高铁场景下OFDM系统性能分析与研究

发布时间：2019-04-03 06:30

【摘要】：近年来,由于高铁的快速发展与普及,这使得高速移动下的移动通信业务的需求迅速增加。正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)作为第四代移动通信(4G)的核心技术之一,具有抗多径衰落,频谱利用率高等优点,将OFDM应用到高铁场景具有很高的实用价值。由于列车高速引起的多普勒频移以及铁路周边复杂的电磁环境会给OFDM系统的信道估计和信道建模带来困难。因此,针对上述问题,本文的研究工作主要包括:(1)研究了高铁场景下无线信道的特性,并对高铁场景下OFDM系统的子载波干扰(Inter Carrier Interference,ICI)进行了分析。深入研究了 OFDM系统的导频的插入方式和基于导频辅助的信道估计算法,并针对基于离散傅里叶变换(Discrete Fourier Transform,DFT)的插值算法不能抑制信道冲击响应中循环前缀长度内的噪声的问题,本文对DFT插值算法进行改进。改进算法通过引入门限值来判别信道冲击响应中循环前缀长度内的噪声并进行噪声消除,然后进行多次迭代运算,增加了插值的精度。实验表明本文改进算法具有较好的性能。(2)针对高铁场景下无线信道快时变的特性,本文重点研究了基扩展模型(BasisExpansion Model,BEM)信道估计算法。为了减小ICI对导频位置的影响,提高基函数系数的精度,本文的导频结构采用了导频束的形式。通过对子载波干扰的分析,本文对导频束结构进行了简化,提高了频谱效率。为了进一步提高高铁场景下OFDM系统的信道估计精确度,本文在基扩展模型算法的基础上提出了一种基扩展模型联合离散傅里叶变换(Discrete Fourier Transform,DFT)的信道估计算法,该算法利用基扩展模型算法得到ICI系数并进行ICI消除,然后利用本文改进的DFT插值算法进行二次降噪并恢复出所有子载波位置的信道信息。实验结果表明本文所提算法具有较好的性能。(3)探究了不同高铁场景下OFDM系统的性能。首先利用抽头延时线(Tapped Delay Line,TDL)对不同高铁场景的无线信道进行建模,然后结合本文所研究的信道估计算法,最后使用Matlab搭建高铁场景下的OFDM系统。在实验中,对于不同的高铁场景,本文探索了不同信噪比,不同区域和不同信道估计方法对OFDM系统吞吐量的影响。
[Abstract]:In recent years, due to the rapid development and popularization of high-speed rail, the demand for mobile communication services under high-speed mobile is increasing rapidly. As one of the core technologies of fourth generation mobile communication (4G), orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing,OFDM) has the advantages of anti-multipath fading and high spectrum efficiency. It is of great practical value to apply OFDM to high-speed railway scenarios. The Doppler frequency shift caused by high speed train and the complex electromagnetic environment around the railway will make the channel estimation and channel modeling of OFDM system difficult. Therefore, in order to solve the above problems, the main work of this paper is as follows: (1) the characteristics of wireless channel in high-speed rail scenario are studied, and the sub-carrier interference (Inter Carrier Interference,ICI) of OFDM system in high-speed rail scenario is analyzed. In this paper, the pilot insertion method and pilot aided channel estimation algorithm for OFDM system are studied in depth, and the discrete Fourier transform based (Discrete Fourier Transform, (discrete Fourier transform) is used to estimate the channel. The interpolation algorithm of DFT can not suppress the noise in the cyclic prefix length in the impulse response of the channel. In this paper, the DFT interpolation algorithm is improved. The improved algorithm uses threshold value to distinguish and eliminate the noise within the cyclic prefix length in the impulse response of the channel, and then performs many iterative operations to increase the accuracy of the interpolation. Experiments show that the improved algorithm has good performance. (2) in view of the fast time-varying characteristics of wireless channel in high-speed railway scenario, this paper focuses on the basis-extended model (BasisExpansion Model,BEM) channel estimation algorithm. In order to reduce the influence of ICI on the pilot position and improve the accuracy of the basis function coefficient, the pilot structure of this paper adopts the form of pilot beam. By analyzing the subcarrier interference, the structure of the pilot beam is simplified and the spectral efficiency is improved. In order to further improve the channel estimation accuracy of OFDM system in high-speed rail scenario, this paper proposes a new channel estimation algorithm based on the basis-extended model algorithm and discrete Fourier transform (Discrete Fourier Transform,DFT). The algorithm uses the basis extended model algorithm to obtain the ICI coefficients and eliminate the ICI. Then the improved DFT interpolation algorithm is used to reduce the noise twice and recover the channel information of all subcarrier positions. The experimental results show that the proposed algorithm has good performance. (3) the performance of OFDM system in different high-speed scenario is investigated. Firstly, the wireless channel of different high-speed railway scenarios is modeled by tap delay line (Tapped Delay Line,TDL), then the channel estimation algorithm is studied in this paper. Finally, the OFDM system in high-speed rail scenario is built by using Matlab. In the experiment, for different high-speed rail scenarios, the effects of different SNR, different regions and different channel estimation methods on the throughput of OFDM system are explored.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.53

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