基于OFDM的无线局域网研究
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摘要
正交频分复用(OFDM)技术是当前移动通信领域的一项关键技术，OFDM技术具有很强的抗符号间干扰、抗多径衰落能力，适合在无线信道中传输高速的数据业务，因而倍受关注。OFDM采用了正交多载波技术，频谱利用率很高，目前已被应用于无线局域网、数字音频广播(DAB)、数字视频广播(DVB)系统中，并且有望成为第四代移动通信系统的核心技术。
本文首先研究了OFDM理论，重点分析了在频率选择性衰落信道中OFDM技术解决码间干扰问题的原理，以及如何用基于DFT和IDFT的技术实现OFDM系统。并介绍了基于OFDM的无线局域网标准IEEE802.11a的物理层相关OFDM参数和其基带IFFT实现原理，结合具体的分组结构，给出了其符号定时、载波频率偏移估计和信道估计方法。本论文在MATLAB平台上对OFDM系统进行了仿真，研究了编码，调制映射和信道对OFDM系统的影响。在论文的最后提出了一种基于小波变换的新的OFDM调制方法(W-OFDM)，并且将其与DFT-OFDM进行了仿真比较，取得了一些有意义的仿真结果，对OFDM技术的研究有一定的参考价值。
Orthogonal Frequency Division Multiplexing is one of key technologies in mobile communication fields. It is suitable for high rate data transmission in wireless channels because it can combat Inter-Symbol interference and multi-path fading efficiently. Now it has become an attractive technology. OFDM is a multiple carriers technology, supports high rate data transmission with high spectrum efficiency. At present, OFDM technology has been used in many fields, such as wireless local network, digital audio broadcasting (DAB), digital video broadcasting (DVB) systems and so on. It is very promising to be a core technology of the fourth generation mobile communications.
In this thesis, we first discuss the basic theory of OFDM, and analyze why OFDM can effectively resolve the FSF and ISI, and how to realize the DFT-based OFDM system. And it is given for the new OFDM based wireless LAN standard IEEE 802. lla. Based on its packet structure, mathematical methods for OFDM symbol timing, carrier Frequency offset and channel estimation are proposed in this paper. In this thesis, we simulate OFDM system in MATLAB platform and analyze the relationship between FER, mapping, channel and OFDM system performance. At the last part we gives a new wavelet transform based OFDM and used to compare with the DFT-OFDM under the same conditions. The results are referential to the research of OFDM technology.
本文首先研究了OFDM理论，重点分析了在频率选择性衰落信道中OFDM技术解决码间干扰问题的原理，以及如何用基于DFT和IDFT的技术实现OFDM系统。并介绍了基于OFDM的无线局域网标准IEEE802.11a的物理层相关OFDM参数和其基带IFFT实现原理，结合具体的分组结构，给出了其符号定时、载波频率偏移估计和信道估计方法。本论文在MATLAB平台上对OFDM系统进行了仿真，研究了编码，调制映射和信道对OFDM系统的影响。在论文的最后提出了一种基于小波变换的新的OFDM调制方法(W-OFDM)，并且将其与DFT-OFDM进行了仿真比较，取得了一些有意义的仿真结果，对OFDM技术的研究有一定的参考价值。
Orthogonal Frequency Division Multiplexing is one of key technologies in mobile communication fields. It is suitable for high rate data transmission in wireless channels because it can combat Inter-Symbol interference and multi-path fading efficiently. Now it has become an attractive technology. OFDM is a multiple carriers technology, supports high rate data transmission with high spectrum efficiency. At present, OFDM technology has been used in many fields, such as wireless local network, digital audio broadcasting (DAB), digital video broadcasting (DVB) systems and so on. It is very promising to be a core technology of the fourth generation mobile communications.
In this thesis, we first discuss the basic theory of OFDM, and analyze why OFDM can effectively resolve the FSF and ISI, and how to realize the DFT-based OFDM system. And it is given for the new OFDM based wireless LAN standard IEEE 802. lla. Based on its packet structure, mathematical methods for OFDM symbol timing, carrier Frequency offset and channel estimation are proposed in this paper. In this thesis, we simulate OFDM system in MATLAB platform and analyze the relationship between FER, mapping, channel and OFDM system performance. At the last part we gives a new wavelet transform based OFDM and used to compare with the DFT-OFDM under the same conditions. The results are referential to the research of OFDM technology.
