4,374 research outputs found
A Comprehensive Analysis of 5G Heterogeneous Cellular Systems operating over - Shadowed Fading Channels
Emerging cellular technologies such as those proposed for use in 5G
communications will accommodate a wide range of usage scenarios with diverse
link requirements. This will include the necessity to operate over a versatile
set of wireless channels ranging from indoor to outdoor, from line-of-sight
(LOS) to non-LOS, and from circularly symmetric scattering to environments
which promote the clustering of scattered multipath waves. Unfortunately, many
of the conventional fading models adopted in the literature to develop network
models lack the flexibility to account for such disparate signal propagation
mechanisms. To bridge the gap between theory and practical channels, we
consider - shadowed fading, which contains as special cases, the
majority of the linear fading models proposed in the open literature, including
Rayleigh, Rician, Nakagami-m, Nakagami-q, One-sided Gaussian, -,
-, and Rician shadowed to name but a few. In particular, we apply an
orthogonal expansion to represent the - shadowed fading
distribution as a simplified series expression. Then using the series
expressions with stochastic geometry, we propose an analytic framework to
evaluate the average of an arbitrary function of the SINR over -
shadowed fading channels. Using the proposed method, we evaluate the spectral
efficiency, moments of the SINR, bit error probability and outage probability
of a -tier HetNet with classes of BSs, differing in terms of the
transmit power, BS density, shadowing characteristics and small-scale fading.
Building upon these results, we provide important new insights into the network
performance of these emerging wireless applications while considering a diverse
range of fading conditions and link qualities
Entropy and Energy Detection-based Spectrum Sensing over F Composite Fading Channels
In this paper, we investigate the performance of energy detection-based
spectrum sensing over F composite fading channels. To this end, an analytical
expression for the average detection probability is firstly derived. This
expression is then extended to account for collaborative spectrum sensing,
square-law selection diversity reception and noise power uncertainty. The
corresponding receiver operating characteristics (ROC) are analyzed for
different conditions of the average signal-to-noise ratio (SNR), noise power
uncertainty, time-bandwidth product, multipath fading, shadowing, number of
diversity branches and number of collaborating users. It is shown that the
energy detection performance is sensitive to the severity of the multipath
fading and amount of shadowing, whereby even small variations in either of
these physical phenomena can significantly impact the detection probability. As
a figure of merit to evaluate the detection performance, the area under the ROC
curve (AUC) is derived and evaluated for different multipath fading and
shadowing conditions. Closed-form expressions for the Shannon entropy and cross
entropy are also formulated and assessed for different average SNR, multipath
fading and shadowing conditions. Then the relationship between the Shannon
entropy and ROC/AUC is examined where it is found that the average number of
bits required for encoding a signal becomes small (i.e., low Shannon entropy)
when the detection probability is high or when the AUC is large. The difference
between composite and traditional small-scale fading is emphasized by comparing
the cross entropy for Rayleigh and Nakagami-m fading. A validation of the
analytical results is provided through a careful comparison with the results of
some simulations.Comment: 30 pages, 11 figures, 1 table, Submitted to IEEE TCO
Simultaneous measurement of cosmology and intrinsic alignments using joint cosmic shear and galaxy number density correlations
Cosmic shear is a powerful method to constrain cosmology, provided that any
systematic effects are under control. The intrinsic alignment of galaxies is
expected to severely bias parameter estimates if not taken into account. We
explore the potential of a joint analysis of tomographic galaxy ellipticity,
galaxy number density, and ellipticity-number density cross-correlations to
simultaneously constrain cosmology and self-calibrate unknown intrinsic
alignment and galaxy bias contributions. We treat intrinsic alignments and
galaxy biasing as free functions of scale and redshift and marginalise over the
resulting parameter sets. Constraints on cosmology are calculated by combining
the likelihoods from all two-point correlations between galaxy ellipticity and
galaxy number density. The information required for these calculations is
already available in a standard cosmic shear dataset. We include contributions
to these functions from cosmic shear, intrinsic alignments, galaxy clustering
and magnification effects. In a Fisher matrix analysis we compare our
constraints with those from cosmic shear alone in the absence of intrinsic
alignments. For a potential future large area survey, such as Euclid, the extra
information from the additional correlation functions can make up for the
additional free parameters in the intrinsic alignment and galaxy bias terms,
