12,091 research outputs found
Novel directed search strategy to detect continuous gravitational waves from neutron stars in low- and high-eccentricity binary systems
We describe a novel, very fast and robust, directed search incoherent method
for periodic gravitational waves (GWs) from neutron stars in binary systems. As
directed search, we assume the source sky position to be known with enough
accuracy, but all other parameters are supposed to be unknown. We exploit the
frequency-modulation due to source orbital motion to unveil the signal
signature by commencing from a collection of time and frequency peaks. We
validate our pipeline adding 131 artificial continuous GW signals from pulsars
in binary systems to simulated detector Gaussian noise, characterized by a
power spectral density Sh = 4x10^-24 Hz^-1/2 in the frequency interval [70,
200] Hz, which is overall commensurate with the advanced detector design
sensitivities. The pipeline detected 128 signals, and the weakest signal
injected and detected has a GW strain amplitude of ~10^-24, assuming one month
of gapless data collected by a single advanced detector. We also provide
sensitivity estimations, which show that, for a single- detector data covering
one month of observation time, depending on the source orbital Doppler
modulation, we can detect signals with an amplitude of ~7x10^-25. By using
three detectors, and one year of data, we would easily gain more than a factor
3 in sensitivity, translating into being able to detect weaker signals. We also
discuss the parameter estimate proficiency of our method, as well as
computational budget, which is extremely cheap. In fact, sifting one month of
single-detector data and 131 Hz-wide frequency range takes roughly 2.4 CPU
hours. Due to the high computational speed, the current procedure can be
readily applied in ally-sky schemes, sieving in parallel as many sky positions
as permitted by the available computational power
Measuring test mass acceleration noise in space-based gravitational wave astronomy
The basic constituent of interferometric gravitational wave detectors -- the
test mass to test mass interferometric link -- behaves as a differential
dynamometer measuring effective differential forces, comprising an integrated
measure of gravity curvature, inertial effects, as well as non-gravitational
spurious forces. This last contribution is going to be characterised by the
LISA Pathfinder mission, a technology precursor of future space-borne detectors
like eLISA. Changing the perspective from displacement to acceleration can
benefit the data analysis of LISA Pathfinder and future detectors. The response
in differential acceleration to gravitational waves is derived for a
space-based detector's interferometric link. The acceleration formalism can
also be integrated into time delay interferometry by building up the
unequal-arm Michelson differential acceleration combination. The differential
acceleration is nominally insensitive to the system free evolution dominating
the slow displacement dynamics of low-frequency detectors. Working with
acceleration also provides an effective way to subtract measured signals acting
as systematics, including the actuation forces. Because of the strong
similarity with the equations of motion, the optimal subtraction of systematic
signals, known within some amplitude and time shift, with the focus on
measuring the noise provides an effective way to solve the problem and
marginalise over nuisance parameters. The -statistic, in
widespread use throughout the gravitation waves community, is included in the
method and suitably generalised to marginalise over linear parameters and noise
at the same time. The method is applied to LPF simulator data and, thanks to
its generality, can also be applied to the data reduction and analysis of
future gravitational wave detectors.Comment: 10 pages, 3 figures, 1 tabl
A new multipath mitigation method for GNSS receivers based on antenna array
the potential of small antenna array for multipath mitigation in GNSS systems is considered in this paper. To discriminate the different incoming signals (Line of sight and multipaths), a new implementation of the well known SAGE algorithm is proposed. This allows a significant complexity reduction and it is fully compatible with conventional GNSS receivers. Theoretical study thanks to the Cramer Rao Bound derivation and tracking simulation results (in static and dynamic scenarios) show that the proposed method is a very promising approach for the multipath mitigation problem in GNSS receivers
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 Dopplerâs 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
Ambiguity function and accuracy of the hyperbolic chirp: comparison with the linear chirp
In this paper, we derive the Ambiguity Function (AF) of a narrowband and a wideband hyperbolic chirp. We calculate the second derivatives of the squared amplitude of the narrowband Complex Ambiguity Function (CAF) and use them to calculate the Fisher Information Matrix (FIM) of the estimators of the target range and velocity. The FIM is then used to calculate the Cramer-Rao Lower Bounds (CRLB) of the variance of the estimators and to ÂŽ carry out an analysis of estimation performance and a comparison with the case of a liner chirp with a rectangular and a Gaussian amplitude modulation. The analysis and the calculations of the CRLB are also extended to a train of hyperbolic chirps. Results corroborate that at narrowband the hyperbolic chirp is less Doppler tolerant than the linear chirp and show that the hyperbolic chirp provides a comparable measurement accuracy to the linear chirp. Results at wideband corroborate the superior Doppler tolerance of the hyperbolic chirp with respect to that of the linear chirp
A New Compact Delay, Doppler Stretch and Phase Estimation CRB with a Band-Limited Signal for Generic Remote Sensing Applications
Since time-delay, Doppler effect and phase estimation are fundamental tasks in a plethora
of engineering fields, tractable lower performance bounds for this problem are key tools of broad
interest for a large variety of remote sensing applications. In the large sample regime and/or the high
signal-to-noise ratio regime of the Gaussian conditional signal model, the CramĂ©râRao bound (CRB)
provides an accurate lower bound in the mean square error sense. In this contribution, we introduce
firstly a new compact CRB expression for the joint time-delay and Doppler stretch estimation,
considering a generic delayed and dilated band-limited signal. This generalizes known results
for both wideband signals and the standard narrowband signal model where the Doppler effect
on the band-limited baseband signal is not considered and amounts to a frequency shift. General
compact closed-form CRB expressions for the amplitude and phase are also provided. These compact
CRBs are expressed in terms of the baseband signal samples, making them especially easy to use
whatever the baseband signal considered, therefore being valid for a variety of remote sensors.
The new CRB expressions are validated in a positioning case study, both using synthetic and real
data. These results show that the maximum likelihood estimator converges to the CRB at high
signal-to-noise ratios, which confirms the exactness of the CRB. The CRB is further validated by
comparing the ambiguity function and its 2nd order Taylor expansion where the perfect match also
proves its exactness
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