MC-CDMA系统中降低峰均比的理论研究及其算法实现
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摘要
多载波通信技术,尤其是本文所研究的MC-CDMA系统,由于具有抑制频率选择性衰落和频谱效率高等诸多优点,是一种适合于无线环境下高速数据传输的技术。但MC-CDMA系统所存在的高峰值平均功率比问题始终是阻碍其广泛应用的主要因素之一,本文就MC-CDMA系统存在的高峰值平均功率比问题展开,做了降低系统峰均比算法的改进和研究。
本文首先介绍了多载波系统的三种结合方案,确定了MC-CDMA系统作为本文的研究对象。通过分析MC-CDMA系统中信号的传输,明确了产生高的峰值信号的客观因素,结合现有的抑制峰均比的研究现状,提出了对现有的降低峰均功率比算法的改进方案。
鉴于无线通信系统的性能主要受移动通信信道的限制,而移动通信信道又表现出很强的随机性和不可预测性,故本文在第3部分依据MC-CDMA系统的信道模型,在Simulink里建模得到了一个较为理想的慢衰落信道幅频响应仿真图。MC-CDMA系统对同步的要求很高,使用慢衰落时变信道可以有效地提高电路响应部分和驱动部分的同步性能。在本章中建立的慢衰落信道模型是第4章、第5章进行算法仿真验证的技术基础。
信号预畸变技术是目前应用最广泛的一类峰值功率比抑制方法。但由于信号裁剪产生的非线性失真将导致带内失真和带外辐射,尤其在限幅门限较低时引入的噪声成为抑制系统性能的主要障碍。本文第4部分通过对信号预畸变技术分析知,该技术在降低峰均比技术上只是在带内失真和带外辐射之间的折衷。本文依据限幅截掉部分的损失功率与限幅噪声功率所具备的对应关系,提出了一种改进的抑制限幅噪声的算法并通过分析建立的数学模型和实验仿真验证了该算法。采用上述方法,尤其在多载波、多用户的情况下,能够降低系统的峰均比。
在本文的第5部分根据信号非畸变降低PAPR算法的主要思想,又鉴于Logistic混沌映射所具有的强的自相关、互相关特性,可以通过用混沌序列来做扩频通信的扩频序列来改变相位序列以此来降低高PAPR出现的概率;同时又由于混沌序列的非周期性和对初始参数的高度敏感性,使得可以产生大量不同的扩谱序列集合,因此最终生成的发射序列不会出现周期重复的现象,从而保持低PAPR。本文通过数学推导和实验仿真证明了Logistic映射产生的混沌序列作为MC-CDMA扩频序列的优越性,并通过与传统序列的仿真对比证明了应用Logistic混沌序列扩频可以改进系统的峰均比和误码率。
Multicarrier communication technology, particularly in the MC-CDMA system which owe to the inhibition spectrum frequency-selective fading and the high spectrum-using efficiency, is suitable for high-speed data transmission technology in wireless environment. However, the high peak-to-average power ratio has always been one of the main obstacle to it widespread application, the article dose a lower system algorithm PAPR improvements and research in MC-CDMA system.
First of all, the fundamental principles of OFDM-CDMA system are introduced. The study is focused on MC-CDMA system. Paper according to analyze the process of signal delivering in MC-CDMA system, then make sure the reasons of high PAPR , and combined with the current researches on reducing PAPR schemes. In the article, we summarize the problems needed to be resolved and proposed lowering of the existing PAPR algorithm improvement.
In view of the performance of wireless communications systems mainly by mobile communication channel restrictions, and mobile communication channel also showed strong randomness and unpredictability, in the third part of this paper is to establish MC-CDMA system channel model. Through Simulink got a multi-path fading channel amplitude frequency response simulation map. The simulate result shows that is an ideal slow fading channel model. Because of MC-CDMA system synchronization in high demand and the slow decline of time-varying channel can be effective in raising circuit response. This part gives technical support to the next two parts.
Signal pre-distortion technology is the most extensive application method to control the PAPR. However, the signal cutting nonlinear distortion will lead to in-band distortion and out-of-band radiation. Particularly when threshold is low, clipping noise performance the major obstacle. In the fourth part, though analyze the pre-distortion of signal to know that the technology is only a compromise between the in-band distortion and out-of-band radiation in reducing PAPR. In this part, based on the relationship of the loss of power and limiting noise power we get an improved clipping noise suppression algorithm, and through analysis of the mathematical simulation model and experimental verification of the algorithm. Using this method, especially in multi-carrier, multi-user circumstances can reduce the PAPR.
