The Study Of Near-field Interference Suppression Technology On Small Moving Platform

The small platform such as the unmanned underwater vehicle (UUV) has been the mainforce of exploring oceans today. But the sonar equipment installed on the moving platform issubject to severe near-field interference, such as crosstalk between different sonar equipmentand propeller noise interference, which also occurs to UUV platform and has a tremendousimpact on the oceans investigation. So scientists from various countries have been drawingmuch attention on suppressing the near-field interference. Based on adaptive filtering andspatial matrix filtering, the paper researches on the near-field interference suppression. Andthe simulation shows that the methods are feasible and effective.The main contents of the paper are showed as follows:First, three kinds of classic DOA estimation method, based on conventional beamformer,MVDR beamformer and MUSIC algorithm, are studied and their performances are compared;in accordance with the practical applications of the line array, strong interference in near-fieldis add as a simulation condition into MUSIC algorithm, resulting in performance affectedseverely, which indicates the necessity of suppressing strong interference in near field.Secondly, near-field interference suppression technology using adaptive filtering isstudied. Adaptive interference cancellation is used. The basic principle of the adaptive filterbased on LMS algorithm and underwater acoustic image measurement is studied. Theresearch on acoustic suppression applies adaptive interference cancellation when thereference signal are extracted from the result of the underwater acoustic image measurement,and simulation indicates its validity of interference cancellation in near-field. Referencesignal is not pure enough as it contains information from other sources, and with the offsettargets and iteration times increase, cancellation performance declines rapidly. Data targetsget more distortion in adaptive cancellation, which will affect the target detection as a result.Finally, because the “pure” reference signal of adaptive filtering is hard to obtain and thedistortional data, the near-field interference suppression technology based on spatial matrixfiltering is studied. The basic principles of the spatial matrix filtering and three standardswhich are used to design the spatial matrix filter are studied. The simulation results show thatthe effect of the near-field interference suppression is good. This technique will attenuatesignals in far-field, sharing the same azimuth with the near-field interference sources, whilewell suppressing near-field interference, leading to lessen filter’s capability of detecting far-filed signal under the same azimuth.