Microphone Arrays from a MIMO Perspective.

As seen throughout the text, the major functionality of a microphone-array system is to reduce noise, thereby enhancing a desired information-bearing speech signal. The term noise, in general, refers to any unwanted signal that interferes with measurement, processing, and communication of the desired speech signal. This broad-sense definition of noise, however, is too encompassing as it masks many important technical aspects of the real problem. To enable better modeling and removal of the effects of noise in the context of microphone array processing, it is advantageous to break the general definition into the following three subcategories: additive noise originating from various ambient sound sources, interfering signals from concurrent competing sources, and reverberation caused by multipath propagation introduced by an enclosure. We have seen from the previous chapters that the use of a microphone array together with proper beamforming techniques can reduce the effect of additive noise. This chapter continues to explore beamforming techniques, with a focus on interference suppression and speech dereverberation. Different from the traditional way of treating beamforming as purely spatial filtering, this chapter studies the problem from a more physically meaningful multiple-input multiple-output (MIMO) signal processing perspective. A general framework based on the MIMO channel impulse responses will be developed. Under this framework, we study different algorithms including their underlying principles and intrinsic connections. [ABSTRACT FROM AUTHOR]