OFDM水声通信系统的时频同步技术研究
摘要
海洋水声信道是一个复杂的时、空、频变信道。信道带宽窄,多途干扰严重,高噪声和时延扩展大,使得在海洋中实现高速率、可靠的通信成为挑战性的研究课题。而由信道多径传播引起的码间干扰和频率选择性衰落是水声通信面临的主要困难。正交频分复用技术(OFDM)具有良好的抗频率选择性衰落性能和充分的带宽利用率,成为目前水声通信研究的热点。但它也存在不足,对同步误差敏感是影响系统性能的主要因素之一。OFDM技术的高频谱利用率和传输的可靠性均以子载波间的正交性为基础,载波频偏的存在破坏了子载波间的正交性,导致严重的子载波间干扰;符号定时误差又会引起符号间干扰。因此,研究OFDM的同步技术,对符号定时和频率偏移进行有效的估计和补偿具有非常重要的意义,本文主要研究无线中的OFDM时频联合同步算法,通过对算法的分析改进使之能够应用于OFDM水声通信系统中,主要工作概括如下:
首先,在综合分析水声信道特性和OFDM技术原理的基础上,介绍了OFDM水声通信系统模型与系统参数的设计,指出OFDM系统的优点和存在的缺点。接着分析了同步误差对系统的影响。详细介绍了基于循环前缀、导频符号和训练序列的OFDM系统符号定时和载波频率联合同步算法,并提出了改进算法。通过仿真,比较分析算法在高斯白噪信道(AWGN)下和多径衰落信道下的同步性能。介绍了符号定时同步参数的选择,并针对水声信道中第一径不是最强径的问题,阐述了第一径检测方法,接着介绍了残余频偏补偿方法。最后进行水池和海洋试验,验证算法在实际水声信道中的性能。结果表明,本文采用的同步算法能够在试验中达到准确同步。
Ocean channel is a complex environment that experiences continual varieties in time, space, frequency. Moreover inter-symbol interference and frequency selective fading make high speed reliable communication in underwater acoustic (UWA) channel even more difficult. Possessing the ability to cope with frequency selective fading and high bandwidth utilization efficiency, orthogonal frequency division multiplexing (OFDM) has become an outstanding solution in UWA communication. By using a large number of orthogonal sub-carriers, OFDM improves the robustness and reliability. However, OFDM system is so sensitive to time and frequency offset that worsen the BER performance of system. In other words, frequency offset destroys the orthogonality among the sub-carriers and thus bring severe inter-carrier interference. Meantime, error of synchronization leads to inter-symbol interference. Therefore, it seems extremely critical to OFDM system to estimate and compensate timing and frequency offset. In this case, this paper will focus on synchronization technology of OFDM in UWA communication and be organized as following:
Firstly, this paper will introduce characteristics of UWA channel and principles of OFDM system, followed by OFDM UWA communication system model and corresponding parameters. The advantages and disadvantages of OFDM will be discussed respectively. Secondly, the paper analyzes how does synchronization error influence OFDM system, and bring forward combined time and frequency synchronization algorithm based on cyclic prefix, pilot symbol and preamble sequence techniques. In addition, an improved algorithm is introduced. Thirdly, this paper will present the simulation results according to related algorithms under both AWGN channel and multipaths fading channel, compare the synchronization performance and discuss timing synchronization parameter selection. In order to solve the problem of timing synchronization when the first path is not the strongest path, the paper analyses the method to detect the first path. And then introduces a method about residual frequency compensation. At last, the results of experiments carried out in lab testing pool and sea will be presented. As it can be seen, the algorithm adopted in this series of experiments can achieve good synchronization performance in actual UWA channel.
