IEEE 802.16 技術具有寬頻擷取的特性並提供保證的QoS及較大的覆蓋範圍。IEEE 802.16e更提供行動使用者在網路範圍內擷取網際網路。802.16j多點跳躍中繼站的操作也延伸了覆蓋範圍並增進了資料的傳輸速率，行動台可以藉著連接移動中繼站減輕甚至移除行動台與基地台之間的換手。換手的程序須要花費時間、浪費頻寬，因而造成延遲、通訊中斷的問題。雖然有一些研究提出了新的換手機制來減少換手造成的延遲，但卻還沒有以減少換手次數為目標的研究。本篇論文主要以在802.16j的協定下以群組換手的方式發展出行動台與移動式中繼站間在行動車輛網路裡的連結策略。這種策略考慮到包括訊號強度、共同連結時間、行動台與移動式中繼站間的相對速度。在效率分析上顯示出這種策略確實可以減少換手次數，並增進頻寬的利用率與網路流量。

The IEEE 802.16 technology is characterized by broadband access, guaranteed QoS as well as enhanced coverage. The IEEE 802.16e further supports mobile users to access the Internet in the network region. To extend the coverage or enhance the data transmission rate, the IEEE 802.16j enables the operation of multi-hop relay stations. A group of mobile MS can therefore connect to a mobile RS to alleviate or even remove the handoffs between mobile stations and base station. Handoff operation usually takes time and consumes bandwidth and hence raises the problems of delay and call dropping. Though some study proposed novel handoff mechanisms to reduce the handoff delay, none of them aims at reducing the number of handoffs. This thesis considers the group handoff functionality supported in IEEE 802.16j and intends to develop connection assignment strategies between MSs and mobile RSs in a vehicular network. The proposed connection assignment strategies take into consideration several critical metrics including the signal strength, connection duration, common segment as well as relative speed between MSs and RSs. Performance study reveals that the proposed strategies significantly reduce the number of handoffs and hence improve performance in terms of bandwidth utilization and network throughput.

Contents
Contents                                                 I
List of Figures                                        III
List of Tables                                          IV
1 Introduction                                           1
2 Preliminary and Basic Concepts                         8
2.1 Frame Structure of IEEE 802.16j                      9
2.2 Handoff procedure in IEEE 802.16e/j                 12
2.3 Basic Concepts                                      14
3 Network Environment & Problem Statement               16
3.1 Network Environment and Assumptions                 16
3.2 Problem Statements                                  17
4 IEEE 802.16j Based Connection Assignment              19
4.1 Strongest Signal Strength First Algorithm           20
4.2 Longest Connection Time Duration First Algorithm    28
5 Performance Study                                     39
6 Conclusions                                           44
References                                              46
Appendix A Conference Version                           47
                 List of Figures
Figure 1: IEEE 802.16 j frame structure                  9
Figure 2: IEEE 802.16 j connection status               10
Figure 3: Strongest signal strength first algorithm     23
Figure 4: Example of bigger signal strength first 
          algorithm                                     25
Figure 5: The Longest Connection Time Duration First
          algorithm                                     34
Figure 6: An example for illustrating the LCTDF 
          algorithm                                     36
Figure 7: The simulation scenario                       39
Figure 8: Performance evaluation of the two proposed
          algorithms and the handoff scheme of 
          standard 802.16e in terms of the average 
          number of handoffs with different ratios of
          the number of MSs by the number of RSs       40
Figure 9: Performance evaluation of the two proposed
          algorithms and the handoff scheme of 
          standard 802.16e in terms of the average 
          number of handoffs with different variances 
          of velocity between MSs and RSs              42
                  List of Tables
Table 1: Notations                                     19
Table 2: Receiver SNR Assumptions                      20
Table 3: Simulation parameters                         40

[1] IEEE 802.16-2004, “IEEE Standard for Local and Metropolitan Area Networks Part 16: Air interface to fixed and mobile broadband wireless access systems,” IEEE 2004.
[2] IEEE 802.16e-2005, “IEEE Standard for Local and Metropolitan Area Networks Part 16: Air interface to fixed and mobile broadband wireless access systems,” IEEE 802.16e, 2004.
[3] IEEE 802.16j, IEEE 802.16’s Mobile Multihop Relay (MMR) Study Group, “http://grouper.ieee.org/groups/802/16/relay/	”
[4] S. Choi, G.-H. Hwang, T. Kwon, A.-R. Lim and D.-H. Cho, “Fast Handover Scheme for Real-Time Downlink Services in IEEE 802.16e BWA System,” in Proc. IEEE VTC, pp.2028-2032, 2005.
[5] D. H. Lee, K. Kyamakya. and J. P. Umondi., “Fast Handover Algorithm for IEEE 802.16e Broadband Wireless Access System,” in Proc. the 1st International Symposium on Wireless Pervasive Computing 2006, pp. 1-6, Jan..
[6] Kyung-ah Kim, Chong-Kwon Kim, Tongsok Kim, “A Seamless Handover Mechanism for IEEE 802.16e Broadband Wireless Access,” International Conference on Computational Science 2005, vol. 2, pp. 527-534.
[7]H. Jang, J. Jee, Y.H. Han, S.D. Park, J. Cha, “Mobile IPv6 fast handovers over IEEE 802.16e Networks,” IETF Internet draft, draft-ietfmipshop- fh80216e-01.txt, Jan. 2007.