基于DFT的OFDM信道估计算法研究
摘要
由于正交频分复用OFDM技术(Orthogonal Frequency Division Multiplexing)具有较高的频谱利用率和较好的抗干扰能力,已经被各种无线数字标准所广泛采用,例如数字音频广播(DAB),数字电视广播(DVB),无线局域网(802.11,HIPERLAN),无线广域网(802.16)等。在实际应用中,信道估计技术是要重点考虑的关键技术。为了保证系统的性能不受信道的多径和衰落效应的影响,就需要采用信道估计的方法来跟踪信道响应的变化。
本文在简单分析OFDM的基本原理和无线信道的传播特性的基础上,详细介绍了基于导频的信道估计技术。它是在发送端信号中的某些固定位置插入一些已知的导频信号,在接收端取出这些导频信号并根据一定的算法获得其所在位置处的传输函数的估计,再采用合适的插值算法进而获得所有位置处的信道传输函数。这种方法能较好的跟踪信道的信息,通过设计合理的导频图案,能够利用较少的导频信息获得信道响应。本文简单介绍导频处的信道估计准则LS(Least Squre)、MMSE(Minimum Mean Square Error)、LMMSE(Low Rank LinearMMSE)、SVD(Singular Value Decomposion)算法以及线性插值、高斯插值、维纳滤波器、基于DFT的插值算法,其中对基于DFT的插值算法进行了重点分析。
本文以COST 207 TU多径信道模型为程序仿真环境,对基于DFT的几种插值算法进行仿真分析,比较了其性能。并对现有的基于DFT信道估计算法进行了改进,为了降低噪声的影响,及插值所带来的噪声误差,将得到的信道响应在变换域中进行去噪处理。对变换域插值算法进行加窗防止频谱泄露,并将线性插值和DFT插值结合进行二维信道估计,仿真结果显示这几种改进的信道估计方法具有较好的性能。在仿真中就不同的导频开销、信道条件及各种调制方式对OFDM系统性能的影响进行了全面的仿真分析和比较。
With high spectral efficiency and better anti-interference ability, OFDM (Orthogonal Frequency Division Multiplexing) has been widely adopted by a variety of wireless digital standerds.Such as digital audio broadcasting (DAB), digital video broadcasting (DVB-T), Wireless Wide Area Network(802.16)and so on.. However in practice, channel estimation is the key technique to consider. Channel estimation can tack the changes of wireless channel environment,hence ensure the performance of the system from muti-path channel and the fading efftct.
For the beginning, we made a simple analysis of the basic principles of OFDM and the wireless channel characteristics, then give a ditail introduction of the pilot-based-channel estimation. It is based on the interpolation of the known pilots into the signals at the transmitter, remove and estimate the channel function in these pilots location at the receiving end, then use appropriate inerpolation algorithm to obtain the whole channel function. This method can track the channel response if using good pilot pattern. This article explain some pilot estimation rules such as LS(Least Squre)、MMSE(Minimum Mean Square Error)、LMMSE(Low Rank LinearMMSE)、SVD(Singular Value Decomposion)and interpolation algorithm such as Linear interpolation, Gauss interpolation, Wiener filter, DFT-based interpolations.
In this paper, COST 207 TU multipath channel model is adopted as the simulation environment. We mainly analysis several DFT-based interpolations, compare the performaces, and made some improves. we add the transform domain filter to decrease the noice, use the improved window funcion to avoid spectral leakage. make a combination of the Linear interpolation and DFT interpolation for two-dimension channel estimation.Simulation results show that these improvement have good performances.At last. We made a discussion which is the effects of the pilot expense, channel conditions and modulation on the channel estimation rusults.
