4,115 research outputs found
Measurement and Modeling of Subway Near Shadowing Phenomenon.
This paper focuses on one vital aspect in propagation characteristics inside subway tunnels: near shadowing phenomenon in a practical environment. In order to characterize this effect, an accurate measurement has been made at 2.4 GHz in a real environment in Madrid subway. By analyzing the numerical results in this measurement, the characteristic of near shadowing phenomenon in propagation process has been revealed and corresponding engineering suggestions have been given in order to compensate the near shadowing effect. Finally, statistical model including the depth, duration and length of near shadowing, fast fading and attenuation inside wide tunnel and narrow tunnel has been built and simulated
Resource Allocation for Device-to-Device Communications Underlaying Heterogeneous Cellular Networks Using Coalitional Games
Heterogeneous cellular networks (HCNs) with millimeter wave (mmWave)
communications included are emerging as a promising candidate for the fifth
generation mobile network. With highly directional antenna arrays, mmWave links
are able to provide several-Gbps transmission rate. However, mmWave links are
easily blocked without line of sight. On the other hand, D2D communications
have been proposed to support many content based applications, and need to
share resources with users in HCNs to improve spectral reuse and enhance system
capacity. Consequently, an efficient resource allocation scheme for D2D pairs
among both mmWave and the cellular carrier band is needed. In this paper, we
first formulate the problem of the resource allocation among mmWave and the
cellular band for multiple D2D pairs from the view point of game theory. Then,
with the characteristics of cellular and mmWave communications considered, we
propose a coalition formation game to maximize the system sum rate in
statistical average sense. We also theoretically prove that our proposed game
converges to a Nash-stable equilibrium and further reaches the near-optimal
solution with fast convergence rate. Through extensive simulations under
various system parameters, we demonstrate the superior performance of our
scheme in terms of the system sum rate compared with several other practical
schemes.Comment: 13 pages, 12 figure
Statistics-dependent quantum co-walking of two particles in one-dimensional lattices with nearest-neighbor interactions
We investigate continuous-time quantum walks of two indistinguishable
particles [bosons, fermions or hard-core bosons (HCBs)] in one-dimensional
lattices with nearest-neighbor interactions. The results for two HCBs are well
consistent with the recent experimental observation of two-magnon dynamics
[Nature 502, 76 (2013)]. The two interacting particles can undergo independent-
and/or co-walking depending on both quantum statistics and interaction
strength. Two strongly interacting particles may form a bound state and then
co-walk like a single composite particle with statistics-dependent walk speed.
Analytical solutions for the scattering and bound states, which appear in the
two-particle quantum walks, are obtained by solving the eigenvalue problem in
the two-particle Hilbert space. In the context of degenerate perturbation
theory, an effective single-particle model for the quantum co-walking is
analytically derived and the walk seep of bosons is found to be exactly three
times of the ones of fermions/HCBs. Our result paves the way for experimentally
exploring quantum statistics via two-particle quantum walks.Comment: 9 pages, 5 figures, an extension with more new results for our
unpublished arXiv:1402.334
Chief Introduction for the Door of Metro made in China
AbstractThis paper describes the types, uses and structure of the door of Metro made in China, making an introduction of the advantages and disadvantages on different structural forms passenger compartment door
The Design & Calculation for Hydraulic Cylinder of Workpiece Hydraulic Clamping System of a Special CNC Machine for Guide Disc
AbstractThis paper describes and introduces the design of hydraulic cylinder, which has ensured the safety and reliability of workpiece hydraulic clamping system of a special CNC Machine Tool for Guide Disc
Propagation Mechanism Analysis Before the Break Point Inside Tunnels
There is no unanimous consensus yet on the propagation mechanism before the break point inside tunnels. Some deem that the propagation mechanism follows the free space model, others argue that it should be described by the multimode waveguide model. Firstly, this paper analyzes the propagation loss in two mechanisms. Then, by conjunctively using the propagation theory and the three-dimensional solid geometry, a generic analytical model for the boundary between the free space mechanism and the multi-mode waveguide mechanism inside tunnels has been presented. Three measurement campaigns validate the model in different tunnels at different frequencies. Furthermore, the condition of the validity of the free space model used in tunnel environment has been discussed in some specific situations. Finally, through mathematical derivation, the seemingly conflicting viewpoints on the free space mechanism and the multi-mode waveguide mechanism have been unified in some specific situations by the presented generic model. The results in this paper can be helpful to gain deeper insight and better understanding of the propagation mechanism inside tunnel
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