7,303 research outputs found
Distributed Detection over Fading MACs with Multiple Antennas at the Fusion Center
A distributed detection problem over fading Gaussian multiple-access channels
is considered. Sensors observe a phenomenon and transmit their observations to
a fusion center using the amplify and forward scheme. The fusion center has
multiple antennas with different channel models considered between the sensors
and the fusion center, and different cases of channel state information are
assumed at the sensors. The performance is evaluated in terms of the error
exponent for each of these cases, where the effect of multiple antennas at the
fusion center is studied. It is shown that for zero-mean channels between the
sensors and the fusion center when there is no channel information at the
sensors, arbitrarily large gains in the error exponent can be obtained with
sufficient increase in the number of antennas at the fusion center. In stark
contrast, when there is channel information at the sensors, the gain in error
exponent due to having multiple antennas at the fusion center is shown to be no
more than a factor of (8/pi) for Rayleigh fading channels between the sensors
and the fusion center, independent of the number of antennas at the fusion
center, or correlation among noise samples across sensors. Scaling laws for
such gains are also provided when both sensors and antennas are increased
simultaneously. Simple practical schemes and a numerical method using
semidefinite relaxation techniques are presented that utilize the limited
possible gains available. Simulations are used to establish the accuracy of the
results.Comment: 21 pages, 9 figures, submitted to the IEEE Transactions on Signal
Processin
Active inference, evidence accumulation, and the urn task
Deciding how much evidence to accumulate before making a decision is a problem we and other animals often face, but one that is not completely understood. This issue is particularly important because a tendency to sample less information (often known as reflection impulsivity) is a feature in several psychopathologies, such as psychosis. A formal understanding of information sampling may therefore clarify the computational anatomy of psychopathology. In this theoretical letter, we consider evidence accumulation in terms of active (Bayesian) inference using a generic model of Markov decision processes. Here, agents are equipped with beliefs about their own behavior--in this case, that they will make informed decisions. Normative decision making is then modeled using variational Bayes to minimize surprise about choice outcomes. Under this scheme, different facets of belief updating map naturally onto the functional anatomy of the brain (at least at a heuristic level). Of particular interest is the key role played by the expected precision of beliefs about control, which we have previously suggested may be encoded by dopaminergic neurons in the midbrain. We show that manipulating expected precision strongly affects how much information an agent characteristically samples, and thus provides a possible link between impulsivity and dopaminergic dysfunction. Our study therefore represents a step toward understanding evidence accumulation in terms of neurobiologically plausible Bayesian inference and may cast light on why this process is disordered in psychopathology
Characterizing Evaporation Ducts Within the Marine Atmospheric Boundary Layer Using Artificial Neural Networks
We apply a multilayer perceptron machine learning (ML) regression approach to
infer electromagnetic (EM) duct heights within the marine atmospheric boundary
layer (MABL) using sparsely sampled EM propagation data obtained within a
bistatic context. This paper explains the rationale behind the selection of the
ML network architecture, along with other model hyperparameters, in an effort
to demystify the process of arriving at a useful ML model. The resulting speed
of our ML predictions of EM duct heights, using sparse data measurements within
MABL, indicates the suitability of the proposed method for real-time
applications.Comment: 13 pages, 7 figure
Constraints on the Neutron Star Equation of State from GW170817
The first detection of gravitational waves from a neutron star-neutron star
merger, GW170817, has opened up a new avenue for constraining the
ultradense-matter equation of state (EOS). The deviation of the observed
waveform from a point-particle waveform is a sensitive probe of the EOS
controlling the merging neutron stars' structure. In this topical review, I
discuss the various constraints that have been made on the EOS in the year
following the discovery of GW170817. In particular, I review the surprising
relationship that has emerged between the effective tidal deformability of the
binary system and the neutron star radius. I also report new results that make
use of this relationship, finding that the radius inferred from GW170817 lies
between 9.8 and 13.2 km at 90% confidence, with distinct likelihood peaks at
10.8 and 12.3 km. I compare these radii, as well as those inferred in the
literature, to X-ray measurements of the neutron star radius. I also summarize
the various maximum mass constraints, which point towards a maximum mass < 2.3
M_sun, depending on the fate of the remnant, and which can be used to
additionally constrain the high-density EOS. I review the constraints on the
EOS that have been performed directly, through Bayesian inference schemes.
Finally, I comment on the importance of disentangling thermal effects in future
EOS constraints from neutron star mergers.Comment: Invited contribution to the EPJA topical issue "The first neutron
star merger observation - Implications for nuclear physics
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