Research On Pilot-Aided OFDM Channel Estimation Methods

OFDM (Orthogonal Frequency Division Multiplexing) is a parallel transmission scheme of Multi-Carrier's Modulation. It transmits information through orthogonal multiple sub-carriers, and has high utilization of frequency spectrum and good capability of countering multi-path interference. It is also adaptive to high-rate data transmission and multimedia data transmission. OFDM has been regarded as the core technology of 4G wireless communications system in the future.Channel estimation is one of the research hotspot. Many related algorithms are presented these years all over the world, which can be generally separated into three kinds: pilot-aided channel estimation, decision feedback channel estimation and blind channel estimation. Pilot-aided channel estimation, which obtains the channel impulse response for all sub-carriers by pilot sub-carriers, can track the variety of channel and obtain high accuracy with low complexity. So it is a practical channel estimation method.This paper firstly analyzes the multi-path and time-variety statistic properties of general wireless channel and presents its mathematics model, based on which the traditional pilot-aided channel estimation is mainly described. After two pilot arrangement types of block and comb are investigated, three estimation criterions of LS, MMSE and SVD and four interpolation methods of linear interpolation, Gauss interpolation, sinc interpolation and interpolation of zero-padding in transform domain are respectively discussed, in which the interpolation method of zero-padding in transform domain is especially considered and proved to be a good interpolation estimation with MATLAB simulation. Then to de-noise the pilot sub-carriers' LS channel estimation at the receiver, a transform domain filtering method based DFT is introduced, combining which with the DCT property, a. new low pass filter suitable to DCT domain is designed. Meanwhile, wavelet transform idea is applied to this paper and a new wavelet de-noising method in OFDM channel estimation is proposed. Simulation results show that the proposed DCT-based filtering algorithm and wavelet de-noising method both can degrade the effects of noise, therefore raise the performance of OFDM channel estimation.