| Summary: | 博士 國立清華大學 資訊工程學系 摘要 在無線通訊系統中交替（Handoff）及移位管理(Mobility Management)是很重要的議題。當通訊中的手機移動超出一個基地台的服務範圍進入新的基地台服務範圍時，手機必須從新的基地台取得通訊頻道以便能使通話服務不致中斷。這種機制稱之為交替。本論文提出一種強制選擇的方法，利用相鄰基地台的涵蓋區域重疊部份進行資源重分配，可以充份利用系統資源以達到增加系統容量及提高服務品質的優點。 移位管理的主要工作為記錄手機的位置並於需要時快速地尋得手機的位置。通常記錄手機位置的頻率不宜過繁以免增加系統負擔，所以一般系統並不會於每次手機移動時即記錄新的位置因此尋找手機時並不能確切地知道手機確實位置一般只知道在一個範圍內。這個範圍為數個基地台服務範圍組成的群組通常稱為註冊區。一般使用雙層式架構的資料庫(HLR,VLR)來記錄手機的位置。HLR負責記錄用戶基本資料及手機在哪個VLR管轄的註冊區，而VLR則記錄實際上在手機在哪個註冊區。本論文提出了一個改良式群組的方法，可以以雙群組的方式降低位置更新的機率並且提高系統使用效率且不會大幅增加尋找手機的延遲時間。 傳統上使用單一HLR資料庫的架構容易使HLR資料庫的更新及查詢成為系統的瓶頸。因此有人提出以分散式資料庫來改善這種問題，但是分散式資料庫有資料不一致及維護資料上的問題。本論文提出改良式的分散式資料庫架構，以固定式指標的方式改善資料不一致及資料維護的難題。且大幅提升系統效率。 Abstract Handoff and mobility management are the essential problems of wireless communication systems. When the MS travels across the cell boundary, a new channel are required to continue the call; these activities are called handoff in general. A strategy called Forced-Jump is presented in this dissertation, capable of making use of the overlap region of cell boundary to raise the utilization of channel resources. The Forced-Jump strategy augments the existing handoff scheme, with the objective of reducing rate of forced termination. When handoff request occurs to a cell in which all channels are occupied, the base station (BS) of this cell attempts to pick up a proper mobile station (MS) in overlap areas of this cell and forces it to use the channel of its neighbor. The mobility management consists of the mechanisms to track user’s location and find the users. Tracking of the mobile user is very important since the mobile users roam around the network. The movement of every mobile unit is noted in the registration records in VLR (Visit Location Register) of the corresponding Registration Area (RA) as well as HLR (Home Location Register) database. E.g. IS-41 is a well-defined implementation for managing location update and mobile tracking within wireless system and has been applied in famous AMPS cellular phone system. In IS-41 standard, RA might consist of one or more cell(s), it performs roaming management by a hierarchical database structure (HLR, and VLR). Each RA has a VLR to record the location of visiting mobiles. The discussion of mobility management issues in this dissertation were categorized into: 1) modified Dual Group method (single HLR solution), and 2) Fixed Pointer Method (multiple HLRs solution). The Group method can effectively reduce the loading of the network caused by tracking mobile users in a mobile cellular system because it joins several cells to form a group. Instead of performing registration and deresgistration for each individual cell, the Group Method performs these tasks on a group scale. Moreover, the Dual Group Method saves network resources because it eliminates unnecessary location updates due to its fewer group boundary passes. The main idea of fixed pointer distributed HLR is using fixed pointers to link distributed database. Each of the database contains part of total system information of the system and some pointers. The pointers point to the location of real data. Since there are pointers point to the data directly, the system can get the required information as soon as possible.
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