Showing papers on "Adaptive beamformer published in 1974"
01 Nov 1974
TL;DR: In this paper, a frequency-domain adaptive array structure is derived that processes data in selected regions of frequency-wave number space to provide an MMSE estimate of a signal component of the observed acoustic field.
Abstract: In this paper a frequency-domain adaptive array structure is derived that processes data in selected regions of frequency-wave-number space to provide an MMSE estimate of a signal component of the observed acoustic field. The desired "optimal" processor structure is derived by appealing to the Sherman-Morrison inversion lemma to invert the sum of a diagonal noise matrix and several diadic matrices corresponding to plane-wave propagating signal and interference fields. The structure reduces to a parallel structure of beamformer-gain elements whose beamformer directions (phase delays) and gains are unknown because of a priori ignorance concerning interference directions and levels. The structure is adapted to these uncertainties by forming a stochastic approximation algorithm for the gains of several beams directed to a finite set of possible interference directions.
6 citations
31 Dec 1974
TL;DR: In this paper, the authors investigated the adaptive beamforming detection gain relative to beamsteering for unmixed long-period seismic events in the presence of background noise and for simulated mixed events where two data samples, each containing a signal, are summed to create a composite sample containing an interfering event.
Abstract: : This report presents time-domain maximum likelihood adaptive beamforming results for data from the Alaska Long-Period Array and the Korean Short-Period Array. Adaptive-beamforming detection gain relative to beamsteering is investigated for unmixed long-period seismic events in the presence of background noise and for simulated mixed events where two data samples, each containing a signal, are summed to create a composite sample containing an interfering event. In the adaptive beamforming studies for background noise, the performance of two different adaptive algorithms, the effect of using closely-spaced partial arrays instead of the full ALPA array, and the effect of different frequency filters applied to the input channels before array beamforming are examined. In the interfering-event analysis, the relative on-azimuth to off-azimuth event strength at which an on-azimuth event detection is possible determines the detection gain of adaptive multichannel filtering over time-shift-and-sum beamforming.
1 citations
01 May 1974
TL;DR: The proposed adaptive array beamformer is to be considered as a component which will be added to an existing radar system with minimal change in the overall configuration.
Abstract: : The proposed adaptive array beamformer is to be considered as a component which will be added to an existing radar system with minimal change in the overall configuration. Measurements were taken under conditions representative of the environment in which an HF system must operate. Specifically, one-hop backscatter signals generated by an FM/CW transmitter format were received in the presence of relatively high noise and interference levels. Adaptive beamforming techniques are ideally suited to these conditions and can provide time variable null-tracking of both the frequency and spatial direction of arrival of interference sources.