62,612 research outputs found
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
MR-BART: Multi-Rate Available Bandwidth Estimation in Real-Time
In this paper, we propose Multi-Rate Bandwidth Available in Real Time
(MR-BART) to estimate the end-to-end Available Bandwidth (AB) of a network
path. The proposed scheme is an extension of the Bandwidth Available in Real
Time (BART) which employs multi-rate (MR) probe packet sequences with Kalman
filtering. Comparing to BART, we show that the proposed method is more robust
and converges faster than that of BART and achieves a more AB accurate
estimation. Furthermore, we analyze the estimation error in MR-BART and obtain
analytical formula and empirical expression for the AB estimation error based
on the system parameters.Comment: 12 Pages (Two columns), 14 Figures, 4 Tables
A synchronised Direct Digital Synthesiser
We describe a Direct Digital Synthesiser (DDS) which provides three frequency-locked synchronised outputs to generate frequencies from DC to 160 MHz. Primarily designed for use in a heterodyning range imaging system, the flexibility of the design allows its use in a number of other applications which require any number of stable, synchronised high frequency outputs. Frequency tuning of 32 bit length provides 0.1 Hz resolution when operating at the maximum clock rate of 400 MSPS, while 14 bit phase tuning provides 0.4 mrad resolution. The DDS technique provides very high relative accuracy between outputs, while the onboard oscillatorâs stability of ±1 ppm adds absolute accuracy to the design
Full field image ranger hardware
We describe the hardware designed to implement a full field heterodyning imaging system. Comprising three key components - a light source, high speed shutter and a signal generator - the system is expected to be capable of simultaneous range measurements to millimetre precision over the entire field of view. Current modulated laser diodes provide the required illumination, with a bandwidth of 100 MHz and peak output power exceeding 600 mW. The high speed shutter action is performed by gating the cathode of an image intensifier, driven by a 50 Vpp waveform with 3.5 ns rise and fall times. A direct digital synthesiser, with multiple synchronised channels, provides high stability between its outputs, 160 MHz bandwidth and tuning of 0.1 Hz
Channel Sounding for the Masses: Low Complexity GNU 802.11b Channel Impulse Response Estimation
New techniques in cross-layer wireless networks are building demand for
ubiquitous channel sounding, that is, the capability to measure channel impulse
response (CIR) with any standard wireless network and node. Towards that goal,
we present a software-defined IEEE 802.11b receiver and CIR estimation system
with little additional computational complexity compared to 802.11b reception
alone. The system implementation, using the universal software radio peripheral
(USRP) and GNU Radio, is described and compared to previous work. By overcoming
computational limitations and performing direct-sequence spread-spectrum
(DS-SS) matched filtering on the USRP, we enable high-quality yet inexpensive
CIR estimation. We validate the channel sounder and present a drive test
campaign which measures hundreds of channels between WiFi access points and an
in-vehicle receiver in urban and suburban areas
The Laser Astrometric Test of Relativity: Science, Technology, and Mission Design
The Laser Astrometric Test of Relativity (LATOR) experiment is designed to
explore general theory of relativity in the close proximity to the Sun -- the
most intense gravitational environment in the solar system. Using independent
time-series of highly accurate measurements of the Shapiro time-delay
(interplanetary laser ranging accurate to 3 mm at 2 AU) and interferometric
astrometry (accurate to 0.01 picoradian), LATOR will measure gravitational
deflection of light by the solar gravity with accuracy of 1 part in a billion
-- a factor ~30,000 better than currently available. LATOR will perform series
of highly-accurate tests in its search for cosmological remnants of scalar
field in the solar system. We present science, technology and mission design
for the LATOR mission.Comment: 12 pages, 4 figures. To appear in the proceedings of the
International Workshop "From Quantum to Cosmos: Fundamental Physics Research
in Space", 21-24 May 2006, Warrenton, Virginia, USA
http://physics.jpl.nasa.gov/quantum-to-cosmos
Experimental Design for the LATOR Mission
This paper discusses experimental design for the Laser Astrometric Test Of
Relativity (LATOR) mission. LATOR is designed to reach unprecedented accuracy
of 1 part in 10^8 in measuring the curvature of the solar gravitational field
as given by the value of the key Eddington post-Newtonian parameter \gamma.
This mission will demonstrate the accuracy needed to measure effects of the
next post-Newtonian order (~G^2) of light deflection resulting from gravity's
intrinsic non-linearity. LATOR will provide the first precise measurement of
the solar quadrupole moment parameter, J2, and will improve determination of a
variety of relativistic effects including Lense-Thirring precession. The
mission will benefit from the recent progress in the optical communication
technologies -- the immediate and natural step above the standard radio-metric
techniques. The key element of LATOR is a geometric redundancy provided by the
laser ranging and long-baseline optical interferometry. We discuss the mission
and optical designs, as well as the expected performance of this proposed
mission. LATOR will lead to very robust advances in the tests of Fundamental
physics: this mission could discover a violation or extension of general
relativity, or reveal the presence of an additional long range interaction in
the physical law. There are no analogs to the LATOR experiment; it is unique
and is a natural culmination of solar system gravity experiments.Comment: 16 pages, 17 figures, invited talk given at ``The 2004 NASA/JPL
Workshop on Physics for Planetary Exploration.'' April 20-22, 2004, Solvang,
C
Bias in particle tracking acceleration measurement
We investigate sources of error in acceleration statistics from Lagrangian
Particle Tracking (LPT) data and demonstrate techniques to eliminate or
minimise bias errors introduced during processing. Numerical simulations of
particle tracking experiments in isotropic turbulence show that the main
sources of bias error arise from noise due to position uncertainty and
selection biases introduced during numerical differentiation. We outline the
use of independent measurements and filtering schemes to eliminate these
biases. Moreover, we test the validity of our approach in estimating the
statistical moments and probability densities of the Lagrangian acceleration.
Finally, we apply these techniques to experimental particle tracking data and
demonstrate their validity in practice with comparisons to available data from
literature. The general approach, which is not limited to acceleration
statistics, can be applied with as few as two cameras and permits a substantial
reduction in the spatial resolution and sampling rate required to adequately
measure statistics of Lagrangian acceleration
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