引文
[1] 刘元安等著，《宽带无线接入和无线局域网》，北京邮电大学出版社，2001．11；
[2] [奥]Andreas F. Molisch编著，《宽带无线数字通信》，电子工业出版社，2002．9；
[3] 曹志刚，钱亚生编著，《现代通信原理》，清华大学出版社，1999．8；
[4] IEEE 802.11a -1999 Supplement to IEEE Standard for Information Technology and Telecommucations and Information Exchange between System-part 11:LAN MAC and PHY Specifications:High Speed Physical Layer in the 5Ghz Band, Sep 1999;
[5] Richard van Nee, A New OFDM Standard for High Rate Wireless LAN in the 5Ghz Band, IEEE VTC' 99, Vol. 1, pp258-262,1999;
[6] Yun Hee Kim, An Efficient Frequency Offset Estimater for Timing and Frequency Synchronization in OFDM Systems, Communication, Computers and Signal Processing, 1999, IEEE Pacific Rim Conference on, 1999, pp580-583;
[7] 杨福生，小波变换的工程分析与应用，科学出版社，2000．11；
[8] 王利宁，乐光新编著，《MATLAB与通讯仿真》，人民邮电出版社，2000．1；
[9] 李建新，刘乃安编著，《现代通信系统分析与仿真-MATLAB通信工具箱》，西安电子科技大学出版社，2000．11；
[10] 胡昌华，张军波编著，《基于MATLAB的系统分析与设计-小波分析》，西安电子科技大学出版社，1999．12；
[11] orthogonal frequency division multiplexing, U.S. Patent 3 488 455. field Nov. 14,1966. issued Jan. 6,1970;
[12] L. J. Cimini. Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing. IEEE Trans.
Comm.. Technology, vol. COM-33, July 1985;
[13] 周一青，胡爱群，利用训练帧进行OFDM系统同步的新算法，《通信学报》，2001年第四期；
[14] 程玉荣，邵晓君，刘鸿，CMFB-DWMT多载波系统与DMT多载波系统的比较，《通信学报》，2002年第一期；
[15] 傅延增，张海林，王育民，OFDM中的自适应均衡技术，西安电子科技大学学报，2001年第二期；
[16] 张小东，徐平平，章国安，毕光国，基于复小波包的OFDM调制方法(CWP-OFDM)的研究，《电子学报》，2002年第四期；1999；
[17] Rohling H., et al., Broad-band OFDM radio transmission for multimedia applications, Proceedings of the IEEE, pp. 1778-1789, October
[18] G.A. Franco and G. Lachs, An orthogonal coding technique for communications, in IRE International Convention Record, vol. 9, pp. 126-133, 1961;
[19] R.W. Chang, Synthesis of band-limited orthogonal signals for multichannel data transmission, Bell Sys. Techn. Journal, vol. 45, Dec 1966;
[20] S.B. Slimane, OFDM schemes with non-overlapping time waveforms, in Proc. IEEE VTC' 98, (Ottawa, Canada), pp. 2067-2071, May 1998;
[21] J.S. Oh, Y.M. Chung, and S.U. Lee, A carrier synchronization technique for OFDM on the frequency-selective fading environment, in Proc. VTC' 96, pp. 1574-1578,1996;
[22] H. Rohling, T. May, K. Brueninghaus, and R. Grnheid, Broadband ofdm radio transmission for multimedia application, Proc. IEEE, vol. 87, pp. 1778-1789,1999;
[23] H. Rohling, K. Brueninghaus, and T. May, Hifh rate ofdm modem with quasicoherent dapsk, in Proc. ICT' 97, Melbournce, April 1997, pp. 211-216, IEEE, 1997;
[24] M. Sandell, Design and Analysis of Estimators for Multicarrier Modulation and Ultrasonic Imaging. PhD thesis, Lulea University of Technology, Lulea, Sweden, Sept. 1996;
[25] Y.G. Li, l.C. Cimini, and N.R. Sollenberger, Robust channel estimation for ofdm systems with rapid dispersive fading channel, IEEE Trans. Comm., vol. 46, pp. 902-915,1998;
[26] T. May, H. Rohling, and V. Engels, Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAM modulated OFDM signals, IEEE Transactions on Communications, vol.46, pp. 182-190, Feb. 1998;
[27] T. Walzman and M. Schwartz, Automatic equalization using the discrete Fourier domain, IEEE Transacations on Information Theory, vol. 19, pp. 59-68, Jan. 1973;
