110 research outputs found
Super-Resolution Radar
In this paper we study the identification of a time-varying linear system
from its response to a known input signal. More specifically, we consider
systems whose response to the input signal is given by a weighted superposition
of delayed and Doppler shifted versions of the input. This problem arises in a
multitude of applications such as wireless communications and radar imaging.
Due to practical constraints, the input signal has finite bandwidth B, and the
received signal is observed over a finite time interval of length T only. This
gives rise to a delay and Doppler resolution of 1/B and 1/T. We show that this
resolution limit can be overcome, i.e., we can exactly recover the continuous
delay-Doppler pairs and the corresponding attenuation factors, by solving a
convex optimization problem. This result holds provided that the distance
between the delay-Doppler pairs is at least 2.37/B in time or 2.37/T in
frequency. Furthermore, this result allows the total number of delay-Doppler
pairs to be linear up to a log-factor in BT, the dimensionality of the response
of the system, and thereby the limit for identifiability. Stated differently,
we show that we can estimate the time-frequency components of a signal that is
S-sparse in the continuous dictionary of time-frequency shifts of a random
window function, from a number of measurements, that is linear up to a
log-factor in S.Comment: Revised versio
Identification of Parametric Underspread Linear Systems and Super-Resolution Radar
Identification of time-varying linear systems, which introduce both
time-shifts (delays) and frequency-shifts (Doppler-shifts), is a central task
in many engineering applications. This paper studies the problem of
identification of underspread linear systems (ULSs), whose responses lie within
a unit-area region in the delay Doppler space, by probing them with a known
input signal. It is shown that sufficiently-underspread parametric linear
systems, described by a finite set of delays and Doppler-shifts, are
identifiable from a single observation as long as the time bandwidth product of
the input signal is proportional to the square of the total number of delay
Doppler pairs in the system. In addition, an algorithm is developed that
enables identification of parametric ULSs from an input train of pulses in
polynomial time by exploiting recent results on sub-Nyquist sampling for time
delay estimation and classical results on recovery of frequencies from a sum of
complex exponentials. Finally, application of these results to super-resolution
target detection using radar is discussed. Specifically, it is shown that the
proposed procedure allows to distinguish between multiple targets with very
close proximity in the delay Doppler space, resulting in a resolution that
substantially exceeds that of standard matched-filtering based techniques
without introducing leakage effects inherent in recently proposed compressed
sensing-based radar methods.Comment: Revised version of a journal paper submitted to IEEE Trans. Signal
Processing: 30 pages, 17 figure
Generating a Super-resolution Radar Angular Spectrum Using Physiological Component Analysis
In this study, we propose a method for generating an angular spectrum using array radar and physiological component analysis. We develop physiological component analysis to separate radar echoes from multiple body positions, where echoes are phase-modulated by propagating pulse waves. Assuming that the pulse wave displacements at multiple body positions are constant multiples of a time-shifted waveform, the method estimates echoes using a simplified mathematical model. We exploit the mainlobe and nulls of the directional patterns of the physiological component analysis to form an angular spectrum. We applied the proposed method to simulated data to demonstrate that it can generate a super-resolution angular spectrum
Density Criteria for the Identification of Linear Time-Varying Systems
This paper addresses the problem of identifying a linear time-varying (LTV)
system characterized by a (possibly infinite) discrete set of delays and
Doppler shifts. We prove that stable identifiability is possible if the upper
uniform Beurling density of the delay-Doppler support set is strictly smaller
than 1/2 and stable identifiability is impossible for densities strictly larger
than 1/2. The proof of this density theorem reveals an interesting relation
between LTV system identification and interpolation in the Bargmann-Fock space.
Finally, we introduce a subspace method for solving the system identification
problem at hand.Comment: IEEE International Symposium on Information Theory (ISIT), Hong Kong,
China, June 201
Super-Resolution Radar Imaging with Sparse Arrays Using a Deep Neural Network Trained with Enhanced Virtual Data
This paper introduces a method based on a deep neural network (DNN) that is
perfectly capable of processing radar data from extremely thinned radar
apertures. The proposed DNN processing can provide both aliasing-free radar
imaging and super-resolution. The results are validated by measuring the
detection performance on realistic simulation data and by evaluating the
Point-Spread-function (PSF) and the target-separation performance on measured
point-like targets. Also, a qualitative evaluation of a typical automotive
scene is conducted. It is shown that this approach can outperform
state-of-the-art subspace algorithms and also other existing machine learning
solutions. The presented results suggest that machine learning approaches
trained with sufficiently sophisticated virtual input data are a very promising
alternative to compressed sensing and subspace approaches in radar signal
processing. The key to this performance is that the DNN is trained using
realistic simulation data that perfectly mimic a given sparse antenna radar
array hardware as the input. As ground truth, ultra-high resolution data from
an enhanced virtual radar are simulated. Contrary to other work, the DNN
utilizes the complete radar cube and not only the antenna channel information
at certain range-Doppler detections. After training, the proposed DNN is
capable of sidelobe- and ambiguity-free imaging. It simultaneously delivers
nearly the same resolution and image quality as would be achieved with a fully
occupied array.Comment: 15 pages, 12 figures, Accepted to IEEE Journal of Microwave
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Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System
Background theory, a reference design, and demonstration
results are given for a Global Navigation Satellite
System (GNSS) interference localization system comprising a
distributed radio-frequency sensor network that simultaneously
locates multiple interference sources by measuring their signalsâ
time difference of arrival (TDOA) between pairs of nodes in
the network. The end-to-end solution offered here draws from
previous work in single-emitter group delay estimation, very long
baseline interferometry, subspace-based estimation, radar, and
passive geolocation. Synchronization and automatic localization
of sensor nodes is achieved through a tightly-coupled receiver
architecture that enables phase-coherent and synchronous sampling
of the interference signals and so-called reference signals
which carry timing and positioning information. Signal and crosscorrelation
models are developed and implemented in a simulator.
Multiple-emitter subspace-based TDOA estimation techniques
are developed as well as emitter identification and localization
algorithms. Simulator performance is compared to the CramérRao
lower bound for single-emitter TDOA precision. Results are
given for a test exercise in which the system accurately locates
emitters broadcasting in the amateur radio band in Austin, TX.Aerospace Engineering and Engineering Mechanic
Cost-effective photonic super-resolution millimeter-wave joint radar-communication system using self-coherent detection
A cost-effective millimeter-wave (MMW) joint radar-communication (JRC) system
with super resolution is proposed and experimentally demonstrated, using
optical heterodyne up-conversion and self-coherent detection down-conversion
techniques. The point lies in the designed coherent dual-band constant envelope
linear frequency modulation-orthogonal frequency division multiplexing
(LFM-OFDM) signal with opposite phase modulation indexes for the JRC system.
Then the self-coherent detection, as a simple and low-cost means, is
accordingly facilitated for both de-chirping of MMW radar and frequency
down-conversion reception of MMW communication, which circumvents the costly
high-speed mixers along with MMW local oscillators and more significantly
achieves the real-time decomposition of radar and communication information.
Furthermore, a super resolution radar range profile is realized through the
coherent fusion processing of dual-band JRC signal. In experiments, a dual-band
LFM-OFDM JRC signal centered at 54-GHz and 61-GHz is generated. The dual bands
are featured with an identical instantaneous bandwidth of 2 GHz and carry an
OFDM signal of 1 GBaud, which help to achieve a 6-Gbit/s data rate for
communication and a 1.76-cm range resolution for radar
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