臺灣博碩士論文加值系統

正交分頻多工及多載波分碼多重接取等技術，被認為是近代高速有線和無線通信的重要發展，主要在於其在高速傳輸下，具有無線電頻率使用效益高及抗多重路徑衰減能力高等因素。然而，多載波通訊系統中因結合正交分頻多工技術，所以其對於載波頻率偏移十分敏感。頻率偏移所發生的原因很多，包括由發送端和接收端的相對運動所造成的都卜勒效應，以及發送端和接收端的本地震盪器發生頻率漂流及不匹配等等。
有鑑於此，本論文主要研究在多載波通訊系統下，載波頻率偏移的估測和校正技術。近年來，一些盲目適應性方法已經在探討這個問題，其主要是應用陣列訊號處理中利用虛擬載波觀念的頻譜估測技術；但這些依賴搜尋架構的演算法，若要使估測值更加精確的話，將導致複雜度和計算量會很大。而且，這些方法並不適用於存有雜訊的環境下使用。
對於正交分頻多工系統，本論文提出適應性步階參數最小均方值演算法來解決上述問題，與傳統固定步階參數最小均方值演算法相比，此演算法利用適應性調整步階參數，以提高原有性能及其收斂速度。此外，此演算法可以在時變頻率偏移下，正確估測和追蹤出頻率偏移量。
對於多載波分碼多重接取系統，我們提出輔助碼之最小變異無失真響應及輔助碼之基於雜訊子空間等兩種估測演算法來提高估測性能，這兩種演算法利用接收端所欲使用者展頻碼來降低干擾，以加速演算法之收斂速度。為了解決因搜尋峰值所造成計算量較大的問題，另外提出根數輔助碼之最小變異無失真響應及根數輔助碼之基於雜訊子空間等兩種利用多項式求根方法來降低計算量的估測演算法。
至於在有色高斯雜訊通道環境下的多載波系統，我們則應用適應性子空間追蹤演算法來估測頻率偏移量，此應用不僅可以正確估測出頻率偏移量，也可以降低因特徵值分解所產生龐大計算量的問題。最後，電腦模擬結果將顯示本論文所提出之估測方法的有效性。

Orthogonal frequency division multiplexing (OFDM) and multi-carrier code division multiple access (MC-CDMA) technologies are considered to be the important evolution of modern for high-speed wired and wireless communications, due to high efficiency of radio frequency usage and high resistance to multipath fading for high-speed transmission. However, a multi-carrier communication (MCM) system with OFDM technology would be very sensitive to carrier frequency offset. The carrier frequency offset results from many reasons, including the Doppler effect caused by the relative movement between the sending and receiving ends, the frequency drifting and mismatch for the local oscillators in the transmitting and receiving circuits.
For this reason, this thesis mainly studies on the estimation and correction techniques for carrier frequency offset in the multi-carrier communication systems. Recently, some of the blind adaptive methods have been explored to this problem by applying array signal processing spectral estimation techniques to the virtual carriers. To achieve more accurate estimation, the reliant searching scheme of the adaptive algorithm results in the formidable complexity and computational load. Moreover, these methods are not applicable in the noise environment.
For the OFDM systems, this thesis proposes an adaptive step-size least mean square (AS-LMS) algorithm to solve the above problems. Compared with the original traditional fixed step-size LMS algorithm, this algorithm enhances the performance and convergence rate by adaptively adjusting the step-size. Besides, this algorithm can correctly estimate and track the offset in the time-varying frequency offset scenario.
For the MC-CDMA systems, we propose two estimation algorithms, the code-aided minimum variance distortionless response (CMVDR) algorithm and the code-aided virtual carrier-plus-noise subspace-based (CVNSB) algorithm to enhance the performances. Both proposed algorithms use the desired user’s spreading code to reduce inference in the receiver to accelerate the convergence speed. To remedy the problem of the large computational load caused by spectral peak searching, two polynomial rooting approaches, root-CMVDR and root-CVNSB, are proposed to reduce the computational load.
