臺灣博碩士論文加值系統

近年來隨著無線網路的普及，手機、平板、筆記型電腦、電視等等，皆可以透過無線網路將裝置接上網際網路，不論是在居家的環境、或是公共場合如捷運站等等，不再受制於網路線，只要處在的地點可以收到無線網路訊號，即可連線上網，對現代人來說無線網路可謂是無所不在的。
目前被廣泛使用的標準為IEEE802.11無線網路存取技術，其中預設是利用分散式協調功能(DCF)機制去競爭通道，於開始傳送資料前需等待倒數一段時間，其值則是從競爭視窗(Contention Window)大小隨機挑選而來，若發生碰撞則將競爭視窗大小調大，進而降低再次發生碰撞的機率，相反地，若資料傳送成功則將之縮小，進而縮減倒數時間，即可用更高的頻率去嘗試傳送資料，相對的碰撞率就會提升，所以決定競爭視窗大小成長或減少的倒退演算法便成了影響無線網路傳輸效能的一個重要關鍵，先前有不少相關的研究，目的都是希望效能可以更加提升；但經過實驗測試後發現距離最佳化皆還有可改善的空間，在此論文中，我們以碰撞率做為調整競爭視窗大小的依據，並透過實驗和數學分析驗證，於不同節點數的環境下也能使效能接近最佳化。

In recent years, Wireless Local Networks (WLANs), generally referred as Wi-Fi, has become more and more popular. Mobile devices, such as smart phones, notebooks or tablets, can connect to Internet through the wireless networks in anywhere, such as coffee shop and MRT station, where wireless signal is available, without restricted to the deployment of wired circuit, wireless networks are ubiquitous in modern life.
The IEEE 802.11 protocol is the one of most deployed wireless access technologies all over the world. In the 802.11 protocol, the fundamental mechanism to access medium is called Distributed Coordination Function (DCF). DCF is based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. In DCF scheme, all nodes compete for the wireless channel with a contention resolution method, named Binary Exponential Backoff (BEB). Before any transmission attempt of a packet, the node needs to countdown a period of time, and the time period is selected from the Contention Window (CW) size randomly, every time the transmission of packet is involved in a collision, to reduce collision rate, the contention window size of node will be increased. Oppositely, after a successful transmission, the contention window size of node will be decreased, to increase the frequency of transmission attempt, but the collision probability will also be increased. The growth or reduction of contention window size is the key to affect the performance of wireless network, there have several backoff algorithm has be proposed to improve system throughput, but after the measurement of DCF and experiments, those methods cannot approach maximum throughput of DCF. In this research, a backoff algorithm, Rapidly Adaptive Collision Backoff Algorithm (RACB) is proposed to improve system throughput. In RACB, the variation of contention window size is adjusted by the collision rate, after the mathematical analysis and the measurement of throughput shows that RACB can let the system throughput approaching maximum throughput in the environment with any number of nodes.

Chapter 1 : Introduction 1
Chapter 2 : Background and Related Works 7
2.1 IEEE 802.11 DCF 7
2.2 Related Works 11
2.2.1 Exponential Increase Exponential Decrease (EIED) 11
2.2.2 Linear Increase Linear Decrease (LILD) 12
2.2.3 Exponential-Linear Backoff Algorithm (ELBA) 13
2.3 Maximum Throughput 14
Chapter 3 : DCF Measurement and DCF Analysis 16
3.1 DCF Measurement 16
3.2 DCF Analysis 18
Chapter 4 : Mathematical Analysis and RACB Algorithm 22
4.1 Mathematical Analysis 22
4.1.1 System Throughput 23
4.1.2 Transmission Probability 25
4.1.3 Collision Rate and System Throughput 28
4.2 Rapidly Adaptive Collision Backoff (RACB) Algorithm 31
Chapter 5 : Simulation Results 34
5.1 Environment Setting 34
5.2 Numerical Results 36
Chapter 6 : Conclusions and Future Work 40
6.1 Conclusions 40
6.2 Future Work 40
Reference 41