首先,在综合分析水声信道特性和OFDM技术原理的基础上,介绍了OFDM水声通信系统模型与系统参数的设计,指出OFDM系统的优点和存在的缺点。接着分析了同步误差对系统的影响。详细介绍了基于循环前缀、导频符号和训练序列的OFDM系统符号定时和载波频率联合同步算法,并提出了改进算法。通过仿真,比较分析算法在高斯白噪信道(AWGN)下和多径衰落信道下的同步性能。介绍了符号定时同步参数的选择,并针对水声信道中第一径不是最强径的问题,阐述了第一径检测方法,接着介绍了残余频偏补偿方法。最后进行水池和海洋试验,验证算法在实际水声信道中的性能。结果表明,本文采用的同步算法能够在试验中达到准确同步。
Ocean channel is a complex environment that experiences continual varieties in time, space, frequency. Moreover inter-symbol interference and frequency selective fading make high speed reliable communication in underwater acoustic (UWA) channel even more difficult. Possessing the ability to cope with frequency selective fading and high bandwidth utilization efficiency, orthogonal frequency division multiplexing (OFDM) has become an outstanding solution in UWA communication. By using a large number of orthogonal sub-carriers, OFDM improves the robustness and reliability. However, OFDM system is so sensitive to time and frequency offset that worsen the BER performance of system. In other words, frequency offset destroys the orthogonality among the sub-carriers and thus bring severe inter-carrier interference. Meantime, error of synchronization leads to inter-symbol interference. Therefore, it seems extremely critical to OFDM system to estimate and compensate timing and frequency offset. In this case, this paper will focus on synchronization technology of OFDM in UWA communication and be organized as following:
Firstly, this paper will introduce characteristics of UWA channel and principles of OFDM system, followed by OFDM UWA communication system model and corresponding parameters. The advantages and disadvantages of OFDM will be discussed respectively. Secondly, the paper analyzes how does synchronization error influence OFDM system, and bring forward combined time and frequency synchronization algorithm based on cyclic prefix, pilot symbol and preamble sequence techniques. In addition, an improved algorithm is introduced. Thirdly, this paper will present the simulation results according to related algorithms under both AWGN channel and multipaths fading channel, compare the synchronization performance and discuss timing synchronization parameter selection. In order to solve the problem of timing synchronization when the first path is not the strongest path, the paper analyses the method to detect the first path. And then introduces a method about residual frequency compensation. At last, the results of experiments carried out in lab testing pool and sea will be presented. As it can be seen, the algorithm adopted in this series of experiments can achieve good synchronization performance in actual UWA channel.
引文
[1]Paul C.Etter.水声建模与仿真(第三版)[M].北京:电子工业出版社,2003.
[2]王德清.水声信道中基于OFDM的同步技术研究[D].厦门大学电子工程系,2005.
[3]常娟.OFDM水声通信中的频率同步与信道估计[D].西北工业大学,2007.
[4]许俊.水声语音通信研究[D].厦门大学电子工程系,2001.
[5]惠俊英.水下声信道[M].北京:国防工业出版社,2002.
[6]魏莉,许芳,孙海信.水声信道的研究与仿真[J].声学技术,2008,27(1):25-29.
[7]佟学俭.OFDM移动通信技术原理与应用[M].北京:人民邮电出版社,2003.
[8]郭攀.OFDM系统的频率偏移估计算法研究[D].东华大学,2007.
[9]Byung-Chul Kim,I-Tai Lu.Parameter study of OFDM underwater communication systems.In Proc.MTS/IEEE Oceans 2000,vol.2,pp:1251-1255,Sept.2000.
[10]F.Classen,H.Meyr.Frequency synchronization algorithms for OFDM systems suitable for communication over frequency selective fading channels.IEEE Vehicular Technology Conference.June 1994.vol.3,pp:1655-1659.
[11]Moose P H.A technique for Orthogonal Frequency Division Multiplexing frequency offset correction[J].IEEE Trans.On Common,1994,42(10):2908-2914.
[12]Van de Beek JJ,Sandel M,Brjesson P Q.ML estimation of timing and frequency offset in OFDM systems[J].IEEE Trans on Signal Processing,1997,45(7):1800-1805.
[13]Pollet T,Van Bladel M,Moeneclaey M.BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise.[J].IEEE Trans on Common,1995,43(234):191-193.