本文在简单分析OFDM的基本原理和无线信道的传播特性的基础上,详细介绍了基于导频的信道估计技术。它是在发送端信号中的某些固定位置插入一些已知的导频信号,在接收端取出这些导频信号并根据一定的算法获得其所在位置处的传输函数的估计,再采用合适的插值算法进而获得所有位置处的信道传输函数。这种方法能较好的跟踪信道的信息,通过设计合理的导频图案,能够利用较少的导频信息获得信道响应。本文简单介绍导频处的信道估计准则LS(Least Squre)、MMSE(Minimum Mean Square Error)、LMMSE(Low Rank LinearMMSE)、SVD(Singular Value Decomposion)算法以及线性插值、高斯插值、维纳滤波器、基于DFT的插值算法,其中对基于DFT的插值算法进行了重点分析。
本文以COST 207 TU多径信道模型为程序仿真环境,对基于DFT的几种插值算法进行仿真分析,比较了其性能。并对现有的基于DFT信道估计算法进行了改进,为了降低噪声的影响,及插值所带来的噪声误差,将得到的信道响应在变换域中进行去噪处理。对变换域插值算法进行加窗防止频谱泄露,并将线性插值和DFT插值结合进行二维信道估计,仿真结果显示这几种改进的信道估计方法具有较好的性能。在仿真中就不同的导频开销、信道条件及各种调制方式对OFDM系统性能的影响进行了全面的仿真分析和比较。
With high spectral efficiency and better anti-interference ability, OFDM (Orthogonal Frequency Division Multiplexing) has been widely adopted by a variety of wireless digital standerds.Such as digital audio broadcasting (DAB), digital video broadcasting (DVB-T), Wireless Wide Area Network(802.16)and so on.. However in practice, channel estimation is the key technique to consider. Channel estimation can tack the changes of wireless channel environment,hence ensure the performance of the system from muti-path channel and the fading efftct.
For the beginning, we made a simple analysis of the basic principles of OFDM and the wireless channel characteristics, then give a ditail introduction of the pilot-based-channel estimation. It is based on the interpolation of the known pilots into the signals at the transmitter, remove and estimate the channel function in these pilots location at the receiving end, then use appropriate inerpolation algorithm to obtain the whole channel function. This method can track the channel response if using good pilot pattern. This article explain some pilot estimation rules such as LS(Least Squre)、MMSE(Minimum Mean Square Error)、LMMSE(Low Rank LinearMMSE)、SVD(Singular Value Decomposion)and interpolation algorithm such as Linear interpolation, Gauss interpolation, Wiener filter, DFT-based interpolations.
In this paper, COST 207 TU multipath channel model is adopted as the simulation environment. We mainly analysis several DFT-based interpolations, compare the performaces, and made some improves. we add the transform domain filter to decrease the noice, use the improved window funcion to avoid spectral leakage. make a combination of the Linear interpolation and DFT interpolation for two-dimension channel estimation.Simulation results show that these improvement have good performances.At last. We made a discussion which is the effects of the pilot expense, channel conditions and modulation on the channel estimation rusults.
引文
[1]范广,孙运强,娄华平.OFDM技术及其在无线局域网中的应用[J],科技情报开发与经济,2006,16(19),223~225.
