907 research outputs found
Large-Scale-Fading Decoding in Cellular Massive MIMO Systems with Spatially Correlated Channels
Massive multiple-input--multiple-output (MIMO) systems can suffer from
coherent intercell interference due to the phenomenon of pilot contamination.
This paper investigates a two-layer decoding method that mitigates both
coherent and non-coherent interference in multi-cell Massive MIMO. To this end,
each base station (BS) first estimates the channels to intra-cell users using
either minimum mean-squared error (MMSE) or element-wise MMSE (EW-MMSE)
estimation based on uplink pilots. The estimates are used for local decoding on
each BS followed by a second decoding layer where the BSs cooperate to mitigate
inter-cell interference. An uplink achievable spectral efficiency (SE)
expression is computed for arbitrary two-layer decoding schemes. A closed-form
expression is then obtained for correlated Rayleigh fading, maximum-ratio
combining, and the proposed large-scale fading decoding (LSFD) in the second
layer. We also formulate a sum SE maximization problem with both the data power
and LSFD vectors as optimization variables. Since this is an NP-hard problem,
we develop a low-complexity algorithm based on the weighted MMSE approach to
obtain a local optimum. The numerical results show that both data power control
and LSFD improves the sum SE performance over single-layer decoding multi-cell
Massive MIMO systems.Comment: 17 pages; 10 figures; Accepted for publication in IEEE Transactions
on Communication
Two-Layer Decoding in Cellular Massive MIMO Systems with Spatial Channel Correlation
This paper studies a two-layer decoding method that mitigates inter-cell
interference in multi-cell Massive MIMO systems. In layer one, each base
station (BS) estimates the channels to intra-cell users and uses the estimates
for local decoding on each BS, followed by a second decoding layer where the
BSs cooperate to mitigate inter-cell interference. An uplink achievable
spectral efficiency (SE) expression is computed for arbitrary two-layer
decoding schemes, while a closed-form expression is obtained for correlated
Rayleigh fading channels, maximum-ratio combining (MRC), and large-scale fading
decoding (LSFD) in the second layer. We formulate a non-convex sum SE
maximization problem with both the data power and LSFD vectors as optimization
variables and develop an algorithm based on the weighted MMSE (minimum mean
square error) approach to obtain a stationary point with low computational
complexity.Comment: 4 figures. Accepted by ICC 2019. arXiv admin note: substantial text
overlap with arXiv:1807.0807
Two-Layer Decoding in Cellular Massive MIMO Systems with Spatial Channel Correlation
This paper studies a two-layer decoding method that mitigates inter-cell
interference in multi-cell Massive MIMO systems. In layer one, each base
station (BS) estimates the channels to intra-cell users and uses the estimates
for local decoding on each BS, followed by a second decoding layer where the
BSs cooperate to mitigate inter-cell interference. An uplink achievable
spectral efficiency (SE) expression is computed for arbitrary two-layer
decoding schemes, while a closed-form expression is obtained for correlated
Rayleigh fading channels, maximum-ratio combining (MRC), and large-scale fading
decoding (LSFD) in the second layer. We formulate a non-convex sum SE
maximization problem with both the data power and LSFD vectors as optimization
variables and develop an algorithm based on the weighted MMSE (minimum mean
square error) approach to obtain a stationary point with low computational
complexity.Comment: 4 figures. Accepted by ICC 2019. arXiv admin note: substantial text
overlap with arXiv:1807.0807
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Symmetry: Modeling the Effects of Masking Noise, Axial Cueing and Salience
Symmetry detection is an interesting probe of pattern processing because it requires the matching of novel patterns without the benefit of prior recognition. However, there is evidence that prior knowledge of the axis location plays an important role in symmetry detection. We investigated how the prior information about the symmetry axis affects symmetry detection under noise-masking conditions. The target stimuli were random-dot displays structured to be symmetric about vertical, horizontal, or diagonal axes and viewed through eight apertures (1.2° diameter) evenly distributed around a 6° diameter circle. The information about axis orientation was manipulated by (1) cueing of axis