depending on the flexibility in the models. For example, the Dark Energy Task
Force figure of merit is recovered even when more than 100 free parameters are
marginalised over. We find that the redshift quality requirements are similar
to those calculated in the absence of intrinsic alignments.Comment: 22 pages, 10 figures; extended discussion, otherwise minor changes to
match accepted version; published in Astronomy and Astrophysic
High-pressure x-ray diffraction study of SrMoO4 and pressure-induced structural changes
SrMoO4 was studied under compression up to 25 GPa by angle-dispersive x-ray
diffraction. A phase transition was observed from the scheelite-structured
ambient phase to a monoclinic fergusonite phase at 12.2(9) GPa with cell
parameters a = 5.265(9) A, b = 11.191(9) A, c = 5.195 (5) A, and beta = 90.9, Z
= 4 at 13.1 GPa. There is no significant volume collapse at the phase
transition. No additional phase transitions were observed and on release of
pressure the initial phase is recovered, implying that the observed structural
modifications are reversible. The reported transition appeared to be a
ferroelastic second-order transformation producing a structure that is a
monoclinic distortion of the low-pressure phase and was previously observed in
compounds isostructural to SrMoO4. A possible mechanism for the transition is
proposed and its character is discussed in terms of the present data and the
Landau theory. Finally, the EOS is reported and the anisotropic compressibility
of the studied crystal is discussed in terms of the compression of the Sr-O and
Mo-O bonds.Comment: 36 pages, 9 figures, 1 tabl
Identified baryon and meson distributions at large transverse momenta from Au+Au collisions at GeV
Transverse momentum spectra of , and up to 12 GeV/c
at mid-rapidity in centrality selected Au+Au collisions at GeV are presented. In central Au+Au collisions, both and
show significant suppression with respect to binary scaling at
4 GeV/c. Protons and anti-protons are less suppressed than
, in the range 1.5 6 GeV/c. The and
ratios show at most a weak dependence and no significant
centrality dependence. The ratios in central Au+Au collisions approach
the values in p+p and d+Au collisions at 5 GeV/c. The results at high
indicate that the partonic sources of , and have
similar energy loss when traversing the nuclear medium.Comment: 6 pages, 4 figure
Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive midrapidity jet production in
polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover
transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order
perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and
disfavor at 98% C.L. maximal positive gluon polarization in the polarized
nucleon.Comment: 6 pages, 3 figures. Minor changes from review process in Phys. Rev.
Lett. Plain text tables of data in STAR publications may be found at
http://www.star.bnl.gov/central/publications
System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider
We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)
Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV
We report a new STAR measurement of the longitudinal double-spin asymmetry
A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions
at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet
transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than
previous measurements. They provide significant new constraints on the gluon
spin contribution to the nucleon spin through the comparison to predictions
derived from one global fit of polarized deep-inelastic scattering
measurements.Comment: 7 pages, 4 figures + 1 tabl
Measurements of meson production in relativistic heavy-ion collisions at RHIC
We present results for the measurement of meson production via its
charged kaon decay channel in Au+Au collisions at
, 130, and 200 GeV, and in and +Au collisions
at GeV from the STAR experiment at the BNL Relativistic
Heavy Ion Collider (RHIC). The midrapidity () meson transverse
momentum () spectra in central Au+Au collisions are found to be well
described by a single exponential distribution. On the other hand, the
spectra from , +Au and peripheral Au+Au collisions show power-law tails
at intermediate and high and are described better by Levy
distributions. The constant yield ratio vs beam species, collision
centrality and colliding energy is in contradiction with expectations from
models having kaon coalescence as the dominant mechanism for production
at RHIC. The yield ratio as a function of is consistent
with a model based on the recombination of thermal quarks up to GeV/, but disagrees at higher transverse momenta. The measured nuclear
modification factor, , for the meson increases above unity at
intermediate , similar to that for pions and protons, while is
suppressed due to the energy loss effect in central Au+Au collisions. Number of
constituent quark scaling of both and for the meson
with respect to other hadrons in Au+Au collisions at =200 GeV
at intermediate is observed. These observations support quark
coalescence as being the dominant mechanism of hadronization in the
intermediate region at RHIC.Comment: 22 pages, 21 figures, 4 table
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