无线OFDM系统中信道估计的研究
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摘要
正交频分复用(OFDM)技术作为一种可以有效对抗多径衰落的高速数据传输技术,在无线通信领域都得到了广泛应用。由于在移动通信中,信道具有时变特性,因此动态地对信道进行估计是十分必要的。信道估计是无线通信领域一项关键的技术,它直接影响着通信系统的性能。对时变衰落信道进行准确的估计是一个挑战性的课题。本文主要研究了无线OFDM系统中基于导频的时变信道估计方法。目前,对于无线OFDM系统的信道估计方法仍处于研究和探索阶段。
本文首先介绍了OFDM系统的发展历程以及其在通信领域的应用。然后详细介绍了无线信道的特征及其统计特性和时变衰落信道的计算机建模方法,并构建了无线OFDM系统的信道模型。接着本文对OFDM系统的基本原理和关键技术做了简要描述,而后着重讨论了无线OFDM系统中基于导频信号的信道估计方法并简要介绍了信道的盲估计方法。
在信道估计中,利用LS或MMSE算法准则估计出导频所在子信道的频率响应,然后再选择适当的插值算法,得到数据信号所在位置的信道估计值。本文详细阐述了LS、MMSE和改进的MMSE算法准则和几种常用的插值算法的原理,并且通过计算机仿真分析了LS和MMSE算法在AWGN和衰落信道中对系统性能的影响。在相同的导频数量的情况下,导频的结构对估计性能有很大的影响。本文就不同的导频结构对系统性能的影响作了较为全面地论述,并且提出了一种改进的导频结构,仿真结果表明这种改进的导频结构与传统的导频结构相比,对系统的性能有了一定的提高。
To be an high-speed data transmission technique, orthogonal frequency division multiplexing(OFDM) has been widely used in wireless communication systems due to its capability to combat multi-path fading. In mobile communication systems, a dynamical estimation is necessary since the channel is frequency-selective and time-varying. Channel estimation is one of the key techniques in wireless communication systems and it directly affects the performance of the system. It is challenging task to estimate time-varying channel quickly and accurately. This thesis mainly focuses on the time-varying channel estimation methods based on pilot tones in wireless OFDM systems. At present, the channel estimation of wireless OFDM systems has been still in the progress of research and exploring.In this paper, we first briefly introduce the development of OFDM and its application in communication fields. Secondly, the characters and statistic properties of wireless channel and the methods to model the wireless channel are discussed. After good study of them, the wireless OFDM systems channel model is constructed. Then we introduce the principle of OFDM system and some key techniques about it. At last, we mainly address the channel estimation methods based on pilot tones and briefly introduce the blind channel estimation in wireless OFDM systems.The pilot sub-channel frequency response can be estimated by using the LS or MMSE algorithm and the data sub-channel frequency response can be obtained by interpolating. We analyze the mechanism of LS, MMSE , modified MMSE algorithm and several popular interpolation methods and compare the bit error rate (BER) of LS and MMSE algorithm on AWGN and fading channels. At the same number of pilot tones, the pilot pattern makes great effects on the quality of channel estimation. We discuss the pilot patterns and investigate a modified pilot pattern. The simulation result shows that there is improvement of the system performance for this modified pilot pattern compared with other traditional pilot patterns.
本文首先介绍了OFDM系统的发展历程以及其在通信领域的应用。然后详细介绍了无线信道的特征及其统计特性和时变衰落信道的计算机建模方法,并构建了无线OFDM系统的信道模型。接着本文对OFDM系统的基本原理和关键技术做了简要描述,而后着重讨论了无线OFDM系统中基于导频信号的信道估计方法并简要介绍了信道的盲估计方法。
在信道估计中,利用LS或MMSE算法准则估计出导频所在子信道的频率响应,然后再选择适当的插值算法,得到数据信号所在位置的信道估计值。本文详细阐述了LS、MMSE和改进的MMSE算法准则和几种常用的插值算法的原理,并且通过计算机仿真分析了LS和MMSE算法在AWGN和衰落信道中对系统性能的影响。在相同的导频数量的情况下,导频的结构对估计性能有很大的影响。本文就不同的导频结构对系统性能的影响作了较为全面地论述,并且提出了一种改进的导频结构,仿真结果表明这种改进的导频结构与传统的导频结构相比,对系统的性能有了一定的提高。
To be an high-speed data transmission technique, orthogonal frequency division multiplexing(OFDM) has been widely used in wireless communication systems due to its capability to combat multi-path fading. In mobile communication systems, a dynamical estimation is necessary since the channel is frequency-selective and time-varying. Channel estimation is one of the key techniques in wireless communication systems and it directly affects the performance of the system. It is challenging task to estimate time-varying channel quickly and accurately. This thesis mainly focuses on the time-varying channel estimation methods based on pilot tones in wireless OFDM systems. At present, the channel estimation of wireless OFDM systems has been still in the progress of research and exploring.In this paper, we first briefly introduce the development of OFDM and its application in communication fields. Secondly, the characters and statistic properties of wireless channel and the methods to model the wireless channel are discussed. After good study of them, the wireless OFDM systems channel model is constructed. Then we introduce the principle of OFDM system and some key techniques about it. At last, we mainly address the channel estimation methods based on pilot tones and briefly introduce the blind channel estimation in wireless OFDM systems.The pilot sub-channel frequency response can be estimated by using the LS or MMSE algorithm and the data sub-channel frequency response can be obtained by interpolating. We analyze the mechanism of LS, MMSE , modified MMSE algorithm and several popular interpolation methods and compare the bit error rate (BER) of LS and MMSE algorithm on AWGN and fading channels. At the same number of pilot tones, the pilot pattern makes great effects on the quality of channel estimation. We discuss the pilot patterns and investigate a modified pilot pattern. The simulation result shows that there is improvement of the system performance for this modified pilot pattern compared with other traditional pilot patterns.
