155 research outputs found
Measurements design and phenomena discrimination
The construction of measurements suitable for discriminating signal
components produced by phenomena of different types is considered. The required
measurements should be capable of cancelling out those signal components which
are to be ignored when focusing on a phenomenon of interest. Under the
hypothesis that the subspaces hosting the signal components produced by each
phenomenon are complementary, their discrimination is accomplished by
measurements giving rise to the appropriate oblique projector operator. The
subspace onto which the operator should project is selected by nonlinear
techniques in line with adaptive pursuit strategies
A Greedy Sparse Method Suitable for Spectral-Line Estimation
Rapport interne de GIPSA-labThis letter presents a variant of Matching Pursuit (MP) method for compressive sensing and sparse signal reconstruction. As an extension of MP, the proposed algorithm incorporates a new backward technique to maintain or replace the previous selected atoms in the case of coherent dictionaries. Computer simulations using Fourier dictionaries are conducted to show the effectiveness of the proposed method compared to some other sparse approximation methods
Sparse Representation of Astronomical Images
Sparse representation of astronomical images is discussed. It is shown that a
significant gain in sparsity is achieved when particular mixed dictionaries are
used for approximating these types of images with greedy selection strategies.
Experiments are conducted to confirm: i)Effectiveness at producing sparse
representations. ii)Competitiveness, with respect to the time required to
process large images.The latter is a consequence of the suitability of the
proposed dictionaries for approximating images in partitions of small
blocks.This feature makes it possible to apply the effective greedy selection
technique Orthogonal Matching Pursuit, up to some block size. For blocks
exceeding that size a refinement of the original Matching Pursuit approach is
considered. The resulting method is termed Self Projected Matching Pursuit,
because is shown to be effective for implementing, via Matching Pursuit itself,
the optional back-projection intermediate steps in that approach.Comment: Software to implement the approach is available on
http://www.nonlinear-approx.info/examples/node1.htm
Sparse Representations & Compressed Sensing with application to the problem of Direction-of-Arrival estimation.
PhDThe significance of sparse representations has been highlighted in numerous signal processing
applications ranging from denoising to source separation and the emerging field
of compressed sensing has provided new theoretical insights into the problem of inverse
systems with sparsity constraints.
In this thesis, these advances are exploited in order to tackle the problem of direction-of-arrival (DOA) estimation in sensor arrays. Assuming spatial sparsity e.g. few sources
impinging on the array, the problem of DOA estimation is formulated as a sparse representation
problem in an overcomplete basis. The resulting inverse problem can be solved
using typical sparse recovery methods based on convex optimization i.e. `1 minimization.
However, in this work a suite of novel sparse recovery algorithms is initially developed,
which reduce the computational cost and yield approximate solutions. Moreover, the
proposed algorithms of Polytope Faces Pursuits (PFP) allow for the induction of structured
sparsity models on the signal of interest, which can be quite beneficial when dealing
with multi-channel data acquired by sensor arrays, as it further reduces the complexity
and provides performance gain under certain conditions.
Regarding the DOA estimation problem, experimental results demonstrate that the
proposed methods outperform popular subspace based methods such as the multiple
signal classification (MUSIC) algorithm in the case of rank-deficient data (e.g. presence
of highly correlated sources or limited amount of data) for both narrowband and wideband
sources. In the wideband scenario, they can also suppress the undesirable effects of spatial
aliasing.
However, DOA estimation with sparsity constraints has its limitations. The compressed
sensing requirement of incoherent dictionaries for robust recovery sets limits to
the resolution capabilities of the proposed method. On the other hand, the unknown
parameters are continuous and therefore if the true DOAs do not belong to the predefined discrete set of potential locations the algorithms' performance will degrade due to
errors caused by mismatches. To overcome this limitation, an iterative alternating descent
algorithm for the problem of off-grid DOA estimation is proposed that alternates
between sparse recovery and dictionary update estimates. Simulations clearly illustrate
the performance gain of the algorithm over the conventional sparsity approach and other
existing off-grid DOA estimation algorithms.EPSRC Leadership Fellowship EP/G007144/1; EU FET-Open Project FP7-ICT-225913
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