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Research on Channel Estimation Technique in OFDM System

Author: WangQi
Tutor: HuiXiaoWei
School: Liaoning Technical University
Course: Communication and Information System
Keywords: OFDM LS LMMSE windowing
CLC: TN919.3
Type: Master's thesis
Year: 2011
Downloads: 19
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Abstract


The main content of this paper is channel estimation technology of orthogonal frequency division multiplexing system, including blind channel estimation and pilot-based channel estimation.At first, the wireless channel characteristics is introduced, including characteristics of the channel fading and channel expansion, several typical channel models are given such as the white Gaussian noise channel, Rayleigh fading channel and Rice fading channel. Then, the basic principles of OFDM system and the model are introduced, including the sub-carrier modulation of OFDM system, guard interval and cyclic prefix, and the realization of the Fourier transform. At last, the synchronization of OFDM system, channel estimation and PAPR technique are briefly elaborated.A blind channel estimation which is based on subspace method in OFDM system is studied, this method obtains channel state information through the correlation of the sending signals and receiving signals, as well as the combination of signal processing techniques. The simulation shows that this method has good estimation accuracy.The choice and mode of the pilot is introduced first in pilot-based channel estimation. The least squares and linear minimum mean square error algorithm are used to estimate the pilot subcarriers. Simulation shows that the improved algorithm has a low complexity by improving the original algorithm, By do interpolations with the estimated value of pilot subcarriers to get other sub-carriers’channel estimates, theoretical analysis and simulation results show that the cubic spline interpolation has a higher estimation precision. Finally a new method is presented in order to solve the problem of the leak in the channel impulse response, which is to add a window processing for the channel impulse response, simulation shows that the method improves the accuracy of channel estimation and reduces the system’s bit error rate.

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