2,076 research outputs found
Self-Stabilizing TDMA Algorithms for Dynamic Wireless Ad-hoc Networks
In dynamic wireless ad-hoc networks (DynWANs), autonomous computing devices
set up a network for the communication needs of the moment. These networks
require the implementation of a medium access control (MAC) layer. We consider
MAC protocols for DynWANs that need to be autonomous and robust as well as have
high bandwidth utilization, high predictability degree of bandwidth allocation,
and low communication delay in the presence of frequent topological changes to
the communication network. Recent studies have shown that existing
implementations cannot guarantee the necessary satisfaction of these timing
requirements. We propose a self-stabilizing MAC algorithm for DynWANs that
guarantees a short convergence period, and by that, it can facilitate the
satisfaction of severe timing requirements, such as the above. Besides the
contribution in the algorithmic front of research, we expect that our proposal
can enable quicker adoption by practitioners and faster deployment of DynWANs
that are subject changes in the network topology
Dictionary learning with large step gradient descent for sparse representations
This is the accepted version of an article published in Lecture Notes in Computer Science Volume 7191, 2012, pp 231-238. The final publication is available at link.springer.com
http://www.springerlink.com/content/l1k4514765283618
Self-stabilizing TDMA Algorithms for Wireless Ad-hoc Networks without External Reference
Time division multiple access (TDMA) is a method for sharing communication
media. In wireless communications, TDMA algorithms often divide the radio time
into timeslots of uniform size, , and then combine them into frames of
uniform size, . We consider TDMA algorithms that allocate at least one
timeslot in every frame to every node. Given a maximal node degree, ,
and no access to external references for collision detection, time or position,
we consider the problem of collision-free self-stabilizing TDMA algorithms that
use constant frame size.
We demonstrate that this problem has no solution when the frame size is , where is the chromatic number for
distance- vertex coloring. As a complement to this lower bound, we focus on
proving the existence of collision-free self-stabilizing TDMA algorithms that
use constant frame size of . We consider basic settings (no hardware
support for collision detection and no prior clock synchronization), and the
collision of concurrent transmissions from transmitters that are at most two
hops apart. In the context of self-stabilizing systems that have no external
reference, we are the first to study this problem (to the best of our
knowledge), and use simulations to show convergence even with computation time
uncertainties
Shared-object System Equilibria: Delay and Throughput Analysis
We consider shared-object systems that require their threads to fulfill the
system jobs by first acquiring sequentially the objects needed for the jobs and
then holding on to them until the job completion. Such systems are in the core
of a variety of shared-resource allocation and synchronization systems. This
work opens a new perspective to study the expected job delay and throughput
analytically, given the possible set of jobs that may join the system
dynamically.
We identify the system dependencies that cause contention among the threads
as they try to acquire the job objects. We use these observations to define the
shared-object system equilibria. We note that the system is in equilibrium
whenever the rate in which jobs arrive at the system matches the job completion
rate. These equilibria consider not only the job delay but also the job
throughput, as well as the time in which each thread blocks other threads in
order to complete its job. We then further study in detail the thread work
cycles and, by using a graph representation of the problem, we are able to
propose procedures for finding and estimating equilibria, i.e., discovering the
job delay and throughput, as well as the blocking time.
To the best of our knowledge, this is a new perspective, that can provide
better analytical tools for the problem, in order to estimate performance
measures similar to ones that can be acquired through experimentation on
working systems and simulations, e.g., as job delay and throughput in
(distributed) shared-object systems
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