基于OFDM通信系统的峰均比抑制技术的仿真与应用研究
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摘要
随着移动通信越来越多的成为人们通信的主要方式,频谱资源变的越来越稀缺,传统的单载波传输已经不能满足用户的的需要,而正交频分复用(OFDM)是一种利用多个子载波进行传输,它是一种高效的接入技术。OFDM无线通信技术作为一种新颖的技术,它具有突出的优点,其中一个主要特点就是在于它能够很好地克服多径效应和频率选择性衰落。同时,我们也可以把正交频分复用看作是一种并行技术,主要是将一个高速的数据块分组成为数个低速数据块,然后每一个数据块用以个子载波来调制,这样就可以实现数据的高速率传输了。众所周知由于每个低速数据块的子载波的速率相对较低,这样OFDM符号的周期相对较长,因而对多径效应造成的时延扩展有很强的抵抗能力,同时,由于每个ofdm符号前面加了保护间隔,又叫做循环前缀(CP),这样可以显著的减少符号间的干扰即ISI。OFDM还有一个重大的优点就是它的多个子载波频谱部分相互重叠,而且每个子载波间互相正交,正是因为这样就很容易从混合叠加的子载波上分离出原始的数据信息,因而频谱利用率很高,因而它对频谱资源稀缺的移动通信而言是一种实用的传输技术。
OFDM技术由于其突出的优点得到了广泛的关注,但是它也有很严重的缺点,如果不去解决,将会影响其推广和应用,它的缺点主要为以下两个方面：
(1)较高的峰波均值功率比即PAPR问题是OFDM技术的一个难点问题,如果不去解决,将会阻碍OFDM技术在现实中的应用。因为OFDM的符号不是恒定的包络,即不是线性的,而非线性的信号进入放大器会导致产生多阶的互调成分,这将严重影响信号的质量和系统的误码率等性能。所以为了提高系统得BER等性能和系统的传输效率,在系统的发射极必须要将包络的峰值和均值因子考虑在内。如果射频功率放大器的输入信号最大幅度不能控制在线性区域内,则功率放大器就不能输出大功率,这将严重影响信号的传输；
(2)对频率偏移和噪声等比较敏感。减少噪声和减少频率偏移对正交频分复用非常重要,如果在技术上不能达到,就会破坏OFDM子载波之间的正交特性,从而就会不可避免的引起各个子载波之间的载波干扰和信号干扰；
本论文第一章首先提出了OFDM技术的研究背景及发展现状,指出了本文的研究目标和创新点以及结构安排,由于其性能优越而被选为下一代代移动通信的主流技术；第二章介绍了OFDM技术的基本原理。首先分析了传统单载波传输的多径效应,进而引出了OFDM技术,然后分析了OFDM技术的正交原理和OFDM的优缺点,最后针对OFDM的缺点即其较高的PAPR问题讨论了其定义和对系统的影响,并介绍了常用的解决办法；第三章讨论了畸变技术和编码技术降低OFDM系统的峰均比,并提出了一种改进的削波方法和一种块编码方法；第四章探讨了非畸变技术降低OFDM的峰均比,主要介绍了选择性映射技术和部分传输序列技术,并提出了改进的方法及装置,最后对融合方法实现的可能性进行了研究,提出了一种适用于多天线的OFDMA系统的融合方法。第五章对全文进行了总结并将来的研究工作进行了展望。
Since the wireless communication becomes the main way of people day by day,the frequency spectrum becomes a more and more scarce resource.The conventional single carrier transmission methods can't meet the needs of users.OFDM(Orthogonal Frequency Division Multiplexing),as a multi-carrier transmission way,which could be reckoned a modulation or multiplexing technique.It has many advantages over other wireless communication technologies, one major reason lies in the way that it has better robustness to frequency-selective fading and multipath.In addition, it is also a parallel technology which a high-speed data stream is divided into a number of low-speed data stream. Since the rate of each modulation signal is low, so that a relatively long cycle, and thus with a stronger resistance to delay spread, coupled with another element of each symbol using cyclic prefix as a guard interval, so the ISI(inter symbol interference) can be significantly reduced. The difference between ofdm and other multi-carrier transmission is that OFDM supports frequence-spectrum overlapping only if the sub-carriers are orthogonal each other,so it has high band-width efficiency. Therefore,it's a high speed transmission technology on wireless communications which the resources are scarce.
