment. In this thesis, the issue of effective hand-off over IP-based OFDMA systems is investigated. Fractional Frequency Reuse (FFR) cell structure is employed to achieve high spectrum efficiency by allowing different reuse factors to be used in the inner and outer areas of a cell. Fast base station switching (FBSS) has been a popular hand-off method for OFDMA systems and was adopted in the IEEE 802.16e-2005 standard to reduce service disruption time. Nevertheless, it may suffer from poor signal quality and the ping-pong effect during hand-off. This thesis proposes a hand-off method with the benefits of FFR cell structure and fast ranging so as to increase the signal quality and reduce the occurrence of the ping-pong rate. Simulation results show that the proposed method can significantly reduce the packet loss rate and ping-pong rate during handoff.