在此論文中，我們針對合作式正交分頻多工（OFDM, orthogonal frequency division multiplexing）系統發展使用共軛傳輸的載波間干擾消除技術，其包含適應性接收機設計和中繼點選擇機制兩部分。我們所提出的適應性接收著重於對載送共軛OFDM信號的兩條接收路徑加上不同的相位旋轉，以及對第二條接收路徑信號的所有子載波加上個別的振幅調整值之設計。相較於先前所有子載波皆使用一個相同振幅調整值的接收機設計，本方法可因應個別子載波之通道狀況分別修改其振幅調整值，以達到最佳載波間干擾消除效果。另一方面，我們亦基於所提出之接收機架構發展新的中繼點選擇機制。其重點在於根據每一組中繼點之訊雜比（SNR, signal-to-noise ratio）以及訊擾比（CIR, carrier-to-interference ratio）下限值進行聯合評估，因而得以選擇具有最高SNR下限值或是最高CIR下限值的中繼點進行轉送。電腦模擬結果顯示我們所提出的適應性接收機可提供相較於先前設計更優異的效能表現，此效能改善在載波間干擾嚴重的環境中尤為顯著。模擬結果亦顯示我們所提出的中繼點選擇機制可達到比其他相關方法更佳的位元錯誤率表現。

In this dissertation, we propose a new intercarrier interference (ICI) cancellation scheme for orthogonal frequency division multiplexing (OFDM) based cooperative relay systems using conjugate transmission, which involves an adaptive receiver design and a relay selection strategy. The proposed adaptive receiver not only applies two phase rotations on the two receive paths carrying conjugate OFDM symbols, but also employs an amplitude scaling factor on each subcarrier of the second receive path. Unlike a previous receiver design where the same amplitude scaling factor is applied to all subcarriers, the proposed one allows individual adjustment of the amplitude scaling factor over each subcarrier to approach optimal ICI cancellation. We also develop a new relay selection mechanism based on the proposed receiver structure, where the signal-to-noise ratio (SNR) and carrier-to-interference ratio (CIR) bounds are jointly evaluated for each relay pair and the one with the highest SNR/CIR bound is selected for transmission. Simulation results show that the proposed adaptive receiver outperforms previous designs, especially in ICI-dominated environments. It is also demonstrated that the proposed relay selection method provides better bit-error-rate performance than other related approaches.

R. van Nee and R. Prasad, OFDM for Wireless Multimedia Communications. Norwood, MA: Artech House, 2000.
[2] IEEE, “IEEE standard for local and metropolitan area networks–Part 11: Wireless LAN medium access control (MAC) and physical layer (PHY) specifications,” IEEE Std. 802.11, Aug. 1999.
[3] ETSI, “Digital video broadcasting (DVB); framing structure, channel coding and modulation for digital terrestrial television,” ETSI EN 300 744 V1.4.1, Jan. 2001.
[4] IEEE, “IEEE standard for local and metropolitan area networks–Part 16: Air interface for fixed broadband wireless access systems–Amendment 2: Physical and medium access control layers for combined fixed and mobile operation in licensed bands,” IEEE Std. 802.16e-2005, Feb. 2006.
[5] ETSI, “LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (3GPP TS 36.211 version 9.1.0 Release 9), ETSI TS 136 211 V9.1.0, Apr. 2010.
[6] P. H. Moose, “A technique for orthogonal frequency division multiplexing frequency offset correction,” IEEE Trans. Commun., vol. 42, pp. 2908–2914, Oct. 1994.
[7] J.-J. van de Beek, M. Sandell, and P. O. Borjesson, “ML estimation of time and frequency offset in OFDM systems,” IEEE Trans. Signal Process., vol. 45, no. 7, pp. 1800–1805, Jul. 1997.
[8] U. Tureli, D. Kivanc, and H. Liu, “Experimental and analytical studies on a high-resolution OFDM carrier frequency offset estimator,” IEEE Trans. Veh. Technol., vol. 50, no. 2, pp. 629–643, Mar. 2001.
[9] W.-S. Hou and B.-S. Chen, “ICI cancellation for OFDM communication systems in time varying multipath fading channels,” IEEE Trans. Wireless Commun., vol. 4, no. 5, pp. 2100–2110, Sep. 2005.
[10] S. Lu and N. Al-Dhahir, “Coherent and differential ICI cancellation for mobile OFDM with application to DVB-H,” IEEE Trans. Wireless Commun., vol. 7, no. 11, pp. 4110–4116, Jul. 2008.
