64 research outputs found
A Review of the Frequency Estimation and Tracking Problems
This report presents a concise review of some frequency estimation and frequency tracking problems. In particular, the report focusses on aspects of these problems which have been addressed by members of the Frequency Tracking and Estimation project of the Centre for Robust and Adaptive Systems. The report is divided into four parts: problem specification and discussion, associated problems, frequency estimation algorithms and frequency tracking algorithms. Part I begins with a definition of the various frequency estimation and tracking problems. Practical examples of where each problem may arise are given. A comparison is made between the frequency estimation and tracking problems. In Part II, block frequency estimation algorithms, fast block frequency estimation algorithms and notch filtering techniques for frequency estimation are dealt with. Frequency tracking algorithms are examined in Part III. Part IV of this report examines various problems associated with frequency estimation. Associated problems include Cramer-Rao lower bounds, theoretical algorithm performance, frequency resolution, use of the analytic signal and model order selection
Rational invariant subspace approximations with applications
Includes bibliographical references.Subspace methods such as MUSIC, Minimum Norm, and ESPRIT have gained considerable attention due to their superior performance in sinusoidal and direction-of-arrival (DOA) estimation, but they are also known to be of high computational cost. In this paper, new fast algorithms for approximating signal and noise subspaces and that do not require exact eigendecomposition are presented. These algorithms approximate the required subspace using rational and power-like methods applied to the direct data or the sample covariance matrix. Several ESPRIT- as well as MUSIC-type methods are developed based on these approximations. A substantial computational saving can be gained comparing with those associated with the eigendecomposition-based methods. These methods are demonstrated to have performance comparable to that of MUSIC yet will require fewer computation to obtain the signal subspace matrix
A unified approach to sparse signal processing
A unified view of the area of sparse signal processing is presented in tutorial form by bringing together various fields in which the property of sparsity has been successfully exploited. For each of these fields, various algorithms and techniques, which have been developed to leverage sparsity, are described succinctly. The common potential benefits of significant reduction in sampling rate and processing manipulations through sparse signal processing are revealed. The key application domains of sparse signal processing are sampling, coding, spectral estimation, array processing, compo-nent analysis, and multipath channel estimation. In terms of the sampling process and reconstruction algorithms, linkages are made with random sampling, compressed sensing and rate of innovation. The redundancy introduced by channel coding i
Super-Resolution of Positive Sources: the Discrete Setup
In single-molecule microscopy it is necessary to locate with high precision
point sources from noisy observations of the spectrum of the signal at
frequencies capped by , which is just about the frequency of natural
light. This paper rigorously establishes that this super-resolution problem can
be solved via linear programming in a stable manner. We prove that the quality
of the reconstruction crucially depends on the Rayleigh regularity of the
support of the signal; that is, on the maximum number of sources that can occur
within a square of side length about . The theoretical performance
guarantee is complemented with a converse result showing that our simple convex
program convex is nearly optimal. Finally, numerical experiments illustrate our
methods.Comment: 31 page, 7 figure
High-resolution sonar DF system
One of the fundamental problems of sonar systems is the determination of the
bearings of underwater sources/targets. The classical solution to this problem,
the 'Conventional Beamformer', uses the outputs from the individual sensors of
an acoustic array to form a beam which is swept across the search sector. The
resolution of this method is limited by the beam width and narrowing this beam
to enhance the resolution may have some practical problems, especially in low
frequency sonar, because of the physical size of the array needed.
During the past two decades an enormous amount of work has been done to
develop new algorithms for resolution enhancements beyond that of the
Conventional Beamformer. However, most of these methods have been based
on computer simulations and very little has been published on the practical
implementation of these algorithms. One of the main reasons for this has been
the lack of hardware that can handle the relatively heavy computational load of
these algorithms. However, there have been great advances in semiconductor
and computer technologies in the last few years which have led to the availability
of more powerful computational and storage devices. These devices have
opened the door to the possibility of implementing these high-resolution Direction
Finding (DF) algorithms in real sonar systems.
The work presented in this thesis describes a practical implementation of some
of the high-resolution DF algorithms in a simple sonar system that has been
designed and built for this purpose. [Continues.
Study on a miniaturized satellite payload for atmospheric temperature measurements
The atmospheric temperature reflects the thermal balance of the atmosphere and is a
valuable indicator of climate change. It has been widely recognized that the atmospheric
gravity wave activity has a profound effect on the large-scale circulation, thermal and
constituent structures in the mesosphere and lower thermosphere (MLT). Temperature
distribution in this region is an essential component to identify and quantify gravity
waves. Observation from remote sensing instruments on satellite platforms is an effective
way to measure the temperature in the MLT region.
A miniaturized satellite payload is developed to measure the atmospheric temperature
in the MLT region via observing the O2A-band emission. Following a Boltzmann
distribution, the relative intensities of the emission lines can be used to derive the temperature
profile. Based on the spatial heterodyne spectroscopy, this instrument is capable
of resolving individual emission lines in the O2A-band for the spatial and spectral
information simultaneously. The monolithic and compact feature of this spectrometer
makes it suitable for operating on satellite platforms.
In this work, the characterization of the instrument is investigated for the purpose
of simultaneously measuring multiple emission lines of the O2A-band. The instrument
is explored through a series of experimental methods, providing characteristics of the
instrument and evaluation of its performance. In spatial and spectral domain, Level-
0 and Level-1 data processors are developed to convert the raw data to the calibrated
spectral radiance for further temperature and gravity wave characterization.
Within this framework, the performance of the utilized detector is evaluated along
with its radiation tolerance in space environment. In the processor, the detector artifacts
are corrected based on the measurements in laboratory or in space. The radiometric
response of the instrument is characterized on a pixel-by-pixel basis using a blackbody.
An interferogram distortion correction algorithm is developed to correct for the spatial
and phase distortion induced by the detector optics. Further, localized phase distortion
correction is implemented to correct for the remaining phase error. Unwanted ghost
emission lines are removed based on two dimensional Fourier transform. In the spectral
domain, the processing steps mainly consist of wavelength calibration and instrument
spectral response correction, including filter response correction and modulation efficiency
correction.
As an in-orbit verification, the AtmoSHINE instrument was successfully deployed
in space on 22th of December, 2018. In the first test phase, the functionality and the
performance of the instrument in space were verified. The detector dark current measurement
in orbit is consistent with the ground-based results. Based on the the calibration
procedures and the developed data processing algorithms, the O2A-band emission
lines can be successfully resolved. A cross-verification of the AtmoSHINE limb radiance
profile with other satellite payload measurements indicates that the radiometric
performance of the instrument is within the expectation. The retrieved temperature parameters
are studied with respect to different number of samples and different objective
functions in the optimization. This work verifies the ability of the instrument to derive
the atmospheric temperature in the MLT region and its potential application in gravity
wave detections
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