Airspace Adaptive Interference Suppression Method For Broadband Aviation Data Link

L-band digital aviation communication system(L-DACS)is one of the three key components of future civil aviation communication infrastructure.L-DACS system mainly provides air traffic control and data communication services for aircraft on land routes,terminal areas and airports.The World Radio Conference recommended that the L-DACS system be deployed in the L-band in 2007.Because the L-band is occupied by multiple systems and the spectrum resources are tight,it was decided that the L-DACS1 system will be deployed in-line between the distance measurement equipment(DME)channels.In order to solve the problem that the OFDM receiver of L-DACS1 system suffers from distance measuring equipment signal interference,the paper conducts three aspects of research.The research content of the paper is as follows:Firstly,in order to solve the problem of DME pulse interference OFDM receiver in L-DACS1 system,an orthogonal projection interference suppression algorithm and RELAX algorithm for DOA estimation in spatial filtering is proposed.First,the array signal is projected to the orthogonal complement space of the interference subspace to eliminate the interference of the DME pulse signal,and then the RELAX algorithm is used to estimate the DOA of the OFDM desired signal.Simulation studies show that the orthogonal projection interference suppression algorithm can effectively suppress interference,and the RELAX algorithm can accurately estimate the direction of the OFDM expected signal.Secondly,in view of the complexity of the RELAX algorithm,based on the cyclostationary theory,an orthogonal projection interference suppression and blind adaptive beamforming interference suppression method is proposed.Fisrt,the orthogonal projection interference suppression algorithm is used for interference cancellation,and then based on the cyclostationary characteristics of the OFDM signal after the interference cancellation signal,use the LS-SCORE algorithm or the CAB algorithm to obtain the optimal weight vector for beamforming.Finally,the optimal weight vector is used for blind beamforming.The simulation results show that the proposed method can form a stable main beam on the OFDM desired signal,and at the same time,it can suppress the interference of the DME pulse signal.Thirdly,for the case where the orthogonal projection interference suppression algorithm can only eliminate high-power and strong pulse interference,the C-CAB algorithm is proposed.First,DOA estimation of the OFDM expected signal is performed,and then the C-CAB algorithm is used to obtain the optimal weight vector of the array antenna.And finally use the optimal weight vector to perform blind beamforming.The simulation results show that the proposed method can form a stable main beam in the direction of the desired OFDM signal,thereby obtaining the direction information of the OFDM desired signal and performing interference suppression.