Are two sides to everything, OFDM techniques also have shortcomings, mainly the following two points:
(1) The high Peak-to-Average Power Ratio(PAPR) issue has been the difficulty and key of OFDM technology,thus become a major obstacle toward practical. Since the OFDM signals non-constant envelope, as we all know, that any non-linear RF amplification will lead to inter-modulation components, thus affecting the neighboring signals and system's performance. In order to improve transmission efficiency and system performance, the signal's peak and mean factor must be taken into account in the transmitter.
(2) High sensitivity to phase noise, timing and frequency drift. When need precise timing, removing noise and reducing the frequency offset become particularly important.If the two points can't be achieved,the orthogonal among the subcarriers will be destroyed,then the ICI and ISI will be seriously.
Chapter 1 of this thesis put forward the investigation background and the development situation of the OFDM technic, pointed out the objectives of the research、innovation points and structural arrangements, because of its superior performance, has been selected as the main technologie of the next generation mobile communication; Chapter 2 describes the the basic principle of OFDM. First of all, the multipath of the conventional single carrier transmission has been discussed, and then putting forward the OFDM technology, representing the orthogonal principles,advantages and disadvantages of OFDM, the last describing the shortcomings of OFDM,that is,its high PAPR,proposing it's definition and resolvent; chapter 3 discusses the distortion technology and coding techniques to reduce PAPR and proposed an improved clipping method and a block coding method; chapter 4 discusses the non-distortion technology to reduce the PAPR,which mainly contains selective mapping and partial transmit sequence, and proposed improved methods and devices, the last part, proposing the realization of syncretic methods and carry out a novel method which is suitable for multi-antenna OFDMA system; chaper 5 of the thesis are summarized and the expectation on the furture.
OFDM技术由于其突出的优点得到了广泛的关注,但是它也有很严重的缺点,如果不去解决,将会影响其推广和应用,它的缺点主要为以下两个方面：
(1)较高的峰波均值功率比即PAPR问题是OFDM技术的一个难点问题,如果不去解决,将会阻碍OFDM技术在现实中的应用。因为OFDM的符号不是恒定的包络,即不是线性的,而非线性的信号进入放大器会导致产生多阶的互调成分,这将严重影响信号的质量和系统的误码率等性能。所以为了提高系统得BER等性能和系统的传输效率,在系统的发射极必须要将包络的峰值和均值因子考虑在内。如果射频功率放大器的输入信号最大幅度不能控制在线性区域内,则功率放大器就不能输出大功率,这将严重影响信号的传输；
(2)对频率偏移和噪声等比较敏感。减少噪声和减少频率偏移对正交频分复用非常重要,如果在技术上不能达到,就会破坏OFDM子载波之间的正交特性,从而就会不可避免的引起各个子载波之间的载波干扰和信号干扰；
本论文第一章首先提出了OFDM技术的研究背景及发展现状,指出了本文的研究目标和创新点以及结构安排,由于其性能优越而被选为下一代代移动通信的主流技术；第二章介绍了OFDM技术的基本原理。首先分析了传统单载波传输的多径效应,进而引出了OFDM技术,然后分析了OFDM技术的正交原理和OFDM的优缺点,最后针对OFDM的缺点即其较高的PAPR问题讨论了其定义和对系统的影响,并介绍了常用的解决办法；第三章讨论了畸变技术和编码技术降低OFDM系统的峰均比,并提出了一种改进的削波方法和一种块编码方法；第四章探讨了非畸变技术降低OFDM的峰均比,主要介绍了选择性映射技术和部分传输序列技术,并提出了改进的方法及装置,最后对融合方法实现的可能性进行了研究,提出了一种适用于多天线的OFDMA系统的融合方法。第五章对全文进行了总结并将来的研究工作进行了展望。
Since the wireless communication becomes the main way of people day by day,the frequency spectrum becomes a more and more scarce resource.The conventional single carrier transmission methods can't meet the needs of users.OFDM(Orthogonal Frequency Division Multiplexing),as a multi-carrier transmission way,which could be reckoned a modulation or multiplexing technique.It has many advantages over other wireless communication technologies, one major reason lies in the way that it has better robustness to frequency-selective fading and multipath.In addition, it is also a parallel technology which a high-speed data stream is divided into a number of low-speed data stream. Since the rate of each modulation signal is low, so that a relatively long cycle, and thus with a stronger resistance to delay spread, coupled with another element of each symbol using cyclic prefix as a guard interval, so the ISI(inter symbol interference) can be significantly reduced. The difference between ofdm and other multi-carrier transmission is that OFDM supports frequence-spectrum overlapping only if the sub-carriers are orthogonal each other,so it has high band-width efficiency. Therefore,it's a high speed transmission technology on wireless communications which the resources are scarce.
