3,353 research outputs found
Space Time MUSIC: Consistent Signal Subspace Estimation for Wide-band Sensor Arrays
Wide-band Direction of Arrival (DOA) estimation with sensor arrays is an
essential task in sonar, radar, acoustics, biomedical and multimedia
applications. Many state of the art wide-band DOA estimators coherently process
frequency binned array outputs by approximate Maximum Likelihood, Weighted
Subspace Fitting or focusing techniques. This paper shows that bin signals
obtained by filter-bank approaches do not obey the finite rank narrow-band
array model, because spectral leakage and the change of the array response with
frequency within the bin create \emph{ghost sources} dependent on the
particular realization of the source process. Therefore, existing DOA
estimators based on binning cannot claim consistency even with the perfect
knowledge of the array response. In this work, a more realistic array model
with a finite length of the sensor impulse responses is assumed, which still
has finite rank under a space-time formulation. It is shown that signal
subspaces at arbitrary frequencies can be consistently recovered under mild
conditions by applying MUSIC-type (ST-MUSIC) estimators to the dominant
eigenvectors of the wide-band space-time sensor cross-correlation matrix. A
novel Maximum Likelihood based ST-MUSIC subspace estimate is developed in order
to recover consistency. The number of sources active at each frequency are
estimated by Information Theoretic Criteria. The sample ST-MUSIC subspaces can
be fed to any subspace fitting DOA estimator at single or multiple frequencies.
Simulations confirm that the new technique clearly outperforms binning
approaches at sufficiently high signal to noise ratio, when model mismatches
exceed the noise floor.Comment: 15 pages, 10 figures. Accepted in a revised form by the IEEE Trans.
on Signal Processing on 12 February 1918. @IEEE201
Signal Processing and Propagation for Aeroacoustic Sensor Networking,â Ch
Passive sensing of acoustic sources is attractive in many respects, including the relatively low signal bandwidth of sound waves, the loudness of most sources of interest, and the inherent difficulty of disguising or concealing emitted acoustic signals. The availability of inexpensive, low-power sensing and signal-processing hardware enables application of sophisticated real-time signal processing. Among th
Sparsity-Cognizant Total Least-Squares for Perturbed Compressive Sampling
Solving linear regression problems based on the total least-squares (TLS)
criterion has well-documented merits in various applications, where
perturbations appear both in the data vector as well as in the regression
matrix. However, existing TLS approaches do not account for sparsity possibly
present in the unknown vector of regression coefficients. On the other hand,
sparsity is the key attribute exploited by modern compressive sampling and
variable selection approaches to linear regression, which include noise in the
data, but do not account for perturbations in the regression matrix. The
present paper fills this gap by formulating and solving TLS optimization
problems under sparsity constraints. Near-optimum and reduced-complexity
suboptimum sparse (S-) TLS algorithms are developed to address the perturbed
compressive sampling (and the related dictionary learning) challenge, when
there is a mismatch between the true and adopted bases over which the unknown
vector is sparse. The novel S-TLS schemes also allow for perturbations in the
regression matrix of the least-absolute selection and shrinkage selection
operator (Lasso), and endow TLS approaches with ability to cope with sparse,
under-determined "errors-in-variables" models. Interesting generalizations can
further exploit prior knowledge on the perturbations to obtain novel weighted
and structured S-TLS solvers. Analysis and simulations demonstrate the
practical impact of S-TLS in calibrating the mismatch effects of contemporary
grid-based approaches to cognitive radio sensing, and robust
direction-of-arrival estimation using antenna arrays.Comment: 30 pages, 10 figures, submitted to IEEE Transactions on Signal
Processin
Sensor array signal processing : two decades later
Caption title.Includes bibliographical references (p. 55-65).Supported by Army Research Office. DAAL03-92-G-115 Supported by the Air Force Office of Scientific Research. F49620-92-J-2002 Supported by the National Science Foundation. MIP-9015281 Supported by the ONR. N00014-91-J-1967 Supported by the AFOSR. F49620-93-1-0102Hamid Krim, Mats Viberg
Multichannel interference mitigation methods in radio astronomy
Radio-astronomical observations are increasingly corrupted by RF
interference, and online detection and filtering algorithms are becoming
essential. To facilitate the introduction of such techniques into radio
astronomy, we formulate the astronomical problem in an array signal processing
language, and give an introduction to some elementary algorithms from that
field. We consider two topics in detail: interference detection by rank
estimation of short-term covariance matrices, and spatial filtering by subspace
estimation and projection. We discuss experimental data collected at the
Westerbork radio telescope, and illustrate the effectiveness of the space-time
detection and blanking process on the recovery of a 3C48 absorption line in the
presence of GSM mobile telephony interference.Comment: 39 pages, 18 figures.Enhanced figures can be downloaded from
http://cas.et.tudelft.nl/~leshem/postscripts/leshem/figs34567.ps.gz To appear
in Astrophysical Journal Supplements serie
Signal direction-of-arrival and amplitude estimation for multiple-row bathymetric sidescan sonars
