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研究生:吳駿毅
研究生(外文):Chun-Yi Wu
論文名稱:應用於正交頻域多工無線區域網路之時間同步研究
論文名稱(外文):Timing Synchronization for OFDM-Based Wireless Local Area Networks
指導教授:趙啟超趙啟超引用關係
指導教授(外文):Chi-chao Chao
學位類別:碩士
校院名稱:國立清華大學
系所名稱:通訊工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:英文
論文頁數:65
中文關鍵詞:時間同步無線區域網路
外文關鍵詞:Timing SynchronizationWireless Local Area NetworksIEEE 802.11a
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由於正交頻率多工系統(orthogonal frequency division multiplexing,簡稱OFDM )對於延遲擴展( delay spread)有較大的容忍度及可利用快速傅利葉 ( fast fourier transform ,簡稱 FFT ) 的架構來作硬體實現等等的主要優點,因此目前成為被廣泛討論的研究領域,如應用在數位廣播系統 ( digital audio broadcasting system ,簡稱 DAB ) ,數位電視系統 ( digital television video system ,簡稱 DTV ) 和無線區域網路系統( wireless local area network,簡稱 wireless LAN )等等。
在此篇論文中,我們將針對無線區域網路系統的時間同步(timing synchronization)問題提出研究的心得。目的是對於延遲擴展 (delay spread)的通道推導出最佳的時間同步理論,並提出簡化後的估測時間飄移的方法。在理論推導過程中,我們採用了IEEE 802.11a標準的實體層(physical layer)的架構,通道包含了可加性白高斯雜訊(additive white Gaussian noise,簡稱AWGN)的多路徑通道(multipath channel),而其中假設通道脈衝回應(channel impulse response)在一個封包(packet)內是不會變化的,但對於不同封包則會有改變。從模擬的結果顯示,我們確實對於可加性的白高斯雜訊通道和多路徑通道推導出最佳的時間同步的理論,另外為了降低硬體實作的複雜度,我們利用了數值分析的方法,提供經過簡化後的理論,不需藉由事先預估通道的統計特性,而對延遲擴展的通道作時間飄移的估測,而從模擬的結果顯示,簡化後的理論對於不同的延遲擴展(delay spread)仍然有不錯的表現。

With the robustness to the delay spread and the efficiency of the
fast Fourier transform algorithm, orthogonal frequency division
multiplexing (OFDM) techniques have been used in wide
applications. Wireless applications are a very hot research topic
in the recent years. In this thesis, we want to perform timing
synchronization based on the physical layer specification of the
IEEE 802.11a standard, which is one of the wireless local area
network standards. We have derived optimal data-aided
maximum-likelihood (DA-ML) timing offset estimation for additive
white Gaussian noise (AWGN) channels and multipath channels. Also
simplified methods for multipath channel are proposed and
evaluated. The multipath channels are quasi-static which are
static during an entire packet and different for other packets.
The simulation results show that our DA-ML estimation algorithms
can provide optimal performance for comparisons and simplified
methods perform well for the environments that the system is
designed for.

摘要.......................................1
致謝.......................................2
目錄.......................................3
附錄 英文論文本...........................4

IEEE 802.11, ``Supplement to 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: High-speed physical layer
in the 5 GHz band,'' Sept. 1999.
T.\ M.\ Pollet, M.\ van Bladel, and M.\ Moeneclaey, ``BER
sensitivity of OFDM systems to carrier frequency offset and
Wiener phase noise,'' {\em IEEE Trans.\ Commun.}, vol.\ 43, pp. 191--193, Feb./Mar./Apr. 1995.
J.\ J.\ van de Beek, M.\ Sandell, and P.\ O.\ Borjesson, ``ML
estimation of timing and frequency offset in OFDM systems,''
{\em IEEE Trans.\ Signal Processing.}, vol.\ 43, pp.\ 761--766,
Aug. 1997.
T.\ Keller and L.\ Hanzo, ``Orthogonal frequency division
multiplex synchronization techniques for wireless local area
networks,'' in {\em Proc. IEEE Int. Symp. Personal, Indoor, and
Mobile Radio Radio Communications, Taipei, Taiwan,} Oct. 1996,
pp.\ 963--967.

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