13,725 research outputs found
Simultaneous Orthogonal Matching Pursuit With Noise Stabilization: Theoretical Analysis
This paper studies the joint support recovery of similar sparse vectors on
the basis of a limited number of noisy linear measurements, i.e., in a multiple
measurement vector (MMV) model. The additive noise signals on each measurement
vector are assumed to be Gaussian and to exhibit different variances. The
simultaneous orthogonal matching pursuit (SOMP) algorithm is generalized to
weight the impact of each measurement vector on the choice of the atoms to be
picked according to their noise levels. The new algorithm is referred to as
SOMP-NS where NS stands for noise stabilization. To begin with, a theoretical
framework to analyze the performance of the proposed algorithm is developed.
This framework is then used to build conservative lower bounds on the
probability of partial or full joint support recovery. Numerical simulations
show that the proposed algorithm outperforms SOMP and that the theoretical
lower bound provides a great insight into how SOMP-NS behaves when the
weighting strategy is modified
Compressed Anomaly Detection with Multiple Mixed Observations
We consider a collection of independent random variables that are identically
distributed, except for a small subset which follows a different, anomalous
distribution. We study the problem of detecting which random variables in the
collection are governed by the anomalous distribution. Recent work proposes to
solve this problem by conducting hypothesis tests based on mixed observations
(e.g. linear combinations) of the random variables. Recognizing the connection
between taking mixed observations and compressed sensing, we view the problem
as recovering the "support" (index set) of the anomalous random variables from
multiple measurement vectors (MMVs). Many algorithms have been developed for
recovering jointly sparse signals and their support from MMVs. We establish the
theoretical and empirical effectiveness of these algorithms at detecting
anomalies. We also extend the LASSO algorithm to an MMV version for our
purpose. Further, we perform experiments on synthetic data, consisting of
samples from the random variables, to explore the trade-off between the number
of mixed observations per sample and the number of samples required to detect
anomalies.Comment: 27 pages, 9 figures. Incorporates reviewer feedback, additional
experiments, and additional figure
Learning linear structural equation models in polynomial time and sample complexity
The problem of learning structural equation models (SEMs) from data is a
fundamental problem in causal inference. We develop a new algorithm --- which
is computationally and statistically efficient and works in the
high-dimensional regime --- for learning linear SEMs from purely observational
data with arbitrary noise distribution. We consider three aspects of the
problem: identifiability, computational efficiency, and statistical efficiency.
We show that when data is generated from a linear SEM over nodes and
maximum degree , our algorithm recovers the directed acyclic graph (DAG)
structure of the SEM under an identifiability condition that is more general
than those considered in the literature, and without faithfulness assumptions.
In the population setting, our algorithm recovers the DAG structure in
operations. In the finite sample setting, if the
estimated precision matrix is sparse, our algorithm has a smoothed complexity
of , while if the estimated precision
matrix is dense, our algorithm has a smoothed complexity of
. For sub-Gaussian noise, we show that our
algorithm has a sample complexity of to achieve element-wise additive
error with respect to the true autoregression matrix with probability at most
, while for noise with bounded -th moment, with being a
positive integer, our algorithm has a sample complexity of
Dynamic Filtering of Time-Varying Sparse Signals via l1 Minimization
Despite the importance of sparsity signal models and the increasing
prevalence of high-dimensional streaming data, there are relatively few
algorithms for dynamic filtering of time-varying sparse signals. Of the
existing algorithms, fewer still provide strong performance guarantees. This
paper examines two algorithms for dynamic filtering of sparse signals that are
based on efficient l1 optimization methods. We first present an analysis for
one simple algorithm (BPDN-DF) that works well when the system dynamics are
known exactly. We then introduce a novel second algorithm (RWL1-DF) that is
more computationally complex than BPDN-DF but performs better in practice,
especially in the case where the system dynamics model is inaccurate.
Robustness to model inaccuracy is achieved by using a hierarchical
probabilistic data model and propagating higher-order statistics from the
previous estimate (akin to Kalman filtering) in the sparse inference process.