引文
[1] Chang R W. Synthesis of band-limited orthogonal signals for multichannel data transmission. Bell Syst. Tech. J, 1996,(45): 1775-1796
[2] Saltzberg B. R.. Performance of an efficient parallel data transmission system,IEEE Trans. Comm., Dec., 1967, COM-15(6): 805～811
[3] Weinstein S B, Ebert P M. Data transmission by frequency division multiplexing using the discrete Fourier transform. IEEE Trans. Comm. 1971, COM-19(10): 628～634
[4] Peled A., Ruiz A.. Frequency domain data transmission using reduced computational complexity algorithms, in Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing, Denver, CO,1980:964～967
[5] Cimini L J, Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing. IEEE Trans. Comm., 1985, COM-33(7): 665～675
[6] Foschini G J., Gans M. J., On limits of wireless communication in a fading environment when using multiple antennas. Wireless Personal Comm., 1998, 6(3): 311～335
[7] Gesbert D., Shafi M., Shru D. S. etal., From theory to practice : An overview of MIMO space-time coded wireless systems. ISEE Comm. Apr. 2003, 21(3)
[8] Raleigh G., Cioffi J. M., Spation-temporal coding for wireless communication. In Proc. IEEE Global Communication Conf., Nov. 1996:1809～1814
[9] 佟学俭,罗涛.OFDM移动通信技术原理与应用.北京:人民邮电出版社,2003.
[10] 张贤达,保铮.通信信号处理,北京:国防工业出版社,2000.12:40～93
[11] Rappaport J. R., Wireless communications: principle and practice. Prentice Hall,1996:204
[12] Vanderveen M. C., Estimation of parametric channel models in wireless communication networks, Ph.D. dissertations, Stanford University, 1998
[13] Sklar B., Rayleigh fading channels in mobile digital communication systems part I: characterization. IEEE Communications Magazines. Jul. 1997:90～100
[14] Jakes W. J., Microwave mobile communications. JohnWilley & Sons, Inc., 1994
[15] Gordon L.S.,裴昌幸 聂敏 岳安军译.移动通信原理(第二版),北京:电子工业出版社 2004:29～80
[16] 王文博,郑侃.《宽带无线通信—OFDM技术》,北京:人民邮电出版杜 2003.11
[17] Coleri S., Ergen M., Puri A., etal. A Study of Channel Estimation in OFDM Systems. IEEE Transactions on Broadcasting, 2002,48 (3): 894～898
[18] 胡蝶,杨绿溪.OFDM系统中基于导频的时变信道估计。电子与信息学报,2004,26(9):1376～1382
[19] Richard V. N., Prasad R., OFDM for wireless multimedia communications,Artech House, Hardcover, Jan. 2001:33～117
[20] Moose P. H., A technique for orthgonoal frequency division multiplexing frequency offset correction. IEEE Trans. Comm., 1994,45(12): 1613～1621
[21] Li X.D., Cimini L.J., Effects of clipping and filtering on the performance of OFDM. IEEE Communications Letters, 1998,2(5): 131～133
[22] Sahananthan K, Tellambura C., Coding to reduce both PAR and PICR of an OFDM signal. IEEE Communications Letters, 2002,6(8):316～318
[23] 郭坚.正交频分复用技术及其在CDMA中的应用,数字通信,1998
[24] LI Y. Pilot-symbol-aided channel estimation for OFDM in wireless systems. IEEE Transactions on Vehicular Technology,2000,49(4): 1207-1215.
[25] Hsieh M. H., Wei Ch. H., Channel estimation for OFDM systems base on comb-type pilot arrangement in frequency selective fading channels. IEEE Transactions on consumer electronic, 1998, 1(44):217～225
[26] Coleri S., Ergen, Anuj M. Puri, etal. Channel estimation techniques based on pilot arrangement in OFDM Systems. IEEE Transact ions on Broadcasting, 2002,48(3):223～229.
