航空场景下OFDM系统频偏和信道估计研究

发布时间：2018-06-10 08:01

本文选题：航空通信 + LTE　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：本文首先介绍了航空通信的研究背景和将LTE应用到航空通信系统的意义,综述了多载波通信的抗多普勒技术和信道估计技术的研究状况。作为频率同步和信道估计技术研究的前提,准确的信道模型至关重要,本文介绍了飞行器在巡航阶段的信道基本特性,针对不同的飞行仰角,参阅相关文献的统计数据建立数学模型。简要介绍了LTE下行链路的物理层标准和相关协议,详细介绍了OFDM技术,并搭建了LTE下行链路基带仿真系统模型,并阐述了将LTE应用到航空通信的优势及面临的问题。在OFDM系统的抗多普勒频偏技术研究中,其主要思路是在接收端进行频偏估计和补偿。限于LTE下行可利用的资源有限,现有的算法大都基于循环前缀或导频符号,利用其相关特征来进行频偏估计。但是在航空情景下,由于终端移动速度更大,多普勒频移更大,且受到散射径的影响,传统算法的估计性能并不理想。本文建立了受多普勒效应影响的信号模型,分析了频偏和多普勒扩展对系统的影响,仿真分析了现有的一些经典估计方案,并针对传统频偏估计算法受散射径影响严重的问题,分析了只利用LOS径估计频偏的技术,该方案首先需进行时域的信道估计,将直射径与散射径分离,仿真表明该方案并不适用于航空场景。利用循环前缀和导频进行联合估计,由于实现简单且性能良好被作为最终的方案。针对航空信道快时变的特点,首先分析了传统LS在不同信道内插方案下的系统性能,以及基于基扩展模型的信道估计算法,仿真表明其并不适用于航空场景下,尤其是散射径延迟比较大时,本文联合ICI消除及最强路径信道估计方案,ICI消除通过求解ICI矩阵重构信号,为降低计算复杂性,采用有限长滤波器来实现矩阵求逆运算,最强路径信道估计方案即在时域抽取能量集中的路径,其他路径置零,然后再变换到频域。该方案能有效地提升了两径信道下的系统性能。
[Abstract]:This paper first introduces the research background of aviation communication and the significance of applying LTE to aviation communication system, and summarizes the research status of anti-Doppler technique and channel estimation technology in multi-carrier communication. As the premise of the research of frequency synchronization and channel estimation, accurate channel model is very important. This paper introduces the basic characteristics of the channel in the cruising phase, aiming at different elevation angles. A mathematical model is established by referring to the statistical data in the relevant literature. This paper briefly introduces the physical layer standard and related protocols of LTE downlink, introduces the OFDM technology in detail, builds the simulation system model of LTE downlink baseband, and expounds the advantages and problems of applying LTE to aviation communication. In the research of anti-Doppler frequency offset in OFDM system, the main idea is to estimate and compensate the frequency offset at the receiver. Due to the limited resources available in the downlink of LTE, most of the existing algorithms are based on cyclic prefixes or pilot symbols to estimate the frequency offset. However, in aeronautical scenarios, the estimation performance of the traditional algorithms is not satisfactory because the terminal moves faster, the Doppler frequency shift is larger, and is affected by the scattering path. In this paper, a signal model affected by Doppler effect is established, the influence of frequency offset and Doppler spread on the system is analyzed, some classical estimation schemes are simulated and analyzed, and aiming at the problem that the traditional frequency offset estimation algorithm is seriously affected by scattering path, This paper analyzes the technique of estimating the frequency offset only by using Los path. Firstly, the channel estimation in time domain is carried out, and the direct and scattering paths are separated. The simulation results show that this scheme is not suitable for aviation scenarios. The joint estimation using cyclic prefix and pilot is considered as the final scheme because of its simple implementation and good performance. In view of the fast time-varying characteristics of aviation channel, the system performance of traditional LS under different channel interpolation schemes and the channel estimation algorithm based on base expansion model are analyzed. The simulation results show that the proposed algorithm is not suitable for aviation scenarios. Especially when the scattering path delay is large, the ICI elimination and the strongest path channel estimation scheme are combined in this paper. By solving the ICI matrix to reconstruct the signal, in order to reduce the computational complexity, the finite length filter is used to realize the matrix inversion operation. The strongest path channel estimation scheme is to decimate the energy-concentrated path in time domain, set the other paths to zero, and then transform to frequency domain. This scheme can effectively improve the system performance in two-path channels.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

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