4,126 research outputs found
Compressive Channel Estimation and Multi-user Detection in C-RAN
This paper considers the channel estimation (CE) and multi-user detection
(MUD) problems in cloud radio access network (C-RAN). Assuming that active
users are sparse in the network, we solve CE and MUD problems with compressed
sensing (CS) technology to greatly reduce the long identification pilot
overhead. A mixed L{2,1}-regularization functional for extended sparse
group-sparsity recovery is proposed to exploit the inherently sparse property
existing both in user activities and remote radio heads (RRHs) that active
users are attached to. Empirical and theoretical guidelines are provided to
help choosing tuning parameters which have critical effect on the performance
of the penalty functional. To speed up the processing procedure, based on
alternating direction method of multipliers and variable splitting strategy, an
efficient algorithm is formulated which is guaranteed to be convergent.
Numerical results are provided to illustrate the effectiveness of the proposed
functional and efficient algorithm.Comment: 6 pages, 3 figure
Electron-phonon coupling and superconductivity in LiBC
By means of the first-principles density-functional theory calculation and
Wannier interpolation, electron-phonon coupling and superconductivity are
systematically explored for boron-doped LiBC (i.e. LiBC), with
between 0.1 and 0.9. Hole doping introduced by boron atoms is treated
through virtual-crystal approximation. For the investigated doping
concentrations, our calculations show the optimal doping concentration
corresponds to 0.8. By solving the anisotropic Eliashberg equations, we find
that LiBC is a two-gap superconductor, whose superconducting
transition temperature, T, may exceed the experimentally observed value of
MgB. Similar to MgB, the two-dimensional bond-stretching
phonon modes along - line have the largest contribution to
electron-phonon coupling. More importantly, we find that the first two acoustic
phonon modes and around the midpoint of - line play a
vital role for the rise of T in LiBC. The origin of strong
couplings in and modes can be attributed to enhanced
electron-phonon coupling matrix elements and softened phonons. It is revealed
that all these phonon modes couple strongly with -bonding electronic
states.Comment: 7 pages, 10 figures, accepted for publication in EP
Weak gravitational lensing by an ESTGB black hole in the presence of a plasma
This paper is devoted to studying the weak-field gravitational lensing
properties of a 4D ESTGB black hole, which is surrounded by the plasma medium.
The effects of the magnetic charges and the three plasma distribution models in
the deflection of light around a 4D ESTGB black hole are investigated in
detail. We find that the uniform plasma leads to a larger deflection of light
rays in comparison with the singular isothermal sphere (SIS), the non-singular
isothermal sphere (NSIS) models. Moreover, the deflection angle increases
slightly as the absolute value of the magnetic charge decreases. Finally, we
analyze the total magnification of image due to weak gravitational lensing
around the black hole. The result shows that the presence of a uniform plasma
medium remarkably enhances the total magnification whereas the non-uniform
plasma reduces the total magnification.Comment: 24 pages, 15 figure
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