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Dive into the research topics where Sayaka Kamei is active.

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Featured researches published by Sayaka Kamei.


international conference on structural information and communication complexity | 2011

Asynchronous mobile robot gathering from symmetric configurations without global multiplicity detection

Sayaka Kamei; Anissa Lamani; Fukuhito Ooshita; Sébastien Tixeuil

We consider a set of k autonomous robots that are endowed with visibility sensors (but that are otherwise unable to communicate) and motion actuators. Those robots must collaborate to reach a single vertex that is unknown beforehand, and to remain there hereafter. Previous works on gathering in ringshaped networks suggest that there exists a tradeoff between the size of the set of potential initial configurations, and the power of the sensing capabilities of the robots (i.e. the larger the initial configuration set, the most powerful the sensor needs to be). We prove that there is no such trade off. We propose a gathering protocol for an odd number of robots in a ring-shaped network that allows symmetric but not periodic configurations as initial configurations, yet uses only local weak multiplicity detection. Robots are assumed to be anonymous and oblivious, and the execution model is the non-atomic CORDA model with asynchronous fair scheduling. Our protocol allows the largest set of initial configurations (with respect to impossibility results) yet uses the weakest multiplicity detector to date. The time complexity of our protocol is O(n2), where n denotes the size of the ring. Compared to previous work that also uses local weak multiplicity detection, we do not have the constraint that k < n/2 (here, we simply have 2 < k < n-3).


international conference on structural information and communication complexity | 2010

Mobile robots gathering algorithm with local weak multiplicity in rings

Tomoko Izumi; Taisuke Izumi; Sayaka Kamei; Fukuhito Ooshita

The gathering problem of anonymous and oblivious mobile robots is one of fundamental problems in the theoretical mobile robotics. We consider the gathering problem in unoriented and anonymous rings, which requires that all robots gather at a non-predefined node. Since the gathering problem cannot be solved without any additional capability to robots, all the previous works assume some capability of robots, such as accessing the memory on node. In this paper, we focus on the multiplicity capability. This paper presents a deterministic gathering algorithm with local-weak multiplicity, which provides the robot with the information about whether its current node has more than one robot or not. This assumption is strictly weaker than that by previous works. Moreover, we show that our algorithm is asymptotically time-optimal one, that is, the time complexity of our algorithm is O(n), where n is the number of nodes. Interestingly, in spite of assuming the weaker assumption, it achieves significant improvement compared to the previous algorithm, which takes O(kn) time for k robots.


international parallel and distributed processing symposium | 2007

A Self-Stabilizing Distributed Approximation Algorithm for the Minimum Connected Dominating Set

Sayaka Kamei; Hirotsugu Kakugawa

Self-stabilization is a theoretical framework of non-masking fault-tolerant distributed algorithms. A self-stabilizing system tolerates any kind and any finite number of transient faults, such as message loss, memory corruption, and topology change. Because such transient faults occur so frequently in mobile ad hoc networks, distributed algorithms on them should tolerate such events. In this paper, we propose a self-stabilizing distributed approximation algorithm for the minimum connected dominating set, which can be used, for example, as a virtual backbone or routing in mobile ad hoc networks. The size of the solution by our algorithm is at most 8 |Dopt | + 1, where Dopt is a minimum connected dominating set. The time complexity is O(n2) steps.


mathematical foundations of computer science | 2012

Gathering an even number of robots in an odd ring without global multiplicity detection

Sayaka Kamei; Anissa Lamani; Fukuhito Ooshita; Sébastien Tixeuil

We propose a gathering protocol for an even number of robots in a ring-shaped network that allows symmetric but not periodic configurations as initial configurations, yet uses only local weak multiplicity detection. Robots are assumed to be anonymous and oblivious, and the execution model is the non-atomic CORDA model with asynchronous fair scheduling. In our scheme, the number of robots k must be greater than 8, the number of nodes n on a network must be odd and greater than k+3. The running time of our protocol is O(n2) asynchronous rounds.


international conference on principles of distributed systems | 2008

A Self-stabilizing Approximation for the Minimum Connected Dominating Set with Safe Convergence

