The Study Of Channel Estimation In OFDM System Based On Pilot Symbols

The sharp increase of demand for wireless communication service promotes the new technology being used in wireless wideband digital communication systems. In wireless broadband digital communication, Inter-Symbol Interference (ISI) caused by time disperse of radio channel is one of main factors that limit bandwidth of communicated information and system performance of communication. In receiver, Orthogonal Frequency Division Multiplexing (OFDM) system can easily cancel ISI and equalize frequency-selective fading that are both caused by time disperse of radio channel, so it is one of the most techniques for wireless broadband mobile communication.Although by employing cyclic prefix, OFDM can effectively eliminate the disturbance from inter-symbol interference introduced by multi-path channel. Accurate channel state information is needed in OFDM systems to perform channel equalization and compensate the multi-path fading. Channel estimation is consequently critical to the whole system performance. In this paper, we will discuss channel estimation under wireless mobile channel according to different types of OFDM systems and provide detailed analyzes of channel estimation.In this thesis, the author makes the following works:1) The current characteristics of the wireless mobile channel is studied, and the multi-path rayleigh fading channel model are described in detail, the advantages and disadvantages of OFDM system is studied and analyzed.2) Three different channel estimation techniques are compared, the results showed that the non-blind channel estimation technique can track the change of the channel timely, so it is widely used in fast fading channel estimation; various interpolation algorithms are discussed simply.3) Several current pilot-symbols insert patterns of non-blind channel estimation are studied intensively. We make detailed analysis and comparison between block and comb pilot-symbol insert patterns, the simulation compares the performance of the two schemes'estimation merits. On this basis, the author proposes a discrete pilot insert program in time domain and frequency domain. Theoretical analysis and computer simulation proved that the improved program not only has a better ability to track the channels, save the spending of the system, but also improve the performance of channel estimation.4) Three recovery algorithms of channel information in pilot position are analyzed in detail. On the basis of compromising the complexity of the LS algorithm and estimation accuracy, the author proposes a noise suppression LS channel estimation algorithm. The simulation shows that in the case of low of channel estimation, although the LS algorithm complexity increased a little. signal to noise ratio, improved algorithm greatly reduces the mean square error...