30,318 research outputs found
An Optimal Game Theoretical Framework for Mobility Aware Routing in Mobile Ad hoc Networks
Selfish behaviors are common in self-organized Mobile Ad hoc Networks
(MANETs) where nodes belong to different authorities. Since cooperation of
nodes is essential for routing protocols, various methods have been proposed to
stimulate cooperation among selfish nodes. In order to provide sufficient
incentives, most of these methods pay nodes a premium over their actual costs
of participation. However, they lead to considerably large overpayments.
Moreover, existing methods ignore mobility of nodes, for simplicity. However,
owing to the mobile nature of MANETs, this assumption seems unrealistic. In
this paper, we propose an optimal game theoretical framework to ensure the
proper cooperation in mobility aware routing for MANETs. The proposed method is
based on the multi-dimensional optimal auctions which allows us to consider
path durations, in addition to the route costs. Path duration is a metric that
best reflects changes in topology caused by mobility of nodes and, it is widely
used in mobility aware routing protocols. Furthermore, the proposed mechanism
is optimal in that it minimizes the total expected payments. We provide
theoretical analysis to support our claims. In addition, simulation results
show significant improvements in terms of payments compared to the most popular
existing methods
Robust Leader Election in a Fast-Changing World
We consider the problem of electing a leader among nodes in a highly dynamic
network where the adversary has unbounded capacity to insert and remove nodes
(including the leader) from the network and change connectivity at will. We
present a randomized Las Vegas algorithm that (re)elects a leader in O(D\log n)
rounds with high probability, where D is a bound on the dynamic diameter of the
network and n is the maximum number of nodes in the network at any point in
time. We assume a model of broadcast-based communication where a node can send
only 1 message of O(\log n) bits per round and is not aware of the receivers in
advance. Thus, our results also apply to mobile wireless ad-hoc networks,
improving over the optimal (for deterministic algorithms) O(Dn) solution
presented at FOMC 2011. We show that our algorithm is optimal by proving that
any randomized Las Vegas algorithm takes at least omega(D\log n) rounds to
elect a leader with high probability, which shows that our algorithm yields the
best possible (up to constants) termination time.Comment: In Proceedings FOMC 2013, arXiv:1310.459
Visual cue training to improve walking and turning after stroke:a study protocol for a multi-centre, single blind randomised pilot trial
Visual information comprises one of the most salient sources of information used to control walking and the dependence on vision to maintain dynamic stability increases following a stroke. We hypothesize, therefore, that rehabilitation efforts incorporating visual cues may be effective in triggering recovery and adaptability of gait following stroke. This feasibility trial aims to estimate probable recruitment rate, effect size, treatment adherence and response to gait training with visual cues in contrast to conventional overground walking practice following stroke.Methods/design: A 3-arm, parallel group, multi-centre, single blind, randomised control feasibility trial will compare overground visual cue training (O-VCT), treadmill visual cue training (T-VCT), and usual care (UC). Participants (n = 60) will be randomly assigned to one of three treatments by a central randomisation centre using computer generated tables to allocate treatment groups. The research assessor will remain blind to allocation. Treatment, delivered by physiotherapists, will be twice weekly for 8 weeks at participating outpatient hospital sites for the O-VCT or UC and in a University setting for T-VCT participants.Individuals with gait impairment due to stroke, with restricted community ambulation (gait spee
Distributed execution of bigraphical reactive systems
The bigraph embedding problem is crucial for many results and tools about
bigraphs and bigraphical reactive systems (BRS). Current algorithms for
computing bigraphical embeddings are centralized, i.e. designed to run locally
with a complete view of the guest and host bigraphs. In order to deal with
large bigraphs, and to parallelize reactions, we present a decentralized
algorithm, which distributes both state and computation over several concurrent
processes. This allows for distributed, parallel simulations where
non-interfering reactions can be carried out concurrently; nevertheless, even
in the worst case the complexity of this distributed algorithm is no worse than
that of a centralized algorithm
Mobile Transaction Supports for DBMS
National audienceIn recent years data management in mobile environments has generated a great interest. Several proposals concerning mobile transactions have been done. However, it is very difficult to have an overview of all these approaches. In this paper we analyze and compare several contributions on mobile transactions and introduce our ongoing research: the design and implementation of a Mobile Transaction Service. The focus of our study is on execution models, the manner ACID properties are provided and the way geographical movements of hosts (during transaction executions) is supported
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