[1]IEEE standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, IEEE Standard 802.11, June 1999.
[2]G. Bianchi. “Performance analysis of the IEEE 802.11 distributed coordination function. IEEE Journal on Selected Areas in Communications, Vol. 18. No. 3, March 2000.
[3]N. Song, B. Kwak, J. Song, and L. E. Miller, “Enhancement of IEEE 802.11 distributed coordination function with exponential increase exponential decrease backoff algorithm, The 57th IEEE Semiannual Spring VTC, vol. 4, April 2003.
[4]Song, Nah-Oak, Byung-Jae Kwak, and Leonard E. Miller. Analysis of EIED backoff algorithm for the IEEE 802.11 DCF. IEEE VEHICULAR TECHNOLOGY CONFERENCE, Vol. 62. No. 4, 2005.
[5]Ye, Shiang-Rung, and Yu-Chee Tseng. A multichain backoff mechanism for IEEE 802.11 WLANs. IEEE Transactions on Vehicular Technology, 1613-1620, 2006.
[6]Cali, Federico, Marco Conti, and Enrico Gregori. IEEE 802.11 protocol: design and performance evaluation of an adaptive backoff mechanism. IEEE Journal on Selected Areas in Communications, 1774-1786, 2000.
[7]Q Ni, L Aad, C Barakat and T Turletti. Modeling and analysis of slow CW decrease IEEE 802.11 WLAN. 14th IEEE Proceedings on Personal, Indoor and Mobile Radio Communications, Vol. 2, 2003.
[8]Yong Peng, Keping Long, Shiduan Cheng and Jian Ma. Performance of reliable transport protocol over IEEE 802.11 wireless LAN: analysis and enhancement. INFOCOM 2002. Twenty-First Annual Joint Conference of the IEEE Computer and Communications Societies, Vol. 2, 2002.
[9]CH Lin, CK Shieh, WS Hwang and CH Ke. An exponential-linear backoff algorithm for contention-based wireless networks. Proceedings of the International Conference on Mobile Technology, Applications, and Systems. ACM, 2008.
[10]CE Weng, CY Chen, CH Chen and CH Chen. Optimal performance study of IEEE 802.11 DCF with contention window. 2011 International Conference on Broadband and Wireless Computing, Communication and Applications (BWCCA), IEEE, 2011.
[11]Y Zheng, K Lu, D Wu and Y Fang. Performance analysis of IEEE 802.11 DCF in imperfect channels. IEEE Transactions on Vehicular Technology, 1648-1656, 2006.
[12]Wang, Ruopeng, Jie Zhang, and Xiangyi Zou. Performance analysis and optimization of IEEE 802.11 DCF with constant contention window. ISECS International Colloquium on Computing, Communication, Control, and Management (CCCM'08), Vol. 2, 2008.
[13]Duda, Andrzej. Understanding the Performance of 802.11 Networks. PIMRC, Vol. 8, 2008.
[14]Kwon, Younggoo, Yuguang Fang, and Haniph Latchman. A novel MAC protocol with fast collision resolution for wireless LANs. INFOCOM 2003. Twenty-Second Annual Joint Conference of the IEEE Computer and Communications, Vol. 2, 2003.
[15]Chen, Yunli, and Dharma P. Agrawal. Effect of Contention Window on the performance of IEEE 802.11 WLANs. 3rd Annual Mediterranean Ad Hoc Networking Workshop, June 2004.
[16]Bianchi, Giuseppe, Luigi Fratta, and Matteo Oliveri. Performance evaluation and enhancement of the CSMA/CA MAC protocol for 802.11 wireless LANs. Seventh IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'96), Vol. 2, 1996.
[17]Tay, Y. C., and Kee Chaing Chua. A capacity analysis for the IEEE 802.11 MAC protocol. Wireless networks, ACM, 159-171, 2001.
[18]Barry, Michael, Andrew T. Campbell, and Andras Veres. Distributed control algorithms for service differentiation in wireless packet networks. INFOCOM 2001. Twentieth Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings, Vol. 1, 2001.
[19]V Bharghavan, A Demers, S Shenker and L Zhang. MACAW: a media access protocol for wireless LAN's. ACM SIGCOMM Computer Communication Review, Vol. 24. No. 4, 1994.
[20]J Lee, H Lee, Y Yi, S Chong, Nardelli B and M Chiang. Making 802.11 dcf near-optimal: Design, implementation, and evaluation. 2013 10th Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks (SECON), 2013.
[21]Jiang, Libin, and Jean Walrand. A distributed CSMA algorithm for throughput and utility maximization in wireless networks. IEEE/ACM Transactions on Networking (TON), 960-972, 2010.
[22]Rajagopalan, Shreevatsa, Devavrat Shah, and Jinwoo Shin. Network adiabatic theorem: an efficient randomized protocol for contention resolution. ACM SIGMETRICS Performance Evaluation Review, Vol. 37. No. 1, 2009.
[23]Calì, Frederico, Marco Conti, and Enrico Gregori. Dynamic tuning of the IEEE 802.11 protocol to achieve a theoretical throughput limit. IEEE/ACM Transactions on Networking (ToN), 785-799, 2000.