Are two sides to everything, OFDM techniques also have shortcomings, mainly the following two points:
(1) The high Peak-to-Average Power Ratio(PAPR) issue has been the difficulty and key of OFDM technology,thus become a major obstacle toward practical. Since the OFDM signals non-constant envelope, as we all know, that any non-linear RF amplification will lead to inter-modulation components, thus affecting the neighboring signals and system's performance. In order to improve transmission efficiency and system performance, the signal's peak and mean factor must be taken into account in the transmitter.
(2) High sensitivity to phase noise, timing and frequency drift. When need precise timing, removing noise and reducing the frequency offset become particularly important.If the two points can't be achieved,the orthogonal among the subcarriers will be destroyed,then the ICI and ISI will be seriously.
Chapter 1 of this thesis put forward the investigation background and the development situation of the OFDM technic, pointed out the objectives of the research、innovation points and structural arrangements, because of its superior performance, has been selected as the main technologie of the next generation mobile communication; Chapter 2 describes the the basic principle of OFDM. First of all, the multipath of the conventional single carrier transmission has been discussed, and then putting forward the OFDM technology, representing the orthogonal principles,advantages and disadvantages of OFDM, the last describing the shortcomings of OFDM,that is,its high PAPR,proposing it's definition and resolvent; chapter 3 discusses the distortion technology and coding techniques to reduce PAPR and proposed an improved clipping method and a block coding method; chapter 4 discusses the non-distortion technology to reduce the PAPR,which mainly contains selective mapping and partial transmit sequence, and proposed improved methods and devices, the last part, proposing the realization of syncretic methods and carry out a novel method which is suitable for multi-antenna OFDMA system; chaper 5 of the thesis are summarized and the expectation on the furture.
引文
[1]佟学俭,罗涛OFDM移动通信技术原理与应用[M].北京：人民邮电出版社,2003.15-80.
[2]尹长川,罗涛.多载波宽带无线通信技术[M].北京：北京邮电大学出版社,2004.5-9.
[3]Y.Wu,W.Y.Zou. Orthogonal Frequeney Division Multiplexing:a multicarrier modulation seheme[J]. IEEE Trans.Broadcast.,1995(8):392-399.
[4]张乃谦,李栋OFDM峰均值功率比研究.第十届海峡两岸无线电技术研究会议论文集[C].中国传媒大学.北京,2005年10月.37-41.
[5]R.van Nee, R.Prasad. OFDM for Wireless Multimedia Communications[M]. Boston:Arieh House, 2000.62-63.
[6]张应中,张德民.数字通信工程[M].北京：人民邮电出版社,1996.4045.
[7]SalehA.A.M.Frequency-independentand frequency-dependent nonlinear models of TWT amplifiers [J]. IEEE Trans. Commun.,1981(2):1715-1729.
[8]H.H.Seung, H.L.Jae. An overview of peak-to-average power ratio reduction Techniques for multicarrier transmission[J]. IEEE Trans.Commun.,2005(4):56-65.
[9]郭岭,郭振民.降低OFDM峰均功率比技术综述[J].现代电子技术.2002(11)：59-61.
[10]X.Li,L.J.Chmini,Jr. Effect of Clipping and Filtering on the Performance of OFDM[J].IEEE Commun.Lett.1988(5):131-133.
[11]黄晓,·陆建华,郑君里.低复杂度OFDM信号峰均功率比压缩技术[J].电子学报2003(3)：398-401.
[12]覃团发,胡永乐.使用μ-law压扩算法降低OFDM系统PAPR的分析[J].电讯技术.2004(2)：38-39.
[13]X.Wang,T.T.Tjhung. Reduction of Peak to Average Power Ratio of OFDM system Using A Companding technique[J].IEEE Trans.On Broadcasting.1999(9):303-307.
[14]T.Jiang,G.x.Zhu.Nonlinear Companding Transform for reducing Peak to Average Power Ratio of OFDM signals[J]. IEEE Trans. On Broadcasting.2004(9):342-346..
[15]艾艳锦,吴长奇.一种基于压扩变换降低OFDM系统峰均比的方法.现代电子技术[J].2003(6)：12-13.
[16]Atarashi H, Abeta S, Sawahashi M. Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing for Broadband Packet Wireless Access [J]. IEICE Trans on Communications, 2003(1):291-299.
[17]R.W.Bauml, R.F.H.Fiseher, J.B.Huber. Reducing the peak-to-average power ratio of multicarrier modulation by selected mapping[J].Electron.Lett.,1996(10):2056-2057.