As for the multi-carrier systems operated in the colored Gaussian noise channel environment, we apply the adaptive subspace tracking techniques to estimate the frequency offset. This application not only correctly estimates the frequency offset, but also reduces large amounts of computation caused by the eigenvalue decomposition (EVD). Finally, the computer simulation results are provided for illustrating the effectiveness of the proposed methods.

誌謝 ii
摘要 iii
Abstract v
目錄 vii
表目錄 x
圖目錄 xi
符號說明和縮寫 xiii
1. 緒論 1
1.1 文獻探討 1
1.2 研究動機與目的 3
1.3 論文架構 6
2. 多載波通訊系統及無線傳輸通道 8
2.1 無線通道的特性 8
2.2 無線通道參數的定義 11
2.3 無線通道的分類 13
2.3.1 頻率非選擇性衰減 13
2.3.2 頻率選擇性衰減 14
2.3.3 快速衰減 14
2.3.4 緩慢衰減 15
2.4 OFDM系統 17
2.5 CDMA系統 22
2.6 MC-CDMA系統 23
3. OFDM系統於頻率偏移下的性能探討及估測方法 28
3.1 頻率偏移對OFDM系統的影響 28
3.2 OFDM系統下頻率偏移估測 30
3.3 AS-LMS演算法 34
3.4 電腦模擬與分析 36
4. MC-CDMA系統於頻率偏移下的性能探討及估測方法 40
4.1 MC-CDMA系統下頻率偏移估測 40
4.1.1 ML演算法 44
4.1.2 ESPRIT-Like 演算法 46
4.2 盲目適應性頻率偏移估測方法 50
4.2.1 MVDR演算法 50
4.2.2 VNSB演算法 54
4.3 展頻碼輔助估測演算法 57
4.3.1 CMVDR演算法 57
4.3.2 CVNSB演算法 60
4.3.3 電腦模擬與分析 61
4.4 多項式求根估測演算法 64
4.4.1 root-CMVDR演算法 64
4.4.2 root-CVNSB演算法 66
4.4.3 電腦模擬與分析 67
4.5 適應性子空間追蹤演算法 74
4.5.1 ACVNSB演算法 75
4.5.2 電腦模擬與分析 78
5. 結論 84
參考文獻 85
附錄壹 載波頻率偏移對OFDM系統之影響 91
附錄貳 ESPRIT-Like演算法於高斯雜訊環境下之推導 93
論文發表 95
自傳 96

[1]http://www.cqinc.com.tw/grandsoft/cm/066/aex661.htm(2012.11.12)
[2]Viterbi, A. J., CDMA Principles of Spread Spectrum Communication, Addison Wesley, Canada, 1995.
[3]Nee, R. and Prasad, R., OFDM Wireless Multimedia Communications, Artech House, Boston, USA, 2000.
[4]Hara, S. and Prasad R., “Overview of Multicarrier CDMA,” IEEE Communications Magazine, Vol. 35, No. 12, pp. 126-144, Dec., 1997.
[5]http://61.129.112.60:82/gate/big5/www.c114.net/technic/ZZHtml_20054/T2005471129479411-1.shtml(2012.11.12)
[6]Bingham, J. A. C., “Multicarrier Modulation for Data Transmission: An Idea Whose Time Has Come,” IEEE Communications Magazine, Vol. 28, No. 5, pp. 5-14, May, 1990.
[7]Jung, P., Baier, P. W., and Steil, A., “Advantages of CDMA and Spread Spectrum Techniques over FDMA and TDMA in Cellular Mobile Radio Applications,” IEEE Transactions on Vehicular Technology, Vol. 42, No. 3, pp. 357-364, Aug., 1993.
[8]Zhao, Y. and Haggman, S. G., “Sensitivity to Doppler Shift and Carrier Frequency Errors in OFDM Systems - The Consequences and Solutions,” Proceedings of the 46th IEEE Vehicular Technology Conference, Atlanta, Georgia, USA, Vol. 3, pp. 1564-1568, April, 1996.