[2] G.A.Doelz, E.T.Heald, D.L.Martin.Binary data transmission techniques for linear systems. Proc. I.R.E., May 1957,45:656~661
[3] L.J.Cimini. Analysis and simulation of a digital mobile channel using Orthogonal Frequency Division Multiplexing. IEEE Trans.on Comm., July 1985 , COM-33(7):665~675
[4] S.B.Weinstein, P.M.Ebert.Data transmission by frequency division multiplexing suing the discrete Fourier transform. IEEE Trans.on Comm , Oct. 1971 , COM-19(5):628~634
[5] A.Peled, A.Ruiz.Frequency domain data transmission using reduced computational complexity algorithms.Proc. IEEE Int.Conf.Acoust Speech Signal Processing, Denver, CO, 1980:964~967
[6]王文博,邓侃.宽带无线通信OFDM技术.人民邮电出版社,2003
[7] Molisch A F, Win M Z, Winters JH. Space-Time-Frequency(STF)Coding for MIMO-OFDM Systems. IEEE Communication Letters , 2002,6(9):370~372
[8] L Wei, Cschlegel.Synchronization requirments for multi-user OFDM on satellite mobile and two-path Rayleigh-fading channels. IEEE Trans.Commun, 1995 , 43 (2/3/4):887~895
[9] W D Warmer, C Leung, OFDM/FM frame synchronization for mobile radio data communication. IEEE Trans. Vehic.Technol , 1993,42(3):302~313
[10] Xiaodong Li, L J Cimini Effects of clipping and filtering on the performance of OFDM. IEEE Communications Letters, 1998,2(5):131~133
[11] N Yee,J-Plinnartz, Gfettweis.Multi-Carrier CDMA in Indoor Wireless Radio Networks. Proc.of IEEE PIMRC’93, Yokohamma,Japan, 1993:109~113
[12] Sari H G Karam, I jeanclaude.Transmission Techniques for Digital Terrestrial TV Broadcasting, IEEE Communication
[13] Eric Phillip LAWREY BE(Hons). Adaptive Techniques for Multiuser OFDM, December 2001
[14] S.Weinstein, P.Ebert. Data transmission by frequency-division multiplexing suingthe discrete Fourier transform.IEEE Trans.on Comm., Oct.1971, 19(5):628~634
[15] J.Bingharm. Multicarrier modulation for data transmission: An idea whose time has com. IEEE Comm.Mag, 1990,28(5):5~14
[16]胡广书.数字信号处理——理论、算法与实现北京清华大学出版社1997
[17] A peled, A Ruiz.Frequency Domain Data Transmission Using Reduced Computational Complexity Algorithms.in IEEE Int. Conf. Acoust.,Speech, Signal Processing, 1980:964~967
[18] Rapp C Effects of HPA-Nonlinearity on a 4-DPSK/OFDM Signal for a Digital Sound Broadcasting System. Procedings of the Second European Conference on Satellite Communications, 1991,10:179~184
[19] Dusan Matia.OFDM as a possible modulation technique for multimedia application in the range of mm waves, 10/30/98/TUD-TVS
[20]张海滨.正交频分复用的基本原理与关键技术国防工业出版社2006
[21] T S Rappaport. Wireless Communications Principles and Practice. Publisher: Pntice Hall press,1996
[22] Bernard Sklar. Digital Communications Fundamentals and Applications 2002
[23] Lee, W C Y Mobile Cellular Telecommunications Systems, McGraw Hill Publications, New York,1989
[24]程佩青.数字信号处理清华大学出版社1995
[25] B.Muquet, M. de Courville, Blind and semi-blind channel idetification methods using second order statistics for OFDM systems, Acoustics,Speech, and Signal Processing, 1999.ICASSP’99.Proceedings.,1999 IEEE International Conference on, Volume:5, 1999, pp.2745-2748, vol 5
[26] S M Kay. Fundamentals of Statistical Signal Processing:Estimation Theory. Prentice-Hall,1998
