1,457 research outputs found
Area Spectral Efficiency Analysis and Energy Consumption Minimization in Multi-Antenna Poisson Distributed Networks
This paper aims at answering two fundamental questions: how area spectral
efficiency (ASE) behaves with different system parameters; how to design an
energy-efficient network. Based on stochastic geometry, we obtain the
expression and a tight lower-bound for ASE of Poisson distributed networks
considering multi-user MIMO (MU-MIMO) transmission. With the help of the
lower-bound, some interesting results are observed. These results are validated
via numerical results for the original expression. We find that ASE can be
viewed as a concave function with respect to the number of antennas and active
users. For the purpose of maximizing ASE, we demonstrate that the optimal
number of active users is a fixed portion of the number of antennas. With
optimal number of active users, we observe that ASE increases linearly with the
number of antennas. Another work of this paper is joint optimization of the
base station (BS) density, the number of antennas and active users to minimize
the network energy consumption. It is discovered that the optimal combination
of the number of antennas and active users is the solution that maximizes the
energy-efficiency. Besides the optimal algorithm, we propose a suboptimal
algorithm to reduce the computational complexity, which can achieve near
optimal performance.Comment: Submitted to IEEE Transactions on Wireless Communications, Major
Revisio
Slim Fractals: The Geometry of Doubly Transient Chaos
Traditional studies of chaos in conservative and driven dissipative systems
have established a correspondence between sensitive dependence on initial
conditions and fractal basin boundaries, but much less is known about the
relation between geometry and dynamics in undriven dissipative systems. These
systems can exhibit a prevalent form of complex dynamics, dubbed doubly
transient chaos because not only typical trajectories but also the (otherwise
invariant) chaotic saddles are transient. This property, along with a manifest
lack of scale invariance, has hindered the study of the geometric properties of
basin boundaries in these systems--most remarkably, the very question of
whether they are fractal across all scales has yet to be answered. Here we
derive a general dynamical condition that answers this question, which we use
to demonstrate that the basin boundaries can indeed form a true fractal; in
fact, they do so generically in a broad class of transiently chaotic undriven
dissipative systems. Using physical examples, we demonstrate that the
boundaries typically form a slim fractal, which we define as a set whose
dimension at a given resolution decreases when the resolution is increased. To
properly characterize such sets, we introduce the notion of equivalent
dimension for quantifying their relation with sensitive dependence on initial
conditions at all scales. We show that slim fractal boundaries can exhibit
complex geometry even when they do not form a true fractal and fractal scaling
is observed only above a certain length scale at each boundary point. Thus, our
results reveal slim fractals as a geometrical hallmark of transient chaos in
undriven dissipative systems.Comment: 13 pages, 9 figures, proof corrections implemente
Centralized Coded Caching with User Cooperation
In this paper, we consider the coded-caching broadcast network with user
cooperation, where a server connects with multiple users and the users can
cooperate with each other through a cooperation network. We propose a
centralized coded caching scheme based on a new deterministic placement
strategy and a parallel delivery strategy. It is shown that the new scheme
optimally allocate the communication loads on the server and users, obtaining
cooperation gain and parallel gain that greatly reduces the transmission delay.
Furthermore, we show that the number of users who parallelly send information
should decrease when the users' caching size increases. In other words, letting
more users parallelly send information could be harmful. Finally, we derive a
constant multiplicative gap between the lower bound and upper bound on the
transmission delay, which proves that our scheme is order optimal.Comment: 9 pages, submitted to ITW201
Highways, railways and entrepreneurship in peripheral cities: evidence from China
Peripheral cities are more susceptible to transportation infrastructure
than core cities in terms of entrepreneurial activities. We use
market access approach to estimate the impacts of highways and
high-speed railways on entrepreneurship in the small and
medium-sized cities in China under knowledge spillover entrepreneurship
framework. The results show that the increased market
potential caused by highways and high-speed railways significantly
improves the entrepreneurial performance of peripheral cities. The
entrepreneurship effects of highways are stronger than high-speed
railways, especially for these cities that are relatively closer to core
cities. On the contrary, the entrepreneurship effects of high-speed
railways are stronger in these cities that are far from core cities.
This study suggests that transportation infrastructure plays an
important role in entrepreneurship, and there is a complementary
effect between highways and high-speed railways
Efficient kinetic method for fluid simulation beyond the Navier-Stokes equation
We present a further theoretical extension to the kinetic theory based
formulation of the lattice Boltzmann method of Shan et al (2006). In addition
to the higher order projection of the equilibrium distribution function and a
sufficiently accurate Gauss-Hermite quadrature in the original formulation, a
new regularization procedure is introduced in this paper. This procedure
ensures a consistent order of accuracy control over the non-equilibrium
contributions in the Galerkin sense. Using this formulation, we construct a
specific lattice Boltzmann model that accurately incorporates up to the third
order hydrodynamic moments. Numerical evidences demonstrate that the extended
model overcomes some major defects existed in the conventionally known lattice
Boltzmann models, so that fluid flows at finite Knudsen number (Kn) can be more
quantitatively simulated. Results from force-driven Poiseuille flow simulations
predict the Knudsen's minimum and the asymptotic behavior of flow flux at large
Kn
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