摘要
在无线信道环境中可靠、高速的传输数据是无线通信技术的目标和要求。正交频分复用(OFDM)技术具有抗多径衰落和时延弥散并且保持较高的传输速率的潜力和优势,同时由于它采用了离散傅立叶变换,大大降低了接收机的实现复杂度,因此,在无线通信领域的应用引起了广泛的关注。
本文主要研究OFDM系统中的信道估计算法,包括基于导频辅助信道估计算法和信道盲估计算法。首先介绍了无线OFDM系统的原理、关键技术及非理想传输条件对系统性能的影响。
然后在基于导频辅助信道估计算法中,总结了基于不同导频结构的现有算法,包括MMSE意义下的维纳滤波、LS意义下的插值滤波等算法,重点讨论了2D维纳内插滤波算法和2×1D维纳内插滤波算法,并分析各种算法的性能。
最后在OFDM系统信道盲估计算法中,本文针对传统的OFDM系统中利用子空间进行信道盲估计的算法提出了一种改进算法。理论分析证明,信道噪声为非白噪声时该算法也同样有效。另外,本文还简要介绍了相关盲信道估计算法。
Data transmission in wireless channels with high speed and reliability is required in future wireless systems. Orthogonal Frequency Division Multiplexing(OFDM) is one of the best solutions to this problem. It can strongly combat multipath and dispersive channel interference. Using DFT, it can be easily realized in transceivers. Therefore, the application of OFDM in wireless communication systems is robust and remarkable.
This thesis mainly focuses on the algorithms for channel estimation in the OFDM systems including pilot assisted channel estimation and channel blind estimation. Above all, the basic principle and key technologies of OFDM are analyzed. Then influence on performance of systems resulted from parameter non-synchronization and error from channel estimation are investigated respectively.
In the section for channel estimation algorithms based on pilot assisted, the existing algorithms including Wiener filtering in the sense of MMSE and interpolation filtering in the sense of LS are summarized systemically, emphasis is on the discussion of two-dimensional and separated two one-dimensional Wiener interpolation filtering. And the performance of different algorithms are analyzed and discussed.
In the another section for channel blind estimation, an improved algorithm is proposed based on the subspace blind estimation algorithm. The improved algorithm improves its performance in theory when channel noise is non-AWGN noise. In the end, a algorithms grounded on conventional channel blind estimation are introduced briefly.
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