CP-FREE OFDM系统MMSE均衡及信道估计
发布时间：2018-10-19 14:41
【摘要】：正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统由于其高速率传输已经在LTE系统中广泛应用了,而其性能的优良和循环前缀的加入有很大关系,保证此系统可以在多径信道下不受到码间干扰的影响。不过在LTE系统中循环前缀的长度有时会占据20%的带宽,随着对频谱利用率要求的提高,传统OFDM系统中由于循环前缀的添加使得其利用率的提升比较有限。为此,许多学者展开了对无循环前缀OFDM系统(Cyclic Prefix-FREE OFDM,CP-FREE OFDM)系统的研究。现已有一个无循环前缀OFDM系统,称作符号循环移位均衡OFDM系统(Symbol Cyclic Shift Equalization OFDM,SCSE-OFDM),由Xiqing Liu提出,其中在接收端利用判决反馈均衡模块将码间干扰问题进行消除,利用CP恢复过程实现了子载波干扰的消除。但是在此系统中,接收端仅考虑了迫零均衡从而产生了噪声放大的问题,同时此系统中也没有考虑信道估计的相关问题。本文为了提升无循环前缀OFDM系统的性能并完善此系统将从多个方面进行研究。为了避免迫零均衡可能导致的噪声放大的问题,本文首先考虑了仅平衡噪声放大问题的最小均方误差(Minimum Mean Square Error,MMSE)均衡器,接下来在Ghosh的判决反馈误差为高斯分布的假设下设计了考虑判决反馈误差的MMSE均衡器。为了了解判决反馈误差的分布情况,对判决反馈误差通过仿真分析首次观察到其服从Alpha稳定分布。为了减弱判决反馈误差,本文通过设置反馈门限从而减少了将严重错判反馈的情况,系统的误码率性能得到了提升。由于接收机的硬判决,性能提升仍然受限。为此,本文将Turbo均衡技术和无循环前缀OFDM系统相结合。在接收机将MMSE均衡和Turbo解码连接起来,利用Turbo译码输出的外部信息在MMSE均衡中进行估计,然后利用估计出来的符号更新每一个比特的外部信息,通过多次循环性能有了很大的提升。为了使无循环前缀OFDM系统更加完整,本文最后对此系统下的信道估计进行了研究。在添加导频的情况下,设计了基于最小二乘(Least Square,LS)和最小均方(LMMSE)的两种信道估计方案。此外,在不添加导频的情况下基于子空间理论提出盲估计方案,利用过采样及重复因子实现了信道估计。最后考虑在信道先验信息不足的情况下,利用自适应滤波进行信道估计。尤其研究了在Alpha稳定分布噪声下基于RLP(Recursive Least P-norm)和LMP(Linear Mean P-norm)的自适应滤波技术,信道估计准确度得到了很好的提升。
[Abstract]:Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing,OFDM) system has been widely used in LTE system because of its high rate transmission, and its excellent performance is related to the addition of cyclic prefix. Ensure that the system can not be affected by inter-symbol interference in multipath channels. However, the length of cyclic prefix sometimes takes up 20% bandwidth in LTE system. With the increase of spectrum efficiency, the efficiency of cyclic prefix in traditional OFDM system is limited due to the addition of cyclic prefix. For this reason, many scholars have carried out researches on the system of OFDM system without cyclic prefix (Cyclic Prefix-FREE OFDM,CP-FREE OFDM). At present, there is a cyclic prefix OFDM system, called symbol cyclic shift equalization OFDM system (Symbol Cyclic Shift Equalization OFDM,SCSE-OFDM), which is proposed by Xiqing Liu, in which the decision feedback equalization module is used at the receiver to eliminate the inter-symbol interference (ISI) problem. The subcarrier interference is eliminated by using CP recovery process. However, in this system, the receiver only considers the problem of zero-forcing equalization to produce noise amplification, and the channel estimation is not considered in this system. In order to improve the performance and improve the performance of the OFDM system without cyclic prefix, this paper will study from many aspects. In order to avoid the problem of noise amplification caused by zero forcing equalization, the minimum mean square error (Minimum Mean Square Error,MMSE) equalizer for only balanced noise amplification is considered in this paper. Then, under the assumption that the decision feedback error of Ghosh is Gao Si distribution, a MMSE equalizer with decision feedback error is designed. In order to understand the distribution of the decision feedback error, the stable distribution of the decision feedback error from Alpha was observed through the simulation analysis for the first time. In order to reduce the decision feedback error, the feedback threshold is set to reduce the serious error feedback, and the BER performance of the system is improved. Performance improvements are still limited due to the hard decision of the receiver. Therefore, this paper combines the Turbo equalization technique with the OFDM system without cyclic prefix. The MMSE equalization is connected with the Turbo decoding in the receiver, and the external information output from the Turbo decoding is estimated in the MMSE equalization, and then the external information of each bit is updated with the estimated symbols. The performance has been greatly improved through multiple loops. In order to make the OFDM system with no cyclic prefix more complete, the channel estimation under this system is studied in the end. Two channel estimation schemes based on least square (Least Square,LS) and least mean square (LMMSE) are designed under the condition of adding pilot frequency. In addition, a blind estimation scheme based on subspace theory is proposed without adding pilot frequency. The channel estimation is realized by over-sampling and repetition factor. Finally, in the case of lack of prior channel information, adaptive filtering is used for channel estimation. In particular, adaptive filtering techniques based on RLP (Recursive Least P-norm and LMP (Linear Mean P-norm) are studied under Alpha stable distributed noise. The accuracy of channel estimation is improved well.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.53
