19,200 research outputs found
Compressive sensing based Bayesian sparse channel estimation for OFDM communication systems: high performance and low complexity
In orthogonal frequency division modulation (OFDM) communication systems,
channel state information (CSI) is required at receiver due to the fact that
frequency-selective fading channel leads to disgusting inter-symbol
interference (ISI) over data transmission. Broadband channel model is often
described by very few dominant channel taps and they can be probed by
compressive sensing based sparse channel estimation (SCE) methods, e.g.,
orthogonal matching pursuit algorithm, which can take the advantage of sparse
structure effectively in the channel as for prior information. However, these
developed methods are vulnerable to both noise interference and column
coherence of training signal matrix. In other words, the primary objective of
these conventional methods is to catch the dominant channel taps without a
report of posterior channel uncertainty. To improve the estimation performance,
we proposed a compressive sensing based Bayesian sparse channel estimation
(BSCE) method which can not only exploit the channel sparsity but also mitigate
the unexpected channel uncertainty without scarifying any computational
complexity. The propose method can reveal potential ambiguity among multiple
channel estimators that are ambiguous due to observation noise or correlation
interference among columns in the training matrix. Computer simulations show
that propose method can improve the estimation performance when comparing with
conventional SCE methods.Comment: 24 pages,16 figures, submitted for a journa
Recent Langley helicopter acoustics contributions
The helicopter acoustics program at NASA Langley has included technology for elements of noise control ranging from sources of noise to receivers of noise. The scope of Langley contributions for about the last decade is discussed. Specifically, the resolution of two certification noise quantification issues by subjective acoustics research, the development status of the helicopter system noise prediction program ROTONET are reviewed and the highlights from research on blade rotational, broadband, and blade vortex interaction noise sources are presented. Finally, research contributions on helicopter cabin (or interior) noise control are presented. A bibliography of publications from the Langley helicopter acoustics program for the past 10 years is included
Acoustical Ranging Techniques in Embedded Wireless Sensor Networked Devices
Location sensing provides endless opportunities for a wide range of applications in GPS-obstructed environments;
where, typically, there is a need for higher degree of accuracy. In this article, we focus on robust range
estimation, an important prerequisite for fine-grained localization. Motivated by the promise of acoustic in
delivering high ranging accuracy, we present the design, implementation and evaluation of acoustic (both
ultrasound and audible) ranging systems.We distill the limitations of acoustic ranging; and present efficient
signal designs and detection algorithms to overcome the challenges of coverage, range, accuracy/resolution,
tolerance to Doppler’s effect, and audible intensity. We evaluate our proposed techniques experimentally on
TWEET, a low-power platform purpose-built for acoustic ranging applications. Our experiments demonstrate
an operational range of 20 m (outdoor) and an average accuracy 2 cm in the ultrasound domain. Finally,
we present the design of an audible-range acoustic tracking service that encompasses the benefits of a near-inaudible
acoustic broadband chirp and approximately two times increase in Doppler tolerance to achieve better performance
Sound Source Localization in a Multipath Environment Using Convolutional Neural Networks
The propagation of sound in a shallow water environment is characterized by
boundary reflections from the sea surface and sea floor. These reflections
result in multiple (indirect) sound propagation paths, which can degrade the
performance of passive sound source localization methods. This paper proposes
the use of convolutional neural networks (CNNs) for the localization of sources
of broadband acoustic radiated noise (such as motor vessels) in shallow water
multipath environments. It is shown that CNNs operating on cepstrogram and
generalized cross-correlogram inputs are able to more reliably estimate the
instantaneous range and bearing of transiting motor vessels when the source
localization performance of conventional passive ranging methods is degraded.
The ensuing improvement in source localization performance is demonstrated
using real data collected during an at-sea experiment.Comment: 5 pages, 5 figures, Final draft of paper submitted to 2018 IEEE
International Conference on Acoustics, Speech and Signal Processing (ICASSP)
15-20 April 2018 in Calgary, Alberta, Canada. arXiv admin note: text overlap
with arXiv:1612.0350
The estimation of geoacoustic properties from broadband acoustic data, focusing on instantaneous frequency techniques
The compressional wave velocity and attenuation of marine sediments are fundamental to marine science. In order to obtain reliable estimates of these parameters it is necessary to examine in situ acoustic data, which is generally broadband. A variety of techniques for estimating the compressional wave velocity and attenuation from broadband acoustic data are reviewed. The application of Instantaneous Frequency (IF) techniques to data collected from a normal-incidence chirp profiler is examined. For the datasets examined the best estimates of IF are obtained by dividing the chirp profile into a series of sections, estimating the IF of each trace in the section using the first moments of the Wigner Ville distribution, and stacking the resulting IF to obtain a composite IF for the section. As the datasets examined cover both gassy and saturated sediments, this is likely to be the optimum technique for chirp datasets collected from all sediment environments
Implementing and Characterizing Real-time Broadband RFI Excision for the GMRT Wideband Backend
The Giant Metrewave Radio Telescope (GMRT) is being upgraded to increase the
receiver sensitivity. This makes the receiver more susceptible to man-made
Radio Frequency Interference (RFI). To improve the receiver performance in
presence of RFI, real-time RFI excision (filtering) is incorporated in the GMRT
wideband backend (GWB). The RFI filtering system is implemented on FPGA and
CPU-GPU platforms to detect and remove broadband and narrowband RFI. The RFI is
detected using a threshold-based technique where the threshold is computed
using Median Absolute Deviation (MAD) estimator. The filtering is carried out
by replacing the RFI samples by either noise samples or constant value or
threshold. This paper describes the status of the real-time broadband RFI
excision system in the wideband receiver chain of the upgraded GMRT (uGMRT).
The test methodology for carrying out various tests to demonstrate the
performance of broadband RFI excision at the system level and on radio
astronomical imaging experiments are also described.Comment: 7 pages, 7 figure
Bandwidth extension of narrowband speech
Recently, 4G mobile phone systems have been
designed to process wideband speech signals whose
sampling frequency is 16 kHz. However, most part of
mobile and classical phone network, and current 3G
mobile phones, still process narrowband speech signals
whose sampling frequency is 8 kHz. During next future,
all these systems must be living together. Therefore,
sometimes a wideband speech signal (with a bandwidth up
to 7,2 kHz) should be estimated from an available
narrowband one (whose frequency band is 300-3400 Hz).
In this work, different techniques of audio bandwidth
extension have been implemented and evaluated. First, a
simple non-model-based algorithm (interpolation
algorithm) has been implemented. Second, a model-based
algorithm (linear mapping) have been designed and
evaluated in comparison to previous one. Several CMOS
(Comparison Mean Opinion Score) [6] listening tests show
that performance of Linear Mapping algorithm clearly
overcomes the other one. Results of these tests are very
close to those corresponding to original wideband speech
signal.Postprint (published version
Experimental and Numerical Investigation of Near-field Rotor Aeroacoustics
This work presents comparisons between experimental and numerical estimates of near-field rotor
aeroacoustics in hover. The experiments took place at the Kazan National Research Technical University
named after A. N. Tupolev (Kazan Aviation Institute). A set of rotor blades with NACA-0012 aerofoil sections
was used to obtain the sound pressure distribution using a linear array of microphones. It is shown that CFD
and experimental results are in good agreement suggesting that the obtained test data can be useful as a
validation case for development of CFD tools
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