| With the rapid development of human society, mobile communication needs to provide higher speed transmission and better service quality. The demanding of huge market is promoting all kinds of wireless communication technology. Of these, orthogonal frequency division multiplexing (OFDM), because of its high-speed data transmission capacity, efficient spectrum utilization and strong ability of anti-multi-path interference, etc, is widely considered to be one of the core technologies in the next generation mobile communication systems., and also is one of the hottest research spot in the field of communications.Channel estimation is a technology of obtaining channel state information (CSI) by processing the received signal, which is one of the key technologies of the OFDM systems. There are many channel estimation algorithms which can be divided into three categories: pilot-based channel estimation, blind channel estimation, and semi-blind channel estimation which is the combination of the before two. Because of never needing to send pilot tones or training symbols that can improve the spectrum using efficiency of the systems, blind channel estimation has gotten more and more research attention. The thesis first briefly introduces the characteristics of wireless channels, the basic principles and matrix model of OFDM system. Based on that, the article analyses the representative methods of the two major kinds of blind channel estimation which are statistical methods and deterministic methods, especially focusing on the noise subspace method. A detailed description of the noise subspace method and simulation analysis of various factors on the performance of this method under the condition of additive white Gaussian noise (AWGN) channel and Rayleigh channel are given. Finally, improves the way of adding data redundancy for noise subspace method, so it can be used in a wider range and gets a better performance, and simulation illustrates the performance of the improved algorithm. |
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