In this article, we develop distributed iterative algorithms that enable the components of a multicomponent system, each with some integer initial value, to asymptotically compute the average of their initial values, ...
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In this article, we develop distributed iterative algorithms that enable the components of a multicomponent system, each with some integer initial value, to asymptotically compute the average of their initial values, without having to reveal to other components the specific value they contribute to the average calculation. We assume a communication topology captured by an arbitrary strongly connected digraph, in which certain nodes (components) might be curious but not malicious (i.e., they execute the distributed protocol correctly, but try to identify the initial values of other nodes). We first develop a variation of the so-called ratio consensus algorithm that operates exclusively on integer values and can be used by the nodes to asymptotically obtain the average of their initial (integer) values, by taking the ratio of two integer values they maintain and iteratively update. Assuming the presence of a trusted node (i.e., a node that is not curious and can be trusted to set up a cryptosystem and not reveal any decrypted values of messages it receives), we describe how this algorithm can be adjusted using homomorphic encryption to allow the nodes to obtain the average of their initial values while ensuring their privacy (i.e., without having to reveal their initial value). We also extend the algorithm to handle situations where multiple nodes set up cryptosystems and privacy is preserved as long as one of these nodes can be trusted (i.e., the ratio of trusted nodes over the nodes that set up cryptosystems decreases).
In this paper, nonsmooth aggregative games are investigated, where the nondifferentiable cost function of every player depends on its own decision as well as the aggregate of the decisions of all players. Moreover, in...
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In this paper, nonsmooth aggregative games are investigated, where the nondifferentiable cost function of every player depends on its own decision as well as the aggregate of the decisions of all players. Moreover, in the problem, the local constraints of players are general and heterogeneous convex sets, and the decisions of players are coupled by linear constraints. For purpose of distributed seeking of the variational generalized Nash equilibrium (GNE) of the game, a distributed algorithm is developed for players. In the algorithm, the dynamic average consensus is used for the estimation of the aggregate of decisions to obtain the approximation of subgradients of cost functions. Besides, the convergence of the algorithm to the variational GNE is analyzed. Finally, simulation examples illustrate the algorithm. (C) 2021 Elsevier Ltd. All rights reserved.
Given a set R of robots, each one located at a different vertex of an infinite regular tessellation graph, we aim to explore the Arbitrary Pattern Formation (APF) problem. Given a multiset F of grid vertices such that...
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ISBN:
(纸本)9781450389334
Given a set R of robots, each one located at a different vertex of an infinite regular tessellation graph, we aim to explore the Arbitrary Pattern Formation (APF) problem. Given a multiset F of grid vertices such that vertical bar R vertical bar = vertical bar F vertical bar, APF asks for a distributed algorithm that moves robots so as to reach a configuration similar to F. Similarity means that robots must be disposed as F regardless of translations, rotations, reflections. So far, as possible discretization of the Euclidean plane only the standard square grid has been considered in the context of the classical Look-Compute-Move model. However, it is natural to consider the other regular tessellation graphs, that are triangular and hexagonal grids. For any regular tessellation graph, we provide a resolution algorithm for APF when the initial configuration is asymmetric.
The continuous search for the k best results given a query (top-k) in a data stream is a problem that has gained a lot of attention in recent years, especially in social media and IoT contexts. In these contexts it is...
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ISBN:
(纸本)9781665439022
The continuous search for the k best results given a query (top-k) in a data stream is a problem that has gained a lot of attention in recent years, especially in social media and IoT contexts. In these contexts it is essential that the system is able to respond reactively. Therefore, in this study we address how to scale the monitoring of approximate continuous top-k queries to guarantee the reactiveness of the system. In this paper we introduce a scalable distributed version of the MinTopK+N algorithm that allows the system to remain reactive when the load increases. In addition, we present a scale-out/in algorithm that allows the system to add instances to cope with workload increments and remove instances to avoid over-provisioning. Furthermore, in a set of managed experiments, we demonstrated how the increase in the workload could affect the system performance and the impact of the instant of triggering scaling actions on the system performance. Finally, we present a study on the impact of the scaling action on the correctness of the result, showing that the scaling algorithm does not negatively impact the correctness of the results, and in certain conditions, it can even improve the quality of the approximation.
As in all distributed systems, having an accurate access to a global notion of time is vital for a modular robot's modules to coordinate their activities and accomplish their goal. In this paper, we present and co...
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ISBN:
(纸本)9781665495509
As in all distributed systems, having an accurate access to a global notion of time is vital for a modular robot's modules to coordinate their activities and accomplish their goal. In this paper, we present and compare two methods for clock skew compensation to enhance the performance of network-wide time synchronization in modular robots with neighbor-to-neighbor communication. The first one, Adaptive Rate Search (ARS), uses a light weight adaptive search method to adapt the drift rate of local clocks. The second one, combines Linear Regression with Bayes estimation (LR+) to reduce the accumulative error induced during the propagation of synchronization messages on large number of hops. We evaluate both methods with Blinky Block robots: using a real modular robots system and simulation. The results show that both methods LR+ and ARS present a significant error reduction compared to least-square linear regression used in previous state of the art synchronization protocol for modular robots with neighbor-to-neighbor communication.
We will present the fundamentals of Byzantine agreement and leader election problems from a modern perspective. Byzantine fault tolerant protocols are at the heart of secure and robust protocols that can tolerate the ...