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1998In practical applications with bathymetric sidescan sonars, the multipath reflections and
other directional interferences are the key limiting factors for a better performance. This
thesis proposes a new scheme to deal with the interferences using a multiple-row bathymetric sidescan sonar. Instead of smoothing the measurements over some time or angle
intervals, which was previously widely investigated, we resolve the multipath interferences from the direct signal. Two approaches on signal direction-of-arrival DOA and
amplitude estimation are developed, the correlated signal direction estimate CSDE for
three-row systems and the ESPRIT-based method. These approaches are compared using
different sonar data models, including a stochastic model from the statistical analysis on
bottom scattering and a coherent model from the analysis on interference field; the simulations show the ESPRIT-based approach is quite robust at the angular separation of 100
between two sources and at the signal-to-noise ratio above 10dB except for highly coherent or temporally correlated signals, for which CSDE works very well. The computer simulation results and the discussions on practical algorithm implementation indicate the
proposed scheme can be applied to a real multiple-row bathymetric sidescan sonar. With
the capability to simultaneously resolve two or more directional signals, the new sonar
model should work better for a wider variety of practical situations in shallow water with
out significant increase of the system cost.Funding supporting my thesis research project was provided by the Office of Naval
Research ONR
Asymptotic optimal SINR performance bound for space-time beamforming
International audienceIn many detection applications, the main performance criterion is the signal to interference plus noise ratio (SINR). After linear filtering, the optimal SINR corresponds to the maximum value of a Rayleigh quotient, which can be interpreted as the largest generalized eigenvalue of two covariance matrices. Using an extension of Szegö's theorem for the generalized eigenvalues of Hermitian block Toeplitz matrices, an expression of the theoretical asymptotic optimal SINR w.r.t. the number of taps is derived for arbitrary arrays with a limited but arbitrary number of sensors and arbitrary spectra. This bound is interpreted as an optimal zero-bandwidth spatial SINR in some sense. Finally, the speed of convergence of the optimal wideband SINR for a limited number of taps is analyzed for several interference scenario
Space-time processing for wireless mobile communications
Intersymbol interference (ISI) and co-channel interference (CCI) are two major
obstacles to high speed data transmission in wireless cellular communications
systems. Unlike thermal noise, their effects cannot be removed by
increasing the signal power and are time-varying due to the relative motion
between the transmitters and receivers. Space-time processing offers a signal
processing framework to optimally integrate the spatial and temporal properties
of the signal for maximal signal reception and at the same time, mitigate
the ISI and CCI impairments. In this thesis, we focus on the development of
this emerging technology to combat the undesirable effects of ISI and CCL
We first develop a convenient mathematical model to parameterize the
space-time multipath channel based on signal path power, directions and
times of arrival. Starting from the continuous time-domain, we derive compact
expressions of the vector space-time channel model that lead to the
notion of block space-time manifold, Under certain identifiability conditions,
the noiseless vector-channel outputs will lie on a subspace constructed from
a set. of basis belonging to the block space-time manifold. This is an important
observation as many high resolution array processing algorithms Can be
applied directly to estimate the multi path channel parameters.
Next we focus on the development of semi-blind channel identification
and equalization algorithms for fast time-varying multi path channels. Specifically.
we develop space-time processing algorithms for wireless TDMA networks that use short burst data formats with extremely short training data.
sequences. Due to the latter, the estimated channel parameters are extremely
unreliable for equalization with conventional adaptive methods. We approach
the channel acquisition, tracking and equalization problems jointly, and exploit
the richness of the inherent structural relationship between the channel
parameters and the data sequence by repeated use of available data through a forward- backward optimization procedure. This enables the fuller exploitation
of the available data. Our simulation studies show that significant performance
gains are achieved over conventional methods.
In the final part of this thesis, we address the problem identifying and
equalizing multi path communication channels in the presence of strong CCl.
By considering CCI as stochasic processes, we find that temporal diversity
can be gained by observing the channel outputs from a tapped delay line. Together with the assertion that the finite alphabet property of the information
sequences can offer additional information about the channel parameters and
the noise-plus-covariance matrix, we develop a spatial temporal algorithm,
iterative reweighting alternating minimization, to estimate the channel parameters
and information sequence in a weighted least squares framework.
The proposed algorithm is robust as it does not require knowledge of the
number of CCI nor their structural information. Simulation studies demonstrate
its efficacy over many reported methods
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