【作者】 孙红春；

【导师】 张振川；

【作者基本信息】 东北大学 ， 通信与信息系统， 2009， 硕士

【摘要】 在无线移动信道中,高速率和高质量的通信服务,是无线通信的目标和要求。正交频分复用技术具有频谱利用率高、能够有效对抗频率选择性衰落的影响而日渐受到人们的普遍关注。OFDM技术中的一个重要部分就是信道估计,本文对单天线和多天线的OFDM系统的信道估计进行研究,做出仿真分析。首先,介绍了无线信道的特性,OFDM系统的基本原理和关键技术,还简述了MIMO和MIMO-OFDM的基本原理和系统模型。在此基础上着重对OFDM系统中基于导频的信道估计算法和内插估计方法进行了研究。常用的导频有块状结构和梳状结构,根据无线信道快变的特点本文多采用梳状导频结构。其次,对单天线OFDM系统的信道估计,本文对经典的LS算法,MMSE算法进行仿真比较,并分别提出改进的算法。改进的LS算法考虑到了信道的相关特性,有效抑制了噪声对信道估计结果的影响,做出更准确的估计。改进的MMSE算法主要在于通过保留大功率信号分量,忽略小功率分量的方法对原算法的进行化简。之后还提出了一种改进的基于判决反馈机制的信道估计方法,为了提高初始估计精度,将频率分集和判决反馈算法相结合的算法,经过仿真分析得出,随着在多径瑞利衰落信道下,本文的方法可以在较低的复杂度下有效地提高信道估计的精度,迭代次数的增加,本算法性能有很大提高。最后,介绍了MIMO-ODFM系统的信道估计。MIMO-OFDM技术将MIMO与OFDM有机结合在一起,能够大幅度提高无线通信系统的信道容量和传输速率,并能有效抵抗多径衰落、抑制干扰和噪声。信道估计也是MIMO-OFDM技术中的一个重要部分。本文分别介绍了时域和频域的两个方面的信道估计方法,采用等间隔的OFDM符号间插入导频的结构的方法,并运用功率归一化和矩阵共轭变换的方法简化了的信道估计方法。这种方法在不降低估计的精度的同时,使计算量下降为原来的1/Nt。更多还原

【Abstract】 Communication service in wireless channels with high speed and quality is required for future wireless communication systems. OFDM (orthogonal frequency division modulation) has gained more and more attraction in recent years due to its high bandwidth efficiency and robustness against frequency selective fading channels. Channel estimation is one of the most important part in OFDM system. This thesis focuses on channel estimation in both single-in single-out OFDM system and multiple-in multiple-out OFDM system, the analysis and comparison of these are made through computer simulation.Firstly, wireless channel characteristic, basic principle and key technology for OFDM System are introduced in this paper. There are brief description of basic principle and system model in MIMO and MIMO-OFDM system. The channel estimation algorithms based on pilot and the method of interpolation estimation in OFDM system are investigated in detail. Block structure and comb structure are two basic structure of training sequence, as the fast changing characteristic of wireless channel, this paper use comb structure.Secondly, on the channel estimation of OFDM system, the thesis mainly research on the LS and the MMSE algorithms, and gave both the simulation of the LS, the MMSE algorithms and their improved algorithms and analysis their performance. The correlation of channel is considered in the modified LS algorithms, the more accurate estimation is got without increasing the calculation complexity. In the modified MMSE algorithms, in order to simplify the MMSE algorithms high power signal components are reserved, and low ones are neglected. A modified channel estimation method based on decision feedback for OFDM system is proposed. Meanwhile, the frequency domain diversity method is exploited to decrease the initial channel estimation errors. Simulation shows that the proposed algorithm improves the performance of channel estimation effectively with lower computing complexity in Rayleigh fading channelLastly, this essay focuses on the channel estimation of MIMO-OFDM system. As a combination of orthogonal frequency division multiplexing (OFDM) with multiple input multiple output (MIMO) technique, MIMO-OFDM can not only effectively enhance the transmission rate and capacity of the wireless communication system but also combat multi-path fading and interference. Channel estimation is an important part for MIMO-OFDM. When the transmitter and the receiver use more than one antenna, MIMO channel is constructed. As information theory indicates, MIMO channel has larger capacity. A simplified MIMO-OFDM channel estimation method is proposed, with inserting pilot between the same interval, power normalizing and conjugate matrix are used to simplified the algorithms.更多还原