MIMO-OFDM信道估计算法研究
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摘要
正交频分复用技术具有高速传输数据、频谱利用率高、抗频率选择性衰落和多径衰落的特点,而多输入多输出技术具有在不增加系统带宽的情况下提高通信系统的容量的特点。MIMO-OFDM系统具备两种技术的优点,能同时获得时间、频率和空间三种分集,是下一代(4G)无线通信的关键技术。信道估计技术是MIMO-OFDM系统发挥其优越性的关键技术,因此有必要对MIMO-OFDM系统的信道估计方法进行研究。
首先,本文介绍了OFDM系统、MIMO系统和MIMO-OFDM系统的基本原理和结构,以及无线信道的空间特点和衰落特性,研究了基于导频符号的信道估计算法,主要是最小二乘法和奇异值分解法。同时,研究了线性插值、高斯插值和拉格朗日插值等常用插值算法,通过计算机仿真得到了性能对比曲线。
其次,针对频率选择性衰落信道下MIMO-OFDM的系统,基于瑞利衰落信道的模型,利用m序列的自相关性,提出了一种基于m序列做梳状导频的多输入多输出正交频分复用最小二乘算法,该算法可以避免对大矩阵求伪逆,以减少计算复杂度,从而提高了信道估计的计算性能。
最后,介绍了叠加导频的MIMO-OFDM系统,采用正交多相序列作为叠加导频,利用导频符号的自相关及导频和接收信号的互相关,并且提出了一种选择性叠加导频信道估计信道的算法。最后,通过理论分析和计算机仿真,表明该方法在快衰落环境中有良好的性能。
OFDM has the characteristic of high-speed data transmission, high spectrum efficiency, selective fading with resisted frequency and multipath fading, while multiple input multiple output technology can improve communication systems capacity in case of not increasing system bandwidth. MIMO-OFDM is the key technology of next generation (4G) wireless communication with the advantages of both technologies, it can obtain three diversities of time, frequency and spatial at the same time. Channel estimation plays key roles in MIMO-OFDM system, it is essential to study the channel estimation method of MIMO-OFDM system.
First, the article describes the basic principle and structure of OFDM systems, MIMO systems, MIMO-OFDM system, also, the spatial characteristic and fading feature of wireless channel, also, studies the channel estimation algorithm based on pilot symbols as for the least squares method and the singular value decomposition method concretely. Also, the article studies the commonly used interpolation algorithm such as linear interpolation, Gauss interpolation and Lagrange interpolation, getting the comparison curve of performance through computer simulation.
Secondly, Focusing on MIMO-OFDM system under frequency selective fading channel, based on the model of Rayleigh fading channel and the autocorrelation of m sequence, the paper proposes a MIMO-OFDM least squares algorithm using m sequence as comb pilot, which avoids pseudo inverse of large matrix so as to reduce the computational complexity and improves the calculation performance of channel estimation.
Finally, the paper introduces the MIMO-OFDM system with superimposed pilot, adopting the orthogonal multi-phase sequence as superimposed pilot, using the autocorrelation of pilot symbols, also the cross correlation of pilot and received signal, we propose a channel estimation algorithm based on selective superimposed pilot channel. Theoretical analysis and computer simulation show that the method has good performance in fast fading environment.
首先,本文介绍了OFDM系统、MIMO系统和MIMO-OFDM系统的基本原理和结构,以及无线信道的空间特点和衰落特性,研究了基于导频符号的信道估计算法,主要是最小二乘法和奇异值分解法。同时,研究了线性插值、高斯插值和拉格朗日插值等常用插值算法,通过计算机仿真得到了性能对比曲线。
其次,针对频率选择性衰落信道下MIMO-OFDM的系统,基于瑞利衰落信道的模型,利用m序列的自相关性,提出了一种基于m序列做梳状导频的多输入多输出正交频分复用最小二乘算法,该算法可以避免对大矩阵求伪逆,以减少计算复杂度,从而提高了信道估计的计算性能。
最后,介绍了叠加导频的MIMO-OFDM系统,采用正交多相序列作为叠加导频,利用导频符号的自相关及导频和接收信号的互相关,并且提出了一种选择性叠加导频信道估计信道的算法。最后,通过理论分析和计算机仿真,表明该方法在快衰落环境中有良好的性能。
OFDM has the characteristic of high-speed data transmission, high spectrum efficiency, selective fading with resisted frequency and multipath fading, while multiple input multiple output technology can improve communication systems capacity in case of not increasing system bandwidth. MIMO-OFDM is the key technology of next generation (4G) wireless communication with the advantages of both technologies, it can obtain three diversities of time, frequency and spatial at the same time. Channel estimation plays key roles in MIMO-OFDM system, it is essential to study the channel estimation method of MIMO-OFDM system.
