臺灣博碩士論文加值系統

近年來，由於無線區域網路提供使用者隨時隨地的掌握網際網路上的豐富資訊而受到業界與學術界的高度矚目。無線區域網路不但具有釵h優點，其中也有相當多值得研究的議題，像是鏈路調節、必v控制以及通道估測等議題。在本論文中，我們將針對封包分割與鏈路調節做進一步的探討與研究。
在無線區域網路系統之規範中，若要傳送的媒體存取控制服務資料單位(Media Access Control Service Data Units，MSDU)大於分割臨界值時，就必須被分割成釵h相同大小的媒體存取控制協定資料單位(Media Access Control Protocol Data Units，MPDU)。過去相當多的研究，僅考慮單一分割臨界值與鏈路調節來提升系統效能，此方法在每次的傳送過程中，雖然傳送端可以動態地依鏈路狀態來調整傳送速率，卻因單一分割臨界值造成每次傳送的位元數皆相同，所以實際提高之系統效能非常有限。為了進一步有效率提高系統效能，在本論文中，我們提出結合動態封包分割與鏈路調節演算法。該演算法摒除了單一分割臨界值的限制，在達到目標錯誤率的條件下，對於不同的傳送速率，有多個分割臨界值的選擇。經由在對數常態遮蔽效應通道模型下之模擬結果，我們驗證了所提出的演算法相對於其他鏈路調節演算法能有更好的效能表現。

In recent years, wireless local area network (WLAN) has received significant attention from the industry and academia because it enables users, wherever they are, to get abundant information from Internet. WLAN not only offers quite a few advantages, but also raises potential research issues, such as link adaptation, power control and channel estimation. This thesis will focus on fragmentation and link adaptation for further discussions and researches.
In the fragmentation scheme of IEEE 802.11 standard, if the size of the MSDU (Media Access Control Service Data Units) is larger than the fragmentation threshold, it is divided into several equal sections of smaller MPDUs (Media Access Control Protocol Data Units). Many previous researches only considered a single fragmentation threshold and link adaptation scheme in order to improve network performances. Although transmitter can adjust the transmission rate dynamically based on channel information, it transmits the same number of bits for each transmission packet due to single fragmentation threshold. This way, however, leads to a limit improvement of network performance. In order to make a significant improvement, in this thesis, we propose dynamic fragmentation and link adaptation algorithm. In the proposed algorithm, multiple fragmentation thresholds, instead of a single one, can be selected according to different transmission rates when a particular target packet error occurs. Under this circumstance, the channel is able to be more effectively utilized as well. We simulate the proposed algorithm under log-normal shadowing channel model and the results show that the proposed algorithm achieves much better performances than other link adaptation schemes.

Acknowledgements
摘要
Abstract
Table of Contents
List of Figures
List of Tables
Chapter 1 Introduction
1.1 Background
1.2 Motivation and Objective
1.3 Organizations of the Thesis
Chapter 2 Overview of Wireless LAN Communications
2.1 Introduction to the Techniques of Wireless LAN
2.1.1 Distributed Coordination Function
2.1.2 Point Coordination Function
2.2 Fragmentation in IEEE 802.11
2.2.1 Defragmentation
2.2.2 Characteristic of Fragmentation
2.3 Link Adaptation Scheme
Chapter 3 An Effective Dynamic Fragmentation and Link Adaptation Scheme
3.1 Dynamic Fragmentation with Link Adaptation Scheme
3.2 The Proposed Algorithm
3.2.1 Proposed Algorithm
3.3 Performance Evaluation
3.3.1 Energy Efficiency Analysis of an IEEE 802.11a DCF System….…
3.3.2 Goodput Analysis of an IEEE 802.11a DCF System
3.4 Wireless Channel Model
3.4.1 Bit Error Probability in AWGN Channel Model
3.4.2 Packet Error Probability
Chapter 4 Simulations
4.1 Error Performance of PHY Modes over the AWGN
4.1.1 Error Performance for Different Packet Lengths
4.2 Performance Analysis for Link Adaptation with Different Fragmentation
Thresholds
4.2.1 Performance Comparison
4.3 Simulations of Effect of the Distance
4.4 Simulations of Impact of the Maximum MSDU Size
Chapter 5 Conclusions
5.1 Conclusions
References

