26,804 research outputs found
Fast Space Optimal Leader Election in Population Protocols
The model of population protocols refers to the growing in popularity
theoretical framework suitable for studying pairwise interactions within a
large collection of simple indistinguishable entities, frequently called
agents. In this paper the emphasis is on the space complexity in fast leader
election via population protocols governed by the random scheduler, which
uniformly at random selects pairwise interactions within the population of n
agents.
The main result of this paper is a new fast and space optimal leader election
protocol. The new protocol utilises O(log^2 n) parallel time (which is
equivalent to O(n log^2 n) sequential pairwise interactions), and each agent
operates on O(log log n) states. This double logarithmic space usage matches
asymptotically the lower bound 1/2 log log n on the minimal number of states
required by agents in any leader election algorithm with the running time
o(n/polylog n).
Our solution takes an advantage of the concept of phase clocks, a fundamental
synchronisation and coordination tool in distributed computing. We propose a
new fast and robust population protocol for initialisation of phase clocks to
be run simultaneously in multiple modes and intertwined with the leader
election process. We also provide the reader with the relevant formal
argumentation indicating that our solution is always correct, and fast with
high probability.Comment: 21 pages, 2 figures, published in SODA 2018 proceeding
Rafting Towards Consensus: Formation Control of Distributed Dynamical Systems
In this paper, we introduce a novel adaptation of the Raft consensus
algorithm for achieving emergent formation control in multi-agent systems with
a single integrator dynamics. This strategy, dubbed "Rafting," enables robust
cooperation between distributed nodes, thereby facilitating the achievement of
desired geometric configurations. Our framework takes advantage of the Raft
algorithm's inherent fault tolerance and strong consistency guarantees to
extend its applicability to distributed formation control tasks. Following the
introduction of a decentralized mechanism for aggregating agent states, a
synchronization protocol for information exchange and consensus formation is
proposed. The Raft consensus algorithm combines leader election, log
replication, and state machine application to steer agents toward a common,
collaborative goal. A series of detailed simulations validate the efficacy and
robustness of our method under various conditions, including partial network
failures and disturbances. The outcomes demonstrate the algorithm's potential
and open up new possibilities in swarm robotics, autonomous transportation, and
distributed computation. The implementation of the algorithms presented in this
paper is available at https://github.com/abbas-tari/raft.git
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
Fast Space Optimal Leader Election in Population Protocols
The model of population protocols refers to the growing in popularity theoretical framework suitable for studying pairwise interactions within a large collection of simple indistinguishable entities, frequently called agents. In this paper the emphasis is on the space complexity in fast leader election via population protocols governed by the random scheduler, which uniformly at random selects pairwise interactions from the population of n agents. The main result of this paper is a new fast and space optimal leader election protocol. The new protocol operates in parallel time O(log2n) equivalent to O(n log2n) sequential pairwise interactions, in which each agent utilises O(log log n) states. This double logarithmic space utilisation matches asymptotically the lower bound [Equation] log log n on the number of states utilised by agents in any leader election algorithm with the running time [Equation], see [7]. Our solution relies on the concept of phase clocks, a fundamental synchronisation and coordination tool in the field of Distributed Computing. We propose a new fast and robust population protocol for initialisation of phase clocks to be run simultaneously in multiple modes and intertwined with the leader election process. We also provide the reader with the relevant formal argumentation indicating that our solution is always correct and fast with high probability
Rational Fair Consensus in the GOSSIP Model
The \emph{rational fair consensus problem} can be informally defined as
follows. Consider a network of (selfish) \emph{rational agents}, each of
them initially supporting a \emph{color} chosen from a finite set .
The goal is to design a protocol that leads the network to a stable
monochromatic configuration (i.e. a consensus) such that the probability that
the winning color is is equal to the fraction of the agents that initially
support , for any . Furthermore, this fairness property must
be guaranteed (with high probability) even in presence of any fixed
\emph{coalition} of rational agents that may deviate from the protocol in order
to increase the winning probability of their supported colors. A protocol
having this property, in presence of coalitions of size at most , is said to
be a \emph{whp\,--strong equilibrium}. We investigate, for the first time,
the rational fair consensus problem in the GOSSIP communication model where, at
every round, every agent can actively contact at most one neighbor via a
\emph{pushpull} operation. We provide a randomized GOSSIP protocol that,
starting from any initial color configuration of the complete graph, achieves
rational fair consensus within rounds using messages of
size, w.h.p. More in details, we prove that our protocol is a
whp\,--strong equilibrium for any and, moreover, it
tolerates worst-case permanent faults provided that the number of non-faulty
agents is . As far as we know, our protocol is the first solution
which avoids any all-to-all communication, thus resulting in message
complexity.Comment: Accepted at IPDPS'1
Fully Distributed Cooperative Spectrum Sensing for Cognitive Radio Networks
Cognitive radio networks (CRN) sense spectrum occupancy and manage themselves to operate in unused bands without disturbing licensed users. The detection capability of a radio system can be enhanced if the sensing process is performed jointly by a group of nodes so that the effects of wireless fading and shadowing can be minimized. However, taking a collaborative approach poses new security threats to the system as nodes can report false sensing data to force a wrong decision. Providing security to the sensing process is also complex, as it usually involves introducing limitations to the CRN applications. The most common limitation is the need for a static trusted node that is able to authenticate and merge the reports of all CRN nodes. This paper overcomes this limitation by presenting a protocol that is suitable for fully distributed scenarios, where there is no static trusted node
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