【作者】 梁治国；

【导师】 郭黎利；

【作者基本信息】 哈尔滨工程大学 ， 信号与信息处理， 2007， 硕士

【摘要】 OFDM技术是一种具有很强抗多径衰落、码间干扰和窄带干扰能力，以及很高频谱利用率的高效数据传输技术。但OFDM对同步误差非常敏感，成为制约OFDM技术发展的瓶颈。而研究同步算法正是本文要完成的主要任务。本文首先简要介绍了多载波正交频分复用(OFDM)技术的发展概况，说明了OFDM的调制解调基本原理与系统参数的设计。在分析无线通信信道特性的基础上，得出了仿真中采用信道的数学模型。就定时同步偏差和频率偏差对OFDM系统性能的影响进行了分析，得出了系统对时频同步的具体要求。符号定时同步部分论述了基于三种不同PN序列结构的同步算法和用于符号细同步的基于导频的相位检测法，最后给出符号定时同步校正框图。载波频率同步部分首先论述基于导频的整数频偏估计方法，而后给出几种经典的频偏估计方法，并指出了已有算法的不足。针对这种情况，本文提出一种新颖的基于循环移位前导序列的OFDM系统载波同步方法。该方法是根据DFT的时移性质，构造循环移位前导序列，设计了两个频偏估计器。由估计器1完成粗同步，而精同步采用两个估计器最优线性组合完成。在多径信道下，优化估计器设计，以此消除均方误差中出现的地板效应。仿真结果表明，新算法与传统的算法相比有估计范围大和精度高的优点，而且估计范围和精度可以灵活调节。同时文中分析并得出了本估计方法的Cramer-Rao下限。接下来对OFDM系统的非数据辅助的三种同步算法进行了理论推导和性能仿真，分析了各自的优缺点。更多还原

【Abstract】 OFDM is an effective data transmission technology which can be against multi-path propagation, inter-code interference and narrow band interference, and it also has a high spectral efficiency. But it is more sensitive to synchronization errors, which bottlenecks the development of OFDM technology. The algorithms of time and frequency synchronization for OFDM systems are mainly investigated in this dissertation.Above all, this dissertation gives an overview on the development of OFDM technology. Transmission principles and system parameters design are introduced. Based on the basic characters of wireless channel, the mathematics model used for simulation is gotten. The effects of timing and frequency synchronization errors on the performance of OFDM system are systemically summarized in this dissertation, and the requirement precision of time and frequency synchronization is given. In the time synchronization, the algorithms based on three different PN sequences structures and pilot phase detect are discussed, and the figure of time emendation is proposed at last. In frequency synchronization, the algorithm of integer frequency offset estimation based on pilot is discussed, then some classical frequency offset estimation algorithms is given, and this dissertation points out the drawbacks of them. A new scheme based on cyclic-shifted preamble sequences is proposed for frequency synchronization in OFDM system. According to the time property of DFT, the preamble sequences are constructed and two estimators are designed. The coarse frequency offset is realized by the first estimator. Once coarse frequency offset compensated, the fine estimation is achieved by the optimized line combination of two estimators. In multi-path channel, two estimators are optimized and can eliminate the floor phenomena. It is demonstrated that, compared with the classical algorithm, the new method has better estimation accuracy and larger estimation span, which can be changed more flexible. At the same time, the Cramer-Rao lower bound of the new method is analyzed and obtained. Finally, this dissertation gives three non data-aided algorithms theory deduction and simulation performance respectively, and analyses their advantages and shortcomings.更多还原