orientation before the trial and (2) varying axis salience by including or excluding the axis region within the noise apertures. The percentage of correct detection of the symmetry was measured at for a range of both target and masking noise densities. The threshold vs. noise density function was flat at low noise density and increased with a slope of 0.75–0.8 beyond a critical density. Axis cueing reduced the target threshold 2–4fold at all noise densities while axis salience had an effect only at high noise density. Our results are inconsistent with an ideal observer or signal-to-noise account of symmetry detection but can be explained by a multiple-channel model is which the response in each channel is the ratio between the nonlinear transform of the responses of sets of early symmetry detectors and the sum of external and intrinsic sources of noise
Angular dependence of superconductivity in superconductor / spin valve heterostructures
We report measurements of the superconducting transition temperature, ,
in CoO/Co/Cu/Co/Nb multilayers as a function of the angle between the
magnetic moments of the Co layers. Our measurements reveal that
is a nonmonotonic function, with a minimum near . Numerical
self-consistent solutions of the Bogoliubov - de Gennes equations
quantitatively and accurately describe the behavior of as a function of
and layer thicknesses in these superconductor / spin-valve
heterostructures. We show that experimental data and theoretical evidence agree
in relating to enhanced penetration of the triplet component of
the condensate into the Co/Cu/Co spin valve in the maximally noncollinear
magnetic configuration.Comment: 9 pages, 9 figure
Can Corporate Social Responsibility Fill Institutional Voids?
We conduct empirical analysis on the relation between firm value and corporate social responsibility (CSR) using 134,823 observations of 2542 firms across 44 countries from 2009 to 2014. We find that the firm value is positively related to the overall CSR score of the firm. At a more granular level, we find that good environmental score is positively related to the firm value and good social and governance scores are negatively related to the firm value. Since these firms operate in different institutional frameworks, we explore whether the institutional voids—the absence of institutions or intermediaries that are instrumental in supporting business operations in a country—may result in greater firm valuation for its CSR and vice versa. Our results show that firms’ environmental scores and social scores receive higher valuation in countries with weaker institutions. Overall, our findings suggest that CSR creates value for firms by filling institutional voids in their home country
A Tale of Two Narrow-Line Regions: Ionization, Kinematics, and Spectral Energy Distributions for a Local Pair of Merging Obscured Active Galaxies
We explore the gas ionization and kinematics, as well as the optical--IR
spectral energy distributions for UGC 11185, a nearby pair of merging galaxies
hosting obscured active galactic nuclei (AGNs), also known as SDSS
J181611.72+423941.6 and J181609.37+423923.0 (J1816NE and J1816SW, ). Due to the wide separation between these interacting galaxies ( kpc), observations of these objects provide a rare glimpse of the
concurrent growth of supermassive black holes at an early merger stage. We use
BPT line diagnostics to show that the full extent of the narrow line emission
in both galaxies is photoionized by an AGN and confirm the existence of a
10-kpc-scale ionization cone in J1816NE, while in J1816SW the AGN narrow-line
region is much more compact (1--2 kpc) and relatively undisturbed. Our
observations also reveal the presence of ionized gas that nearly spans the
entire distance between the galaxies which is likely in a merger-induced tidal
stream. In addition, we carry out a spectral analysis of the X-ray emission
using data from {\em XMM-Newton}. These galaxies represent a useful pair to
explore how the [\ion{O}{3}] luminosity of an AGN is dependent on the size of
the region used to explore the extended emission. Given the growing evidence
for AGN "flickering" over short timescales, we speculate that the appearances
and impact of these AGNs may change multiple times over the course of the
galaxy merger, which is especially important given that these objects are
likely the progenitors of the types of systems commonly classified as "dual
AGNs."Comment: 15 pages, 10 figures, accepted by the Astrophysical Journa
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