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  本文關鍵詞：基于訓練序列的OFDM系統(tǒng)定時同步技術研究　出處：《吉林大學》2014年碩士論文　論文類型：學位論文

  更多相關文章： 正交頻分復用 定時同步 訓練序列 循環(huán)前綴

【摘要】：正交頻分復用(OFDM)技術依靠其較高的頻譜利用率、較快的傳輸速度以及出色的抗多徑干擾能力等優(yōu)良特性，已經(jīng)成為了第四代（4G）移動通信系統(tǒng)中的核心技術。在OFDM技術的支撐下，不僅通信系統(tǒng)的容量可以得到大幅度的提升，其所提供的各種服務（如語音、數(shù)據(jù)、視頻等）的質(zhì)量也將會上升到一個新的層次。 OFDM作為一種多載波高效調(diào)制技術，在其系統(tǒng)中，它的全部帶寬被劃分成許多相互正交的子載波,因此系統(tǒng)頻譜的利用率得到了極大的提高，并且循環(huán)前綴這一特殊結(jié)構(gòu)有效的解決了符號間干擾和子信道間干擾等問題。然而這一切優(yōu)良特性存在的前提是各個子載波間能保持良好的正交性—這種正交性會受到頻率偏移的較大影響，而要想校正這種偏移，則需要系統(tǒng)有一個良好的同步性能。正是基于這種情況，文章對OFDM系統(tǒng)的同步技術進行了重點研究。 本文首先介紹了移動通信與OFDM技術的相關知識，闡明了同步過程對于整個OFDM系統(tǒng)的重要性并介紹了同步技術的研究現(xiàn)狀。接下來是對OFDM技術基本原理的敘述，，內(nèi)容涵蓋了無線信道、調(diào)制與解調(diào)、保護間隔與循環(huán)前綴等，并總結(jié)了OFDM技術的優(yōu)缺點。隨后又給出了OFDM系統(tǒng)的總體同步方案，并指出了各種同步對OFDM系統(tǒng)的影響。 定時同步是本文的研究重點。文章首先將其劃分為非數(shù)據(jù)輔助的以及基于數(shù)據(jù)輔助的兩大類別，并分別介紹了每種分類中已有的一些典型算法。第一類算法中以ML算法為代表進行了介紹，而第二類算法中重點介紹的則是SC算法、Minn算法以及Park算法。經(jīng)過對第二類中幾種算法的研究發(fā)現(xiàn)已有算法均存在著一些缺陷，如SC算法的“平頂區(qū)域”問題；Minn、Park算法的“副峰”問題，并且低信噪比下主峰峰值與副峰峰值較為接近；此外Park算法還存在著計算量較大的問題。鑒于此種情況，文章提出了一種改進算法，通過對訓練序列以及度量函數(shù)的重新設計，解決了上述問題，提升了定時精度以及系統(tǒng)性能。之后通過MATLAB仿真進一步證明了該算法的優(yōu)良特性。在文章最后給出了一種自適應門限算法的改進思路，解決了突發(fā)OFDM系統(tǒng)中因信噪比發(fā)生變化而導致的漏判問題。
[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.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN929.53

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本文編號：1428357