分散式HLR環境中的一次指標遞轉式定位方法

Abstract

在個人通訊服務的系統中，如何定位隨時四處漫遊的行動手機是相當關鍵 性的挑戰，這項系統動作稱為定位。要達成這樣的工作需要大量的網路訊 號和資料庫查詢，因此目前除了IS-41和GSM所採用的二階層式定位法外， 有些改善定位效率的方法也陸續被提出。指標遞轉被用以減少昂貴的家定 位器處理；分散式家定位器被提出來避免家定位器成為網路瓶頸。然而， 在分散式家定位器環境中，遞轉指標鏈的長度會被加長。在本論文中，我 們提出一個定位方法來克服此潛在問題。此方法的主要觀念是在手機作註 冊動作時，會設法調整系統中的所有追尋路徑，使得任一條遞轉指標鏈長 度不超過一。模擬實驗的結果證明本方法可在定位代價上獲致相當明顯的 降低，事實上，因為追尋路徑的長度不超過一，所以可以提供定位時間的 上限，此外本法可以回收客定位器中過時的資料項。 One of the main challenges in PCS system is to locate a lot of mobiles that may move frequently from place to place. This system operation is called location tracking. It requires a lot of network signals flow and database queries to achieve such a work. In addition to the two-level hierarchical strategy in IS-41 and GSM, several strategies have been proposed to improve to efficiency of location tracking. Pointer forwarding was used to reduce the expensive HLR accesses. Distributed HLRs scheme was proposed to prevent HLR becoming bottleneck in the signaling network. However, the length of forwarding pointer chain may be lengthened in a distributed HLR environment. In this thesis, we propose a modified strategy to overcome this potential problem. The underlying idea of this strategy is to migrate the locating paths in the distributed HLR system when a mobile issues a registration operation. The length of any forwarding pointer chain is not more than 1 in our strategy. The simulation results show that our strategy significantly decreases the locating cost. In fact, this strategy provides an upper bound of location tracking time because of its length of any locating path is not more than 1. Furthermore, obsolete entry in local database (VLR) is able to be reclaimed in this strategy.