We demonstrate the properties of these algorithms on both simulated data as
well as natural video sequences. Taken together, the algorithms presented in
this paper represent the first strong performance analysis of dynamic filtering
algorithms for time-varying sparse signals as well as state-of-the-art
performance in this emerging application.Comment: 26 pages, 8 figures. arXiv admin note: substantial text overlap with
arXiv:1208.032
Theoretical Bounds on MAP Estimation in Distributed Sensing Networks
The typical approach for recovery of spatially correlated signals is
regularized least squares with a coupled regularization term. In the Bayesian
framework, this algorithm is seen as a maximum-a-posterior estimator whose
postulated prior is proportional to the regularization term. In this paper, we
study distributed sensing networks in which a set of spatially correlated
signals are measured individually at separate terminals, but recovered jointly
via a generic maximum-a-posterior estimator. Using the replica method, it is
shown that the setting exhibits the decoupling property. For the case with
jointly sparse signals, we invoke Bayesian inference and propose the
"multi-dimensional soft thresholding" algorithm which is posed as a linear
programming. Our investigations depict that the proposed algorithm outperforms
the conventional -norm regularized least squares scheme while
enjoying a feasible computational complexity.Comment: 5 pages, 3 figures; To be presented at 2018 IEEE International
Symposium on Information Theory (ISIT
Sparse source travel-time tomography of a laboratory target: accuracy and robustness of anomaly detection
This study concerned conebeam travel-time tomography. The focus was on a
sparse distribution of signal sources that can be necessary in a challenging in
situ environment such as in asteroid tomography. The goal was to approximate
the minimum number of source positions needed for robust detection of
refractive anomalies, e.g., voids within an asteroid or a casting defects in
concrete. Experimental ultrasonic data were recorded utilizing as a target a
150 mm plastic cast cube containing three stones with diameter between 22 and
41 mm. A signal frequency of 55 kHz (35 mm wavelength) was used. Source counts
from one to six were tested for different placements. Based on our statistical
inversion approach and analysis of the results, three or four sources were
found to lead to reliable inversion. The source configurations investigated
were also ranked according to their performance. Our results can be used, for
example, in the planning of planetary missions as well as in material testing.Comment: 19 pages, 9 figure
Channel Estimation and Hybrid Precoding for Distributed Phased Arrays Based MIMO Wireless Communications
Distributed phased arrays based multiple-input multiple-output (DPA-MIMO) is
a newly introduced architecture that enables both spatial multiplexing and
beamforming while facilitating highly reconfigurable hardware implementation in
millimeter-wave (mmWave) frequency bands. With a DPA-MIMO system, we focus on
channel state information (CSI) acquisition and hybrid precoding. As benefited
from a coordinated and open-loop pilot beam pattern design, all the sub-arrays
can perform channel sounding with less training overhead compared with the
traditional orthogonal operation of each sub-array. Furthermore, two sparse
channel recovery algorithms, known as joint orthogonal matching pursuit (JOMP)
and joint sparse Bayesian learning with reweighting (JSBL-),
are proposed to exploit the hidden structured sparsity in the beam-domain
channel vector. Finally, successive interference cancellation (SIC) based
hybrid precoding through sub-array grouping is illustrated for the DPA-MIMO
system, which decomposes the joint sub-array RF beamformer design into an
interactive per-sub-array-group handle. Simulation results show that the
proposed two channel estimators fully take advantage of the partial coupling
characteristic of DPA-MIMO channels to perform channel recovery, and the
proposed hybrid precoding algorithm is suitable for such array-of-sub-arrays
architecture with satisfactory performance and low complexity.Comment: accepted by IEEE Transactions on Vehicular Technolog
The Random Frequency Diverse Array: A New Antenna Structure for Uncoupled Direction-Range Indication in Active Sensing
In this paper, we propose a new type of array antenna, termed the Random
Frequency Diverse Array (RFDA), for an uncoupled indication of target direction
and range with low system complexity. In RFDA, each array element has a narrow
bandwidth and a randomly assigned carrier frequency. The beampattern of the
array is shown to be stochastic but thumbtack-like, and its stochastic
characteristics, such as the mean, variance, and asymptotic distribution are
derived analytically. Based on these two features, we propose two kinds of
algorithms for signal processing. One is matched filtering, due to the
beampattern's good characteristics. The other is compressive sensing, because
the new approach can be regarded as a sparse and random sampling of target
information in the spatial-frequency domain. Fundamental limits, such as the
Cram\'er-Rao bound and the observing matrix's mutual coherence, are provided as
performance guarantees of the new array structure. The features and
performances of RFDA are verified with numerical results.Comment: 13 pages, 10 figure
Recovering Model Structures from Large Low Rank and Sparse Covariance Matrix Estimation
Many popular statistical models, such as factor and random effects models,
give arise a certain type of covariance structures that is a summation of low
rank and sparse matrices. This paper introduces a penalized approximation
framework to recover such model structures from large covariance matrix
estimation. We propose an estimator based on minimizing a non-likelihood loss
with separable non-smooth penalty functions. This estimator is shown to recover
exactly the rank and sparsity patterns of these two components, and thus
partially recovers the model structures. Convergence rates under various matrix
norms are also presented. To compute this estimator, we further develop a
first-order iterative algorithm to solve a convex optimization problem that
contains separa- ble non-smooth functions, and the algorithm is shown to
produce a solution within O(1/t^2) of the optimal, after any finite t
iterations. Numerical performance is illustrated using simulated data and stock
portfolio selection on S&P 100.Comment: 35 pages, 3 figures. Presented at JSM 2011 and various invited
seminars since February, 2011. R package available from
http://cran.r-project.org/web/packages/lorec/index.htm
Exploiting Restricted Boltzmann Machines and Deep Belief Networks in Compressed Sensing
This paper proposes a CS scheme that exploits the representational power of
restricted Boltzmann machines and deep learning architectures to model the
prior distribution of the sparsity pattern of signals belonging to the same
class. The determined probability distribution is then used in a maximum a
posteriori (MAP) approach for the reconstruction. The parameters of the prior
distribution are learned from training data. The motivation behind this
approach is to model the higher-order statistical dependencies between the
coefficients of the sparse representation, with the final goal of improving the
reconstruction. The performance of the proposed method is validated on the
Berkeley Segmentation Dataset and the MNIST Database of handwritten digits.Comment: Accepted for publication at IEEE Transactions on Signal Processin
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