評估在 Mobile WiMAX 的頻道掃描策略

Abstract

移動全球互通微波存取(Mobile WiMAX)在移動網路中已經成為寬頻無線存取(Broadband Wireless Access, BWA)的一項重要技術，它提供完全的分封交換(Packet-Switched)服務；而在移動的環境中支援分封交換的聲音與影像服務上，如何提供行動用戶端(Mobile Station, MS)在服務期間執行不同基地台(Base Station, BS)之間的無間隙換手(Seamless Handover)成為一項非常重要的議題。在移動全球互通微波存取的系統中，行動用戶端在真正執行換手之前，必須先掃描鄰近基地台，並做量程(Ranging)來調整與鄰近基地台的傳輸的功率以及時間同步；但這個過程會造成服務的中斷，使得通訊的服務品質(Quality of Service, QoS)受到影響。因此在本篇論文中，研究掃描及量程所需要的時間以及對執行中的聲音和影像通訊所造成的影響，以建立三種不同對於掃描及量程的策略和數學模型；此三種策略的執行效能也透過數值分析及模擬的方式來完成評估。

IEEE Std 802.16e or Mobile Worldwide Interoperability for Microwave Access (Mobile WiMAX), which offers pure packet-switched services, has become one of the most important technologies for broadband wireless access (BWA) in mobile environment. One of the most important issues for supporting packet voice or video over a mobile environment is to provide seamless handover between base stations (BSs) during a voice/video communication session. In a Mobile WiMAX system, a mobile station (MS) has to scan the BSs, perform ranging procedures to adjust power and timing with neighboring BSs before handover, and these scanning/ranging procedures may introduce service interrupts and influence the QoS of a session. In this paper, we investigate the scanning and ranging latencies, and their interferences to the active voice/video sessions. The mathematical models for three different scanning and ranging strategies are developed and these strategies are evaluated through analytic and simulation analyses.