多載波分碼多工 (MC-CDMA) 是一種結合分碼多工 (CDMA)與正交分頻多工 (OFDM) 之傳輸技術，它已被視為第四代無線行動通訊系統設計上的一項重要技術。此系統雖然同時具有CDMA與OFDM的優點，但也同時存在有此兩種傳輸技術的問題。在MC-CDMA系統中，載波間干擾 (ICI) 是影響系統效能的重要因素；這是由於載波頻率間隔 (subcarrier spacing) 窄以及允許頻譜重疊，使得載波間的正交特性 (orthogonality) 易受傳送、接收兩端震盪器不匹配及都卜勒 (Doppler) 效應所破壞的緣故。
在此篇研究中，我們提出了一具有自動消除載波間干擾的新型展頻碼，因而不需透過頻率偏移補償或頻域等化器 (FEQ)等，即可大幅降低載波間干擾。另外，我們將所提出的展頻碼結合Alomouti的空時碼建構出一多輸入多輸出的MC-CDMA系統，更進一步地提升系統的效能。為了驗證系統效能，我們提供了載波能量對干擾能量比(CIR)以及位元錯誤率 (BER) 的電腦模擬結果，兩者都顯示了我們所提出的新型展頻碼能更有效的壓抑載波間干擾。此外，我們也模擬了在下鏈傳輸環境下，使用多種信號偵測技術的模擬結果，由模擬結果可以發現，在存在有頻率偏移的環境下，由於我們所提出的展頻碼具有消除載波間干擾的特性，因而可以獲得較高的載波能量對干擾能量比(CIR)以及達到較低的位元錯誤率 (BER)，顯示我們所提出的展頻碼可以在不增加系統複雜度的情況下大幅度地提升系統效能。

Multicarrier code division multiple access (MC-CDMA) is a multiple access scheme that combines CDMA and orthogonal frequency division multiplexing (OFDM) techniques. One major problem associated with MC-CDMA is that the intercarrier interference (ICI) caused by the frequency offset may significantly degrade the system performance. In this thesis, we propose a new spreading code which has ICI self-cancellation capability for MC-CDMA systems. Besides, we also construct a multiple-antenna MC-CDMA system in which the proposed spreading code and Alamouti’s space time block code are both utilized. In downlink transmission, several detection techniques simulation result shows that the proposed spreading code can achieve high CIR and well BER performance and offer excellent immunity to interference.

[1] H. Atarashi and M. Sawahashi, “Investigation of inter-carrier interference due to Doppler spread in OFDM broadband packet wireless access”, IEICE Trans. Commun., Vol. E85-B, No. 12, pp. 2684-2693, Jan. 2004.
[2] H. Harada and Y. Kamio, “A feasibility study of the 16QAM-OFDM transmission scheme for multimedia mobile access communication systems”, IEICE Trans. Commun., Vol. E84-B, No. 8, pp. 2207-2218, Aug. 2001.
[3] S. Hara and R. Prasad, “Overview of multicarrier CDMA,” IEEE Commun. Mag., pp. 126-133, Dec. 1997.
[4] H. Atarashi, S. Abeta and M. Sawahashi, “Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing for Broadband Packet Wireless Access”, IEICE Trans. Commun., Vol. E86-B, No.1, pp. 291-299, Jan. 2003.
[5] S. M. Alamouti, “A simple transmit diversity technique for wireless Communication,” IEEE J. Select. Areas Commun., Vol. 16, pp. 1451-1458, Oct. 1998 .
[6] N. Yee, J. P. Linnartz, and G. Fettweis, "Multicarrier CDMA in indoor wireless radio networks," in Proc. 1993 IEEE Int. Symp. Personal, Indoor and Mobile Radio Commun. (PIMRC ’93), pp. 109-113, Sept. 1993.
[7] R. van Nee and R. Prasad, OFDM for Wireless Multimedia Communications, Boston/London: Artech House, 1999.
[8] J. G. Proakis, Digital Communications. Mc-Graw Hill International Editions, 3rd ed., 1995.
[9] Y. Zhao and S.-G. Haggman, “Intercarrier interference self-cancellation scheme for OFDM mobile communication systems”, IEEE Trans. Commun. vol. 49, Issue 7, pp.1185-1191, July 2001 .
[10] 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, Issue 8, pp. 214-216, Aug. 1998.
[11] Y. Zhao, “In-band and out-band spectrum analysis of OFDM communication systems using ICI cancellation methods” Communication Technology Proceedings, 2000. WCC - ICCT 2000. International Conference, vol. 1, Aug. 2000, pp. 773-776.
[12] Yu-Chih Huang, An Intercarrier Interference Suppression Technique Using Time-Domain Windowing for OFDM Systems.MS Thesis, Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan, 2005.
[13] R. L. Peterson, R. E.Ziemer, and D. E. Borth, Introduction to Spread Spectrum Communication, Prentice Hall ,1995.
[14] IEEE, “IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems”, IEEE Std 802.16-2004 (Revision of IEEE Std 802.16-2001).
[15] J. Armstrong, P. M. Grant, and G. Povey, “Polynomial cancellation coding of OFDM to reduce intercarrier interference due to Doppler spread”, in Proc. 1998 IEEE Global Telecommun. Conf. (GLOBECOM ‘98), vol. 5, Nov. 1998, pp. 2771-2776.
[16] J. Jang and K. B. Lee, “Effects of frequency offset on MC/CDMAsystem performance,” IEEE Commun. Lett., vol. 3, pp. 196–198, July 1999.
[17] L. Liu, P. Zhang, H.Hamaguchi and H. Wakana, “Impact of frequency offset on the spreading and despreading in broadband MC-CDMA systems”, in Proc. 2004 IEEE Veh. Technol. Conf. (VTC 2004), Vol. 1, Sept. 2004, pp. 699- 703.
[18] Y. Kim, S. Choi, C. You, and D. Hong, “BER computation of an MC-CDMA system with carrier frequency offset,” IEEE ICASSP ’99, vol. 5, Mar. 1999, pp. 2555-2558.
[19] X. Cai and A. N. Akansu, "Multicarrier CDMA systems with transmit diversity", in Proc. 2000 IEEE Veh. Technal. Conf. (VTC), vol. 6, Oct. 2000, pp. 2817-2821.
[20] Y. Li, C. N. Georghiades, and G. Huang, “Performance of downlink multicarrier CDMA with space diversity,” in Proc. IEEE Global Telecommun. Conf. (GLOBECOM 2000), Nov./Dec. 2000, pp. 887–889.
[21] L. Tomba and W. A. Krzymien, “Sensitivity of the MC-CDMA access scheme to carrier phase noise and frequency offset,” IEEE Trans. on Vehicular Tech., vol. 48, no. 5, pp. 1657–1665, Sep. 1999.