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ISBN:
(纸本)9781450385480
We will present the fundamentals of Byzantine agreement and leader election problems from a modern perspective. Byzantine fault tolerant protocols are at the heart of secure and robust protocols that can tolerate the presence of malicious nodes in a distributed system, such as a Peer-to-Peer (P2P) network, which allows a large number of peers to enter the network with little or no admission control. Such malicious peers acting alone or in collaboration can cause disruption of service in P2P systems. Our tutorial is largely inspired by recent P2P applications like Blockchain and cryptocurrencies that espouse permissionless settings whereby peers can anonymously and dynamically join and leave the network at will. Our presentation will be in three parts. In the first part, we will present the historic foundations of Byzantine agreement and leader election and describe the fundamentals that underlie our modern understanding of these problems. Much of the classical results focus on complete networks where nodes have global knowledge. In the second part, motivated by real-world distributed networks such as P2P networks which are typically sparse and bounded degree with nodes having only local knowledge, we focus on Byzantine protocols for sparse networks. While the first two parts will focus on static settings, motivated by modern applications such as blockchains and cryptocurrencies which operate on dynamic P2P networks, the third part will delve into Byzantine procotols for dynamic networks where nodes continuously join and leave the system. The tutorial will cover various tools and techniques that are useful in designing Byzantine protocols in sparse and dynamic networks and will discuss key open problems in the area.
We consider strongly monotone games with convex separable coupling constraints, played by dynamical agents, in a partial-decision information scenario. We start by designing continuous-time fully distributed feedback ...
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We consider strongly monotone games with convex separable coupling constraints, played by dynamical agents, in a partial-decision information scenario. We start by designing continuous-time fully distributed feedback controllers, based on consensus and primal-dual gradient dynamics, to seek a generalized Nash equilibrium in networks of single-integrator agents. Our first solution adopts a fixed gain, whose choice requires the knowledge of some global parameters of the game. To relax this requirement, we conceive a controller that can be tuned in a completely decentralized fashion, thanks to the use of uncoordinated integral adaptive weights. We further introduce algorithms specifically devised for generalized aggregative games. Finally, we adapt all our control schemes to deal with heterogeneous multi-integrator agents and, in turn, with nonlinear feedback-linearizable dynamical systems. For all the proposed dynamics, we show convergence to a variational equilibrium, by leveraging monotonicity properties and stability theory for projected dynamical systems. (C) 2021 The Author(s). Published by Elsevier Ltd.
This paper considers the problem of Byzantine dispersion and extends previous work along several parameters. The problem of Byzantine dispersion asks: given n robots, up to f of which are Byzantine, initially placed a...
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ISBN:
(纸本)9781665440660
This paper considers the problem of Byzantine dispersion and extends previous work along several parameters. The problem of Byzantine dispersion asks: given n robots, up to f of which are Byzantine, initially placed arbitrarily on an n node anonymous graph, design a terminating algorithm to be run by the robots such that they eventually reach a configuration where each node has at most one non-Byzantine robot on it. Previous work solved this problem for rings and tolerated up to n - 1 Byzantine robots. In this paper, we investigate the problem on more general graphs. We first develop an algorithm that tolerates up to n - 1 Byzantine robots and works for a more general class of graphs. We then develop an algorithm that works for any graph but tolerates a lesser number of Byzantine robots. We subsequently turn our focus to the strength of the Byzantine robots. Previous work considers only "weak" Byzantine robots that cannot fake their IDs. We develop an algorithm that solves the problem when Byzantine robots are not weak and can fake IDs. Finally, we study the situation where the number of the robots is not n but some k. We show that in such a scenario, the number of Byzantine robots that can be tolerated is severely restricted. Specifically, we show that it is impossible to deterministically solve Byzantine dispersion when inverted right perpendiculark/ninverted left perpendicular > inverted right perpendicular( k - f)/ninverted left perpendicular.
The restoration lemma by Afek, Bremler-Barr, Kaplan, Cohen, and Merritt [Dist. Comp. '02] proves that, in an undirected unweighted graph, any replacement shortest path avoiding a failing edge can be expressed as t...
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ISBN:
(纸本)9781450385480
The restoration lemma by Afek, Bremler-Barr, Kaplan, Cohen, and Merritt [Dist. Comp. '02] proves that, in an undirected unweighted graph, any replacement shortest path avoiding a failing edge can be expressed as the concatenation of two original shortest paths. However, the lemma is tiebreaking-sensitive: if one selects a particular canonical shortest path for each node pair, it is no longer guaranteed that one can build replacement paths by concatenating two selected shortest paths. They left as an open problem whether a method of shortest path tiebreaking with this desirable property is generally possible. We settle this question affirmatively with the first general construction of restorable tiebreaking schemes. We then show applications to various problems in fault-tolerant network design. These include a faster algorithm for subset replacement paths, more efficient fault-tolerant (exact) distance labeling schemes, fault-tolerant subset distance preservers and +4 additive spanners with improved sparsity, and fast distributed algorithms that construct these objects. For example, an almost immediate corollary of our restorable tiebreaking scheme is the first nontrivial distributed construction of sparse fault-tolerant distance preservers resilient to three faults.
An intelligent speed advisory system can be used to recommend speed for vehicles travelling in a given road network in cities. In this paper, we extend our previous work where a distributed speed advisory system has b...
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ISBN:
(纸本)9781728189642
An intelligent speed advisory system can be used to recommend speed for vehicles travelling in a given road network in cities. In this paper, we extend our previous work where a distributed speed advisory system has been devised to recommend an optimal consensus speed for a fleet of Internal Combustion Engine Vehicles (ICEVs) in a highway scenario. In particular, we propose a novel optimisation framework where the exact format of each vehicle's cost function can be implicit, and our algorithm can be used to recommend multiple consensus speeds for vehicles travelling on different lanes in an urban highway scenario. Our studies show that the proposed scheme based on an improved whale optimisation algorithm can effectively reduce CO2 emission generated from ICEVs while providing different recommended speed options for groups of vehicles.
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