Impulse Interference Mitigation Research For OFDM Receiver Based On Wavelet Analysis

As the rapid development of the air transport industry, there occurs a problem of the lack of capacity for the existing air-ground communication system. In order to solve the problem and meet the need of any more complex information exchange in the future air-ground communication, ICAO put forward a candidate, L-Band Digital Aeronautical Communication System1. L-DACS1 is deployed in the L-band and inlaid between DME(DME) working channels, thus L-DACS1 system has to subject to the serious interference from DME pulse signals. DME interference suppression researches have been carried out in this paper, the main research contents are as follows:Firstly, the principle and signal mode of DME system are described in the paper.According to the relevant protocols, the simulation platform of L-DACS1 is set up in this paper. Then the deterioration effect that DME pulse signals have on the L-DACS1 link transmission performance is verified on the platform.Secondly, a DME interference suppression method which combines wavelet transform and residual interference whitening is proposed. The received time-domain signal was transformed into wavelet-domain via wavelet transform at the Orthogonal Frequency Division Multiplexing(OFDM) receiver. The wavelet coefficients of DME impulse signal were extracted according to their differences with those of useful OFDM signal, the DME impulse interference signal was reconstructed and eliminated from the received signal in time domain. Then, to avoid the burst errors of demodulator, the residual impulse interference was converted into white Gaussian noise by using the de-interleaver and inverse orthogonal transformer., the simulation results reveal that the proposed method can effectively suppress the DME interference signals and improve the reliability of the L-DACS1 link significantly.Finally, in order to overcome the shortcomings of traditional threshold processing of wavelet coefficient a modified pulse suppression method based on wavelet transform is presented. Then, the correctness of the algorithm is proved by theoretical analysis. Further, the fact that the improved wavelet transform have more advantages over the traditional one in suppressing DME interference signals is verified with simulation.