[27] 张继东,郑宝玉.基于导频的OFDM信道估计及其研究进展,通信学报 2003 24(11):116～124
[28] 周利岗,傅海阳.OFDM系统中基于导频插入的信道估计技术,通信技术2003.140:27～29
[29] Muquet B., Courville M. de, Duhamel P. Subspace based Blind and semi-blind channel estimation for OFDM systems, IEEE Trans. On Signal Processing, 2002,50(7): 1699～1712
[30] Wang H., Lin Y., Chen B.,Data efficient blind OFDM channel estimation using receiver diversity, IEEE Trans. On Signal Processing, 2003, 5:2613～2624
[31] Vande Beek J. J, Edfors O., Sandell M., et al. On channel estimation in OFDM systems. IEEE 45th Vehicular Technology Conference, Chicago, 1995, 815-819.
[32] Edfors O., Sandell M., Vande Beek J. J., etal., OFDM channel estimation by singular value decomposition. In Proc. IEEE 46th Vehicular Technology Conference,Atlanta, GA,USA, 1996,4:923～927
[33] 丁颢 张海滨 罗汉文等.OFDM系统中的信道估计方法分析,通信技术,2002 132:29～31
[34] 董江波,王刚,李道本.线性插值信道估计中导频间隔的最优化设计,北京邮电大学学报 2005,27(增):207～211
[35] NegiI R, Cioffi J. Pilot tone selection for channel estimation in a mobile OFDM system. IEEE Transactions on ConsumerElectronics, 1998, 44(3): 1122-1128.
[36] Stamoulis, A.;Diggavi, S.N.;A1-Dhahir, N.;Estimation of fast fading channels in OFDM. Wireless Communications and Networking Conference, 2002. WCNC2002. 2002 IEEE Volume1, 17-21 2002:465-470
[37] Zhao Y., Huang A., A novel channel estimation methods for OFDM mobile communication systems based on pilot signals and transform domain processing. In Proc. IEEE 47th Vehicular Technology Conference, Phoenix, USA,1997,3:2089-2093
[38] Yang B. G., Letaief K. B., Cheng R. S., et al .Windowed DFT based pilot-symbol-aided channel estimation for OFDM systems in multipath fading channels. Proc IEEE VTC'2000. 2000: 1480-1484.
[39] 邝育军,乐光新.OFDM系统信道估计中插值算法性能分析,北京邮电大学学报.2003 26(1):41～46
[40] Otikakamthorn N., Suzuki, On identifiablility of OFDM blind channel estimation, in Proc. VTC Amsterdam, Netherland, Sep. 1999:2358-2361
[41] Petropulu A.P.,Zhang R., Lin R., Blind OFDM channel estimation through simple linear precoding. IEEE Trans. On wireless communication,Mar. 2004
[42] 李子,蔡跃明,阚春荣等.OFDM系统中的盲信道估计,信号处理,2005,21(5):508～514
[2] Saltzberg B. R.. Performance of an efficient parallel data transmission system,IEEE Trans. Comm., Dec., 1967, COM-15(6): 805～811
[3] Weinstein S B, Ebert P M. Data transmission by frequency division multiplexing using the discrete Fourier transform. IEEE Trans. Comm. 1971, COM-19(10): 628～634
[4] Peled A., Ruiz A.. Frequency domain data transmission using reduced computational complexity algorithms, in Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing, Denver, CO,1980:964～967
[5] Cimini L J, Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing. IEEE Trans. Comm., 1985, COM-33(7): 665～675
[6] Foschini G J., Gans M. J., On limits of wireless communication in a fading environment when using multiple antennas. Wireless Personal Comm., 1998, 6(3): 311～335
[7] Gesbert D., Shafi M., Shru D. S. etal., From theory to practice : An overview of MIMO space-time coded wireless systems. ISEE Comm. Apr. 2003, 21(3)
[8] Raleigh G., Cioffi J. M., Spation-temporal coding for wireless communication. In Proc. IEEE Global Communication Conf., Nov. 1996:1809～1814
[9] 佟学俭,罗涛.OFDM移动通信技术原理与应用.北京:人民邮电出版社,2003.