[14]尹长川,罗涛,乐光新.多载波宽带无线通信技术[M].北京:北京邮电大学出版社,2004.
[15]严春林.正交频分复用系统中的同步技术研究[D].电子科技大学,2004.
[16]Xiaoyi Hu,Ru Xu,Wei Wei,Jing Liu,Yongjun Xie.A novel scheme of timing synchronization for OFDM underwater communication system.Oceans' 2008
[17]Seung Duk Choi,Jung Min Choi,Jae Hong Lee.An initial timing offset estimation method for OFDM systems in Rayleigh fading channel.IEEE 64th Vehicular Technology Conference,pp:1-5,sept.2006.
[18]T.M.Schmidl,D.C.Cox.Robust frequency and timing synchronization for OFDM[J].IEEE Trans.Commun,vol.45.pp.1613-1621.Dec.1997.
[19]H.Minn,M.Zeng,V.K.Bhargava.On timing offset estimation for OFDM system.IEEE Comm,Lett,vol.4,pp:242-244,July 2000.
[20]Michele Morelli,Umberto Mengali.An improved frequency offset estimator for OFDM applications,IEEE Commn.Letters,Vol.3,No.3,pp.75-78,March 1999.
[21]刘俊林,邓单,朱近康,邱玲.一种基于频域相关实现OFDM时频同步方法[J].电子与信息学报,2006,28(8):1354-1359.
[22]王顶,许家栋,杨川.OFDM系统的自适应符号同步算法[J].信息安全与通信保密,2006,第1期:77-79
[23]Guangliang Ren,Yilin Chang,Hui Zhang,Huming Zhang.Synchronization method based on a new constant envelop preamble for OFDM systems.IEEE Trans.Broadcast,vol 51,No.1,pp:139-143,Mar.2005.
[24]严春林,李少谦,唐友喜,罗霄,房家奕.利用CAZAC序列的OFDM频率同步方法[J].电子与信息学报,2006,28(1):139-142.
[25]李军科,宋荣方,张士兵,张力军.基于训练符号的OFDM系统符号定时方案研究[J].南京邮电大学学报(自然科学版),2006,26(6):16-21.
[26]张杰,胡钰.基于CAZAC序列的突发通信定时同步算法[J].无线电工程,2005,35(11):47-49.
[27]宁广志,全录贤.QPSK数字化解调中载波同步技术研究[J]信息传输与接入技术,2006,32(6):19-21.
[28]U.H.Rohrs,L.P.Linde.Some unique properties and applications of perfect squares minimum phase CAZAC sequences.IEEE Communication and Signal Processing,pp:155-160,Sept.1992.
[29]Salberg A.B,Swami A.Doppler and frequency-offset synchronization in wideband OFDM.[J].IEEE Transactions on Wireless Communications,Vol.4,No.6,pp:2870-2881,Nov.2005.
[30]Yanxin Yah,Tomisawa M,Yi Gong,Yong Liang Guan,Gang Wu,Choi Look Law.Joint timing and frequency synchronization for IEEE 802.16 OFDM systems[J].IEEE Mobile WiMAX Symposium,pp:17-21,Mar.2007.
[31]Frassati F,Lafon C,Laurent P.A,Passerieux J.M.Experimental assessment of OFDM and DSSS modulations for use in littoral waters underwater acoustic communications.IEEE Europe Oceans 2005,Vol.2,pp:826-831,Jun.2005
[32]David C,CHU.Polyphase codes with good periodic correlation properties[J].IEEE Trans on IT,Vol.IT-7,pp:256-257,Oct.1961.
[33]Mandar Chitre,S.H.Ong,John Potter.Performance of coded OFDM in very shallow water channels and snapping shrimp noise.In Proc.MTS/IEEE Oceans 2005,vol.2,pp:996-1001.
[34]H.C.So,Y.T.Chan,Q.Ma.Comparison of various periodograms for single tone detection and frequency estimation,in IEEE Int.Symp.Gircuits Syst,Hong Kong,Jun.9-12.1997,pp:2529-2532.
