高铁环境下OFDM系统信道估计与信号检测技术研究

发布时间：2018-05-06 04:35

本文选题：正交频分复用 + 高铁信道模型　；参考：《电子科技大学》2014年硕士论文

【摘要】：高铁环境下,无线信道的快时变性使OFDM技术面临子载波间干扰;为了节省带宽或者适应不同的多径环境,OFDM系统的循环前缀有可能不够充分,这种循环前缀不足的情况会为OFDM系统带来符号间干扰。为了尽可能地消除子载波间干扰和符号间干扰,实现数据准确传输,本文主要研究高铁环境下OFDM系统信道估计和信号检测。本文第二章主要研究基于基扩展模型的高铁信道模型。首先研究高铁环境下典型信道模型以及基扩展模型的概念及其分类,重点研究了广受关注的复指数基扩展模型,针对其所存在的高频部分采样误差,利用改进复指数基扩展模型使采样点都落在多普勒扩展谱内部,最高采样频率等于最大多普勒频移;其次,研究并提出改进复指数基扩展模型的基维数和基函数的优化设计方法,理论分析和仿真证明,基维数主要取决于信道最大多普勒频移和信噪比,在导频数目固定的条件下,基维数越高,建模误差越小,但参数估计的准确度也会降低,需要在二者之间进行折中,基函数则会在基维数确定后,影响对多普勒扩展谱描述的准确性。本文第三章研究时变信道下OFDM系统梳状导频的优化设计方法。首先研究基于线性最小均方误差准则的最优的簇型梳状结构导频设计,基于OFDM系统信道时域矩阵和频域矩阵的等效转换关系,建立信道频域矩阵的离散Karhuen-Loeve基扩展模型等效模型,并分析接收端采用基于线性最小均方误差估计准则的估计方程和性能指标,讨论在导频功率一定的条件下,均方误差最优的梳状导频设计需满足的条件。研究了基于频域Kronecker函数的簇型梳状导频结构(每簇中中间有一个非零导频,其它两边都是零导频构成的保护间隔)的改进,增加每簇中非零导频数目的个数以增加所携带的信息量,虽然其子载波间干扰有所提升,但信道估计性能反而能得到提高;针对传统的要求簇与簇之间导频数据相同,并且每簇中导频数据为零相关区序列的导频结构,分析验证可以在每簇导频数据前通过伪随机序列加扰的方法,来降低该结构的峰均比。本文第四章研究快变信道下基于梳状导频的OFDM系统信道估计与信号检测算法。首先提出梳状导频结构下基于多个OFDM符号信道估计的算法,该算法将多个OFDM符号作为一组进行信道估计,在该段持续时间内基扩展模型只进行一次基维数向上取整的近似,总的估计量减少,此时利用相同的导频观测量进行信道估计,带来实际估计性能的提高;接下来,针对多径时延较大的环境,提出时变信道中循环前缀不足条件下,基于基扩展模型的OFDM系统信道估计和信号检测技术,理论推导出基扩展模型下符号间干扰消除和循环卷积重构技术,数字仿真结果证明,本文算法能取得较好的系统性能。综上,本文从高铁信道模型、发端导频设计以及接收端信道估计和信号检测的角度,讨论基扩展模型的运用,具有理论研究和实际应用价值。
[Abstract]:In the high speed environment, the fast time variability of the wireless channel makes the OFDM technology face intercarrier interference. In order to save bandwidth or adapt to different multipath environments, the cyclic prefix of the OFDM system may not be sufficient. The insufficiency of this kind of cyclic prefix will bring the intercarrier interference to the OFDM system. In order to eliminate the inter carrier interference and symbol as much as possible This paper mainly studies the channel estimation and signal detection of OFDM system in the high speed rail environment. In this paper, the second chapter mainly studies the model of the high speed iron channel based on the base extended model. The complex exponential base expansion model, aiming at its high frequency partial sampling error, uses the improved complex exponential base extension model to make the sampling points fall inside the Doppler spread spectrum, and the highest sampling frequency is equal to the maximum Doppler frequency shift. Secondly, the optimization design method for improving the base dimension and basic function of the complex exponential base expansion model is proposed. The theoretical analysis and simulation prove that the base dimension mainly depends on the maximum Doppler shift and the signal to noise ratio of the channel. Under the condition of the fixed number of pilots, the higher the base dimension, the smaller the modeling error, but the accuracy of the parameter estimation will be reduced. It is necessary to compromise between the two, and the base function will affect the Doppler expansion spectrum after the base dimension is determined. The third chapter studies the optimal design method of comb like pilot of OFDM system in time-varying channel. Firstly, the optimal pilot design of cluster comb structure based on linear minimum mean square error criterion is studied. Based on the equivalent transfer relationship between the time domain matrix and the frequency domain matrix of the OFDM system, the discrete Karhu of the frequency domain matrix of the channel is established. The equivalent model of en-Loeve based extended model is used, and the estimation equation and performance index based on the linear minimum mean square error estimation criterion are analyzed. Under the condition of certain pilot power, the conditions for the design of comb like pilot with the best mean square error are discussed. The cluster comb pilot structure based on the frequency domain Kronecker function is studied. In the middle of the cluster, there is a non zero pilot in the middle, and the other sides are the protection interval of zero pilot. The number of non zero pilot frequencies in each cluster is increased to increase the amount of information carried. Although the inter carrier interference is improved, the channel estimation performance can be raised, and the pilot data between clusters and clusters is required. In the fourth chapter, the fourth chapter studies the channel estimation and signal detection algorithm based on comb pilot in the fast changing channel. The algorithm is based on multiple OFDM symbol channel estimation. The algorithm uses multiple OFDM symbols as a group to estimate the channel. In the duration of the interval, the base extension model only performs an approximation of the base dimension of one base dimension. The total estimation is reduced. At this time, the same channel estimation is used to estimate the channel, which brings the actual estimation. In order to improve the performance, next, the OFDM system channel estimation and signal detection technology based on the base extended model are proposed for the environment of large multipath delay, and the technology of channel estimation and signal detection based on the base extended model is proposed. The algorithm of inter symbol interference cancellation and cyclic convolution reconstruction under the base extended model is derived. The results of digital simulation prove the algorithm of this paper. In conclusion, this paper discusses the application of the base expansion model from the angle of the high speed iron channel model, the design of the originator pilot and the channel estimation and signal detection of the receiver, which has theoretical research and practical application value.

【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

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