Near-field beamformer design problems

Abstract

This thesis is concerned with the near-field beamformer design problems in reverberant environment and the microphone array placement design problems. Firstly, we study the influence of room acoustics on the design of broadband beamformer. We introduce the image source method to estimate the room impulse responses, and establish several optimization models for the broadband beamformer design. We also study the barrier beamformer design problem, and introduce the space-time conservation element and solution element method to estimate the corresponding barrier impulse responses. Secondly, we study the time-domain beamformer design problem in the reverberant environment. We formulate the beamformer design problem as a linear system, and convert it into the least squares problem, whereas it has large scale and bad condition in the reverberant environment. Thus we introduce the Tikhonov regularization technique to improve the condition of the original problem. Moreover, we analyze the effectiveness of beamformer design as the filter length increases. With considering the nondirectional background noise of speech enhancement, the indoor LCMV beamformer problem is studied in the next. We use the estimated room impulse responses to formulate the model of indoor LCMV beamformer design, then construct a relaxed optimization problem to solve the filter coeffcients approximately. Moreover, post-filtering technique combining with indoor LCMV beamformer is studied to further improve the speech quality, and it is found that the MSIG post-filter combining with indoor LCMV beamformer has the best performance. Then we study the microphone array placement design problem, and formulate a composite optimization model for it. With the help of infinite length technique, we convert the subproblem on the solving of filter coefficients into the performance limit estimation problem. Moreover, we develop a hybrid descent method with genetic algorithm to solve the problem of microphone array placement design, the descent method can find the best solution around the current placement, and the genetic technique can jump out from the local solution. Finally, we study the microphone array placement design problem in reverberant environment. We introduce the LCMV framework combining with the infinite length technique to evaluate the effectiveness of placement design. And we also introduce the hybrid descent method to find the optimal array placement design eventually.