個人通訊服務系統之整合

Abstract

個人行動通訊的服務最近在全世界有很高的成長率，很多行動通訊技術已經被發展出來了，比如說，低階無線行動系統、高階無線行動系統、雙頻系統、衛星無線系統、以及微細胞/大細胞系統。每種系統都有自己的長處，整合這些系統優點成為一個新系統，對於日益快速成長的使用者是一個很大的誘因。因此，整合不同系統來提供使用者更好的服務是很重要的一件事。在本文中，我們研究有關個人行動通訊系統的整合問題，並提出三種系統架構來探討無線行動系統的整合。 個人行動通訊系統將系統服務分為兩大類，一則為高階系統，其訊號覆蓋範圍比較大而且連續，因此可以支援高速行動。另一種為低階系統，其無線訊號覆蓋範圍為小區域範圍，因此只能支援移動速度比較小的使用者。雙階行動閘道(TTMGs)被設計來使低階使用者在高速行動中可以使用高階系統的服務。行動雙階閘道與低階系統的漫遊管理協定也在文中提出，低階HLR資料庫也必須修改才可以支援位置註冊與尋找程序。系統模擬結果可得知，使用行動雙階閘道將使低階使用者的無線電頻道使用率高於高階系統。 其次，我們將研究在單雙頻手機混用的環境下的雙階系統頻寬分配問題，採用負載平衡方式來分配頻道可以改進系統的效能。為了平衡雙頻負載，基地台將依據兩個頻道的負載量選用一個頻道來服務雙頻手機使用者。更進一步，頻道再分配策略將能更進一步改善系統效能。分析結果顯示採用平衡負載以及頻道再分配的策略，於雙頻使用者增加時可以大幅改善系統效能。若能結合這兩種策略，只要雙頻使用者達到全部使用者的25%，系統效能提升就有很明顯的效果了。 為了整合數據服務，我們先研究有關無線廣播問題。無線廣播系統可很有效率將廣播資料送給一大群使用者，採用資料索引技術將可減少手機與基地台的聯繫次數(tuning time)進而降低電池電力消耗，索引的結構會影響資料索引的效率，我們提出演算法來組織索引並可減少手機聯繫基地台的次數，進而節省手機的使用電量。我們更提出一個評估原來手機聯繫基地台次數的效能量測參數來分析我們提出的方法。分析結果建議當資料的評存取機率的分配趨向均一時，索引結構中的索引連結數最好是3可以得到較低的手機聯繫成本。若資料的存取機率分布越不平均，即機率分配越偏斜，則索引連結數則最好是採用2比較可得到較低的手機聯繫成本。

The demand for personal communications service (PCS) has been steadily growing worldwide. Many technologies for PCS systems have been developed, such as low-tier, high-tier, dual-band, satellite, and microcell/macrocell systems. Every system has its merits in PCS. It is very fascinating to coordinate the merits in PCS systems for the steadily growing users. Therefore, it is important to integrate different PCS systems to provide users better service. In this dissertation, we study issues in integrating PCS networks. Three PCS network services provided by the integration in PCS are described and studied. First, we consider the integration of two major technologies in the PCS, high-tier and low-tier systems. High-tier PCS systems cover large continuous areas and support users moving at high speed. Low-tier PCS systems cover small zonal areas and only support users moving at low speed. Two-tier mobile gateways (TTMGs) are proposed to enable low-tier mobile users to use high-tier services so that low-tier users moving at high speed can also be served. The roaming management protocols for TTMGs and low-tier mobile users have been developed. The low-tier HLR database has been modified to support efficient registration and location tracking. The simulation results indicate that low-tier users using TTMGs experience higher utilization for radio channels than high-tier mobile users. Second, we investigate the channel assignment problem of dual-band PCS systems where single-band and dual-band handsets co-exist. Load-balancing channel assignment schemes are proposed to improve the system performance. To balance the loads of both bands, the BSC selects a band to serve a call request of a dual-band handset based on the loads of both bands. In addition, a channel re-assignment scheme is used to further improve the system capacity. The analytic results indicate that both load-balancing and channel re-assignment techniques significantly increase the system capacity as the percentage of dual-band handsets increases. Furthermore, the load-balancing with channel re-assignment scheme that combines both techniques achieves the best system performance even when the percentage of dual-band handset is as low as 25%. To integrate the data service and voice service, we study the issue of the wireless data broadcast. Data broadcast is an effective approach to disseminate information to a massive number of users. Indexing techniques for broadcasting data can reduce the battery power consumptions of mobile terminals by decreasing the tuning time. The organization of the indexes affects the efficiency of data searching. We investigate how the degree of the index node affects the tuning time, and thus minimize the power consumption of user’s terminals. We proposed a performance measurement for the tuning time and a cyclic indexing algorithm. The numerical results suggest the degree of an index node be 3 when the access probabilities of the data tend to be uniformly distributed so that the expected tuning time is minimal. When the access distribution of the data nodes is skewer, the tuning time can be minimized by setting the degree in the index node 2.