[9]Pollet, T., Bladel, V. M., and Meneclaey, M., “BER Sensitivity of OFDM Systems to Carrier Frequency Offset and Wiener Phase Noise,” IEEE Transactions on Communications, Vol. 43, No. 234, pp. 191-193, Feb./March/April, 1995.
[10]Jang, J. and Lee, K. B., “Effects of Frequency Offset on MC-CDMA System Performance,” IEEE Communications Letters, Vol. 3, No. 7, pp. 196-198, July, 1999.
[11]Tomba, L. and Krzymien, W. A., “Sensitivity of the MC-CDMA Access Scheme to Carrier Phase Noise and Frequency Offset,” IEEE Transactions on Vehicular Technology, Vol. 48, No. 5, pp. 1657-1665, Sep., 1999.
[12]IEEE Standard 802.11a, “Part II: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: High-Speed Physical Layer in the 5GHz Band,” 1999.
[13]Takanashi, H., “Proposal of PHY Specification for 5GHz Band,” Proposal to IEEE 802.11 Committee, Jan., 1998.
[14]Draft prETS-300401, “Radio Broadcast System: Digital Audio Broadcasting (DAB) to Mobile Portable and Fixed Receivers,” 1994.
[15]林漢年，“數位廣播(DAB)接收系統的技術整合與未來發展(上)” ，視訊多媒體月刊，1月號，第2-3頁，2001。
[16]Taura, K., Tsujishita, M., Kato, H., and Ishida, Y., “A Digital Audio Broadcasting (DAB) Receiver,” IEEE Transactions on Consumer Electronics, Vol. 42, No. 3, pp. 322-327, Aug., 1996.
[17]Van de Beek, J. J., Sandel, M., and Borjesson, P. O., “ML Estimation of Time and Frequency Offset in OFDM Systems,” IEEE Transactions on Signal Processing, Vol. 45, No. 7, pp. 1800-1805, July, 1997.
[18]Yang, F., Li, K. H., and Teh, K. C., “A Carrier Frequency Offset Estimator with Minimum Output Variance for OFDM Systems,” IEEE Communications Letters, Vol. 8, No. 11, pp. 677-679, Nov., 2004
[19]Liu, H. and Tureli, U., “A High Efficiency Carrier Estimator for OFDM Communications,” IEEE Communications Letters, Vol. 2, No. 4, pp. 104-106, April, 1998.
[20]Tureli, U., Liu, H., and Zoltowski, M. D., “OFDM Blind Carrier Offset Estimation: ESPRIT,” IEEE Transactions on Communications, Vol. 48, No. 9, pp. 1459-1461, Sep., 2000.
[21]Schmidt, R.O., “Multiple Emitter Location and Signal Parameter Estimation,” IEEE Transactions on Antennas and Propagation, Vol. 34, No. 3, pp. 276-280, March, 1986.
[22]Roy, R., “ESPRIT - Estimation of Signal Parameters viaRotational Invariance Techniques,” IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. 37, No. 7, pp. 984-995, July, 1989.
[23]Huang, C. C., Chang, A. C., and Su, I. J., “Blind Frequency Offset Estimation Using Adaptive Step-Size LMS Algorithm for OFDM Communications,” IEICE Transactions on Communications, Vol. E90-B, No. 5, pp. 1274-1277, May, 2007.
[24]Haykin, S., Adaptive Filter Theory, Upper Saddle River, NJ, USA: Prentice Hall, Third-Edition, 1996.
[25]Huang, C. C., Su, I. J., and Chang, A. C., “Blind Estimation of MC-CDMA Carrier Frequency Offset,” IEICE Transactions on Communications, Vol. E89-B, No. 9, pp. 2646-2651, Sep., 2006.
[26]Huang, C. C., Chang, A. C., and Su, I. J., “Blind Subspace-based CFO Estimation via Polynomial Rooting for MC-CDMA Systems,” IEICE Transactions on Communications, Vol. E90-B, No. 8, pp. 2175-2178, Aug., 2007.