First, the article describes the basic principle and structure of OFDM systems, MIMO systems, MIMO-OFDM system, also, the spatial characteristic and fading feature of wireless channel, also, studies the channel estimation algorithm based on pilot symbols as for the least squares method and the singular value decomposition method concretely. Also, the article studies the commonly used interpolation algorithm such as linear interpolation, Gauss interpolation and Lagrange interpolation, getting the comparison curve of performance through computer simulation.
Secondly, Focusing on MIMO-OFDM system under frequency selective fading channel, based on the model of Rayleigh fading channel and the autocorrelation of m sequence, the paper proposes a MIMO-OFDM least squares algorithm using m sequence as comb pilot, which avoids pseudo inverse of large matrix so as to reduce the computational complexity and improves the calculation performance of channel estimation.
Finally, the paper introduces the MIMO-OFDM system with superimposed pilot, adopting the orthogonal multi-phase sequence as superimposed pilot, using the autocorrelation of pilot symbols, also the cross correlation of pilot and received signal, we propose a channel estimation algorithm based on selective superimposed pilot channel. Theoretical analysis and computer simulation show that the method has good performance in fast fading environment.
引文
[1]陈奎,徐钊.OFDM系统二维变换域信道估计算法[J].电子科技大学学报,2009,38(6):927-931.
[2]刘刚,葛建华,郭漪.MIMO-OFDM系统中一种链式加权LS信道估计算法[J].电子与信息学报,2009,31(7):1763-1766.
[3]肖丽萍,郝磊,段再超.基于失配序列的OFDM信道估计[J].信号处理,2010,26(4):583-587.
[4]张阳,李维英,李建东,庞立华.基于前导序列的OFDM定时同步与信道估计算法[J].电路与系统学报,2009,14(6):111-115.
[5]陈宁,黄一平.基于加窗型DCT-Ⅳ的OFDM系统的信道估计算法[J].计算机工程与应用,2010,46(1):87-89.
[6]刘英男,蒋伟,任术波,梁庆林.时间-频率双选择性衰落信道的最小二乘估计方法[J].电子与信息学报,2008,30(9):2185-2188.
[7]张晓瀛,黄勤飞,魏急波.时变条件下MIMO-OFDM系统中的信道估计算法[J].电路与系统学报,2009,14(5):20-25.
[8]李明奇,李玉柏,彭启琮.导频符号调制方式对OFDM信道估计的影响[J].电子科技大学学报,2009,38(1):25-27.
[9]陈雪娟,李小文.TD-LTE下行发射分集自适应信道估计研究分析[J].计算机应用研究,2010,27(12):4701-4704.
[10]俞晓帆,赵春明.基于多中继导频频分复用的协同通信系统信道估计算法[J].信号处理,2010,26(4):588-595.
[11]王芳,王启国.一种基于ZCZ序列的OFDM信道估计[J].计算机工程与应用,2008,44(20):111-113.
[12]Ozdemir M K,Arslan H.Channel Estimation for Wireless OFDM Systems[J].IEEE Communications Surveys&Tutorials,2007,9(02):18-48.
[13]Jiachin Lin.Least-Squares Channel Estimation for Mobile OFDM Communication on Time-Varying Frequency-Selective Fading Channels[J].IEEE Transactions on Vehicular Technology,2008,57(06):3538-3550
[14]Dong Xiao-dai.Linear interpolation in pilots system assisted channel estimation for OFDM[J].IEEE Trans on Wireless Comm,2007,6(5).