[35]张晓辉.OFDM系统定时与载波频率同步研究[D].西安电子科技大学.2007.
[36]周一青,胡爱群.利用训练帧进行OFDM系统同步的新算法[J].通信学报,2001,22(4):43-48.
[37]S Coalelan,A Glavieux.Design and Test of A coding OFDM system on shallow water acoustic channel[C].Oceans 95,MTS/IEEE,1995,[3]:2065-2070
[38]Gell Tiger,Lee Pittman.Simulation of an orthogonal frequency division multiplexing based model for the underwater acoustic sound channel[D].Naval Postgraduate School,2001
[39]Jianguo Huang,Jing Sun,Chengbing He,Xiaohong Shen and Qunfei Zhang.High-speed underwater acoustic communication based on OFDM.IEEE MAPE 2005,Vol.2,pp:1135-1138.
[40]J.Lee,H Lou,D.Toumpakaris.Maximum likelihood estimation of time and frequency offset for OFDM systems.IEEE Electronics Letters,Oct.2004,40(22):1428-1429.
[41]H.Liu,U.Tureli.A high-efficiency carrier estimator for OFDM communication.IEEE Commu,Let.Apr.1998,2(4):104-106.
[42]Tureli Ufuk,Hui Liu.OFDM Blind carrier offset estimation ESPRIT.IEEE Trans On Commu,2000,48(9):1459-1461.
[43]胡梅霞,张海林.基于循环平稳特性的OFDM盲同步算法[J].西安电子科技大学学报,2005,32(9):264-267.
[44]B.Park,H.Chen.A novel timing estimation method for OFDM systems.IEEE Commu Let,1999,3(3):75-77.
[45]Y.H.Kim,I.Song,S.yoon.An efficient frequency offset estimator for OFDM systems and its performance characteristics.IEEE Trans on Vehicular technology,2001,50(5):1307-1312.
[46]E.Bejjani,J.C.Belfiore.Multicarrier coherent communication for the underwater acoustic channel.Proc.IEEE Oceanx'96:1125-1130.
[47]W.K.Lam,R.F.Ormondroyd.A novel broadband COFDM modulation scheme for robust communication over the underwater acoustic channel.Proc.IEEE Oceans'98:794-799.
[48]Kazuyoshi Miyoshi.Preliminary design of OFDM and CDMA acoustic communication system.IEEE Oceans'2001:2216-2219P
[49]Baosheng Li,Shengli Zhou,Milica Stojanovic,Lee Freitag.Pilot-tone based ZP-OFDM demodulation for an underwater acoustic channel.In Proc.MTS/IEEE Oceans 2006.pp:1-5.Pollet T,Van Bladel M,Moeneclaey M.BER sensitivity of OFDM systems to carrier frequency offset and wiener phase noise.[J].IEEE Trans on Commun,1995,43(234):191-193.
[50]Pollet T,Van Bladel M,Moeneclaey M.BER sensitivity of OFDM systems to carrier frequency offset and wiener phase noise.[J].IEEE Trans on Commun,1995,43(234):191-193.
[51]王永刚.OFDM水下通信信道估计与同步技术研究[D].哈尔滨工程大学,2007年.
[2]王德清.水声信道中基于OFDM的同步技术研究[D].厦门大学电子工程系,2005.
[3]常娟.OFDM水声通信中的频率同步与信道估计[D].西北工业大学,2007.
[4]许俊.水声语音通信研究[D].厦门大学电子工程系,2001.
[5]惠俊英.水下声信道[M].北京:国防工业出版社,2002.
[6]魏莉,许芳,孙海信.水声信道的研究与仿真[J].声学技术,2008,27(1):25-29.
[7]佟学俭.OFDM移动通信技术原理与应用[M].北京:人民邮电出版社,2003.
[8]郭攀.OFDM系统的频率偏移估计算法研究[D].东华大学,2007.
[9]Byung-Chul Kim,I-Tai Lu.Parameter study of OFDM underwater communication systems.In Proc.MTS/IEEE Oceans 2000,vol.2,pp:1251-1255,Sept.2000.
