IEEE802.16 WiMAX網路下無接縫移動機制之研究與設計

Abstract

隨著高品質多媒體應用與4G WiMAX網路技術的盛行，使用者能隨時隨地的透過WiMAX無線網路存取多媒體服務。然而，對於那些在WiMAX無線網路移動的使用者而言，換手程序導致的服務中斷時間與封包掉落造成令人無法接受的服務品質。尤其在IEEE 802.16j行動中繼站模式下，此情況更為嚴重。因此，在WiMAX網路中，減少服務中斷時間與封包掉落對於提供無接縫的移動與令人滿意之服務品質是非常重要的議題。 為了提供無接縫的移動，數個著名的移動機制被提出來。Mobile IPv6 (MIPv6)對於IP層的行動性提出一個基本的換手機制；Fast MIPv6 (FMIPv6)則在link層與IP層之間提供了一套平行的換手機制以減少服務中斷時間；Hierarchical MIP (HMIP)利用階層式的方式來執行區域性的行動管理；Proxy MIPv6 (PMIPv6)則提供一套網路為基礎的移動機制。在此機制下，行動節點的IP層換手程序行動節點改交由網路端的路由器代為執行，行動節點本身不需要參與IP層換手程序。這些方法各自提出有效減少服務中斷時間與封包掉落的方法。然而，這些方法並沒有針對WiMAX網路做最佳化之處理，且上述之移動機制在IEEE 802.16j行動中繼站模式下，仍然有高服務中斷時間與封包掉落的缺點，這些問題或問題的起因包含了循序的換手、耗時的重覆位址偵測程序、第二層網路重新進入的延遲時間、以及link層的換手是由行動中繼站執行而不是行動節點執行等。在此論文中，我們對於WiMAX網路中包含的IEEE802.16e模式與IEEE802.16j行動中繼站模式各自提出改進服務中斷時間與封包掉落的機制以達到無接縫的移動。 第一個提出的方案主要是針對IEEE802.16e網路。此行動機制整合了第二與第三層的控制訊息，並且提出一個快速第二層網路重新進入機制以減少換手所需的控制訊息與服務中斷時間。在此機制下，行動節點將與基地台溝通協調以預先的完成某些第二層網路重新進入程序。我們所提出的預先第二層網路重新進入程序包含了專屬測距時槽的取得、暫時認證機制、以及預先服務流的配置。因此，在行動節點完成測距程序之後，即可恢復收送封包，有效的減少了服務中斷時間。 第二個提出的方案則針對IEEE802.16j行動中繼站模式。此方案為一個主機為基礎的行動機制。此行動機制利用行動中繼站link層與行動節點IP層的相互合作以達成平行的換手程序。當行動中繼站在執行link層換手程序時，它會通知行動節點的IP層開始執行IP層的換手。透過提出的平行換手程序，服務中斷時間可以顯著的減少。此外為了減少換手期間的封包掉落，我們也提出一套封包暫存的機制。最後我們將第一個方案提出的方法整合套用至第二個方案，以進一步的減少服務中斷時間。 第三個方案同樣針對IEEE802.16j行動中繼站模式，我們提出一個網路為基礎的行動機制。透過行動中繼站的link層與路由器的IP層合作，同樣可達到平行的換手機制，且行動節點無需參與IP層的換手程序。這個網路為基礎的行動機制減少了主機為基礎的行動機制中耗時的重複位址偵測時間。為了進一步的減少服務中斷時間，我們同樣將第一個所提出的方法中之快速第二層網路重新進入機制導入此方法內。 根據分析與模擬顯示我們提出的機制有效地減少服務中斷時間與封包掉落。因此，對於在WiMAX網路下之移動使用者而言，其能獲得無接縫的換手與令人滿意的服務品質。

As technologies for the high quality multimedia application and 4G WiMAX network prevail, one can easily be under services everywhere through WiMAX wireless network. However, the service disruption time (SDT) and packet loss caused by handover procedure leads to an unacceptable quality of Service (QoS) for mobile users in WiMAX wireless net-work, especially in IEEE 802.16j mobile relay station (MRS) mode. Therefore, minimizing SDT and packet loss are necessary in supporting seamless mobility and satisfactory QoS for mobile users in WiMAX network. For supporting seamless mobility, several notable mobility schemes were proposed. Mobile IPv6 (MIPv6) provides the fundamental handover methods for mobility management at IP layer. Fast MIPv6 (FMIPv6) provides a parallel handover mechanism between link-layer and IP layer to reduce the SDT. Hierarchical MIP (HMIP) employs hierarchical architecture to perform local mobility management. Proxy MIPv6 (PMIPv6) provides a network-based mobility scheme in which mobile station (MS) needs not participate in the IP layer handover procedure. However, the above schemes are general solutions and do not aim at WiMAX network. They still suffer high SDT and packet loss problem in IEEE 802.16j MRS mode in which the link-layer handover is performed by the MRS instead of MS. In this dissertation, for supporting seamless mobility, we proposed three enhanced mechanisms to reduce the SDT and packet loss in the IEEE 802.16e and IEEE 802.16j MRS mode. The first proposed scheme aims at IEEE 802.16e. The proposed cross-layer IPv6 fast handover scheme which features integrated layer 2/layer 3 messages and pre-layer 2 network re-entry procedure (Pre-L2NR). It can reduce the SDT and the numbers of control messages during handover. In the proposed scheme, the MS will negotiate with the base station (BS) to perform the layer 2 network re-entry procedure in advance. The Pre-L2NR includes acquire-ment of dedicated ranging time slot, temporary authentication mechanism, and pre-service flow construction. Therefore, the MS can resume receiving/sending packets after it completes the ranging procedure, leading to the reduced SDT. The second proposed scheme is for IEEE 802.16j MRS mode. It is a host-based mobility approach. It utilizes the cooperation between the MRS’s link-layer and MS’s IP layer to achieve the parallel handover. The MRS’s link-layer will notify the MS’s IP layer to perform IP layer handover procedure when the MRS performs link-layer handover. The parallel handover reduces the SDT efficiently. On the other hand, the proposed buffering mechanism can avoid packet loss during handover. We also integrated the first mechanism into the second mechanism to further reduce the SDT. The third proposed scheme also aims at IEEE 802.16j MRS mode. A network-based mobility approach is presented to improve the SDT and packet loss in the MRS mode. Through the cooperation between the MRS’s link-layer and access router’s (AR’s) IP layer, the parallel handover can be achieved, and the MS needs not participate in the IP layer handover procedure. The proposed network-based mobility approach can reduce the time for considerably longer duplicate address detection (DAD) process in the host-based mobility approach. The third proposed scheme further reduces SDT by Pre-L2NR. According to the results of analyses and simulations, the proposed schemes can reduce the SDT and packet loss efficient. As a result, the seamless mobility and satisfactory QoS can be achieved for mobile users in WiMAX network.