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博碩士論文 etd-0910109-150938 詳細資訊
Title page for etd-0910109-150938
論文名稱
Title
在正交分頻多工系統下盲蔽頻率與時間同步演算法之研究
A study on Blind Frequency and Timing Synchronization in OFDM Systems
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
78
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2009-07-21
繳交日期
Date of Submission
2009-09-10
關鍵字
Keywords
正交分頻多工、週期穩態、同步
cyclostationarity, synchronization, OFDM
統計
Statistics
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中文摘要
正交分頻多工(orthogonal frequency division multiplexing,OFDM)系統對於同步誤差 (synchronization errors) 十分敏感,所以系統需要頻率偏移 (frequency offset) 與時間誤差 (timing error) 的資訊。大多數的文獻提出資料輔助 (data-aided) 的估測演算法,而資料輔助主要是導航符號 (pilot symbols) 或訓練序列 (training sequences),但是使用訓練資料 (training data)會降低既有的資料速率。因此我們選擇非資料輔助(nondata-aided)的方法來避免降低資料速率,而這類的估測器大概都使用保護區間 (guard interval),循環字首 (cyclic prefix) 進行估測。近年來,有許多文獻研究利用週期穩態特性 (cyclostationarity) 來估測同步誤差。目前有F. Gini與G. B. Giannakis用週期穩態特性來估測單載波系統的時間誤差與頻率偏移;而H. Bolcskei則是用它來估測正交分頻多工系統的時間誤差與頻率偏移。
本論文延續F. Gini與G. B. Giannakis的單載波系統同步估測方法與H. Bolcskei的正交分頻多工系統同步估測方法,在AWGN通道下,改良型盲蔽式同步演算法可以正確估測到正交分頻多工系統的同步參數。參考B. Park的研究可以得知,我們不需要使用子載波權重 (sub-carrier weighting) 以增加同步參數的估測樣本數來做平均估測值,據此,改良型盲蔽式同步演算法也可以達到我們要得估測效能。
Abstract
orthogonal frequency division multiplexing (OFDM) systems are very sensitive to synchronization errors. Therefore, OFDM systems require the knowledge of symbol timing and frequency offset. Most OFDM synchronization algorithms proposed in the literature are data-aided estimation structures. Data-aided estimators use pilot symbols or training sequences to perform synchronization. However, the use of training data reduces the transmission data rate. The alternative, which we consider in this thesis, is nondata-aided methods that perform synchronization by utilizing the redundant guard interval or cyclic prefix. Recently, cyclo-stationarity of signals is applied for estimating synchronization error. Gini and Giannakis utilized the property for single carrier systems and Bolcskei applied the property for OFDM systems.
In this thesis, we proposed a modified synchronization algorithm, which is extended from Giannakis and Bolcskei algorithms, in additive white Gaussian noise (AWGN) environment. According to Park’s study, additional sub-carrier weightings are not needed to enhance the estimation performance. From simulation results, the proposed modified blind synchronization algorithm can achieve better performance.
目次 Table of Contents
誌謝 i
摘要 ii
Abstract iii
目錄 iv
圖索引 vi
表索引 ix
第一章 簡介………1
第二章 盲蔽式同步演算法………2
2.1 單載波系統的同步演算法………2
2.1.1 單載波系統模型………2
2.1.2 單載波信號的週期穩態特性………5
2.1.3 傅立葉係數的統計特性………11
2.2 正交分頻多工系統的同步演算法 ………12
2.2.1 正交分頻多工的概念………12
2.2.2 保護區間………14
2.2.3 正交分頻多工系統模型………19
2.2.4 正交分頻多工信號的週期穩態特性………22
2.2.5 傅立葉係數的統計特性………27
第三章 改良的盲蔽式同步演算法………29
3.1 系統模型………29
3.2 週期穩態特性………32
3.3 傅立葉級數的統計特性………37
3.4 改良的盲蔽式同步演算法………39
第四章 系統模擬………51
4.1 改良式估測器的同步估測效能模擬………51
4.2 改良式估測器在多重通道下的估測效能模擬………63
第五章 結論………65
參考文獻………66
參考文獻 References
[1] ETSI ETS 300 401, “Radio broadcasting systems; Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers,” ETSI, Tech. Rep., Feb. 1995.
[2] ETSI ETS 300 744, “Digital Video Broadcasting (DVB); frame structure, channel coding and modulation for digital terrestrial television (DVB-T),” ETSI, Tech. Rep., Mar. 1997.
[3] ITU-T Recommendation G.992.1, “Asymmetric digital subscriber line transceivers(ADSL),” Jul. 1999.
[4] IEEE 802.11a, Part II: Wireless LAN medium access control (MAC) and physical layer (PHY) specifications: High-speed physical layer in the 5GHz band, Sept. 1999.
[5] F. Gini and G. B. Giannakis, “Frequency offset and symbol timing recovery in flat-fading channels: A cyclostationary approach,” IEEE Trans. Commun., vol. 46, no. 3, pp. 400–411, Mar. 1998.
[6] H. Bolcskei, “Blind estimation of symbol timing and carrier frequency offset in wireless OFDM systems,” IEEE Trans. Commun., vol. 49, no. 6, pp. 988–998, June 2001.
[7] B. Park, H. Cheon, and E. Ko, “A blind OFDM synchronization algorithm based on cyclic correlation,” IEEE Signal Processing Letters, vol. 11, no. 2, pp. 83–85, Feb. 2004.
[8] H. Bolcskei, P. Duhamel, and R. Hleiss, “Design of pulse shaping OFDM/ OQAM systems for high data-rate transmission over wireless channels,” in Proc. IEEE Inc. Conf. Communications (ICC), Vancouver, BC, Canada, pp. 559–564, June 1999.
[9] P. H. Moose, “A technique for orthogonal frequency division multiplexing frequency offset correction,” IEEE Trans. Commun., vol. 42, pp. 2908–2914, Oct. 1994.
[10] W. A. Gardner, Ed., Cyclostationarity in Communications and Signal Processing. Piscataway, New Jersey: IEEE Press, 1995.
[11] S. M. Kay, Fundamentals of Statistical Signal Processing: Estimation Theory. Englewood Cliffs, New Jersey: Prentice-Hall, 1993.
[12] J. G. Proakis, Digital Communications, 4th ed., New York: McGraw-Hill, 2001.
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