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1 

Tracking and convergence of multichannel kalman filters for active noise control
The feedforward broadband active noise control problem can be formulated as a state estimation problem to achieve a faster rate of convergence than the filtered reference least mean squares algorithm and possibly also a better tracking performance. A multiple input/multiple output Kalman algorithm is used to perform this state estimation. To make the algorithm more suitable for real Time applications the Kalman filter is written in a fast array form and the secondary path state matrices are implemented in output normal form. The implementation was tested in simulations and in real Time experiments. It was found that for a constant primary path the Kalman filter has a fast rate of convergence and is able to track changes in the spectrum. For a forgetting factor equal to unity the system is robust, but the filter is unable to track rapid changes in the primary path. It is shown that a forgetting factor lower than unity gives a significantly improved tracking performance. Numerical issues of the fast array form of the algorithm for such forgetting factors are discussed and possible solutions are presented. Copyright © (2013) by Austrian Noise Abatement Association (OAL). Organisation: International Institute of Noise Control Engineering (IINCE)

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2 

A liquidindependent volume flow measurement principle
A novel flow measurement principle is presented enabling nonintrusive volume flow measurements of liquids in the ml/min range. It is based on an optoacoustical timeofflight principle, where the time interval is recorded in which a thermal label travels a known distance through a flow channel. Big advantages are the insensitivity to temperature drift and the fact that user calibration is unnecessary. The paper presents a set of physicsbased criteria that define the working range of the measurement principle. A prototype of a flow meter was developed and evaluated in a test rig with flows of water, isopropyl alcohol (IPA) and mixtures of both liquids. Pure water and IPA flows of 0.1 to 2 ml min<sup>1</sup> were measured and found to coincide with the reference flows within 4%. The rootmeansquare (RMS) value of the fluctuations did not exceed 3%. For flows of 2 ml min<sup>1</sup> the limited power of the laser source caused deviations of 7% with 5% fluctuations. Finally, flow measurements were done in waterIPA mixtures with concentrations between 10% and 90%w/w at a flow rate of 15 g h<sup>1</sup> (≈0.3 ml min<sup>1</sup>). The ratio of measured and reference flow appeared to be 4% to 5% below the theoretical value, but it was hardly a function of mixture composition. Hence, liquid independence of the measurement principle was proven. © 2010 IOP Publishing Ltd.

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3 

A discretetime channel simulator driven by measured scattering functions
Insitu measurements of the scattering function are used to drive a channel simulator developed in the context of underwater acoustic telemetry. Two operation modes of the simulator are evaluated. A replay mode is accomplished by interpolation of measured impulse responses. A second, stochastic mode delivers multiple realizations of a given scattering function. The initial assumption of widesense stationary uncorrelated scattering is violated by strong phase correlations between taps. It is shown that timevarying Doppler shifts due to platform motion must be eliminated from measured scattering functions in order to provide the stochastic tap gains with the true Doppler spectrum of the channel. The simulator is validated through a comparison of acoustic data measured at sea, and emulated data, governed by the same scattering function. This comparison is based on scattering and coherence functions, multipath phase measurements, and application of a decisionfeedback equalizer. After the Doppler correction, the synthetic data are indistinguishable from the acoustic data in terms of delayDoppler spread, temporal coherence, phase behavior, equalizer mean square error, and bit error ratio.

[Abstract]

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