[11] Y. Mostofi and D. C. Cox, “ICI mitigation for pilot-aided OFDM mobile systems,” IEEE Trans. Wireless Commun., vol. 4, no. 2, pp. 765–774, Mar. 2005.
[12] M. Toeltsch and A. F. Molisch, “Equalization of OFDM-systems by interference cancellation techniques,” in Proc. 2001 IEEE Int. Conf. Commun. (ICC 2001), Jun. 2001, pp. 1950–1954.
[13] X.-D. Cai and G. B. Giannakis, “Bounding performance and suppressing intercarrier interference in wireless mobile OFDM,” IEEE Trans. Commun., vol. 51, no. 12, pp. 2047–2056, Dec. 2003.
[14] P. Schniter, “Low-complexity equalization of OFDM in doubly selective channels,” IEEE Trans. Signal Processing, vol. 52, no. 4, pp. 1002–1011, Apr. 2004.
[15] Y. Zhao and S.-G. Häggman, “Intercarrier interference self-cancellation scheme for OFDM mobile communication systems,” IEEE Trans. Commun., vol. 49, no. 7, pp. 1185–1191, Jul. 2001.
[16] J. Armstrong, “Analysis of new and existing methods of reducing intercarrier interference due to carrier frequency offset in OFDM,” IEEE Tran. Commun., vol. 47, no. 3, pp. 365–369, Mar. 1999.
[17] K. Sathananthan, C. R. N. Athaudage, and B. Qiu, “A novel ICI cancellation scheme to reduce both frequency offset and IQ imbalance effects in OFDM,” in Proc. IEEE 9th Int. Symp. Comput. Commun., Jul. 2004, pp. 708–713.
[18] Y. Zhao, J. D. Leclercq, and S. G. Haggman, “Intercarrier interference compression in OFDM communication systems by using correlative coding,” IEEE Commun. Lett., vol. 2, pp. 214–216, Aug. 1998.
[19] C.-L. Wang, Y.-C. Huang, and P.-C. Shen, “An intercarrier interference suppression technique using time-domain windowsing,” in Proc. 2006 IEEE Veh. Technol. Conf. - Spring (VTC 2006-Spring), May 2006, pp. 2518–2522.
[20] H.-G. Yeh, Y.-K. Chang, and B. Hassibi, “A scheme for cancelling intercarrier interference using conjugate transmission in multicarrier communication systems,” IEEE Trans. Wireless Commun., vol. 6, no. 1, pp. 3–7, Jan. 2007.
[21] C.-L. Wang and Y.-C. Huang, “Intercarrier interference cancellation using general phase rotated conjugate transmission for OFDM systems,” IEEE Trans. Commun., vol. 58, no. 3, pp. 812–819, Mar. 2010.
[22] C.-L. Wang, Y.-C. Lin, and P.-C. Shen, “Design of an adaptive receiver for OFDM systems using conjugate transmission,” in Proc. 2010 IEEE Wireless Commun. and Netw. Conf. (WCNC 2010), Sydney, Australia, Apr. 2010.
[23] C.-L. Wang, P.-C. Shen, and J.-H. Huang, “An improved adaptive receiver for OFDM systems using conjugate transmission,” in Proc. 2011 IEEE Vehicular Technol. Conf. – Spring (VTC 2011-Spring), Budapest, Hungary, May. 2011.
[24] C.-L. Wang, P.-C. Shen, M.-C. Bai, and H.-C. Wang, “An adaptive receiver design for OFDM-based cooperative relay systems using conjugate transmission,” in Proc. 2012 IEEE Global Telecommun. Conf. (GLOBECOM 2012), Anaheim, California, USA, Dec. 2012, pp. 3644-3648.
[25] P. M. Clarkson. Optimal and Adaptive Signal Processing. Boca Raton: CRC Press, 1993.
[26] S. Haykin, Adaptive Filter Theory. 4th ed., Upper Saddle River, NJ: Prentice-Hall, 2002.
[27] M. Tarrab and A. Feuer, “Convergence and performance analysis of the normalized LMS algorithm with uncorrelated Gaussian data,” IEEE Trans. Inform. Theory, vol. 34, pp. 680–691, Jul. 1988.
[28] B. O’Hara and A. Petrick, The IEEE 802.11 Handbook: A Designer’s Companion. The Institute of Electrical and Electronics Engineer, In., Dec. 1999.