[15]刘刚,郭漪,葛建华.MIMO-OFDM系统中的信道估计[J].华中科技大学学报.2005,(9):26-29.
[16]王许菲.MIMO-OFDM系统关键技术研究[D].北京邮电大学硕士论文,2008.
[17]Weichang Li, James C. Preisig. Estimation of Rapidly Time-Varying Sparse Channels.[J] IEEE journal of oceanic engineering.2007,32(4):927-939.
[18]Die Hu,Lianghua He,Luxi Yang.Joint Pilot Tone and Channel Estimator Design for OFDM Systems[J].IEEE Communications Letters,2006,10(10):695-697.
[19]Yang H W. A road to future broadband wireless access:MIMO-OFDM-based air interface[J].IEEE Communications Magazine,2005,43(1):53-60.
[20]Song Won-Gyu and Lim Jong-Tae.Channel estimation and signal detection for MIMO-OFDM with time varying channels[J].IEEE Communications Letters,2006,10(7): 540-542. .[21]Hlaing Minn and Al-Dhahir N.Optimal training signals for MIMO-OFDM channel estimation[J].IEEE Transactions on Wireless Communications,2006,5(5):1158-1168.
[22]HIJAZI H,ROS L.Polynomial Estimation of Time-varying Multi-path Gains with Intercarrier Interference Mitigation in OFDM Systems[J].IEEE Transactions on Vehicular Technology,2009,58(01):140-151.
[23]Li Dong,Guo Feng,LiGuosong,et al.Enhanced DFT interpolation-based channel estimation for OFDM system with virtual subcarriers.[C].VehieularTechnology Conferenee.2006,4:1580-1584.
[24]SongXiaojin,SongTiecheng,ShenLianfeng,etal. Improved Kalman filter channel Estimation method for OFDM systems in fast time-varying environment[J].Joumal of Southeast University(EnglishEdition).2005,21(4):389-392.
[25]TANG Shi-gang,PENG Ke-wu,GONG K,et al.Channel estimation for cyclic postfixed OFDM[J].Journal of Electronic Science and Technology of China,2008,6(3):200-204.
[26]DONG X,LU W,SOONG A C K.Linear interpolation inpilot assisted channel estimation for OFDM[J].IEEE TransWireless Commun,2007,6:1910-1920.
[27]胡广书.数字信号处理一理论算法与实现[M].北京:清华大学出版社,2003.
[28]樊昌信.通信原理(第6版)[M].北京:国防工业出版社,2006.
[29]肖明波.通信系统仿真原理与无线应用[M].北京:机械工业出版社,2005.
[30]B lcskei H, Gesbert D, Paulraj A J. On the Capacity of OFDM Based SpatialMultiplexing Systems [J]. IEEE Trans on Commun, 2002, 50(11): 225-234.
[31]Suehiro N, Hatori M. Modulatable Orthogonal Sequences and their Application to SSMA Systems [J]. IEEE Trans on Inf Th,1988,34(1):93-100.
[32]Ghogho M,McLernon D,Alameda-Hernandez E,et al.Channel Estimation and Symbol Detection for Block Transmission Using Data-Dependent Superimposed Training[J].IEEE SignalProcessing Lett.,2005,12(3):226-229.
[33]张忠民,郭黎利,禹永植.BICM-OFDM中利用叠加导频的迭代信道估计[J].通信技术,2009,6(42):1-4.
[34]陆震,葛建华,王勇.基于PN序列的MIMO-OFDM系统信道估计[J].华中科技大学学报,2007,35(4):1-4.
[35]张蕊萍,张太镒.叠加导频OFDM系统的EM信道估计算法[J].哈尔滨工业大学学报,2008,40(11):1834-1839.
[36]周加铳,陈咏恩.OFDM系统中基于离散余弦变换的信道估计[J].计算机工程与应用,2007,43(4):115-118.
[37]陈奎,徐钊.二维内插的OFDM导频信道估计的研究[J].计算机工程与应用,2009,45(12):149-152.
[38]赵军辉,王东明,桂益俊.WCDMA系统的迭代信道估计研究[J].电路与系统学报,2009,14(3):45-51.
