由於OFDM (Orthogonal Frequency Division Multiplexing)符元(Symbol)有較長的符元長度，可以有效抵抗多路徑通道造成的頻率衰減，OFDM技術已經被廣泛應用於各種先進數位通訊系統，如DVB (Digital Video Broadcast)、WLAN(Wireless Local Area Network)、UWB (Ultra Wide Band)。近幾年來不論是學術或是工業界，如何有效實現OFDM系統已是一大課題。本論文主要探討目前熱門的802.11a OFDM系統之VLSI架構。有效率的OFDM架構設計包括研究其演算法並平衡演算法效能與硬體成本。本論文於系統模擬階段，使用Matlab建構IEEE802.11a基頻傳接機與已知的通道模型，用以改善接收機同步演算法，包括：「封包偵測」、「時間同步」、「載波頻率位移估測」、「通道估測」與「殘餘相位追蹤」。本論文採用在多路徑通道影響與嚴重雜訊下，仍然表現優異之封包偵測與時間同步方法，當SNR>3時，偵測成功率幾近100%。最後，已面積最佳化之適合於VLSI實現之同步模組於本論文中提出，僅需要約5個複數乘法器、388個移位暫存器與一些加法器及簡單的邏輯電路。這些同步模組並與single-path radix-23 FFT/IFFT (Fast Fourier Transform/Inverse FFT)整合為高效率之OFDM基頻處理器暨同步電路。

OFDM (Orthogonal Frequency Division Multiplexing) technology, due to its longer symbol duration that decease the amount of dispersion in time caused by multipath delay spread, has been widely used in many advanced digital communication systems such as DVB (Digital Video Broadcast), WLAN (Wireless Local Area Network), and UWB (Ultra Wide Band). How to realize efficient OFDM systems has been a very important issue for either academic or industry fields in recent years. This thesis aims to explore the VLSI implementation of the OFDM system targeted on its application on the wildly popular IEEE802.11a WLAN systems. An efficient OFDM architecture design involves the algorithm exploration and the tradeoff between the algorithm performance and hardware implementation. Therefore, in this thesis, a Matlab simulation platform for the IEEE802.11a baseband receiver is first built to refine several key synchronization algorithms including frame detection, timing recovery, carrier frequency offset, channel estimation as well as phase tracking under some given channel models. An excellent frame detection and timing recovery method is adopted such that nearly perfect synchronization can be achieved at SNR> 3. Furthermore, area-efficient architecture suitable for VLSI implementation for each synchronization module has also been proposed. In summary, 4 complex multipliers with 388 shift registers are required in our synchronization circuits. These modules are integrated with a core single-path radix-23 IFFT (Inverse Fast Fourier Transform) block to build a highly efficient WLAN baseband.

摘要 i
ABSTRACT ii
誌謝 iii
LIST OF CONTENTS iv
LIST OF TABLES vi
LIST OF FIGURES vii
第一章　簡介 1
1.1　通訊系統簡介 1
1.2　OFDM 系統簡介 1
第二章　IEEE 802.11a傳接機與通道模型 4
2.1　IEEE802.11a基頻傳接機模型 4
2.2　Channel Model 6
2.2.1　Multi-path Channel Model 7
2.2.2　CFO Channel Model 9
第三章　OFDM 基頻處理器電路設計 10
3.1　FFT/IFFT 10
3.1.1　Radix-23 FFT 11
3.1.2　IFFT 15
3.2　Pilots Insertion 16
3.3　Cyclic Prefix Function 16
第四章　接收端同步電路設計 18
4.1　Frame Detection 19
4.1.1　Algorithm 19
4.1.2　Hardware Implementation 21
4.2　Carrier Frequency Offset Synchronization 24
4.2.1　Algorithm 24
4.2.2　Hardware Implementation 26
4.3　Timing Recovery 28
4.3.1　Algorithm 28
4.3.2　Hardware Implementation 31
4.4　Channel Estimation and Compensation 31
4.4.1　Algorithm 32
4.4.2　Hardware Implementation 33
4.5　Phase Tracking 34
4.5.1　Algorithm 34
4.5.2　Hardware Implementation 35
4.6　Overall Synchronization Circuits 35
第五章　結論與未來目標 39
5.1　結論 39
5.2　未來目標 39
第六章　參考文獻 41

