臺灣博碩士論文加值系統

隨著網際網路的蓬勃發展，資訊與通訊技術的快速進步，無線區域網路
技術成為現今熱門的焦點之一。
相較於有線區域網路，無線區域網路具有如下優點：
不需施工佈線與線路規劃，可節省成本與時間
可與既存之有線網路資源結合
資源分享更加便利
即便是行動中，仍可隨時隨地使用
故具備了無線繫絆，高移動性的特點。
IEEE 802.11是美國電子電機學會所制定的無線區域網路標準，採用的存取機制為分散協調功能(DCF)即載波感測多重存取/碰撞避免(CSMA/CA)。
而其中無線網路架構分為隨意型網路(Ad hoc Network)與
具基礎架構網路(Infrastructure Network)兩種。
雖然IEEE 802.11使用了DCF的機制，以減少競爭時碰撞可能發生的機會。
但在行動節點彼此競爭傳送權的過程中，還是極有可能會引起隱藏節點(hidden node)或暴露節點(exposed node)的問題。
進而發生碰撞或降低利用率，造成整體傳輸效能的下降。
而且機制中使用的返回(backoff)方式亦有傳輸媒介分配不公平的現象。
本研究針對隨意型網路環境下現有IEEE 802.11無線區域網路標準的缺失進行探討改善，
進而避免造成無線傳輸的效能不彰，以達到較佳的頻寬利用率。

With the developing of Internet and the rapidly advance of information and communication technology, wireless LAN technology has become the popular topic nowadays. Comparing with wired LAN, wireless LAN has the following advantages:
Without wiring construction and planning circuit, cost and time can be reduced.
Integrated with already existing wired LAN resources.
Resources sharing gets more convenient.
Even moving, resources can be employed anytime or anywhere.
It possesses the characteristics: no wiring hassle and high mobility.
IEEE 802.11 is the wireless LAN standard drawn by American Institute of Electrical and Electronic Engineers, and using the Distributed Coordination Function (DCF) aka Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) as the access mechanism. The topologies which wireless LAN supports are ad hoc network and infrastructure network.
Although IEEE 802.11 uses DCF as MAC protocol to reduce the probability of collision while contention. However during the contention among mobile nodes, it has the strong probability causing the hidden node problem or exposed node problem. The former will suffer collisions and the latter will reduce utility rate. The random backoff scheme may also cause the unfairness of medium access though.
This study focuses on improving the weaknesses of the wireless LAN standard IEEE 802.11 working in ad hoc network and avoiding the low efficiency to achieve the enhanced utility rate of bandwidth.

CHAPTER 1 Introduction
CHAPTER 2 Background
CHAPTER 3 IEEE 802.11 Standard
CHAPTER 4 Enhanced Method
CHAPTER 5 Simulation Results and Analyses
CHAPTER 6 Conclusion
REFERENCES

