A Haar Wavelet Decision Feedback Channel Estimation Method in OFDM Systems

Abstract

Channel estimation is a key technology in improving the performance of the orthogonal frequency division multiplexing (OFDM) system. The pilot-based channel estimation method decreases the spectral efficiency and data transmission rate. Some conventional channel estimation methods cannot suppress the noise effectively, which affects the quality of the final received signals. To solve these two problems, a Haar wavelet decision feedback (DF) channel estimation method, also named the Haar wavelet method, is proposed in this paper. The proposed Haar wavelet method can suppress the noise existing at the estimated channel impulse response (CIR) effectively, based on a time-domain threshold which is a standard deviation of noise obtained by wavelet decomposition. At the same time, the proposed Haar wavelet method just requires inserting one block pilot symbol in front of the first OFDM symbol, which therefore improves the data transmission rate and spectrum efficiency greatly. Simulation results are shown to verify the effectiveness of the proposed Haar wavelet method in multipath channel propagation conditions.

A Novel Noise Suppression Channel Estimation Method Based on Adaptive Weighted Averaging for OFDM Systems

“…In recent years, researchers have put forward some noise suppression channel estimation methods. To suppress the noise effect, a threshold, which is often obtained through noise variance estimation, is applied at the LS estimation of the CIR to find the positions of the most significant taps (MSTs) [16,25]. However, a fixed threshold often cannot distinguish the paths with smaller energy from the noise.…”

“…Moreover, some researchers utilize the averaging of AWGN to further suppress the noise effect, which can be combined with the above-mentioned conventional noise suppression method [16,[27][28][29][30]. In [31], a simple noise suppression channel estimation method based on inter-frame pilot averaging is proposed.…”

“…There have been many researches on channel estimation in OFDM systems. In general, channel estimation methods can be divided into three categories: pilot-based channel estimation, blind channel estimation, and semi-blind channel estimation [16]. Blind and semi-blind estimation perform channel estimation with non-pilot and few pilots, respectively, and thus have higher spectral efficiency.…”

“…Pilot-based channel estimation method estimates the channel impulse response (CIR) or channel frequency response (CFR) by multiplexing the known pilot sequences into OFDM symbols. In practice, pilot symbols are inserted in various patterns, such as block-type, comb-type, and scatter-type, to adapt to different channel environments [16]. In this paper, comb-type pilot-based channel estimation is used in OFDM systems since comb-type pilot is more robust to a time-varying channel with low to high Doppler spread.…”

Analysis on Wavelet Family based Channel Estimation for MIMO-OFDM System

“…Also provides less noise suppression. To minimize the computational difficulties Linear Minimum Mean Square Error (LMMSE) channel estimation approach is described in [8].suppression of noise threshold scheme is proposed in [9], Minimum Mean Square Error (MMSE) in [7], Least Square error (LS scheme) in [6], decision feedback based channel estimation using Haar Wavelet [10], wavelet based channel estimation for ofdm system [11] and so many schemes. transform and Fractional spline wavelet transform [12].…”