【作者】 刘平；

【导师】 田亚菲；

【作者基本信息】 兰州大学 ， 通信与信息系统， 2006， 硕士

【摘要】 OFDM系统以其有效对抗频率选择性衰落和窄带干扰的特性以及较高的频谱资源利用率受到广泛的关注,并被视为新一代移动通信系统的核心技术。但是由于载波频率偏移会破坏子载波间的正交性,很小的载波频偏都将导致解调性能的急剧下降。因此,OFDM系统对载波频率偏移比单载波敏感。同时,符号定时的变化会增加OFDM系统对时延扩展的敏感程度。所以,载波频率和符号定时的同步成为OFDM系统中的研究重点和热点。 在OFDM系统中主要包括三个方面的同步:载波同步、符号定时同步、采样钟同步。本文主要研究载波和符号定时的联合同步。首先介绍了OFDM系统的基本原理和无线信道的特征,然后分析了频率偏移和定时偏差对OFDM系统性能的影响。接着对当前的两个典型同步算法分别进行了分析和改进。在分析基于循环前缀的最大似然(ML)算法的基础上,分别在AWGN信道和多径信道下提出了两种改进算法,并进行了计算机仿真,分析了其性能。同时针对基于导频的Schmidl算法中存在的定时不准确的缺点,提出了一种新的同步方案,并通过计算机仿真验证了其良好的估计性能。更多还原

【Abstract】 In recent years, great interest was focused on OFDM just because its inherent technical advantages in combating multi-path fading and its high resource utilization, and it is considered as the core technical of the next generation mobile communication. But frequency offset will destroy the orthogonal character of sub-channels and very small carrier frequency offset may induce large demodulation errors in the receiver, so it is more sensitive to the carrier frequency offset than sing-carrier systems, besides, the change of symbol timing may increase the sensitivity to time-delay. Therefore carrier synchronization and symbol timing synchronization are the emphasis and focus. There are three kinds of synchronal modes in OFDM system: symbol timing synchronization, carrier synchronization, sampling-bell synchronization. This paper chiefly studies joint symbol timing and carrier frequency synchronization. Here firstly introduces the basic principle of OFDM technique and the characteristics of wireless fading channel and so on, then analyses the influence of timing error and carrier frequency offset on the system performance. It is followed that two typical synchronization algorithms are analyzed and modified .based on the analysis of the current (ML) method which is using cycle prefix, two new methods are proposed in AWGN channel and multi-path channel. Moreover, aiming at the problem of imprecise timing synchronization in Schmidl’ algorithm which is using pilot symbol, a new synchronization scheme is proposed. These algorithms are simulated and confirmed in computer.更多还原