1,688 research outputs found
Meeting Real-Time Constraint of Spectrum Management in TV Black-Space Access
The TV set feedback feature standardized in the next generation TV system,
ATSC 3.0, would enable opportunistic access of active TV channels in future
Cognitive Radio Networks. This new dynamic spectrum access approach is named as
black-space access, as it is complementary of current TV white space, which
stands for inactive TV channels. TV black-space access can significantly
increase the available spectrum of Cognitive Radio Networks in populated urban
markets, where spectrum shortage is most severe while TV whitespace is very
limited. However, to enable TV black-space access, secondary user has to
evacuate a TV channel in a timely manner when TV user comes in. Such strict
real-time constraint is an unique challenge of spectrum management
infrastructure of Cognitive Radio Networks. In this paper, the real-time
performance of spectrum management with regard to the degree of centralization
of infrastructure is modeled and tested. Based on collected empirical network
latency and database response time, we analyze the average evacuation time
under four structures of spectrum management infrastructure: fully
distribution, city-wide centralization, national-wide centralization, and
semi-national centralization. The results show that national wide
centralization may not meet the real-time requirement, while semi-national
centralization that use multiple co-located independent spectrum manager can
achieve real-time performance while keep most of the operational advantage of
fully centralized structure.Comment: 9 pages, 7 figures, Technical Repor
Spin-dependent localized Hartree-Fock density-functional approach for the accurate treatment of inner-shell excitation of close-shell atoms
We present a spin-dependent localized Hartree-Fock (SLHF) density-functional
approach for the treatment of the inner-shell excited-state calculation of
atomic systems. In this approach, the electron spin-orbitals in an electronic
configuration are obtained first by solving Kohn-Sham (KS) equation with SLHF
exchange potential. Then a single-Slater-determinant energy of the electronic
configuration is calculated by using these electron spin-orbitals. Finally, a
multiplet energy of an inner-shell excited state is evaluated from the
single-Slater-determinant energies of the electronic configurations involved in
terms of Slater's diagonal sum rule. This procedure has been used to calculate
the total and excitation energies of inner-shell excited states of close-shell
atomic systems: Be, B^+, Ne, and Mg. The correlation effect is taken into
account by incorporating the correlation potentials and energy functionals of
Perdew and Wang's (PW) or Lee, Yang, and Parr's (LYP) into calculation. The
calculated results with the PW and LYP energy functionals are in overall good
agreement with each other and also with available experimental and other ab
initio theoretical data. In addition, we present some new results for highly
excited inner-shell states.Comment: 8 pages and 9 table
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