臺灣博碩士論文加值系統

近幾年手持式行動裝置因硬體製造技術的純熟和無線通訊技術的演進，搭配雙重通訊媒介已成為一股趨勢。以往的手持式行動裝置只有基本通話和收發簡訊功能，因硬體效能的提升使得手持式行動裝置可安裝一套小型的作業系統，使得桌上型電腦部份功能移植至手持式行動裝置上，大大提升了行動運算的層面。Android手機作業系統自2008年發佈以來受到各大廠商關切，相較於其它手機作業系統，Android在網路上公布該平台原始程式碼和開放套件讓開發者免費存取，使得該平台的相關研究及資訊迅速拓展。
當行動節點和原先建立連線的基地台在移動的情況下，因遠離的關係或訊號干擾使得通訊品質下降造成通訊中斷。此時行動節點掃描周遭可用的基地台並嘗試與之建立連線，迨行動節點從原本基地台切換至新基地台，再次存取網路資源，此過程稱之為換手程序。現今無線網路充斥著許多不同通訊技術，如何在異質間和同質間的無線網路換手並沒有一套標準的程序。IEEE 802.21主旨在制定異質間和同質間網路提供一套換手相關訊息服務的機制。
本論文依照IEEE 802.21概念，設立三個門檻值收集不同訊號區間偵測的基地台資訊，比對同一基地台出現次數和該基地台訊號品質前後變動量，依此規則挑選基地台作為換手考量的對象。實作上把Android Wi-Fi API對應至相關的IEEE 802.21 MIH SAPs (Service Access Points)，並依照Android Wi-Fi有限狀態機設計演算法，最後在配有Android作業系統的手持行動裝置上驗證此換手程序。

Thanks to ever-progressing hardware manufacturing and radio access technology, handheld devices equipped with multiple network interfaces have become a norm. Nowadays a mobile handset has rich functionality, performing many other jobs than simple voice services. A recent demand for handsets of higher intelligence drives the need to develop handy operating systems for such mobile devices. Among others, Android has received much attention worldwide since it was first released in 2008 in that it has been available as open source along with software development tools. As a result, developers can easily enrich the functionality of the devices, making Android the second most popular mobile development target.
When a mobile user roams about, the mobile handset is capable of retaining network connectivity over due wireless media in course of movements, leading the handset to switch its radio link to different access points (APs) from time to time. Such a handover involves AP discovery, connection teardown and setup such as IP (Internet Protocol) address acquisition, and authentication with the network, causing a blackout during which the handset cannot deliver data frames to and from the system. Thus, fast handover is essential to streamlining communication. In view that IEEE 802.21 has recently standardized protocol service primitives for fast handover within homogeneous and heterogeneous networks, we aim to develop an IEEE 802.21conformant handover mechanism.
Following IEEE 802.21 operational principles, this thesis presents the design and implementation of a handover mechanism over the Android platform. Our handover mechanism operates with three different received-signal-strength thresholds to trigger AP discovery and record information about APs in range. We compare the collected information to find out how many times these discovered APs were present on record as well as the changes of received signal strength from each AP. We then determine a list of preferred candidate APs for the handset accordingly This thesis also relates IEEE 802.21 service primitives to Android Wi-Fi API (Application Programming Interface) to clarify their correspondence in-between. Our implementation is based on, Android Wi-Fi finite state machines as well. Lastly we conduct field trial experiments to demonstrate the effectiveness and usefulness of our development.

摘 要 i
Abstract ii
誌 謝 iv
目 錄 v
表 目 錄 vi
圖 目 錄 vii
第一章 序論 1
1.1. 研究背景 1
1.2. 研究動機 1
1.3. 研究目的 1
1.4. 論文架構 2
第二章 相關文獻探討 3
2.1 802.21 Media Independent Handover Services (MIH) 3
2.1.1 Media Independent Command Services (MICS) 4
2.1.2 Media Independent Event Services (MIES) 5
2.1.3 Media Independent Information Service (MIIS) 6
2.1.4 Service Access Points (SAPs) 7
2.2 水平式換手演算法 8
2.3 IEEE 802.21相關文獻 9
第三章 Android系統介紹 12
3.1 Android 軟體架構 12
3.2 Android Application Components 14
3.3 Android Activity 15
3.4 Android Intent 18
3.5 Android IPC 機制及Service 類別 20
3.6 Android Wi-Fi Module 24
第四章 方法實作 26
4.1 系統架構 26
4.3 虛擬碼 31
4.4 Android Wi-Fi 有限狀態機 35
4.5 換手流程圖 37
4.6 實作結果 39
第五章 結論與未來展望 45
參 考 文 獻 46

[1]IEEE Std 802.21TM-2008, “IEEE Standard for Local and metropolitan area networks—Part 21: Media Independent Handover Services,” January 2009.
[2]George Lampropoulos, Apostolis K. Salkintzis and Nikos Passas, “Media-independent handover for seamless service provision in heterogeneous networks,” IEEE Communications Magazine, pp. 64—71, January 2008.
[3]Mariano Molina-Garcia, Alfonso Fernandez Duran, Raquel Perez Leal, and Jose I. Alonso, “Method to assess the effect of the horizontal handover decision on voice quality in wireless convergent networks,” Proceedings of the 1st European Wireless Technology Conference, pp. 226—229, October 2008.
[4]Filippo Cacace and Luca Vollero, “Managing Mobility and Adaptation in Upcoming 802.21 Enabled Devices,” Wireless mobile applications and services on WLAN hotspots, pp.1—10, September 2006.
[5]Android Architecture,
http://developer.android.com/guide/basics/what-is-android. html
[6]Activity，
http://developer.android.com/reference/android/app/Activity.html
[7]Frank Ableson, Charlie Collins, and Robi Sen, Unlocking Android, Manning, Apr. 2009.
[8]Rick Rogers, John Lombardo, Zigurd Mednieks, and G. Blake Meike, Android Application Development: Programming with the Google SDK, O''Reilly Media, 2009.
[9]Android Wi-Fi，
http://stulog.com/?post=194
[10]WifiManager，http://developer.android.com/reference/android/net/wifi/WifiManager.html
[11]Chien-Chao Tseng, Kuang-Hui Chi, Ming-Deng Hsieh, and Hung-Hsing Chang,” Location-based Fast Handoff for 802.11 Networks,” IEEE COMMUNICATIONS LETTERS, VOL. 9, NO. 4, pp. 304—306, APRIL 2005.
[12]Lambros Sarakis, George Kormentzas, and Francisco Moya Guirao, “Seamless service provision for multi heterogeneous access,” IEEE Wireless Communications, pp. 32—40, October 2009.
[13]Ashutosh Dutta et al, “Seamless proactive handover across heterogeneous access networks,” Wireless Personal Communications, Vol. 43, January 2007.