[10]F.Classen,H.Meyr.Frequency synchronization algorithms for OFDM systems suitable for communication over frequency selective fading channels.IEEE Vehicular Technology Conference.June 1994.vol.3,pp:1655-1659.
[11]Moose P H.A technique for Orthogonal Frequency Division Multiplexing frequency offset correction[J].IEEE Trans.On Common,1994,42(10):2908-2914.
[12]Van de Beek JJ,Sandel M,Brjesson P Q.ML estimation of timing and frequency offset in OFDM systems[J].IEEE Trans on Signal Processing,1997,45(7):1800-1805.
[13]Pollet T,Van Bladel M,Moeneclaey M.BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise.[J].IEEE Trans on Common,1995,43(234):191-193.
[14]尹长川,罗涛,乐光新.多载波宽带无线通信技术[M].北京:北京邮电大学出版社,2004.
[15]严春林.正交频分复用系统中的同步技术研究[D].电子科技大学,2004.
[16]Xiaoyi Hu,Ru Xu,Wei Wei,Jing Liu,Yongjun Xie.A novel scheme of timing synchronization for OFDM underwater communication system.Oceans' 2008
[17]Seung Duk Choi,Jung Min Choi,Jae Hong Lee.An initial timing offset estimation method for OFDM systems in Rayleigh fading channel.IEEE 64th Vehicular Technology Conference,pp:1-5,sept.2006.
[18]T.M.Schmidl,D.C.Cox.Robust frequency and timing synchronization for OFDM[J].IEEE Trans.Commun,vol.45.pp.1613-1621.Dec.1997.
[19]H.Minn,M.Zeng,V.K.Bhargava.On timing offset estimation for OFDM system.IEEE Comm,Lett,vol.4,pp:242-244,July 2000.
[20]Michele Morelli,Umberto Mengali.An improved frequency offset estimator for OFDM applications,IEEE Commn.Letters,Vol.3,No.3,pp.75-78,March 1999.
[21]刘俊林,邓单,朱近康,邱玲.一种基于频域相关实现OFDM时频同步方法[J].电子与信息学报,2006,28(8):1354-1359.
[22]王顶,许家栋,杨川.OFDM系统的自适应符号同步算法[J].信息安全与通信保密,2006,第1期:77-79
[23]Guangliang Ren,Yilin Chang,Hui Zhang,Huming Zhang.Synchronization method based on a new constant envelop preamble for OFDM systems.IEEE Trans.Broadcast,vol 51,No.1,pp:139-143,Mar.2005.
[24]严春林,李少谦,唐友喜,罗霄,房家奕.利用CAZAC序列的OFDM频率同步方法[J].电子与信息学报,2006,28(1):139-142.
[25]李军科,宋荣方,张士兵,张力军.基于训练符号的OFDM系统符号定时方案研究[J].南京邮电大学学报(自然科学版),2006,26(6):16-21.
[26]张杰,胡钰.基于CAZAC序列的突发通信定时同步算法[J].无线电工程,2005,35(11):47-49.
[27]宁广志,全录贤.QPSK数字化解调中载波同步技术研究[J]信息传输与接入技术,2006,32(6):19-21.
[28]U.H.Rohrs,L.P.Linde.Some unique properties and applications of perfect squares minimum phase CAZAC sequences.IEEE Communication and Signal Processing,pp:155-160,Sept.1992.
[29]Salberg A.B,Swami A.Doppler and frequency-offset synchronization in wideband OFDM.[J].IEEE Transactions on Wireless Communications,Vol.4,No.6,pp:2870-2881,Nov.2005.
[30]Yanxin Yah,Tomisawa M,Yi Gong,Yong Liang Guan,Gang Wu,Choi Look Law.Joint timing and frequency synchronization for IEEE 802.16 OFDM systems[J].IEEE Mobile WiMAX Symposium,pp:17-21,Mar.2007.