[2] [奥]Andreas F. Molisch编著，《宽带无线数字通信》，电子工业出版社，2002．9；
[3] 曹志刚，钱亚生编著，《现代通信原理》，清华大学出版社，1999．8；
[4] IEEE 802.11a -1999 Supplement to IEEE Standard for Information Technology and Telecommucations and Information Exchange between System-part 11:LAN MAC and PHY Specifications:High Speed Physical Layer in the 5Ghz Band, Sep 1999;
[5] Richard van Nee, A New OFDM Standard for High Rate Wireless LAN in the 5Ghz Band, IEEE VTC' 99, Vol. 1, pp258-262,1999;
[6] Yun Hee Kim, An Efficient Frequency Offset Estimater for Timing and Frequency Synchronization in OFDM Systems, Communication, Computers and Signal Processing, 1999, IEEE Pacific Rim Conference on, 1999, pp580-583;
[7] 杨福生，小波变换的工程分析与应用，科学出版社，2000．11；
[8] 王利宁，乐光新编著，《MATLAB与通讯仿真》，人民邮电出版社，2000．1；
[9] 李建新，刘乃安编著，《现代通信系统分析与仿真-MATLAB通信工具箱》，西安电子科技大学出版社，2000．11；
[10] 胡昌华，张军波编著，《基于MATLAB的系统分析与设计-小波分析》，西安电子科技大学出版社，1999．12；
[11] orthogonal frequency division multiplexing, U.S. Patent 3 488 455. field Nov. 14,1966. issued Jan. 6,1970;
[12] L. J. Cimini. Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing. IEEE Trans.
Comm.. Technology, vol. COM-33, July 1985;
[13] 周一青，胡爱群，利用训练帧进行OFDM系统同步的新算法，《通信学报》，2001年第四期；
[14] 程玉荣，邵晓君，刘鸿，CMFB-DWMT多载波系统与DMT多载波系统的比较，《通信学报》，2002年第一期；
[15] 傅延增，张海林，王育民，OFDM中的自适应均衡技术，西安电子科技大学学报，2001年第二期；
[16] 张小东，徐平平，章国安，毕光国，基于复小波包的OFDM调制方法(CWP-OFDM)的研究，《电子学报》，2002年第四期；1999；
[17] Rohling H., et al., Broad-band OFDM radio transmission for multimedia applications, Proceedings of the IEEE, pp. 1778-1789, October
[18] G.A. Franco and G. Lachs, An orthogonal coding technique for communications, in IRE International Convention Record, vol. 9, pp. 126-133, 1961;
[19] R.W. Chang, Synthesis of band-limited orthogonal signals for multichannel data transmission, Bell Sys. Techn. Journal, vol. 45, Dec 1966;
[20] S.B. Slimane, OFDM schemes with non-overlapping time waveforms, in Proc. IEEE VTC' 98, (Ottawa, Canada), pp. 2067-2071, May 1998;
[21] J.S. Oh, Y.M. Chung, and S.U. Lee, A carrier synchronization technique for OFDM on the frequency-selective fading environment, in Proc. VTC' 96, pp. 1574-1578,1996;
[22] H. Rohling, T. May, K. Brueninghaus, and R. Grnheid, Broadband ofdm radio transmission for multimedia application, Proc. IEEE, vol. 87, pp. 1778-1789,1999;
[23] H. Rohling, K. Brueninghaus, and T. May, Hifh rate ofdm modem with quasicoherent dapsk, in Proc. ICT' 97, Melbournce, April 1997, pp. 211-216, IEEE, 1997;
[24] M. Sandell, Design and Analysis of Estimators for Multicarrier Modulation and Ultrasonic Imaging. PhD thesis, Lulea University of Technology, Lulea, Sweden, Sept. 1996;
[25] Y.G. Li, l.C. Cimini, and N.R. Sollenberger, Robust channel estimation for ofdm systems with rapid dispersive fading channel, IEEE Trans. Comm., vol. 46, pp. 902-915,1998;
[26] T. May, H. Rohling, and V. Engels, Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAM modulated OFDM signals, IEEE Transactions on Communications, vol.46, pp. 182-190, Feb. 1998;
[27] T. Walzman and M. Schwartz, Automatic equalization using the discrete Fourier domain, IEEE Transacations on Information Theory, vol. 19, pp. 59-68, Jan. 1973;