27,109 research outputs found
EZ-AG: Structure-free data aggregation in MANETs using push-assisted self-repelling random walks
This paper describes EZ-AG, a structure-free protocol for duplicate
insensitive data aggregation in MANETs. The key idea in EZ-AG is to introduce a
token that performs a self-repelling random walk in the network and aggregates
information from nodes when they are visited for the first time. A
self-repelling random walk of a token on a graph is one in which at each step,
the token moves to a neighbor that has been visited least often. While
self-repelling random walks visit all nodes in the network much faster than
plain random walks, they tend to slow down when most of the nodes are already
visited. In this paper, we show that a single step push phase at each node can
significantly speed up the aggregation and eliminate this slow down. By doing
so, EZ-AG achieves aggregation in only O(N) time and messages. In terms of
overhead, EZ-AG outperforms existing structure-free data aggregation by a
factor of at least log(N) and achieves the lower bound for aggregation message
overhead. We demonstrate the scalability and robustness of EZ-AG using ns-3
simulations in networks ranging from 100 to 4000 nodes under different mobility
models and node speeds. We also describe a hierarchical extension for EZ-AG
that can produce multi-resolution aggregates at each node using only O(NlogN)
messages, which is a poly-logarithmic factor improvement over existing
techniques
No-boarding buses: Synchronisation for efficiency
We investigate a no-boarding policy in a system of buses serving bus
stops in a loop, which is an entrainment mechanism to keep buses synchronised
in a reasonably staggered configuration. Buses always allow alighting, but
would disallow boarding if certain criteria are met. For an analytically
tractable theory, buses move with the same natural speed (applicable to
programmable self-driving buses), where the average waiting time experienced by
passengers waiting at the bus stop for a bus to arrive can be calculated. The
analytical results show that a no-boarding policy can dramatically reduce the
average waiting time, as compared to the usual situation without the
no-boarding policy. Subsequently, we carry out simulations to verify these
theoretical analyses, also extending the simulations to typical human-driven
buses with different natural speeds based on real data. Finally, a simple
general adaptive algorithm is implemented to dynamically determine when to
implement no-boarding in a simulation for a real university shuttle bus
service.Comment: 49 pages, 9 figures. Video available here:
https://www.youtube.com/watch?v=SBNqvTr1Aj
Formal and Informal Methods for Multi-Core Design Space Exploration
We propose a tool-supported methodology for design-space exploration for
embedded systems. It provides means to define high-level models of applications
and multi-processor architectures and evaluate the performance of different
deployment (mapping, scheduling) strategies while taking uncertainty into
account. We argue that this extension of the scope of formal verification is
important for the viability of the domain.Comment: In Proceedings QAPL 2014, arXiv:1406.156
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