11,933 research outputs found
Signal representation for compression and noise reduction through frame-based wavelets
Published versio
Reproducing formulas for generalized translation invariant systems on locally compact abelian groups
In this paper we connect the well established discrete frame theory of
generalized shift invariant systems to a continuous frame theory. To do so, we
let , , be a countable family of closed, co-compact
subgroups of a second countable locally compact abelian group and study
systems of the form with generators in and with each
being a countable or an uncountable index set. We refer to systems of this form
as generalized translation invariant (GTI) systems. Many of the familiar
transforms, e.g., the wavelet, shearlet and Gabor transform, both their
discrete and continuous variants, are GTI systems. Under a technical
local integrability condition (-LIC) we characterize when GTI systems
constitute tight and dual frames that yield reproducing formulas for .
This generalizes results on generalized shift invariant systems, where each
is assumed to be countable and each is a uniform lattice in
, to the case of uncountably many generators and (not necessarily discrete)
closed, co-compact subgroups. Furthermore, even in the case of uniform lattices
, our characterizations improve known results since the class of GTI
systems satisfying the -LIC is strictly larger than the class of GTI
systems satisfying the previously used local integrability condition. As an
application of our characterization results, we obtain new characterizations of
translation invariant continuous frames and Gabor frames for . In
addition, we will see that the admissibility conditions for the continuous and
discrete wavelet and Gabor transform in are special cases
of the same general characterizing equations.Comment: Minor changes (v2). To appear in Trans. Amer. Math. So
Explicit constructions and properties of generalized shift-invariant systems in
Generalized shift-invariant (GSI) systems, originally introduced by
Hern\'andez, Labate & Weiss and Ron & Shen, provide a common frame work for
analysis of Gabor systems, wavelet systems, wave packet systems, and other
types of structured function systems. In this paper we analyze three important
aspects of such systems. First, in contrast to the known cases of Gabor frames
and wavelet frames, we show that for a GSI system forming a frame, the
Calder\'on sum is not necessarily bounded by the lower frame bound. We identify
a technical condition implying that the Calder\'on sum is bounded by the lower
frame bound and show that under a weak assumption the condition is equivalent
with the local integrability condition introduced by Hern\'andez et al. Second,
we provide explicit and general constructions of frames and dual pairs of
frames having the GSI-structure. In particular, the setup applies to wave
packet systems and in contrast to the constructions in the literature, these
constructions are not based on characteristic functions in the Fourier domain.
Third, our results provide insight into the local integrability condition
(LIC).Comment: Adv. Comput. Math., to appea
Geometric Aspects of Frame Representations of Abelian Groups
We consider frames arising from the action of a unitary representation of a
discrete countable abelian group. We show that the range of the analysis
operator can be determined by computing which characters appear in the
representation. This allows one to compare the ranges of two such frames, which
is useful for determining similarity and also for multiplexing schemes. Our
results then partially extend to Bessel sequences arising from the action of
the group. We apply the results to sampling on bandlimited functions and to
wavelet and Weyl-Heisenberg frames. This yields a sufficient condition for two
sampling transforms to have orthogonal ranges, and two analysis operators for
wavelet and Weyl-Heisenberg frames to have orthogonal ranges. The sufficient
condition is easy to compute in terms of the periodization of the Fourier
transform of the frame generators.Comment: 20 pages; contact author: Eric Webe
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