7,076 research outputs found
Jointly Optimal Channel and Power Assignment for Dual-Hop Multi-channel Multi-user Relaying
We consider the problem of jointly optimizing channel pairing, channel-user
assignment, and power allocation, to maximize the weighted sum-rate, in a
single-relay cooperative system with multiple channels and multiple users.
Common relaying strategies are considered, and transmission power constraints
are imposed on both individual transmitters and the aggregate over all
transmitters. The joint optimization problem naturally leads to a mixed-integer
program. Despite the general expectation that such problems are intractable, we
construct an efficient algorithm to find an optimal solution, which incurs
computational complexity that is polynomial in the number of channels and the
number of users. We further demonstrate through numerical experiments that the
jointly optimal solution can significantly improve system performance over its
suboptimal alternatives.Comment: This is the full version of a paper to appear in the IEEE Journal on
Selected Areas in Communications, Special Issue on Cooperative Networking -
Challenges and Applications (Part II), October 201
Dynamically Spontaneous Symmetry Breaking and Masses of Lightest Nonet Scalar Mesons as Composite Higgs Bosons
Based on the (approximate) chiral symmetry of QCD Lagrangian and the bound
state assumption of effective meson fields, a nonlinearly realized effective
chiral Lagrangian for meson fields is obtained from integrating out the quark
fields by using the new finite regularization method. As the new method
preserves the symmetry principles of the original theory and meanwhile keeps
the finite quadratic term given by a physically meaningful characteristic
energy scale , it then leads to a dynamically spontaneous symmetry
breaking in the effective chiral field theory. The gap equations are obtained
as the conditions of minimal effective potential in the effective theory. The
instanton effects are included via the induced interactions discovered by 't
Hooft and found to play an important role in obtaining the physical solutions
for the gap equations. The lightest nonet scalar mesons(, ,
and ) appearing as the chiral partners of the nonet pseudoscalar mesons
are found to be composite Higgs bosons with masses below the chiral symmetry
breaking scale GeV. In particular, the mass of the
singlet scalar (or the ) is found to be MeV.Comment: 15 pages, Revtex, published version, Eur. Phys. J. C (2004) (DOI)
10.1140/epjcd/s2004-01-001-
Dominant Resource Fairness in Cloud Computing Systems with Heterogeneous Servers
We study the multi-resource allocation problem in cloud computing systems
where the resource pool is constructed from a large number of heterogeneous
servers, representing different points in the configuration space of resources
such as processing, memory, and storage. We design a multi-resource allocation
mechanism, called DRFH, that generalizes the notion of Dominant Resource
Fairness (DRF) from a single server to multiple heterogeneous servers. DRFH
provides a number of highly desirable properties. With DRFH, no user prefers
the allocation of another user; no one can improve its allocation without
decreasing that of the others; and more importantly, no user has an incentive
to lie about its resource demand. As a direct application, we design a simple
heuristic that implements DRFH in real-world systems. Large-scale simulations
driven by Google cluster traces show that DRFH significantly outperforms the
traditional slot-based scheduler, leading to much higher resource utilization
with substantially shorter job completion times
Dynamic Control of Tunable Sub-optimal Algorithms for Scheduling of Time-varying Wireless Networks
It is well known that for ergodic channel processes the Generalized
Max-Weight Matching (GMWM) scheduling policy stabilizes the network for any
supportable arrival rate vector within the network capacity region. This
policy, however, often requires the solution of an NP-hard optimization
problem. This has motivated many researchers to develop sub-optimal algorithms
that approximate the GMWM policy in selecting schedule vectors. One implicit
assumption commonly shared in this context is that during the algorithm
runtime, the channel states remain effectively unchanged. This assumption may
not hold as the time needed to select near-optimal schedule vectors usually
increases quickly with the network size. In this paper, we incorporate channel
variations and the time-efficiency of sub-optimal algorithms into the scheduler
design, to dynamically tune the algorithm runtime considering the tradeoff
between algorithm efficiency and its robustness to changing channel states.
Specifically, we propose a Dynamic Control Policy (DCP) that operates on top of
a given sub-optimal algorithm, and dynamically but in a large time-scale
adjusts the time given to the algorithm according to queue backlog and channel
correlations. This policy does not require knowledge of the structure of the
given sub-optimal algorithm, and with low overhead can be implemented in a
distributed manner. Using a novel Lyapunov analysis, we characterize the
throughput stability region induced by DCP and show that our characterization
can be tight. We also show that the throughput stability region of DCP is at
least as large as that of any other static policy. Finally, we provide two case
studies to gain further intuition into the performance of DCP.Comment: Submitted for journal consideration. A shorter version was presented
in IEEE IWQoS 200
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