On The Importance of Acoustic Reflections in Beamforming

Acoustic reflections are known to limit the capabilities of traditional beamformers (BFs), which are based on zero-order steering vector, to extract a desired source and to suppress interference signals from noisy measurements. To alleviate these performance limitations, echo-aware BFs that take into account the acoustic reflections of the source and interfering signals, were introduced more than two decades ago. In this paper,1 we propose a systematic methodology to analyze the performance of these BFs, highlighting the importance of the acoustic reflections in the BF design. Under this methodology, we redefine beampatterns to consider the entire reflection pattern, while the direction of arrivals (DOAs) of the sources are merely used as an indication of the positions of the sources that impinge the array from a circle around the microphone array. We further define measures of the quality of the BFs, namely the beampattern shape, the width of the main beam, the directivity, the null depth, and the signal-to-interference ratio (SIR) improvement. Using this methodology, we are able to clearly demonstrate the advantages of echo-aware BFs over traditional BFs that only consider the direct-arrival of the sources in their design.