正交分頻多工(Orthogonal Frequency Division Multiplexing, OFDM) 技術，已經廣泛使用於現代的無線網路實體層中，在射頻電路的架構方面，直接轉換接收機(Direct-conversion) 也越來越受到廣泛的使用，因其具備低成本與小面積等優點。伴隨著此結構容易受到射頻元件與震盪電路的誤差帶來IQ 不平衡(IQ Imbalance)、直流偏移(DC Offset) 與載波頻率偏移(Carrier Frequency Offset) 等問題，降低接收機性能。因此在本篇論文，提出了使用訓練符元以最小平方(Least square) 做參數估計，達到在無線區域
網路系統中快速同步的目的，並且較現有演算法有更好的效能。最後，基於我們的演算法提出同步電路架構，並以VHDL 撰寫RTL 驗證我們的電路結構效能。

Orthogonal Frequency Division Multiplexing (OFDM) is a widely used technique in the physical layer of modern communication system. Unfortunately,OFDM system is sensitive to imperfect synchronization and non-ideal front-end effects such as IQ Imbalance, DC Offset and carrier frequency offset, leading to serve system performance degradation. In this thesis, we consider recovering the WLAN OFDM signals in the presence of these imperfect conditions, we propose least-square (LS) equalization for Joint IQ Imbalance and carrier frequency offset estimation. From computer simulation results, the proposed algorithm has better performance than existing algorithms. Finally, the VHDL Design is used to verity the feasibility in electric circuit structure.

[1] B. Razavi, “Design considerations for direct-conversion receivers,”IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing, vol. 44, no. 6, pp. 428 –435, Jun 1997.
[2] S.-L. Su and Y.-J. Chiu, “Adaptive iq imbalance compensation scheme with frequency offset for communication channel,” in 2006. CCNC 2006. 3rd IEEE Consumer Communications and Networking Conference,, vol. 2, Jan. 2006, pp. 1038 –1042.
[3] Y.-J. Chiu and S.-P. Hung, “Estimation scheme of the receiver iq imbalance under carrier frequency offset in communication system,”IET Communications, vol. 4, no. 11, pp. 1381 –1388, 23 2010.
[4] J.-R. Liang and C.-H. Kuo, “Ls-based joint estimation of carrier frequency offset and iq imbalance in ofdm systems,”in 2010 International Symposium on Next-Generation Electronics (ISNE), Nov.2010, pp. 52 –55.
[5] Y.-H. Chung, K.-D. Wu, and S.-M. Phoong, “Joint estimation of i/q imbalance, cfo and channel response for ofdm systems,”in IEEE International Conference on Acoustics Speech and Signal Processing,2009. ICASSP 2009., April 2009, pp. 2573 –2576.
[6] L. Lanante, M. Kurosaki, and H. Ochi, “A new joint estimation scheme for carrier frequency offset and i/q imbalance,”in IEEE International Conference on Communications, 2009. ICC ''09., June 2009, pp. 1 –5.
[7] G.-T. Gil, I.-H. Sohn, J.-K. Park, and Y. Lee, “Joint ml estimation of carrier frequency, channel, i/q mismatch, and dc offset in communication receivers,”IEEE Transactions on Vehicular Technology,vol. 54, no. 1, pp. 338 –349, Jan. 2005.
[8] J. Tubbax, B. Come, L. Van der Perre, L. Deneire, S. Donnay, and M. Engels, “Compensation of iq imbalance in ofdm systems,”in IEEE International Conference on Communications, 2003. ICC''03., vol. 5, May 2003, pp. 3403 –3407 vol.5.
[9] J. Tubbax, A. Fort, L. Van der Perre, S. Donnay, M. Engels,M. Moonen, and H. De Man, “Joint compensation of iq imbalance and frequency offset in ofdm systems,”in 2003. GLOBECOM ''03.IEEE Global Telecommunications Conference, vol. 4, Dec. 2003,pp. 2365 –2369 vol.4.
