【作者】 孙山林；

【导师】 侯春萍；

【作者基本信息】 天津大学 ， 通信与信息系统， 2006， 硕士

【摘要】 正交频分复用调制(OFDM)技术利用许多并行的子载波来实现高速的数据通信。特别适合在无线信道中传输高速的数据业务。下一代移动无线通信系统的目标是实现无所不在的、高质量的、高速率的宽带多媒体通信。由于OFDM的高频谱利用率、易于硬件实现、抗频率选择性衰落和窄带干扰能力突出等优点,使它成为未来移动通信的首选技术,是当前移动通信领域技术研究的热点。本文分析了OFDM系统发展的历史与现状,阐述了OFDM的基本原理;总结了OFDM系统的优缺点及其采用的关键技术;探讨了OFDM符号的频率细同步问题,对最大似然法、虚载波法、导频法的优缺点及应用场合进行了研究,对其性能进行了仿真验证。提出了一种OFDM符号定时同步的多符号改进算法,所提出的算法的运算量大大减小,同时也克服了多符号法需要大采样数据才能保证系统性能的缺点,改进算法只需要很少的采样数据就可以保证系统的性能要求,推导并提出了新的用于判决的相关函数,缩短了定时捕获时间;此外,还构造了一种多径环境下的OFDM定时偏差估计器,该估计器即使在强多径环境下仍能有效工作,并通过仿真验证了该估计器的性能。更多还原

【Abstract】 Orthogonal frequency division multiplexing modulation uses many parallel sub-carriers, which transmit low-speed data, to realize high-speed communication. Because it’s various advantages in lessening the severe effects of inter-symbol interference, OFDM is suitable for high-speed data transmission in wireless channel. The next generation wireless mobile communication system is expected to provide ubiquitous, high-quality, and high-rate mobile multimedia transmission. Due to OFDM’s advantages such as high spectral utilization rate, simple hardware implement and specially the ability to oppose the frequency-selective decline and narrowband interference, it is highly recommended in the next generation of mobile communication. It is hot-point problem of current mobile communication research.This thesis introduces the history and current situation of OFDM technology at first, then narrates the basic principle of OFDM including OFDM’s basic structure, time domain and frequent domain characteristics, etc. To make OFDM system’s principle more clear, the typical figures of each part of OFDM are drawn. Furthermore, the advantages and key technologies of the OFDM system are presented. OFDM system is very sensitive to the synchronous errors of carrier frequency. In order to reduce the influence of frequency offset in OFDM system, it needs to estimate and compensate it. This paper reasearches on the advantages/disadvantages and the applying situation of the Maximum Likelihood Estimation (MLE), void-carries, pilot-frequency, and simulates to test its performance. What’s more, the improved algorithm of time synchronization for a kind of OFDM symbol is proposed. This method can overcome the faults of required great sample data using the multi-symbol algorithm and shorten the time of time-capture. And the method deduces and puts forward the new related function used in decision. This paper builds a kind of the OFDM time offset estimation in the multi-path. This estimation can till work effectively even in the heavy multi-situation. Finally, this estimation performance is validated by simulation. Orthogonal Frequency Division Multiplexing; Channel estimation;更多还原