無線區域網路中以位置認知及使用者習性為基礎的遞交演算法

Abstract

隨著WLAN以及VOIP技術的成熟，以及雙網整合的實現，在未來，WLAN中的AP將會扮演行動通訊中的基地台的角色。因此，WLAN中的遞交將成為一個重要的課題。遞交演算法的優劣，不只影響通話品質，也會影響頻道的使用效率。在行動通訊中，信號的強度對通訊的品質有直接與立即的影響。因此，利用接收信號的強度（RSS）來作為判斷是否遞交(handoff)到新的基地台的條件，似乎是既合理又簡單的方法。在無死角無阻礙的開放空間中，這種方法的確沒有問題。但在WLAN的環境下，由於信號除了受到雜訊干擾外，亦受到多重路徑干擾(multi-path reflecting)的影響，使得信號的強度極有可能在相鄰的區域亦會相差甚遠，因而使得正在傳輸中的行動基地台將信號切換到鄰近信號較佳的基地台上。但是由於信號可能只是暫時地減弱，若是遞交過去的基地台也只是一時信號較佳，將造成強迫斷訊(forced terminated)或多餘的遞交。本篇論文即是以通話品質(call quality)作為決定遞交依據的方法。並利用使用者習慣路徑和信號強度表兩種方法，來修正以在無線區域網路通話品質作為遞交依據的缺點。

With the growth of WLAN and VOIP, access points (AP) in WLAN will play the role of base station in cellular system in the future. As the reason, handoff algorithm in WLAN will be an important issue in the future. The performance of handoff algorithms effect not only call quality, but also the spectral efficiency. In mobile communication, signal strength has immediate effect on communication quality. As the reason, it’s reasonable to use received signal strength (RSS) as the matrix of deciding handoff. This method performs well in an open space. However, due to the severe effect of multi-path fading in WLAN, signal strength changes rapidly in close distance probably. This effect may cause unnecessary handoffs and service failures (forced termination), which both influence call quality. In this thesis, we use call quality criterion as handoff algorithm. We propose location-aware and profile-based methods to tackle problems signal strength prediction in WLAN.