[10] Y. Egashira, Y. Tanabe, and K. Sato, “A novel iq imbalance compensation method with pilot-signals for ofdm system,” in 2006 IEEE 64th Vehicular Technology Conference, 2006. VTC-2006 Fall., Sept. 2006, pp. 1 –5.
[11] S. Traverso, M. Ariaudo, I. Fijalkow, J.-L. Gautier, and C. Lereau,“Decision-directed channel estimation and high i/q imbalance compensation in ofdm receivers,”IEEE Transactions on Communications,vol. 57, no. 5, pp. 1246 –1249, May 2009.
[12] D. Tandur and M. Moonen, “Joint adaptive compensation of transmitter and receiver iq imbalance under carrier frequency offset in ofdm-based systems,”IEEE Transactions on Signal Processing,vol. 55, no. 11, pp. 5246 –5252, Nov. 2007.
[13] K.-Y. Sung and C. chao Chao, “Estimation and compensation of i/q imbalance in ofdm direct-conversion receivers,”IEEE Journal of Selected Topics in Signal Processing, vol. 3, no. 3, pp. 438 –453,June 2009.
[14] J. Chang and I.-T. Lu, “Analysis of a virtual carrier based carrier frequency offset estimation algorithm in the presence of i/q imbalance in ofdm systems,”in 2008 IEEE Sarnoff Symposium, April
2008, pp. 1 –5.
[15] M. Valkama, M. Renfors, and V. Koivunen, “Blind i/q imbalance compensation in ofdm receivers based on adaptive i/q signal decorrelation,”in 2005. ISCAS 2005. IEEE International Symposium on Circuits and Systems, May 2005, pp. 2611 –2614 Vol. 3.
[16] P. Rykaczewski, M. Valkama, and M. Renfors, “On the connection of i/q imbalance and channel equalization in direct-conversion transceivers,”IEEE Transactions on Vehicular Technology, vol. 57,no. 3, pp. 1630 –1636, May 2008.
[17] M.-F. Sun, J.-Y. Yu, and T.-Y. Hsu, “Estimation of carrier frequency offset with i/q mismatch using pseudo-offset injection in ofdm systems,”IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 55, no. 3, pp. 943 –952, April 2008.
[18] Y. Chen, A. Jayalath, J. Zhang, and T. Pollock, “Frequency offset estimation for ofdm systems in the presence of i/q mismatch,”in IEEE 18th International Symposium on Personal Indoor and Mobile Radio Communications, 2007. PIMRC 2007., Sept. 2007, pp. 1
–5.
[19] Y.-C. Pan and S.-M. Phoong, “A new algorithm for carrier frequency offset estimation in the presence of i/q imbalance,”in 2010 IEEE 71st Vehicular Technology Conference (VTC 2010-Spring),May 2010, pp. 1 –5.
[20] W.-J. Cho, T.-K. Chang, Y.-H. Chung, S.-M. Phoong, and Y.-R. Lin,“Frame synchronization and joint estimation of iq imbalance and channel response for ofdm systems,”in IEEE International Conference on Acoustics Speech and Signal Processing, 2008. ICASSP 2008., 31 2008-April 4 2008, pp. 3029 –3032.
[21] Y.-H. Chung and S.-M. Phoong, “Joint estimation of transmitter and receiver i/q imbalances, cfo, and channel response for ofdm systems,”in 2010 International Conference on Green Circuits and Systems (ICGCS), June 2010, pp. 247 –252.
[22] IEEE 802.11a, Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications : High-speed Physical Layer in the 5 GHz Band., IEEE Std., 1999.
[23] J. E. Volder, “The cordic trigonometric computing technique,”IRE Transactions on Electronic Computers, vol. EC-8, no. 3, pp.330 –334, Sept. 1959.
[24] S. Wang, V. Piuri, and J. Wartzlander, E.E., “Hybrid cordic algorithms,”IEEE Transactions on Computers, vol. 46, no. 11, pp.1202 –1207, Nov 1997.