2,041 research outputs found
Micro-doppler-based in-home aided and unaided walking recognition with multiple radar and sonar systems
Published in IET Radar, Sonar and Navigation. Online first 21/06/2016.The potential for using micro-Doppler signatures as a basis for distinguishing between aided and unaided gaits is considered in this study for the purpose of characterising normal elderly gait and assessment of patient recovery. In particular, five different classes of mobility are considered: normal unaided walking, walking with a limp, walking using a cane or tripod, walking with a walker, and using a wheelchair. This presents a challenging classification problem as the differences in micro-Doppler for these activities can be quite slight. Within this context, the performance of four different radar and sonar systems – a 40 kHz sonar, a 5.8 GHz wireless pulsed Doppler radar mote, a 10 GHz X-band continuous wave (CW) radar, and a 24 GHz CW radar – is evaluated using a broad range of features. Performance improvements using feature selection is addressed as well as the impact on performance of sensor placement and potential occlusion due to household objects. Results show that nearly 80% correct classification can be achieved with 10 s observations from the 24 GHz CW radar, whereas 86% performance can be achieved with 5 s observations of sonar
Perturbed Orthogonal Matching Pursuit
Cataloged from PDF version of article.Compressive Sensing theory details how a sparsely
represented signal in a known basis can be reconstructed with
an underdetermined linear measurement model. However, in reality
there is a mismatch between the assumed and the actual
bases due to factors such as discretization of the parameter
space defining basis components, sampling jitter in A/D conversion,
and model errors. Due to this mismatch, a signal may
not be sparse in the assumed basis, which causes significant performance
degradation in sparse reconstruction algorithms. To
eliminate the mismatch problem, this paper presents a novel
perturbed orthogonal matching pursuit (POMP) algorithm that
performs controlled perturbation of selected support vectors to
decrease the orthogonal residual at each iteration. Based on detailed
mathematical analysis, conditions for successful reconstruction
are derived. Simulations show that robust results with much
smaller reconstruction errors in the case of perturbed bases can
be obtained as compared to standard sparse reconstruction techniques
Sparse ground-penetrating radar imaging method for off-the-grid target problem
Cataloged from PDF version of article.Spatial sparsity of the target space in subsurface or through-the-wall imaging applications has been successfully used within the compressive-sensing framework to decrease the data acquisition load in practical systems, while also generating high-resolution images. The developed techniques in this area mainly discretize the continuous target space into grid points and generate a dictionary of model data that is used in image-reconstructing optimization problems. However, for targets that do not coincide with the computation grid, imaging performance degrades considerably. This phenomenon is known as the off-grid problem. This paper presents a novel sparse ground-penetrating radar imaging method that is robust for off-grid targets. The proposed technique is an iterative orthogonal matching pursuit-based method that uses gradient-based steepest ascent-type iterations to locate the off-grid target. Simulations show that robust results with much smaller reconstruction errors are obtained for multiple off-grid targets compared to standard sparse reconstruction techniques. (c) 2013 SPIE and IS&
A robust compressive sensing based technique for reconstruction of sparse radar scenes
Cataloged from PDF version of article.Pulse-Doppler radar has been successfully applied to surveillance and tracking of both moving and
stationary targets. For efficient processing of radar returns, delay–Doppler plane is discretized and FFT
techniques are employed to compute matched filter output on this discrete grid. However, for targets
whose delay–Doppler values do not coincide with the computation grid, the detection performance
degrades considerably. Especially for detecting strong and closely spaced targets this causes miss
detections and false alarms. This phenomena is known as the off-grid problem. Although compressive
sensing based techniques provide sparse and high resolution results at sub-Nyquist sampling rates,
straightforward application of these techniques is significantly more sensitive to the off-grid problem.
Here a novel parameter perturbation based sparse reconstruction technique is proposed for robust delay–
Doppler radar processing even under the off-grid case. Although the perturbation idea is general and can
be implemented in association with other greedy techniques, presently it is used within an orthogonal
matching pursuit (OMP) framework. In the proposed technique, the selected dictionary parameters are
perturbed towards directions to decrease the orthogonal residual norm. The obtained results show that
accurate and sparse reconstructions can be obtained for off-grid multi target cases. A new performance
metric based on Kullback–Leibler Divergence (KLD) is proposed to better characterize the error between
actual and reconstructed parameter spaces. Increased performance with lower reconstruction errors are
obtained for all the tested performance criteria for the proposed technique compared to conventional
OMP and 1 minimization techniques.
