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研究生:卓建宏
研究生(外文):Cho Chian-Hung
論文名稱:應用於正交分頻多工無線區域網路之碼框同步與自動增益控制
論文名稱(外文):Frame Synchronization and Digital Automatic Gain Control for OFDM Wireless LAN System
指導教授:溫瓌岸
指導教授(外文):Kuei-Ann Wen
學位類別:碩士
校院名稱:國立交通大學
系所名稱:電子工程系
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:中文
論文頁數:93
中文關鍵詞:正交分頻多工無線區域網路碼框同步自動增益控制
外文關鍵詞:OFDMWireless LANFrame SynchronizationAutomatic Gain Control
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本論文提出一個有效率,應用在IEEE所制訂的無線區域網路標準IEEE 802.11a之碼框同步(Frame synchronization),符元同步(Symbol synchronization),以及數位自動增益控制。IEEE 802.11a所使用的方式是正交分頻多工(Orthogonal Frequency Division Multiplexing), OFDM),在一個多路徑衰減的室內通道之中,正交分頻多工被證明能有效的對抗由多路徑衰減所帶來的不理想因素,就由此調變可使傳輸率提升至54 Mbps。
所提出的架構利用安置在每個封包之前的preamble,在低訊號雜訊比和多路徑衰減的通道時可以快速,正確的達到框碼同步。在實現部分,使用了FPGA和DSP實現所提出的演算法。對於測試和量測部分,我們提出並建立一個快速且方便的測試方法,兩種實現方式皆經由此測試部分印證成功。

In this thesis, an efficient frame and symbol synchronization, and digital automatic gain control (AGC) for Orthogonal Frequency Division Multiplexing (OFDM) based wireless LAN (WLAN) defined in IEEE 802.11a had been proposed. The architecture contains frame detection, symbol timing estimation and signal power estimation. The estimated signal power can be used in AGC. The proposed method enables a rapid and accurate synchronization even under very low SNR and multi-path fading channel by using ten short training symbols at the start of every frame. For implementation part, DSP and FPGA are both used to implement. By writing c code and assembly code, the proposed frame synchronization is implemented by using TI TMS320CC6201 EVM and is verified. The implementation on FPGA by writing hardware description language is also verified. For the test and measurement, a fast and convenient test methodology is proposed and built. The two implementations are tested and measured under the proposed test methodology with real-time signal processing.

中文摘要……………………………………………………………………………I
ABSTRACT…….……………………………………………….……………….…II
ACKNOWLEDGE……………………………………………………………….III
CONTENT………..……………………………………………………………….IV
LIST OF TABLES……………………………………………………………….VII
LIST OF FIGURES………………………………………………….………….VIII
1 Introduction
1.1 Introduction to OFDM and WLAN……………………………………..………1
1.2 Organization of this thesis…………...…………………………………..…..….2
2 OFDM System Overview and Channel Model
2.1 OFDM System Overview………..………………………...………………..…..4
2.1.1 Techniques to combat the channel………………………...……………..4
2.1.2 OFDM Basics……………………………………………………...…….6
2.2 Channel Model……………………………………………………………….10
2.2.1 Characteristic of Channel Model……………………………………...10
2.2.2 Indoor Channel Model for Wireless LAN…………………………….13
2.3 Simulation Environment……………………………………………………..19
3 OFDM-WLAN Transmitter for IEEE 802.11a
3.1 WLAN IEEE 802.11a Physical Layer Specification……………………..……20
3.2 Transmitter Consideration………………………………………………..……24
3.3 PAPR Problem…………………………………………………………………27
3.2.1 Statistical properties of OFDM signals………………………….……..29
3.2.2 Clipping Effects On WLAN System : Case I………………………….30
3.2.3 Clipping Effects On WLAN System : Case II…………………………32
4 Frame Synchronization and Digital AGC for WLAN
4.1 Preamble Format and Requirement of the Specification……………………..37
4.2 Proposed Architecture and Behavior of Frame Synchronization……………..38
4.3 Frame Detection………………………………………………………………43
4.4 Digital AGC Algorithm……………………………………………………….50
4.4.1 Choice of Desired Signal Level…………………………………………..51
4.4.2 Proposed AGC Algorithm………………………………………………...52
4.4.3 Consideration of AGC Implementation…………………………………..56
4.5 Symbol Synchronization………………………………………………………57
4.5.1 Observation of Matched Filter……………………………………………57
4.5.2 Proposed Method for Detection of Symbol Timing………………………60
4.5.3 Performance Evaluation of Symbol Timing Detection…………………...63
4.6 End of Short Symbol Detection……………………………………………….64
4.7 Why Both Correlator and Matched filter...………………………………….…65
4.8 Performance Evaluation……………………………………………………….65
5 Implementation and Measurement
5.1 DSP Implementation……………………………………………………..……..67
5.1.1 TMSC6201 DSP Description……...………………………….….…….67
5.1.2 TMSC6201 EVM Description……...………………………….………71
5.1.3 Procedure of DSP Implementation…………………………….………72
5.1.4 Design Goal………….………………………………………….……..75
5.1.5 Architecture and Ping-Pong Buffer…………………………….………75
5.1.6 Peripheral………………………………………………………………77
5.1.6.1 DMA.………….……………………………………………..77
5.1.6.2 Timer…………………………………………………………78
5.1.7 Speed Analysis…………………………………………………………79
5.1.8 Implementation…………………………………………………………81
5.2 FPGA Implementation…………………………………………………….…….84
5.3 Measurement……………………………………………………………………87
5.3.1 Flow of Testing Establishment………………………………………....87
5.3.2 Measurement…….……………………………………………………..89
6 Conclusions…………………………………………………………………..94
References…………………………………………………………….…………95