[1] ETSI, "Digital Video Broadcasting: framing structure, channel coding, and modulation for digital terrestrial television," European Telecommunication Standard 300 744, European Telecommunication Standard Institute, 1997.
[2] IEEE, "Std 802.11a-1999, Supplement to IEEE Standard for Information technology-Telecommunications and information exchange between systems- LAN/MAN Specific requirements-Part 11: Wireless LAN MAC and PHY specifications: High-speed Physical Layer in the 5GHz Band," 1999.
[3] IEEE, “Std 802.11b-1999, 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: Higher-Speed Physical Layer Extension in the 2.4 GHz Band,” 1999.
[4] IEEE, “Std 802.11g-2003, 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: Amendment 4: Further Higher Data Rate Extension in the 2.4 GHz Band,” 2003.
[5] ETSI, “ETSI TS 101 475 V1.3.1-Technical Specification: Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Physical (PHY) layer,” 2001.
[6] IEEE P802.15 Working Group for WPANs, “Multi-band OFDM Physical Layer Proposal for IEEE 802.15 Task Group 3a,” Mar. 2004.
[7] An introduction to Ultra Wideband (UWB) wireless, available: http://deviceforge.com/articles/AT8171287040.html
[8] S. L. Lai, Clock offset and I-Q imbalance compensation for OFDM system, National Chiao Tung University, 2003.
[9] J. F. Xu, Design of an OFDM baseband transceiver for IEEE802.11a WLAN, National Taiwan University, 2000.
[10] J. Terry and J. Heiskala, OFDM Wireless LANS: A Theoretical and Practical Guide, SAMS, 2002.
[11] IEEE, “std 802.11-1999, 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,” 1999.
[12] R. Van Nee and R. Parasad, OFDM for wireless multimedia communication, Artech House, Boston, 2000.
[13] S. He and M. Torkelson, “Design and implementation of a 1024-point pipeline FFT processor,” IEEE Custum Integrated Circuits Conference, pp. 131-134, May 1998.
[14] S. He and M. Torkelson, “Designing pipeline FFT processor for OFDM (de)modulation,” ISSSE, pp. 257-262, Sept. 1998.
[15] L. Jia, Y. Gao, and H. Tenhunen, “Efficient VLSI implementation of radix-8 FFT algorithm,” IEEE Pacific Rim Conference on Communications, Computers and Signal Processing, pp. 468-471, August 1999
[16] L. Jia, Y. Gao, J. Isoaho, and etc., “A new VLSI-oriented FFT algorithm and implementation,” ASIC Conference, pp. 337-341, Sept. 1998.
[17] L. D. Kabulepa, A. Ortiz, M. Glesner, “Design of an efficient OFDM burst synchronization scheme” ISCAS, vol. 3, pp. 449-452, May 2002.
[18] J. Li, G. Liu, and G. B. Giannakis, “Carrier frequency offset estimation for OFDM-based WLANs,” IEEE Signal Processing Letters, vol. 8, Issue 3, pp. 80-82, Mar. 2001.
[19] B. Park, H. Cheon, C. Kang, and etc., “A simple preamble for OFDM timing offset estimation,” IEEE VTC, vol. 2, pp. 729-732, Sept. 2002.
[20] J. J. van de Beek, M. Sandell, and P. O. Borjesson, “ML estimation of time and frequency offset in OFDM systems,” IEEE Trans. on Signal Processing, vol. 45, Issue 7, pp. 1800-1805, July 1997.
[21] T. Kim, N. Cho, J. Cho, and etc., “A fast burst synchronization for OFDM based Wireless Asynchronous Transfer mode systems,” GLOBECOM, vol. 1A, pp. 543-547, 1999.
[22] S. A. Fechtel and A. Blaickner, “Efficient FFT and equalizer implementation for OFDM receivers,” IEEE Trans. on Consumer Electronics, vol. 45, Issue 4, pp. 1104-1107, Nov. 1999.
[23] C.-S. Peng; K.-A. Wen, “Synchronization for carrier frequency offset in wireless LAN 802.11a system,” The 5th International Symposium on Wireless Personal Multimedia Communications, vol. 3, pp. 1083-1087, Oct. 2002.
[24] T. M. Schmidl and D. C. Cox, “Robust frequency and timing synchronization for OFDM,” IEEE Trans. On Comm., vol. 45, no. 12, pp. 1613-1621, Dec. 1997.
[25] A survey of CORDIC algorithms for FPGAs, available: http://www.andraka.com/files/crdcsrvy.pdf
[26] H. Zhana, Z. Wang, and S. S. Chandra, “Implementation of frequency offset correction using CORDIC algorithm for 5 GHz WLAN applications,” ICCS, vol. 2, pp. 983-987, Nov. 2002.
[27] L. Schwoerer, “VLSI suitable synchronization algorithms and architecture for IEEE 802.11a physical layer,” ISCAS, Vol. 5, pp. 721-724, May 2002.
[28] A. Doufexi, S. Armour, M. Butler, and etc., “A comparison of the HIPERLAN/2 and IEEE 802.11a Wireless LAN Standards,” IEEE Communication Magazine, 2002.
[29] B. Johnson, L. Huang, D. Tadas, and etc., “An effective signal quality measure using OFDM pilot symbols,” Available: http://grouper.ieee.org/groups/802/11/.
[30] M. C. Chen, “Design of 802.11a baseband transmitter and synchronization,” National Chiao Tung University, 2003.
[31] C.-F. Hsu , Y.-H. Huang, and T.-D. Chiueh, “Design of an OFDM receiver for high-speed wireless LAN,” ISCAS, vol. 4, pp. 558-561, May 2001.