In the fifth part of this thesis, According to the signal lower-distortion algorithm's main ideas, and in view of the Logistic chaotic map with the strong self-related, inter-related features. One can do chaotic sequence as spread spectrum sequence in spread spectrum communication to change the phase sequence in order to reduce the high probability of PAPR. At the same time, due to the non-cyclical and chaotic sequence of the initial parameters of the highly sensitive nature, it can make a lot of different sequence spread spectrum collection; the final generation of launch sequence not appears to repeat the cycle, thereby maintaining low PAPR. Through mathematical analysis and simulation experiments proved that the Logistic map is prior to do spread spectrum sequences in MC-CDMA system, and through comparing the simulation with the traditional sequence prove that apply Logistic chaotic spread spectrum sequence can improve the PAPR and BER in MC-CDMA system.
本文首先介绍了多载波系统的三种结合方案,确定了MC-CDMA系统作为本文的研究对象。通过分析MC-CDMA系统中信号的传输,明确了产生高的峰值信号的客观因素,结合现有的抑制峰均比的研究现状,提出了对现有的降低峰均功率比算法的改进方案。
鉴于无线通信系统的性能主要受移动通信信道的限制,而移动通信信道又表现出很强的随机性和不可预测性,故本文在第3部分依据MC-CDMA系统的信道模型,在Simulink里建模得到了一个较为理想的慢衰落信道幅频响应仿真图。MC-CDMA系统对同步的要求很高,使用慢衰落时变信道可以有效地提高电路响应部分和驱动部分的同步性能。在本章中建立的慢衰落信道模型是第4章、第5章进行算法仿真验证的技术基础。
信号预畸变技术是目前应用最广泛的一类峰值功率比抑制方法。但由于信号裁剪产生的非线性失真将导致带内失真和带外辐射,尤其在限幅门限较低时引入的噪声成为抑制系统性能的主要障碍。本文第4部分通过对信号预畸变技术分析知,该技术在降低峰均比技术上只是在带内失真和带外辐射之间的折衷。本文依据限幅截掉部分的损失功率与限幅噪声功率所具备的对应关系,提出了一种改进的抑制限幅噪声的算法并通过分析建立的数学模型和实验仿真验证了该算法。采用上述方法,尤其在多载波、多用户的情况下,能够降低系统的峰均比。
在本文的第5部分根据信号非畸变降低PAPR算法的主要思想,又鉴于Logistic混沌映射所具有的强的自相关、互相关特性,可以通过用混沌序列来做扩频通信的扩频序列来改变相位序列以此来降低高PAPR出现的概率;同时又由于混沌序列的非周期性和对初始参数的高度敏感性,使得可以产生大量不同的扩谱序列集合,因此最终生成的发射序列不会出现周期重复的现象,从而保持低PAPR。本文通过数学推导和实验仿真证明了Logistic映射产生的混沌序列作为MC-CDMA扩频序列的优越性,并通过与传统序列的仿真对比证明了应用Logistic混沌序列扩频可以改进系统的峰均比和误码率。
Multicarrier communication technology, particularly in the MC-CDMA system which owe to the inhibition spectrum frequency-selective fading and the high spectrum-using efficiency, is suitable for high-speed data transmission technology in wireless environment. However, the high peak-to-average power ratio has always been one of the main obstacle to it widespread application, the article dose a lower system algorithm PAPR improvements and research in MC-CDMA system.
First of all, the fundamental principles of OFDM-CDMA system are introduced. The study is focused on MC-CDMA system. Paper according to analyze the process of signal delivering in MC-CDMA system, then make sure the reasons of high PAPR , and combined with the current researches on reducing PAPR schemes. In the article, we summarize the problems needed to be resolved and proposed lowering of the existing PAPR algorithm improvement.
In view of the performance of wireless communications systems mainly by mobile communication channel restrictions, and mobile communication channel also showed strong randomness and unpredictability, in the third part of this paper is to establish MC-CDMA system channel model. Through Simulink got a multi-path fading channel amplitude frequency response simulation map. The simulate result shows that is an ideal slow fading channel model. Because of MC-CDMA system synchronization in high demand and the slow decline of time-varying channel can be effective in raising circuit response. This part gives technical support to the next two parts.
Signal pre-distortion technology is the most extensive application method to control the PAPR. However, the signal cutting nonlinear distortion will lead to in-band distortion and out-of-band radiation. Particularly when threshold is low, clipping noise performance the major obstacle. In the fourth part, though analyze the pre-distortion of signal to know that the technology is only a compromise between the in-band distortion and out-of-band radiation in reducing PAPR. In this part, based on the relationship of the loss of power and limiting noise power we get an improved clipping noise suppression algorithm, and through analysis of the mathematical simulation model and experimental verification of the algorithm. Using this method, especially in multi-carrier, multi-user circumstances can reduce the PAPR.
In the fifth part of this thesis, According to the signal lower-distortion algorithm's main ideas, and in view of the Logistic chaotic map with the strong self-related, inter-related features. One can do chaotic sequence as spread spectrum sequence in spread spectrum communication to change the phase sequence in order to reduce the high probability of PAPR. At the same time, due to the non-cyclical and chaotic sequence of the initial parameters of the highly sensitive nature, it can make a lot of different sequence spread spectrum collection; the final generation of launch sequence not appears to repeat the cycle, thereby maintaining low PAPR. Through mathematical analysis and simulation experiments proved that the Logistic map is prior to do spread spectrum sequences in MC-CDMA system, and through comparing the simulation with the traditional sequence prove that apply Logistic chaotic spread spectrum sequence can improve the PAPR and BER in MC-CDMA system.
