OFDM系统载频同步算法的研究
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摘要
正交频分复用(OFDM)技术是一种多载波数字调制技术,虽然OFDM的概念已经存在了很长时间,但是直到最近随着多媒体业务的发展,它才被人们认识到是一种实现高速双向无线数据通信的良好方法。随着DSP芯片技术的发展,傅里叶变换、高速Modem采用的64／128／256QAM技术、网络编码技术、软判决技术、信道自适应技术、插入保护时段、减少均衡计算量等成熟技术的引入,人们开始集中越来越多的精力开发OFDM技术在移动通信领域的应用,预计第三代以后的移动通信的主流技术将是OFDM技术。
由于OFDM系统各个子载波之间要保持正交的自身特点,决定了同步技术是其的重点和难点。本文主要研究了现有的同步技术,并针对目前的最大似然(ML)估计算法定时不够精确、频偏估计范围过小、不宜应用于多径衰落信道等缺点,提出了新的同步算法。该算法是在原有的ML算法基础上对插入的保护间隔进行改进。仿真结果说明,新算法克服了ML算法的缺点,更能应用于实际中。
OFDM is a kind of digital technology by using multiple carriers to modulate. The concept of OFDM has been put forwarded for quite a long time, but it does not been recognized as a favorable method to realize wireless digital telecommunication with high speed until the development of recent multimedia. With the development of DSP technology, and the introduction of technology like Fourier transformation, the 64/128/256QAM with speedy modem, the network code, the soft decision technology, the auto-adapted channel technology, the interval of protecting timing, the mature technology of reduced quantity, more and more investment will be focused on the exploration of the application of OFDM in telecommunication. It is expected that OFDM will be the main technology in post-third generation mobile telecommunication.
OFDM is characterized by each of its carriers maintaining its own orthogonal. This laid down some difficulties for synchronization technology. This article explores the present synchronization technology, finds out the faults of non-precision of ML(maximum likelihood) algorithm for estimating the fixed time; of the small scope of frequency and of failure of application of multi-path fading channel; and it proposes to a new synchronization algorithm. The new one does some improvements by inserting gap protection of the original ML algorithm. The result of computer simulation has showed that the new algorithm overcomes the shortcomings of the original one and can be applied much easily to practice.
由于OFDM系统各个子载波之间要保持正交的自身特点,决定了同步技术是其的重点和难点。本文主要研究了现有的同步技术,并针对目前的最大似然(ML)估计算法定时不够精确、频偏估计范围过小、不宜应用于多径衰落信道等缺点,提出了新的同步算法。该算法是在原有的ML算法基础上对插入的保护间隔进行改进。仿真结果说明,新算法克服了ML算法的缺点,更能应用于实际中。
OFDM is a kind of digital technology by using multiple carriers to modulate. The concept of OFDM has been put forwarded for quite a long time, but it does not been recognized as a favorable method to realize wireless digital telecommunication with high speed until the development of recent multimedia. With the development of DSP technology, and the introduction of technology like Fourier transformation, the 64/128/256QAM with speedy modem, the network code, the soft decision technology, the auto-adapted channel technology, the interval of protecting timing, the mature technology of reduced quantity, more and more investment will be focused on the exploration of the application of OFDM in telecommunication. It is expected that OFDM will be the main technology in post-third generation mobile telecommunication.
OFDM is characterized by each of its carriers maintaining its own orthogonal. This laid down some difficulties for synchronization technology. This article explores the present synchronization technology, finds out the faults of non-precision of ML(maximum likelihood) algorithm for estimating the fixed time; of the small scope of frequency and of failure of application of multi-path fading channel; and it proposes to a new synchronization algorithm. The new one does some improvements by inserting gap protection of the original ML algorithm. The result of computer simulation has showed that the new algorithm overcomes the shortcomings of the original one and can be applied much easily to practice.
