基于训练序列的OFDM系统定时同步技术研究

发布时间：2018-01-15 12:22

本文关键词：基于训练序列的OFDM系统定时同步技术研究　出处：《吉林大学》2014年硕士论文　论文类型：学位论文

【摘要】：正交频分复用(OFDM)技术依靠其较高的频谱利用率、较快的传输速度以及出色的抗多径干扰能力等优良特性，已经成为了第四代（4G）移动通信系统中的核心技术。在OFDM技术的支撑下，不仅通信系统的容量可以得到大幅度的提升，其所提供的各种服务（如语音、数据、视频等）的质量也将会上升到一个新的层次。 OFDM作为一种多载波高效调制技术，在其系统中，它的全部带宽被划分成许多相互正交的子载波,因此系统频谱的利用率得到了极大的提高，并且循环前缀这一特殊结构有效的解决了符号间干扰和子信道间干扰等问题。然而这一切优良特性存在的前提是各个子载波间能保持良好的正交性—这种正交性会受到频率偏移的较大影响，而要想校正这种偏移，则需要系统有一个良好的同步性能。正是基于这种情况，文章对OFDM系统的同步技术进行了重点研究。本文首先介绍了移动通信与OFDM技术的相关知识，阐明了同步过程对于整个OFDM系统的重要性并介绍了同步技术的研究现状。接下来是对OFDM技术基本原理的叙述，，内容涵盖了无线信道、调制与解调、保护间隔与循环前缀等，并总结了OFDM技术的优缺点。随后又给出了OFDM系统的总体同步方案，并指出了各种同步对OFDM系统的影响。定时同步是本文的研究重点。文章首先将其划分为非数据辅助的以及基于数据辅助的两大类别，并分别介绍了每种分类中已有的一些典型算法。第一类算法中以ML算法为代表进行了介绍，而第二类算法中重点介绍的则是SC算法、Minn算法以及Park算法。经过对第二类中几种算法的研究发现已有算法均存在着一些缺陷，如SC算法的“平顶区域”问题；Minn、Park算法的“副峰”问题，并且低信噪比下主峰峰值与副峰峰值较为接近；此外Park算法还存在着计算量较大的问题。鉴于此种情况，文章提出了一种改进算法，通过对训练序列以及度量函数的重新设计，解决了上述问题，提升了定时精度以及系统性能。之后通过MATLAB仿真进一步证明了该算法的优良特性。在文章最后给出了一种自适应门限算法的改进思路，解决了突发OFDM系统中因信噪比发生变化而导致的漏判问题。
[Abstract]:Orthogonal Frequency Division Multiplexing (OFDM) technology depends on its high spectral efficiency, faster transmission speed and excellent ability to resist multipath interference. It has become the core technology of 4th generation 4G) mobile communication system. With the support of OFDM technology, not only the capacity of communication system can be greatly improved. The quality of its services (voice, data, video, etc.) will also rise to a new level. As a multi-carrier efficient modulation technique, OFDM is divided into many orthogonal sub-carriers in its system, so the spectrum efficiency of the system has been greatly improved. And the special structure of cyclic prefix effectively solves the problems of inter-symbol interference and inter-channel interference. However, the premise of the existence of all these excellent characteristics is that each subcarrier can maintain a good orthogonality-this orthogonality. Will be greatly affected by frequency offset. In order to correct this offset, the system needs a good synchronization performance. Based on this situation, this paper focuses on the synchronization technology of OFDM system. This paper first introduces the related knowledge of mobile communication and OFDM technology. This paper expounds the importance of synchronization process to the whole OFDM system and introduces the research status of synchronization technology. Then it describes the basic principle of OFDM technology including wireless channel modulation and demodulation. The advantages and disadvantages of OFDM technology are summarized, and then the overall synchronization scheme of OFDM system is given, and the influence of synchronization on OFDM system is pointed out. Timing synchronization is the focus of this paper. Firstly, it is divided into two categories: non-data-assisted and data-aided. Some typical algorithms in each classification are introduced respectively. In the first kind of algorithm, ML algorithm is represented, and in the second kind of algorithm, SC algorithm is emphasized. Minn algorithm and Park algorithm. Through the research of several algorithms in the second kind, it is found that there are some defects in the existing algorithms, such as the "flat-top region" problem of SC algorithm; The "secondary peak" problem of the Minn Park algorithm, and the main peak and the secondary peak are close to each other at low SNR. In addition, the Park algorithm also has the problem of large computation. In view of this situation, this paper proposes an improved algorithm, through the re-design of training sequence and metric function, to solve the above problems. The timing accuracy and the system performance are improved. Then the excellent characteristics of the algorithm are further proved by MATLAB simulation. At the end of this paper, an improved method of adaptive threshold algorithm is given. The problem of missing judgment caused by the change of signal-to-noise ratio in burst OFDM system is solved.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

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