| With the rapid development of wireless communications technology, spectrum resources are strained increasingly, how to save the existing spectrum resources become an urgent problem needed to solve, orthogonal frequency division multiplexing (OFDM) technology has received extensive attention for its high spectrum efficiency and good ability to anti-multipath interference, so it is necessary to make a through research on OFDM technology.As one of the key technologies of OFDM system, channel estimation plays a very important role in OFDM system. In addition, a good channel estimator must rely on Signal Noise Ratio (SNR) estimation, therefore, this thesis will investigate channel estimation and SNR estimation together.Chapter One of this thesis briefly described the advantages/disadvantages and development history of OFDM technology, and pointed out the significance of OFDM in wireless communications and the importance of channel estimation in OFDM technology, then analysed the current research of channel estimation. For channel estimation is inseparable from the comprehensive understanding of wireless channel. In Chapter Two, the channel fading features was analyzed firstly, and then the OFDM channel model was explained .Finally, DVB channel model are introduced.In Chapter Three, the existing channel estimation algorithm and interpolation algorithm are overviewed at first, and then the advantages and disadvantages of different algorithms were compared through theoretical analysis and simulation. It also pointed out that transform domain channel estimation algorithm is a good algorithm for its low complexity and better performance. Because Minimum Mean Square Error (MMSE) channel estimation algorithm need base on channel and noise second-order statistical property, a solution method of channel auto correlation matrix is given, and a simple and effective SNR and noise estimation algorithm is proposed in multi-path channel at last, which can get a good estimation performance with a simple treatment.Chapter Four of this thesis focuses on channel estimation in Non-Contiguous OFDM (NC-OFDM) system. The workflow of NC-OFDM system was introduced at first, for the sub-carriers of NC-OFDM system are non-contiguous, the characteristics of its pilot patterns was analyzed, a modified transform domain channel estimation algorithm was proposed, based on Least Square (LS) estimation, this algorithm can achieve noise reduction and interpolation processing by using simple matrix operations, thereby improving the estimation performance. The last chapter is the conclusion part, and we pointed out the existing legacy issues and future work. |