引文
[1]Juha Heiskala, John Terry. OFDM无限局域网,电子工业出版社,2003.3
[2]Meng-Han Hsieh; Che-Ho Wei; A low-complexity frame synchronization and frequency offset compensation scheme for OFDM systems over fading channels Vehicular Technology, IEEE Transactions on Volume 48, Issue 5, Sept.1999
[3]Cvetkovic, Z.; Tarokh, V.; Seokho Yoon; "Frequency synchronization in OFDM" Acoustics, Speech, and Signal Processing,2004. Proceedings. (ICASSP'04). IEEE International Conference on, Volume:4,17-21 May 2004 Pages:iv-373-iv-376 vol.4
[4]Peng Liu; Bing-bing Li; Zhao-yang Lu; Feng-kui Gong; "A new frequency synchronization scheme for OFDM" Consumer Electronics, IEEE Transactions on, Volume:50, Issue:3, Aug.2004 Pages:823-828
[5]Jan-Jaap van de Beek,SANDELL M, et al.ML estimation of timing and frequency offset in multicarrier systems[R].TULEA 1996:09,Division of Signal Processing,Lulea University of Technology,April 1996
[6]茅永峻,蔡觉平,罗汉文,宋文涛.高精度的正交频分复用频率同步新算法.上海交通大学学报,Vol.37 No.3 Mar.2003
[7]罗汉文,丁建木,宋文涛.一种新型的正交频分复用载波频偏相偏联合估计算法.上海交通大学学报,Vol.37 No.3 M ar.2003
[8]束锋,刘毅峰,罗琳,吴乐南.正交频分复用通信系统的联合同步算法.应用科学学报Vol.19,No.4 Dec.2001
[9]Athaudage, C.R.N.; Krishnamurthy, V.; A low complexity timing and frequency synchronization algorithm for OFDM systems Global Telecommunications Conference,2002. GLOBECOM'02. IEEE Volume 1,17-21 Nov.2002 Page(s):244-248 vol.1
[10]Yi-Ching Liao; Kwang-Cheng Chen; "Data-aided maximum likelihood frequency synchronization for OFDM systems" Global Telecommunications Conference,2003. GLOBECOM'03. IEEE, Volume:4,1-5 Dec.2003 Pages:2395-2399 vol.4
[11]Wei, L.; Schlegel, C.; Synchronization requirements for multi-user OFDM on satellite mobile and two-path Rayleigh fading channels Communications, IEEE Transactions on Volume 43, Issue 234, Feb-Mar-Apr 1995 Page(s):887-895
[12]Chen, N.; Tanaka, M.; Heaton, R.; OFDM timing synchronisation under multi-path channels Vehicular Technology Conference,2003. VTC 2003-Spring. The 57th IEEE Semiannual Volume 1,22-25 April 2003 Page(s):378-382 vol.1
[13]Zhang, J.L.; Wang, M.Z.; Zhu, W.L.; A novel OFDM frame synchronization scheme Communications, Circuits and Systems and West Sino Expositions, IEEE 2002 International Conference on Volume 1,29 June-1 July 2002 Page(s):119-123 vol.1
[14]阮象华.基于OFDM传输中的频率偏移和信道估计.电视技术.2001年第5期.总第227期.
[15]叶志猛,季卫华OFDM应用中的关键技术.中国数据通信.2003.12
[16]周飞,周宗仪.OFDM系统中的帧同步与频率跟踪算法.通信技术.No.7.2003.No.139totally.
[17]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,2003.6
[18]李伟华,章蓓蕾,吴伟陵OFDM系统定时与频率偏移估计.北京邮电大学学报.Vol.27 No.1 Feb.2004.
[19]Jun Wu; Qun Zhou; Cheng, K.K.M.; The adaptive algorithm of symbol timing and carrier phase estimation in OFDM systems Communications,2001. ICC 2001. IEEE International Conference on Volume 1,11-14 June 2001 Page(s):156-160 vol.1
[20]Jun Wu; Qun Zhou; Cheng, K.K.M.; A joint estimation algorithm of symbol timing and carrier offset in OFDM systems Vehicular Technology Conference,2001. VTC 2001 Spring. IEEE VTS 53rd Volume 1,6-9 May 2001 Page(s):712-716 vol.1
[21]Tufvesson, F.; Edfors, O.; Faulkner, M.; Time and frequency synchronization for OFDM using PN-sequence preambles Vehicular Technology Conference,1999. VTC 1999-Fall. IEEE VTS 50th Volume 4,19-22 Sept.1999 Page(s):2203-2207 vol.4
[22]Chunlin Yan; Jiayi Fang; Youxi Tang; Shaoqian Li; Yingtao Li; OFDM synchronization using PN sequence and performance Personal, Indoor and Mobile Radio Communications,2003. PIMRC 2003.14th IEEE Proceedings on Volume 1, 7-10 Sept.2003 Page(s):936-939 Vol.1
[23]移动通信俱乐部http://www.mobileclub.org
[24]吴伟陵.移动通信中的关键技术.北京邮电大学出版社.2000.11
[25]张森,张正亮MATLAB仿真技术与实例应用教程.北京：机械工程出版社.2004.1
[26]Chin-Liang Wang; Ming-Hsuan Chiang; Hung-Chin Wang; A new synchronization scheme for OFDM systems Vehicular Technology Conference,2004. VTC 2004-Spring.2004 IEEE 59th Volume 2,17-19 May 2004 Page(s):1100-1104 Vol.2
