A Study Of Timing Synchronization And Channel Estimation Based On The OFDM System

OFDM(Orthogonal Frequency Division Multiplexing) is well known to be robust against inter-symbol interference resulting from multipath propagation and high spectrum efficiency. However, timing synchronization error and channel fading has great impact on the orthogonal frequency division multiplexing modulation technique.In terms of timing synchronization, owing to the maximum likelihood estimation method needs the information of signal to noise ratio, this paper introduces an improved timing algorithm. The simulation shows that the timing performance of the new algorithm which is easy to implement close to that of MLE method. Owing to the Schmidl&Cox method has low timing accuracy and high hardware complexity, an improved method which normalizes the timing metric during a sliding window is introduced. The simulation shows that the new method which eliminates the peak platform basically has high symbol timing accuracy. Due to the Minn method and the Park method has high sidelobe, this paper introduces a timing method based on the conjugate symmetric sequence. Simulation shows that the method eliminates sidelobe and has peak similar to the ideal impulse function. Therefore, compared to the above timing algorithms, there is the better timing offset estimation performance.In terms of channel estimation, this paper studied the traditional channel estimation based on DFT(Discrete Fourier Transform) interpolation in time domain, and proposes an improved threshold filtering method to eliminate the noise further in cyclic prefix. This method is also suitable for the communication system existing impulse noise.In the multipath channels, the first path of which is not the strongest one, the conventional algorithms will just find the strongest path, but not the first path. It will make the initial point of FFT(Fast Fourier Transform) window located in the data domain, resulting in severe ISI. This paper improves the fine timing algorithm of the conventional timing method, and focuses on a method that fine timing synchronization is combined with channel estimation. Simulation shows that the combined method has higher timing precision in this type of universal multipath channel than the conventional timing synchronization algorithms, especially for the first path which is not the strongest one. Meanwhile, there are many improvements in channel estimation performance.