本文编号：2281443
[Abstract]:Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing,OFDM) system has been widely used in LTE system because of its high rate transmission, and its excellent performance is related to the addition of cyclic prefix. Ensure that the system can not be affected by inter-symbol interference in multipath channels. However, the length of cyclic prefix sometimes takes up 20% bandwidth in LTE system. With the increase of spectrum efficiency, the efficiency of cyclic prefix in traditional OFDM system is limited due to the addition of cyclic prefix. For this reason, many scholars have carried out researches on the system of OFDM system without cyclic prefix (Cyclic Prefix-FREE OFDM,CP-FREE OFDM). At present, there is a cyclic prefix OFDM system, called symbol cyclic shift equalization OFDM system (Symbol Cyclic Shift Equalization OFDM,SCSE-OFDM), which is proposed by Xiqing Liu, in which the decision feedback equalization module is used at the receiver to eliminate the inter-symbol interference (ISI) problem. The subcarrier interference is eliminated by using CP recovery process. However, in this system, the receiver only considers the problem of zero-forcing equalization to produce noise amplification, and the channel estimation is not considered in this system. In order to improve the performance and improve the performance of the OFDM system without cyclic prefix, this paper will study from many aspects. In order to avoid the problem of noise amplification caused by zero forcing equalization, the minimum mean square error (Minimum Mean Square Error,MMSE) equalizer for only balanced noise amplification is considered in this paper. Then, under the assumption that the decision feedback error of Ghosh is Gao Si distribution, a MMSE equalizer with decision feedback error is designed. In order to understand the distribution of the decision feedback error, the stable distribution of the decision feedback error from Alpha was observed through the simulation analysis for the first time. In order to reduce the decision feedback error, the feedback threshold is set to reduce the serious error feedback, and the BER performance of the system is improved. Performance improvements are still limited due to the hard decision of the receiver. Therefore, this paper combines the Turbo equalization technique with the OFDM system without cyclic prefix. The MMSE equalization is connected with the Turbo decoding in the receiver, and the external information output from the Turbo decoding is estimated in the MMSE equalization, and then the external information of each bit is updated with the estimated symbols. The performance has been greatly improved through multiple loops. In order to make the OFDM system with no cyclic prefix more complete, the channel estimation under this system is studied in the end. Two channel estimation schemes based on least square (Least Square,LS) and least mean square (LMMSE) are designed under the condition of adding pilot frequency. In addition, a blind estimation scheme based on subspace theory is proposed without adding pilot frequency. The channel estimation is realized by over-sampling and repetition factor. Finally, in the case of lack of prior channel information, adaptive filtering is used for channel estimation. In particular, adaptive filtering techniques based on RLP (Recursive Least P-norm and LMP (Linear Mean P-norm) are studied under Alpha stable distributed noise. The accuracy of channel estimation is improved well.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.53
【参考文献】
相关博士学位论文 前4条
1 樊同亮;OFDM系统的信道估计和信号均衡技术的研究[D];重庆大学;2012年
2 杨伟超;Alpha稳定分布噪声下通信信号调制识别研究[D];哈尔滨工程大学;2012年
3 于蕾;OFDM系统的信道估计技术研究[D];哈尔滨工程大学;2009年
4 罗天放;通信系统中的Turbo码及Turbo均衡问题研究[D];哈尔滨工程大学;2003年
相关硕士学位论文 前8条
1 王鹏;基于子空间的MIMO-OFDM信道估计算法研究[D];西安科技大学;2016年
2 任航;脉冲噪声下OFDM系统的参数估计研究[D];西安电子科技大学;2014年
3 孙有铭;信道阶数估计和确定性盲辨识算法的鲁棒性研究[D];解放军信息工程大学;2013年
4 任梅;基于高阶统计量的MIMO系统盲信道估计技术[D];西安电子科技大学;2013年
5 沈祖超;基于过采样的SIMO系统盲辨识与均衡算法研究[D];华东理工大学;2013年
6 谢雨翔;CP不足的OFDM系统中数据检测的研究[D];华中科技大学;2012年
7 魏启蒙;无线通信中的Turbo码及Turbo均衡技术研究[D];电子科技大学;2008年
8 王卓;α-稳定脉冲噪声中的自适应算法研究及应用[D];西安电子科技大学;2006年
，本文编号：2281443
本文链接：https://www.wllwen.com/kejilunwen/xinxigongchenglunwen/2281443.html
