IEEE 802.16無線都會網路(又稱為全球互通微波存取, WiMAX)具無線、遠距、寬頻等特性，極有可能成為解決最後一哩存取問題的技術。而IEEE 802.16j標準建議藉由行動中繼傳輸（Mobile Multi-hop Relay）設備之佈建來強化WiMAX系統效能，解決訊號傳輸上可能出現的死角問題，同時擴大無線行動寬頻技術的傳輸範圍，降低整體WiMAX系統建置成本。藉由中繼傳輸，傳送路徑從單躍（Single Hop）變成雙躍（Two Hops）、或是多躍（Multi-Hop），行動用戶於細包內之連線建立選擇及細包內遞交機制是中繼傳輸WiMAX網路設計時的主要議題。
本論文研究支援中繼傳輸之WiMAX網路中由移動用戶(mobile station)觸發之集中式與非集中式細包內遞交與連線建立法則，基地台(base station)及相關的透通式中繼點(relay station)會偵測與行動戶用間之訊雜比，做為遞交決策之依據。集中式遞交機制中基地台主導移動用戶之連線建立與遞交決策；而在非集中式遞交機制中，移動用戶連線之建立與遞交決策則需要支援中繼傳輸之中繼站的參與。論文中首先定義符合WiMAX規格之詳細信號交換流程，提出同訊框轉送方法以避免多躍傳送造成額外的傳送延遲。模擬結果顯示出集中式與非集中式細包內遞交與連線建立法則明顯改善封包成功傳輸率及封包傳送延遲，有效增進網路傳輸效能。
WiMAX支援多媒體資料傳輸，但因無線傳輸易受干擾且通道具時變特性，已排定傳送之資料在即將傳送時可能因為已建立連線之通道不良而無法傳送成功，造成頻寬浪費。吾人提出frame-based跨層級的多使用者排程機制，每位使用者依接收到之平均訊雜比（SNR）來設計適應性調變/編碼（Adaptive Modulation/Coding）。將實體層的平均訊雜比結果提供給資料連結層的排程器用以提升系統的傳輸速率。本排程機制首先評估即時性封包可容忍之延遲時間，並依通道的狀態來安排應於那一個框架中傳送，剩餘的資源就可分配給非即時性封包來傳輸。模擬結果顯示此跨層級排程機制可有效改善網路產出，在滿足即時性資料流服務品質（QoS）需求之外，同時兼顧到非即時性資料流傳送之長程公平性。
雖然多媒體資料在網路傳輸上日益重要，但是像全球資訊網(WWW)存取與檔案傳輸之類的『竭力』(best effort)資料流仍在網際網路資料傳輸中佔了極大比例，不容忽視。因此若能改善竭力資料流的傳輸效率，將可以提升WiMAX網路的傳輸效能。在WiMAX網路中，竭力資料流用戶需透過競爭方式向基地台提出頻寬請求以取得傳送之機會，並使用truncated binary exponential backoff 法則處理在競爭過程中產生碰撞後之重傳。若能有效的控制競爭窗的大小，就可以降低重傳碰撞率，提高竭力資料流頻寬請求競爭的傳送成功率，進一步改善竭力資料流的傳送效率。本論文研究出在基地台運作的競爭窗指定機制。基地台依據頻寬請求之到達率及發生頻寬請求傳送碰撞之使用者數量，動態的調整競爭窗大小，模擬結果顯示所提出之機制可有效改善BE資料流頻寬請求之傳送率及改善傳送延遲，可最佳化竭力資料流之頻寬請求傳送。

Constructing conventional wired networks at urban and suburban areas will result in issues such as high cost and the difficulty of deployment. However, with the massive high bandwidth demand of subscribers, IEEE 802.16/16e wireless metropolitan network (worldwide interoperability for microwave access, WiMAX) wishes to use wireless communication, long distance transmission, and high bandwidth to overcome the last mile access problem. IEEE 802.16j standard mainly rely on multi-hop relay node deployment to enhance the WiMAX system performance; this will eliminate the possibility of shadowing and blocking problems on wireless transmission, while at the same time, increase the transmission range and reduce implementation cost. Multi-hop relaying helps transmission path evolve from single hop to two hops or multiple hops, the connection establishment and Intra-BS handoff scheme for mobile users was the main topic in multi-hop relay WiMAX networks.
In this thesis, we study centralized and decentralized MS-triggered Intra-BS handoff and connection establishment schemes. Both base satation (BS) and corresponding transparent relay nodes will detect the SNR between mobile users and BS/relay nodes as basis for handoff decision. In centralized Intra-BS handoff scheme, BS lead connection setup and handoff decision for mobile users; in decentralized Intra-BS handoff scheme, mobile users connection setup and handoff decision would need support of relay nodes from multi-hop relay. We first define the detailed signaling procedures based on the IEEE 802.16/16e standard. The method of same-frame-delivery is proposed to avoid unnecessary transmission delay that multi-hop relay might cause. The proposed centralized and decentralized Intra-BS handoff and connection establishment schemes can improve packet transmission rate and transmission delay, and enhance the network performance.