© 2013 Elsevier Inc. All rights reserve
SAR image reconstruction by expectation maximization based matching pursuit
Cataloged from PDF version of article.Synthetic Aperture Radar (SAR) provides high resolution images of terrain and target reflectivity. SAR systems are indispensable in many remote sensing applications. Phase errors due to uncompensated platform motion degrade resolution in reconstructed images. A multitude of autofocusing techniques has been proposed to estimate and correct phase errors in SAR images. Some autofocus techniques work as a post-processor on reconstructed images and some are integrated into the image reconstruction algorithms. Compressed Sensing (CS), as a relatively new theory, can be applied to sparse SAR image reconstruction especially in detection of strong targets. Autofocus can also be integrated into CS based SAR image reconstruction techniques. However, due to their high computational complexity, CS based techniques are not commonly used in practice. To improve efficiency of image reconstruction we propose a novel CS based SAR imaging technique which utilizes recently proposed Expectation Maximization based Matching Pursuit (EMMP) algorithm. EMMP algorithm is greedy and computationally less complex enabling fast SAR image reconstructions. The proposed EMMP based SAR image reconstruction technique also performs autofocus and image reconstruction simultaneously. Based on a variety of metrics, performance of the proposed EMMP based SAR image reconstruction technique is investigated. The obtained results show that the proposed technique provides high resolution images of sparse target scenes while performing highly accurate motion compensation. (C) 2014 Elsevier Inc. All rights reserved
Supplier diversification under binomial yield
Cataloged from PDF version of article.We consider supplier diversification in an EOQ type inventory setting with multiple suppliers and
binomial yields. We characterize the optimal policy for the model and show that, in this case, it does
not pay to diversify, in contrast to previous results in the random yield literature.
© 2008 Elsevier B.V. All rights reserved
Characterization of an embedded RF-MEMS switch
An RF-MEMS capacitive switch for mm-wave integrated circuits, embedded in the BEOL of 0.25ÎĽm BiCMOS process, has been characterized. First, a mechanical
model based on Finite-Element-Method (FEM) was developed by taking the residual stress of the thin film membrane into account. The pull-in voltage and the capacitance values obtained with the mechanical model agree very well with the
measured values. Moreover, S-parameters were extracted using Electromagnetic (EM) solver. The data observed in this way also agree well with the experimental ones measured up to 110GHz. The developed RF model was applied to a transmit/receive (T/R) antenna switch design. The results proved the feasibility of using the FEM model in circuit simulations for the development of RF-MEMS switch embedded, single-chip multi-band RF ICs
Test beam studies of the TRD prototype filled with different gas mixtures based on Xe, Kr, and Ar
Towards the end of LHC Run1, gas leaks were observed in some parts of the
Transition Radiation Tracker (TRT) of ATLAS. Due to these leaks, primary Xenon
based gas mixture was replaced with Argon based mixture in various parts.
Test-beam studies with a dedicated Transition Radiation Detector (TRD)
prototype were carried out in 2015 in order to understand transition radiation
performance with mixtures based on Argon and Krypton. We present and discuss
the results of these test-beam studies with different active gas compositions.Comment: 5 pages,12 figures, The 2nd International Conference on Particle
Physics and Astrophysics (ICPPA-2016); Acknowledgments section correcte
Some results of test beam studies of Transition Radiation Detector prototypes at CERN
Operating conditions and challenging demands of present and future
accelerator experiments result in new requirements on detector systems. There
are many ongoing activities aimed to develop new technologies and to improve
the properties of detectors based on existing technologies. Our work is
dedicated to development of Transition Radiation Detectors (TRD) suitable for
different applications. In this paper results obtained in beam tests at SPS
accelerator at CERN with the TRD prototype based on straw technology are
presented. TRD performance was studied as a function of thickness of the
transition radiation radiator and working gas mixture pressure
Gas and seismicity within the Istanbul seismic gap
Understanding micro-seismicity is a critical question for earthquake hazard
assessment. Since the devastating earthquakes of Izmit and Duzce in 1999, the
seismicity along the submerged section of North Anatolian Fault within the Sea
of Marmara (comprising the “Istanbul seismic gap”) has been extensively
studied in order to infer its mechanical behaviour (creeping vs locked). So
far, the seismicity has been interpreted only in terms of being tectonic-
driven, although the Main Marmara Fault (MMF) is known to strike across
multiple hydrocarbon gas sources. Here, we show that a large number of the
aftershocks that followed the M 5.1 earthquake of July, 25th 2011 in the
western Sea of Marmara, occurred within a zone of gas overpressuring in the
1.5–5 km depth range, from where pressurized gas is expected to migrate along
the MMF, up to the surface sediment layers. Hence, gas-related processes
should also be considered for a complete interpretation of the micro-
seismicity (~M < 3) within the Istanbul offshore domain
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