Carl-Inge Colombo Nilsen

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Applying the Capon adaptive beamformer in medical ultrasound imaging results in enhanced resolution by improving the interference-suppressing capabilities of the array. This improvement comes at the expense of an increased computational complexity. We have investigated the application of a beamspace adaptive beamformer for medical ultrasound imaging, which(More)
The coherence factor (CF) is used for aberration correction and sidelobe suppression in ultrasound imaging. Unfortunately, it suffers from artifacts when the SNR is low. We show how the CF can be interpreted as an implementation of the Wiener postfilter for a delay-and-sum beamformer. In addition, we show that a minimum-variance, distortionless-response(More)
In this paper we investigate the use of GPUs as digital beamformers. We specify a parallel implementation of a beamformer in time and frequency domain and measure its performance. We also give examples of the processing limits of NVIDIA Geforce 8800 GPU with respect to application parameters: number of sensors, sampling frequency, bandwidth, and number of(More)
We have analyzed a compact, digital delay- and-sum beamformer using 1-bit delta-sigma A/D converters, where dynamic delays are applied directly to the delta-sigma modulated bitstream. It has previously been shown that the introduction of this time-variant operation into the time-invariant delta-sigma demodulator distorts the output signal, and several(More)
Spherical microphone arrays are suited for phase mode processing, which complements spatio-temporal processing and often simplifies both the understanding and development of different beamforming techniques. Since a spherical geometry cannot benefit directly from methods specially developed for uniform linear arrays, the weight and algorithm design for(More)
To reduce the variance of speckle in coherent imaging systems, one must average images with different speckle realizations. Traditionally, these images have been formed by observing the target region from slightly different angles (spatial compounding) or by varying the involved temporal frequencies (frequency compounding). In this paper, we investigate a(More)
Correlated signals lead to signal cancellation in adaptive beamformers applied to microphone arrays. This is commonly counteracted by spatial smoothing. Unfortunately, spatial smoothing can only be used with array geometries consisting of identical, shifted subarrays, making it unsuitable for spherical arrays in general. We suggest a transformation that(More)
We present a beamspace realization of the generalized sidelobe canceller (GSC) applied to audio and speech capture, and show that it has some specific advantages compared to the standard GSC implementation for certain noise assumptions. Specifically, we demonstrate that for this application the herein proposed implementation is less prone to signal(More)
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