WiMAX networks support multimedia traffic transmission. Due to the fact that wireless transmission is prone to interference and channel condition is time varying, scheduled packets may not be transferred because of bad channel condition. Based on average received SNR each user is assigned to proper adaptive modulation/coding. The SNR from physical layer presents to the scheduler of data link layer for packet scheduling to improve system throughput. This scheduling scheme first evaluates the delay tolerance of real-time packets, schedules real-time packet transmission is based on the channel condition, then the residual bandwidth is allocated to non-real-time packets. The proposed cross-layer scheduling scheme can greatly improve network throughput, fulfill QoS requirement of real-time traffic, and provide long-term fairness of non-real-time traffic at the same time.
Multimedia traffic plays an important role in the Internet, however, Best effort (BE) traffics such as World Wide Web access and file transfer still take up a substantial portion of Internet traffic. Improving transmission rate of BE traffic will improve WiMAX’s network throughput as well. In WiMAX networks, users with BE traffic contend for bandwidth from BS in order to get transmission opportunity. Truncated binary exponential backoff scheme is employed for retransmission. Parameters of contention window are controlled by BS and are periodically broadcast to users. If contention window size could be properly managed, collision rate can be reduced and therefore improves BE traffic throughput. In this thesis, we study contention window assignment scheme in the BS. According to bandwidth requests and the number of user collided, the BS dynamically changes contention window size. This scheme can optimize the transmission rate and transmission delay of bandwidth request for BE traffics.

[1] http://hspa.gsmworld.com/
[2] WiMAX Forum, http://www.wimaxforum.org/
[3] http://www.itu.int/newsroom/press_releases/2007/30.html
[4] C. Eklund, R. B. Marks, K. L. Stanwood and S. Wang, ”IEEE Standard 802.16:A Technical Overview of the WirelessMAN. Air Interfacefor Broadband Wireless Access," IEEE Communications Magazine, Vol. 40, pp. 98-107, June. 2002
[5] IEEE 802.16 WirelessMAN, http://wirelessman.org/
[6] Takashi Shono, “Mobile WiMAX Evolution Toward IMT-Advanced (4G),” http://www.ric.co.jp/expo/fair2007/download/a3.pdf
[7] http://wirelessman.org/relay/index.html
[8] V. Genc, S. Murphy, Y. Yang and J. Murphy, “IEEE 802.16J relay-based wireless access networks: an overview,” IEEE Wireless Communications, Vol. 15, Issue 5, Oct. 2008, pp. 56 - 63
[9] http://wirelessman.org/tgm/
[10] IEEE 802.16j Pre-Draft Baseline Document, 2007, IEEE 802.16j-06/026r4, http://www.ieee802.org/16/relay/
[11] R.B. Marks, “IEEE 802 Tutorial: 802.16 Mobile Multihop Relay,” IEEE 802.16mmr-06/006, http://www.ieee802.org/16/sg/mmr/
[12] C. M. Chou, T. M. Lin, F. C. Ren, C. C. Tseng, and W. H. Sheen, “Handover Scenarios for 802.16 MMR,” IEEE C802.16mmr-06/005, http://www.ieee802.org/16/sg/mmr/
[13] G. Shen, W. Ni, W. Zou, K. Zhang, J. Liu, S. Jin, T. Fahldieck and R. Muenzner, “Handover Schemes in IEEE 802.16j,” IEEE C802.16j-06/005, http://www.ieee802.org/16/relay/
[14] G. Shen, W. Ni, W. Zou and S. Jin, “Recommendation on 802.16 MMR with Backward Compatibility,” IEEE C802.16mmr-05/023, http://www.ieee802.org/16/sg/mmr/
[15] K. Suh, J. Cho, K. Han, S. Yoon, and J. Cho, “Open Problems in Mobile Multi-Hop Relay System,” IEEE C802.16mmr-05/028, http://www.ieee802.org/16/sg/mmr/
[16] IEEE 802.16j Contribution Documents, 2008, http://www.ieee802.org/16/relay/
[17] IEEE 802.16 Standard, 2004, “Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems”, IEEE Std 802.16-2004
[18] S. Ann, K. G. Lee and H. S. Kim, “A Path Selection Method in IEEE 802.16j Mobile Multi-hop Relay Networks,” International Conference on Sensor Technologies and Applications (SENSORCOMM '08), Aug. 2008, pp. 808-812