[18]S.H.Han, J.H.Lee. Modified selected mapping technique for PAPR reduction of coded OFDM signals[J]. IEEE Trans.Broadcast.,2004(9):335-341.
[19]C.L.Wang, Y.O.Yang. Low-complexity selected mapping schemes for peak-to-average power ratio reduction in OFDM systems[J].IEEE Transactions on Signal Processing,2005(12):4652-4660.
[20]H.Breiling, S.H.Muller-Weinfurtner, J.B.Huber. SLM Peak-Power Reduction without Explicit Side Information[J]. IEEE Commun.Lett.,2001(6):239-241
[21]A.D.S.Jayalath,C.Tellambura.Side information in PAR reduced SLM-OFDM signals[J]. Indoor and Mobile Radio Communications, IEEE Proceedings,2003(9):226-230.
[22]李云云.基于PTS算法的峰值平均功率比减小方法[J].无线电工程.2005(7)：11-12.
[23]冯景锋.一种降低OFDM信号峰值平均功率比的优化算法[J].北京邮电大学学报.2003(3)：43-45
[24]Cimini L.J, Sollenberger N.Peak-to-Average Power Ratio Reduction of an OFDM Signal Using Partial Transmit Sequences[J].IEEE Commu.Lett.2000 (3):86-87
[25]Wu H C, Wu Y. A New ICI Matrices Estimation Scheme Using Hadamard Sequence for OFDM Systems[J]. IEEE Trans. on Broadcasting.2005 (3):305-314.
[26]姜永权,刘伟.OFDM通信系统中一种降低峰均比的PTS迭代算法.广东通信技术[J].2007(2)：56-57
[27]Zhao Y P, Haggman S G. Inter-Carrier Interference Self-Cancellation Scheme for OFDM Mobile Communication Systems[J]. IEEE Trans on Communications.2001(7):1185-1191.
[28]Muller S H,Huber J B.OFDM with Reduced Peak to Average Power Ratio by Optimum Combination of Partial Rransmit Sequences[J].Electronics Letters.1997(5):368-369.
[29]Marco B,Stefan W, Peak-power reduction without explict side information[J].IEEE Commum Letters.2001(5):239-241.
[30]洪善艳.MIMO-OFDM系统中峰均功率比降低算法的研究[D].杭州：浙江大学,2006.21-26.
[31]江涛.OFDM无线系统中峰均功率比研究研究[D].武汉：华中科技大学,2007.15-18.
[32]曲姚俊.滤波多音调制系统中峰均功率比的研究[D].济南：山东大学,2007.8-9.
[33]V.Tarokh,N.Seshadri,A.R.Calderbank.Space-Time codes for high data rate wireless communication: performance criterion and code construction[J].IEEE Trans.1998(2):744-765.
[34]G J. Foschini, Jr. and.On limits of wireless communication in a fading environment when using multiple antennas[J].Wireless Personal Commun..1997(6):331-335.
[35]S. M. Alamouti. A simple transmitter diversity scheme for wireless communications[J].IEEE J. Select. Areas Commun.1997(10):1451-1458
[36]方志远.OFDM信道估计技术研究[D].南京：河海大学,2007：10-13.
[2]尹长川,罗涛.多载波宽带无线通信技术[M].北京：北京邮电大学出版社,2004.5-9.
[3]Y.Wu,W.Y.Zou. Orthogonal Frequeney Division Multiplexing:a multicarrier modulation seheme[J]. IEEE Trans.Broadcast.,1995(8):392-399.
[4]张乃谦,李栋OFDM峰均值功率比研究.第十届海峡两岸无线电技术研究会议论文集[C].中国传媒大学.北京,2005年10月.37-41.
[5]R.van Nee, R.Prasad. OFDM for Wireless Multimedia Communications[M]. Boston:Arieh House, 2000.62-63.
[6]张应中,张德民.数字通信工程[M].北京：人民邮电出版社,1996.4045.
[7]SalehA.A.M.Frequency-independentand frequency-dependent nonlinear models of TWT amplifiers [J]. IEEE Trans. Commun.,1981(2):1715-1729.
[8]H.H.Seung, H.L.Jae. An overview of peak-to-average power ratio reduction Techniques for multicarrier transmission[J]. IEEE Trans.Commun.,2005(4):56-65.
[9]郭岭,郭振民.降低OFDM峰均功率比技术综述[J].现代电子技术.2002(11)：59-61.
