Adaptive beamformer

About: Adaptive beamformer is a research topic. Over the lifetime, 4934 publications have been published within this topic receiving 93100 citations.

Maximally Robust Capon Beamformer

Abstract: The standard Capon beamformer (SCB) achieves the maximum output signal-to-interference-plus-noise ratio in the error-free case. However, estimation errors of the signal steering vector and the array covariance matrix can result in severe performance deteriorations of the SCB, especially if the training data contains the desired signal component. A popular technique to improve the robustness against model errors is to compute the Capon beamformer with the maximum output power, considering an uncertainty set for the signal steering vector. However, maximizing the total beamformer output power may result in an insufficient suppression of interferers and noise. As an alternative approach to mitigate the detrimental effect of model errors, we propose to compute the Capon beamformer with the minimum sensitivity, considering the uncertainty set for the signal steering vector. The proposed maximally robust Capon beamformer (MRCB) is at least as robust as the maximum output power Capon beamformer with the same uncertainty set for the signal steering vector. We show that the MRCB can be implemented efficiently using Lagrange duality. Simulation results demonstrate that the MRCB outperforms state-of-the-art robust adaptive beamformers in many scenarios.

Fully spatial wide-band beamforming using a rectangular array of planar monopoles

Abstract: This paper describes a spatial beamformer which by using a rectangular array antenna steers a beam in azimuth over a wide frequency band without frequency filters or tap-delay networks. The weighting coefficients are real numbers which can be realized by attenuators or amplifiers. A prototype including a 4/spl times/4 array of square planar monopoles and a feeding network composed of attenuators, power divider/combiners and a rat-race hybrid is developed to test the validity of this wide-band beamforming concept. The experimental results prove the validity of this wide-band spatial beamformer for small size arrays.

Multi-rate adaptive beamforming (MRABF)

Abstract: An important trend in underwater acoustics is the use of large arrays with many elements and small resolution cells in an effort to detect weak signals. Frequently, the background noise is dominated by multiple moving surface ships that act like discrete interferers. These interferers may move through many spatial resolution cells in the time required to obtain sufficient "snapshots" for covariance matrix estimation. The non-stationarity of the background limits the performance of adaptive algorithms. Reduced degree-of-freedom approaches that can track and rapidly null interferers before they move too far are of great interest. The paper presents a new class of algorithms in which a low-rank, dynamically changing interference sub-space is estimated and tracked using a short-term average. An orthogonal projection is then applied to the data to null components in the interference sub-space. A second stage of adaptive beamforming that uses a longer averaging time is then applied to the projected data. Unlike most sub-space approaches that work for strong signals, there is no requirement that the signal be contained in the interference sub-space. It is shown how multiple interferers moving rapidly across beams can be tracked and nulled to reveal the presence of a weak target not visible with conventional, adaptive, or usual sub-space methods. The effectiveness of multi-rate adaptive beamforming is illustrated by examples. It is shown that moving interferers are effectively nulled to allow detection of weak signals when other methods including MVDR, conventional, and signal subspace fail.

Acoustic scene analysis using estimated impulse responses

Abstract: Pre-processing for hearing aids, such as adaptive beamforming, is sensitive to characteristics of the acoustic environment, in particular, reverberation. We conjecture that knowledge of the acoustic environment can aid selection of an optimal signal processing strategy. In this paper we present a method for estimation of direct-to-reverberant energy ratio from partial room responses to an impulsive sound at one receiver location, and of source distance, average absorption, reverberation time, and room volume as intermediate results.

Effects of motion on adaptive arrays

Abstract: Adaptive beamforming procedures based on linear least-squares estimation of a wanted signal, such as the sample matrix inverse (SMI) algorithm, have been shown to successfully excise unwanted interference from the beamformer output. It is usually assumed that the signal environment is stationary, however under nonstationary conditions, such as those experienced by an array mounted on a rapidly moving platform, performance may be significantly degraded. The paper examines the effects of array motion on the structure of the sample covariance matrix and derives expressions for the resulting eigenvalues. These results are used to show that even when the same data is used both to compute the adaptive weights and to form the beamformer output, performance can be sensitive to extremely small movements of the array. In particular, simple closed-form expressions are derived for the limiting angular displacements of linear arrays which can be tolerated without significant performance degradation during the time taken to acquire sufficient data to update the weights.