[1] IEEE Standard for Information Technology - Telecommunications and Information Exchange between Systems-Local and Metropolitan Area Networks - Specific Requirements - Part 11: Wireless Lan Medium Access Control (MAC) and Physical Layer (PHY) Specifications ISO/IEC 8802-11; ANSI/IEEE Std 802.11, 1999 edition, 20 Aug. 1999
[2] V. Bharghavan, A. Demers, S. Shenker and L. Zhang, MACAW: a Media Access Protocol for Wireless LAN's, In Proceedings of the Conference on Communications Architectures, Protocols and Applications (SIGCOMM '94), Volume 24, Issue 4, pp. 212-225, Oct. 1994.
[3] P. Karn, MACA - A New Channel Access Method for Packet Radio, In ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pp. 134-140, 22 Sept. 1990.
[4] J. Broch, D.A. Maltz, D.B. Johnson, Y.C. Hu, J. Jetcheva, A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols, In Proceedings of the 4th Annual ACM/IEEE International Conference on Mobile Computing and Networking (MobiCom '98), pp. 85-97, 25-30 Oct. 1998.
[5] J. Weinmiller, H. Woesner and A. Wolisz, Analyzing and Improving the IEEE 802.11-MAC Protocol for Wireless LANs, In Proceedings of the 4th International Workshop on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems (MASCOTS '96), pp. 200-206, 1-3 Feb. 1996.
[6] M. Natkaniec and A.R. Pach, An Analysis of the Backoff Mechanism used in IEEE 802.11 Networks, In Proceedings of 5th IEEE Symposium on Computers and Communications (ISCC 2000), pp. 444-449, 3-6 July 2000.
[7] M. Natkaniec and A.R.Pach, An analysis of the modified backoff mechanism for IEEE 802.11 networks, In First Polish-German Teletraffic Symposium (PGTS2000), pp. 89-96, 24-26 Sept. 2000.
[8] M. Natkaniec and A.R. Pach, An Analysis of the Influence of the Threshold Pparameter on the IEEE 802.11 Network Performance, In IEEE Wireless Communications and Networking Conference (WCNC 2000), Volume: 2, pp. 819-823, 23-28 Sept. 2000.
[9] E. Dutkiewicz, Impact of Transmit Range on Throughput Performance in Mobile Ad Hoc Networks, In IEEE International Conference on Communications (ICC 2001), Volume: 9, pp. 2933-2937, 11-14 June 2001.
[10] C. Ware, J. Judge, J. Chicharo, and E. Dutkiewicz, Unfairness and Capture Behaviour in 802.11 Adhoc Networks, In IEEE International Conference on Communications (ICC 2000), Volume: 1, pp. 159-163, 18-22 June 2000.
[11] J.L. Sobrinho and A.S. Krishnakumar, Quality-of-Service in Ad Hoc Carrier Sense Multiple Access Wireless Networks, IEEE Journal on Selected Areas in Communications, Volume: 17, Issue: 8, pp. 1353-1368, Aug. 1999.
[12] S. Xu, T. Saadawi and M. Lee, Comparison of TCP Reno and Vegas in Wireless Mobile Ad Hoc Networks, In Proceedings of 25th Annual IEEE Conference on Local Computer Networks (ICLCN 2000), pp. 42-43, 8-10 Nov. 2000.
[13] S. Xu and T. Saadawi, Does the IEEE 802.11 MAC Protocol Work Well in Multihop Wireless Ad Hoc Networks?, IEEE Communications Magazine, Volume: 39, Issue: 6, pp. 130-137, June 2001.
[14] S. Xu and T. Saadawi, Revealing and Solving the TCP Instability Problem in 802.11 Based Multi-hop Mobile Ad Hoc Networks, In IEEE VTS 54th Vehicular Technology Conference (VTC 2001), Volume: 1, pp. 257-261, Fall. 2001.
[15] S. Xu and T. Saadawi, Revealing TCP Unfairness Behavior in 802.11 Based Wireless Multi-hop Networks, In 12th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Volume: 2, pp. E-83 - E-87, Sep/Oct 2001.
[16] S. Xu and T. Saadawi, Revealing TCP Incompatibility Problem in 802.11-based Wireless Multi-Hop Networks, In IEEE Global Telecommunications Conference (GLOBECOM '01), Volume: 5, pp. 2847-2851, 25-29 Nov. 2001.
[17] B. Bensaou, Y. Wang and C. C. Ko, Fair Medium Access in 802.11 Based Wireless Ad-Hoc Networks, In 2000 First Annual Workshop on Mobile and Ad Hoc Networking and Computing, pp. 99-106, 11 Aug. 2000.
[18] F. Eshghi and A.K. Elhakeem, Performance Analysis of Ad-Hoc Wireless LANs for Real-Time Traffic, In The 5th International Symposium on Wireless Personal Multimedia Communications (ISWPMC 2002), Volume: 3, pp. 1356-1360, 27-30 Oct. 2002.
[19] S.T. Sheu, T. Chen, J. Chen and F. Ye, The Impact of RTS Threshold on IEEE 802.11 MAC Protocol, In Proceedings of 9th International Conference on Parallel and Distributed Systems (ICPDS 2002), pp. 267-272, 17-20 Dec. 2002.
[20] S.Y. Wang, C.L. Chou, C.H. Huang, C.C. Hwang, Z.M. Yang, C.C. Chiou, and C.C. Lin, "The Design and Implementation of the NCTUns 1.0 Network Simulator," Computer Networks, Vol. 42, Issue 2, pp. 175-197, June 2003.