1,211 research outputs found
Traffic Driven Resource Allocation in Heterogenous Wireless Networks
Most work on wireless network resource allocation use physical layer
performance such as sum rate and outage probability as the figure of merit.
These metrics may not reflect the true user QoS in future heterogenous networks
(HetNets) with many small cells, due to large traffic variations in overlapping
cells with complicated interference conditions. This paper studies the spectrum
allocation problem in HetNets using the average packet sojourn time as the
performance metric. To be specific, in a HetNet with base terminal stations
(BTS's), we determine the optimal partition of the spectrum into possible
spectrum sharing combinations. We use an interactive queueing model to
characterize the flow level performance, where the service rates are decided by
the spectrum partition. The spectrum allocation problem is formulated using a
conservative approximation, which makes the optimization problem convex. We
prove that in the optimal solution the spectrum is divided into at most
pieces. A numerical algorithm is provided to solve the spectrum allocation
problem on a slow timescale with aggregate traffic and service information.
Simulation results show that the proposed solution achieves significant gains
compared to both orthogonal and full spectrum reuse allocations with moderate
to heavy traffic.Comment: 6 pages, 5 figures IEEE GLOBECOM 2014 (accepted for publication
Traffic-Driven Spectrum Allocation in Heterogeneous Networks
Next generation cellular networks will be heterogeneous with dense deployment
of small cells in order to deliver high data rate per unit area. Traffic
variations are more pronounced in a small cell, which in turn lead to more
dynamic interference to other cells. It is crucial to adapt radio resource
management to traffic conditions in such a heterogeneous network (HetNet). This
paper studies the optimization of spectrum allocation in HetNets on a
relatively slow timescale based on average traffic and channel conditions
(typically over seconds or minutes). Specifically, in a cluster with base
transceiver stations (BTSs), the optimal partition of the spectrum into
segments is determined, corresponding to all possible spectrum reuse patterns
in the downlink. Each BTS's traffic is modeled using a queue with Poisson
arrivals, the service rate of which is a linear function of the combined
bandwidth of all assigned spectrum segments. With the system average packet
sojourn time as the objective, a convex optimization problem is first
formulated, where it is shown that the optimal allocation divides the spectrum
into at most segments. A second, refined model is then proposed to address
queue interactions due to interference, where the corresponding optimal
allocation problem admits an efficient suboptimal solution. Both allocation
schemes attain the entire throughput region of a given network. Simulation
results show the two schemes perform similarly in the heavy-traffic regime, in
which case they significantly outperform both the orthogonal allocation and the
full-frequency-reuse allocation. The refined allocation shows the best
performance under all traffic conditions.Comment: 13 pages, 11 figures, accepted for publication by JSAC-HC
Scalable Spectrum Allocation for Large Networks Based on Sparse Optimization
Joint allocation of spectrum and user association is considered for a large
cellular network. The objective is to optimize a network utility function such
as average delay given traffic statistics collected over a slow timescale. A
key challenge is scalability: given Access Points (APs), there are
ways in which the APs can share the spectrum. The number of variables is
reduced from to , where is the number of users, by
optimizing over local overlapping neighborhoods, defined by interference
conditions, and by exploiting the existence of sparse solutions in which the
spectrum is divided into segments. We reformulate the problem by
optimizing the assignment of subsets of active APs to those segments. An
constraint enforces a one-to-one mapping of subsets to spectrum, and
an iterative (reweighted ) algorithm is used to find an approximate
solution. Numerical results for a network with 100 APs serving several hundred
users show the proposed method achieves a substantial increase in total
throughput relative to benchmark schemes.Comment: Submitted to the IEEE International Symposium on Information Theory
(ISIT), 201
Comment on ``Relativistic kinetic equations for electromagnetic, scalar and pseudoscalar interactions''
It is found that the extra quantum constraints to the spinor components of
the equal-time Wigner function given in a recent paper by Zhuang and Heinz
should vanish identically. We point out here the origin of the error and give
an interpretation of the result. However, the principal idea of obtaining a
complete equal-time transport theory by energy averaging the covariant theory
remains valid. The classical transport equation for the spin density is also
found to be incorrect. We give here the correct form of that equation and
discuss briefly its structure.Comment: 5 pages LaTe
Mott Insulator - Superfluid Transitions in a Two Band Model at Finite Temperature and Possible Application to Supersolid 4He
We study Mott insulator - superfluid transition in a two-band boson Hubbard
model, which can be mapped onto a spin-1/2 XY model with spins coupled to an
additional Ising degree of freedom. By using a modified mean field theory that
include the effects of phase fluctuations, we show that the transition is first
order at both zero and finite temperatures. On the Mott insulator side, there
may be reentrance in phase transition. These features are consequences of the
underlying transition between competing defect poor and defect rich phases. The
relevance of the model and our results to supersolid 4He and cold bosonic atoms
in optical lattices are discussed
Characterization of the denaturation and renaturation of human plasma vitronectin I. Biophysical characterization of protein unfolding and multimerization
Upon treatment with denaturing agents, vitronectin has been observed to exhibit conformational alterations which are similar to the structural changes detected when vitronectin binds the thrombin-antithrombin complex or associates with the terminal attack complex of complement. Denaturation and renaturation of vitronectin isolated from human plasma were characterized by changes in intrinsic fluorescence. Unfolding by chemical denaturants was irreversible and accompanied by self-association of the protein to form vitronectin multimers. Self-association was evaluated by equilibrium analytical ultracentrifugation which demonstrated that multimers form only during the refolding process after removal of denaturant, that multimeric vitronectin dissociates to constituent subunits readily upon treatment with chemical denaturant, and that intermolecular disulfide cross-linking occurs primarily at the dimer level among a subset of constituent vitronectin subunits within the multimer. The monomeric form of vitronectin isolated from human plasma partially unfolds at intermediate concentrations of denaturant to an altered conformation with a high propensity to associate into multimers. Folding of vitronectin in vivo appears to be regulated by partitioning of folding intermediates toward either of two conformations, one that exists as a stable monomer and another that associates into a multimeric form
- …