具無縫換手之Network Mobility管理方案

Abstract

無線網路存取技術進步，開創行動網際網路的新時代，連帶車載通訊的需求也越來越高。然而車輛的高移動特性，突顯通訊裝置(device)本身電力與硬體的限制，從裝置到地面基地台這段無線線路品質因高速移動而低落。Network mobility是將全部一起移動的群體視為一個整體(entity)的概念，特別適合用來改善車載通訊的品質。在車輛行駛時，無可避免的需頻繁執行換手作業，所以需要有效率的換手協定，以符合即時通訊(real-time communications)的服務品質(QoS)要求。然而，車輛如是以高速移動，則用來完成換手程序的時限更短，再加上都卜勒效應會提高無線線路傳輸錯誤率，再再增加移動管理的難度。 在這篇論文中，我們首先研究面對高速行駛的車輛時，network mobility的移動管理協定之議題，並徹底檢視與比較各種network mobility解決方案的特點。基於使用彈性，路由效率和安全方面等原因，我們建議把車輛上的節點(nodes)根據他們自己的特點分成不同的網路，並用智能移動路由器(MRs)統一管理。 為了從通訊協定上支援高速行駛車輛的QoS-handover，我們提出在all-IP網路中，考量服務品質的network mobility架構和協議，稱之為Hi-NEMO，包含兩個互補的QoS-handover協定。Hi-NEMO不會在地面基地台(BS)與移動路由器(MR)間，增加額外的信令。模擬實驗顯示Hi-NEMO大幅降低在容易有傳輸錯誤的無線環境中的換手延遲(handover delay)。此外，有鑑於在這綠色科技的時代，高速鐵路系統日益流行，我們進一步研究以無線裝置連接到WiMAX的高速長途列車的移動管理。目前商業化設備產品中已設計了資源預留機制，以確保在換手過程中的QoS，不過仍有改進的空間。我們利用高速列車車長特性，提出2MR方案，於車上部署兩個移動路由器，並為在火車上的移動節點(mobile nodes)設計無縫換手協定。

The evolution of wireless access technologies has led to a new era of mobile Internet for high speed vehicles. Network mobility is particularly suitable for vehicles because it considers the mobility of an entire network. Vehicles perform handover frequently thus efficient handover is essential to meet the QoS requirements for real-time communications. When moving with high speed, the time constraint is even stricter and the Doppler Effect increases the transmission error rate that both add challenges in mobility management. In this dissertation, we first study the mobility management protocols for network mobility and the issues when applying to high-speed vehicles. A thorough review and feature comparison of network mobility solutions are presented. For the reasons of flexibility, route efficiency and security concern, we suggest that the nodes in the vehicle to be separated into different networks based on their characteristics, and managed by smart mobile routers (MRs). To provide protocol-support for QoS-handover to high-speed vehicles, we propose a QoS incorporated network mobility architecture and protocols, called Hi-NEMO, for all-IP networks. Two complementary QoS-handover protocols are proposed, and Hi-NEMO does not introduce additional signaling between the BS and the MR. As a result, handover delay in an error-prone wireless environment can be reduced substantially. Furthermore, in the era of green technology, high-speed rail systems are increasingly popular. Therefore, we investigate the mobility provisioning for long distance high-speed trains in WiMAX. In practice, resource reservation mechanisms have been designed to ensure the QoS during handover; however, there are rooms for improvement. We take advantage of the long physical size of high-speed trains and proposed the 2MR scheme that deploys two MRs, and then design handover protocols to provide seamless handover for the mobile nodes on the train.