Blind Processing Technology For Overlapped ADS-B Signals Based On Array Antenna

Automatic Dependent Surveillance-Broadcast(ADS-B)is an aerial surveillance means used by aircrew in air command system.Airborne ADS-B broadcasts the aircraft identification number,longitude,latitude,altitude and other information,so that the surrounding aircraft and ground stations can monitor them at same time.ADS-B transmits data by broadcasting,which can be received by all users.There will inevitably be overlapping problems.Increasing airspace flow makes the overlapping problem more serious,which will result in the error or loss of decoding information of the receiver and reduce the security and reliability of ADS-B surveillance.Aiming at the research of overlapping of ADS-B signals,two algorithms are presented.The principle of the two algorithms is analyzed and improved.The results are as follows:PA is applied to solve the overlapping problem of ADS-B.Which is simple,and the effect is better when the signals have relative delay.However,PA can only exclude one signal and can not enhance the target ADS-B signal.So the gain of array antennas with PA is combined,and presents a high-gain algorithm,Capon-PA algorithm.This method can use Capon beamforming to form the main lobe gain upward from the target ADS-B signal and improve the output signal-to-noise ratio of the signal based on the estimation of the direction vector by PA.Considering that when PA estimates direction vector,the smaller relative delay makes fewer samples available for the direction vector,which may result in estimation error.Therefore Robust Capon Beamforming(RCB)algorithm is applied to improve the robustness of PA,be called RCB-PA.This algorithm reduces the requirement of time delay and the estimation error of direction vector,thus further improving the robustness of the algorithm.RCB-PA algorithm improves the output signal-to-noise ratio,but it can not process the overlapped signal with relatively delay less than 1 ?s.Therefore,thesis gives a stable and convergent algorithm for ADS-B signal based on FastICA,which is insensitive to time delay.Through the relationship between the subspace projection of the target ADS-B signal and the weight vector,the algorithm sets the initial value of the subspace projection iteration,reduces the search scope of the iteration operation.At the same time,it solves the sensitivity of the traditional FastICA algorithm to the initial value.The simulation and experimental results show that the error rate of the two algorithms is reduced,the RCB-PA algorithm improves the output signal-to-noise ratio of the signal,and the computational complexity is small,but it still has the problem of time-delay sensitivity.The improved FastICA algorithm converges more stably and has little requirement for the relative delay,but its computational complexity is large due to the iterative operation.