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研究生:王超勳
研究生(外文):Chow-Shiun Wang
論文名稱:正交分頻多工系統中結合時序與頻率偏移估測之研究
論文名稱(外文):Joint Timing And Frequency Offset Estimation Research For OFDM System
指導教授:黃穎聰黃穎聰引用關係
指導教授(外文):Yin-Tsung Hwang
學位類別:碩士
校院名稱:國立雲林科技大學
系所名稱:電子與資訊工程研究所碩士班
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:2004
畢業學年度:92
語文別:英文
論文頁數:109
中文關鍵詞:正交分頻多工取樣時序偏移載波頻率偏移同步估測
外文關鍵詞:OFDMsynchronization estimationsampling clock offsetcarrier frequency offset
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OFDM技術由於其頻寬效率及對抗頻率選擇性衰減上有很好的效能,近年來已被廣泛的應用在各種無線傳輸技術上,特別是像無線區域網路WLAN,數位語音廣播DAB,數位影像廣播DVB以及數位無線中頻廣播DRM等等。儘管OFDM系統有許多優點,但是仍有許多問題要克服。一個最重要的缺點就是,OFDM對頻率偏移效應相當敏感,這是由於接收端與發射端間頻率誤差的結果;它會引起內部載波干擾,且會破OFDM信號組的正交性。其他如取樣頻率偏移,以及多路徑通道效應,同樣會造成系統效能的下降。因此,在接收端需要有一個良好的估測系統來還原信號。
在本篇論文中,我們基於802.11a無線區域網路的基礎上,將展現幾種估測演算法,並提出一個可行的OFDM系統同步架構。這個架構包括時域上的訊框起始點檢測,訊框的邊緣估測與頻率偏移估測,以及頻域上的殘餘時序與相位偏移補償。為了配合實際環境的需要與實驗的真實性,我們採用了動態模擬來幫助我們了解實際可能遭遇之狀況;因此,我們加入頻寬限制,振幅調變與解調,低通濾波,連續時間之取樣等實驗流程,並在加成白色高斯雜訊以及雷利衰退通道下進行電腦動態模擬。根據模擬,我們所提出的系統在802.11a的IEEE通道模型下可以獲得良好的同步效果。
Due its performance edges in channel bandwidth efficiency and in combating frequency selective fading, OFDM based wireless transmission techniques have become increasingly popular these days. The OFDM technique has been adopted in various applications such as wireless LAN, Digital Audio Broadcasting, Digital Video Broadcasting and Digital Radio Monial etc. Despite of these advantages, there are still many challenges lying ahead of the OFDM systems. In this thesis, our focus will be on the synchronization problem. First of all, the performance of an OFDM system is very sensitive to the carrier frequency offset. This will destroy the orthogonality among sub-carriers and lead to inter-carrier interference (ICI). Secondly, frame detection error and sampling timing error also have crucial impact on the system performance. These problems are further complicated by the effect of multi-path fading. Therefore, a robust synchronization block capable of tackling these problems must be employed at the receiver side. The synchronization process basically consists of two measures: estimation and compensation.
In this thesis, based on the system requirement of the 802.11a standard, we investigate several estimation algorithms for timing and frequency offsets and propose a novel synchronization architecture. The architecture consists of different processing blocks for 1) frame start detection 2) frame bound estimation 3) frequency offset estimation in time domain, and 4) residual timing and phase error compensation in frequency domain. To mimic the entire synchronization process, we conduct dynamic simulation to show the variations of system behavior along the time. To make the simulation as close to the real system as possible, we also add the features such as transmission bandwidth limitation (pulse shaping), RF modulation/demodulation, low pass filtering, and A/D sampling error into our simulation platform. The channel model adopted is the combination of an IEEE compliant Rayleigh fading channel and AWGN channel. Simulation results indicate, the proposed joint timing and frequency offset scheme can achieve satisfactory synchronization.
