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Assessing the Spoofing Threat: Development of a Portable GPS Civilian Spoofer
A portable civilian GPS spoofer is implemented on a digital
signal processor and used to characterize spoofing effects and develop defenses against civilian spoofing. This
work is intended to equip GNSS users and receiver manufacturers
with authentication methods that are effective
against unsophisticated spoofing attacks. The work also
serves to refine the civilian spoofing threat assessment
by demonstrating the challenges involved in mounting a
spoofing attack.Aerospace Engineering and Engineering Mechanic
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Signal Characteristics of Civil GPS Jammers
This paper surveys the signal properties of 18 commercially
available GPS jammers based on experimental
data. The paper is divided into two distinct tests.
The first characterizes the jamming signals, and the
second test determines the effective range of 4 of the
jammers. The first test uses power spectra from discrete
Fourier transforms (DFTs) of the time series data
to show that all the jammers employ approximately the same jamming method, i.e. linear frequency modulation
of a single tone. The spectra also show that
there are significant jammer-to-jammer variations, including
between jammers of the same model, and that
a given jammer’s signal may vary over time. The first
test also includes measurements of signal power within
frequency bands centered at the L1 and L2 frequencies,
along with the sweep periods and the sweep range at
both frequencies. The second test presents measurements
of the attenuation of the jamming signal necessary
to allow a commercially available GPS receiver to
acquire and track signals from a GPS simulator. From
the attenuation levels and some assumptions about the
antennas used, upper limits on the effective jamming
ranges are calculated for 4 of the jammers, with a resulting
maximum range of 6–9 km.Aerospace Engineering and Engineering Mechanic
The late-time singularity inside non-spherical black holes
It was long believed that the singularity inside a realistic, rotating black
hole must be spacelike. However, studies of the internal geometry of black
holes indicate a more complicated structure is typical. While it seems likely
that an observer falling into a black hole with the collapsing star encounters
a crushing spacelike singularity, an observer falling in at late times
generally reaches a null singularity which is vastly different in character to
the standard Belinsky, Khalatnikov and Lifschitz (BKL) spacelike singularity.
In the spirit of the classic work of BKL we present an asymptotic analysis of
the null singularity inside a realistic black hole. Motivated by current
understanding of spherical models, we argue that the Einstein equations reduce
to a simple form in the neighborhood of the null singularity. The main results
arising from this approach are demonstrated using an almost plane symmetric
model. The analysis shows that the null singularity results from the blueshift
of the late-time gravitational wave tail; the amplitude of these gravitational
waves is taken to decay as an inverse power of advanced time as suggested by
perturbation theory. The divergence of the Weyl curvature at the null
singularity is dominated by the propagating modes of the gravitational field.
The null singularity is weak in the sense that tidal distortion remains bounded
along timelike geodesics crossing the Cauchy horizon. These results are in
agreement with previous analyses of black hole interiors. We briefly discuss
some outstanding problems which must be resolved before the picture of the
generic black hole interior is complete.Comment: 16 pages, RevTeX, 3 figures included using psfi
Radiative falloff in Einstein-Straus spacetime
The Einstein-Straus spacetime describes a nonrotating black hole immersed in
a matter-dominated cosmology. It is constructed by scooping out a spherical
ball of the dust and replacing it with a vacuum region containing a black hole
of the same mass. The metric is smooth at the boundary, which is comoving with
the rest of the universe. We study the evolution of a massless scalar field in
the Einstein-Straus spacetime, with a special emphasis on its late-time
behavior. This is done by numerically integrating the scalar wave equation in a
double-null coordinate system that covers both portions (vacuum and dust) of
the spacetime. We show that the field's evolution is governed mostly by the
strong concentration of curvature near the black hole, and the discontinuity in
the dust's mass density at the boundary; these give rise to a rather complex
behavior at late times. Contrary to what it would do in an asymptotically-flat
spacetime, the field does not decay in time according to an inverse power-law.Comment: ReVTeX, 12 pages, 14 figure
Singularity deep inside the spherical charged black hole core
We study analytically the spacelike singularity inside a
spherically-symmetric, charged black hole coupled to a self-gravitating
spherical massless scalar field. We assume spatial homogeneity, and find a
generic solution in terms of a formal series expansion. This solution is tested
against fully-nonlinear and inhomogeneous numerical simulations. We find full
compliance between our analytical solution and the pointwise behavior of the
singularity in the numerical simulations. This is a strong scalar-curvature
monotonic spacelike singularity, which connects to a weak null singularity at
asymptotically-late advanced time.Comment: 6 pages, to be published in Phys. Rev.
Black hole formation from massive scalar fields
It is shown that there exists a range of parameters in which gravitational
collapse with a spherically symmetric massive scalar field can be treated as if
it were collapsing dust. This implies a criterion for the formation of black
holes depending on the size and mass of the initial field configuration and the
mass of the scalar field.Comment: 11 pages, RevTeX, 3 eps figures. Submitted to Class. Quantum Gra
Quantum Effects in Black Hole Interiors
The Weyl curvature inside a black hole formed in a generic collapse grows,
classically without bound, near to the inner horizon, due to partial absorption
and blueshifting of the radiative tail of the collapse. Using a spherical
model, we examine how this growth is modified by quantum effects of conformally
coupled massless fields.Comment: 13 pages, 1 figure (not included), RevTe
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