6,479 research outputs found
Exploiting Device-to-Device Communications to Enhance Spatial Reuse for Popular Content Downloading in Directional mmWave Small Cells
With the explosive growth of mobile demand, small cells in millimeter wave
(mmWave) bands underlying the macrocell networks have attracted intense
interest from both academia and industry. MmWave communications in the 60 GHz
band are able to utilize the huge unlicensed bandwidth to provide multiple Gbps
transmission rates. In this case, device-to-device (D2D) communications in
mmWave bands should be fully exploited due to no interference with the
macrocell networks and higher achievable transmission rates. In addition, due
to less interference by directional transmission, multiple links including D2D
links can be scheduled for concurrent transmissions (spatial reuse). With the
popularity of content-based mobile applications, popular content downloading in
the small cells needs to be optimized to improve network performance and
enhance user experience. In this paper, we develop an efficient scheduling
scheme for popular content downloading in mmWave small cells, termed PCDS
(popular content downloading scheduling), where both D2D communications in
close proximity and concurrent transmissions are exploited to improve
transmission efficiency. In PCDS, a transmission path selection algorithm is
designed to establish multi-hop transmission paths for users, aiming at better
utilization of D2D communications and concurrent transmissions. After
transmission path selection, a concurrent transmission scheduling algorithm is
designed to maximize the spatial reuse gain. Through extensive simulations
under various traffic patterns, we demonstrate PCDS achieves near-optimal
performance in terms of delay and throughput, and also superior performance
compared with other existing protocols, especially under heavy load.Comment: 12 pages, to appear in IEEE Transactions on Vehicular Technolog
Band Gap Closing in a Synthetic Hall Tube of Neutral Fermions
We report the experimental realization of a synthetic three-leg Hall tube
with ultracold fermionic atoms in a one-dimensional optical lattice. The legs
of the synthetic tube are composed of three hyperfine spin states of the atoms,
and the cyclic inter-leg links are generated by two-photon Raman transitions
between the spin states, resulting in a uniform gauge flux penetrating
each side plaquette of the tube. Using quench dynamics, we investigate the band
structure of the Hall tube system for a commensurate flux .
Momentum-resolved analysis of the quench dynamics reveals that a critical point
of band gap closing as one of the inter-leg coupling strengths is varied, which
is consistent with a topological phase transition predicted for the Hall tube
system.Comment: 8 pages, 8 figure
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