[10]X.Li,L.J.Chmini,Jr. Effect of Clipping and Filtering on the Performance of OFDM[J].IEEE Commun.Lett.1988(5):131-133.
[11]黄晓,·陆建华,郑君里.低复杂度OFDM信号峰均功率比压缩技术[J].电子学报2003(3)：398-401.
[12]覃团发,胡永乐.使用μ-law压扩算法降低OFDM系统PAPR的分析[J].电讯技术.2004(2)：38-39.
[13]X.Wang,T.T.Tjhung. Reduction of Peak to Average Power Ratio of OFDM system Using A Companding technique[J].IEEE Trans.On Broadcasting.1999(9):303-307.
[14]T.Jiang,G.x.Zhu.Nonlinear Companding Transform for reducing Peak to Average Power Ratio of OFDM signals[J]. IEEE Trans. On Broadcasting.2004(9):342-346..
[15]艾艳锦,吴长奇.一种基于压扩变换降低OFDM系统峰均比的方法.现代电子技术[J].2003(6)：12-13.
[16]Atarashi H, Abeta S, Sawahashi M. Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing for Broadband Packet Wireless Access [J]. IEICE Trans on Communications, 2003(1):291-299.
[17]R.W.Bauml, R.F.H.Fiseher, J.B.Huber. Reducing the peak-to-average power ratio of multicarrier modulation by selected mapping[J].Electron.Lett.,1996(10):2056-2057.
[18]S.H.Han, J.H.Lee. Modified selected mapping technique for PAPR reduction of coded OFDM signals[J]. IEEE Trans.Broadcast.,2004(9):335-341.
[19]C.L.Wang, Y.O.Yang. Low-complexity selected mapping schemes for peak-to-average power ratio reduction in OFDM systems[J].IEEE Transactions on Signal Processing,2005(12):4652-4660.
[20]H.Breiling, S.H.Muller-Weinfurtner, J.B.Huber. SLM Peak-Power Reduction without Explicit Side Information[J]. IEEE Commun.Lett.,2001(6):239-241
[21]A.D.S.Jayalath,C.Tellambura.Side information in PAR reduced SLM-OFDM signals[J]. Indoor and Mobile Radio Communications, IEEE Proceedings,2003(9):226-230.
[22]李云云.基于PTS算法的峰值平均功率比减小方法[J].无线电工程.2005(7)：11-12.
[23]冯景锋.一种降低OFDM信号峰值平均功率比的优化算法[J].北京邮电大学学报.2003(3)：43-45
[24]Cimini L.J, Sollenberger N.Peak-to-Average Power Ratio Reduction of an OFDM Signal Using Partial Transmit Sequences[J].IEEE Commu.Lett.2000 (3):86-87
[25]Wu H C, Wu Y. A New ICI Matrices Estimation Scheme Using Hadamard Sequence for OFDM Systems[J]. IEEE Trans. on Broadcasting.2005 (3):305-314.
[26]姜永权,刘伟.OFDM通信系统中一种降低峰均比的PTS迭代算法.广东通信技术[J].2007(2)：56-57
[27]Zhao Y P, Haggman S G. Inter-Carrier Interference Self-Cancellation Scheme for OFDM Mobile Communication Systems[J]. IEEE Trans on Communications.2001(7):1185-1191.
[28]Muller S H,Huber J B.OFDM with Reduced Peak to Average Power Ratio by Optimum Combination of Partial Rransmit Sequences[J].Electronics Letters.1997(5):368-369.
[29]Marco B,Stefan W, Peak-power reduction without explict side information[J].IEEE Commum Letters.2001(5):239-241.
[30]洪善艳.MIMO-OFDM系统中峰均功率比降低算法的研究[D].杭州：浙江大学,2006.21-26.
[31]江涛.OFDM无线系统中峰均功率比研究研究[D].武汉：华中科技大学,2007.15-18.
[32]曲姚俊.滤波多音调制系统中峰均功率比的研究[D].济南：山东大学,2007.8-9.
[33]V.Tarokh,N.Seshadri,A.R.Calderbank.Space-Time codes for high data rate wireless communication: performance criterion and code construction[J].IEEE Trans.1998(2):744-765.
[34]G J. Foschini, Jr. and.On limits of wireless communication in a fading environment when using multiple antennas[J].Wireless Personal Commun..1997(6):331-335.
[35]S. M. Alamouti. A simple transmitter diversity scheme for wireless communications[J].IEEE J. Select. Areas Commun.1997(10):1451-1458
[36]方志远.OFDM信道估计技术研究[D].南京：河海大学,2007：10-13.