Overlapped Signals Separation For ADS-B System

As a major surveillance technique recommended by ICAO,Automatic Dependent Surveillance-Broadcast(ADS-B)is being paid much more attention,it is incorporated to the growing number of aircraft.As the broadcast property and the increasing of the aircraft,there will be overlapping among the different ADS-B signal,which will lead to a serious problem for the decoding of ADS-B signals.If the ADS-B signal cannot be properly decoded,the information of target will be lost or error recorded.Firstly,this paper introduces the existing ADS-B signal system,and describes the corresponding decoding and error correction method for the most widely used 1090 ES signal mode.The improved decoding method and the improved error correction technique are introduced for the multi-target environment.In the case of single antenna,the method of overlapped signal processing based on accumulation and classification is presented.Firstly,this paper estimate the start time of the signal by the detection of valid pulse position,and the overlapping position is detected by Hilbert transform,then the time delay between the overlapped signals is obtained;secondly,divide the sample points into intervals based on the estimated time delay and the pulse width,and the signal power on each interval can be obtained by adopting step by step integration.Finally,the data of different signal can be determined by the classification results of integral values based on K-means algorithm.In the case of multiple antennas,overlapping detection is conducted by eigenvalue decomposition of two antennas.Firstly,the method of overlapped signal separation based on DOA estimation is proposed,the method is explicit,but two-dimensional peak search has to be conducted for DOA estimation,and the error of amplitude and phase of array must be precisely know.To solve the above problems,the method of overlapped signal processing based on spatial filtering is presented,the data block consists of the first signal is chosen according to the distribution of eigenvalue for covariance matrix estimation,then the second signal is obtained by power inversion method;the first signal can be obtained in the same way.If the time delay of overlapped signals is relatively shot,and there is no data block consists of single signal available,the time delay can be obtained by VPP test of the signal received by the reference antenna,as the frame length of ADS-B signal is already known,and the optimum weight vector is calculated by ?sing the preamble signal as reference,and the overlapped signals are separated.Finally a large number of simulation experiments are conducted to verify the validity of the algorith,the result is also satisfactory when applying to real data.