OFDM系统的信道估计研究与实现

发布时间：2018-07-31 17:14

【摘要】：无线通信技术作为最有朝气的科研领域之一,它打破了存在物理方面的限制和制约的有线通信的桎梏,使得各用户可以任意的在无线电波能够辐射到的地区进行通信,极大的开拓了通信的时间尺度和空间尺度。随着越来越大的数据量和越来越快的传输速率的需求,作为一种关键技术,通信系统对信道估计也有着更加严苛的要求。本文的主要内容是研究不同导频图案以及不同信道估计算法的性能,并选取一种低复杂度的算法完成基于FPGA的实现。本文首先阐述了无线通信系统中信道估计理论的研究背景与研究意义,并对信道估计的国内外研究现状进行了简单分析。由于信道估计的本质是对信道响应的求解,所以本文就大尺度衰落和小尺度衰落两种无线信道衰落特征进行简要介绍,并对两种常用的适用于频选信道的Jakes模型和可以对时频双选性衰落信道精确近似的复指数基扩展模型进行数学建模分析。本论文研究并借助计算机进行仿真分析的信道估计算法包括LS、DFT消噪和MMSE算法。研究中还对块状、梳状和菱形三种导频图案进行分析,研究在不同速度下各个导频图案信道估计的性能变化。本文研究的另一个重点是在FPGA中对相关的信道估计算法进行实现。由于LS信道估计算法和线性插值的性能较好,且复杂度很低,所以在进行FPGA实现时采用这种算法。相较于大多数的基于FPGA+DSP架构的基带设计,把信道估计算法的实现从DSP中搬移到FPGA中实现可以降低二者的数据通信带来的效率问题和设计难度问题。本论文中基于FPGA的设计有着估计方案可变的优势,即可以通过用户定义来完成块状、梳状、菱形导频图案的切换,也可以实现不同时域间隔和频域间隔的设置,以满足不同应用场景的需求。论文主要围绕OFDM系统的基本框架进行阐述。第一章简要描述了无线通信中信道估计理论的研究背景与研究意义,并对信道估计的国内外研究现状进行了简单分析,随后还对本文所做工作和论文章节安排进行简单梳理。第二章探究了无线信道的特征和常用的无线信道模型,主要就大尺度衰落和小尺度衰落两种无线信道衰落特征进行简要介绍,并对两种常用的Jakes模型和复指数基扩展模型进行数学建模分析。第三章首先分析了 OFDM的基本原理,然后从导频图案着手展开详细的研究,对比分析了不同的导频图案适用于何种信道。研究发现,梳状导频最适用于高速移动的环境,但是菱形导频在保证与梳状导频性能接近的前提下,需要的导频资源更少,提高了频谱利用率。此外还研究了菱形导频图案中导频间隔对信道估计性能的影响。第四章对第三章的结果做总结分析,选出较容易实现的LS信道估计算法在FPGA中进行实现。在设计方案中首先给出了系统顶层文件和时序规划的设计思想,并对各个模块的设计原理以及波形仿真等方面进行论述。设计中采用可变参数的设计思路,例如所要移除的CP长度、导频的初始位置、导频个数、导频的时频域间隔等均可以由用户定义,具有很好的移植性。
[Abstract]:As one of the most active research fields, wireless communication technology has broken the shackles of wired communication, which is restricted and restricted by physics, so that users can communicate freely in areas where radio waves can be radiated, greatly expanding the time scale and space scale of communication. With the increasing amount of data As a key technology, as a key technology, the communication system has more stringent requirements for channel estimation. The main content of this paper is to study the performance of different pilot patterns and different channel estimation algorithms, and to select a low complexity algorithm to complete the implementation based on FPGA. The research background and significance of channel estimation theory in line communication system are discussed, and the research status of channel estimation at home and abroad is briefly analyzed. Since the essence of channel estimation is to solve the channel response, this paper briefly introduces two kinds of wireless channel fading characteristics of large scale fading and small scale fading, and two kinds of frequent. The Jakes model applied to the frequency selective channel and the complex exponential base extension model which can accurately approximate the time-frequency doubly selective fading channel are modeled and analyzed. The channel estimation algorithms of this paper and the computer simulation analysis include the LS, the DFT denoising and the MMSE algorithm. In the study, three pilots of block, comb and diamond are also used in the study. The pattern is analyzed and the performance changes of the channel estimation for each pilot pattern at different speeds are studied. Another focus of this paper is to implement the related channel estimation algorithms in FPGA. Because of the better performance and low complexity of the LS channel estimation algorithm and linear interpolation, this algorithm is used in the implementation of the FPGA. Compared with most of the Baseband Design Based on FPGA+DSP architecture, the implementation of the implementation of channel estimation algorithm from DSP to FPGA can reduce the efficiency and design difficulty of the data communication of two persons. In this paper, the design based on FPGA has the advantage of variable estimation, that is, the block can be completed by user definition. In order to meet the needs of different application scenes, the paper mainly focuses on the basic framework of the OFDM system. The first chapter briefly describes the research background and research significance of the channel estimation theory in wireless communication and the channel estimation. In the second chapter, the characteristics of wireless channel and the common wireless channel model are explored, and the characteristics of two wireless channel fading of large scale fading and small scale fading are briefly introduced, and two kinds of commonly used Jake are introduced. The mathematical modeling and analysis of S model and complex exponential base extension model are carried out. The basic principle of OFDM is analyzed in the third chapter. Then the detailed study is carried out from pilot pattern, and the different pilot patterns are compared and analyzed. The research shows that the comb pilot is most suitable for the high-speed moving environment, but the diamond guide frequency is guaranteed. On the premise of approaching the comb pilot performance, the required pilot resources are less and the spectrum utilization is improved. In addition, the influence of pilot interval on channel estimation performance in rhombus pilot pattern is also studied. The fourth chapter summarizes and analyzes the results of the third chapter, and selects the LS channel estimation algorithm which is easier to implement in the design of the FPGA. The design idea of the top layer file and time sequence planning of the system is given first, and the design principle of each module and the waveform simulation are discussed. The design ideas of variable parameters, such as the length of the CP to be removed, the initial position of the pilot, the number of pilot, the interval of the time-frequency domain of the pilot and so on, can be used by the user. Definition, with good portability.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.53

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