引文
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[3]PRASAD R.CDMA for wireless personal communications[M].London:Artech House Boston,1996.
[4]Richard V N.OFDM Wireless Multimedia Communications[M].Boston:Artech House,Jan.2000.
[5]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.2003:1-20.
[6]K.Fzael and L.Papke.On the Performance of Convolutionally-Coded CDMA/OFDM for Communication System[J].IEEE PIMRC'93,September 1993,pp.468-472.
[7]N.Yee,J-P.Linnartz and G.Fettweis,Multi-carrier CDMA in indoor Wireless Radio Networks[J].IEEE PIMRC'93,September 1993,pp.109-113.
[8]A.Chouly,A.Brajal and S.Jourdan,Orthogonal Multicarrier Techniques Applied to Direct Sequence Spread Spectrum CDMA Systems[C].GLOBE-COM'93,1993,pp.1723-1728.
[9]V.M.Dasilva and E.S.Sousa,Performance of Orthogonal CDMA Codes for Quasi-Synchronous Communication Systems[J].IEEE ICUPC'93,1993,pp.995-999.
[10]S.Kondo and L.B.Milstein,Performance of Multicarrier DS-CDMA System [J].IEEE Trans.Commun.Vol.44.No.2.February 1996.pp.238-246
[11]E.A.sourour and M.Nakagawa,Performance of Orthogonal Multicarrier CDMA in a Multipath Fading Channel[J].IEEE Trans.Commun,Vol.44,No.3,March 1996,pp.356-367.
[12]L.Vandendorpe,Multitone Direct Sequence CDMA System in an Indoor Wireless Environment[J].IEEE First Symposium of Communications and Vehicular Technology,1993,pp.411-418.
[13]N.Yee,J.P.Linnartz,G.Fettweis.Multicarrier CDMA in indoor wireless radio networks[J].Proc.of IEEE PIMRC'93,Yokohama,Japan,1993,pp:109-113.
[14]王文博,郑侃.宽带无线通信OFDM技术[M].北京:人民邮电出版社.2003:1-113
[15]鸾英姿.移动通信中的MC-CDMA技术[D].西安电子科技大学硕士学位论 文.2003年10月.
[16]程云鹏等.矩阵论[M].西安:西北工业大学出版社.1989年
[17]X.Li,L.J.Cimini Jr.Effects of chipping and filtering on the performance of OFDM[J].IEEE Commun.Lett,May.1998,vol.2,no.5,pp:131-133.
[18]N Raungsurat,R Rajatheva.An Investigation of Peak to Average Power Ratio in MC-CDMA Combined with Partial Transmit Sequence[J].IEEE VTC 2001(Vol.1)[C],2003,pp:761-765.
[19]H.Yoshimi,T.Ohtsuki.An OFDM system with modified predistorter and MLS [J].IEEE VTC 2001-fall,Atlantic City,Oct.2001,vol.3,pp:1677-1681.
[20]M.J.Gans.A Power Spectral Theory of Propagation in the Mobile Radio Environment[J].IEEE Trans.On Vehicular Technology,Vol.VT-21 February 1972:27-38P.
[21]J.Smith.A Computer Generated Multipath Fading Simulation for Mobile Radio [J].IEEE Trans.On Vehicular Technology,Vol.VT-24,No.3,August 1975:39-40P.
[22]M.Hsieh and C.Wei.Channel estimation for OFDM systems based on comb-typed pilot arrangement in frequency selective fading channels[J].IEEE Trans.Consumer Electron,Vol.44,No.1,Feb.1998:217-225P.
[22]S.Coleri,M.Ergen,A.Purietal.Channel estimation techniques based on pilot arrangement in OFDM systems[J].IEEE Trans Broadcasting,Vol.48,No.3.Sep.2002:223-229P.
[23]约翰.G.普罗克斯,马苏德.萨勒赫著.现代通信系统--使用MATLAB[M].刘树棠译.西安交通大学出版社,2001.
[24]Rohit Negi and John Cioffi.Pilot tone selection for channel estimation in a mobile OFDM system[J].IEEE Trans on Consumer Electronics.Vol.44,No.3,Aug.1998
[25]Mestdagh D J G,Spruyt P,Biran B.Analysis of clipping effect in DMT-based ADSL systems[C].IEEE ICC'94:843-847.
[26]Chen H,Haimovich,A M,Iterative estimation and cancellation of clipping noise for OFDM signals[J].IEEE Commun.Lett,2003,7(7):305-307.
[27]Chen H,Haimovich,A M,An iterative method to restore the performance of clipped and filtered OFDM signals[C].IEEE ICC'2003,5:3438-3442.
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