47,698 research outputs found
An adaptive neuro-fuzzy propagation model for LoRaWAN
This article proposes an adaptive-network-based fuzzy inference system (ANFIS) model for accurate estimation of signal propagation using LoRaWAN. By using ANFIS, the basic knowledge of propagation is embedded into the proposed model. This reduces the training complexity of artificial neural network (ANN)-based models. Therefore, the size of the training dataset is reduced by 70% compared to an ANN model. The proposed model consists of an efficient clustering method to identify the optimum number of the fuzzy nodes to avoid overfitting, and a hybrid training algorithm to train and optimize the ANFIS parameters. Finally, the proposed model is benchmarked with extensive practical data, where superior accuracy is achieved compared to deterministic models, and better generalization is attained compared to ANN models. The proposed model outperforms the nondeterministic models in terms of accuracy, has the flexibility to account for new modeling parameters, is easier to use as it does not require a model for propagation environment, is resistant to data collection inaccuracies and uncertain environmental information, has excellent generalization capability, and features a knowledge-based implementation that alleviates the training process. This work will facilitate network planning and propagation prediction in complex scenarios
RADAMESH: Cosmological Radiative Transfer for Adaptive Mesh Refinement Simulations
We present a new three-dimensional radiative transfer (RT) code, RADAMESH,
based on a ray-tracing, photon-conserving and adaptive (in space and time)
scheme. RADAMESH uses a novel Monte Carlo approach to sample the radiation
field within the computational domain on a "cell-by-cell" basis. Thanks to this
algorithm, the computational efforts are now focused where actually needed,
i.e. within the Ionization-fronts (I-fronts). This results in an increased
accuracy level and, at the same time, a huge gain in computational speed with
respect to a "classical" Monte Carlo RT, especially when combined with an
Adaptive Mesh Refinement (AMR) scheme. Among several new features, RADAMESH is
able to adaptively refine the computational mesh in correspondence of the
I-fronts, allowing to fully resolve them within large, cosmological boxes. We
follow the propagation of ionizing radiation from an arbitrary number of
sources and from the recombination radiation produced by H and He. The chemical
state of six species (HI, HII, HeI, HeII, HeIII, e) and gas temperatures are
computed with a time-dependent, non-equilibrium chemistry solver. We present
several validating tests of the code, including the standard tests from the RT
Code Comparison Project and a new set of tests aimed at substantiating the new
characteristics of RADAMESH. Using our AMR scheme, we show that properly
resolving the I-front of a bright quasar during Reionization produces a large
increase of the predicted gas temperature within the whole HII region. Also, we
discuss how H and He recombination radiation is able to substantially change
the ionization state of both species (for the classical Stroemgren sphere test)
with respect to the widely used "on-the-spot" approximation.Comment: 19 pages, 24 figures; accepted for publication in MNRAS, version with
high-resolution figures is avalaible at
http://www.ast.cam.ac.uk/~cantal/Papers/CP10.pd
Pathfinder first light: alignment, calibration, and commissioning of the LINC-NIRVANA ground-layer adaptive optics subsystem
We present descriptions of the alignment and calibration tests of the
Pathfinder, which achieved first light during our 2013 commissioning campaign
at the LBT. The full LINC-NIRVANA instrument is a Fizeau interferometric imager
with fringe tracking and 2-layer natural guide star multi-conjugate adaptive
optics (MCAO) systems on each eye of the LBT. The MCAO correction for each side
is achieved using a ground layer wavefront sensor that drives the LBT adaptive
secondary mirror and a mid-high layer wavefront sensor that drives a Xinetics
349 actuator DM conjugated to an altitude of 7.1 km. When the LINC-NIRVANA MCAO
system is commissioned, it will be one of only two such systems on an 8-meter
telescope and the only such system in the northern hemisphere. In order to
mitigate risk, we take a modular approach to commissioning by decoupling and
testing the LINC-NIRVANA subsystems individually. The Pathfinder is the
ground-layer wavefront sensor for the DX eye of the LBT. It uses 12 pyramid
wavefront sensors to optically co-add light from natural guide stars in order
to make four pupil images that sense ground layer turbulence. Pathfinder is now
the first LINC-NIRVANA subsystem to be fully integrated with the telescope and
commissioned on sky. Our 2013 commissioning campaign consisted of 7 runs at the
LBT with the tasks of assembly, integration and communication with the LBT
telescope control system, alignment to the telescope optical axis, off-sky
closed loop AO calibration, and finally closed loop on-sky AO. We present the
programmatics of this campaign, along with the novel designs of our alignment
scheme and our off-sky calibration test, which lead to the Pathfinder's first
on-sky closed loop images
Determining the Phase and Amplitude Distortion of a Wavefront using a Plenoptic Sensor
We have designed a plenoptic sensor to retrieve phase and amplitude changes
resulting from a laser beam's propagation through atmospheric turbulence.
Compared with the commonly restricted domain of (-pi, pi) in phase
reconstruction by interferometers, the reconstructed phase obtained by the
plenoptic sensors can be continuous up to a multiple of 2pi. When compared with
conventional Shack-Hartmann sensors, ambiguities caused by interference or low
intensity, such as branch points and branch cuts, are less likely to happen and
can be adaptively avoided by our reconstruction algorithm. In the design of our
plenoptic sensor, we modified the fundamental structure of a light field camera
into a mini Keplerian telescope array by accurately cascading the back focal
plane of its object lens with a microlens array's front focal plane and
matching the numerical aperture of both components. Unlike light field cameras
designed for incoherent imaging purposes, our plenoptic sensor operates on the
complex amplitude of the incident beam and distributes it into a matrix of
images that are simpler and less subject to interference than a global image of
the beam. Then, with the proposed reconstruction algorithms, the plenoptic
sensor is able to reconstruct the wavefront and a phase screen at an
appropriate depth in the field that causes the equivalent distortion on the
beam. The reconstructed results can be used to guide adaptive optics systems in
directing beam propagation through atmospheric turbulence. In this paper we
will show the theoretical analysis and experimental results obtained with the
plenoptic sensor and its reconstruction algorithms.Comment: This article has been accepted by JOSA
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