69 research outputs found
A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends
This paper examines the security vulnerabilities and threats imposed by the
inherent open nature of wireless communications and to devise efficient defense
mechanisms for improving the wireless network security. We first summarize the
security requirements of wireless networks, including their authenticity,
confidentiality, integrity and availability issues. Next, a comprehensive
overview of security attacks encountered in wireless networks is presented in
view of the network protocol architecture, where the potential security threats
are discussed at each protocol layer. We also provide a survey of the existing
security protocols and algorithms that are adopted in the existing wireless
network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term
evolution (LTE) systems. Then, we discuss the state-of-the-art in
physical-layer security, which is an emerging technique of securing the open
communications environment against eavesdropping attacks at the physical layer.
We also introduce the family of various jamming attacks and their
counter-measures, including the constant jammer, intermittent jammer, reactive
jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the
integration of physical-layer security into existing authentication and
cryptography mechanisms for further securing wireless networks. Finally, some
technical challenges which remain unresolved at the time of writing are
summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201
Massively Parallel Algorithms for the Stochastic Block Model
Learning the community structure of a large-scale graph is a fundamental problem in machine learning, computer science and statistics. Among others, the Stochastic Block Model (SBM) serves a canonical model for community detection and clustering, and the Massively Parallel Computation (MPC) model is a mathematical abstraction of real-world parallel computing systems, which provides a powerful computational framework for handling large-scale datasets. We study the problem of exactly recovering the communities in a graph generated from the SBM in the MPC model. Specifically, given kn vertices that are partitioned into k equal-sized clusters (i.e., each has size n), a graph on these kn vertices is randomly generated such that each pair of vertices is connected with probability p if they are in the same cluster and with probability q if not, where p > q > 0.
We give MPC algorithms for the SBM in the (very general) s-space MPC model, where each machine is guaranteed to have memory s = ?(log n). Under the condition that (p-q)/?p ? ??(k^{1/2} n^{-1/2+1/(2(r-1))}) for any integer r ? [3,O(log n)], our first algorithm exactly recovers all the k clusters in O(kr log_s n) rounds using O?(m) total space, or in O(rlog_s n) rounds using O?(km) total space. If (p-q)/?p ? ??(k^{3/4} n^{-1/4}), our second algorithm achieves O(log_s n) rounds and O?(m) total space complexity. Both algorithms significantly improve upon a recent result of Cohen-Addad et al. [PODC\u2722], who gave algorithms that only work in the sublinear space MPC model, where each machine has local memory s = O(n^?) for some constant ? > 0, with a much stronger condition on p,q,k. Our algorithms are based on collecting the r-step neighborhood of each vertex and comparing the difference of some statistical information generated from the local neighborhoods for each pair of vertices. To implement the clustering algorithms in parallel, we present efficient approaches for implementing some basic graph operations in the s-space MPC model
Massively Parallel Algorithms for the Stochastic Block Model
Learning the community structure of a large-scale graph is a fundamental
problem in machine learning, computer science and statistics. We study the
problem of exactly recovering the communities in a graph generated from the
Stochastic Block Model (SBM) in the Massively Parallel Computation (MPC) model.
Specifically, given vertices that are partitioned into equal-sized
clusters (i.e., each has size ), a graph on these vertices is randomly
generated such that each pair of vertices is connected with probability~ if
they are in the same cluster and with probability if not, where . We give MPC algorithms for the SBM in the (very general) \emph{-space
MPC model}, where each machine has memory . Under the
condition that for any integer , our first algorithm exactly recovers all the clusters in
rounds using total space, or in
rounds using total space. If , our second algorithm achieves
rounds and total space complexity. Both algorithms
significantly improve upon a recent result of Cohen-Addad et al. [PODC'22], who
gave algorithms that only work in the \emph{sublinear space MPC model}, where
each machine has local memory~ for some constant ,
with a much stronger condition on .
Our algorithms are based on collecting the -step neighborhood of each
vertex and comparing the difference of some statistical information generated
from the local neighborhoods for each pair of vertices. To implement the
clustering algorithms in parallel, we present efficient approaches for
implementing some basic graph operations in the -space MPC model
Improved Tradeoffs for Leader Election
We consider leader election in clique networks, where nodes are connected
by point-to-point communication links. For the synchronous clique under
simultaneous wake-up, i.e., where all nodes start executing the algorithm in
round , we show a tradeoff between the number of messages and the amount of
time. More specifically, we show that any deterministic algorithm with a
message complexity of requires rounds, for . Our result holds even if
the node IDs are chosen from a relatively small set of size ,
as we are able to avoid using Ramsey's theorem. We also give an upper bound
that improves over the previously-best tradeoff. Our second contribution for
the synchronous clique under simultaneous wake-up is to show that is in fact a lower bound on the message complexity that holds for any
deterministic algorithm with a termination time . We complement this
result by giving a simple deterministic algorithm that achieves leader election
in sublinear time while sending only messages, if the ID space is
of at most linear size. We also show that Las Vegas algorithms (that never
fail) require messages. For the synchronous clique under
adversarial wake-up, we show that is a tight lower bound for
randomized -round algorithms. Finally, we turn our attention to the
asynchronous clique: Assuming adversarial wake-up, we give a randomized
algorithm that achieves a message complexity of and an
asynchronous time complexity of . For simultaneous wake-up, we translate
the deterministic tradeoff algorithm of Afek and Gafni to the asynchronous
model, thus partially answering an open problem they pose
Equivalent stiffness and dynamic response of new mechanical elastic wheel
To investigate the stiffness characteristics of the new mechanical elastic wheel (MEW), the elastic foundation closed circle curved beam model of MEW was established by curved beam theory. With the Laplace transformation and boundary conditions of the governing differential equations, the analytical relations among the radial deformation, bending stiffness of elastic wheel, the elastic foundation stiffness of hinges, elastic wheel laminated structure parameters and excitation frequency were analyzed. The correctness of the curved beam model was validated by the finite element method. Curved beam model validation and the application of the nonlinear finite element model show that the influence of elastic wheel laminated structure and deformation on dynamic response is equal to the equivalent stiffness. The results indicate that the equivalent stiffness and dynamic response of MEW become increased nonlinearly with component content of elastic bead ring, moreover, the equivalent stiffness and dynamic response of MEW increase nonlinearly with the deformation amount of MEW, and the dynamic response significantly decreases with the increase of excitation frequency, under this circumstance that the laminated structure of elastic wheel has been unchanged
Equivalent stiffness and dynamic response of new mechanical elastic wheel
To investigate the stiffness characteristics of the new mechanical elastic wheel (MEW), the elastic foundation closed circle curved beam model of MEW was established by curved beam theory. With the Laplace transformation and boundary conditions of the governing differential equations, the analytical relations among the radial deformation, bending stiffness of elastic wheel, the elastic foundation stiffness of hinges, elastic wheel laminated structure parameters and excitation frequency were analyzed. The correctness of the curved beam model was validated by the finite element method. Curved beam model validation and the application of the nonlinear finite element model show that the influence of elastic wheel laminated structure and deformation on dynamic response is equal to the equivalent stiffness. The results indicate that the equivalent stiffness and dynamic response of MEW become increased nonlinearly with component content of elastic bead ring, moreover, the equivalent stiffness and dynamic response of MEW increase nonlinearly with the deformation amount of MEW, and the dynamic response significantly decreases with the increase of excitation frequency, under this circumstance that the laminated structure of elastic wheel has been unchanged
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