[27] M.L Moher, J.H. Lodge, TCMP-a modulation and coding strategy for Rician-fading channels, IEEE Journal on Selected Areas, Commu, Vol.7, No.9, pp.1347-1355, Dec 1989
[28] MICHELE M, UMBERTO M. A comparision of pilot-aided channel estimation methods for OFDM systems [J].IEEE Transanctions On Signal Processing , 2001,49(12):3065-3073
[29] Ahmad R.S.Bahai and Burton R. Saltzberg, Multi-Carrier Digital Communications: Theory and Application of OFDM, Algorex, Inc, Iselin, New Jersey,1999
[30] Richard van Nee, Ramjee Prasad.OFDM wireless multimedia communications. Boston, London: Artech House,2000
[31]佟学俭等.OFDM移动通信技术原理与应用.北京:人民邮电出版社,2003
[32] T S Rappaport. Wireless Communications Principles and Practice. Publisher: Prentice Hall press,1996
[33]尹长川,罗涛,乐光新.多载波宽带无线通信
[34] J.J.van de Beek, O. Edfors, P. O.Borjesson, M. Walhlqvist and C.Ostberg, A conceptual study of ofdm-based multiple access schemes: Part 2-channel estimation in the uplink, Technical Raport Tdoc 116/96, ETSI STC SMG2 Meeting No 18, Helsinki, Finland , May.1996
[35] J.J.van de Beek, O. Edfors, P. O.Borjesson, M. Walhlqvist and C.Ostberg, A conceptual study of ofdm-based multiple access schemes: Part 3-performance evaluation of a coded system, T echnical Raport Tdoc 116/96, ETSI STC SMG2 Meeting No 19, Dusseldorf, Germany , Sept.1996
[36] L L Scharf. Statistical Signal Processing : Detection,Estimation, and Time Series Analysis. Reading, MA: Addison-Wesley, 1991
[37]郑君里,杨为理,应启衍.信号与系统.高等教育出版社,1998
[38] Chen-Shen Yeh Yinyi Lin, Yiyan Wu OFDM system channel estimation using time-domain training sequence for mobile reception of digital terrestrial broadcasting, Broadcasting, IEEE Transactions on, Volume:46 Issue:3, Sep 2000,pp.215-220,vol.2
[39] Moon J K,Choi S I. Performance of channel estimation methods for OFDM systems in a multipath fading channels.IEEE Transaction on Consumer Electronics, February 2000,46(1):161~170
[40] Hoeher P, Kaiser S. Two-dimensional pilot-symbol-aided channel estimation by Wiener Filtering.in Proc.IEEE ICASSP’97,Munich,Germany, April 1997,1845~1848
[41]汪裕民.OFDM关键技术与应用机械工业出版社2007
[42] J.J.vandeBeek, M.Sandell. Estimation of time and frequency offset in ofdm system[M]. IEEE Trans.Signal Processing, 1997.45:1807-1811.
[43]徐文颖,张静,董建萍.导频信道估计中的插值算法[J],上海师范大学学报(自然科学版),2007,36(6),41~45.
[44] Fernadez-Getino Garcia, M.J. Paez-Borrallo, J.M. Zazo, S. DFT-based channel estimation in 2D-pilot-symbol-aided OFDM wireless systems. Vehicular Technology Conference 2001.VTC 2001 Spring. IEEE VTS 53rd Volume 2,6~9 May 2001,810~814
[45] Y Zhao, A Huang. 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, May Proc.IEEE 47thVTC, 1997,3:2089~2093
[46]韦岗,季飞,傅娟.通信系统建模与仿真电子工业出版社2007
[47] YANG B G, CAO Z G, LETAIEF K B. Analysis of low-complexity windowed DFT-based MMSE channel estimator for OFDM system[J]. IEEE Transactions on Communications, 2001, 49(11):1977-1987
[48] DUC NGUYEN V, KUCHENBECKER H P. Intercarrier and inter-symbol interference analysis of OFDM systems on time-varying channels[M]. Signal Processing Advances in Wireless Communications, SPAWC 2003 . 4th IEEE, 2003.140-144.