[1] IEEE 802.11 WG, Part 11: Wireless LAN Medium Access Control (MAC) and
Physical (PHY) Layer Specifications, Standard, The IEEE Inc., Piscataway,
NJ, Sep. 1999.
[2] IEEE 802.11b, Part 11: Wireless LAN Medium Access Control (MAC) and
Physical (PHY) Layer Specifications: High-speed Physical Layer in the
2.4GHz Band, Supplement to IEEE 802.11 Standard, Sep. 1999.
[3] IEEE 802.11a, Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications: High-speed Physical Layer in the 5GHz
Band, Supplement to IEEE 802.11 Standard, Sep. 1999.
[4] A. Kramling, M. Siebert, M. Lott, and M. Weckerle, “Interaction of power
control and link adaptation for capacity enhancement and QoS assistance,”
in Proceeding IEEE PIMRC’02, vol. 2, pp. 697-701, Sep. 2002.
[5] A. Kamerman and L. Monteban, “WaveLAN-II: A high-performance wireless LAN
for the unlicensed band,” Bell Labs. Technical Journal, vol.2, no.3, pp.
118-133, 1997.
[6] G. Holland, N. Vaidya, and P. Bahl, “A rate-adaptive MAC protocol for
wireless networks,” in Proceeding ACM MOBICOM’01, Rome, Italy, pp. 236-
251, July 2001.
[7] D. Qiao, S. Choi, and K. G. Shin, “Goodput analysis and link adaptation
for IEEE 802.11a wireless LANs,” IEEE Transactions on Mobile Computing,
vol. 1, no.4, pp. 278–291, Dec. 2002.
[8] B. Kim, Y. Fang, T. Wong and Y. Kwon, “Throughput enhancement through
dynamic fragmentation in wireless LANs,” IEEE Transactions on Vehicular
Technology, vol. 54, no.4, pp. 1415-1425, July 2005.
[9] B.P. Crow, I. K. Widjaja, J. Geun and P. T. Sakai, , “IEEE 802.11
wireless local area networks communications,” IEEE Communications
Magazine, vol. 35, issue 9, pp. 116–126, Sep. 1997.
[10] R. Blake, Wireless Communication Technology, Delmar, Thomson Learning,
Albany, NY, 2001.
[11] A. Goldsmith and S. G. Chua, “Adaptive coded modulation for fading
channels,” IEEE Transactions on Communications, vol. 46, no. 5, pp. 595-
602, May 1998.
[12] Z. Lin, G. Malmgren, and J. Torsner, ”System performance analysis of
link adaptation in HiperLAN type 2,” in Proceeding IEEE VTC ’00,
Rhodes, Greece, pp. 1719-1725, 2000.
[13] B. Sadeghi, V. Kanodia, A. Sabharwal, and E. Knightly, “Opportunistic
media access for multirate ad hoc networks,” Proceedings of MOBICOM’02,
Atlanta, Georgia, USA, pp.24-35, Sep.23–28, 2002.
[14] C. R. Lin and Y. H. J. Chang, “AAR: an adaptive rate control protocol
for mobile ad hoc networks,” Proceedings of the 11th IEEE International
Conference on Networks (ICON 2003), Sydney, Australia, pp.585-590, Sep.
2003.
[15] D. Qiao and S. Choi, “Goodput enhancement of IEEE 802.11a wireless LAN
via link adaptation,” in Proceeding IEEE ICC’01, Helsinki, Finland,
vol. 7, pp. 1995–2000, Jun. 2001.
[16] S. Ci and H. Sharif, “Adaptive approaches to enhance throughput of IEEE
802.11 wireless LAN with bursty channel,” in Proceeding IEEE LCN’00,
pp. 44-45, Nov. 2000.
[17] J. Tourrihes, “Dwell adaptive fragmentation: how to cope with short
dwells required by multimedia wireless LANs,” in Proceeding IEEE
GLOBECOM’ 00, vol. 1, pp. 57–61, 2000.
[18] J. Tourrihes, “fragment adaptive reduction: coping with various
interferers in radio unlicensed bands,” in Proceeding IEEE ICC’01,
Helsinki Finland, vol. 1, pp. 239–244, 2001.
[19] J. P. Ebert and A. Wolisz, “Combined tuning of RF power and medium
access control for WLANs,” Mobile Networks & Applications, vol. 5, no.
6, pp. 417-426, Sep. 2001.
[20] D. Qiao, S. Choi, A. Jain, and K. G. Shin, “MiSer: An optimal low-energy
transmission strategy for IEEE 802.11a/h,” in Proceeding ACM MOBICOM,
San Diago, CA, pp. 161-175, Sep. 2003.
[21] T. S. Rappaport. Wireless Communications: Principles & Practice, chapter
3: Mobile radio propagation: large scale path loss, pp. 69-185, Prentice
Hall, New Jersey, 1996.
[22] P. Chevillat, J. Jelitto, A. N. Barreto, and H. L. Truong, “A dynamic
link adaptation algorithm for IEEE 802.11a wireless LANs,” in Proceeding
ICC’03, Anchorage, AK, vol. 2, pp. 1141–1145, May 2003.
[23] J. G. Proakis, Digital Communications, 3rd ed., McGraw Hill, New York,
NY, 1995.
[24] M. B. Pursley and D. J. Taipale, “Error probabilities for spread-
spectrum packet radio with convolutional codes and viterbi decoding,”
IEEE Transactions on Communications, vol. COM-35, no. 1, pp. 1–12, Jan.
1987.
[25] G.C. Clark, Jr. and J.B. Cain, Error-correction Coding for Digital
Communications, Plenum Press, New York, NY, 1981.