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[2] R. Van Nee, “A new OFDM standard for high rate wireless LAN in the 5 GHz band,” Proc. of IEEE VTC’99, vol.1, pp.258-262, Sept. 1999.
[3] IEEE Std. 802.11a-1999, Wireless LAN Medium Access Control and Physical Layer specifications: High-speed physical layer in the 5 GHz band.
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[5] H. Kobayashi, ”A novel symbol frame and carrier frequency synchronization for burst mode OFDM signal,” Proc. of IEEE VTC’00, vol.3, pp.1392-1396, Sept. 2000.
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[10] S. Weinstein and P. Ebert, “Data transmission by frequency division multiplexing using the discrete fourier transform,” IEEE Trans. Commun. Techn., vol. COM-19, pp.628-634, Oct. 1971.
[11] van de Beek, J. J., O. Edfors, M. Sandell, S. K. Wilson, and P. O. Borjesson, “On Channel Estimation in OFDM Systems,” Proceeding s of IEEE Vehicular Technology Conference, Rosemont, IL, pp. 715-719, July 1995.
[12] M. H. Hsieh and C. H. Wei, ”Channel estimation for OFDM systems based on comb-type pilot arrangement in frequency selective fading channels,” IEEE Trans. Consumer Electronics, vol.44, pp.217-225, Feb. 1998.
[13] J. van de Beek M. Sakasson, and O. Borjesson, “Low complexity frame synchronization in OFDM system,” in Proc. IEEE ICUPC’95,pp. 1800-1805,July 1997.
[14] Schmidl, T. M. and D.C Cox, “Robust Frequency and Timing Synchronization for OFDM ,” IEEE Trans. on Comm., vol. 45, no. 12, pp. 1613-1621, Dec. 1997.
[15] Le Floch, B., M. Alard, and C. Berrou, “Coded Orthogonal Frequency Division Multiplex,” Proceedings of the IEEE, vol. 83, no. 6, June 1995.
[16] Zogakis, T. N., and J. M. Cioffi, “The Effect of Timing Jitter on the Performance of a Discrete Multitone System,” IEEE Trans. On Comm., vol. 44, no 7, pp. 799-808, July 1996.
[17] Tomba, L., “On the Effects of Wiener Phase Noise in OFDM Systems,” IEEE Trans. On Comm., vol 46, no 5, pp. 580-583, May 1998.
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[19] May, T., H. Rohling, “Reducing the Peak-to-Average Power Ratio in OFDM Radio Transmission System,” Proceedings of IEEE VTC ’98, Ottawa, Canada, pp.2774-2778, May 1998.
[20] “TMS320C6000 CPU and Instruction Set User’s Guide”, TEXAS INSTRUMENTS corporation, 1999.
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[22] “TMS320C6000 Optimizing C Compiler User’s Guide”, TEXAS INSTRUMENTS corporation, 1999.
[23] “Code Composer Studio User’s Guide”, TEXAS INSTRUMENTS corporation, 1999.

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