583 research outputs found
Signal Recovery in Perturbed Fourier Compressed Sensing
In many applications in compressed sensing, the measurement matrix is a
Fourier matrix, i.e., it measures the Fourier transform of the underlying
signal at some specified `base' frequencies , where is the
number of measurements. However due to system calibration errors, the system
may measure the Fourier transform at frequencies
that are different from the base frequencies and where
are unknown. Ignoring perturbations of this nature can lead to major errors in
signal recovery. In this paper, we present a simple but effective alternating
minimization algorithm to recover the perturbations in the frequencies \emph{in
situ} with the signal, which we assume is sparse or compressible in some known
basis. In many cases, the perturbations can be expressed
in terms of a small number of unique parameters . We demonstrate that
in such cases, the method leads to excellent quality results that are several
times better than baseline algorithms (which are based on existing off-grid
methods in the recent literature on direction of arrival (DOA) estimation,
modified to suit the computational problem in this paper). Our results are also
robust to noise in the measurement values. We also provide theoretical results
for (1) the convergence of our algorithm, and (2) the uniqueness of its
solution under some restrictions.Comment: New theortical results about uniqueness and convergence now included.
More challenging experiments now include
Low-complexity Multiclass Encryption by Compressed Sensing
The idea that compressed sensing may be used to encrypt information from
unauthorised receivers has already been envisioned, but never explored in depth
since its security may seem compromised by the linearity of its encoding
process. In this paper we apply this simple encoding to define a general
private-key encryption scheme in which a transmitter distributes the same
encoded measurements to receivers of different classes, which are provided
partially corrupted encoding matrices and are thus allowed to decode the
acquired signal at provably different levels of recovery quality.
The security properties of this scheme are thoroughly analysed: firstly, the
properties of our multiclass encryption are theoretically investigated by
deriving performance bounds on the recovery quality attained by lower-class
receivers with respect to high-class ones. Then we perform a statistical
analysis of the measurements to show that, although not perfectly secure,
compressed sensing grants some level of security that comes at almost-zero cost
and thus may benefit resource-limited applications.
In addition to this we report some exemplary applications of multiclass
encryption by compressed sensing of speech signals, electrocardiographic tracks
and images, in which quality degradation is quantified as the impossibility of
some feature extraction algorithms to obtain sensitive information from
suitably degraded signal recoveries.Comment: IEEE Transactions on Signal Processing, accepted for publication.
Article in pres
Convex Optimization Approaches for Blind Sensor Calibration using Sparsity
We investigate a compressive sensing framework in which the sensors introduce
a distortion to the measurements in the form of unknown gains. We focus on
blind calibration, using measures performed on multiple unknown (but sparse)
signals and formulate the joint recovery of the gains and the sparse signals as
a convex optimization problem. We divide this problem in 3 subproblems with
different conditions on the gains, specifially (i) gains with different
amplitude and the same phase, (ii) gains with the same amplitude and different
phase and (iii) gains with different amplitude and phase. In order to solve the
first case, we propose an extension to the basis pursuit optimization which can
estimate the unknown gains along with the unknown sparse signals. For the
second case, we formulate a quadratic approach that eliminates the unknown
phase shifts and retrieves the unknown sparse signals. An alternative form of
this approach is also formulated to reduce complexity and memory requirements
and provide scalability with respect to the number of input signals. Finally
for the third case, we propose a formulation that combines the earlier two
approaches to solve the problem. The performance of the proposed algorithms is
investigated extensively through numerical simulations, which demonstrates that
simultaneous signal recovery and calibration is possible with convex methods
when sufficiently many (unknown, but sparse) calibrating signals are provided
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