[2]Meng-Han Hsieh; Che-Ho Wei; A low-complexity frame synchronization and frequency offset compensation scheme for OFDM systems over fading channels Vehicular Technology, IEEE Transactions on Volume 48, Issue 5, Sept.1999
[3]Cvetkovic, Z.; Tarokh, V.; Seokho Yoon; "Frequency synchronization in OFDM" Acoustics, Speech, and Signal Processing,2004. Proceedings. (ICASSP'04). IEEE International Conference on, Volume:4,17-21 May 2004 Pages:iv-373-iv-376 vol.4
[4]Peng Liu; Bing-bing Li; Zhao-yang Lu; Feng-kui Gong; "A new frequency synchronization scheme for OFDM" Consumer Electronics, IEEE Transactions on, Volume:50, Issue:3, Aug.2004 Pages:823-828
[5]Jan-Jaap van de Beek,SANDELL M, et al.ML estimation of timing and frequency offset in multicarrier systems[R].TULEA 1996:09,Division of Signal Processing,Lulea University of Technology,April 1996
[6]茅永峻,蔡觉平,罗汉文,宋文涛.高精度的正交频分复用频率同步新算法.上海交通大学学报,Vol.37 No.3 Mar.2003
[7]罗汉文,丁建木,宋文涛.一种新型的正交频分复用载波频偏相偏联合估计算法.上海交通大学学报,Vol.37 No.3 M ar.2003
[8]束锋,刘毅峰,罗琳,吴乐南.正交频分复用通信系统的联合同步算法.应用科学学报Vol.19,No.4 Dec.2001
[9]Athaudage, C.R.N.; Krishnamurthy, V.; A low complexity timing and frequency synchronization algorithm for OFDM systems Global Telecommunications Conference,2002. GLOBECOM'02. IEEE Volume 1,17-21 Nov.2002 Page(s):244-248 vol.1
[10]Yi-Ching Liao; Kwang-Cheng Chen; "Data-aided maximum likelihood frequency synchronization for OFDM systems" Global Telecommunications Conference,2003. GLOBECOM'03. IEEE, Volume:4,1-5 Dec.2003 Pages:2395-2399 vol.4
[11]Wei, L.; Schlegel, C.; Synchronization requirements for multi-user OFDM on satellite mobile and two-path Rayleigh fading channels Communications, IEEE Transactions on Volume 43, Issue 234, Feb-Mar-Apr 1995 Page(s):887-895
[12]Chen, N.; Tanaka, M.; Heaton, R.; OFDM timing synchronisation under multi-path channels Vehicular Technology Conference,2003. VTC 2003-Spring. The 57th IEEE Semiannual Volume 1,22-25 April 2003 Page(s):378-382 vol.1
[13]Zhang, J.L.; Wang, M.Z.; Zhu, W.L.; A novel OFDM frame synchronization scheme Communications, Circuits and Systems and West Sino Expositions, IEEE 2002 International Conference on Volume 1,29 June-1 July 2002 Page(s):119-123 vol.1
[14]阮象华.基于OFDM传输中的频率偏移和信道估计.电视技术.2001年第5期.总第227期.
[15]叶志猛,季卫华OFDM应用中的关键技术.中国数据通信.2003.12
[16]周飞,周宗仪.OFDM系统中的帧同步与频率跟踪算法.通信技术.No.7.2003.No.139totally.
[17]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,2003.6
[18]李伟华,章蓓蕾,吴伟陵OFDM系统定时与频率偏移估计.北京邮电大学学报.Vol.27 No.1 Feb.2004.
[19]Jun Wu; Qun Zhou; Cheng, K.K.M.; The adaptive algorithm of symbol timing and carrier phase estimation in OFDM systems Communications,2001. ICC 2001. IEEE International Conference on Volume 1,11-14 June 2001 Page(s):156-160 vol.1
[20]Jun Wu; Qun Zhou; Cheng, K.K.M.; A joint estimation algorithm of symbol timing and carrier offset in OFDM systems Vehicular Technology Conference,2001. VTC 2001 Spring. IEEE VTS 53rd Volume 1,6-9 May 2001 Page(s):712-716 vol.1
[21]Tufvesson, F.; Edfors, O.; Faulkner, M.; Time and frequency synchronization for OFDM using PN-sequence preambles Vehicular Technology Conference,1999. VTC 1999-Fall. IEEE VTS 50th Volume 4,19-22 Sept.1999 Page(s):2203-2207 vol.4
[22]Chunlin Yan; Jiayi Fang; Youxi Tang; Shaoqian Li; Yingtao Li; OFDM synchronization using PN sequence and performance Personal, Indoor and Mobile Radio Communications,2003. PIMRC 2003.14th IEEE Proceedings on Volume 1, 7-10 Sept.2003 Page(s):936-939 Vol.1
[23]移动通信俱乐部http://www.mobileclub.org
[24]吴伟陵.移动通信中的关键技术.北京邮电大学出版社.2000.11
[25]张森,张正亮MATLAB仿真技术与实例应用教程.北京：机械工程出版社.2004.1
[26]Chin-Liang Wang; Ming-Hsuan Chiang; Hung-Chin Wang; A new synchronization scheme for OFDM systems Vehicular Technology Conference,2004. VTC 2004-Spring.2004 IEEE 59th Volume 2,17-19 May 2004 Page(s):1100-1104 Vol.2