13,653 research outputs found
Hybrid Transceiver Optimization for Multi-Hop Communications
Multi-hop communication with the aid of large-scale antenna arrays will play
a vital role in future emergence communication systems. In this paper, we
investigate amplify-and-forward based and multiple-input multiple-output
assisted multi-hop communication, in which all nodes employ hybrid
transceivers. Moreover, channel errors are taken into account in our hybrid
transceiver design. Based on the matrix-monotonic optimization framework, the
optimal structures of the robust hybrid transceivers are derived. By utilizing
these optimal structures, the optimizations of analog transceivers and digital
transceivers can be separated without loss of optimality. This fact greatly
simplifies the joint optimization of analog and digital transceivers. Since the
optimization of analog transceivers under unit-modulus constraints is
non-convex, a projection type algorithm is proposed for analog transceiver
optimization to overcome this difficulty. Based on the derived analog
transceivers, the optimal digital transceivers can then be derived using
matrix-monotonic optimization. Numeral results obtained demonstrate the
performance advantages of the proposed hybrid transceiver designs over other
existing solutions.Comment: 32 pages, 6 figures. This manuscript has been submitted to IEEE
Journal on Selected Areas in Communications (special issue on Multiple
Antenna Technologies for Beyond 5G
Topological Dirac states beyond orbitals for silicene on SiC(0001) surface
The discovery of intriguing properties related to the Dirac states in
graphene has spurred huge interest in exploring its two-dimensional group-IV
counterparts, such as silicene, germanene, and stanene. However, these
materials have to be obtained via synthesizing on substrates with strong
interfacial interactions, which usually destroy their intrinsic
()-orbital Dirac states. Here we report a theoretical study on the
existence of Dirac states arising from the orbitals instead of
orbitals in silicene on 4H-SiC(0001), which survive in spite of the strong
interfacial interactions. We also show that the exchange field together with
the spin-orbital coupling give rise to a detectable band gap of 1.3 meV. Berry
curvature calculations demonstrate the nontrivial topological nature of such
Dirac states with a Chern number , presenting the potential of realizing
quantum anomalous Hall effect for silicene on SiC(0001). Finally, we construct
a minimal effective model to capture the low-energy physics of this system.
This finding is expected to be also applicable to germanene and stanene, and
imply great application potentials in nanoelectronics.Comment: 6 Figures , Accepted by Nano Letter
A Posteriori Error Estimate for Finite Volume Element Method of the Second-Order Hyperbolic Equations
We establish a posteriori error estimate for finite volume element method of a second-order hyperbolic equation. Residual-type a posteriori error estimator is derived. The computable upper and lower bounds on the error in the H1-norm are established. Numerical experiments are provided to illustrate the performance of the proposed estimator
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