74 research outputs found
Compressive Source Separation: Theory and Methods for Hyperspectral Imaging
With the development of numbers of high resolution data acquisition systems
and the global requirement to lower the energy consumption, the development of
efficient sensing techniques becomes critical. Recently, Compressed Sampling
(CS) techniques, which exploit the sparsity of signals, have allowed to
reconstruct signal and images with less measurements than the traditional
Nyquist sensing approach. However, multichannel signals like Hyperspectral
images (HSI) have additional structures, like inter-channel correlations, that
are not taken into account in the classical CS scheme. In this paper we exploit
the linear mixture of sources model, that is the assumption that the
multichannel signal is composed of a linear combination of sources, each of
them having its own spectral signature, and propose new sampling schemes
exploiting this model to considerably decrease the number of measurements
needed for the acquisition and source separation. Moreover, we give theoretical
lower bounds on the number of measurements required to perform reconstruction
of both the multichannel signal and its sources. We also proposed optimization
algorithms and extensive experimentation on our target application which is
HSI, and show that our approach recovers HSI with far less measurements and
computational effort than traditional CS approaches.Comment: 32 page
Structured Sparsity Models for Multiparty Speech Recovery from Reverberant Recordings
We tackle the multi-party speech recovery problem through modeling the
acoustic of the reverberant chambers. Our approach exploits structured sparsity
models to perform room modeling and speech recovery. We propose a scheme for
characterizing the room acoustic from the unknown competing speech sources
relying on localization of the early images of the speakers by sparse
approximation of the spatial spectra of the virtual sources in a free-space
model. The images are then clustered exploiting the low-rank structure of the
spectro-temporal components belonging to each source. This enables us to
identify the early support of the room impulse response function and its unique
map to the room geometry. To further tackle the ambiguity of the reflection
ratios, we propose a novel formulation of the reverberation model and estimate
the absorption coefficients through a convex optimization exploiting joint
sparsity model formulated upon spatio-spectral sparsity of concurrent speech
representation. The acoustic parameters are then incorporated for separating
individual speech signals through either structured sparse recovery or inverse
filtering the acoustic channels. The experiments conducted on real data
recordings demonstrate the effectiveness of the proposed approach for
multi-party speech recovery and recognition.Comment: 31 page
Inexact Gradient Projection and Fast Data Driven Compressed Sensing
We study convergence of the iterative projected gradient (IPG) algorithm for
arbitrary (possibly nonconvex) sets and when both the gradient and projection
oracles are computed approximately. We consider different notions of
approximation of which we show that the Progressive Fixed Precision (PFP) and
the -optimal oracles can achieve the same accuracy as for the
exact IPG algorithm. We show that the former scheme is also able to maintain
the (linear) rate of convergence of the exact algorithm, under the same
embedding assumption. In contrast, the -approximate oracle
requires a stronger embedding condition, moderate compression ratios and it
typically slows down the convergence. We apply our results to accelerate
solving a class of data driven compressed sensing problems, where we replace
iterative exhaustive searches over large datasets by fast approximate nearest
neighbour search strategies based on the cover tree data structure. For
datasets with low intrinsic dimensions our proposed algorithm achieves a
complexity logarithmic in terms of the dataset population as opposed to the
linear complexity of a brute force search. By running several numerical
experiments we conclude similar observations as predicted by our theoretical
analysis
A temporal multiscale approach for MR Fingerprinting
Quantitative MRI (qMRI) is becoming increasingly important for research and
clinical applications, however, state-of-the-art reconstruction methods for
qMRI are computationally prohibitive. We propose a temporal multiscale approach
to reduce computation times in qMRI. Instead of computing exact gradients of
the qMRI likelihood, we propose a novel approximation relying on the temporal
smoothness of the data. These gradients are then used in a coarse-to-fine (C2F)
approach, for example using coordinate descent. The C2F approach was also found
to improve the accuracy of solutions, compared to similar methods where no
multiscaling was used.Comment: 4 pages, 3 figures. Title revise
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