[19] B. Wang and M. Mutka, “Path Selection for Mobile Stations in IEEE 802.16 Multihop Relay Networks,” International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM 2008) Jun. 2008, pp. 1-8
[20] B. Lin, P. H. Ho, L. L. Xie and X. Shen, “Relay Station Placement in IEEE 802.16j Dual-Relay MMR Networks,” IEEE International Conference on Communications (ICC '08), May 2008, pp. 3437-3441
[21] IEEE Std. 802.16e, “IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems,” IEEE Std. 802.16e-2006
[22] T. S. Rappaport, Wireless Communications Principles and Practice Second Edition, Prentice Hall, NJ, USA, 2002
[23] V. S. Abhayawardhana, I. J. Wassell, D. Crosby, M. P. Sellars, and M. G. Brown, “Comparison of Empirical Propagation Path Loss Models for Fixed Wireless Access Systems,” 2005 IEEE 61st Vehicular Technology Conference, Vol. 1, pp. 73-77, 2005
[24] G. Senarath, W. Tong, P. Zhu, H. Zhang, D. Steer, D. Yu, M. Naden and D. Kitchener, “Multihop System Evaluation Methodology: Traffic Models,” IEEE C802.16j-06/024r1, http://www.ieee802.org/16/relay/
[25] H. Fattah and C. Leung, “An Overview of Scheduling Algorithms in Wireless Multimedia Networks,” IEEE Wireless Communications, Vol. 9, No. 5, Oct. 2002, pp. 76-83
[26] Y. Cao and O. K. L. Victor, “Scheduling Algorithms in Broadband Wireless Networks,” IEEE Proceedings, Vol. 89, No. 1, Jan. 2001, pp. 76-87
[27] K. Wongthavarawat and A. Ganz, “IEEE 802.16 Based Last Mile Broadband Wireless Military Networks with Quality of Service Support,” In Proc. of the IEEE Military Communications Conference (MILCOM’03), Vol. 2, Oct. 13-16, 2003, pp. 779 784
[28] M. Shreedhar and G. Varghese, “Efficient Fair Queuing Using Deficit Round-Robin,” IEEE/ACM Transactions on Networking, Vol. 4, No. 3, June 1996, pp. 375-385
[29] T. Y. Tsai and Z. H. Tsai, “Design of a Packet Scheduling Scheme for Downlink Channel in IEEE 802.16 BWA Systems,” IEEE Wireless Communications and Networking Conference (WCNC 2008), Mar. 2008, pp. 1453 - 1458
[30] C. Cicconetti, L. Lenzini, E. Mingozzi and C. Eklund, “Qality of Service Support in IEEE 802.16 Networks,” IEEE Network, Vol. 20, No. 2, March-April 2006, pp. 50-55
[31] V. S. Abhayawardhana, I. J. Wassell, D. Crosby, M. P. Sellars and M. G. Brown, “Comparison of Empirical Propagation Path Loss Models for Fixed Wireless Access Systems,” In Proc. of the IEEE Vehicular Technology Conference (VTC’05), Vol. 1, May 30-Jun 1, 2005, pp. 73-77
[32] T. S. Rappaport, Wireless Communications Principles and Practice Second Edition, 2002, NJ, Prentice Hall
[33] G. Senarath, W. Tong, P. Zhu, H. Zhang, D. Steer, D. Yu, M. Naden and D. Kitchener, “Multihop System Evaluation Methodology: Traffic Models,” IEEE C802.16j-06/024r1, May 2006, http://www.ieee802.org/16/relay/
[34] H. L. Chao and W. J. Liao, “Credit-Based Slot Allocation for Multimedia Mobile Ad Hoc Network,” IEEE Journal on Selected Areas in Communications,” Vol. 21, No. 10, Dec. 2003, pp. 1642-1651
[35] D. Niyato and E. Hossain, Queue-Aware Uplink Bandwidth Allocation and Rate Control for Polling Service in IEEE 802.16 Broadband Wireless Networks, IEEE Trans. on mobile computing, Vol. 5, No. 6, Apr. 2006, 668 - 679
[36] Q. Liu, X. Wang and G. B. Giannakis, A cross-layer scheduling algorithm with QoS support in wireless networks, IEEE Trans. on vehicular technology, Vol. 55, No. 3, May 2006, 839 - 847
[37] D. H. Cho, J. H. Song, M. S. Kim and K. J. Han, Performance Analysis of the IEEE 802.16 Wireless Metropolitan Area Network, IEEE Proc. of the First International Conf. on Distributed Frameworks for multimedia applications (DFMA’05), Feb. 2005, 130 - 136
[38] S. M. Oh and J. H. Kim, The Analysis of the Optimal Contention Period for Broadband Wireless Access Network, IEEE Proc. of the 3rd Int’l Conf. On Pervasive Computing and Communications (PerCom) Workshops, March 2005, 215 - 219
[39] D. Bertsekas and R. Gallager, Computer Networks 2nd Edition, Prentice Hall, 1992
[40] L. Kleinrock and S.S. Lam, Packet Switching in a Multiaccess Broadcast Channel: Performance Evaluation, IEEE Trans. on Communications, Vol. COM-23, No.4, Apr. 1975, 410 - 423