249,678 research outputs found
Buffer Sizing for 802.11 Based Networks
We consider the sizing of network buffers in 802.11 based networks. Wireless
networks face a number of fundamental issues that do not arise in wired
networks. We demonstrate that the use of fixed size buffers in 802.11 networks
inevitably leads to either undesirable channel under-utilization or unnecessary
high delays. We present two novel dynamic buffer sizing algorithms that achieve
high throughput while maintaining low delay across a wide range of network
conditions. Experimental measurements demonstrate the utility of the proposed
algorithms in a production WLAN and a lab testbed.Comment: 14 pages, to appear on IEEE/ACM Transactions on Networkin
Increasing the Reliability of Adaptive Quadrature Using Explicit Interpolants
We present two new adaptive quadrature routines. Both routines differ from
previously published algorithms in many aspects, most significantly in how they
represent the integrand, how they treat non-numerical values of the integrand,
how they deal with improper divergent integrals and how they estimate the
integration error. The main focus of these improvements is to increase the
reliability of the algorithms without significantly impacting their efficiency.
Both algorithms are implemented in Matlab and tested using both the "families"
suggested by Lyness and Kaganove and the battery test used by Gander and
Gautschi and Kahaner. They are shown to be more reliable, albeit in some cases
less efficient, than other commonly-used adaptive integrators.Comment: 32 pages, submitted to ACM Transactions on Mathematical Softwar
Simple and Efficient Fully-Functional Succinct Trees
The fully-functional succinct tree representation of Navarro and Sadakane
(ACM Transactions on Algorithms, 2014) supports a large number of operations in
constant time using bits. However, the full idea is hard to
implement. Only a simplified version with operation time has been
implemented and shown to be practical and competitive. We describe a new
variant of the original idea that is much simpler to implement and has
worst-case time for the operations. An implementation based on
this version is experimentally shown to be superior to existing
implementations
Algorithms and Data Structures for Multi-Adaptive Time-Stepping
Multi-adaptive Galerkin methods are extensions of the standard continuous and
discontinuous Galerkin methods for the numerical solution of initial value
problems for ordinary or partial differential equations. In particular, the
multi-adaptive methods allow individual and adaptive time steps to be used for
different components or in different regions of space. We present algorithms
for efficient multi-adaptive time-stepping, including the recursive
construction of time slabs and adaptive time step selection. We also present
data structures for efficient storage and interpolation of the multi-adaptive
solution. The efficiency of the proposed algorithms and data structures is
demonstrated for a series of benchmark problems.Comment: ACM Transactions on Mathematical Software 35(3), 24 pages (2008
Algorithms to Approximate Column-Sparse Packing Problems
Column-sparse packing problems arise in several contexts in both
deterministic and stochastic discrete optimization. We present two unifying
ideas, (non-uniform) attenuation and multiple-chance algorithms, to obtain
improved approximation algorithms for some well-known families of such
problems. As three main examples, we attain the integrality gap, up to
lower-order terms, for known LP relaxations for k-column sparse packing integer
programs (Bansal et al., Theory of Computing, 2012) and stochastic k-set
packing (Bansal et al., Algorithmica, 2012), and go "half the remaining
distance" to optimal for a major integrality-gap conjecture of Furedi, Kahn and
Seymour on hypergraph matching (Combinatorica, 1993).Comment: Extended abstract appeared in SODA 2018. Full version in ACM
Transactions of Algorithm
Gap Processing for Adaptive Maximal Poisson-Disk Sampling
In this paper, we study the generation of maximal Poisson-disk sets with
varying radii. First, we present a geometric analysis of gaps in such disk
sets. This analysis is the basis for maximal and adaptive sampling in Euclidean
space and on manifolds. Second, we propose efficient algorithms and data
structures to detect gaps and update gaps when disks are inserted, deleted,
moved, or have their radius changed. We build on the concepts of the regular
triangulation and the power diagram. Third, we will show how our analysis can
make a contribution to the state-of-the-art in surface remeshing.Comment: 16 pages. ACM Transactions on Graphics, 201
Approaching Throughput-optimality in Distributed CSMA Scheduling Algorithms with Collisions
It was shown recently that CSMA (Carrier Sense Multiple Access)-like
distributed algorithms can achieve the maximal throughput in wireless networks
(and task processing networks) under certain assumptions. One important, but
idealized assumption is that the sensing time is negligible, so that there is
no collision. In this paper, we study more practical CSMA-based scheduling
algorithms with collisions. First, we provide a Markov chain model and give an
explicit throughput formula which takes into account the cost of collisions and
overhead. The formula has a simple form since the Markov chain is "almost"
time-reversible. Second, we propose transmission-length control algorithms to
approach throughput optimality in this case. Sufficient conditions are given to
ensure the convergence and stability of the proposed algorithms. Finally, we
characterize the relationship between the CSMA parameters (such as the maximum
packet lengths) and the achievable capacity region.Comment: To appear in IEEE/ACM Transactions on Networking. This is the longer
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