[49] O Edfors Msandelll, J-J van de Beek, SK Wilson.OFDM channel estimation by singular value decomposition.in Proc. IEEE 46th Vehicular Technology Conference , Atlanta, GA, USA, 1996,4:923~927
[50] Chen-Shen Yeh Yinyi Lin, Channel estimation using pilot tones in OFDM systems , Broadcasting, IEEE Transactions on, Volume:45 Issue:4, Dec 1999, pp.400-409, vol.5
[2] G.A.Doelz, E.T.Heald, D.L.Martin.Binary data transmission techniques for linear systems. Proc. I.R.E., May 1957,45:656~661
[3] L.J.Cimini. Analysis and simulation of a digital mobile channel using Orthogonal Frequency Division Multiplexing. IEEE Trans.on Comm., July 1985 , COM-33(7):665~675
[4] S.B.Weinstein, P.M.Ebert.Data transmission by frequency division multiplexing suing the discrete Fourier transform. IEEE Trans.on Comm , Oct. 1971 , COM-19(5):628~634
[5] A.Peled, A.Ruiz.Frequency domain data transmission using reduced computational complexity algorithms.Proc. IEEE Int.Conf.Acoust Speech Signal Processing, Denver, CO, 1980:964~967
[6]王文博,邓侃.宽带无线通信OFDM技术.人民邮电出版社,2003
[7] Molisch A F, Win M Z, Winters JH. Space-Time-Frequency(STF)Coding for MIMO-OFDM Systems. IEEE Communication Letters , 2002,6(9):370~372
[8] L Wei, Cschlegel.Synchronization requirments for multi-user OFDM on satellite mobile and two-path Rayleigh-fading channels. IEEE Trans.Commun, 1995 , 43 (2/3/4):887~895
[9] W D Warmer, C Leung, OFDM/FM frame synchronization for mobile radio data communication. IEEE Trans. Vehic.Technol , 1993,42(3):302~313
[10] Xiaodong Li, L J Cimini Effects of clipping and filtering on the performance of OFDM. IEEE Communications Letters, 1998,2(5):131~133
[11] N Yee,J-Plinnartz, Gfettweis.Multi-Carrier CDMA in Indoor Wireless Radio Networks. Proc.of IEEE PIMRC’93, Yokohamma,Japan, 1993:109~113
[12] Sari H G Karam, I jeanclaude.Transmission Techniques for Digital Terrestrial TV Broadcasting, IEEE Communication
[13] Eric Phillip LAWREY BE(Hons). Adaptive Techniques for Multiuser OFDM, December 2001
[14] S.Weinstein, P.Ebert. Data transmission by frequency-division multiplexing suingthe discrete Fourier transform.IEEE Trans.on Comm., Oct.1971, 19(5):628~634
[15] J.Bingharm. Multicarrier modulation for data transmission: An idea whose time has com. IEEE Comm.Mag, 1990,28(5):5~14
[16]胡广书.数字信号处理——理论、算法与实现北京清华大学出版社1997
[17] A peled, A Ruiz.Frequency Domain Data Transmission Using Reduced Computational Complexity Algorithms.in IEEE Int. Conf. Acoust.,Speech, Signal Processing, 1980:964~967
[18] Rapp C Effects of HPA-Nonlinearity on a 4-DPSK/OFDM Signal for a Digital Sound Broadcasting System. Procedings of the Second European Conference on Satellite Communications, 1991,10:179~184
[19] Dusan Matia.OFDM as a possible modulation technique for multimedia application in the range of mm waves, 10/30/98/TUD-TVS
[20]张海滨.正交频分复用的基本原理与关键技术国防工业出版社2006
[21] T S Rappaport. Wireless Communications Principles and Practice. Publisher: Pntice Hall press,1996
[22] Bernard Sklar. Digital Communications Fundamentals and Applications 2002
[23] Lee, W C Y Mobile Cellular Telecommunications Systems, McGraw Hill Publications, New York,1989
[24]程佩青.数字信号处理清华大学出版社1995
[25] B.Muquet, M. de Courville, Blind and semi-blind channel idetification methods using second order statistics for OFDM systems, Acoustics,Speech, and Signal Processing, 1999.ICASSP’99.Proceedings.,1999 IEEE International Conference on, Volume:5, 1999, pp.2745-2748, vol 5
[26] S M Kay. Fundamentals of Statistical Signal Processing:Estimation Theory. Prentice-Hall,1998