[27]Su, I. J. and Huang, C. C., “Robust MVDR Estimation via Polynomial Rooting for MC-CDMA CarrierFrequency Offset,” Applied Mechanics and Materials, Vol. 284-287, pp. 2687-2693, Jan., 2013.
[28]Krusevac, S., Rapajic, P., and Kennedy, R., “Channel Capacity Estimation for MIMO Systems with Correlated Noise,” Proceedings of IEEE Global Telecommunications Conference, St. Louis, Missourl, USA, Vol. 5, pp. 2812-2816, Dec., 2005.
[29]Wang, X. and Poor, H. V., “Robust Multiuser Detection in Non-Gaussian Channels,” IEEE Transactions on Signal Processing, Vol. 47, No. 2, pp. 289-305, Feb., 1999.
[30]Kassam, S. A. and Poor, H. V., “Robust Techniques for Signal Processing: A Survey,” Proceedings of the IEEE, Vol. 73, No. 3, pp. 433-481, March, 1985.
[31]Huang, C. C. and Su, I. J., “Blind Frequency Offset Estimation Using Adaptive Subspace Tracking Algorithm for MC-CDMA System over Unknown Colored Noise Channels,” Advances in information Sciences and Service Sciences, Vol. 5, No. 7, pp. 299-307, Apr., 2013.
[32]Proakis, J. G., Digital Communication, McGraw-Hill, Singapore, Fourth Ed, pp. 800-851, 2001.
[33]Rappapor, T. S., Wireless Communication Principles & Practice, Prentice Hall, Upper Saddle River, New Jersey, pp. 177-181, 1996.
[34]Sklar, B., “Rayleigh Fading Channels in Mobile Digital Communication Systems Part I: Characterization,’’ IEEE Communications Magazine, Vol. 35, No. 7, pp. 90-100, July, 1997.
[35]Chang, R. W., “Synthesis of Band-limited Orthogonal Signals for Multi-channel data Transmission,” Bell systems Technical Journal, Vol. 45, pp. 1775-1796, Dec., 1966.
[36]Muller, T., Rohling, H., and Grunheid, R., “Comparison of Different Detection Algorithms for OFDM-CDMA in Broadband Rayleigh Fading,” Proceedings of the 45th IEEE Vehicular Technology Conference, Chicago, Illinois, USA, Vol. 2, pp. 835-838, July, 1995.
[37]Jeon, W. G., Chang, K. H., and Cho, Y. S., “An Equalization Technique for OFDM and MC-CDMA in a Time Varying Multipath Fading Channels,” Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Munich, Germany, Vol. 3, pp. 2529-2532, April, 1997.
[38]Visser, M. A., Zong, P., and Bar-Ness, Y., “A Novel Method for Blind Frequency Offset Correction in an OFDM System,” Proceedings of IEEE International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), Boston, Massachusetts, USA, Vol. 2, pp. 816-820, Sep., 1998.
[39]Chen, B., “Maximum Likelihood Estimation of OFDM Carrier Frequency Offset,” IEEE Signal Processing Letters, Vol. 9, No. 4, pp. 123-126, April, 2002.
[40]Ma, Y., Li, K. H., Kot, A. C., and Ye, G., “A Blind Code Timing Estimator and Its Implementation for DS-CDMA Signals in Unknown Colored Noise,” IEEE Transactions on Vehicular Technology, Vol. 51, No. 6, pp. 1600-1607, Nov., 2002.
[41]Yang, J. F. and Kaveh, M., “Adaptive Eigensubspace Algorithm for Direction or Frequency Estimation and Tracking,” IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. 36, No. 2, pp. 241-251, Feb., 1988.
[42]Wu, Y. and Tam, K. W., “On Determination of the Number of Signals in Spatially Correlated Noise,” IEEE Transactions on Signal Processing, Vol. 46, No. 11, pp. 3023-3029, Nov., 1998.