Near-field Microphone Array Beamforming Method

Microphone array system has been widely used in sonar, medical, aerospace and many other fields. It mainly includes two core technologies: Sound Source Parameters Estimation and Beamforming. Most of microphone array processing approaches are based on far-field models. While it is reasonable to assume that plane-wave arrival at the array only when the distance between the array and target signal is approximately larger than 2 d 2/λ, where d is the largest array dimension, andλis the operating wavelength. However, the far-field assumption may not hold in practical applications such as speech acquisition with microphone arrays in small rooms or hands-free mobile telephone in automobiles. Consequently, there is a practical need for near-field microphone array processing methods. This thesis focuses on microphone array beamforming approaches which are based on near-field model, and hence the received wavefront from a signal soure is spherical.Firstly, Based on acoustic propagation model, this thesis concludes near-field spherical wavefront array response matrix, and contrast with far-field plane wavefront array response matrix. Near-field array response matrix array is a function of the direction and the distance, while far-field response matrix array is only a function of the direction. Compared to far-field, near-field microphone array signal processing is more complex. At last give out the array response matrix of near-field with specific array. Next, this paper researchs on near-field MUSIC algorithm using array spherical wavefront model. Then sound source azimuth, pitch angle and distance parameters can be obtained through searching for the peaks, and realize three-dimensional spatial sound source parameter estimation; Analysis of two delay estimation algorithm in the acoustic source location, and combine LMS with GCC delay estimation algorithm to enhance anti-jamming capability. Next, researching on beamforming methods of Near-field based on far-field beamforming algorithm, this paper concludes optimal rule of microphone array beamforming and adaptive beamforming algorithm in near-field circumstance. Realize near-field beamforing through the method using distance and azimuth compensation, and simulation results show that the method can form the desired signal beam in near-field. Meanwhile, for the spherical wave propagation model of near-field, the paper researchs on robust ADL-SMI algorithm and apply it in near-field point-constraint beamforming, also extends ESB-PCMV algorithm to realize near-field point-constraint beamforming, and enhance the robustness of the algorithm. At last, summarize the methods of far-field beamforming optimization. Base on this, Deduce the imposed interference algorithm and the auadratically constrained algorithm for near-field, and realize arbitrary microphone array beamforming optimization which contain direction pattern and space pattern.