[27] M.L Moher, J.H. Lodge, TCMP-a modulation and coding strategy for Rician-fading channels, IEEE Journal on Selected Areas, Commu, Vol.7, No.9, pp.1347-1355, Dec 1989
[28] MICHELE M, UMBERTO M. A comparision of pilot-aided channel estimation methods for OFDM systems [J].IEEE Transanctions On Signal Processing , 2001,49(12):3065-3073
[29] Ahmad R.S.Bahai and Burton R. Saltzberg, Multi-Carrier Digital Communications: Theory and Application of OFDM, Algorex, Inc, Iselin, New Jersey,1999
[30] Richard van Nee, Ramjee Prasad.OFDM wireless multimedia communications. Boston, London: Artech House,2000
[31]佟学俭等.OFDM移动通信技术原理与应用.北京:人民邮电出版社,2003
[32] T S Rappaport. Wireless Communications Principles and Practice. Publisher: Prentice Hall press,1996
[33]尹长川,罗涛,乐光新.多载波宽带无线通信
[34] J.J.van de Beek, O. Edfors, P. O.Borjesson, M. Walhlqvist and C.Ostberg, A conceptual study of ofdm-based multiple access schemes: Part 2-channel estimation in the uplink, Technical Raport Tdoc 116/96, ETSI STC SMG2 Meeting No 18, Helsinki, Finland , May.1996
[35] J.J.van de Beek, O. Edfors, P. O.Borjesson, M. Walhlqvist and C.Ostberg, A conceptual study of ofdm-based multiple access schemes: Part 3-performance evaluation of a coded system, T echnical Raport Tdoc 116/96, ETSI STC SMG2 Meeting No 19, Dusseldorf, Germany , Sept.1996
[36] L L Scharf. Statistical Signal Processing : Detection,Estimation, and Time Series Analysis. Reading, MA: Addison-Wesley, 1991
[37]郑君里,杨为理,应启衍.信号与系统.高等教育出版社,1998
[38] Chen-Shen Yeh Yinyi Lin, Yiyan Wu OFDM system channel estimation using time-domain training sequence for mobile reception of digital terrestrial broadcasting, Broadcasting, IEEE Transactions on, Volume:46 Issue:3, Sep 2000,pp.215-220,vol.2
[39] Moon J K,Choi S I. Performance of channel estimation methods for OFDM systems in a multipath fading channels.IEEE Transaction on Consumer Electronics, February 2000,46(1):161~170
[40] Hoeher P, Kaiser S. Two-dimensional pilot-symbol-aided channel estimation by Wiener Filtering.in Proc.IEEE ICASSP’97,Munich,Germany, April 1997,1845~1848
[41]汪裕民.OFDM关键技术与应用机械工业出版社2007
[42] J.J.vandeBeek, M.Sandell. Estimation of time and frequency offset in ofdm system[M]. IEEE Trans.Signal Processing, 1997.45:1807-1811.
[43]徐文颖,张静,董建萍.导频信道估计中的插值算法[J],上海师范大学学报(自然科学版),2007,36(6),41~45.
[44] Fernadez-Getino Garcia, M.J. Paez-Borrallo, J.M. Zazo, S. DFT-based channel estimation in 2D-pilot-symbol-aided OFDM wireless systems. Vehicular Technology Conference 2001.VTC 2001 Spring. IEEE VTS 53rd Volume 2,6~9 May 2001,810~814
[45] Y Zhao, A Huang. 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, May Proc.IEEE 47thVTC, 1997,3:2089~2093
[46]韦岗,季飞,傅娟.通信系统建模与仿真电子工业出版社2007
[47] YANG B G, CAO Z G, LETAIEF K B. Analysis of low-complexity windowed DFT-based MMSE channel estimator for OFDM system[J]. IEEE Transactions on Communications, 2001, 49(11):1977-1987
[48] DUC NGUYEN V, KUCHENBECKER H P. Intercarrier and inter-symbol interference analysis of OFDM systems on time-varying channels[M]. Signal Processing Advances in Wireless Communications, SPAWC 2003 . 4th IEEE, 2003.140-144.
[49] O Edfors Msandelll, J-J van de Beek, SK Wilson.OFDM channel estimation by singular value decomposition.in Proc. IEEE 46th Vehicular Technology Conference , Atlanta, GA, USA, 1996,4:923~927
[50] Chen-Shen Yeh Yinyi Lin, Channel estimation using pilot tones in OFDM systems , Broadcasting, IEEE Transactions on, Volume:45 Issue:4, Dec 1999, pp.400-409, vol.5