[31]Frassati F,Lafon C,Laurent P.A,Passerieux J.M.Experimental assessment of OFDM and DSSS modulations for use in littoral waters underwater acoustic communications.IEEE Europe Oceans 2005,Vol.2,pp:826-831,Jun.2005
[32]David C,CHU.Polyphase codes with good periodic correlation properties[J].IEEE Trans on IT,Vol.IT-7,pp:256-257,Oct.1961.
[33]Mandar Chitre,S.H.Ong,John Potter.Performance of coded OFDM in very shallow water channels and snapping shrimp noise.In Proc.MTS/IEEE Oceans 2005,vol.2,pp:996-1001.
[34]H.C.So,Y.T.Chan,Q.Ma.Comparison of various periodograms for single tone detection and frequency estimation,in IEEE Int.Symp.Gircuits Syst,Hong Kong,Jun.9-12.1997,pp:2529-2532.
[35]张晓辉.OFDM系统定时与载波频率同步研究[D].西安电子科技大学.2007.
[36]周一青,胡爱群.利用训练帧进行OFDM系统同步的新算法[J].通信学报,2001,22(4):43-48.
[37]S Coalelan,A Glavieux.Design and Test of A coding OFDM system on shallow water acoustic channel[C].Oceans 95,MTS/IEEE,1995,[3]:2065-2070
[38]Gell Tiger,Lee Pittman.Simulation of an orthogonal frequency division multiplexing based model for the underwater acoustic sound channel[D].Naval Postgraduate School,2001
[39]Jianguo Huang,Jing Sun,Chengbing He,Xiaohong Shen and Qunfei Zhang.High-speed underwater acoustic communication based on OFDM.IEEE MAPE 2005,Vol.2,pp:1135-1138.
[40]J.Lee,H Lou,D.Toumpakaris.Maximum likelihood estimation of time and frequency offset for OFDM systems.IEEE Electronics Letters,Oct.2004,40(22):1428-1429.
[41]H.Liu,U.Tureli.A high-efficiency carrier estimator for OFDM communication.IEEE Commu,Let.Apr.1998,2(4):104-106.
[42]Tureli Ufuk,Hui Liu.OFDM Blind carrier offset estimation ESPRIT.IEEE Trans On Commu,2000,48(9):1459-1461.
[43]胡梅霞,张海林.基于循环平稳特性的OFDM盲同步算法[J].西安电子科技大学学报,2005,32(9):264-267.
[44]B.Park,H.Chen.A novel timing estimation method for OFDM systems.IEEE Commu Let,1999,3(3):75-77.
[45]Y.H.Kim,I.Song,S.yoon.An efficient frequency offset estimator for OFDM systems and its performance characteristics.IEEE Trans on Vehicular technology,2001,50(5):1307-1312.
[46]E.Bejjani,J.C.Belfiore.Multicarrier coherent communication for the underwater acoustic channel.Proc.IEEE Oceanx'96:1125-1130.
[47]W.K.Lam,R.F.Ormondroyd.A novel broadband COFDM modulation scheme for robust communication over the underwater acoustic channel.Proc.IEEE Oceans'98:794-799.
[48]Kazuyoshi Miyoshi.Preliminary design of OFDM and CDMA acoustic communication system.IEEE Oceans'2001:2216-2219P
[49]Baosheng Li,Shengli Zhou,Milica Stojanovic,Lee Freitag.Pilot-tone based ZP-OFDM demodulation for an underwater acoustic channel.In Proc.MTS/IEEE Oceans 2006.pp:1-5.Pollet T,Van Bladel M,Moeneclaey M.BER sensitivity of OFDM systems to carrier frequency offset and wiener phase noise.[J].IEEE Trans on Commun,1995,43(234):191-193.
[50]Pollet T,Van Bladel M,Moeneclaey M.BER sensitivity of OFDM systems to carrier frequency offset and wiener phase noise.[J].IEEE Trans on Commun,1995,43(234):191-193.
[51]王永刚.OFDM水下通信信道估计与同步技术研究[D].哈尔滨工程大学,2007年.