一個IEEE 802.16j 移動式中繼站改進換手延遲的預先認證機制

Abstract

在無線網路通訊中，IEEE 802.16 (WiMAX) 是一項越來越普及的技術，而IEEE 802.16j 則是增加了多躍式中繼站來擴展通訊的涵蓋範圍。在標準中，移動式中繼站是指在行動通訊系統上加入中繼站，而本論文是在移動式中繼站的其中一種特殊應用上，將中繼站設置在大眾交通運輸工具之上，使得裡面的使用者可以透過此中繼站跟無線網路基地台做連結。然而在移動中，為了維持執行交遞時的安全性，必須重新做一次認證，但這會浪費過多的時間在交遞的中斷時間上，而往往造成上層服務的中斷。 在移動式中繼站的機制下，使用者移動到另一個基台時，只需執行網路層的交遞程序，而媒體存取控制層的交遞程序則交給移動式中繼站來執行。而本論文所提出的方法是將媒體存取控制層的交遞程序中，影響中斷時間最大的認證程序提前至使用者尚未移動到目標基台前執行，進而減少了大量使用者在交遞程序的中斷時間，改進了通訊的傳輸品質。我們設計了一套模擬實驗，在FMIPv6下，不管是 predictive 模式還是 reactive 模式都能有效地減少交遞程序的中斷延遲，而在 predictive 模式下還可降低封包的遺失率。

IEEE 802.16 (WiMAX) is becoming one of the popular technologies in wireless communications. Multi-hop relay station (RS) is used to extend the coverage area in IEEE 802.16j. Mobile RS (MRS) is a relay station that is used while in motion. A MRS mounted on a vehicle is a special application case for the research in this thesis. The MRS provides a fixed access link to the end mobile terminals riding on a vehicle. In order to maintain the security of wireless communications, re-authentication should be considered when the mobile station (MS) performs handover. However, it usually wastes too much time that may interrupt higher layer applications during a handover. When a MS moving together with MRS changes BS for higher signal quality or better QoS, it performs network layer handover procedure while MRS performs link layer handover procedure. In this thesis, we proposed a pre-authentication scheme to reduce the interruption time of link layer handover by performing the authentication procedures before the MS roams to another BS. We developed a simulation experiment to evaluate our scheme. The result shows that with Fast Mobile IPv6, our scheme is able to reduce the interruption latency efficiently both in predictive mode and reactive mode, as well as reduce the packet loss rate in predictive mode.