| Passive sonar plays an important role in the military and civilian sectors by passively receiving acoustic signals in the water to obtain valuable information.Due to the complexity and variability of the marine environment,the target signal is often subject to environmental and human interference,which seriously undermines the quality of the sonar reception signal and makes it difficult to effectively extract useful information.Therefore,the study of anti-jamming technology is an important topic in the field of passive sonar signal processing,which is of great significance for achieving reliable underwater communication and effective target identification.This paper is dedicated to the research of spatial adaptive anti-interference technology for broadband signals,focusing on the stability of spatial broadband adaptive beamforming antiinterference performance,the spatial adaptive anti-interference problem under the sample length of SMS and the spatial adaptive anti-interference problem under the multipath coherent and noncoherent mixed signals.The main work is as follows:1.To address the problem that the immunity performance of frequency-domain constrained space-time broadband beamforming(FCSTBB)depends on the array phase center reference point.a method for solving the optimal array phase center reference point of FCSTBB based on uniform line array is proposed.First,the dependence of the beam response of the FCSTBB on the array phase center reference point is demonstrated by theoretical derivation and simulation examples.Second,a criterion for the selection of the optimal array phase center reference point is given:minimizing the static output power.Then,a closed-form solution for the location of the optimal array phase center reference point of FCSTBB when the constraint matrix contains two preselected points is derived based on the proposed selection criterion under the uniform line array condition.Finally,for the case when the constraint matrix contains any preselected points,the suboptimal solution of the optimal array phase center location of FCSTBB is derived analytically on the basis of the closed-form solution.The numerical simulation results show that the suboptimal solution results in the narrowest main lobe width and lowest secondary lobe level for the FCSTBB beam response,and improves the interference zero-trap depth and the output signal interference noise ratio(SINR).2.To address the problem that the performance of air-frequency anti-interference method degrades when the signal sample is small,a broadband signal anti-interference processing method applicable to the sample length of SMS number is proposed.The method first combines the frequency derivative constraint and space-time minimum variance distortionless response(FDCSTMVDR)algorithm to estimate the target signal direction,and then the FCSTBB algorithm is then used to achieve anti-jamming reception based on the direction of the target signal.The frequency optimization capability of the space-time processing method can suppress the "leakage" of the spectral energy under the short signal samples and improve the angular resolution of the anti-interference processing method in the angular estimation and the nulling performance in the beam formation,but it also leads to a high frequency sweep density when the STMVDR algorithm estimates the target signal direction.To this end,the introduction of frequency derivative constraint to widen the frequency response main flap of STMVDR can effectively reduce the frequency sweep density of the algorithm while maintaining the angular resolution and estimation accuracy of the algorithm.Numerical simulation results show that the FDC-STMVDR algorithm effectively reduces the running time by 90% compared to that of STMVDR alone,and there is no significant loss of angular resolution and estimation accuracy of the algorithm.When oriented to the sample length of SMS number,the proposed method has better angular resolution than similar nullfrequency anti-interference methods,and can obtain higher output SINR under strong interference conditions.3.Aiming at the problem that the expected signal of adaptive beamformer is cancelled by multipath coherent interference in the scene of multipath coherent and incoherent mixed signals,a space-time adaptive anti-jamming method suitable for multipath coherent and incoherent mixed signals is proposed.Firstly,based on the theory of frequency domain construction of space-time covariance matrix,space smoothing(SS)technology and Rotational Signal-Subspace(RSS)frequency focusing technology are used to preprocess the space-time covariance matrix,and then SS-RSS-STMVDR beamforming algorithm is proposed in combination with STM VDR criterion.Secondly,the angle-frequency two-dimensional power spectrum of array signals is obtained based on SS-RSS-STMVDR algorithm,and then whether it is multipath coherent interference is judged according to Pearson correlation coefficient of frequency spectrum sequence between interference signal and expected signal,so as to obtain the angle of multipath coherent interference;Finally,based on FCSTBB structure,zero constraint is set in the direction of multipath interference,and unity gain constraint is set in the expected direction to realize anti-jamming reception of signals.Numerical simulation results show that the proposed method can effectively suppress multipath coherent signal cancellation under the condition of multipath coherent and incoherent mixed signals,and at the same time adaptively suppress incoherent interference.Aiming at the problem that the expected signal of adaptive beamformer is cancelled by multipath coherent interference in the scene of multipath coherent and incoherent mixed signals,a space-time adaptive anti-jamming method suitable for multipath coherent and incoherent mixed signals is proposed.Firstly,based on the theory of frequency domain construction of space-time covariance matrix,space smoothing(SS)technology and Rotational Signal-Subspace,RSS)frequency focusing technology are used to preprocess the space-time covariance matrix,and then SS-RSS-STMVDR beamforming algorithm is proposed in combination with STM VDR criterion.Secondly,the angle-frequency twodimensional power spectrum of array signals is obtained based on SS-RSS-STMVDR algorithm,and then whether it is multipath coherent interference is judged according to Pearson correlation coefficient of frequency spectrum sequence between interference signal and expected signal,so as to obtain the angle of multipath coherent interference;Finally,based on FCSTBB structure,zero constraint is set in the direction of multipath interference,and unity gain constraint is set in the expected direction to realize anti-jamming reception of signals.Numerical simulation results show that the proposed method can effectively suppress multipath coherent signal cancellation under the condition of multipath coherent and incoherent mixed signals,and at the same time adaptively suppress incoherent interference. |
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