327 research outputs found
Optimizing the robustness of electrical power systems against cascading failures
Electrical power systems are one of the most important infrastructures that
support our society. However, their vulnerabilities have raised great concern
recently due to several large-scale blackouts around the world. In this paper,
we investigate the robustness of power systems against cascading failures
initiated by a random attack. This is done under a simple yet useful model
based on global and equal redistribution of load upon failures. We provide a
complete understanding of system robustness by i) deriving an expression for
the final system size as a function of the size of initial attacks; ii)
deriving the critical attack size after which system breaks down completely;
iii) showing that complete system breakdown takes place through a first-order
(i.e., discontinuous) transition in terms of the attack size; and iv)
establishing the optimal load-capacity distribution that maximizes robustness.
In particular, we show that robustness is maximized when the difference between
the capacity and initial load is the same for all lines; i.e., when all lines
have the same redundant space regardless of their initial load. This is in
contrast with the intuitive and commonly used setting where capacity of a line
is a fixed factor of its initial load.Comment: 18 pages including 2 pages of supplementary file, 5 figure
k-Connectivity in Random Key Graphs with Unreliable Links
Random key graphs form a class of random intersection graphs and are
naturally induced by the random key predistribution scheme of Eschenauer and
Gligor for securing wireless sensor network (WSN) communications. Random key
graphs have received much interest recently, owing in part to their wide
applicability in various domains including recommender systems, social
networks, secure sensor networks, clustering and classification analysis, and
cryptanalysis to name a few. In this paper, we study connectivity properties of
random key graphs in the presence of unreliable links. Unreliability of the
edges are captured by independent Bernoulli random variables, rendering edges
of the graph to be on or off independently from each other. The resulting model
is an intersection of a random key graph and an Erdos-Renyi graph, and is
expected to be useful in capturing various real-world networks; e.g., with
secure WSN applications in mind, link unreliability can be attributed to harsh
environmental conditions severely impairing transmissions. We present
conditions on how to scale this model's parameters so that i) the minimum node
degree in the graph is at least k, and ii) the graph is k-connected, both with
high probability as the number of nodes becomes large. The results are given in
the form of zeroone laws with critical thresholds identified and shown to
coincide for both graph properties. These findings improve the previous results
by Rybarczyk on the k-connectivity of random key graphs (with reliable links),
as well as the zero-one laws by Yagan on the 1-connectivity of random key
graphs with unreliable links.Comment: Published in IEEE Transactions on Information Theor
Performance of the Eschenauer-Gligor key distribution scheme under an ON/OFF channel
We investigate the secure connectivity of wireless sensor networks under the
random key distribution scheme of Eschenauer and Gligor. Unlike recent work
which was carried out under the assumption of full visibility, here we assume a
(simplified) communication model where unreliable wireless links are
represented as on/off channels. We present conditions on how to scale the model
parameters so that the network i) has no secure node which is isolated and ii)
is securely connected, both with high probability when the number of sensor
nodes becomes large. The results are given in the form of full zero-one laws,
and constitute the first complete analysis of the EG scheme under non-full
visibility. Through simulations these zero-one laws are shown to be valid also
under a more realistic communication model, i.e., the disk model. The relations
to the Gupta and Kumar's conjecture on the connectivity of geometric random
graphs with randomly deleted edges are also discussed.Comment: Submitted to IEEE Transactions on Information Theory in November,
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