[10] 张贤达,保铮.通信信号处理,北京:国防工业出版社,2000.12:40～93
[11] Rappaport J. R., Wireless communications: principle and practice. Prentice Hall,1996:204
[12] Vanderveen M. C., Estimation of parametric channel models in wireless communication networks, Ph.D. dissertations, Stanford University, 1998
[13] Sklar B., Rayleigh fading channels in mobile digital communication systems part I: characterization. IEEE Communications Magazines. Jul. 1997:90～100
[14] Jakes W. J., Microwave mobile communications. JohnWilley & Sons, Inc., 1994
[15] Gordon L.S.,裴昌幸 聂敏 岳安军译.移动通信原理(第二版),北京:电子工业出版社 2004:29～80
[16] 王文博,郑侃.《宽带无线通信—OFDM技术》,北京:人民邮电出版杜 2003.11
[17] Coleri S., Ergen M., Puri A., etal. A Study of Channel Estimation in OFDM Systems. IEEE Transactions on Broadcasting, 2002,48 (3): 894～898
[18] 胡蝶,杨绿溪.OFDM系统中基于导频的时变信道估计。电子与信息学报,2004,26(9):1376～1382
[19] Richard V. N., Prasad R., OFDM for wireless multimedia communications,Artech House, Hardcover, Jan. 2001:33～117
[20] Moose P. H., A technique for orthgonoal frequency division multiplexing frequency offset correction. IEEE Trans. Comm., 1994,45(12): 1613～1621
[21] Li X.D., Cimini L.J., Effects of clipping and filtering on the performance of OFDM. IEEE Communications Letters, 1998,2(5): 131～133
[22] Sahananthan K, Tellambura C., Coding to reduce both PAR and PICR of an OFDM signal. IEEE Communications Letters, 2002,6(8):316～318
[23] 郭坚.正交频分复用技术及其在CDMA中的应用,数字通信,1998
[24] LI Y. Pilot-symbol-aided channel estimation for OFDM in wireless systems. IEEE Transactions on Vehicular Technology,2000,49(4): 1207-1215.
[25] Hsieh M. H., Wei Ch. H., Channel estimation for OFDM systems base on comb-type pilot arrangement in frequency selective fading channels. IEEE Transactions on consumer electronic, 1998, 1(44):217～225
[26] Coleri S., Ergen, Anuj M. Puri, etal. Channel estimation techniques based on pilot arrangement in OFDM Systems. IEEE Transact ions on Broadcasting, 2002,48(3):223～229.
[27] 张继东,郑宝玉.基于导频的OFDM信道估计及其研究进展,通信学报 2003 24(11):116～124
[28] 周利岗,傅海阳.OFDM系统中基于导频插入的信道估计技术,通信技术2003.140:27～29
[29] Muquet B., Courville M. de, Duhamel P. Subspace based Blind and semi-blind channel estimation for OFDM systems, IEEE Trans. On Signal Processing, 2002,50(7): 1699～1712
[30] Wang H., Lin Y., Chen B.,Data efficient blind OFDM channel estimation using receiver diversity, IEEE Trans. On Signal Processing, 2003, 5:2613～2624
[31] Vande Beek J. J, Edfors O., Sandell M., et al. On channel estimation in OFDM systems. IEEE 45th Vehicular Technology Conference, Chicago, 1995, 815-819.
[32] Edfors O., Sandell M., Vande Beek J. J., etal., OFDM channel estimation by singular value decomposition. In Proc. IEEE 46th Vehicular Technology Conference,Atlanta, GA,USA, 1996,4:923～927
[33] 丁颢 张海滨 罗汉文等.OFDM系统中的信道估计方法分析,通信技术,2002 132:29～31
[34] 董江波,王刚,李道本.线性插值信道估计中导频间隔的最优化设计,北京邮电大学学报 2005,27(增):207～211
[35] NegiI R, Cioffi J. Pilot tone selection for channel estimation in a mobile OFDM system. IEEE Transactions on ConsumerElectronics, 1998, 44(3): 1122-1128.
[36] Stamoulis, A.;Diggavi, S.N.;A1-Dhahir, N.;Estimation of fast fading channels in OFDM. Wireless Communications and Networking Conference, 2002. WCNC2002. 2002 IEEE Volume1, 17-21 2002:465-470
[37] Zhao Y., Huang A., A novel channel estimation methods for OFDM mobile communication systems based on pilot signals and transform domain processing. In Proc. IEEE 47th Vehicular Technology Conference, Phoenix, USA,1997,3:2089-2093
[38] Yang B. G., Letaief K. B., Cheng R. S., et al .Windowed DFT based pilot-symbol-aided channel estimation for OFDM systems in multipath fading channels. Proc IEEE VTC'2000. 2000: 1480-1484.
[39] 邝育军,乐光新.OFDM系统信道估计中插值算法性能分析,北京邮电大学学报.2003 26(1):41～46
[40] Otikakamthorn N., Suzuki, On identifiablility of OFDM blind channel estimation, in Proc. VTC Amsterdam, Netherland, Sep. 1999:2358-2361
[41] Petropulu A.P.,Zhang R., Lin R., Blind OFDM channel estimation through simple linear precoding. IEEE Trans. On wireless communication,Mar. 2004
[42] 李子,蔡跃明,阚春荣等.OFDM系统中的盲信道估计,信号处理,2005,21(5):508～514