Sayaka Kamei; Hirotsugu Kakugawa

In wireless ad hoc or sensor networks, a connected dominating set is useful as the virtual backbone because there is no fixed infrastructure or centralized management. Additionally, in such networks, transient faults and topology changes occur frequently. A self-stabilizing system tolerates any kind and any finite number of transient faults, and does not need any initialization. An ordinary self-stabilizing algorithm has no safety guarantee and requires that the network remains static during converging to the legitimate configuration. Safe converging self-stabilization is one of the extension of self-stabilization which is suitable for dynamic networks such that topology changes and transient faults occur frequently. The safe convergence property guarantees that the system quickly converges to a safe configuration, and then, it moves to an optimal configuration without breaking safety. In this paper, we propose a self-stabilizing 7.6-approximation algorithm with safe convergence for the minimum connected dominating set in the networks modeled by unit disk graphs.


international symposium on stabilization safety and security of distributed systems | 2009

Randomized Gathering of Mobile Robots with Local-Multiplicity Detection

Taisuke Izumi; Tomoko Izumi; Sayaka Kamei; Fukuhito Ooshita

Let us consider the gathering problem of n anonymous and oblivious mobile robots, which requires that all robots meet in finite time at a non-predefined point. While the gathering problem cannot be solved deterministically without any additional capability to robots, randomized approach easily allows it to be solvable. However, only the randomized solution taking expected round complexity exponential of n is currently known. Motivated by this fact, we investigate the feasibility of polynomial-expected-round randomized gathering in this paper. Our first contribution is to give a negative result about the round complexity of randomized gathering. It is proved that any algorithm without no additional assumption has


parallel and distributed computing: applications and technologies | 2003

A self-stabilizing algorithm for the distributed minimal k-redundant dominating set problem in tree networks

Sayaka Kamei; Hirotsugu Kakugawa

{\it \Omega}(\mathrm{exp}(n))


IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences | 2005

A Self-Stabilizing Approximation Algorithm for the Distributed Minimum k -Domination *

Sayaka Kamei; Hirotsugu Kakugawa

expected-round lower bound. This lower bound yields a question: What additional assumptions are necessary to achieve gathering in polynomial expected rounds? We address this question from the aspect of multiplicity detection. This paper newly introduces two weaker variants of multiplicity detection capability, called local-strong and local-weak multiplicity, and investigates whether those capabilities permit polynomial-expected-round gathering or not. Our second contribution is to reveal the power of local (strong/weak) multiplicity by showing that local-strong multiplicity detection allows O (n )-expected round gathering but local-weak multiplicity detection takes an exponential-time lower bound. These results imply that those two kinds of multiplicity-detection capabilities have inherently large difference about their computational powers.


parallel and distributed computing: applications and technologies | 2003

A quorum-based distributed algorithm for group mutual exclusion

M. Toyomura; Sayaka Kamei; Hirotsugu Kakugawa

Self-stabilization is a theoretical framework of nonmasking fault-tolerant distributed algorithms. We investigate self-stabilizing distributed solutions to the minimal k-redundant dominating set (MRDS) problem in tree networks. The MRDS problem is a generalization of the well-known dominating set problem in graph theory. For a graph G=(V,E), a set M/spl sube/V is a k-redundant dominating set of G if and only if each vertex not in M is adjacent to at least k vertices in M. We propose a self-stabilizing distributed algorithm that solves the MRDS problem for anonymous tree networks.


IEEE Transactions on Parallel and Distributed Systems | 2013

Feasibility of Polynomial-Time Randomized Gathering for Oblivious Mobile Robots

Tomoko Izumi; Sayaka Kamei; Fukuhito Ooshita

Self-stabilization is a theoretical framework of nonmasking fault-tolerant distributed algorithms. In this paper, we investigate a self-stabilizing distributed approximation for the minimum k-dominating set (KDS) problem in general networks. The minimum KDS problem is a generalization of the well-known dominating set problem in graph theory. For a graph G = (V, E), a set Dk ⊆ V is a KDS of G if and only if each vertex not in Dk is adjacent to at least k vertices in Dk. The approximation ratio of our algorithm is Δ/k(1 + (k-1/Δ+1)), where Δ is the maximum degree of G, in the networks of which the minimum degree is more than or equal to k.

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Fukuhito Ooshita

Nara Institute of Science and Technology

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Yoshiaki Katayama

Nagoya Institute of Technology

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Taisuke Izumi

Nagoya Institute of Technology

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Anissa Lamani

University of Picardie Jules Verne

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