[39]黎玉玲,张延华.基于MATLAB的通信系统仿真平台设计[J].计算机应用研究,2006, (10):248-250.
[40]孙艳华,王浩,张延华.复数域格缩减的MIMO检测算法研究[J].电子科学大学学报,2010,39(5):670-675.
[41]张宇,张乃通.一种有效的MIMO-OFDM系统时变信道估计算法[J].哈尔滨工业大学学报,2009,41(3):18-21.
[42]高群毅,肖立民,周世东,等.一种信道估计频域插值算法[J].清华大学学报(自然科学版),2006,46(10):1715-1719.
[43]徐海波,杜欢,张振仁.OFDM信道估计的子空间方法[J].电子科技大学学报,2006,35(5):752-754.
[44]TANG Shi-gang,PENG Ke-wu,GONG Ke,et al.Channel estimation for cyclic postfixed OFOM[J].Jounal of Electronic Science and Technology of China,2008,6(2):264-268.
[2]刘刚,葛建华,郭漪.MIMO-OFDM系统中一种链式加权LS信道估计算法[J].电子与信息学报,2009,31(7):1763-1766.
[3]肖丽萍,郝磊,段再超.基于失配序列的OFDM信道估计[J].信号处理,2010,26(4):583-587.
[4]张阳,李维英,李建东,庞立华.基于前导序列的OFDM定时同步与信道估计算法[J].电路与系统学报,2009,14(6):111-115.
[5]陈宁,黄一平.基于加窗型DCT-Ⅳ的OFDM系统的信道估计算法[J].计算机工程与应用,2010,46(1):87-89.
[6]刘英男,蒋伟,任术波,梁庆林.时间-频率双选择性衰落信道的最小二乘估计方法[J].电子与信息学报,2008,30(9):2185-2188.
[7]张晓瀛,黄勤飞,魏急波.时变条件下MIMO-OFDM系统中的信道估计算法[J].电路与系统学报,2009,14(5):20-25.
[8]李明奇,李玉柏,彭启琮.导频符号调制方式对OFDM信道估计的影响[J].电子科技大学学报,2009,38(1):25-27.
[9]陈雪娟,李小文.TD-LTE下行发射分集自适应信道估计研究分析[J].计算机应用研究,2010,27(12):4701-4704.
[10]俞晓帆,赵春明.基于多中继导频频分复用的协同通信系统信道估计算法[J].信号处理,2010,26(4):588-595.
[11]王芳,王启国.一种基于ZCZ序列的OFDM信道估计[J].计算机工程与应用,2008,44(20):111-113.
[12]Ozdemir M K,Arslan H.Channel Estimation for Wireless OFDM Systems[J].IEEE Communications Surveys&Tutorials,2007,9(02):18-48.
[13]Jiachin Lin.Least-Squares Channel Estimation for Mobile OFDM Communication on Time-Varying Frequency-Selective Fading Channels[J].IEEE Transactions on Vehicular Technology,2008,57(06):3538-3550
[14]Dong Xiao-dai.Linear interpolation in pilots system assisted channel estimation for OFDM[J].IEEE Trans on Wireless Comm,2007,6(5).
[15]刘刚,郭漪,葛建华.MIMO-OFDM系统中的信道估计[J].华中科技大学学报.2005,(9):26-29.
[16]王许菲.MIMO-OFDM系统关键技术研究[D].北京邮电大学硕士论文,2008.
[17]Weichang Li, James C. Preisig. Estimation of Rapidly Time-Varying Sparse Channels.[J] IEEE journal of oceanic engineering.2007,32(4):927-939.
[18]Die Hu,Lianghua He,Luxi Yang.Joint Pilot Tone and Channel Estimator Design for OFDM Systems[J].IEEE Communications Letters,2006,10(10):695-697.
[19]Yang H W. A road to future broadband wireless access:MIMO-OFDM-based air interface[J].IEEE Communications Magazine,2005,43(1):53-60.
