Abstract
Noise, interference, and echo present problems in the use of hands-free communication systems in cars. In this study a microphone system integrating various array signal processing technologies is developed to overcome these problems. The microphone array acts like a spatial filter so that both signal-to-noise ratio and directivity can be improved. In the system the method of steered-response power-phase transform, which is robust to reverberant environments, is employed to estimate the direction of arrival (DOA) of the incoming sound signal. Once the DOA is found, the main beam of the microphone array is steered electronically in that direction to receive the signals. In order to attain a sharp spatial resolution, a superdirective design is employed in beamforming. A low-pass filter is used in postprocessing the array output to enhance human speech. In addition the system copes with acoustic echo by using an adaptive filter based on the least-mean-squares method. All algorithms have been integrated and implemented on the platform of a digital signal processor. Experimental results demonstrate that the proposed system is effective in car hands-free applications.