Contents
Abstract (in Chinese)----------------------------------------------------Ⅰ
Abstract (in English)----------------------------------------------------Ⅱ
Acknowledgment ----------------------------------------------------------Ⅳ
Contents ---------------------------------------------------------------Ⅴ
List of Figures----------------------------------------------------------Ⅶ
List of Tables------------------------------------------------------------X
Chapter 1 Introduction ---------------------------------------------------1
Chapter 2 Theoretical Background------------------------------------------5
2.1 Principle Of OFDM Transmission-------------------------------------7
2.2 OFDM Bandwidth Efficiency -------------------------------------------11
2.3 The Effect Of Guard Interval By Using The Cyclically Prefixed--------13
2.4 Windowing Effect-----------------------------------------------------15
2.5 Some Blocking Problem for the OFDM System Synchronization------------17
Chapter 3 Utility of the IEEE 802.11a Stander ---------------------------22
3.1 OFDM PLCP Sublayer --------------------------------------------------24
3.2 Mathematical conventions in the signal descriptions------------------26
3.3 PLCP preamble (SYNC)-------------------------------------------------28
3.4 Subcarrier modulation mapping----------------------------------------30
3.5 Pilot subcarriers----------------------------------------------------32
3.6 OFDM modulation------------------------------------------------------33
3.7 Some requirement parameter-------------------------------------------35
Chapter 4 Timing And Frequency Synchronization---------------------------38
4-1 ML algorithm introduce-----------------------------------------------41
4-2 ML algorithm with PASM ----------------------------------------------44
4-3 ML algorithm for low complexity design-------------------------------46
4-4 Joint Timing And Frequency Offset Estimation For OFDM System---------49
4-4-1 The Energy and Frame Arrival Time Estimation Scheme----------------50
4-4-2 Frame Position Estimation Scheme-----------------------------------52
4-4-3 Joint Time and Frequency Offset Acquisition Scheme-----------------55
4.5 A New Method Of The Carrier Frequency Offset Estimation--------------59
4.6 Error Tracking ------------------------------------------------------62
4-6-1 Channel Estimation Scheme------------------------------------------63
4-6-2 Error Tracking Estimation Scheme-----------------------------------64
4-6-3 Modified Error Tracking Estimation Scheme--------------------------65
Chapter 5 System Model Simulation----------------------------------------67
5-1 Mapping and Pilot Insert Model --------------------------------------69
5-2 Pulse Shaping--------------------------------------------------------71
5-3 AM Modulation--------------------------------------------------------74
5-4 Channel Model -------------------------------------------------------77
5-5 AM Demodulation And LPF Procession-----------------------------------80
5-6 Sampling and Timing Drift Model--------------------------------------82
5-7 Frame Arrival Detection----------------------------------------------86
5-8 Frame Position detection---------------------------------------------88
5-9 Auto Frequency Compensation------------------------------------------90
5-10 New Auto Frequency Compensation Scheme------------------------------96
5-11 Channel Equalization ----------------------------------------------100
5-12 Error Tracking-----------------------------------------------------101
Chapter 6 Conclusion and the future work--------------------------------106
Reference---------------------------------------------------------------108
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Standards Information Nerwork IEEE Press, USA.
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NO. 5, SEPTEMBER 1999 pp.1595-1609
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[7]Terng-Yin Hsu, Bai-Jue Shieh, and Chen-Yi Lee “An All-Digital Phase-Locked
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[8]W. Eberle, L, Deneire, H. De Man, B. Gyselinvkx, M, Engels, “Automatic
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[9]Yin-Tsung Hwang, Kuo-Wei Liao, Chien-Hsin Wu, “ FPGA realization of an
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der Perre, M. Vergara, B. Gyselinckx, M. Engels, I, Bolsens, “Flexible
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[11]Hsuan-Yu Liu, Yi-Hsin Yu, Chien-Jen Hung, Terng-Yin Hsu, and Chen-Yi
Lee. ”Combining Adaptive Smoothing And Decision-Directed Channel
Estimation Schemes for OFDM WLAN Systems” in ROC. IEEE 2003 pp.149-152
[12]Yih-Min, Chen. ” Handout of the Process of Baseband Signals in Wireless
Communication for 802.11a OFDM-base,” ROC. NCU. 2003.
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Using a Pilot Symbol: Algorithms” Selected Areas in Communications, IEEE
Journal on , Volume: 19 , Issue: 12 , Dec. 2001 Pages:2486 - 2494
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