[20]Song Won-Gyu and Lim Jong-Tae.Channel estimation and signal detection for MIMO-OFDM with time varying channels[J].IEEE Communications Letters,2006,10(7): 540-542. .[21]Hlaing Minn and Al-Dhahir N.Optimal training signals for MIMO-OFDM channel estimation[J].IEEE Transactions on Wireless Communications,2006,5(5):1158-1168.
[22]HIJAZI H,ROS L.Polynomial Estimation of Time-varying Multi-path Gains with Intercarrier Interference Mitigation in OFDM Systems[J].IEEE Transactions on Vehicular Technology,2009,58(01):140-151.
[23]Li Dong,Guo Feng,LiGuosong,et al.Enhanced DFT interpolation-based channel estimation for OFDM system with virtual subcarriers.[C].VehieularTechnology Conferenee.2006,4:1580-1584.
[24]SongXiaojin,SongTiecheng,ShenLianfeng,etal. Improved Kalman filter channel Estimation method for OFDM systems in fast time-varying environment[J].Joumal of Southeast University(EnglishEdition).2005,21(4):389-392.
[25]TANG Shi-gang,PENG Ke-wu,GONG K,et al.Channel estimation for cyclic postfixed OFDM[J].Journal of Electronic Science and Technology of China,2008,6(3):200-204.
[26]DONG X,LU W,SOONG A C K.Linear interpolation inpilot assisted channel estimation for OFDM[J].IEEE TransWireless Commun,2007,6:1910-1920.
[27]胡广书.数字信号处理一理论算法与实现[M].北京:清华大学出版社,2003.
[28]樊昌信.通信原理(第6版)[M].北京:国防工业出版社,2006.
[29]肖明波.通信系统仿真原理与无线应用[M].北京:机械工业出版社,2005.
[30]B lcskei H, Gesbert D, Paulraj A J. On the Capacity of OFDM Based SpatialMultiplexing Systems [J]. IEEE Trans on Commun, 2002, 50(11): 225-234.
[31]Suehiro N, Hatori M. Modulatable Orthogonal Sequences and their Application to SSMA Systems [J]. IEEE Trans on Inf Th,1988,34(1):93-100.
[32]Ghogho M,McLernon D,Alameda-Hernandez E,et al.Channel Estimation and Symbol Detection for Block Transmission Using Data-Dependent Superimposed Training[J].IEEE SignalProcessing Lett.,2005,12(3):226-229.
[33]张忠民,郭黎利,禹永植.BICM-OFDM中利用叠加导频的迭代信道估计[J].通信技术,2009,6(42):1-4.
[34]陆震,葛建华,王勇.基于PN序列的MIMO-OFDM系统信道估计[J].华中科技大学学报,2007,35(4):1-4.
[35]张蕊萍,张太镒.叠加导频OFDM系统的EM信道估计算法[J].哈尔滨工业大学学报,2008,40(11):1834-1839.
[36]周加铳,陈咏恩.OFDM系统中基于离散余弦变换的信道估计[J].计算机工程与应用,2007,43(4):115-118.
[37]陈奎,徐钊.二维内插的OFDM导频信道估计的研究[J].计算机工程与应用,2009,45(12):149-152.
[38]赵军辉,王东明,桂益俊.WCDMA系统的迭代信道估计研究[J].电路与系统学报,2009,14(3):45-51.
[39]黎玉玲,张延华.基于MATLAB的通信系统仿真平台设计[J].计算机应用研究,2006, (10):248-250.
[40]孙艳华,王浩,张延华.复数域格缩减的MIMO检测算法研究[J].电子科学大学学报,2010,39(5):670-675.
[41]张宇,张乃通.一种有效的MIMO-OFDM系统时变信道估计算法[J].哈尔滨工业大学学报,2009,41(3):18-21.
[42]高群毅,肖立民,周世东,等.一种信道估计频域插值算法[J].清华大学学报(自然科学版),2006,46(10):1715-1719.
[43]徐海波,杜欢,张振仁.OFDM信道估计的子空间方法[J].电子科技大学学报,2006,35(5):752-754.
[44]TANG Shi-gang,PENG Ke-wu,GONG Ke,et al.Channel estimation for cyclic postfixed OFOM[J].Jounal of Electronic Science and Technology of China,2008,6(2):264-268.