無線細胞網路中整批更新及以移動方向為主的位置

Abstract

在個人通訊網路的移動管理中，位置追蹤是最重要的課題之一。目前的移動管理標準像EIA/TIA IS-41 和 ETSI GSM MAP 都是以單一home location register (HLR) 和多個visit location registers (VLRs)的兩階層架構來追蹤使用者。在這種HLR/VLRs兩階層架構下，當使用人口不斷增加時，單HLR可能變成網路執行位置追蹤及通訊連接(call delivery)的瓶頸。為了解決單HLR的瓶頸問題，已經有一些研究提出多HLRs的方法來降低網路的傳輸交通及通訊接通的時間。但無論的如何，多HLRs的方法會因每個HLRs需要資料同步更新而產生額外負擔。在本論文的第一部分，我們提出在分散式HLRs架構下整批更新的方法，而非立即更新，來降低網路傳送訊號的負擔。實驗數據顯示，和IS-41標準相比，分散式HLRs架構可以有效減少網路上位置註冊及通訊連接所需的傳送成本。而我們整批更新的方法則可以進一步降低HLRs資料同步更新的額外負擔。 另一方面，我們知道網路中使用者的位置更新與呼叫(location update and paging)存在著成本折衝。很多研究紛紛提出使位置更新與呼叫成本最佳化的方法，其中大多數的研究都致力於發展個人化的方法，也就是根據使用者移動模式來動態調整位置更新與呼叫動作的方法。但，根據最近研究結果發現，正常狀況下，大多數的使用者會因某種目的而朝向特定地方移動，並非毫無目的的隨意走，而這個觀察結果目前尚未被利用。在本論的第二部分，我們提出一個當使用者改變移動方向時就必須作位置更新的方法。因為這個以移動方向為主的方法可以有效利用移動者向前移動傾向的特性，因此可以降低位置更新與呼叫動作的訊號傳送成本。實驗數據顯示，在正常移動模式下，我們以移動方向為主的方法表現得比以距離為主的方法來得好。

Location tracking is one of the most important issues of mobility management in Personal Communication System (PCS) networks. Current mobility management standards, such as EIA/TIA IS-41 and ETSI GSM MAP, employ a two-level architecture of location databases with a single home location register (HLR) and visit location registers (VLRs) architecture for tracking the locations of mobile subscribers. In the two-level HLR/VLRs architecture, the single HLR may become the bottleneck in location tracking or call setup procedures as the number of mobile subscriber increases. In order to resolve the bottleneck problem of the single HLR architecture, several researchers have proposed multiple HLR schemes to reduce both signal traffics and/or call setup time. However, multiple HLR schemes incur extra signaling in updating multiple HLR databases. In the first part of this thesis, we propose a batch-update strategy, instead of the immediate update method, to reduce the signaling overhead for the location tracking schemes with replicated location information. The numerical results show that the distributed HLRs architecture, compared with the IS-41 standard, can effectively decrease the signaling cost of location registration and call delivery, and our batch-update approach can further reduce the multiple HLR update overhead incurred by the immediate update method. On the other hand, it is well known that there is a trade-off between location update and paging. Many researchers have proposed different location update strategies in order to optimize the signaling cost of location update and/or paging procedure. Most of the previous research efforts focus on the per-user-based schemes that dynamically adjust the location update and paging operations according to the moving pattern of mobile subscribers. However, according to some recent research results, the majority of users normally move toward a specific target with a particular purpose, instead of “walking” in a random way, which has not been exploited in the previous investigations. In the second part of this thesis, we propose a novel location tracking approach that performs a location update when the mobile changes its direction of movement. Since the direction-based approach can utilize effectively the forward-prone moving characteristic of the mobile subscribers, it can reduce the signal cost of both location update and paging procedure. Our numerical result shows that the direction-based approach outperforms the most recognized distance-based scheme for the mobile subscribers with normal-walking behavior.